Table of Content

25 June 2022, Volume 43 Issue 12
Food Chemistry
Effect of Interaction between EGCG and Soy β-Conglycinin/Glycinin on Protein Structure
HUANG Guo, TIAN Zepeng, XUE Liying, CHEN Qi, WANG Di, YI Yanjiao, LI Meng, SUN Shujing, SUI Xiaonan
2022, 43(12):  1-6.  doi:10.7506/spkx1002-6630-20210508-081
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The interaction between β-conglycinin (7S)/glycinin (11S) and (–)-epigallocatechin-3-gallate (EGCG) under neutral conditions was characterized by fluorescence spectroscopy, ultraviolet-visible (UV-Vis) absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and molecular docking. The results showed that EGCG and 7S/11S could interact with each other at pH 7.0, which induced a change in the microenvironment of amino acid residues. EGCG could quench the intrinsic fluorescence of 7S/11S in dynamic and static manners. EGCG had higher affinity to 11S than to 7S. The reaction between EGCG and 7S/11S was a spontaneous binding process, resulting in the formation of a complex at 1:1 molar ratio by hydrogen bonding and van der Waals force. EGCG could reduce the surface hydrophobicity of 7S/11S. With increasing EGCG concentration, 11S showed a greater change in surface hydrophobicity. FTIR and molecular docking studies suggested that in addition to hydrogen bonds, hydrophobic interactions were also involved in the formation of complexes. Binding to EGCG could cause different changes in the secondary structure of 7S/11S subsequently resulting in protein unfolding.
Effect of Sour Soup on Characteristic Flavor and Quality of Beef in Sour Soup
WU Wenyan, HU Ping, LI Juan, WANG Xiaoyu, FENG Dandan, SHI Yuanyuan, ZHANG Lei, JIANG Jingzhu, ZHU Qiujing
2022, 43(12):  10-14.  doi:10.7506/spkx1002-6630-20210702-014
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The effect of cooking beef in sour soup (red sour soup, white sour soup, or their mixture) on the sensory quality, pH, color, moisture content, cooking loss percentage, tenderness and texture properties were studied. The volatile components of beef in sour soup were analyzed by gas chromatography-ion mobility spectrometry (GC-IMS) to evaluate the overall quality. The results showed that compared with the control group (cooked in water), sour soup significantly improved the tenderness and moisture content, reduced the cooking loss percentage, hardness, chewability and viscosity, and improved the color and sensory quality of beef. The cooking loss percentage, hardness, adhesiveness and chewability of beef in white sour soup were the lowest and the moisture content was the highest followed by beef in red sour soup. There was no significant difference in beef tenderness between red sour soup and white sour soup, while red sour soup significantly improved the redness and yellowness of beef. The mixed sour soup was more effective in enhancing beef brightness. The content of lactic acid in red and white sour soup (23.27 and 4.90 mg/mL, respectively) higher than that in their mixture. A total of 55 volatile flavor compounds were detected across the three groups of beef in sour soup and there were significant differences in volatile components among them. Compared with the control group, the relative content of aldehydes was reduced and the relative content of lipids was increased by cooking beef in sour soup. The relative contents of lipids, acids and ketones in beef in red sour soup were relatively high, and the relative content of aldehydes was low. Beef in red sour soup scored highest in sensory evaluation, exhibiting the best taste and flavor. The major characteristic flavor substances of beef in red sour soup were ethyl lactate, butyral, acetic acid, benzaldehyde (dimmer), and 2-methylpropionic acid. The major characteristic flavor substances of beef in white sour soup were propanol, 2-butanone, 3-pentanone and propionic acid. The major characteristic flavor substances of beef in the mixed sour soup were ketones. The content of some flavor substances increased in beef in sour soup compared to the control group, contributing to the characteristic flavor of beef in sour soup. In summary, beef in red sour soup was rich in volatile flavor components, and had a higher sensory score and better overall quality. Red sour soup was a suitable choice for making beef in sour soup.
Effect and Underlying Mechanism of Milk Protein on the Physical Characteristics of Soymilk Gel
XU Ruolin, LIU Ping, PANG Zhihua, CHEN Cunshe, LIU Xinqi, ZHAO Yixin, LI Tong
2022, 43(12):  18-21.  doi:10.7506/spkx1002-6630-20210707-069
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In order to improve soy yogurt products, the effect and underlying mechanism of different types of milk proteins, whey protein isolate (WPI), milk protein concentrate (MPC), and sodium caseinate (NaCas), on the gelation behavior of soymilk were investigated. The results showed that the incorporation of WPI (≥ 20%) or 40% NaCas could effectively enhance the strength of soymilk gels, and WPI (≥ 20%) had the most positive effect. Low levels of replacement of milk proteins could significantly decrease the particle size of soymilk gels, while high proportions of WPI replacement had the opposite effect. In term of microstructure, MPC led to more organized and denser networks. NaCas induced the formation of filamentous networks. WPI induced the formation of a less organized but denser gel structure. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that WPI (≤ 20%) might promote the involvement of the β subunit of soybean 7S protein in gel formation, while NaCas might hinder the gelation of the basic subunit of soybean 11S protein.
Hydrophobic Modification of Food-Grade Starch Nanoparticles by Acetylation and Its Digestion Characteristics
YAO Xianchao, SHI Yonggui, JIAO Siyu, WU Yashan, YANG Wanyan, LIN Rihui
2022, 43(12):  25-28.  doi:10.7506/spkx1002-6630-20210731-375
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Cassava starch nanoparticles with an average size of (273.8 ± 26.41) nm were prepared by ultrasonic crushing followed by ethanol sedimentation and were esterified with acetic anhydride to prepare hydrophobic nanoparticles. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy showed that the degree of substitution (DS) of the esterified products was as high as 0.53 without adding any catalysts during esterification. X-ray diffraction (XRD) analysis showed that the crystal structure of starch nanoparticles did not change significantly after modification, and both the original and modified nanoparticles were amorphous. Scanning electron microscopy (SEM) showed that the morphology of the nanoparticles did not change significantly after modification. The three-phase contact angle increased with increasing DS, reaching a maximum of (109 ± 3.56)°, and the higher the DS, the longer the contact angle was maintained. The modified product was easier to disperse in the oil phase, leading to the formation of microemulsions. Surface modification changed the hydrophilic/hydrophobic properties of starch nanoparticles, and improved its potential for emulsification at the oil-water interface. In contrast to the unmodified sample, the modified sample showed similar enzymatic digestion curves and no fundamental change in eating quality, but lower enzymatic digestibility at the same time points, suggesting stronger resistance of the modified product with higher DS to enzymatic hydrolysis.
