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Table of Content

25 December 2023, Volume 44 Issue 24
Food Chemistry
Preparation of Redispersible Chitin Nanofibers and Its Application in Stabilizing Pickering Emulsion
DONG Tongjun, WEI Kongju, SHUANG Yuan, DING Beibei, WANG Xuedong, DING Wenping
2023, 44(24):  1-8.  doi:10.7506/spkx1002-6630-20230221-193
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Chitin nanofibers (ChNFs) with both amino and carboxyl groups were obtained by carboxymethylation of partially deacetylated chitin (DE-chitin) with chloroacetic acid. ChNFs could be dispersed again in deionized water after drying and removing the dispersing medium. The aspect ratio of ChNFs had little change before and after dispersion. Further, ChNFs could effectively stabilize oil-in-water (O/W) Pickering emulsions. The emulsion (comprising 10% oil) stabilized with ChNFs at concentrations greater than 0.5% was stabile for 90 days. In addition, ChNFs could stabilize the emulsion in a wide pH range (3–11). Overall, ChNFs is expected to be used as a novel Pickering stabilizer to protect and deliver pH-sensitive active substances in the field of food biology.
Effect of Calcium Chloride on Energy Level and Quality of Tan Sheep Meat during Postmortem Aging
CHEN Xueyan, LUO Ruiming, ZHANG Qian, WANG Jinxia, LI Rong, HU Lijun
2023, 44(24):  9-15.  doi:10.7506/spkx1002-6630-20230411-095
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Our purpose was to clarify the effect of CaCl2 treatment on the energy level and quality of Tan sheep meat during postmortem aging. Tan sheep hind leg meat was injected with 200 mmol/L CaCl2 solution, and aged at 4 ℃ for 0, 2, 4, 6, and 8 days. The protein expression of phosphofructokinase (PFKM) was detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot to verify whether the glycolysis pathway could be activated by CaCl2. At the same time, the energy level and meat quality indexes were measured during postmortem aging to analyze the mechanism by which the glycolysis pathway affects the metabolic level and quality of Tan sheep meat. The results showed that the protein expression of PFKM decreased during postmortem aging, indicating activation of the glycolytic pathway. CaCl2 treatment accelerated the glycolysis process after slaughter, thereby promoting the decomposition of glycogen, increasing the production of lactic acid, and resulting in a rapid decrease in pH. Water-holding capacity (WHC), myofibril fragmentation index (MFI) and b* value were higher and shear force and a* were lower in the treatment group than in the control and blank groups. Therefore, CaCl2 could affect the color, WHC and tenderness of Tan sheep meat at different aging stages. By accelerating the decrease of pH and the accumulation of energy metabolites, the glycolytic pathway increased the level of energy metabolism during postmortem aging, while inhibiting the production of oxymyoglobin, activating the activity of calpain, changing the structure of myofibrils and shortening the space between muscle protein molecules, which accelerated the process of myofibril fragmentation and the hydrolysis of myofibrillar protein, and led to a deterioration in meat color and an increase in water loss and meat tenderness.
Release Characteristics, Mucus Permeability, and Cellular Uptake of Glabridin/Hydroxypropyl-β-Cyclodextrin Inclusion Complex
LI Defeng, FAN Jinling, YAO Peipei, REN Guoyan, DU Lin, ZHANG Xiaoyu
2023, 44(24):  16-25.  doi:10.7506/spkx1002-6630-20230120-155
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GLD/HP-β-CD inclusion complexes were prepared by encapsulating glabridin (GLD) with hydroxypropyl (HP) and β-cyclodextrin (β-CD) to improve the solubility of GLD in water. The morphology, the existing form of GLD, the interaction between GLD and HP-β-CD and the spatial conformation of the inclusion complexes were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and molecular docking, respectively. Furthermore, the dissolution and release characteristics of GLD/HP-β-CD inclusion complexes were investigated in vitro in simulated gastric and intestinal fluids. The permeability of GLD/HP-β-CD through the mucus layer was studied using the Transwell method, and the spatial conformation and interaction of GLD and mucins were investigated by molecular docking. The small intestinal uptake of GLD in GLD/HP-β-CD inclusion complexes was studied using Caco-2 cells, and the effect of the vector HP-β-CD on GLD uptake and the possible underlying mechanism were investigated. The results showed that the encapsulation efficiency and drug loading of GLD in GLD/HP-β-CD were 90.03% and 14.51%, respectively, and HP-β-CD could significantly increase the saturation solubility of GLD in water to 109.36 mg/mL. SEM showed that the GLD/HP-β-CD solid inclusion complexes were irregularly flake-shaped. DSC showed that GLD in the GLD/HP-β-CD inclusion complexes was present in an amorphous non-crystalline form. FTIR and DSC fully demonstrated that HP-β-CD encapsulated GLD in the cavity to form an inclusion complex. Molecular docking showed that GLD molecules were able to completely enter the cavity of HP-β-CD, the optimal binding energy between GLD and HP-β-CD was −7.37 kcal/mol, and the interaction between molecules was mainly maintained by van der Waals force. Compared with free GLD, the cumulative dissolution rate of GLD/HP-β-CD at 1 h in simulated gastric and intestinal fluids was increased by 15.75 and 12.4 folds, respectively, and the total cumulative release rate at 24 h in simulated gastric and intestinal fluids was increased by 54 folds. The apparent permeability coefficient through the mucus layer was increased from 9.24 × 10-9 to 1.43 × 10-5 cm/s. Molecular docking showed a strong interaction between GLD and the mucin MUC2, and the uptake by Caco-2 cells was increased from 0.039 to 0.349 mg/g. The present study shows that GLD/HP-β-CD complexes can significantly increase the dissolution and release of GLD, and greatly improve the permeability of GLD through the mucus layer of the intestinal epithelial surface and the uptake of GLD by intestinal epithelial cells, thereby having the potential to enhance GLD absorption and improve the bioavailability of GLD.
Effect of Trypsin Modification on Heat Resistance and Structural Properties of Liquid Egg White during Heat Sterilization
QI Tengda, MA Yanqiu, CHI Yujie, CHI Yuan
2023, 44(24):  26-33.  doi:10.7506/spkx1002-6630-20230321-209
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In order to increase the pasteurization temperature and heat resistance of liquid egg white, the effect of trypsin modification on the heat resistance and structural properties of liquid egg white was investigated in this study. The sample in this study consisted of two groups: unmodified and enzyme-modified. Each group was kept at 25 ℃ (control) or sterilized at 56, 62, 68 or 72 ℃ for 3 min. The changes of heat resistance were measured by turbidity and supernatant protein content, and the structure of egg white protein was characterized by apparent viscosity, particle size, surface hydrophobicity, Fourier transform infrared (FTIR) spectroscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and scanning electron microscopy (SEM). Trypsin modification significantly reduced egg white turbidity and increased the protein content of the supernatant (P < 0.05). As the sterilization temperature increased, the turbidity and particle size of egg white gradually increased, while the protein content of the supernatant gradually decreased. At the same sterilization temperature, the turbidity and apparent viscosity of the modified egg white were significantly lower, while the surface hydrophobicity was significantly higher (P < 0.05) and the particle size distribution was closer to the normal distribution compared with that of the unmodified egg white. Enzymatic modification could inhibit protein thermal aggregation and improve heat resistance. SEM results showed that enzymatic modification increased the surface porosity of egg white protein and the dispersity of the particles; at the same sterilization temperature the number of particles retained on the surface was higher in modified than in unmodified egg white. SDS-PAGE analysis showed that enzymatic modification promoted the degradation of large molecular mass proteins in egg white. Fourier transform infrared spectroscopy showed that at temperatures below 68 ℃, the relative content of α-helix of the modified egg white was significantly higher than that of the unmodified egg white (P < 0.05), while the relative content of random coil was significantly lower than that of the unmodified egg white. In conclusion, trypsin can effectively improve the thermal aggregation of egg white proteins during heat sterilization and improve the heat resistance of liquid egg white, which is important for expanding its sales radius.
Evaluation of Stability and Biocompatibility of Chitosan/Sodium Tripolyphosphate and Chitosan/Flaxseed Gum Composite Nanoparticles Loaded with Bighead Carp Peptides
ZHENG Changliang, CHEN Mengting, WANG Lan, QU Yinghong, SHI Wenzheng, SHI Liu, CHEN Sheng, QIAO Yu, LI Xin, GUO Xiaojia, WU Wenjin, YANG Yuping
2023, 44(24):  34-40.  doi:10.7506/spkx1002-6630-20230404-032
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Chitosan nanoparticle is becoming an excellent carrier for the delivery of bioactive components due to the advantages of simple preparation, low cost and high biocompatibility. Previous studies have shown that chitosan/sodium tripolyphosphate (CS/TPP) and chitosan/flaxseed gum (CS/FG) nanoparticles loaded with bighead carp peptides (BCP) have the advantages of small particle size, high encapsulation rate and significant slow-release effect. This study explored the effects of ionic strength, pH, simulated digestion and storage time on the preparation of chitosan/sodium tripolyphosphate (CS/TPP-BCP) and chitosan/flaxseed gum (CS/FG-BCP) nanoparticles, and evaluated the extracellular lactate dehydrogenase content and antioxidant capacity in vivo of Caco-2 cells treated with the chitosan nanoparticles and their cellular uptake. The results showed that the two kinds of chitosan nanoparticles were stable under acidic conditions and sensitive to a solution with opposite charges. The stability of the nanoparticles loaded with bighead peptides was higher than that of free peptides and both nanoparticles showed higher biocompatibility and cell uptake.
