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Food Chemistry
Effects of Changes in Sulfhydryl Content and Surface Hydrophobicity of Myofibrillar Protein Induced by Gallic Acid on Its Gel Properties
JIA Na, LIN Shiwen, WANG Letian, LIU Dengyong
2020, 41(22):  1-7.  doi:10.7506/spkx1002-6630-20190829-323
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The sulfhydryl content, surface hydrophobicity, solubility, gel strength, water-holding capacity and rheological properties of myofibrillar protein (MP) added with different levels (0, 10, 50, 100 and 200 μmol/g) of gallic acid were measured. Also, the microstructure of the obtained gels was observed. The effects of changes in sulfhydryl content and surface hydrophobicity induced by gallic acid on the gel properties of MP were studied. The results showed that gallic acid caused a significant reduction of sulfhydryl content (P < 0.05), but there was no significant difference among different concentrations (P > 0.05). The addition of gallic acid significantly increased the surface hydrophobicity of MP (P < 0.05). The solubility increased significantly when gallic acid was added at 50, 100 and 200 μmol/g (P < 0.05). The gel strength and water-holding capacity of the MP gel with 10 μmol/g gallic acid were not significantly different from those of the control (P > 0.05) and the rheological curve was similar to that of the control. When gallic acid concentration increased to 50, 100 and 200 μmol/g, the gel strength and water-holding capacity decreased significantly (P < 0.05) and the rheological curve tended to be flat. The microstructure observation showed that when gallic acid concentration increased, the gel network structure was gradually loosened, showing bigger pores. Therefore, the low concentration of gallic acid (10 μmol/g) had no adverse effect on the gel properties of MP, while the medium and high concentrations of gallic acid (50, 100 and 200 μmol/g) impaired protein gelation and reduced the gel strength and water-holding capacity of MP gels, probably by promoting hydrophobic aggregation or the formation of thiol-quinone adducts.
Isolation, Purification and Structural Identification of Calcium-Chelating Peptides from Goose Bone Collagen Hydrolysate
ZHOU Mingyang, HE Yuxin, SUN Yangying, PAN Daodong, CAO Jinxuan
2020, 41(22):  8-14.  doi:10.7506/spkx1002-6630-20200201-004
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In this paper, alkaline protease was used to hydrolyze goose bone collagen to prepare calcium-chelating peptides, which were separated and purified by Sephadex G-25 column chromatography and reversed-phase high-performance liquid chromatography. The amino acid composition and structure of the purified peptides were identified by automatic amino acid analyzer, liquid chromatography-tandem mass spectrometry, ultraviolet (UV) spectroscopy and Fourier transform infrared spectroscopy. The calcium-chelating peptides were rich in Glu (12.67%) and Asp (7.47%) and were identified as DSYVGDEAQSKR and KLLDEGR, with molecular masses of 1 353.62 and 829.47 u, respectively. It was proved that the calcium chelating capacities of the synthesized peptides were (70.08 ± 2.20) and (68.18 ±1.31) mg/g, respectively. The intensity of UV absorption decreased, the amine I and amide II bands exhibited a red shift and the N-H band showed a blue shift. Accordingly, we speculated that the peptides may chelate calcium ions mainly through the carboxyl and amino groups of amino acid residues.
Effect of pH Treatment on Structure, Rheological Properties and Emulsifying Properties of Black Bean Protein Isolate
ZENG Qi, HU Miao, WANG Huan, ZHONG Mingming, QI Baokun, JIANG Lianzhou
2020, 41(22):  15-21.  doi:10.7506/spkx1002-6630-20190906-080
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Black bean protein isolate (BBPI), obtained by alkali solution and acid precipitation, was treated under different pH conditions (2.0–11.0) for 2 h and then returned to neutral pH condition. The surface hydrophobicity, solubility, secondary and tertiary structures, emulsion stability and rheological properties of BBPI were determined. The results showed that the protein sample treated at pH 5.0 had the lowest solubility and emulsion stability, while that treated at pH values far from 5.0 showed an increasing trend in solubility and emulsion stability, which were better under alkaline conditions. With the increase in acid and alkaline intensity, the unfolding degree of protein tertiary structures increased, and the β-sheet secondary structure transformed to α-helix. The higher the solubility, the lower surface hydrophobicity, which was positively correlated with the β-sheet content but negatively correlated with the β-turn content. With increasing the shear rate from 0.1 to 100 s-1, the apparent viscosity gradually decreased, and the emulsion showed a shear-thinning behavior; with the increase in pH, the apparent viscosity initially decreased and then increased. The dynamic rheological analysis showed that with the increase in angular frequency from 0 to 70 rad/s, the G’ of emulsions stabilized by BBPI treated with different pH values increased. At pH 3.0, the protein had stronger interface viscoelasticity, and the formed emulsion had better interfacial rheological properties. At pH 11.0, the protein was conducive to better oil-water interfacial combination, and displayed the best emulsifying performance.
Effect of Poly-γ-Glutamic Acid on Quality of Frozen Dough and Steamed Bread
XIE Xinhua, WU Xiuyuan, WU Junhong, SHEN Yue, WANG Na, ZHANG Bei, XU Lina
2020, 41(22):  22-27.  doi:10.7506/spkx1002-6630-20190908-105
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A dynamic rheometer, a fermentation rheometer, differential scanning calorimetry, and scanning electron microscopy were used to study the effect of poly-γ-glutamic acid (γ-PGA) addition on the rheological properties, fermentation characteristics, thermodynamic characteristics and microstructure of frozen dough, and the effect on the hardness, moisture distribution and porosity of steamed bread made from frozen dough was evaluated using a texture analyzer, nuclear magnetic resonance and an electronic eye. The results showed that dough supplemented with 0.7% (relative to dry flour mass) γ-PGA exhibited the maximum storage modulus and loss modulus, highest fermentation height and gas-holding capacity, and lowest melting enthalpy. Dough pores became larger more and uniformly distributed and showed improved continuity with increasing addition of γ-PGA. The migration of the water state from weakly bound to free significantly declined in steamed bread with 0.7% γ-PGA with the prolongation of storage time. After 5 days of storage, the hardness was 21.7% lower than that of the control group, and the porosity was 17.92%, lower than that (28.46%) of the control group. The above results indicate that γ-PGA can effectively weaken damage to dough network structure caused by frozen storage, and improve the frozen storage stability of dough and the quality of steamed bread.
Interactions among Pectin, Chiooligosaccharide, and Bovine Serum Albumin and Their Effects on Loading Efficiency of BSA
FAN Liping, ZHANG Liyan, CHEN Liehuan
2020, 41(22):  28-33.  doi:10.7506/spkx1002-6630-20190927-330
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Interactions among pectin, bovine serum albumin (BSA) and chiooligosaccharide (COS), and their effects on the loading efficiency of BSA were investigated through the determination of the turbidity and macroscopic and microscopic properties of binary and ternary polyelectrolyte complex (PEC) solutions of these three compounds, PEC yield, the complexation and loading rate of BSA, and the ultrastructure and Fourier transform infrared (FTIR) spectrum of PEC. The results showed that complexation methods significantly affected the turbidity, structure and state of PEC. The three compounds interacted with each other mainly through electrostatic interactions and COS competed with BSA for interacting with pectin. Pectin preferred to form complexes with a reticular structure with COS, resulting in a lower loading efficiency of PEC for BSA. The secondary structures of BSA changed due to the conformational changes of pectin during complexation in the presence of COS.
Effect of pH-shifting Treatment on the Structure and Emulsifying Properties of Cyperus esculentus L. Protein
WANG Lin, ZHOU Guowei, YU Zhichao, MENG Luobing, WANG Yuying, ZHANG Anqi, WANG Xibo, JIANG Lianzhou
2020, 41(22):  34-41.  doi:10.7506/spkx1002-6630-20191014-113
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The effect of pH-shifting treatment on the structure of Cyperus esculentus L. protein was studied by Fourier infrared spectroscopy, fluorescence spectroscopy, UV absorption spectroscopy and 8-anilino-1-naphthalene sulfonate (ANS) fluorescence probe emission spectroscopy. Furthermore, the effect on the emulsifying properties of C. esculentus L. protein was analyzed by measuring changes in the surface hydrophobicity, solubility, turbidity and particle size. The results showed that the content of β-sheet decreased, the relative content of α-helix increased significantly and the contents of β-turn and random coil increased slightly as the pH increased. The average particle size of the protein decreased with increasing alkaline pH, the particle size distribution gradually changed from bimodal to monomodal, indicating that more uniform dispersion of the protein. Fluorescence and UV absorption spectroscopy showed that pH-shifting treatment resulted in protein conformational changes; the polypeptide chains in the protein molecule were partially folded, hydrophobic groups were exposed, and the protein structure became more stretched under alkaline pH conditions. As the pH increased, the turbidity decreased significantly, indicating that the protein molecule became more dispersed. The surface hydrophobicity and emulsion stability of the protein first decreased and then increased with increasing pH, indicating that the protein structure was unfolded with increasing alkaline pH. In addition, hydrophobic groups buried inside the protein molecules became exposed, accompanied by an increase in the surface activity and emulsifying activity. These results showed that pH-shifting treatment could change the structure and emulsifying properties of C. esculentus L. protein.