Adding Casein Hydrolytic Peptides to Improve the Processing Characteristics of Yogurt
WANG Yihui, CAI Miao, ZHANG Min, ZHAO Hua, LIU Jing, YANG Zhennai
2022, 43(12):  34-35.  doi:10.7506/spkx1002-6630-20210906-066
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Yogurt was prepared from raw milk added with peptides from bromelain hydrolyzed casein at different concentrations (0.1%, 0.3% and 0.5%), and the changes in physicochemical, microbial and flavor characteristics of yogurt during fermentation and cold storage were determined. The results showed that adding casein hydrolytic peptides (CHP) accelerated the pH decline during the late fermentation period, and reduced the fermentation time of yogurt. When 0.1% CHP was added, the fermentation time was reduced by 34 minutes compared to the control group. Microrheological measurement showed that adding CHP decreased the elasticity index (EI) and fluidity index (FI), but increased the macroscopic viscosity index (MVI) of yogurt during the late fermentation period. Scanning electron microscopy showed that the yogurt samples in each group had a porous network structure. Proper addition of CHP (0.1%) improved the colloid structure and made the network structure of yogurt more compact and uniform. During the cold storage of yogurt, adding CHP increased the count of viable starter bacteria, and promoted the formation of flavor compounds such as acids, aldehydes and ketones, and adding 0.3% CHP reduced the EI value of yogurt. With increasing addition of CHP from 0.3% to 0.5%, the hardness and adhesiveness of yogurt decreased gradually, but water-holding capacity, cohesiveness and viscosity did not significantly change. The results of this study provide technical references for the application of CHP in yogurt processing and the improvement of product quality and functionality.
Effect of Konjac Glucomannan on Gelling Properties of Myofibrillar Protein from the Pacific White Shrimp Litopenaeus vannamei
SUN Lechang, ZHOU Dianying, DU Han, WENG Ling, MIAO Song, LIU Guangming, CAO Minjie
2022, 43(12):  42-42.  doi:10.7506/spkx1002-6630-20210822-286
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In order to investigate the effect of konjac glucomannan (KGM) on the gelling properties of shrimp myofibrillar protein (SMP), composite gel systems were prepared with different ratios to KGM and SMP (1:50, 1:20 and 1:10, m/m), named as SK50, SK20 and SK10, respectively. The surface hydrophobicity, endogenous fluorescence, turbidity, particle size, rheological properties, Fourier transform infrared (FTIR) spectra, protein composition and microstructure of the composite systems were investigated. The results showed that the surface hydrophobicity, turbidity and particle size of SMP and SMP-KGM composite systems increases with increasing KGM addition. Rheological analysis showed that shear thinning occurred in both SMP and SMP-KGM composite systems, and the storage modulus (G’) value of SK20 was the highest, indicating that the gel network in SK20 had the highest structural stability. FT-IR analysis showed the characteristic spectral bands of SMP and SMP-KGM composite systems were similar. SDS-PAGE analysis showed that addition of KGM did not significantly change the bands of SMP. After heating, the band densities of myosin heavy chain, paramyosin and actin were significantly decreased compared with the unheated group, indicating that the three proteins underwent aggregation during heating. Scanning electron microscope and fractal dimension analysis showed the formation of a dense and ordered gel with increasing KGM content. In general, adding an appropriate amount of KGM can improve the gel strength, and the product quality of shrimp surimi.
Effect of Gelatin on the 3D Printing Forming Stability of Chicken Meat Paste
YANG Genghan, HAN Yu, TAO Yang, ZHU Xiaoyu, XU Xinglian
2022, 43(12):  51-50.  doi:10.7506/spkx1002-6630-20210719-210
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In this study, the effects of gelatin (0%, 2%, 4%, 6% and 8% (relative to meat mass)) on the 3D printing forming stability of chicken meat paste were investigated by rheological tests, gel strength measurement, nuclear magnetic resonance, and scanning electron microscopy. The results showed that chicken meat paste had shear thinning behavior irrespective of whether or not gelatin was added, which was suitable for 3D printing. Gelatin addition enhanced the viscosity and gel strength of chicken meat gel systems, thus effectively improving the 3D printing forming stability of chicken meat paste. However, excessive addition of gelatin affected the extrusion process of chicken meat paste and reduced the shape accuracy of printed samples. Addition of 4% gelatin resulted in good accuracy and forming stability, and the collapse rate of the printed shape was 2.46%. The cooking quality of the 3D printed sample with 4% gelatin was evaluated. It was found that 3D printing could increase its cooking loss, but improve its texture properties.
Preparation in Vitro Digestibility of Perilla Oil Multilayer Emulsion
LIAO Yi, SUN Yufan, PENG Xinhui, WANG Qi, WU Lichun, YAN Shichang, LIU Guannan, ZHU Huaping, QI Baokun, LI Yang,
2022, 43(12):  58-58.  doi:10.7506/spkx1002-6630-20210621-244
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In view of the fact that perilla oil tends to be oxidized during storage, with soy protein isolate (SPI) or its blends with chitosan (CS) and sodium alginate (SA) as the emulsifier, electrostatic layer-by-layer self-assembly was used to encapsulate perilla oil to maintain its physical stability and for its sustained release. The microscopic morphology and stability of the perilla oil single-layer emulsion, double-layer emulsion and three-layer emulsion were investigated, and an in vitro simulated digestion model was established to determine changes in the fatty acid composition of the three emulsions before and after digestion by gas chromatography. The results showed that the three emulsions, prepared using a wall material composed of 1.0% SPI solution, 2.0% CS solution, and 1.5% SA solution, had small particle size, high potential, and good physical and chemical stability. Under acidic conditions, the multi-layer emulsions could better protect polyunsaturated fatty acids. As the number of layers increased, the oxidation rate of perilla oil became slower. The in vitro simulated digestion results showed that the three-layer emulsion had a better sustained-release effect than the single-layer and double-layer emulsions, and the multi-layer emulsion could ensure the effective release of fatty acids from the oil. These findings can guide the development of slow-release systems for oils.
Preparation, Structure Characterization and Antioxidant Activity of Selenylated Low-Molecular-Mass Pectin
TAO Wen, ZHANG Rui, YANG Ning, WU Muci, HE Jingren
2022, 43(12):  66-65.  doi:10.7506/spkx1002-6630-20210621-247
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In this study, apple pectin was used as a raw material to prepare selenylated low-molecular-mass pectin by hydrolysis with pectinase followed by ultrasonic-assisted nitric acid-sodium selenite (HNO3-Na2SeO3) treatment. Using pectin, selenylated pectin and low-molecular-mass pectin as the controls, the structure of selenylated low-molecular-mass pectin was determined using size exclusion chromatography with refractive index and multi-angle laser light scattering detection (SEC-RI-MALLS), ion chromatography (IC), Fourier transform infrared (FTIR) spectroscopy, ultraviolet (UV) spectroscopy, thermal gravimetric analysis (TGA), particle size and potential. The selenium content was measured by hydride generation atomic fluorescence spectrometry (HG-AFS), and the galacturonic acid content was detected by the carbazole-sulfuric acid method. The in vitro antioxidant activity and α-glucosidase inhibitory effect were characterized. The results showed that the yield of selenylated low-molecular-mass pectin was (78.07 ± 1.66)%, with selenium content of (148.29 ± 1.97) μg/g, and galacturonic acid content of (68.02 ± 3.21)%. The relative molecular mass was concentrated at 8.905 × 103. In terms of monosaccharide composition, selenylated low-molecular-mass pectin was the same as pectin, selenylated pectin and low-molecular-mass pectin. They were mainly composed of rhanose, arabinose, galactose, glucose, xylose and galacturonic acid, but there were differences in the molar ratio among monosaccharides. Se=O and C–O–Se bonds were found in the structure by FTIR analysis, suggesting the formation of selenylated low-molecular-mass pectin. An absorption peak was found at around 200 nm in the UV spectrum, which is characteristic of pectin polysaccharides. After enzymatic hydrolysis and selenylation treatment, the thermal stability of pectin decreased, the degree of dispersion became higher and the stability of the system was enhanced. Meanwhile, pectin, selenylated pectin, low-molecular-mass pectin, and selenylated low-molecular-mass pectin had high scavenging effects on hydroxyl and superoxide anion radicals and α-glucosidase inhibitory effect in a dose-dependent manner, and selenylated low-molecular-mass pectin had the strongest effect.