Effect of Protamex Hydrolysis on Foaming Properties and Structural Properties of Corn Glutelin
FAN Guangqi, WANG Juntong, LI Dan, CUI Suping, LI Jing, ZHENG Xiqun
2023, 44(24):  41-49.  doi:10.7506/spkx1002-6630-20230212-110
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The effects of different durations of hydrolysis with Protemex on the foaming properties, surface tension, physicochemical properties and static rheological properties of corn glutelin were determined. The results showed that the solubility and foaming properties of corn glutelin were significantly improved by Protamex hydrolysis. The foaming capacity of the 120 min hydrolysate was highest, which was 2.8 times higher than that of corn glutelin, and its foam stability was also good. The hydrolysate had the lowest surface tension and the highest apparent viscosity. The microscopic morphology of the foam formed was fine and uniform, with a thick protein film. With the prolongation of hydrolysis time, the average particle size of corn glutelin hydrolysates decreased continuously, the endogenous fluorescence intensity and surface hydrophobicity increased gradually, while the surface net charge decreased first and then increased. The results of Raman spectroscopy showed that after appropriate hydrolysis, the α-helix content decreased, and the random coil and β-angle contents increased; the peak intensity ratio of tyrosine residues (I850/I830) increased, and the peak intensity of tryptophan residues (I760) decreased. Nevertheless, the β-folding content changed little. Long-time hydrolysis significantly increased the content of random coil and decreased the peak intensity ratio of tyrosine residues (I850/I830). Therefore, restricted hydrolysis can change the structure and interface properties of corn glutelin, improve its foam properties, and consequently increase the potential utilization rate of corn gluten meal in the food field.
Construction and Evaluation of Steady-State System of Anthocyanin-Chondroitin Sulfate Co-pigmentation Complex Binding to Pullulan
BAO Yiwen, REN Guangyu, LI Jiaxin, TIAN Jinlong, YANG Shufang, YANG Yiyun, SI Xu, LI Bin
2023, 44(24):  50-57.  doi:10.7506/spkx1002-6630-20221206-065
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In this study, a co-pigmentation complex formed by ionic complexation of blueberry anthocyanins (BA) with chondroitin sulfate (CS) was bound to pullulan (PU) to prepare a steady-state BA-CS-PU system by a combination of co-pigmentation and encapsulation technology. The co-pigmentation and stabilizing effects of CS on BA were evaluated by ultraviolet-visible (UV-visible) spectroscopy and color parameters. The structure of BA-CS-PU was characterized by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA), and the mechanism of co-pigmentation and encapsulation was explained. The processing and digestive stability of the steady-state system were evaluated under simulated heat, acid-base strength, co-existence with vitamin C (VC) and in vitro digestion conditions. The results showed that the addition of CS caused a red shift in the UV spectrum and an increase in absorbance, and enhanced the redness, thereby resulting in co-pigmentation effect, which was related to the ionic complexation between the sulfate group of CS and the flavylium ion of BA. The encapsulation effect of PU could be achieved through hydrogen bonding. In addition, co-pigmentation with CS and encapsulation with PU significantly improved the retention rate and a value of BA under heat, acid-base strength and VC co-existence conditions, and also enhanced the gastrointestinal digestive stability, with an 8.63% increase in retention rate. The results of this study provide a basis for in-depth processing of anthocyanin-rich berries.
Effects of Sweet Potato Starch and Soybean Protein Isolate on Konjac Gel Properties and Preparation of Composite Gels
HE Longji, LI Shiqi, CHEN Zhigang
2023, 44(24):  58-67.  doi:10.7506/spkx1002-6630-20230106-036
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The effects of adding different amounts of sweet potato starch (SPS) and soy protein isolate (SPI) on the texture, color, sensory evaluation, moisture distribution, rheological properties and microstructure of konjac gels were investigated. The results showed that the increase in SPS concentration from 0% to 2.5% had a significant effect (P < 0.05) on the textural properties of konjac gels, increasing the hardness and elasticity by 86.43% and 27.69%, respectively, and significantly increasing the gel strength and water-holding capacity (P < 0.05); the addition of SPI below 2% significantly increased the L* and b* values, gel strength and water-holding capacity of gels (P < 0.05) as well as the hardness and elasticity by 13.41% and 15.38%, respectively, and decreased the adhesiveness by 54.19%. The results of rheological analysis showed that the G’ and G” values of gels gradually increased with increasing concentration of SPS and SPI, indicating the formation of a stronger gel structure. Low-field nuclear magnetic resonance (NMR) results showed that the addition of SPS and SPI significantly increased the content bound water in the gel system (P < 0.05), with no significant changes in free water content or relaxation time. The textural properties of the composite gels were further improved by optimized addition of SPS and SPI. Scanning electron microscopy (SEM) results showed that the optimized composite gels formed a denser structure that was continuous and stable. The optimal concentrations of SPS and SPI in the composite gels were 2.5% and 1.0%, respectively. Overall, the results of this study provide a good experimental and theoretical basis for the application of konjac gels in ready-to-eat foods.
Effects of Whey Protein Denaturation and Whey Protein/Casein Ratio on the Stability and Whipping Properties of Recombined Cream
LI Yue, XIE Yufei, LI Yang, LI Yan, ZHANG Liebing, YAN Jianguo
2023, 44(24):  68-74.  doi:10.7506/spkx1002-6630-20230407-054
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In this study, the effects of the denaturation degree of whey protein (WP) and whey protein/casein (WP/CN, m/m) ratio in milk powder on the emulsion stability and whipping properties of recombined cream were investigated. The results showed that the cream prepared from milk power with 60% of WP denaturation had good emulsion stability, and the stability of the system decreased with increase in denaturation degree. An increase in the degree of WP denaturation shortened the whipping time and reduced the leakage rate of whey. The emulsion stability at a WP/CN ratio of 1:4 first increased and then decreased to a level higher than the initial one with increasing proportion of WP. In addition, the whipping time of the cream was shortened, and whey leakage was reduced, while foaming rate declined and bubble collapse rate increased. In summary, the cream prepared from milk power with 60% of WP denaturation showed good emulsion stability and whipping properties; it had the best stability at a WP/CN ratio of 2:4 and better foaming capacity and foam stability at a WP/CN ratio of 1:4. Therefore, WP/CN ratio can be adjusted according to the practical needs to improve the functional characteristics of cream products.
Preparation and Membrane Permeability of Curcumin Nanoparticles by Subcritical Water Technology
ZHAO Wenying, ZHENG Wendi, SONG Xiaoxu, WANG Yao, LIU Bei, CHEN Lei, ZHU Qingshu
2023, 44(24):  75-80.  doi:10.7506/spkx1002-6630-20230212-100
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Curcumin (Cur) nanoparticles were prepared by subcritical water (SBCW) method and its membrane permeability was evaluated. The processing conditions for the preparation of curcumin nanoparticles were investigated in terms of its particle size distribution, polydispersity index (PDI) and zeta potential, and the prepared nanoparticles were characterized and evaluated for in vitro membrane permeability. The results showed that nanoparticles with a diameter of 166 nm and a drug loading of 70.2% were obtained under the conditions: SBCW temperature 120 ℃, receiving solvent temperature 0 ℃, subcritical water/receiving solution ratio 1:3 (V/V), 0.04 g/100 mL lactose as stabilizing agent, and 30% (V/V) ethanol as entrainer. Fourier transform infrared (FTIR) spectroscopy showed no structural changes in Cur. Scanning electron microscopy (SEM) showed that Cur nanoparticles were uniformly spherical in shape. Differential scanning calorimetry (DSC) analysis showed a decrease in the crystallinity of the nanoparticles. Cur nanoparticles exhibited excellent membrane permeability in vitro, and the permeation rate in the first two hours was 25 folds higher than that of free Cur. Furthermore, Cur nanoparticles exhibited good transmembrane capacity in rabbits and significantly enhanced the bioavailability of Cur. The preparation of Cur nanoparticles using subcritical water method has the advantages of high drug loading, good membrane permeability, no need for carriers, simple process, and green environmental protection.
Characteristics of Pickering Emulsion Stabilized by Tea Polyphenols-Starch Nanoparticles
WANG Ran
2023, 44(24):  81-87.  doi:10.7506/spkx1002-6630-20230412-113
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Novel nanoparticles were prepared by addition of tea polyphenols (TP) into gelatinizing waxy maize starch slurry followed by ethanol precipitation and were used to stabilize food-grade Pickering emulsions. The effects of adding TP on the structure and granular properties of starch nanoparticles (SNP) and on the physical stability and oxidative stability of Pickering emulsions were investigated. The results showed that TP could interact with the hydroxyl groups of starch through hydrogen bonding. Moreover, the addition of TP increased the mean particle size of SNP from 187.00 to 233.80 nm, the contact angle from 53.41° to 80.60°, and the absolute value of zeta potential from |−17.20| to |−22.10| mV. Large amounts of small oil droplets were formed in the emulsion stabilized by TP-SNP. Confocal laser scanning microscopy (CLSM) showed that TP-SNP could adsorb onto the oil/water interface to form a physical barrier, which could inhibit oil droplet coalescence. Based on the amount of lipid oxidation products in Pickering emulsions stored for up to 15 days, TP-SNP could delay lipid oxidation of emulsions. These facts indicated that the TP-SNP can be a novel food-grade particle emulsifier with antioxidant capacity for stabilizing Pickering emulsions.