Stabilization of Pickering Emulsion by Octenyl Succinic Anhydride Modified Millet Starch
LU Lanfang, YANG Peng, WANG Zhan, SHEN Wangyang, YU Bo
2020, 41(22):  42-48.  doi:10.7506/spkx1002-6630-20190925-312
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In this study, millet starch was extracted by alkaline extraction, and hydrophobically modified with octenyl succinic anhydride (OSA). The structure of the native and modified starches was characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. It was found that the OSA group was successfully introduced into millet starch, resulting in no change in the crystal structure of starch. The effects of the degree of substitution of starch, starch granule concentration and the proportion of oil phase on the properties of Pickering emulsion were analyzed by measuring emulsification index, emulsion droplet size and rheological properties. The results showed that the emulsifying properties of millet starch were greatly improved after the modification. Emulsification index increased with the increase in starch granule concentration and the proportion of oil phase, while emulsion droplet size decreased with the increase in starch granule concentration and increased with the increase in the proportion of oil phase. Emulsion stability increased with increasing starch granule concentration and the proportion of oil ratio. The rheological analysis indicated that the emulsion may form an internal network structure with a gel-like behavior.
Effect of Steam Blanching Pretreatment on Physical and Functional Properties, Dissolution of Functional Components and Taste of Tibetan-Grown Prunus mira Koehne Powder
LÜ Jian, ZUO Lixu, BI Jinfeng, ZHONG Zhengchang, GUO Chongting, LI Xuan
2020, 41(22):  49-56.  doi:10.7506/spkx1002-6630-20190916-190
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Prunus mira Koehne from Tibet, China was processed into powder by steam blanching-vacuum freeze drying combined with mechanical pulverization. The physical and functional properties, dissolution of functional components and taste stability of P. mira Koehne powder were analyzed. Results showed that particle size of P. mira Koehne powder with steam blanching pretreatment shifted rightward and consequently exhibited a high proportion of big particles compared with the control group. Steam blanching made the surface of the powder particles rough, reduced the intensity of light reflection and L value, degraded the green color of pulp, and increased a value. In addition, steam blanching increased bulk density, decreased compressibility and improved flowability. Hygroscopicity, water content and glass transition temperature (Tg) were measured to evaluate the storage characteristics of P. mira Koehne powder. The powder with steam blanching pretreatment needed stricter storage conditions. Steam blanching pretreatment could significantly improve the hydration characteristics of P. mira Koehne powder as estimated by its water-holding capacity, oil-holding capacity and solubility. The amounts of dissolved pectin and polysaccharide from the powder pretreated by steam blanching increased by 2–4 and 15.62 mg/g relative to those of the control group, respectively, while the dissolution of polyphenols showed a slight decrease. The taste of P. mira Koehne powder changed significantly after steam blanching pretreatment but remained stable during the grinding processing.
Structural Characteristics and Antioxidant Properties of Enzymatically Synthesized Linolenic Acid Phospholipid
XIAO Zhigang, YANG Guoqiang, YANG Qingyu, WANG Lishuang, ZHANG Xueping, GUO Shilong, LI Zhe, YANG Shu
2020, 41(22):  57-63.  doi:10.7506/spkx1002-6630-20190901-001
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Linolenic acid phospholipid (LNA-P) was prepared from soybean phospholipid (SP) and peony seed oil through enzymatic transesterification using Lipozyme RM IM as a catalyst. The structural characteristics of LNA-PC were analyzed using gas chromatography, Fourier transform infrared spectrometry, X-ray diffraction, and differential scanning calorimetry. Additionally, the antioxidant capacity of LNA-PC was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation, and hydroxyl radical scavenging assays. The results showed that when Lipozyme RM IM was added at concentrations of 4%, 6%, 8% and 12%, relative contents of LNA of 8.4%, 13.7%, 18.4% and 23.4% were obtained, respectively. Infrared spectroscopic analysis confirmed the occurrence of the transesterification reaction and the formation of LNA-P through the shift of C–O and C–O–C absorption bands. X-ray diffraction and thermal analyses showed the crystal structure was damaged and the thermal properties of linolenic acid and SP were changed after the transesterification reaction. The diffraction peak at 7.82° disappeared and the intensity of peak at 20.47° decreased after formation of LNA-P. A new melting peak appeared as the relative content of linolenic acid increased in LNA-P, and the melting temperature gradually rose and reached 147.99 ℃ when the relative content of LNA was 23.4%. Antioxidant assays showed that the DPPH, ABTS cation, and hydroxyl radical scavenging abilities of LNA-P were higher than those of SP and concentration dependent. When the relative content of LNA in LNA-P was 23.4%, DPPH, ABTS cation, and hydroxyl radical scavenging activities reached maximum values of 45.2%, 52.2% and 73.4%, respectively. This study revealed that LNA-P with high antioxidant ability can be successfully prepared through enzymatic transesterification, which provides theoretical support for the development and application of soybean phospholipids.
Rheological Characterization of Pectic Polysaccharides from Okra Wine Pomace
CHEN Fahe, ZHOU Yanqiang, WU Guangbin
2020, 41(22):  64-73.  doi:10.7506/spkx1002-6630-20190916-180
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The physicochemical and rheological characteristics of pectic polysaccharides from okra wine pomace were studied. The results showed that the intrinsic viscosity [η] of the pectic polysaccharides from okra and from okra wine pomace were 41.12 and 4.66 dL/g, and the viscosity average molecular masses were 1.466 × 106 and 2.470 × 105 g/mol, respectively. The intrinsic viscosity of the pectic polysaccharide from okra wine pomace was lower than that of the pectic polysaccharide from okra, while Huggies constants were slightly different between the two samples, which were 0.59 and 0.55, respectively, indicating that both have good molecular chain flexibility. The results of flow sweep experiments showed that the pectic polysaccharide from okra wine pomace was a non-Newtonian pseudoplastic fluid that had a shear thinning behavior. The flow curve was fitted to the Cross mode and on the basis of this model combined with the double logarithmic curve, we obtained a critical concentration c*, about 4 g/dL, and the molecular space occupied was about 20 in the pectic polysaccharide from okra wine pomace, while there was no critical concentration c* for the pectic polysaccharide from okra. The results of oscillation amplitude experiments showed that the linear viscoelastic region appeared within the strain range of 2%–10%. Furthermore, the pectic polysaccharide from okra wine pomace was a weak gel without obvious gelling point in the experimental temperature range. The results of oscillation frequency experiments showed that the storage modulus of the pectic polysaccharide solution from okra was greater than its loss modulus, suggesting that its elasticity was more dominant than its viscosity; the loss modulus of the pectic polysaccharide solution from okra wine pomace was greater than its storage modulus, showing that it was more prone to viscosity characteristics. Cox Merz model fitting showed that the complex viscosity of the pectic polysaccharide from okra wine pomace at low shear rate was greater than its steady shear viscosity, indicating that a new structure may be formed between its molecules, which was more sensitive to steady shear. The degrees of esterification of the pectic polysaccharides from okra wine pomace and from okra were 74.45% and 55.817%, respectively, and both of them were high-ester pectins. Monosaccharide composition analysis showed that the two pectin polysaccharides consisted of mannose, glucose, rhamnose (Rha), galacturonic acid (GalA), glucuronic acid, galactose (Gal) and arabinose (Ara), altogether accounting for 52.3% and 54.7% of pectin polysaccharides, respectively, indicating that both were acidic heteropolysaccharides. Based on the monosaccharide composition data, the proportions of rhamnogalacturonan I (RG I) in the pectin polysaccharides from okra wine pomace and from okra were 46.74% and 90.00%, respectively, the proportions of homogalacturonan (HG) were 16.76% and 2.21% respectively, and the ratios of (Ara + Gal)/Rha were 3.29 and 2.54, respectively. We speculated that the length or number of side chains of RG I in the pectin polysaccharide from okra wine pomace were larger than that in the pectin polysaccharide from okra. The results of this study can provide a theoretical guidance for the application of pectin polysaccharides from okra wine pomace.