Effect of Ginkgo biloba Fruit Powder on Rheological Properties, Water Distribution and Mobility of Wheat Dough
QIAN Xin, LI Liangyi, ZHOU Wenhua, TAN Yuheng, MA Yan, ZHAO Peirui
2022, 43(12):  74-72.  doi:10.7506/spkx1002-6630-20210507-065
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Objective: The aim of this study was to explore the effects of adding different proportions of Ginkgo biloba fruit powder on rheological properties, water distribution and mobility in wheat dough. Methods: The rheological properties were determined by using a farinograph, a rapid viscosity analyzer (RVA) and a rheometer, and the water distribution and mobility were measured by differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). Results: From the rheological results, it was found that the water absorption percentage, tolerance index and broadband of wheat flour-G. biloba fruit powder blends gradually increased with increasing addition of G. biloba fruit powder. Dough development time decreased first and then increased. Addition of 12% G. biloba fruit powder resulted in the shortest formation time of gluten network. Each tested gelatinization parameter showed a downward trend. The storage modulus (G’) and loss modulus (G’’) gradually increase with increasing frequency. The tangent of loss angle reached a maximum value upon the addition of 18% G. biloba fruit powder, but an inflection point began to appear as the addition amount continued to increase, which was not conducive to the viscoelasticity. The results of water distribution and mobility indicated that with increasing addition of G. biloba fruit powder, the enthalpy of water melting and the content of freezable water decreased gradually, the content of non-freezable water increased gradually, and the water fluidity in the system decreased. The contents of weakly bound water and free water decreased, while the content of strongly bound water began to increase gradually with increasing addition of G. biloba fruit powder from 18%. Conclusion: In summary, the rheological properties and water distribution of wheat dough were significantly affected by the addition of G. biloba fruit powder in the range of 12%–18% (P < 0.05), which resulted in better dough quality.
Foaming Characteristics and Underlying Mechanism of Rice Bran Protein-Ovalbumin Mixtures
ZHANG Yanpeng, ZHANG Manjun, DIAO Yunchun, ZHANG Weinong, HU Zhixiong, XU Wei
2022, 43(12):  81-80.  doi:10.7506/spkx1002-6630-20210506-042
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The foaming characteristics of rice bran protein (RBP)-ovalbumin (OVA) mixtures were investigated, and the physicochemical properties of the two proteins in solution and foam under specific pH and NaCl concentration were analyzed to elucidate the effects of the interaction between them on their foaming characteristics. The results showed that the two proteins had a synergistic effect on their foaming ability at pH 4.0, and the foaming ability and foam stability of the 3:1 mixture of RBP and OVA were significantly increased by addition of 1% NaCl. However, at pH 7.0, the two proteins showed no obviously synergistic effect on their foaming properties without NaCl, but instead showed an antagonistic effect when 1% NaCl was added. Under pH 4.0 and 1% NaCl conditions, the physicochemical properties of the two proteins in the solution and foam were complementary to each other. Therefore, the interaction between RBP and OVA can improve the foaming ability and foam stability of their mixtures from the perspective of different physicochemical properties.
Effects of Non-phosphate Water-Retaining Agents on the Physicochemical and Microstructure Properties of Sturgeon Fillets Subjected to Repeated Freeze-thaw Cycles
LI Guimin, ZHAO Chunqing, DOU Rongrong, YAN Ziheng, SANG Yaxin, KANG Chunyu, SUN Jilu
2022, 43(12):  87-87.  doi:10.7506/spkx1002-6630-20210511-117
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To explore the effects of a phosphorus-free water-retaining agent consisting of sodium bicarbonate, sodium citrate and sorbitol on the physicochemical properties and microstructure of sturgeon slices under repeated freeze-thaw conditions, sturgeon fillets were treated with the water-retaining agent or distilled water as a control before being repeatedly thawed and frozen up to five times. At each cycle, the thawing loss percentage, cooking loss percentage, pH, thiobarbituric acid (TBA) value, myofibrillar protein solubility, Ca2+-ATPase activity and texture characteristics were measured. Meanwhile, the microstructure was examined. The results showed that with the increase in the number of freeze-thaw cycles, the thawing loss percentage, cooking loss percentage and TBA value were significantly increased (P < 0.05), the water-retaining agent treatment plus quick freezing group exhibiting a slower rate of increase in these parameters compared with the water-retaining agent treatment plus slow freezing group and the control group. For all groups, pH decreased first and then increased, water content, myofibrillary protein solubility, Ca2+-ATPase activity, hardness and elasticity significantly decreased (P < 0.05), and the rate of decrease in these parameters was slower in the water-retaining agent treatment groups than in the control group. Cross-sectional images showed that the microstructure of sturgeon fillets could be maintained better by water-retaining agent treatment compared to the blank control group. These findings show that the water-retaining agent can inhibit the quality deterioration of sturgeon fillets under repeated freeze-thaw cycles.
Effect of Covalent Crosslinking of Soybean Protein Isolate with Genistein on Protein Characterization and Structure
LÜ Siyao, ZHU Dengzhao, BAO Yunxiang, ZHANG Debin, YU Hansong, GU Chunmei
2022, 43(12):  94-96.  doi:10.7506/spkx1002-6630-20210706-051
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In order to explore the effects covalent crosslinking between soybean protein isolate (SPI) and genistein on protein characterization and structure, covalent complexes between SPI and genistein, prepared by adding different concentrations (0, 1.2, 1.5 and 2.0 mg/mL) of genistein to SPI solution, were characterized by measuring particle size, zeta potential, turbidity and surface hydrophobicity, and the structural changes of SPI were analyzed by using an ultraviolet spectrophotometer, a fluorescence spectrophotometer and a Fourier transform infrared spectrometer. The results showed that the median particle size of SPI declined from 135.6 to a minimum value of 98.0 μm, the absolute value of zeta potential increased from 15.0 mV to a maximum value of 21.4 mV, the surface hydrophobicity decreased from 216.0 to a minimum value of 115.5, and the total sulfhydryl group content decreased from 31.5 μmol/g to a minimum value of 20.4 μmol/g after covalent complexation with genistein. Compared with the control group, the turbidity of the covalent complexes increased, and the turbidity of the SPI-Ge-1.2 complex was lower than that of the SPI-Ge-1.5 and SPI-Ge-2.0 complexes. Spectral analysis showed that genistein had a quenching effect on SPI. After covalent cross-linking, the hydrophobicity of the microenvironments of tryptophan and tyrosine residues in SPI decreased, the contents of α-helix and β-turn increased, and the contents of β-sheet and random coil decreased. The addition of 1.2 mg/mL genistein had a better effect on the characterization and structure of SPI. The results indicated that the covalent cross-linking of genistein with SPI can affect the characterization and structure of the protein.