Effect of Mild Heating Assisted Alkaline pH Shift Treatment on the Structural and Functional Properties of Porcine Liver Protein
TANG Yongxin, PENG Songlin, GUO Chenchen, XU Yi, SHANG Yongbiao
2023, 44(24):  88-96.  doi:10.7506/spkx1002-6630-20230407-059
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In this study, a combined method of physical and chemical modification was used to improve the functional characteristics of porcine liver protein (PLP). PLP was modified by mild heating assisted alkaline pH shift treatment. The hydration properties, surface properties, particle size distribution, denaturation degree and molecular structure of modified PLP were measured. The results showed that heat treatment combined with a large shift in pH toward the alkaline side significantly increased the solubility and emulsifying activity of PLP, reduced the particle size while resulting in uniform size distribution, increased the absolute value of zeta potential, and decreased the free sulfhydryl content, changed the primary, secondary and tertiary structures, and increased the surface hydrophobicity. The combined treatment was superior to either treatment alone. In terms of improvements in the hydration and surface properties of PLP, heating at 50 ℃ combined with pH shift toward pH 11 was the best modification condition for PLP.
Bioengineering
Metabolism of Functional Oligosaccharides and Antagonism of Foodborne Pathogens by Resting Cells of Limosilactobacillus reuteri
ZOU Kaixiang, LIU Le, LI Xinrui, ZHU Ke, WEI Hua, ZHANG Zhihong
2023, 44(24):  97-104.  doi:10.7506/spkx1002-6630-20230320-200
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Based on the metabolic activity and biotransformation capacity of the resting cells of Limosilactobacillus reuteri, its ability to metabolize functional oligosaccharides and antagonize foodborne pathogens was explored. A phylogenetic tree for L. reuteri was constructed based on its 16S rRNA gene sequence. The environmental tolerance of the resting cells of L. reuteri was analyzed by acid and bile salt tolerance, and antibiotic sensitivity assays. The effects of functional oligosaccharides on the metabolism, surface hydrophobicity, adhesion capacity and reuterin (a broad-spectrum antibacterial) production ability of L. reuteri were evaluated by using modified media. Then, the inhibitory effect of the resting cells of L. reuteri on the adhesion of Staphylococcus aureus to Caco-2 cells and its growth in skim milk was explored. Results showed that both L. reuteri strains tested could tolerate extreme acidic conditions and bile salts for more than 3 h and were susceptible to common antibiotics. All functional oligosaccharides tested except xylo-oligosaccharides could be metabolized by the resting cells, and its growth, surface hydrophobicity and adhesion capacity were improved significantly by raffinose (P < 0.05). Raffinose could promote the production of reuterin from L. reuteri HLRE13 by utilizing glycerol, attaining a concentration of (1.34 ± 0.03) g/L. Glycerol promoted the inhibitory effect of L. reuteri HLRE13 on a variety of foodborne pathogens significantly (P < 0.001), and inhibited the adhesion of S. aureus to Caco-2 cells by 41.67% through exclusion. Furthermore, glycerol could promote L. reuteri HLRE13 to reduce the number of S. aureus to 103 CFU/mL during co-culture. This study will provide a scientific basis for the functional development of resting cells of L. reuteri and its synergistic efficacy with functional oligosaccharides.
Sequencing and Analysis of MicroRNAs in Bovine Milk Exosomes
SHANG Jingwen, CHAI Yuxia, CAO Xueyan, YUE Xiqing, YANG Mei
2023, 44(24):  105-111.  doi:10.7506/spkx1002-6630-20230316-164
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In this study, density-gradient centrifugation was used to extract bovine milk exosomes, and the small non-coding RNA (sRNA) in the exosomes were sequenced by Illumina sequencing technology to explore the expression profile of bovine milk microRNAs (miRNAs). Through quality control of the original sequence, a total of 3 899 629 pure sRNA sequences were obtained, and their length was concentrated at 28 nt. By comparison with the database, 61 known miRNAs and 346 novel miRNAs were identified. The results of gene ontology enrichment analysis showed that miRNAs from bovine milk exosomes played a critical role in various biological processes such as cell process, single organism process and metabolic process. It mainly consisted of cells and organelles and was mainly involved in molecular functions such as binding, catalytic activity and transporter activity. The results of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that the known miRNAs and the new miRNA target genes were significantly enriched in pertussis (ko05133), chemokine signal pathway (ko04062), endocytosis (ko04144), lysosome (ko04142) and other pathways, and bovine milk exosome miRNAs played an important role in specific signaling pathways.
Postmortem Degradation of Qinchuan Beef Protein by Proteasome and Its Mediated Ubiquitin-Proteasome Pathway
HU Lijun, ZHANG Qian, CHEN Xueyan, WANG Jinxia, LI Rong, LI Yalei, LUO Ruiming
2023, 44(24):  112-117.  doi:10.7506/spkx1002-6630-20230320-196
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In this study, the Longissimus dorsi muscle of Qinchuan cattle was injected with the proteasome inhibitor MG-132 immediately postmortem and then stored at 4 ℃. The effect of the ubiquitin-proteasome pathway (UPP) on protein degradation as well as changes in the proteasome activity, ubiquitin content and microstructure of the muscle during postmortem storage was explored in order to provide theoretical support for precise postmortem regulation of beef quality. With the extension of storage time, proteasome activity was lower and the contents of total soluble protein and ubiquitin were higher in the MG-132 group than in the control group. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results showed that the band intensity of total soluble proteins between 40 and 250 kDa was greater in the MG-132 group than in the control group; muscle structure was better preserved in the MG-132 group, and the Z line and the boundary between light and dark bands were clearer than those in the control group. The contents of total soluble protein and ubiquitin showed a significantly positive correlation (P < 0.05). In conclusion, postmortem injection of MG-132 inhibited the proteasome activity and the degradation of ubiquitinated proteins in the UPP in Qinchuan beef, which in turn altered protein degradation and attenuated muscle damage. This suggests that the UPP has a potential role in meat quality formation; the proteasome not only degrades proteins by itself alone to destroy beef myofibrillar structure, but also influences postmortem beef protein degradation through mediating the UPP, ultimately affecting postmortem beef quality.
Isolation, Structural Identification and in Vitro Activity Evaluation of Angiotensin-Converting Enzyme Inhibitory Peptides from Moringa oleifera Seeds
ZHONG Yuwang, XU Wanli, FAN Yaozhu, LI Yiyan, WANG Xuefeng
2023, 44(24):  118-126.  doi:10.7506/spkx1002-6630-20220926-284
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In this study, angiotensin-converting enzyme (ACE) inhibitory peptides from an enzymatic hydrolysate of Moringa oleifera seeds were separated by sequential ultrafiltration and ion exchange chromatography. The peptide sequences were identified by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and potential ACE inhibitory peptides were selected by bioinformatics and molecular docking; their secondary structure was analyzed by Fourier transform infrared (FTIR) spectroscopy and their in vitro activity was evaluated by enzymatic inhibition kinetics and the methyl thiazolyl tetrazolium (MTT) method. The results showed that peptide fraction F-b had a good antihypertensive effect. A total of 11 peptide sequences were identified. Peptide QGPRPQ was identified as a potential ACE inhibitory peptide with a half-maximum inhibitory concentration (IC50 ) (1.15 ± 0.3) mmol/L. Molecular docking showed that QGPRPQ could better bind to ACE through hydrogen bond and hydrophobic interaction. Secondary structure analysis showed that QGPRPQ was composed of 22.8% α-helix, 33.3% β-fold and 43.9% β-turn. The mode of inhibition of QGPRPQ was mixed type, and it had no toxic effect on HepG2 cells at a concentration lower than 0.01 mg/mL. This study can provide an important theoretical basis for the development and utilization of hypotensive peptides derived from M. oleifera seed protein.
Scale-Up Production of Chicken Myoblasts in Microcarrier-Based System
LIU Yisen, CAI Jiaqi, LI Shilei, LI Yingying, WANG Shouwei, YANG Feng, HU Haijuan, LIU Wenting, LI Yushuang, DONG Shengyan, CHEN Jiaxuan, LIANG Jun
2023, 44(24):  127-137.  doi:10.7506/spkx1002-6630-20230330-310
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With the rapid development of the cultivated meat industry, large-scale cell culture technology applied to cultivated meat production has received extensive attention. In this study, two microcarriers, Cytodex 1 and 3D TableTrix™, were used for suspension culture of myoblasts in spinner flasks to select a more suitable one for large-scale culture of myoblasts, and then the effects of different culture conditions on the large-scale culture of cells were explored. The microscopic results showed that Cytodex 1 was spheres with a smooth surface and no macroporous structure, and 3D TableTrix™ was irregular spheres with a porous surface and large pores. The results of cell culture in spinner flasks showed that the cells grew on 3D TableTrix™ more efficiently, and after 10 days of culture, the cell yield was 8.97 × 105 cells/mL. The optimal conditions for cell attachment were intermittent stirring at 40 r/min for 10 min with intervals of 50 min. The best cell culture efficiency was obtained by using cell inoculation density of 1 × 105 cells/mL, microcarrier density of 2 mg/mL, agitation speed of 40 r/min, and initial culture serum concentration of 20% as well as replacing the medium with a new one containing 10% serum (V/V) after 24 h of culture, and replacing 50% of the medium with a new one with every other day. By bead to bead transfer of the microcarriers, the cells were transferred to a 2 L spinner flask. Finally, 1.07 × 109 cells were harvested with a survival rate of more than 95%. Microcarriers loaded with cells could be cryopreserved and resuscitated, and no significant differences in proliferation status and morphology were observed compared with thawed cells. The optimized microcarrier based culture process will have promising applications in the industrial scale production of cultivated meat.