Bioengineering
Effect of Fermentation with Peel on the Quality of ‘Jinyan’ Kiwifruit Vinegar
ZHONG Wu, WANG Tengteng, ZHANG Nawei, GONG Lijuan, YU Ce, LI Erhu
2020, 41(22):  74-81.  doi:10.7506/spkx1002-6630-20190917-218
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Kiwifruit vinegars were made from ‘Jinyan’ kiwifruits through alcoholic and acetic acid fermentation with peel and without peel, and the quality was evaluated. The results indicated that fermentation with peel showed no significant impact on the acetic acid fermentation process or VC content compared with fermentation without peel, but it could increase acetic acid content and reduce protein content. The contents of citric and malic acid in fruit vinegar were significantly lower than those of fresh fruit, but the tartaric acid content significantly increased. Fermentation with peel could further reduce the contents of tartaric and citric acid. In addition, fermentation with peel could significantly increase the contents of total phenolic and total flavonoids in vinegar. Gas chromatography-mass spectrometry (GC-MS) analysis showed that fermentation with peel effectively increased the contents of volatile components and enriched the varieties and consequently improved the flavor characteristics of kiwifruit vinegar. This was consistent with the results of electronic nose, indicating that there were significant differences in the aroma profiles of the two samples.
Heterologous Expression, Purification and Enzymatic Analysis of Candida albicans Cyclic Nucleotide Phosphodiesterase 2
LI Chixia, CHEN Ying, ZHANG Meng, CHEN Yujuan, TIAN Yuanyuan, WANG Yousheng
2020, 41(22):  82-87.  doi:10.7506/spkx1002-6630-20191012-092
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For the purpose of preparing high-purity Candida albicans phosphodiesterases 2 (PDE2), the genomic DNA of C. albicans was used as a template to amplify the target gene by PCR. The expression plasmid pET28a-C. albicans pde2 was constructed, and transformed into E. coli BL21 cells to obtain genetically engineered bacteria with high expression stability. The expressed protein from the culture supernatant was consecutively purified by affinity chromatography (Ni-NAT), ion exchange column chromatography (Q-Sepharose) and Sephacryl S200 column chromatography. After that, the hydrolysis characteristics of the purified PDE2 (~62 kDa) on single and double substrates were determined by high performance liquid chromatography (HPLC). It was shown that the hydrolysis efficiency of cAMP and cGMP both at 0.4 mmol/L was 60%–70%, and the affinity was higher for cAMP. Furthermore the enzyme had high biological activity and stability. This study provides a theoretical basis for the crystallographic analysis of the protein and for understanding its role in the physiological and pathological mechanism of C. albicans in the future.
Polyphenols Synthesis in Suspension-Cultured Origanum vulgare Cells and Its Stimulation by Aspergillus niger Elicitor
LI Yanping, LIU Yuan, WANG Xiaoqiang, SHEN Beiyun, ZHOU Xiangju, ZHAO Wenjia, CHEN Jiguang, YIN Zhongping
2020, 41(22):  88-96.  doi:10.7506/spkx1002-6630-20190918-229
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Origanum vulgare cells were suspension-cultured to synthesize polyphenols, which were further identified by ultra-high performance liquid chromatography-time of flight-tandem mass spectrometry (UPLC-TOF-MS/MS). Aspergillus niger elicitor (ANE) was used to promote polyphenol synthesis in the cultured cells, and the effects of elicitor concentration, addition time and subsequent culture duration on cell growth and polyphenols synthesis were investigated as well. A total of six polyphenols in the cultured cells were identified, including procatechin-O-hexanoside, salidroside, salicylate-O-glucoside, rosmarinic acid-3-O-glucoside, rosmarinic acid (ROA) and methyl rosmarinate, with the most abundant being ROA as a landmark phenolic compound. Adding 50 μg/mL ANE at the mid-log phase (the 10th day) hardly affected the growth or morphology of cells cultured for another two days, while it promoted polyphenol synthesis, resulting in a 3.25-fold and 3.33-fold increase in the content and production (reaching 361.38 mg/L) of ROA with a simultaneous 2.90-fold increase in the production of total phenolics. Our results indicated that suspension-cultured O. vulgare cells could synthesize a variety of polyphenols. ANE treatment can effectively enhance the polyphenol content in O. vulgare cells, and therefore, is an effective method to improve the polyphenol yield including ROA as a representative component.
Effects of Different Lactic Acid Bacteria on the Total Acid Content and Flavor Compounds of Rice Vinegar Produced by Liquid-state Fermentation
DENG Yongjian, LU Zhenming, ZHANG Xiaojuan, CHAI Lijuan, LI Xin, YU Yongjian, LI Huazhong, SHI Jinsong, XU Zhenghong
2020, 41(22):  97-102.  doi:10.7506/spkx1002-6630-20191011-083
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In this study, fermented leachate of wheat bran with different strains of lactic acid bacteria was mixed with rice wine and then inoculated with acetic acid bacteria for acetic acid fermentation. High performance liquid chromatography (HPLC) and headspace solid phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) were used to detect the composition of organic acids and volatile compounds in rice vinegar. The results showed that fermentation with the lactic acid bacteria could change the organic acid composition of the fermented leachate. Adding the lactic acid bacteria-fermented bran leachate could increase the lactic acid content of rice vinegar (about 0.35 g/L). Lactobacillus brevis L-02, L. fermentum L-03 and L. reuteri L-05 could increase the types and contents of volatile flavors of rice vinegar.
Proteolysis and Bioactivity of Cheddar Cheese as Influenced by Milk-clotting Enzyme from Bacillus amyloliquefaciens GSBa-1
ZHAO Xiao, CAI Miao, YANG Zhijie, LUO Tianqi, CHEN Chao, CAO Yongqiang, YANG Zhennai
2020, 41(22):  103-111.  doi:10.7506/spkx1002-6630-20190911-145
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Commercial rennet, 70% commercial rennet + 30% milk-clotting enzyme (GSBa-1 MCE) from Bacillus?amyloliquefaciens GSBa-1 and GSBa-1 MCE were used for making Cheddar cheeses A, B and C, respectively. Changes in physicochemical parameters, proteolysis and bioactivity of cheese during 12 weeks of ripening were studied. Microrheological results?showed that GSBa-1 MCE had good milk coagulation ability similar to that of commercial rennet. Compared to cheese A, cheese C exhibited significantly lower pH, higher moisture content, and the content of Lactococcus lactis in cheese C decreased significantly from 9.77 (lg(CFU/g)) to 5.08 (lg(CFU/g)); its proteolytic activity, pH 4.6 soluble nitrogen and 12% trichloroacetic acid (TCA) soluble nitrogen content were higher. During cheese ripening, cheese C showed significantly higher calcium- and zinc-chelating ability and stronger antioxidant capacity in terms of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical scavenging ability. The metal chelating ability and antioxidant capacity of cheese B were in the middle. Antidiabetic effect in terms of α-amylase and α-glucosidase inhibition showed no significant difference among the three cheeses. Therefore, GSBa-1 MCA can be use as a partial substitute for commercial rennet for making Cheddar cheese owing to its ability to control proteolysis during ripening, improve the functionality of cheese, and maintain a good quality of cheese.
Comparison of Characteristics of Lactic Acid Bacteria as Starter Cultures for Cheese and Application in Fresh Cheese Production
CHEN Senyi, LIU Zhenmin, JIAO Jingkai, PANG Jiakun, YU Yi
2020, 41(22):  112-118.  doi:10.7506/spkx1002-6630-20191010-074
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In this paper, seven representative strains of lactic acid bacteria isolated from cheese samples collected from Xinjiang, Yunnan and Tibet were selected for evaluation of their acid-producing ability, viscosity-producing ability, degree of autolysis and aminopeptidase activity. The texture and rheological characteristics of fresh cheese produced using each strain were analyzed. The results showed that both Lactococcus lactis E11 and C44 were advantageous in the four characteristics. In terms of acid production, ΔpH (between 0 and 24 h) was high, the viscosity was moderate, and they were highly autolytic and displayed high aminopeptidase activity. Correlation analysis demonstrated that for fresh cheese made with single strains, moisture content had a highly significantly negative correlation with hardness but was extremely significantly positively correlated with adhesivenes. In addition, pH, protein content, and fat content also had a significantly positive correlation with texture. In terms of texture, there was a significant difference among the cheeses evaluated (P < 0.05). The dynamic rheological analysis showed that elastic properties were dominant for all cheeses (G’ > G”). The cheeses made with E11 and C44 exhibited hardness, cohesiveness, and elasticity closer to those of the control group. Collectively, these results proved that L. lactis E11 and C44 could be selected as starter culture for in the perparation of fresh cheese, and mixed starter cultures of these strains and others may be available in the future.