Effect of Aniseed Shikimic Acid on Color of Duck Thigh during Heat Treatment
WU Binbin, FU Caiqi, XU Wei, GUO Danjun, HE Wenjie, YI Yang, WANG Hongxun
2022, 43(12):  101-106.  doi:10.7506/spkx1002-6630-20210905-055
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In this study, the effect of shikimic acid-rich aniseed extract on the color of heat-treated duck thigh by determining the color difference and myoglobin content. Meanwhile, the mechanism of action of aniseed shikimic acid on myoglobin in different mixing mass ratios was explored through fluorescence spectroscopy, thermogravimetric analysis, particle size measurement, and Fourier infrared spectroscopy. The results showed that the aniseed extract could improve the color of duck thigh to a certain extent. When shikimic acid mixed with myoglobin at a mass ratio of 1:10 000 underwent heat treatment for 30 min, shikimic acid could fully bind to the iron porphyrin ring and tryptophan in myoglobin, and the surface particle size of myoglobin decreased from 756 to 183 nm. Compared with the blank group, the α-helix proportion of myoglobin increased by 14.55% in the treated group, and the proportion of random coil decreased from 46.61% to 31.63%. In conclusion, the addition of a proper amount of aniseed shikimic acid can effectively maintain the structural stability of myoglobin and improve the color of duck legs.
Effect of Mixtures of Emulsifiers with Different HLB Value on Fat Coalescence and Crystallization of Whipped Cream
WANG Jidong, ZHENG Yuanrong, LIU Zhenmin, WANG Qinggang, XU Xingmin
2022, 43(12):  107-113.  doi:10.7506/spkx1002-6630-20210906-057
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In this investigation, emulsifiers with different values of hydrophile lipophilic balance (HLB) were prepared with different ratios of mono- and di-glycerin fatty acid esters and sucrose esters in order to study their effect on fat coalescence and crystallization in whipped cream and on its emulsion properties and whipping properties. The results showed that as the HLB value of emulsifiers increased, the particle size and apparent viscosity of emulsions increased, thereby prolonging the whipping time. Based on the results of thermodynamics and Avrami isothermal crystallization kinetics, it was found that the melting temperature of high melting point milk fat was significantly improved by using the emulsifier with an HLB value of 10, resulting in the fastest crystallization rate. The emulsifier with HLB value between 8 and 10 improved the whipping characteristics of whipped cream, reduced the percentage of serum leakage and improved the spreadability and therefore could be more suitable for the industrial production of high-quality decorative whipped cream.
In Vitro Simulated Gastrointestinal Digestion Properties of Free and Nanocapsulated α-Glucosidase Inhibitory Peptide from Soft-Shelled Turtle Egg
XIAO Ting, QIU Leyun, WANG Ruiyan, LI Nan, DENG Zeyuan, ZHENG Liufeng
2022, 43(12):  114-118.  doi:10.7506/spkx1002-6630-20210715-165
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In this study, the effect of in vitro simulated gastrointestinal digestion on the α-glucosidase inhibitory activity of SGTLLHK, an α-glucosidase inhibitory peptide from soft-shelled turtle egg. The digestion properties and products of SGTLLHK were analyzed by ultra-high performance liquid chromatography-quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS/MS). Bovine milk exosomes and solid lipid nanoparticles (SLN) were then prepared to encapsulate SGTLLHK, and the particle characteristics (microstructure, zeta potential, particle size, polymer dispersity index (PDI)) were investigated. The encapsulation efficiency and the stability of encapsulated SGTLLHK in a simulated gastrointestinal environment were determined by high performance liquid chromatography (HPLC). Results revealed that SGTLLHK was completely hydrolyzed after gastric digestion, and two peptides (SGTLL and GTLL) were identified from the digested products. After further intestinal digestion, GTLL was completely degraded, while SGTLL was still intact. The α-glucosidase inhibitory activity of SGTLLHK was increased significantly after gastric digestion, and markedly decreased after intestinal digestion, reaching a level lower than that of the original peptide. SGTLLHK was successfully encapsulated in the exosomes and SLN. Meanwhile, the exosome encapsulation system showed high stability, having an average particle size of (125.87 ± 2.66) nm and a PDI of 0.17 ± 0.01. After gastrointestinal digestion, the retention rate of SGTLLHK-loaded exosomal particles was 72.52%, while that of SGTLLHK-SLN was 48.43%, indicating that both the exosomes and SLN could protect SGTLLHK against degradation by gastrointestinal digestive enzymes, the former being more effective than the latter.
Effects of Different Protective Agents on the Physicochemical Properties of and Sustained Anthocyanin Release from Freeze-Dried Powder of Lonicera edulis
ZHANG Xiuling, LI Chen, JI Run, LI Fengfeng, ZHANG Wentao
2022, 43(12):  122-123.  doi:10.7506/spkx1002-6630-20210515-188
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In order to improve the quality of vacuum freeze-dried Lonicera edulis powder, five freeze-dried L. edulis powders were prepared using different cryoprotectants, namely, maltodextrin and its binary mixtures with sodium carboxymethyl cellulose, sodium alginate, gum arabic, and β-cyclodextrin. Based on the color, yield and anthocyanin content of freeze-dried L. edulis powder, the optimal addition levels of carboxymethyl sodium cellulose, sodium alginate, gum arabic and β-cyclodextrin were determined to be 2.5%, 1.5%, 2%, and 1%, respectively. The anthocyanin content of freeze-dried L. edulis powder with 2% gum arabic was the highest, (18.09 ± 0.98) mg/g, and it had the strongest ability to scavenge 2,2’-azinobis(3-ethylberizothiazoline-6-sulfonic acid) (ABTS) radical cation, (93.04 ± 0.30)%. Freeze-dried L. edulis powder with 1% β-cyclodextrin added had the highest contents of total polyphenols and total flavonoids. Compared with the single protective agent, L. edulis powders with the mixed protective agents showed a rounder and smoother spherical shape under a scanning electron microscope (SEM). The anthocyanins in L. edulis powder were more stable to gastric digestion than to intestinal digestion. As the in vitro digestion proceeded, the anthocyanin content showed a downward trend, and the retention rate of anthocyanins in L. edulis powder with the mixed protective agents was higher than that in L. edulis powder with malt alone. The retention rate of anthocyanins in the maltodextrin/sodium carboxymethylcellulose (D1) and maltodextrin/gum arabic (D3) groups was higher.
Regulatory Effect of Matrix Structures on Bioaccessibility of Lutein Loaded into Nanostructured Lipid Carriers
LI Xintian, XU Yayuan, ZHANG Zhongyuan, DAI Zhuqing, FENG Lei, NIE Meimei, LI Dajing, ZHANG Guodong, ZHANG Xing
2022, 43(12):  130-132.  doi:10.7506/spkx1002-6630-20210421-300
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In this study, the effects of matrix structures on the crystal thermodynamic properties and solidified layer thickness of lutein-loaded nanostructured lipid carriers as well as lipid digestibility, lutein release, micelle formation and lutein bioaccessibility in Lutein-NLCs were investigated. The results showed that as the concentration of linseed oil increased, the melting point and enthalpy value of Lutein-NLCs first increased and then decreased, and the thickness of the solidified layer gradually decreased. The degree of lipid hydrolysis, the release of free fatty acids (FFAs) and monoacylglycerols (MAGs), and the bioaccessibility of lutein gradually decreased with increasing concentration of linseed oil up to 90%. The rate and extent of hydrolysis of MAGs and FFAs in Lutein-NLCs with four different matrix structures were positively correlated with their rate and extent of micellization. The release rate of lutein from Lutein-NLCs with linseed oil concentration higher than 10% was negatively correlated with the hydrolysis rate of TAGs. The micellization rate of lutein was negatively correlated with those of MAGs and FFAs, and was positively correlated with lutein release rate. The bioaccessibility of lutein was positively correlated with its release degree.