Effects of Mixed-Strain Starter Culture on Quality, Flavor and Antioxidant Activity of Fermented Fish Sausage
FENG Meiqin, LI Tianyi, SUN Jian
2023, 44(24):  138-145.  doi:10.7506/spkx1002-6630-20230906-044
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To explore the effect of functional starter cultures on the quality, flavor and antioxidant activity of fermented fish sausage, we prepared fermented fish sausage by inoculation with a cocktail of the functional starter culture strains Lactobacillus plantarum CD101 and Staphylococcus simulans NJ201 or natural fermentation as a control, and we measured the pH, texture, color difference, antioxidant capacity, volatile flavor substances and free amino acids of the prepared samples. The results showed that inoculation with functional starter culture could rapidly reduce the pH of fish sausage during fermentation and improve the stability and safety of the sausage; improve the hardness and chewiness, and enhance the brightness and color, thereby making the sausage have better quality; significantly increase the scavenging capacity of sausage-derived peptides against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical cation and hydroxyl radical, contributing to improving the antioxidant activity of sausage-derived peptides; and increase the contents of ketones, esters and other flavor substances, enriching the flavor of the sausage and making it have a stronger sweetness and fruity aroma. Moreover, inoculation with functional starter culture promoted the release of free amino acids from the sausage, which was conducive to enhancing the nutritional properties, antioxidant capacity and flavor of the sausage.
Improvement of Antioxidant Activity of Defatted Selenium-Enriched Rice Bran by Lactic Acid Bacteria Fermentation
ZHANG Jiani, ZHANG Xiaoxuan, WANG Damao, ZHAO Guohua, YU Junlei, LEI Lin
2023, 44(24):  146-154.  doi:10.7506/spkx1002-6630-20230416-150
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Selenium-enriched rice bran is a major by-product in the production of selenium-enriched polished rice, which is rich in selenium, dietary fiber, and active substances such as phenolic compounds. However, the high-value utilization of selenium-enriched rice bran has not been fully explored. In this study, four strains of lactic acid bacteria (Lactobacillus acidophilus, Streptococcus thermophilus, L. plantarum, and L. delbrueckii subsp.) were used to ferment defatted selenium-enriched rice bran. The physicochemical properties, nutritional characteristics, microstructure, physicochemical properties and antioxidant activity of selenium-enriched rice bran were compared before and after fermentation. The results showed that lactic acid bacteria fermentation increased the insoluble dietary fiber/water-soluble dietary fiber ratio in selenium-enriched rice bran by 20%–45%, the contents of total phenols and total flavonoids by 5%–6% and 16%–31%, respectively, and the conversion efficiency of inorganic selenium to SeCys2 by 42%–49%. Moreover, the fermentation reduced the particle size of selenium-enriched rice bran, made the surface more loose and porous, and enhanced the hydration properties, cholesterol adsorption capacity and antioxidant activity. The decreasing order of the comprehensive scores of fermented selenium-enriched rice bran in principal component analysis (PCA) was L. plantarum > L. delbrueckii subsp. > S. thermophilus > L. acidophilus. Among these samples, the sample fermented with L. plantarum exhibited the strongest antioxidant activity in vitro, as well as the highest contents of total acid, SeCys2, total phenols and total flavonoids. This study provides a theoretical basis for the intensive development and utilization of selenium-enriched rice bran.
Isolation, Purification, Identification and Hypolipidemic Activity of Lipase Inhibitory Peptide from Chlorella pyrenoidosa
LIN Luan, LIU Wenjun, HUANG Junyuan, JIA Aijing, WANG Dengmi, LIU Bin, ZHAO Chao
2023, 44(24):  155-163.  doi:10.7506/spkx1002-6630-20230302-021
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In this study, pancrelipase inhibitory peptides (PES) from an enzymatic protein hydrolysate of Chlorella pyrenoidosa were isolated and purified by ultrafiltration and Sephadex gel chromatography. The in vivo hypolipidemic activity of PES was evaluated by fat deposition and the levels of triglyceride (TG) and total cholesterol (TC) in Caenorhabditis elegans fed a high sugar diet. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to identify the peptide sequence of PES, and molecular docking was used to select potential pancreatic lipase inhibitory peptides, and the pancreatic lipase inhibitory activity of the synthesized peptides was verified. The results showed that PES had good hypolipidemic activity at a concentration of 1 mg/mL; it inhibited lipid deposition by 22.5%, and reduced the levels of TG and TC by 27.4% and 29.4%, respectively. In total, 999 peptides were identified, and four potential lipase inhibitory peptides were obtained. Among them, FLGPF had the best inhibitory effect on pancreatic lipase, with an inhibition rate of 50.12% at 8 mg/mL. The inhibition was reversible and non-competitive, with an inhibition constant of 5.23 mg/mL. Molecular docking showed that FLGPF could better bind to human pancreatic triacylglycerol lipase (PTL) via π-hydrogen, π-cation and hydrogen bond interactions. This study can provide a theoretical reference for the development and utilization of C. pyrenoidosa protein-derived hypolipidemic peptide.
Inhibitory Effect and Mechanism of Lactiplantibacillus plantarum HB13-2 on Candida albicans
NING Yawei, SUN Ying, ZHANG Dongchun, ZHANG Yajuan, SI Haishan, KANG Yapeng, WANG Zhixin, WANG Shijie
2023, 44(24):  164-170.  doi:10.7506/spkx1002-6630-20230308-074
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This study explored the inhibitory effect and mechanism of the culture supernatant of Lactiplantibacillus plantarum HB13-2 on Candida albicans. The minimum inhibitory concentration was determined by the double dilution method. Then, the fluorescent dye calcofluor white (CFW) was used to stain the cell wall and observe it. The results showed that the supernatant enhanced the fluorescence intensity and damaged the cell wall. Flow cytometry and fluorescence microscopy showed that the supernatant changed the membrane permeability of C. albicans. The transmembrane potential was detected using the fluorescent probe DiSC3(5), and it was found that the fluorescence intensity was enhanced, indicating that the supernatant caused dissipation of the transmembrane potential. Through microstructural observation by scanning electron microscopy (SEM), it was found that the supernatant of Lactobacillus plantarum HB13-2 caused cellular deformation and leakage of intracellular contents. As detected by fluorescence staining with 2’,7’-dichlorodihydrofluorescin diacetate (DCFH-DA) and Rhodamine-123, the supernatant resulted in accumulation of a large amount of intracellular reactive oxygen species (ROS) and increased mitochondrial membrane potential. In conclusion, the supernatant of L. plantarum HB13-2 can deform cells by destroying the cell wall and membrane and lead to mitochondrial damage, thereby inhibiting C. albicans. This study will provide a scientific basis for the development of L. plantarum HB13-2 as an oral probiotic.
Effect of Soymilk Fermented by Different Lactic Acid Bacteria on Dough Fermentation Characteristics and Steamed Bun Quality
SHAO Tong, WANG Xingben, WU Ran, ZHANG Yiyun, ZHANG Chenchen, GU Ruixia, CHEN Xia
2023, 44(24):  171-178.  doi:10.7506/spkx1002-6630-20230321-211
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The effects of soymilk fermented with single and mixed (1:1:1) cultures of three strains of lactic acid bacteria (LAB) isolated from sourdough from Fuchun Teahouse in Yangzhou City on the fermentation characteristics of dough and the quality of steamed bun were investigated. The results showed that the acidity and viable bacterial count of soymilk fermented with the mixed culture were 85.06 °T and 9.66 (lg(CFU/mL)), respectively, which were higher than those of the single culture fermented samples. Meanwhile, compared with the control group, the addition of fermented soymilk significantly increased the organic acid content and viable bacterial count of dough. The lactic acid content and viable bacterial count of dough supplemented with Lactobacillus pentosus 203 fermented soymilk were the highest, which were 18.57 mg/g and 8.94 (lg(CFU/g)), respectively. Dough added with Lactobacillus fermentum 202 fermented soymilk had the highest acetic acid content (3.81 mg/g). Compared with control steamed buns, the specific volume, elasticity and height to diameter ratio of four steamed buns supplemented with fermented soymilk were significantly increased, while the hardness and chewiness were significantly decreased. Steamed buns added with mixed-culture fermented soymilk had the highest overall acceptability. A total of 48 volatile flavor substances were detected in the five groups of steamed buns. Among them, the relative contents and types of flavor substances in the mixed culture group were the highest, which were 71.62% and 47, respectively. After being stored at 4 ℃ for 4 days, the moisture loss rate and retrogradation enthalpy of steamed buns added with fermented soymilk were significantly lower than those of the control group; the highest moisture content of 38.53% and the lowest retrogradation enthalpy of 1.00 J/g were found in the mixed culture group. In conclusion, adding fermented soymilk can effectively improve the quality and flavor and delay the aging of steamed buns, this effect being most pronounced with the incorporation of mixed-culture fermented soymilk.