Effect of Culture Conditions on the Formation of Selenium Nanoparticles with Different Particle Sizes by Microbial Reduction Using Lactobacillus plantarum and Their Bioactivity Evaluation
ZHANG Yuzhu, WANG Bingyi, ZENG Zi’ao, XU Ruoyun, LI Jun, FAN Mingtao, WEI Xinyuan
2020, 41(22):  119-126.  doi:10.7506/spkx1002-6630-20191013-098
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This study aimed to analyze the factors that influence the reduction of sodium selenite by Lactobacillus plantarum to form selenium nanoparticles and to compare the biological activity of selenium nanoparticles with different particle sizes. We selected strain WZ8 capable of tolerating sodium selenite from 13 strains of L. plantarum isolated from traditional fermented foods. After that, strain WZ8 was used to explore the effects of culture conditions, such as initial pH, temperature, inoculum concentration, the concentration of sodium selenite and stress time on the size of selenium nanoparticles by single factor experiments. In addition, the correlation between the size of selenium nanoparticles and its in vitro antibacterial and antioxidant activity. The results revealed that the size of selenium nanoparticles was affected by the culture conditions. Furthermore, the biological activity test showed that the smaller the size of selenium nanoparticles was, the stronger the bacteriostatic activities were against Salmonella typhimurium, Staphylococcus aureus, Escherichia coli and Listeria monocytogene. Selenium nanoparticles with different sizes had different total reducing powers and scavenging capacities against 1,1-diphenyl-2-picryhydrazyl (DPPH), 2,2’-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) cation and hydroxyl radicals.
Biofilm Formation Ability of Escherichia coli O157:H7 on Stainless Steel Surface and Its Relationship with Bacterial Characteristics
WU Lina, DONG Pengcheng, ZHANG Yimin, MAO Yanwei, LIANG Rongrong, YANG Xiaoyin, ZHU Lixian, LUO Xin
2020, 41(22):  127-132.  doi:10.7506/spkx1002-6630-20190912-154
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This study aimed to investigate the effect of two different media: tryptic soy broth (TSB) and beef extract (BE) on the biofilm formation ability of Escherichia coli O157:H7 on a stainless steel surface and the correlation between the biofilm formation ability and the bacterial characteristics. The results showed biofilm formation capability was significantly influenced by interactions among the strain, the media used, and incubation time (P < 0.05). Significant differences in cell surface hydrophobicity, autoaggregation ability and motility were observed among the strains tested (P < 0.05). Biofilm formation ability was significantly positively correlated with swarming motility upon culture in TSB (P < 0.05) while it was significantly positively correlated with hydrophobicity (P < 0.05) upon culture in BE. In addition, there was no correlation of the biofilm formation ability between two culture media of the strains. In conclusion, this study provides useful information for developing effective biofilm removal techniques to control the hazard of E. coli O157:H7 biofilms in the beef industry.
Isolation and Identification of Yeast Capable of Efficiently Degrading Citric Acid and Its Acid Degradation Characteristics in Red Raspberry Juice
CHEN Sirui, TANG Linlin, FENG Jianwen, SUN Lina, WANG Jinling
2020, 41(22):  133-139.  doi:10.7506/spkx1002-6630-20191008-024
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This study aimed to obtain yeast strains with high citric acid-degrading ability and to apply them to reduce the acidity of red raspberry juice. The target strains were isolated and purified from red raspberry orchard soil and fruit surfaces and changes in organic acid concentrations of red raspberry juice inoculated with these isolates during fermentation were determined by high performance liquid chromatography (HPLC). The results obtained indicated that strain T2, isolated from soil, and strain G4, isolated from red raspberry fruit, both had a strong acid-degrading capability. The degradation efficiency of 20 g/L citric acid by inoculation with strains T2 and G4 was 63.73% and 67.23%, respectively. Strains T2 and G4 reduced 58.55% and 59.54% citric acid in red raspberry juice, consequently increasing the pH from 3.08 to 3.27 and 3.36, respectively. According to their morphological features, physiological and biochemical characteristics and molecular identification, both strains were identified as Issatchenkia terricola. The experimental results provide a new way of reducing the acidity of red raspberry juice and provide reference for research on bio-deacidification.
Modelling and Evaluating Growth/No-growth Interface of Bacillus subtilis Isolated from Penaeus vannamei Affected by Nisin, ɛ-Polylysine and pH
GUO Quanyou, LIU Ling, LI Baoguo, YANG Xu, JIANG Chaojun
2020, 41(22):  140-147.  doi:10.7506/spkx1002-6630-20190916-182
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The inactivation characteristics of nisin, ?-polylysine (?-PL) and pH on Bacillus subtilis isolated from vacuum packed cooked Penaeus vannamei were studied. Growth/no-growth interface models were fitted using simple Logistic and polynomial Logistic equations and validated, and the synergistic or antagonistic effects between the antibacterial factors were comparatively analyzed. The results showed that the R2-Nagelkerke values of the simple Logistic and the polynomial Logistic models were 0.79 and 0.91, respectively; the Hosmer-Lemeshow test showed χ2 of 2.00 and 0.76, and P of 0.981 and 1 for the simple and polynomial Logistic models, respectively, indicating that both models can well describe the growth/no-growth of B. subtilis under the influence of nisin, ?-PL, pH and their interactions, and that the polynomial Logistic model can better predict the probability of growth of the spores of B. subtilis. In addition, nisin, ?-polylysine, pH and their interactions had significant effects on the growth/no-growth interface of B. subtilis isolated from shrimp (P < 0.05). With increasing the concentration of nisin and ?-PL or decreasing the pH, the growth area gradually decreased, while the no-growth area gradually expanded, and the growth of B. subtilis was inhibited. As the nisin concentration increased, the growth/no-growth limit of B. subtilis shifted in the direction of higher ?-PL concentration and lower pH. Regardless of the concentration of ?-PL, when the nisin concentration was 60, 100, 140 or 180 μg/mL, B. subtilis showed no growth at pH values of 4.0, 4.25, 4.5, and 5.0. When the ?-PL concentration was 60, 100, 140 or 180 μg/mL, the growth probability of B. subtilis was zero at pH values of 4.0, 4.5, 4.75, and 5.25. At pH < 5.0, the growth of B. subtilis was strongly inhibited, and pH below 5.0 was a major factor affecting the growth/no-growth of B. subtilis. The growth/no-growth model predicting growth probability of B. subtilis can provide an effective means for quantitatively describing microbial inhibition on aquatic products and for microbial risk assessment.
Preparation and Identification of α-Amylase Inhibitory Peptides from Camel Milk Protein
SU Na, YI Li, Jirimutu
2020, 41(22):  148-157.  doi:10.7506/spkx1002-6630-20190926-319
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In this study, alcalase and papain were separately used to hydrolyze camel milk protein, and the hydrolysis process, α-amylase inhibitory activity, amino acid composition, molecular mass distribution and peptide sequence were comparatively investigated so as to obtain peptides with strong α-amylase inhibitory activity. The results showed that the α-amylase inhibitory activity of camel milk protein was enhanced after enzymatic hydrolysis. Compared with that obtained using alcalase (JX), the protein hydrolysate (MG) prepared using papain under the following optimum conditions: enzyme dosage, 4%; temperature, 55 ℃; pH, 7.0; and hydrolysis time, 2 h possessed higher α-amylase inhibitory activity. A total of 110 and 69 peptides were identified from JX and MG, respectively, of which IPLPLPLPLP and LPLPLPLR were the most effective α-amylase inhibitory peptides. Therefore, camel milk protein can be a potential source of anti-diabetes ingredients in functional foods or health products.
Diversity of Microbial Community and Key Substances in Naturally Fermented Stinky Egg
CHEN Wei, LI Yang, GU Xinxi, TAN Suhui, LU Haiqiang
2020, 41(22):  158-165.  doi:10.7506/spkx1002-6630-20190927-329
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The bacterial 16S rDNA V3-V4 region and the fungal internal transcribed spacer-1 (ITS1) region in stinky egg brine were sequenced by high-throughput sequencing technology to explore the microbial community composition and diversity. The contents of key substances including free amino acids, hydrolytic amino acids, biogenic amines and cholesterol in stinky eggs were determined. The results showed that a total of 3 460 operational taxonomic units (OTUs) were identified including 712 and 2 748 OTUs for fungi (belonging to 41 genera in 6 phyla) and bacteria (belonging to 68 genera in 7 phyla), respectively. Among them, the dominant bacterial phylum was Halanaerobiaeota (53.96%), and the dominant bacterial genus was Halanaerobium (53.89%); the dominant fungal phylum was Ascomycota (35.04%), and the dominant fungal genus was Lecanicillium (11.64%). Three of the six common biogenic amines were found in stinky eggs, which were tryptamine ((69.02 ± 0.74) mg/kg), histamine ((8.33 ± 0.53) mg/kg) and tyramine ((129.45 ± 1.12) mg/kg). The contents of free and hydrolytic amino acids in stinky eggs were (3.42 ± 0.111)% and (6.89 ± 0.440)%, respectively. The content of free amino acids was 11.4-fold higher than that of fresh eggs, and the contents of total cholesterol, triglyceride and low-density lipoprotein cholesterol were 44%, 47% and 30% lower than those of fresh eggs, respectively, while the content of high-density lipoprotein cholesterol was 59% higher than that of fresh eggs. This study provides a theoretical basis for exploring the fermentation mechanism of stinky eggs and standardizing their production and quality safety.