Effect of Modification Methods of Cellulose Microfibrils on the Performance of Collagen Fiber Composite Films
JIAO Ting, ZHANG Wenhui, ZHANG Xue, ZHANG Haiyan, WANG Wenhang, ZHANG Hongjie
2022, 43(12):  139-141.  doi:10.7506/spkx1002-6630-20210802-021
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In this study, composite films were prepared with collagen fiber (CF) and cellulose microfibrils (CMF) with different degrees of carboxylation coated with metal-polyphenol network (MPN) in order to evaluate the influence of the modification methods of CMF on the properties of the composite films. The results showed that compared to CF-CMF films, the oxidation resistance of CF-CMF-MPN films was increased by 51.49%, and the elongation at break and light resistance were also improved significantly. CMF modified with MPN and high content of carboxymethyl groups could minimize the impact of MPN on the mechanical strength of composite films. CMF modified with MPN and high content of carboxyethyl groups could increase the water vapor and oxygen barrier performance by 1.30 and 3.48 times, respectively. Scanning electron microscopy and infrared spectroscopic analysis showed that different modified CMFs and collagen fibers physically cross-linked and had good compatibility with each other. In conclusion, this study has provided a new means to improve the performance of composite films for better applications in the field of food packaging.
Effect of Sodium Alginate Addition on the Extrusion Characteristics of Soy Protein Concentrate
DOU Wei, ZHANG Xin, ZHAO Yu, SUI Xiaonan, JIANG Lianzhou
2022, 43(12):  147-149.  doi:10.7506/spkx1002-6630-20210817-202
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Plant-based meat was prepared from soy protein concentrate (SPC) with different proportions of added sodium alginate (SA) by twin screw high-moisture extrusion under varying die temperature. The macrostructure and microstructure of plant-based meat were characterized by texturization degree, chewiness, color, and scanning electron microscopy. The structural properties of the extrudates were investigated by specific mechanical energy, cooking characteristics, and water absorption capacity. The results showed that the addition of sodium alginate could improve the texturization degree and enhance the chewiness of extrudates. And all extruded samples obtained at a die temperature of 150 ℃ had a higher texturization degree. The specific mechanical energy and water absorption capacity showed that sodium alginate enhanced the protein-protein and protein-water interactions, and consequently increased the water holding capacity of the extrudates. Scanning electron microscopy showed that excessive sodium alginate caused the product to form a dense lamellar, non-fibrous structure. As a result, we found that extrudates with 6% SA had the most abundant fibrous structure and good cooking performance.
Acid Stress Response Mechanism in Oenococcus oeni SD-2a Analyzed by RNA Sequencing
LIU Longxiang, PENG Shuai, ZHAO Hongyu, YUAN Lin, LI Hua,, WANG Hua
2022, 43(12):  153-155.  doi:10.7506/spkx1002-6630-20210626-305
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The response of Oenococcus oeni SD-2a to short-term acid stress (3 h) was detected by?RNA sequencing (RNA-seq). The transcriptome data were analyzed using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Besides, some physiological indicators related to the stress response were also measured. Based on the obtained results, a schematic diagram illustrating the stress response mechanism was drawn. It turned out that under acid stress condition, the bacterial cells synthesized more ATP to pump H+ out of them, and the ATPase activity was significantly increased. A suitable pH could maintain an appropriate enzymatic reaction environment for life activities. The cell membrane fluidity was decreased by adjusting the contents of total unsaturated fatty acids and total cyclic fatty acids. In conclusion, the intracellular energy production was greatly increased, and some energy dissipation responses favorable for resistance to acid stress were significantly increased, while some unrelated energy dissipation responses were inhibited. Furthermore, in order to deal with the damage caused by acid stress, the expression levels of DNA-repairing genes and chaperone protein genes were greatly increased. Our findings provide insights into the regulatory network associated with acid stress responses in O. oeni.
Characterization and Analysis of Differentially Abundant Proteins in Milk Fat Globule Membranes between Bovine Colostrum and Mature Milk
LI Mohan, ZHANG Xiumin, WANG Yining, CHEN Jiali, REHANGULI, YU Haikun, ZHANG Juan, SONG Wanying, LIU Aicheng, YUE Xiqing, ZHENG Yan
2022, 43(12):  163-161.  doi:10.7506/spkx1002-6630-20210408-101
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In order to clarify the differences in bovine milk fat globular membrane proteins during different lactation periods, milk fat globular membrane proteins in bovine colostrum and mature milk were characterized by quantitative proteomics. The differentially abundant proteins between the two groups were identified and analyzed by bioinformatics. A total of 763 proteins were identified in this study, of which 197 were shared by the two groups. Meanwhile, 80 differentially abundant proteins were further identified, of which, 41 were up-regulated while the rest were down-regulated (bovine colostrum/mature milk). Bioinformatics analysis of the differentially abundant proteins demonstrated that the main cellular components involving these proteins were exosomes, extracellular space, and extracellular regions. The main metabolic pathways involving them were metabolic pathways, purine metabolism, phenylalanine metabolism, tyrosine metabolism, pyruvate metabolism, and glycolysis/gluconeogenesis. Furthermore, 31 key proteins that could interact with other proteins were identified, including haptoglobin and 2-phospho-D-glycerol acid hydrolase. These findings will help to understand the changes of milk protein composition and its functionality during lactation, and lay the foundation for the deep processing of bovine dairy products.
Changes in the Microbial Community Structure during the Digitally Managed Fermentation of High-temperature Daqu
ZHENG Yalun, ZHAO Ting, WANG Jiasheng, CAI Kaiyun, CHEN Ping, DENG Junsong, FANG Shangling, CAO Jinghua, CHEN Maobin
2022, 43(12):  171-171.  doi:10.7506/spkx1002-6630-20210626-302
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The microbial community diversity during the fermentation process of digital high-temperature Daqu and traditional high-temperature Daqu was analyzed by high-throughput sequencing on the Illumina MiSeq platform. Meanwhile, correlation analysis and bioinformatics analysis were conducted based on microbial species information and physicochemical properties. The results showed that the microbial community structure of high-temperature Daqu significantly changed during the fermentation process. At the end of fermentation, the major bacterial genera in high-temperature Daqu were Kroppenstedtia, Saccharopolyspora, Bacillus, Thermomyces, and Lactobacillus, and the major fungal genera were Thermoascus, Thermomyces, and Aspergillus. The results of non-metric multidimensional scale (NMDS) analysis and hierarchical clustering analysis (HCA) showed that the microbial community composition of the two types of Daqu was roughly similar at the same time points of fermentation.