Impact of Sequential Fermentation with Different Non-Saccharomyces Yeasts and Saccharomyces cerevisiae on the Aroma of Yinhong Plum Wine
LI Tian, LEI Yu, LI Dong, LI Jingya, JIN Lei
2023, 44(24):  179-187.  doi:10.7506/spkx1002-6630-20230313-118
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In order to enhance the flavor and mouthfeel of Yinhong plum wine, this study investigated the impact of mixed culture fermentation with different non-Saccharomyces yeasts and Saccharomyces cerevisiae on the quality of Yinhong plum wine, aiming to identify the optimal yeast combination for mixed culture fermentation. Four non-Saccharomyce yeasts were selected, including Wickerhamomyces anomalus Wa3, Hanseniaspora uvarum Hu12, three strains of Pichia kluyveri (Pk2A2, PkW2 and PkY2), and Pichia guilliermondii Pg1. Plum wine was fermented by sequential inoculation with non-Saccharomyces and S. cerevisiae strain FX10 at a ratio of 1:1, and its quality was comprehensively evaluated by measuring yeast biomass changes, alcohol concentration, glycerol, organic acids, flavor compounds, and sensory characteristics. The results indicated that the growth of both S. cerevisiae and non-Saccharomyces yeasts was inhibited during mixed culture fermentation. Non-Saccharomyces yeasts died during 6–8 days of primary fermentation. Compared with fermentation with FX10 alone as a control, mixed culture fermentation increased glycerol production, decreased lactate and ethanol contents, and reduced the utilization of reducing sugars in Yinhong plum wine. The concentration of aroma-active esters in Yinhong plum wine from mixed culture fermentation (1.293–4.842 mg/L) was significantly higher than that in the control (1.026 mg/L). Particularly, the wine fermented by PkY2 + FX10 exhibited the highest content of ester compounds, which was 4.72 times higher than that of the control. Principal component analysis (PCA) revealed a significant difference between the wine fermented by P. kluyveri + FX10 and the control group, which was closely associated with elevated levels of ethyl esters and acetic esters, contributing to the intense floral and fruity aroma of Yinhong plum wine. Overall, this study suggested that mixed culture fermentation with P. kluyveri and S. cerevisiae holds promising potential for enhancing the aroma and sensory quality of Yinhong plum wine.
Dynamic Succession of Microbial Communities in Soybean Paste Made with Broomcorn Millet as an Additive and Its Correlation with Flavor and Nutritional Properties during the Brewing Process
MA Lixue, YU Qiaoru, WU Mengna, WANG Xiaoyu, SU Tingting, YANG Xiyuan, LIU Yuhang, YAO Di, WANG Changyuan
2023, 44(24):  188-200.  doi:10.7506/spkx1002-6630-20230414-134
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To obtain a full understanding the quality and microbial characteristics of soybean paste made from a mixture of soybean and broomcorn millet flour, its physicochemical properties (amino nitrogen and nitrite), and total phenols (TP), γ-aminobutyric acid (GABA), free amino acids (FAAs), volatile compounds, and microbial community composition were investigated. The results showed that the amino nitrogen content increased to 0.71%, and the nitrite content decreased to within the standard range (1.37 mg/kg). The contents of TP, key FAAs and volatile compounds increased significantly during the fermentation process. The core microbial communities included Enterobacter, Pseudomonas, Stenotrophomonas, Aspergillus, and Alternaria. The results of correlation analysis confirmed that bacteria (Bacillus, Knoellia, and Blastococcus) and fungi (Epicoccum and Saccharomyces) played a significant role in the bioactivity changes and flavor generation in soybean paste. This study will be of great significance for understanding the quality and flavor of novel soybean paste made with cereal flour as an additive.
A Dual-Bacterial Coupled Fermentation Strategy for Nicotinamide Mononucleotide Synthesis
SUN Ting, ZHANG Hongtao, YANG Feng, CHAI Wengang, XUE Haoyang, TAN Shuyin
2023, 44(24):  201-210.  doi:10.7506/spkx1002-6630-20230321-203
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In this study, a dual-bacterial coupled fermentation system containing nicotinamide nucleoside kinase (NRK) and polyphosphatase (PPK) was constructed, and the application of PPK-based ATP regeneration system in NMN production was achieved. First, engineering strains expressing NRK1 and NRK2 were constructed, and the highly active Escherichia coli BL21 (DE3)-pET28a-NRK1 was selected, with NMN yield and productivity of 5.17 g/L and 77.4%, respectively. Then, the induced expression conditions of NRK1 were optimized, and a low temperature of 16 ℃, an isopropyl-β-D-thiogalactopyranoside (IPTG) concentration of 0.7 mmol/L, an inoculation amount of 3% and an induction duration of 22 h were found to be optimal the soluble expression of NRK1 protein. The optimal synthesis conditions of NMN by E. coli BL21 (DE3)-pET28a-NRK1 were explored. It was found that after 12 h culture at 18 ℃ at an initial cell concentration of 100 g/L and a ratio of ATP to NR of 1:1.5, the highest yield of NMN of 5.73 g/L was obtained with a productivity of 85.78%. Finally, the optimal conditions that provided maximal NMN production (11.81 g/L) by coupled fermentation with E. coli BL21 (DE3) pET28a-PPK and E. coli BL21 (DE3)-pET28a-NRK1 were determined as 1:3.5, 1:2 and 16 h for ATP to NR ratio, initial cell concentration and fermentation time, respectively. The high-density dual-bacterial coupled fermentation strategy established in this study opens up a new pathway for high-efficiency, low-cost and large-scale production of NMN.
Analysis of Fungal Community Structure and Flavor Quality of High-temperature Daqu from Xiangyang, China
XIANG Fanshu, CAI Wenchao, TIAN Longxin, LIU Juzhen, ZHOU Jiaping, YE Mingbo, SHAN Chunhui, GUO Zhuang
2023, 44(24):  211-219.  doi:10.7506/spkx1002-6630-20230327-255
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The fungal community structure and flavor quality of white, yellow and black high-temperature Daqu from company A in Xiangyang, China were analyzed using MiSeq high-throughput sequencing and electronic nose technology. The sequencing results showed no significant differences in the α-diversity or β-diversity of fungal community among different colored Daqu (P > 0.05); the dominant fungal genera belonged to Ascomycota including Thermomyces (36.50%), Thermoascus (27.15%), Saccharomycopsis (9.23%) and Dipodascus (1.19%), and Mucoromycota including Aspergillus (9.36%), Rhizopus (1.44%) and Rhizomucor (1.03%). The electronic nose exhibited high sensor responses to volatile organic sulfides, terpenoids, hydroxides and ethanol and low sensor responses to aromatic substances in high-temperature Daqu; the Mann-Whitney test revealed significantly higher sensor responses to aromatic substances (P < 0.01) and lower sensor responses to the other aroma components (P < 0.05) in yellow than black Daqu. In addition, based on the fungal sequence data from the MG-RAST database for three different colored high-temperature Daqu produced by company B, comparative analysis of the fungal community structure of high-temperature Daqu produced by companies A and B was carried out. It was found that there were highly significant differences (P < 0.01) in the α-diversity and β-diversity of fungal community between Daqu produced by the two companies, and the results of cluster analysis showed that the Mahalanobis distance between the different colored high-temperature Daqu from the same company was closer. Finally, in this study, four strains of S. fibuligera were isolated from high-temperature Daqu produced by company A by traditional pure culture method. In conclusion, there was a significant difference between the fungal communities of high-temperature Daqu produced by companies A and B, which was greater than the difference between different colored high-temperature Daqu produced by the same company.
Component Analysis
Contribution of Stems and Leaves to the Quality of Keemun Black Tea
ZHOU Hanchen, YANG Jihong, LIU Yaqin, WANG Hui, XU Yujie, HUANG Jianqin, LEI Pandeng
2023, 44(24):  220-228.  doi:10.7506/spkx1002-6630-20230328-267
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In order to understand the contribution of stems and leaves to the quality of Keemun black tea, this study analyzed the differences in aroma, taste quality and metabolites among black tea manufactured from tender leaves, tender stems, single buds and intact buds with leaves (mainly one bud with two leaves) from the tea variety ‘Fuzao 2’ by gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), sensory evaluation, and preference evaluation. The results showed that all four black teas were sweet aroma type, and the bud-leaf tea had a strong sweet aroma. The single-bud tea had a fresh and brisk taste. The tender-stem tea scored highest in preference evaluation. Metabolite analysis showed the content of catechins was the highest in the single-bud black tea and the lowest in the tender-stem black tea, while free amino acids were significantly enriched in the tender-stem black tea, reaching up to 80 mg/g. The contents of quercetin and rutin were higher in the stem black tea, while the contents of kaempferol-3-O-glucoside and kaempferol-3-O-rutinoside were the highest in the leaf black tea. The ratio of thearubigins to theaflavins was 11.6, 9.4, 14.6, and 8.2 in black tea made from intact buds with leaves, buds, leaves, and tender stems, respectively. The total amount of volatile compounds in the tender-stem black tea (32.37 μg/g) was significantly lower than that in the bud (100.01 μg/g), leaf (95.67 μg/g), and bud-leaf black tea (92.42 μg/g). The contents of benzaldehyde, benzeneacetaldehyde and indole were higher in the tender stem black tea, while the contents of β-ionone, α-ionone and linalool oxide in the leaf black tea were higher than those in the other three black teas. This study shows that high contents of theanine in tender stems and glycoside aroma precursors in tea leaves contribute primarily to the formation of the quality of Keemun black tea.