Optimization of Intelligent Post-fermentation and Quality Analysis of Pixian Broad-bean Paste
LIU Ping, WANG Xuemei, XIANG Qin, SUN Wenjia, LI Yalong, LI Jiayi, CHEN Zhiwei, CHE Zhenming
2020, 41(22):  166-176.  doi:10.7506/spkx1002-6630-20190906-086
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Intelligent post-fermentation of Pixian broad-bean paste (PBP) was carried out using the equipment independently designed by our group and the quality of the finished product was evaluated. One-factor-at-a-time experiments were performed to examine the effects of stirring frequency, light and environmental humidity on amino nitrogen, soluble nitrogen, total acidity, reducing sugar and characteristic flavor components. The optimum fermentation conditions were determined as follows: stirring for one minute per day, no light,?28 ℃ and natural indoor humidity. The results showed that PBP produced by intelligent fermentation had lower level of salinity, but higher moisture content, color value and total acidity than did naturally fermented PBP. Moreover, the consumption rate of reducing sugar, the production rate of amino nitrogen and soluble nitrogen and the contents of organic acid and free amino acids were higher in PBP produced by intelligent fermentation, which produced most characteristic aroma compounds (except aldehydes) but less varieties of aroma compounds and accumulated excess amounts of acid, causing an overall imbalance in the flavor profile. In spite of this, PBP produced by intelligent fermentation was superior in other quality indicators and a shorter fermentation cycle. Thus, controlling acid accumulation to optimize the intelligent post-fermentation process can provide data support for promoting the industrialization of intelligent fermentation.
Microflora Structure and Flavor Components and Correlation between Them in Fermented Stinky Tofu
SUN Na, ZHANG Yating, YU Hansong, ZHU Xianming, ZHU Shijie, ZHOU Shuhui, REN Dayong
2020, 41(22):  177-183.  doi:10.7506/spkx1002-6630-20190929-360
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High-throughput sequencing technology and gas chromatography and mass spectrometry (GC-MS) were respectively used to analyze the microbial diversity and flavor components of fermented?stinky?tofu?brine at the beginning and end of fermentation. Further, the correlation between them was analyzed. The results indicated that the microbial community structure changed significantly at the genus level, especially for the genera Leuconostoc and Halanaerobium. In total, 45 and 27 volatile components were found to exist at the beginning and end of fermentation, respectively. Six volatile component were common to both. The offensive odorants sulfur-containing compounds and indole were detected exclusively at the end of fermentation. The correlation analysis indicated that Leuconostoc and Halanoerobium as the main sources of stinky odor were closely related to sulfur-containing compounds and indole. Lactobacillus, Tetragenococcus and Chishuiella were most correlated with esters, ketones, and alcohols, imparting the aroma to fermented stinky tofu.
Structure and Diversity of Culturable Mold Communities in Different Fermentation Rounds in Main Maotai-Flavored Liquor-Brewing Areas of Maotai Town
ZHU Zhiyu, HUANG Yongguang
2020, 41(22):  184-192.  doi:10.7506/spkx1002-6630-20190918-226
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Based on our previous study on metagenomic analysis of microbial community structure, the structure and diversity of culturable mold communities in Daqu and environmental samples from 7 different fermentation rounds in the main Maotai-flavored liquor-brewing areas of Maotai town, Guizhou were investigated by traditional culture method and 18S rRNA gene sequencing. A total of 614 and 486 strains of mold were isolated from the Daqu and environmental samples, respectively and out of these, 256 strains were selected for further analysis by morphological features and 18S rRNA gene sequencing analysis. Finally, 57 mold species belonging to 27 genera were identified from the environmental samples. In the Daqu samples, 31 mold species in 15 genera were identified. Lichtheimia, Mucor, Aspergillus, Monascus, Rhizomucor, Paecilomyces, and Schizophyllum were the dominant molds in the brewing environment, while Lichtheimia, Aspergillus, Penicillium, Phanerochaete, and Thermoascus were the dominant molds in Daqu. This study confirmed the significance of molds in the brewing environment and Daqu for the fermentation of Maotai-flavored liquor, and highlighted that high-temperature Daqu and stacking fermentation are both indispensable for the production of Maotai-flavored liquor.
Effects of Salt Concentration on Microbial Communities and Quality of Pixian Broad Bean Paste Mash during Fermentation
LI Xiongbo, LI Heng, DENG Weiqin, ZHANG Qisheng, CHEN Xiangjie, FAN Zhiyi, LI Jiezhi, CHEN Gong
2020, 41(22):  193-199.  doi:10.7506/spkx1002-6630-20190902-019
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The effects of salt concentration on the microbial load and community structure in Pixian broad bean paste mash and its quality during fermentation were studied in this paper. The results showed that the total number of molds decreased continuously during the fermentation process. The lower the salt concentration was, the faster the decline rate was. For each salt concentration, the total amount of bacteria decreased at first, then increased slowly, and finally remained at around 7.3 (lg(CFU/g)). Lactic acid bacteria were detected only at the early stage of fermentation for low-salt broad bean paste mash (6% and 9%), which resulted in significant differences in the total bacterial quantity at the early stage of fermentation among broad bean paste mashes with different salt concentrations. High-throughput sequencing indicated that Aspergillus was the dominant fungus in the fermentation process of broad bean paste mash for all salt concentrations. However, there were significant changes in the bacterial composition in broad bean paste mash with salt concentration. The dominant bacteria in low-salt broad bean paste mash (6% and 9%) were Lactobacillus, Staphylococcus and Weissella, while in high-salt broad bean paste mash (12% and 15%), the dominant bacteria were Staphylococcus, Tetragenococcus and Bacillus. There was a significant influence of salt concentration on the contents of total acids, amino nitrogen and reducing sugars. The total acid and amino nitrogen contents increased, while the reducing sugar content decreased with decreasing salt concentration. Sensory evaluation showed that broad bean paste mash with 12% salt was the best in sensory quality, followed by that with 15% salt concentration, and the samples with 6% and 9% salt was the worst. Low-salt broad bean paste mash (6% and 9%) scored lower in sensory evaluation, mainly because it had a very high acidity and was too soft and out of shape. All the results indicated that the fermentation of broad bean paste mash should not blindly pursue low salt, and the salt concentration should be controlled at above 12%.
Correlation Analysis of Microbial Community Succession in Fermented Grains of Xifeng-Flavor Chinese Liquor with Its Physicochemical Indexes
CHEN Xue, ZHANG Yongli, YAN Zongke, MENG Qinyan, QI Huan, LI Haohao, JIA Zhiyong
2020, 41(22):  200-205.  doi:10.7506/spkx1002-6630-20190910-126
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The structure and succession of the microbial community in fermented grains of Xifeng-flavor Chinese liquor were analyzed by high throughput sequencing. The results showed that a total of 216 genera were detected during the fermentation process, including 183 bacterial ones and 33 fungal ones. The dominant microorganisms were Rhizopus, Naumovozyma, Thermoascus, Aspergillus, Candida, Pseudeurotium, Saccharomycopsis, Pichia, Saccharomyces, Lactobacillus, Bacillus, Pediococcus and Streptomyces, Naumovozyma and Lactobacillus being absolutely dominant. The correlation analysis between physicochemical indexes and microbial diversity showed that bacterial diversity was significantly negatively correlated with fermentation temperature, but significantly positively with the contents of starch and reducing sugar, while there was no significant correlation between each physicochemical index and fungal diversity.