Preparation of Flavin Adenine Dinucleotide Aptamer-Based Sensor and Its Application for Glucose Detection
WANG Yan, WANG Yue, ZHANG Shuai, ZHAO Ning, XIN Jiaying, SUN Lirui, GUAN Huanan
2022, 43(12):  179-179.  doi:10.7506/spkx1002-6630-20210410-137
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An flavin adenine dinucleotide (FAD) aptamer-based sensor was constructed with gold nanoparticles (AuNPs) as the main body, and methanobactin (Mb) and FAD as the ligands. Mb was used to wrap AuNPs, which has a strong adsorption capacity for Mb, to form a stable Mb-AuNPs structure. The Mb-AuNPs structure was used to modify the surface of the bare gold electrode by the drip-coating method, and FAD was introduced into the Mb-AuNPs structure, in which the –COOH groups could firmly bind to FAD, to improve the ability to recognize glucose. As a result, a novel aptamer biosensor with glucose oxidase-like activity could be constructed. Cyclic voltammetry and the time-current curve method were used to explore the feasibility of its application in glucose detection. At 25 ℃ and pH 7.2, there was a good linear relationship between glucose concentration in the range of 10–200 mmol/L and the response current of the biosensor, with a correlation coefficient (R2) of 0.997 91, and the detection limit was 4.22 × 10-8 mol/L (RSN = 3). The aptamer-based sensor has several advantages such as simple preparation, low price, easy operation and rapid detection.
Fusion Expression of Human Acetaldehyde Dehydrogenase 2 with NusA
MIAO Shitao, HU Min, GONG Xingwen
2022, 43(12):  187-188.  doi:10.7506/spkx1002-6630-20210620-237
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Aldehyde dehydrogenase 2 (ALDH2) was fused with NusA-tag to solubly express a recombinant protein with good activity in Escherichia coli. Primers were designed according to the gene sequence of Aldh2, and the restriction enzyme sites EcoRI and XhoI were inserted into the 5’ end to amplify the Aldh2 gene fragment, which was then ligated into the pMD19-T-Simple vector and transformed into E. coli DH5α. After sequencing, the correct Aldh2 gene fragment was cloned into the expression vector pET44b(+) at the downstream of NusA-tag between EcoRI and XhoI and transformed into E. coli BL21(DE3). Protein expression was induced using isopropyl-β-D-thiogalactopyranoside (IPTG), and the resultant fusion protein had good solubility and mainly existed in the supernatant. The optimal expression conditions were found to be induction at 37 ℃ for 3 h with 0.25 mmol/L IPTG. The optimal reaction pH and temperature for the recombinant protein were 7.0 and 37 ℃, respectively. The metal ions Ca2+, K+, Na+, Mg2+ and Mn2+ could improve the enzyme activity, and Mg2+ had the most pronounced effect, increasing the activity to 1.64 U/mL. The wild-type ALDH2 was expressed as an inclusion body in E. coli with an activity of 1.43 U/mL. These results indicated that the fusion expression with NusA is a good method for the preparation of recombinant ALDH2 in E. coli.
Isolation and Identification of Lactobacillus sakei from Fermented Mandarin Fish and Its Application in Fermented Mandarin Fish
ZHOU Yingqin, SUN Ziyi, HUANG Jingjing, YAN Yan, ZHENG Haibo, XIE Ningning
2022, 43(12):  194-198.  doi:10.7506/spkx1002-6630-20210818-232
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A Lactobacillus strain named SMF-L5 from traditional fermented mandarin fish was isolated using MRS medium with bromocresol green and identified as Lactobacillus sakei by morphological, physiological and biochemical assays and 16S rDNA sequence analysis. L. sakei SMF-L5 grew well in MRS liquid medium, entered the stable growth period after 14 h, and produced the highest viable cell count of 7.0 × 109 CFU/mL. The production of lactic acid of the strain was 10 g/L after 24 h cultivation. The optimal culture conditions were as follows: culture temperature 30.9 ℃, initial pH 6.15 and inoculum amount 1.94%. Strain SMF-L5 had tolerance to 0.08 g/mL NaCl, and obvious inhibitory effects on Escherichia coli, Staphylococcus aureus. The fermented mandarin fish inoculated with L. sakei SMF-L5 had superior color, texture and flavor than spontaneously fermented mandarin fish. These results showed that L. sakei SMF-L5 has the potential for application as an excellent starter in the industrial production of smelly mandarin fish .
Investigation of Bacterial Flora on the Surface of Pig Carcasses and in the Environment during Slaughter
TANG Lin, GUO Keyu, LAI Jinghui, LI Jianlong, LI Qin, YANG Yong, ZOU Likou, LIU Shuliang
2022, 43(12):  203-206.  doi:10.7506/spkx1002-6630-20210803-025
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The combination of the traditional culture-dependent method and high-throughput sequencing was used to investigate the level of microbial contamination on the surface of pig carcasses during the slaughter and segmentation process. Meanwhile, the number of microbial colonies on the slaughter knives and the contact surfaces of the segmentation workshop were counted to identify the key pollution links in the slaughter and segmentation process. The results showed that a total of 881 458 valid sequences and 864 operational taxonomic units (OTUs) were obtained by sequencing. The samples were annotated to 22 phyla, 33 classes, 79 orders, 162 families, 382 genera and 613 species of microorganisms. Proteobacteria, Bacteroidota and Firmicutes were the dominant bacterial phyla. Acinetobacter and Aeromonas were the major dominant bacterial genus. The bacterial community diversity during the slaughter and segmentation process was in decreasing order as follows: bleeding > dehairing > segmentation > evisceration > final wash > chilling. The microbial diversity on the carcass surface was the lowest in the chilling stage, and increased after segmentation, indicating that the segmentation stage was the key contamination link. The results of traditional microbial counting were consistent with the results of sequencing. From dehairing to chilling, the number of each bacterial group on the surface of pig carcasses was decreased, but increased significantly after segmentation. The total number of bacterial colonies on the carcass surfaces in the segmentation workshop was 6.11 (lg(CFU/cm2)) on average, which was higher than that on the slaughter knives (4.86 (lg(CFU/cm2)) on average), indicating that the contact surfaces of the segmentation workshop were the key pollution source, and so the segmentation link was the key pollution link.
Component Analysis
Analysis of Variations in Contents of Extractable Components and Taste Quality of Pu-erh Raw Tea with Different Brewing Cycles
LI Yan, WANG Wenfu, WANG Jintao, HU Yongdan, REN Dabing, YI Lunzhao
2022, 43(12):  210-213.  doi:10.7506/spkx1002-6630-20210519-237
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The contents of extractable components and taste characteristics of Pu-erh raw tea infusions obtained at different brewing times were analyzed by employing ultra performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS) combined with sensory evaluatio in this study. The results showed that a total of 138 extractable components were identified, the predominant ones being amino acids, catechins and their derivatives, phenolic acids and their derivatives, flavonoids and alkaloids. These substances made a significant contribution to the umami, bitterness and astringency of tea influsions. The sensory score for taste of Pu-erh raw tea infusion was positively correlated with the degree of bitterness, astringency and thickness; there was also a positive correlation between the total amount of extractable components and the sensory score for taste for tea infusion obtained at each brewing cycle. The total amount of extractable components and the taste score reached their maximum values at the second brewing cycle, and then the total amount of extractable components decreased and the taste became increasingly plainer and thinner with increasing number of brewing cycles. These findings help to reveal the durability of Yunnan Pu-erh raw tea and the taste change of tea infusion during the brewing process.