Comprehensive Evaluation of Tea Cultivars Suitable for Matcha Production Using Multivariate Statistical Analysis
YUAN Liping, LEI Zhendong, WANG Huanhuan, QIN Xinxue, YANG Shuya, WEN Xiaoju, WU Weihe, NI Dejiang, CHEN Yuqiong
2023, 44(24):  229-234.  doi:10.7506/spkx1002-6630-20130110-079
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Matcha was prepared from 36 tea cultivars grown in the same tea garden according to the shading requirements for fresh leaves to be used for the production of matcha and its 11 quality indexes such as sensory quality, major physicochemical properties and chroma values were analyzed. In order to select tea cultivars suitable for the manufacturing of matcha, a comprehensive evaluation model of matcha quality was established by cluster analysis (CA), principal component analysis (PCA) and multiple linear regression analysis. The CA results showed that the 36 cultivars could be divided into three groups. Matcha from group I had the best quality with green color, fresh and mellow taste, and low phenol/ammonia ratio. Matcha from group II had high phenol/ammonia ratio and strong astringent taste. Matcha from Group III, consisting of etiolated and albino cultivars, had poor color and aroma quality. The PCA results showed that the cumulative contribution rate of the first five principal components was 88.152%. Comprehensive evaluation of matcha using the evaluation function constructed based on the first five principal components showed that the top 10 cultivars were Zhongcha 102, Taicha 12, Zhongcha 108, Fuding Dahao, Meizhan, Fuding Dabai, Fuyun 6, Zi Mudan, Maolv and Yingshuang. The model describing the relationship between sensory quality and physicochemical properties established by multiple linear regression analysis was as follows: y = 3.167|a*| + 46.850 (R2 = 0.710, P < 0.001). The scores of matcha cultivars evaluated by this model were highly consistent with the comprehensive evaluation results based on principal components, indicating that the a* value of dried tea could be used as a representative index to evaluate the quality of matcha. The results of this study can provide a reference for evaluating the suitability of tea cultivars for matcha manufacturing.
Odor Characteristics and Formation Pathways of Low-Salted Large Yellow Croaker
GUAN Junlan, YAO Yuxuan, WU Ling, WANG Yongxing, SHEN Xibing, DU Xiping, NI Hui
2023, 44(24):  235-244.  doi:10.7506/spkx1002-6630-20230220-189
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In this study, our purpose was to investigate the effect of mild salting on the flavor of large yellow croaker. The volatile flavor compounds of raw (unsalted) and low-salted large yellow croaker were determined by solid phase microextraction (SPME) combined with gas chromatography-mass spectrometry (GC-MS) and evaluated by gas chromatography-olfactometry (GC-O) and odor activity values (OAV) analysis. The GC-MS analysis showed that the contents of hexanal, nonanal, heptanal, 1-octene-3-ol, anethole and hexanol in both samples were higher than those of other volatile compounds identified. GC-O and OAV analysis showed that the flavor of raw large yellow croaker was significantly affected by 1-octene-3-ol, octanal, nonanal, hexanal, heptanal, (E,Z)-2,6-nonadienal, trans-2-octenal and anethole (OAV > 1); the flavor of low-salted large yellow croaker was significantly affected by linalool, nonanal, hexanal, octanal, 1-octene-3-ol, anethole, (E,Z)-2,6-nonadienal and heptanal (OAV > 1). The changes in flavor after salting treatment was attributed to a significant increase in the OAV of linalool and anethole, and a significant decrease in the OAV of 1-octene-3-ol, hexanal, nonanal, trans-2-octenal, (E,Z)-2,6-nonadienal, heptanal and octanal. The changes of some flavor components might be related to reactions such as the oxidative degradation of unsaturated fatty acids, the biosynthesis of terpenoids, the isomerization of aromatic alcohols, the oxidation and reduction of aliphatic aldehyde and esterification.
Metabolomics Analysis of Colostrum and Mature Milk from Saanen Goats
KANG Jiaxin, LI Meng, LIAO Minhe, SHANG Jiaqi, REN Haowei, LU Xicheng, LIU Ning
2023, 44(24):  245-252.  doi:10.7506/spkx1002-6630-20221210-107
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The differences in metabolites and related metabolism pathways in colostrum and mature milk from Saanen goats at different lactation stages were explored by untargeted metabolomics based on ultra-high performance liquid chromatography-quadrupole electrostatic field orbitrap mass spectrometry (UPLC-QE-orbitrap-MS). The results showed that a total of 118 differential metabolites were found between colostrum and mature milk, among which 62 had higher relative contents in colostrum than in mature milk and 56 had lower relative contents in colostrum than in mature milk. These metabolites were mainly lipids, amino acids, and nucleosides. Nine key metabolic pathways most associated with these metabolites were selected, which jointly regulated the lactation process of Saanen goats, and the citric acid cycle could act as a bridge connecting other metabolic pathways. The number of differential metabolites involved in these metabolic pathways was 12. The differential metabolites with relatively high contents in colostrum were taurine, hypotaurine, taurocholic acid, L-phenylalanine, L-tyrosine, succinic acid, isocitrate, D-maltose, α-lactose, 4-hydroxyphenylpyruvate and glycine. The differential metabolite with relatively high contents in mature milk was N1-methyl-4-pyridone-3-carboxamide. They could be used as potential marker metabolites in the colostrum and mature milk of Saanen goats. Metabolomics technology can also be used for identifying differential metabolites in milk from other dairy species at different lactation stages.
Aroma Components of Huiming Tea
YOU Qiushuang, LIU Jianping, HE Weizhong, ZHU Yin, LIN Zhi, LÜ Haipeng
2023, 44(24):  253-261.  doi:10.7506/spkx1002-6630-20230330-311
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In this study, the volatile components and key aroma-active compounds of 13 representative Huiming tea samples were analyzed using stir bar sorptive extraction (SBSE) combined with gas chromatography-olfactometry-mass spectrometry (GC-O-MS). Results showed that a total of 120 volatile components were identified, mainly including 26 alcohols, 26 esters, and 14 ketones. Among them, the contents of the aroma compounds geraniol, 2,2,4-trimethyl-3-hydroxypentyl isobutyrate, indole, (Z)-jasmone, and 1-octen-3-ol were the highest. Moreover, a total of 42 key aroma-active compounds were identified by GC-O analysis, including 2-ethyl-3,5-dimethylpyrazine, 6-methyl-5-heptene-2-one, linalool, (Z)-3-hexenyl butanoate, 3,5-octadiene-2-one, and (E)-β-ionone, which played an important role in the formation of the fresh and floral aromas of Huiming tea. The results of this study will contribute to revealing the chemical basis of the aroma quality of Huiming tea, and provide a theoretical basis for improving the aroma quality of Huiming tea.
Characteristic Aroma and Molecular Sensory Analysis of Black Teas from Different Regions by Gas Chromatography-Mass Spectrometry and Gas Chromatography-Olfactometry
ZHENG Fangling, GAN Shiya, ZHAO Lei, CHEN Yingqi, ZHAO Xiaoyi, JIANG Qing, QIU Tong, ZHANG Ying, ZHENG Pengcheng, XIA Tao, DAI Qianying
2023, 44(24):  262-268.  doi:10.7506/spkx1002-6630-20230110-073
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In order to investigate the differences in the characteristic aroma of black teas from different regions, the volatile aroma compounds of Keemun black tea, Yichang black tea, Dianhong black tea and Yingde black tea were identified by solid phase extraction (SPE) combined with gas chromatography-mass spectrometry (GC-MS) and were evaluated by gas chromatography-olfactory (GC-O). Odor activity value (OAV) calculation and correlation analysis between sensory aroma profile and key aroma-active compounds were performed to analyze the sensory attributes and chemical basis of the characteristic aroma of black tea. The results showed that the four black teas differed in the sensory attributes of seven aroma notes such as floral, sweet and herbal notes. Additionally, 24 differential key aroma compounds were identified (P < 0.05, OAV > 1). Geraniol contributed most to black tea aroma with the highest OAV in Keemun black tea (16 581.33), followed by Yichang black tea (7 463.65), Dianhong black tea (2 832.13) and Yingde black tea (467.96). Partial least squares (PLS) regression analysis and Pearson correlation analysis showed that β-ionone, geraniol and indole were responsible for the floral and sweet aroma of Keemun black tea, (Z)-3-hexenol and α-terpineol contributed to the fruity and woody aroma of Dianhong black tea, and 2-heptanol and (Z)-linalooloxide were responsible for the herbal aroma of Yingde black tea. In conclusion, this study has preliminarily clarified the characteristic aroma profiles of black tea from the four regions and their material basis at the molecular level.
Effects of Different Base Wine Volumes on Volatile Compound Profile of Distilled Merlot Wine Analyzed by Headspace Solid-Phase Microextraction Combined with Gas Chromatography-Mass Spectrometry
GUO Yayun, SHAO Xuedong, ZHANG Zhengwen, LI Bo, XUE Wei, SHI Hongmei
2023, 44(24):  269-276.  doi:10.7506/spkx1002-6630-20230408-074
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The effects of different base wine volumes (150, 200, and 250 L) during the distillation process on the volatile compounds of distilled wine made from Merlot grapes from the Jiaodong Peninsula were investigated in order to optimize the distillation conditions of distilled Merlot wine. In this study, headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to qualitatively and quantitatively analyze the volatile compounds of the intermediate distillates from different volumes of base wine. In addition, statistical analysis of the volatile composition data was performed by principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA). In total, 67, 67, and 64 aroma compounds were detected in the distillate samples from 150, 200, and 250 L of base wine, respectively. In each sample, 37 esters were found. Ester content was significantly higher in the distillate from 150 L than 200 and 250 L from base wine. PCA and OPLS-DA results consistently showed that 13, 1, and 1 aroma substances had positive effects on distilled samples from 150, 200, and 250 L of base wine, respectively. This study will lay the foundation for the production of high-quality distilled wine and thereby contribute to the development of the wine industry.