Component Analysis
Analysis of Characteristic Polyphenols and Triterpenic Acids in Ripe Pears of 36 Cultivars by UPLC-MS/MS
SUN Liqiong, HAO Wenjing, TANG Xiaoqing, WANG Kangcai, ZHANG Shaoling
2020, 41(22):  206-214.  doi:10.7506/spkx1002-6630-20200423-301
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In this work, 102 polyphenols and 16 triterpenic acids in ripe pears of 36 cultivars were analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) with multiple reaction monitoring (MRM) mode, changes in the major components were investigated in comparison with data from our previous research on young fruits. It was found that pear fruits were rich in polyphenols and triterpenoids, among which, chlorogenic acid, quinic acid and arbutin were the primary polyphenols and ursolic acid was the predominant triterpenoid. The contents of most of these compounds were significantly reduced in ripe pears compared with young pears. Generally, 12 phenolic acid compounds such as quinic acid and chlorogenic acid, eight phenolic glycosides such as arbutin, five flavonoid compounds such as rutin and isorhamnetin-3-O-rutinoside, five flavan-3-ols such as catechin and epicatechin, and 10 triterpenic acids, such as betulinic acid, oleanolic acid and ursolic acid were ubiquitously detected in all cultivars and tentatively identified as the characteristic polyphenolic and triterpenoid constituents. Furthermore, the results of principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) showed that there was no significant difference among various pear cultivars and Pyrus ussuriensis Maxim cultivars exhibited strong species specificity. This study provides reference for further improving the pear quality evaluation system and for cultivar selection for various functional products in the future.
Effect of Cluster Thinning on Flavonoids Compounds of Cabernet Sauvignon Grape Skin
ZENG Guihua, GAO Feifei, GAO Banglao, XI Zhumei,, ZHANG Zhenwen
2020, 41(22):  215-221.  doi:10.7506/spkx1002-6630-20191010-077
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In this study, we investigated the effect of cluster thinning on flavonoids compounds in Cabernet Sauvignon grape skin. The results showed that cluster thinning increased berry mass and horizontal diameter. In addition, it increased the contents of reducing sugar and soluble solid and reduced total acid content. A total of 18 monomeric anthocyanins, 6 flavanols and 15 flavonols were determined in grape skins for each level of cluster thinning. Compared with the control group without cluster thinning, the contents of anthocyanins and flavonols in grape skins increased by 4.43% and 10.89% after 27% of clusters were thinned per plant, respectively, and increased by 16.59% and 77.80% in grape skins after 54% of clusters were thinned, respectively. Principal component analysis (PCA) and cluster analysis (CA) further showed that the contents of flavonoids in grape skins significantly increased after cluster thinning, and the first and second principal components (PC1 and PC2) explained 45.24% and 28.87% of the total variance, respectively. Overall, both 27% and 54% cluster thinning increased the contents of flavonoids in grape skins, but the former is recommended taking into consideration flavonoids contents and economic?benefits.
Determination of Volatile Components in Buckwheat Honey and Correlation Analysis with Honey Maturity
WANG Taohong, ZHANG Shaobo, ZHANG Huimin, ZHAO Guangyue, LI Xuemin, WEI Yuhai, CUI Zongyan
2020, 41(22):  222-230.  doi:10.7506/spkx1002-6630-20190927-328
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A headspace solid phase microextrction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS) method was developed for the determination of the volatile compounds of 14 samples of buckwheat honey with different maturity levels. The SPME parameters (extraction fiber, time and temperature) and the GC conditions (capillary column and rising temperature program) were optimized. Under the optimal experimental conditions, a total of 168 volatile compounds were identified, mainly including alcohols, esters, aldehydes, acids and lactones. There were significant differences in the volatile components of buckwheat honey at different maturity levels. Esters and alcohols were the main volatile compounds in buckwheat honey at lower maturity levels, while aldehydes and acids were dominant in buckwheat honey at higher maturity levels.
Analysis of Characteristic Flavor Substances of Traditional Shaoxing Rice Wines of Different Ages
ZHAO Peicheng, CAI Jihao, GU Saiqi, QIAN Bin, WANG Lan, LÜ Fei, DING Yuting
2020, 41(22):  231-237.  doi:10.7506/spkx1002-6630-20191021-214
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The volatile flavor compounds, organic acids, free amino acids and sensory characteristics of 1-, 3-, 5-, 8- and 10-year old traditional Shaoxing rice wines were determine. Principal component analysis (PCA) performed on descriptive sensory scores for aroma and volatile flavor compounds with aroma activity values greater than 1 indicated that the younger wines had a stronger alcoholic aroma with the main characteristic volatile flavor substances being phenylethyl alcohol and phenylacetaldehyde. The older wines had a stronger ester and more well-balanced aroma, which was greatly affected by ethyl acetate, ethyl lactate, ethyl octanoate, phenylethyl acetate and ethyl phenylacetate. PCA performed on free amino acids and organic acids with taste activity values greater than 1 and descriptive sensory scores for taste showed that succinic acid and isoleucine contributed significantly to the taste of the younger wines, which tasted more alcoholic and sour. Lactic acid, citric acid and methionine contributed greatly to the taste of the older wines, which was more well-balanced. Therefore, ethyl acetate, ethyl phenylacetate, citric acid and methionine play an important role in the flavor of traditional Shaoxing rice wine.
Analysis of Volatile Flavor Components of Fish Sauce during Fermentation by Using Comprehensive Two-dimensional Gas Chromatography-Mass Spectroscopy
CHEN Lili, BAI Chunqing, YUAN Meilan, JIANG Yong, ZHAO Li
2020, 41(22):  238-244.  doi:10.7506/spkx1002-6630-20191016-155
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Static headspace solid phase micro-extraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC-MS) was used to analyze the changes of volatile compounds during the fermentation process of fish sauce. Samples were taken at different fermentation time points and used for comparison. The compounds whose contents obviously changed during fermentation were selected for comparison. A total of 116 compounds were identified by their mass spectra and retention indexes. Future, principal component analysis (PCA) and heat map were used to analyze the changes of volatile compounds. The results showed that the flavor of fish sauce could be clearly distinguished after 20 days of fermentation, indicating that the flavor compounds of fish sauce were mainly produced in the late stage of fermentation.
Comparison of Flavor Substances of Water-boiled Lotus Roots from Different Varieties
HAN Lijuan, HUANG Chuxiong, LI Jie, YAN Shoulei, LIU Yiman
2020, 41(22):  245-251.  doi:10.7506/spkx1002-6630-20191104-037
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In order to explore the difference in flavor substances of water-boiled roots of wild lotus and three different cultivars (‘Miancheng’, ‘Elian 5’and ‘Maojie’) in Hubei province, central China, lotus root dices were boiled in water for 30 min and investigated for their volatile compounds by headspace solid-phase microextraction coupled to gas chromatography-mass spectrometry (SPME-GC-MS), electronic nose (E-nose), and sensory evaluation. A total of 38 volatile flavor compounds were detected by GC-MS, 8 of which were common to the 4 varieties. Aldehydes, furans, ketones, alcohols and ethers made prominent contributions to the flavor of lotus roots. Principal component analysis (PCA) could effectively distinguish these varieties. The results of electronic nose showed that there were significant differences in the flavor substances among the varieties, which were basically consistent with the results of SPME-GC-MS analysis. Sensory evaluation revealed that the wild lotus roots were mealy in texture and rich in flavor, which were more suitable for simmering soup on the basis of these data combined with GC-MS and electronic nose data. The results of this study provide useful data on flavor compounds for selecting suitable lotus cultivars for simmering soup.
Seasonal Variability of Aroma Components of Lingyun Pekoe Green Tea
TIAN Tian, WEI Jinjian, WEN Jinhua, ZENG Xianglin
2020, 41(22):  252-259.  doi:10.7506/spkx1002-6630-20191020-206
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This study aimed to understands the main aroma components of Lingyun pekoe green tea and to explore the differences in aroma components among different harvest seasons. Dynamic headspace-gas chromatography-mass spectrometry (DHS-SPME-GC-MS) was used to determine the aroma components of Lingyun pekoe tea in spring, summer and autumn. Based on the relative content of each aroma component, we used partial least square-discriminant analysis (PLS-DA) to establish discriminant models for tea samples harvested in different seasons, then found out the aroma components crucial to tea sample classification, and finally drew a heat map to determine the distribution pattern of the key aroma components in different harvest seasons using hierarchical cluster analysis (HCA). Results showed that a total of 37 compounds were identified in the tea samples, the predominant ones being alcohols and aldehydes. The main aroma components were linalool, n-amyl alcohol, geraniol, L-menthol, isobutyraldehyde, isoglutaraldehyde, nonaldehyde, ethyl acetate, dimethyl sulfide and indoles. The established PLS-DA model could obviously distinguish tea samples harvested in the three seasons, with good reliability. A total of 12 aroma components, nonaldehyde, betarecolone, l-menthol, 3,5-octadiene-2-ketone, trans-orange-flower tert alcohol, benzyl alcohol, n-amyl alcohol, tridecane, cis-2-pentene-1-alcohol, cis-jasmonone, tetradecane and leaf alcohol were identified as the key compounds to distinguish Lingyun pekoe tea in different seasons. Collectively, the heat map and cluster analysis of the 12 aroma components showed that l-menthol and beta-violetone were the most abundant in autumn tea as its characteristic aroma components, which were different from those of spring tea and summer tea and were mainly associated with floral, fruity and peppermint-like aromas. Benzyl alcohol and n-amyl alcohol were the most abundant in spring tea as its characteristic aroma components, which distinguished spring tea from summer tea and autumn tea and mainly contributed to fruity aromas and apricot kernel-like bitter taste. Nonaldehyde, 3,5-octadiene-2-ketone and trans-orange flower tertiary alcohol were the most abundant in summer tea as its characteristic aroma components and were mainly responsible for lemon-like and sweet fruity aroma.