Identification of Characteristic Volatiles in Vinegar Prepared with Monascus-fermented Rice during Acetic Acid Fermentation Using Multivariate Statistical Analysis
GAO Hang, XU Dandan, WANG Wenping, ZHAO Yan, ZHANG Jian, DING Jie, TAN Lei, ZHANG Xin
2022, 43(12):  219-219.  doi:10.7506/spkx1002-6630-20210806-078
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An electronic nose, gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O) were used to explore the changes of aroma compounds in vinegar prepared with Monascus-fermented rice during its acetic acid fermentation process. Different multivariate statistical analysis, such as cluster analysis, principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were used to investigate the differences in volatile compounds between different stages of fermentation and to identify the characteristic volatile components. The results showed that the electronic nose could clearly discriminate samples from different acetic acid fermentation stages. A total of 54 volatile compounds were identified by GC-MS and GC-O during the acetic acid fermentation process. The characteristic aroma components were n-octanol, isobutanol and ethyl valerate for the early stage; benzoic acid, ethyl palmitate, n-hexanol, 2,4-di-tert-butylphenol and ethyl lactate for the middle stage; propyl acetate, ethyl lactate and isobutyl acetate for the mid-to-late stage; L(+)-2,3-butanediol and ethyl heptanate for the late stage. The results of this study provide a theoretical basis for aroma regulation and flavor improvement of vinegar prepared with Monascus-fermented rice.
Composition and Contents of Organic Acids in Different Grape Germplasms
NIU Shengyang, LIU Chonghuai, LIU Qiang, FAN Xiucai, ZHANG Ying, SUN Lei, ZHANG Xiaoli, JIANG Jianfu
2022, 43(12):  228-226.  doi:10.7506/spkx1002-6630-20210704-030
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In order to select excellent grape germplasms, the organic acid composition and content of 302 grape germplasms preserved in the Zhengzhou National Grape Germplasm Repository were analyzed by high performance liquid chromatography (HPLC). The obtained data were analyzed by cluster analysis (CA) and principal component analysis (PCA). The results showed that tartaric acid was more abundant than malic acid in 93.8% of the 302 samples, in 5.12% of these samples, malic acid content was similar to citric acid content (the difference between them did not exceed 2%), and 7.37% of the grape samples had higher malic acid content than tartaric acid content. In cultivated grapes, tartaric acid was more abundant than malic acid. For wild grapes (except Vitis davidii Fox.), the malic acid content of Vitis ficifolia, Vitis adenoclada Hand-Mazz, Vitis pseudoreticulata Wang Tian Wang and Vitis riparia was 1.2–1.7 times higher than the tartaric acid. Moreover, it was found that the organic acid content of wine grapes was significantly higher than that of grape accessions used for other purposes, and the pH (3.776) of table grapes was significantly higher than that of grape accessions used for other purposes. In addition, the content of organic acids in grape populations from East Asia, especially tartaric acid (8.325 mg/mL), was higher than that in other populations. The variation coefficients of tartaric acid content, total acid content and acidity among samples were small, while the contents of oxalic acid, malic acid and citric acid varied greatly among samples. Tartaric acid was significantly positively correlated with other organic acids but not with pH or oxalic acid. Total acid content was significantly positively correlated with the content of tartaric acid, oxalic acid, malic acid, citric acid, titratable acid and acidity value. The organic acid content of wild grapes was much higher than that of cultivated grapes. Notably, the organic acid content of Vitis amurensis Rupr. N43-3, belonging to the East Asian population endemic to China, was the highest. Therefore, wild grape resources can be used as special resources for breeding or directly utilized.
Separation, Identification and Taste Characteristics of Umami Peptides from Straw Mushroom
JIANG Xixi, PEI Fei, ZHAO Liyan, MA Ning, FANG Donglu, ZHONG Lei, HU Qiuhui
2022, 43(12):  235-235.  doi:10.7506/spkx1002-6630-20211110-124
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To analyze umami peptides in the water extract of straw mushroom, fractionation guided by sensory evaluation and an electronic tongue of the extract was performed through sequential ultrafiltration and gel filtration chromatography. Fraction F1, which was found to make the greatest contribution to the overall umami, was further fractionated by reversed-phase high performance liquid chromatography combined with principal component analysis. Subfraction F1-a was found to have similar taste to straw mushroom. In addition the umami peptides from F1-a were identified by ultra-high performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. The synthetic counterparts of the identified umami peptides were evaluated for their taste characteristics through sensory evaluation and electronic tongue analysis. The results showed that the umami peptides were identified as Asp-Asp-Cys-Pro-Asp-Lys, Leu-Val-Asp-Lys-Pro-Arg, Gln-Ala-Asp-Lys-Arg-Lys, and Asp-Thr-Phe-Asn-Asp-Lys, with umami taste threshold of 0.10, 0.33, 0.42, and 0.17 mg/mL, respectively. The flavor characteristics of these four umami peptides were attributed to the formation of specific structures by amino acids through peptide bonds. Among them, the umami peptide Asp-Asp-Cys-Pro-Asp-Lys was the most effective in enhancing the umami taste of monosodium glutamate (MSG) solution at a concentration of 20 mg/mL.
Optimization of an Automatic Thermal Desorption-Gas Chromatography-Mass Spectrometry Detection Method for Oolong Tea and Analysis of Aroma Components in Different Grades of Rougui Oolong Tea
BI Wanjun, ZHENG Yucheng, LIU Zhenzhang, CHEN Bin, DENG Huili, HU Qingcai, SUN Yun
2022, 43(12):  243-246.  doi:10.7506/spkx1002-6630-20210729-344
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An automatic thermal desorption-gas chromatography-mass spectrometry (ATD-GC-MS) method was developed, optimized and applied in combination with chemometrics for the detection of the aroma components of three different grades (superfine, grade A and grade B) of Rougui oolong tea. In automatic thermal desorption, the operating parameters adsorption temperature, adsorption time and cold trap temperature were optimized by single factor experiments and response surface methodology. The optimal parameters were determined as follows: adsorption temperature of 55 ℃, adsorption time of 37 min and cold trap temperature of ?29 ℃. A total of 173 aroma components were identified, 90 of which were common to all the three grades. In addition, a partial least squares discriminant analysis (PLS-DA) model to distinguish the different grades of Rougui oolong tea was established based on the peak areas of the aroma components of Rougui oolong tea. and the distribution of 47 characteristic aroma components in the three different grades of Rougui oolong tea was discussed by hierarchical cluster analysis. The results of this study could provide a theoretical basis for the identification of the aroma quality and grade of Rougui oolong tea.
Determination of Volatile Phenols in Grape and Wine by Gas Chromatography-Triple Quadrupole Mass Spectrometry
YANG Weixi, ZHANG Siqi, XIANG Xiaofeng, SHI Ying, DUAN Changqing, LAN Yibin
2022, 43(12):  252-254.  doi:10.7506/spkx1002-6630-20210731-380
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A method for the simultaneous determination of 19 volatile phenols in grape and wine was developed by solid phase extraction (SPE) combined with gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS/MS) operated in the multi-reaction monitoring (MRM) mode and was validated on grape juice and wine. The limits of detection and quantification of the developed method were found to be 0.02–1.01 μg/L and 0.08–3.36 μg/L, respectively. The method had a wide linear range with a correlation coefficient (R2) greater than 0.99. The recoveries of standard addition were in the range of 81.99%–122.72%. The method was proved to be highly sensitive, accurate and precise. Furthermore, this method was successfully applied to investigate the concentrations of volatile phenols in 10 grape samples and 10 wine samples. A total of 19 volatile phenols were detected in each of the 20 samples. The major volatile phenols in grape were vanillic acid, vanilaldehyde and 4-vinylphenol, while 4-ethylphenol, 3-ethylphenol and 4-vinylphenol were the major volatile phenols in wine. The content of volatile phenols in the measured samples was within the linear range of the method, indicating the universal applicability of this method.