Analysis and Evaluation of Fruit Quality and Volatile Composition of F1 Hybrids between ‘Yuluxiang’ and ‘Shinseiki’ Pear
YUE Yu, HUANG Ping, CHEN Hu, YU Chunliang, PENG Jianying
2023, 44(24):  277-285.  doi:10.7506/spkx1002-6630-20230324-239
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In order to explore the genetic variation between hybrid fruits and their parents and conduct comprehensive evaluation of hybrid fruits, seven promising F1 hybrids (7-93, 8-44, 8-176, 9-188, 9-193, 10-101 and 10-173) between ‘Yuluxiang’ and ‘Shinseiki’ pears, the female parent ‘Yuluxiang’ and the popular cultivar ‘Akizuki’ were evaluated for quality indicators such as single fruit mass, fruit shape index, hardness, soluble solid content, soluble sugar content, titratable acid content, sugar/acid ratio, vitamin C content, and aroma composition. Meanwhile, the differences in aroma among different cultivars were evaluated using orthogonal partial least squares-discriminant analysis (OPLS-DA). The results showed that there was a significant difference in fruit quality among the seven F1 hybrids, with 8-44 having a fruit shape index equal to 1 and the highest soluble solids and sugar content. Altogether, 83 volatile components were detected from the nine cultivars, of which 10-173 and 8-44 had the highest total amount of volatile components, and 10-173 and 10-101 contained the highest number of volatile compounds. The major aroma components in pears were alcohols, esters, and aldehydes. The OPLS-DA results showed that the aroma components of 10-101 and 10-173 were significantly different from those of the other strains. Fruit quality traits of 10-101 had a significantly positive correlation with ethyl acetate and hexyl acetate; fruit quality traits of 10-173 had a significantly positive correlation with ethyl octanoate and α-farnesene and trans-2-hexenal, and their contents were significantly higher than those in the other strains, making the flavor more prominent. According to variable importance in the projection (VIP) results, we predicted 42 aroma markers that differed among varieties, and through odor activity value (OAV) analysis, we identified key volatile compounds that contributed to the characteristic odor of each strain. Through correlation analysis, we identified the association between pear quality traits and characteristic aromas. Principal component analysis (PCA) showed that the comprehensive scores of 8-44, 10-173 and 10-101 had the highest ranking, indicating that they had better fruit quality than the other strains. In summary, 8-44, 10-101, and 10-173 can be regarded as potential pear strains. This study can provide a reference for the breeding and promotion of new pear varieties.
Safety Detection
Hyperspectral Nondestructive Detection of Maturity of Preserved Eggs Using Deep Learning Combined with Two-Dimensional Correction Spectral Image
CHEN Yuanzhe, WANG Qiaohua, FAN Wei, LIU Shiwei, LIN Weiguo
2023, 44(24):  286-296.  doi:10.7506/spkx1002-6630-20230111-085
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In this study, hyperspectral imaging was used for nondestructive detection of preserved eggs at different maturity levels during the pickling period. First, the optimal waveband was determined based on the one-dimensional spectra and two-dimensional correlation spectra in the time-series mode, separately. Then, the modeling effects of traditional machine learning and the improved ResNet20_SE model in the optimal waveband were compared, and the results showed that the improved ResNet20_SE model was better; the overall recognition accuracy was 97.29% for the synchronous spectral dataset, and the average detection speed for a single image was 24.62 ms. Finally, the better synchronous spectral dataset ResNet20_SE model was applied to the hyperspectral pixel spectral image to calculate the value of each pixel point, and a pseudo-color technique was used for the visual detection of the spatial distribution of preserved egg maturity during the pickling process. The results of this study showed that hyperspectral imaging combined with deep learning is useful for nondestructive detection of preserved egg maturity during curing, which can lay a theoretical foundation for high-throughput online sorting of preserved egg maturity in the future.
Colorimetric and Fluorescent Dual-Mode Detection of Aflatoxin B1 Using Composite Nanomaterial
LI Yang, LU Dai, ZHOU Zhou, CHEN Liye, XIE Xinhui, WU Jiahao, ZHAO Qian, SHI Xingbo
2023, 44(24):  297-305.  doi:10.7506/spkx1002-6630-20221222-219
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In this study, a highly sensitive portable platform with colorimetric and fluorescent dual-mode signal output for the detection of aflatoxin B1 (AFB1) was developed based on the reaction between glutathione and a composite nanomaterial consisting of manganese dioxide (MnO2) nanoparticles and graphene quantum dots (GQDs) as a substrate. The recognition probe was prepared by using silica nanoparticles as a carrier to enrich glutathione and AFB1 aptamers. Under optimal conditions, analytical figures of merit such as specificity of this method were studied. The regression equation for colorimetric signal was ΔA = − 0.275 − 0.021lgC and the detection limit was 2.732 × 10-12 g/mL; the regression equation for fluorescence signal was ΔF = 928.733 + 71.779lgC and the detection limit was 1.667 × 10-12 g/mL. Both methods had good detection specificity. The proposed method was applied in the detection of food samples, such as milk, rice, oatmeal, soy sauce and white vinegar with higher accuracy, compared with the traditional method.
Physical Characterization and Volatile Organic Compound Monitoring of Recycled Polyethylene Terephthalate under Mechanical Recycling
ZENG Yan, JIN Lili, ZHU Lei, WU Yongning, LUO Shipeng, SHANG Guiqin, WANG Zhiwei, LIU Guihua, HU Changying
2023, 44(24):  306-315.  doi:10.7506/spkx1002-6630-20221011-100
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In this study, physical characterization and monitoring of volatile organic compounds (VOCs) were investigated on recycled polyethylene terephthalate (rPET) from a mechanical recycling process and rPET bottles made with different rPET contents, with the aim of tracing the source of rPET and assessing its safety when use as a food contact material. It was found that rPET had a similar thermal stability to that of virgin PET (vPET). rPET bottles did not show any significant changes in groups or structure and exhibit similar crystallization and melting behaviors to vPET. However, there were minor mechanical scratches in the surface micromorphology of rPET bottles, and the color of rPET bottles became darker, greener and yellower as the content of recycled material increased. The solid-state polycondensation process was found to play an important role in the removal of VOCs, as detected by headspace gas chromatography-mass spectrometry (HS-GC-MS), resulting in a very small amount of residual VOCs in rPET. Four VOCs (acetaldehyde, glycol and nonanal at levels less than 1.00 mg/kg; 2-methyl-1,3 dioxolane at levels of 1.72-5.76 mg/kg) were detected in the rPET bottles. This study shows that rPET bottles are qualified for reuse in food contact in terms of thermal properties, structure, morphology and VOC residues, although there is variability in color.
Fast Quantification of Phosphorus in Crude Soybean Oil by Near-Infrared Spectroscopy
WANG Xue, ZHANG Hairong, WU Dandan, WANG Weining, WANG Liqi, LUO Shunian, YU Dianyu
2023, 44(24):  316-322.  doi:10.7506/spkx1002-6630-20230822-158
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The existing methods for the determination of phosphorus content are unable to regulate the addition of acid and base in the refining process of crude soybean oil through real-time monitoring. Therefore, a novel rapid method for determining the phosphorus content of crude soybean oil based on near-infrared spectroscopy was proposed in this study. It was found that standard normal variate transformation was more effective than two other spectral preprocessing methods evaluated for denoising the spectral data indicative of the phosphorus content in soybean crude oil. The characteristic absorption band of phosphorus was optimized by synergy interval partial least squares (SiPLS). A back propagation (BP) neural network prediction model of the phosphorus content in crude soybean oil was established with learning efficiency of 0.005 and 108 training cycles. The determination coefficient (R2), root mean square error (RMSE) and relative standard deviation (RSD) for the correction set were 0.979 7, 0.859 3 and 1.89%, respectively. The R2, RMSE and RSD for the validation set were 0.978 5, 0.963 8 and 2.15%, respectively. The above results showed that NIR spectroscopy can achieve rapid, accurate and non-destructive detection of the phosphorus content in, and provide a feasible method for the refining of crude soybean oil.
Tailored Aptamer-Based Visual Colorimetric Detection of Staphylococcal Enterotoxin A Using Gold Nanoparticles
CUI Liwei, WEI Rong, CHANG Weidan, YUE Xiaoyu, XU Wentao
2023, 44(24):  323-328.  doi:10.7506/spkx1002-6630-20230404-029
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Objective: To select and use aptamers as molecular recognition elements to construct a biosensor based on the salt effect of gold nanoparticles for the rapid quantitative detection of staphylococcal enterotoxin A (SEA). Methods: Molecular docking and molecular dynamics simulation were used to truncate the SEA aptamer and predict the results. The simulation results were verified colorimetrically using gold nanoparticles. The optimal SEA aptamer was used as the molecular recognition element. The reaction system was optimized, the relationship between SEA mass concentration and absorbance ratio was explored, and the accuracy, precision and specificity of the developed method were evaluated. Results: An SEA aptamer with short sequence, high affinity, strong specificity and stability was selected. This method was characterized by low limit of detection (LOD) and satisfactory recoveries for spiked samples. Conclusion: Molecular simulation can effectively improve the screening efficiency of aptamers, and the proposed method can be used for rapid detection of SEA.