Analysis and Evaluation of Fatty Acid Composition of Sheep Milk
WANG Haiyan, GE Wupeng, MA Xiaoyi, SONG Yuxuan, ZHAO Lili, ZHANG Yan, WANG Yuxin
2020, 41(22):  260-264.  doi:10.7506/spkx1002-6630-20191024-257
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The aim of this study was to characterize the fat acid profiles of Hu sheep milk, East Friesian sheep milk and Hu × East Friesian crossbred F1 sheep milk at different lactation stages by gas chromatography. Goat milk and human milk were used as the controls to evaluate the fatty acid composition of sheep milk. The results showed that sheep milk fat was mainly composed of oleic acid (C18:1 cis), palmitic acid (C16:0) stearic acid (C18:0) and myristic acid (C14:0). The proportion of oleic acid (C18:1 cis) in sheep milk was significantly higher than that in goat milk (P < 0.05), and the proportion of palmitic acid (C16:0) was significantly higher than that in human milk (P < 0.05). The proportions of monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) in Hu × East Friesion crossbred F1 sheep milk were significantly higher than those in goat milk (P < 0.05), implying that the former is a good source of high-quality animal fat. The proportion of fatty acids in sheep milk varied during lactation. According to the cluster analysis, the fatty acid composition of sheep milk was similar to that of goat milk. East Friesian sheep milk was similar in fatty acid composition to Hu × East Friesian crossbred F1 sheep milk.
Effects of Different Drying Methods on Nutritional and Volatile Aroma Components in Flowers of Elaegnus angustifolia
ZHAO Jinmei, SUN Rui, GONG Lili, GONG Yuwen, JIAO Yang, LI Caixia, XIE Yinyin, HOU Ailin
2020, 41(22):  265-270.  doi:10.7506/spkx1002-6630-20191110-100
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The effects of three drying methods including vacuum freeze-drying, natural drying in the shade and hot-air drying were investigated on the nutritional composition, amino acid composition and volatile flavor components of Elaegnus angustifolia flowers. The results indicated that E. angustifolia flowers dried by various drying methods demonstrated significant differences in terms of nutritional components and volatile flavor components. Hot-air drying brought about a significant reduction in the contents of reducing sugar, protein and total amino acids in E. angustifolia flowers than did the two other drying methods (P < 0.05). The contents of total amino acids and total phenols and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity in the vacuum freeze-dried sample were significantly higher than those in the samples dried by the other methods (P < 0.05). Hot air drying caused the maximum loss of flavor amino acids in the flowers, thereby lightening the umami and sweet tastes. The proportion of essential amino acids in the flowers, close to that needed by human body, was nearly independent of the drying methods. Electronic nose analysis showed significant differences in volatile flavor components among flower samples dried by different methods. The volatile flavor components of the samples dried by vacuum freeze drying and natural drying were more similar to those of fresh flowers. The vacuum freeze dried sample had the best quality and flavor. Taking into account both economy and drying efficiency, natural drying in the shade was also more suitable for E. angustifolia flowers. The results of this study provide a theoretical basis and practice rationale for the development of drying techniques for E. angustifolia flowers to develop new products.
Identification of Characteristic Aroma Compounds in Prunes Using Gas Chromatography-Olfactometry, Odor Activity Value and S-curve Method
Zhang Yipeng, Liao Tougen, HE Banghua, NIU Yunwei, ZHU Jiancai, WANG Mingfeng
2020, 41(22):  271-278.  doi:10.7506/spkx1002-6630-20191008-046
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Thirty-eight, 35 and 32 non-sulfur aroma compounds were identified in three different varieties of prunes, respectively and 4 sulfur-containing compounds in each variety using gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame photometric detection (GC-FPD). Hexanol (453.14–6 836.14 μg/kg), (E)-2-hexenal (926.67–4 153.65 μg/kg), hexanal (438.72–3 567.04 μg/kg), (Z)-2-hexenol (194.26–608.03 μg/kg), and phenylacetaldehyde (18.46–446.06 μg/kg) were identified as the main compounds. The results of gas chromatography-olfactometry (GC-O) and odor activity value (OAV) showed higher values for β-damascenone, hexanol, hexanal, 2-methybutanal, (E)-2-hexenal, and 3-methylthiopropanal, indicating that these compounds contribute greatly to the characteristic aroma of prunes. Furthermore, principal component analysis (PCA) revealed significant differences in aroma compounds among different varieties of prunes. Finally, four aroma compounds (β-damascenone, hexanal, 3-methylthiopropanal and (E)-2-pentenal) were selected to verify the accuracy of aroma identification of prunes by S-curve method. The results showed that the aroma compounds contributing greatly to the aroma of prunes had the most significant effects on reducing the threshold of the recombinant liquid and consequently could improve the aroma intensity. This study provides a scientific basis for the effective utilization of prunes.
Processing Technology
Formulation Optimization of Egg Tofu and Micro-Analysis of Its Texture Characteristics
GUO Meng, HE Chuan, ZHAI Wenyi, GUO Huiyuan, LÜ Ying, TONG Qigen
2020, 41(22):  279-288.  doi:10.7506/spkx1002-6630-20191021-223
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In order to develop egg products suitable for various cooking procedures by using egg and soybean as the main raw materials, the formulations of soft and firm egg tofu were optimized by comparing texture properties with others of the same type. The results showed that the optimal formulation of soft egg tofu was as follows: volume ratio of liquid whole egg to soy milk (with protein content of 6.5%) 2:9, pyrophosphate concentration 0.7%, agar concentration 0.02%, and δ-glucolactone concentration 0.3%. The hardness of this formulation was 392.75 g/cm2 and the chewiness was 17.75 mJ. The optimal formulation of hard egg tofu was as follows: volume ratio of liquid whole egg to soy milk (with protein content of 10.0%) 4:7, pyrophosphate concentration 1.0%, and agar concentration 0.02%. The hardness of this formulation was 1 002.17 g/cm2 and the chewiness was 53.52 mJ. When the volume ratio of liquid whole egg to soy milk was 2:9 or 5:6 for protein contents of soy milk of 7.5% and 9.5%, respectively, there was a deviation from the positive correlation between tofu hardness and the amount of liquid whole egg added. This deviation was verified by scanning electron microscopy and microscopic analysis based on differential thermal analysis (DTA), but the underlying mechanism needs further study.
Safety Detection
Discrimination of Water-injected Ground Meat Using Low-field Nuclear Magnetic Resonance and Magnetic Resonance Imaging
GAI Shengmei, YOU Jiawei, ZHANG Xuejiao, ZHANG Zhonghui, LIU Dengyong
2020, 41(22):  289-294.  doi:10.7506/spkx1002-6630-20190709-129
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In this paper, water-injected ground meat was detected quickly and non-destructively by using low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) techniques. Based on their relaxation characteristics, qualitative and quantitative analyses were carried out on ground meat with different proportions of water injected. The results showed that with the increase in the proportion of water injection, the single-component relaxation time Tw value of water-injected ground meat increased linearly (R2 = 0.953 5), and the multi-component relaxation time (T22 and T23) increased significantly (P < 0.05). LF-NMR combined with principal component analysis (PCA) revealed that ground meat samples injected with different proportions of water were distinctly distinguished on the principal component score plot. The partial least squares regression (PLSR) and principal component regression (PCR) models showed determination coefficient R2 for validation set of 0.92, and root mean square error (RMSE) of 1.27% and 1.25%, respectively. The proton density-weighted images of ground meat indicated that as the proportion of water injection increased, the color of the pseudo-color map gradually changed from blue to yellow and red, thereby allowing to visually distinguish the water-injected ground meat. All above results indicate that LF-NMR and MRI techniques can be used to quickly and accurately determine whether or not ground meat is water-injected.