Discriminant Analysis of Jiang-Flavor Baijiu of Different Grades by Gas Chromatography-Mass Spectrometry and Electronic Tongue
LIN Xianli, ZHANG Xiaojuan, LI Chen, CHAI Lijuan, LU Zhenming, XU Hongyu, WANG Songtao, ZHANG Suyi, SHEN Caihong, SHI Jingsong, XU Zhenghong
2023, 44(24):  329-338.  doi:10.7506/spkx1002-6630-20230115-117
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Gas chromatography-mass spectrometry (GC-MS) and electronic tongue were used to quantitatively determine the volatile compounds and taste indices of 21 Jiang-flavor baijiu samples of different grades. These samples were differentiated by chemometrics, and key differential compounds among grades were identified. Finally, a discriminant model was established by machine learning. The results showed that there were differences in the contents of volatile compounds in Jiang-flavor baijiu of three grades, indicating the feasibility of further discriminant analysis. The total content of flavor compounds in second-grade baijiu (4 908 mg/L) was significantly lower than that in premium-grade (6 583 mg/L) and first-grade baijiu (8 254 mg/L), while the proportion of several esters responsible for floral and fruity aromas in total esters showed a decreasing trend as the grade decreased. Partial least squares-discriminant analysis (PLS-DA) identified 16 key differential compounds represented by ethyl palmitate and acetic acid. The results of electronic tongue showed that the taste indexes of premium-grade baijiu were more consistent, with lower bitterness and astringency aftertaste. The taste indexes of second-grade baijiu showed significant intersample differences. Principal component analysis (PCA) showed clear discrimination of Jiang-flavor baijiu of different grades according to their taste indexes. The above results provide a basis for the establishment of Jiang-flavor baijiu quality system. Four discriminant models were established based on 25 differential compounds and taste indexes identified. The accuracy of all models was higher than 90%, and the support vector machine (SVM) model performed best, with an accuracy of 100%.
Comparison of Two Methods for Osmolality Determination of Foods for Special Dietary Uses
PAN Lirong, WU Yuan, ZHAO Ziyan, YUAN Wenxuan, FANG Enhua, XU Dunming
2023, 44(24):  339-345.  doi:10.7506/spkx1002-6630-20221201-008
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A total of 46 samples from nine types of commercially available foods for special dietary uses were collected for osmolality measurement by a freezing point and a dew point osmometer, and the differences between the two methods were analysed. The results showed that the detection range of the freezing point osmometer was 195–763 mOsmol/kg with relative standard deviation (RSD) of 0.20%–4.08%, and the detection range of the dew point osmometer was 197–649 mmol/kg with RSD of 0.00%–3.66%. It was found that different reconstitution methods had a significant effect on the determination results, and the temperature of the solution also affected the parallelism of the determination results. Statistical analysis using t-test showed that there were significant differences between the results of the two methods for each of 31 samples. It was inferred from the experiments that whether the sample solution reached an ideal dilute solution state was the major factor affecting the significant difference between both methods. This study provides a theoretical basis for further research on the detection of osmolality in foods for special dietary uses, and highlights some key issues that need urgent attention in the design and production of foods for special dietary uses.
Application of Industrial Standard Methods for Detection of Horse- and Donkey-Derived Ingredients for Detecting Mule Meat
ZHOU Cang, XIANG Jialin, LIU Libing, WANG Jinfeng, FU Qi, SUN Xiaoxia, WANG Jianchang
2023, 44(24):  346-351.  doi:10.7506/spkx1002-6630-20230417-154
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Both horse- and donkey-derived ingredients have been detected in mule meat by real-time polymerase chain reaction (PCR) as described in China’s industry standards for detection of horse (SN/T 3730.5-2013) and donkey (SN/T 3730.4-2013) ingredients in food and feed, respectively. This contradicts the theory of strict maternal inheritance of mitochondrial DNA (mtDNA). Therefore, in this study, 3 horse meat samples, 3 donkey meat samples and 3 mule meat samples were detected by mitochondrial gene and nuclear gene sequencing based on PCR and the China’s industry standard methods for horse and donkey ingredients, respectively, and the results of the SN/T 3730.4-2013 method for mule meat were analyzed. According to the results of mitochondrial gene and nuclear gene sequencing, all 3 mule meat samples were derived from mules. Both donkey and horse ingredients were detected in the 3 mule meat samples by the SN/T 3730.4-2013 and SN/T 3730.5-2013 methods. The cycle threshold (Ct) of the SN/T 3730.5-2013 method for horse ingredient was in the range of ≤ 20.00, and that of the SN/T 3730.4-2013 method for donkey ingredient were in the range of 25.00-35.00. The sequencing results of PCR products using the primers described in the SN/T 3730.4-2013 method showed that the 3 mule meat samples had no homology with horse or donkey meat. This might be because the SN/T 3730.4-2013 target sequence appeared in the form of nuclear mitochondrial DNA segments in low repeat numbers in the mule nuclear genome, and some base insertions and deletions occurred. The possibility that mule ingredient may be present should be considered when the Ct value of the SN/T 3730.4-2013 is ≤ 20.00, while the Ct value of the SN/T 3730.5-2013 is in the range of 25.00-35.00 for horse and donkey ingredients in known samples of single animal-derived ingredients, respectively.
Colorimetric Determination of Peroxidation Values of Edible Pure Vegetable Oil by Using Fe3O4@COOH Nanozyme
LI Xin, LUO Lei, XIONG Yingzi, WANG Ling, LI Maiquan, LIU Xia
2023, 44(24):  352-359.  doi:10.7506/spkx1002-6630-20230116-121
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A colorimetric method for the determination of the peroxide value (POV) of edible vegetable oils was established based on the peroxidase-like catalytic activity of Fe3O4@COOH nanoenzyme. For five edible vegetable oils (corn oil, peanut oil, sunflower oil, rapeseed oil, and soybean oil), POV over the range of 0–0.3 g/100 g exhibited a good linear relationship with absorbance values. The proposed method could accurately detect the POV of edible vegetable oils oxidized in three different ways (ultraviolet lamp irradiation, oven heating and natural oxidation). The differences between the POV determined by this method and the national standard method for 25 oil samples were less than 0.05, and the relative standard deviations (RSDs) for corn oil, peanut oil, sunflower oil, rapeseed oil, and soybean oil were 6.13 %, 5.84 %, 6.82 %, 3.62 % and 5.75 %, respectively, indicating good practicability of the colorimetric method. This study provides a fast and convenient method for determining the POV of edible pure vegetable oils.
Quality Comparison of Pepper Oleoresins from Different Geographical Origins by Multi-instrumental Analysis Combined with Chemometrics
LI Tong, WANG Yuhang, WANG Xianghong, ZHANG Yuhan, MI Si
2023, 44(24):  360-368.  doi:10.7506/spkx1002-6630-20230111-084
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Objective: To establish chemical fingerprints of pepper oleoresins from different geographical origins and comprehensively analyze and compare their quality characteristics. Methods: The compositions of piperines, chemical elements and volatile flavor compounds in pepper oleoresins from Indonesia, Sri Lanka and Vietnam were quantitatively analyzed by high performance liquid chromatography-ultraviolet detection (HPLC-UVD), inductively coupled plasma-mass spectrometry (ICP-MS) and gas chromatography-ion mobility spectrometry (GC-IMS), respectively. Furthermore, chemometrics was applied to identify the potential chemical markers to discriminate geographical origins of pepper oleoresin. Results: Sample II from Sri Lanka contained significantly higher levels of piperine (31.57%) and piperonylic acid (0.72%) than the other samples, whereas sample I from Indonesia showed significantly higher contents of piperonol (1.88%) and piperlongumine (1.89%) than the other samples. A total of 54 chemical elements were simultaneously quantified in pepper oleoresin. Among them, 13 were determined as major differential elements, including Cs, Na, Cu, Rb, Ru, P, Mg, Sn, Ag, K, Mo, Cr and Co. The abundance of elements decreased in the order of Vietnam > Indonesia > Sri Lanka. Altogether, 90 volatile compounds were identified. Vietnam samples had the strongest aroma, followed by Indonesian samples. The significantly differential volatiles identified were n-pentane cyanide, 1-cyanopropene, linalool, 2-ethylpyrazine, ethyl valerate, valeraldehyde, n-caproic acid, 2-ethylfuran, isobutyraldehyde and limonene. In conclusion, there are significant differences in the chemical fingerprints of pepper oleoresin from different geographical origins. Overall, pepper oleoresin from Vietnam exhibits superior quality to those from the other two countries.
An Intelligent Method for Pork Freshness Identification Based on EfficientNet Model
LIU Chao, ZHANG Jiayu, QI Chao, HUANG Jichao, CHEN Kunjie
2023, 44(24):  369-377.  doi:10.7506/spkx1002-6630-20221218-182
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A method for measuring pork freshness based on images and the EfficientNet framework was established. A total of 2 500 images of pork with different freshness were collected as original dataset and processed by image enhancement to construct a new dataset of 60 000 images. First, EfficientNet was trained with the CIFAR-10 dataset to determine the basic structure and initial weights of the model. Then, the model was trained and improved using the constructed dataset to make the model suitable for five classification problems. Finally, the established model was tested, verified, and compared with the current mainstream convolutional neural network (CNN) models of Alexnet, VGG16 and ResNet50. The results showed that the average correct recognition rate of the EfficientNet model was as high as 98.62%, which was significantly better than that of the Alexnet, VGG16 and ResNet50 models. The correct recognition rate of the EfficientNetB2 model was 99.22%, and the training time was only 157 min. The comprehensive performance of the EfficientNetB2 model was the best, making it the most suitable method for pork freshness identification. In order to improve its generalization ability, the optimizer algorithm of the EfficientNetB2 model was improved, and the performances of stochastic gradient descent (SGD), adaptive moment estimation (Adam), root mean square propagation (RMSProp) and rectified adaptive moment estimation (RAdam) were compared. The results showed that the RAdam optimizer failed to further improve the accuracy of the model but instead helped to improve its generalization capability, which will of practical significance for engineering applications.