Gas Chromatography-Mass Spectrometry Method for Determination of Chloropropanol Esters and Glycidyl Esters in Infant Formula
LIN Lishan , FU Wusheng, ZHANG Yike, GAO Bo, LAN Lihua, PANG Jie
2020, 41(22):  295-300.  doi:10.7506/spkx1002-6630-20200218-185
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A novel gas chromatography-mass spectrometry (GC-MS) method was developed to determinate the contents of chloropropanol esters (MCPDE) and glycidyl esters (GE) in infant formula. The extraction conditions were optimized as follows: milk powder 1.50 g, ammonia solution 3.0 mL, drying temperature 105 ℃, and drying time 1 h. Under these conditions, satisfactory results were obtained. The limits of detection (LODs) were 5 and 10 μg/kg for MCPDE and GE (calculated as fat), respectively. A good linear range was obtained in the concentration range of 100–2 000 μg/kg with a correlation coefficient of 0.999. When a mixed standard was spiked to the fat extracted from infant formula YL-34 at levels of 100, 400, and 1 000 μg/kg, which were calculated on the basis of milk powder as 20.5, 82.0, and 205 μg/kg , respectively, the recoveries varied from 81.5% to 114% with relative standard derivations (RSDs) of 2.6%–10% (n = 6). When this method was applied in FAPAS international proficiency test, satisfactory results were obtained. Our results showed that the novel method had good accuracy and repeatability, and was suitable for quantification of both MCPDE and GE in infant formula. Therefore, the procedure has been included in the Chinese national food safety risk monitoring manual.
Detection of Aflatoxin B1 in Pixian Broad-Bean Paste by Using Hybridization Chain Reaction Based on Aptamer
HUANG Yukun, TAO Xuan, SHAO Kun, WANG Chong, WANG Lijun, CHE Zhenming, CHEN Xianggui
2020, 41(22):  301-307.  doi:10.7506/spkx1002-6630-20190903-037
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A fluorescence method for the detection of aflatoxin B1 (AFB1) in Pixian broad-bean paste by using hybridization chain reaction (HCR) based on aptamer was established. The effects of the concentration of cDNA, HP1, HP2 and graphene oxide (GO), and incubation time for hybridization were studied on the performed of the method. The optimal conditions were obtained as follows: 50 nmol/L cDNA, 60 nmol/L HP1, 60 nmol/L HP2, 60 min incubation time, and 50 μg/mL GO. Under these conditions, the method showed a good linear relationship in the concentration range of 2–60 ng/mL, the detection limit was 1.84 ng/mL, and the recovery for spiked samples were 85.73%–94.25%. When the method was applied to the detection of 12 different brands of Pixian broad-bean pastes, satisfactory results were obtained which showed no significant difference from those of enzyme-linked immunosorbent assay in the national standard (P > 0.05). This method can detect AFB1 in various Pixian broad-bean pastes easily, quickly and sensitively, and has the potential for fast detection of AFB1 in complex samples.
Preparation of Magnetic Three-Dimensional Reduced Graphene and Its Application in Electrochemical Immunoassay of Mycobacterium tuberculosis H37Ra in Milk
LIU Xiya, TIAN Chunmei, ZHENG Lufei, ZHONG Pingsheng, ZHANG Xinfang, REN Jiali
2020, 41(22):  308-314.  doi:10.7506/spkx1002-6630-20200508-078
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In this paper, an electrochemical immunosensor based on magnetic three-dimensional ferroferric oxide/reduced graphene nanocomposite (Fe3O4@3D-RGO) was developed and applied to rapidly detect Mycobacterium tuberculosis H37Ra in milk. Fe3O4@3D-RGO was synthesized by a one-step hydrothermal reduction method and then characterized by scanning electron microscopy, electron energy spectroscopy and Raman spectroscopy. A modified electrode was prepared with 75% ethanol and 0.1% Nafion solution as dispersion system. The electrochemical performance was investigated using electrochemical impedance spectroscopy (EIS). Under the optimal conditions, M. tuberculosis H37Ra was detected. The results showed that the sensor displayed a strong linear relationship between the electrode impedance and the logarithmic concentration of M. tuberculosis H37Ra in the range of 1 × 103–1 × 108 CFU/mL. The regression equation was y = 19.77lgN ? 49.14, the limit of detection (LOD) was 1 × 102 CFU/mL and the detection time was as short as 15 min. This method had strong specificity and good repeatability and stability. The one-step hydrothermal reduction method, thanks to its simplicity and environmental friendliness, provides technical support for the development of portable electrochemical immunosensors.
Detection of Freshness Indexes of Imported Chilled Beef Using Hyperspectral Imaging Technology
SUN Zongbao, LIANG Liming, YAN Xiaojing, ZOU Xiaobo, WANG Tianzhen, LIU Xiaoyu, LI Junkui
2020, 41(22):  315-323.  doi:10.7506/spkx1002-6630-20191005-002
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In order to quickly and non-destructively identify the freshness of imported chilled beef, we applied hyperspectral imaging technology combined with chemometrics to detect the characteristic freshness indexes. Firstly, chilled beef with different storage times were evaluated for their total volatile basic nitrogen (TVN-N) content, color parameters (L*, a* and b*), and deoxymyoglobin, oxymyoglobin and metmyoglobin contents. The characteristic freshness indexes were selected from them by significance and correlation analysis. Then, hyperspectral imaging technology was used to collect spectral and image information of samples. Based on the spectral data, partial least squares, interval partial least squares, competitive adaptive reweighted sampling-partial least squares (CARS-PLS) models were developed to predict the characteristic indicators, and the prediction results from these models were compared. The results showed that TVB-N content, a* and b* were selected as the characteristic freshness indexes of chilled beef with different storage times. The best prediction model for TVB-N content, a* and b* was CARS-PLS, with correlation coefficient of calibration (rc) values of 0.965 8, 0.949 5 and 0.964 2; root mean square error of cross-validation (RMSECV) values of 1.06 mg/100 g, 0.7 and 0.76; correlation coefficient of prediction (rp) values of 0.963 7, 0.949 4 and 0.942 3; and root mean square error of prediction (RMSEP) values of 1.12 mg/100 g, 0.72 and 0.77 respectively. The CARS-PLS model combined with image processing was used to draw a visual distribution map for these characteristic indicators, which visually represented the trend of freshness of chilled beef during storage. This study proves that hyperspectral imaging technology allows the rapid detection and distribution visualization of chilled beef freshness indexes.
A Rapid Technique for the Detection of T-2 Toxin Based on Specific Aptamer-Capped Mesoporous Nanomaterials
XU Qunbo, TAN Hongxia, MA Liang
2020, 41(22):  324-329.  doi:10.7506/spkx1002-6630-20190714-182
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In this paper, using mesoporous silica nanoparticles (MSN) to enrich the signal probe and using the T-2 toxin aptamer as a recognition probe and a switch to control the signal probe, a rapid label-free technique for the quantitative detection of T-2 toxin was proposed based on the relationship between the signal intensity and the content of the target toxin. In the detection system, the target T-2 toxin could specifically bind to its aptamer, releasing the signal probe. The results showed that when this method was applied to corn, barley and wheat samples, the spiked recoveries of T-2 toxin were in the range between 85.8% and 111.4% with relative standard deviation (RSD) less than 4.6%, indicating that this method has good accuracy and repeatability. The method was sensitive with a limit of detection of 1.25 ng/mL and showed a good linearity in the concentration range of 0–50 and 50–250 ng/mL. Compared with the traditional method, this novel method was more rapid, simpler and cheaper and allowed sensitive and quantitative detection of T-2 toxin with a wider linear range.
Determination of Ten Cephalosporin Residues in Bee Products by Ultra-high Performance Liquid ChromatographyTandem Mass Spectrometry Coupled with PRIME HLB Solid Phase Extraction
ZHANG Hao, WU Yinliang, ZHANG Yiwen, CHEN Guo, JIANG Xiaoxiao
2020, 41(22):  330-336.  doi:10.7506/spkx1002-6630-20190717-224
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An ultra-high performance liquid chromatography-tandem mass spectrometry method for the simultaneous quantitative determination of residues of 10 cephalosporins in bee products, including honey, royal jelly and lyophilized royal jelly powder, was established. The samples were extracted with 10% formic acid solution. After being purified by solid-phase microextraction using an Oasis PRIME HLB cartridge, the extract was blown to dryness under a stream of nitrogen gas and then re-dissolved. The analytes were separated on an Acquity UPLC BEH C18 column with a mixture of 0.1% formic acid solution and methanol as the mobile phase by gradient elution. The analysis was carried out using a positive electrospray ion source in the multiple reaction monitoring mode. The matrix-matched external standard method was applied for the quantitative analysis. There were good linear relationships for 10 cephalosporins in certain concentration ranges, with correlation coefficients of more than 0.999. The limits of detection (LODs) for 10 cephalosporins were 0.1–1 μg/kg, and the limits of quantitation (LOQs) were 0.3–3 μg/kg. The recoveries for the analytes spiked into blank bee products were in the range of 80.0%–95.5%, with relative standard deviations of 1.5%–4.8%. This method was time-saving and suitable for the determination of cephalosporins in different bee products due to its simplicity and reliability.