Structural Characterization and Anticoagulant Activity of Oligosaccharides Derived from Sargassum fusiforme Fucoidan
LIU Xue, REN Chenyu, LIU Xin, ZHANG Miansong, BAI Xinfeng, WANG Lingshu, CUI Tingting, SHI Yaping, LIU Changheng, JIA Airong
2022, 43(12):  260-262.  doi:10.7506/spkx1002-6630-20210512-135
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In order to study the anticoagulant oligosaccharides derived from Sargassum fusiforme fucoidan (SFF), the monosaccharide composition, molecular mass and physicochemical characteristics of SFF were determined by high performance liquid chromatography (HPLC), high performance gel permeation chromatography (HPGPC) and chemical methods, respectively. Degradation of SFF was carried out using hydrochloric acid (HCl). The degradation products were separated by gel permeation chromatography on Bio-gel P4. The anticoagulant activity of the resultant oligosaccharide fractions was evaluated by activated partial thromboplastin time (APTT), thrombin time (TT), and prothrombin time (PT) assays. The oligosaccharide fraction with the highest anticoagulant activity and lower molecular mass was selected and its structural characteristics were analyzed by negative-ion electrospray mass spectrometry (ES-MS). Results indicated that SFF mainly consisted of fucose, galactose, mannose and glucose in a molar ratio of 67.11:26.69:2.54:3.66. The average molecular mass of SFF was 708 kDa and the contents of total sugar, protein and sulfate ester in it were 56.44%, 1.14% and 26.22%, respectively. Five oligosaccharide fractions, named P1 to P5, were obtained by degradation of SFF with hydrochloric acid. They all could prolong the APTT and fractions P1, P2 and P3 were more effective than P4 and P5, especially P3; however they were ineffective in prolonging TT or PT. P3, a highly pure oligosaccharide, was mainly composed of Fuc3(SO4)2 .
Flavor Characteristic Analysis of Fried Allium tenuissimum L. Flowers by Electronic Nose and Headspace-Gas Chromatography-Ion Mobility Spectrometry
WEN You, ZHAO Xiaoying, WANG Chenghua, LIU Xiaoling
2022, 43(12):  267-270.  doi:10.7506/spkx1002-6630-20210527-339
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Flavour characteristics of Allium tenuissimum L. (AtL) flowers processed by the Chinese traditional stir-frying method were investigated by electronic nose (E-Nose) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). E-nose detection with principal component analysis (PCA) revealed that the main volatile components of AtL flowers were nitrogen oxides, terpenes, organic sulfides and sulfur-containing organic compounds, while the stir-frying process distinctly changed the flavor pattern of AtL flowers, resulting in significantly increased levels of sulfur-containing compounds. A total of 56 components were detected across fried AtL (FAtL) and raw AtL flowers, of which 25 were identified as volatile compounds by HS-GC-IMS. The contents of five fat-soluble and two water-soluble compounds in FAtL were far higher than those in AtL, confirming that stir-frying changed the flavor of AtL flowers. In conclusion, the combination of E-Nose and HS-GC-IMS represents an efficient, accurate and sensitive method for the determination of flavor components in Allium plants.
Effect of the Addition of Edible Mushrooms on the Quality and Flavor of Chicken Soup
LAI Jing, FENG Cuiping, WANG Ying, ZHANG Xin, ZHOU Liyuan, ZHU Yingchun
2022, 43(12):  274-280.  doi:10.7506/spkx1002-6630-20210809-117
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In order to investigate the effect of the addition of edible mushrooms on the quality and flavor of chicken soup, chicken soups were prepared from three-yellow chicken and one of five edible mushrooms, Lentinus edodes, Clitocybe squamulose, Agrocybe aegerita, Sparassis crispa, or Hericium erinaceus, and their ash, crude fat, total sugar, flavor-active nucleotide content and volatile flavor components were determined. The results showed that the contents of ash, total sugar and flavor-active nucleotides in chicken soup with edible mushroom were significantly increased (P < 0.05) and the content of crude fat was significantly decreased (P < 0.05) compared with the blank chicken soup. Among the chicken soups with different edible mushroom, the contents of the ash, total sugar and total flavor-active nucleotides were the highest in the chicken soup with Clitocybe squamulose, which were 0.73%, 2.19 mg/mL and 733.58 mg/L, respectively. A total of 116 volatile flavor substances were identified by solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS), the main ones being alkanes and aldehydes, and the contents of alkanes and aldehydes in chicken soup with edible mushroom were higher than those in the blank chicken soup. The characteristic volatile flavor components in chicken soup with edible mushroom were analyzed using unsupervised principal component analysis (PCA), and supervised orthogonal partial least squares-discriminant analysis (OPLS-DA) was used to distinguish the overall differences between groups. Then, clustering analysis combined with heat map was performed, revealing that the volatile composition of chicken soup with Clitocybe squamulose and Agrocybe aegerita differed significantly from that of the blank chicken soup. Based on projection importance of variables (VIP) scores and S-plots, heptadecane, hexanal, 2-methyl-pentadecane, hexadecane, 2,6,10-trimethyl-pentadecane and 2,4-decadienal were found to be the main characteristic markers of chicken soup with Clitocybe squamulose and Agrocybe aegerita. In conclusion, the addition of edible mushrooms can improve the nutritional quality of chicken soup and promote the formation of flavor substances, and the quality of chicken soup with Clitocybe squamulose is the best.
Comparative Analysis of Main Components and Oxidation Stability of Pumpkin Seed Oil from Different Geographic Regions
CAO Zilun, LEI Fenfen, ZHENG Jingcheng, HE Dongping, WAN Fangyun
2022, 43(12):  283-288.  doi:10.7506/spkx1002-6630-20210821-271
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Pumpkin seeds from eight regions of China were selected as raw materials to prepare pumpkin seed oil using a twin-screw press. The basic physical and chemical properties and oxidation stability of different pumpkin seed oils were analyzed. The results showed that pumpkin seed oil mainly contained four fatty acids (palmitic acid, stearic acid, oleic acid and linoleic acid) with unsaturated fatty acids accounting for 80.565%–84.964% of total fatty acids. Pumpkin seed oils were rich in bioactive substances, such as total phenols (167.21–204.50 mg/kg), total sterols (1 204.38–1 604.51 mg/kg), α-tocopherol (25.7–58.7 mg/kg), γ-tocopherol (1 839.8–2 728.3 mg/kg) and δ-tocopherol (248.8–518.7 mg/kg). The results of Pearson’s bivariate correlation analysis showed that total phenol had a significant correlation with the free radical-scavenging capacity of polar components (P < 0.05). Lipid concomitants such as α-tocopherol made some contributions to the antioxidant ability of pumpkin seed oil. The results of principal component analysis (PCA) and cluster analysis (CA) showed that the functional components of pumpkin seed oils from different production areas were similar, which fell into two distinct clusters according to different contents of functional components. The pumpkin seed oil from Baiyin City, Gansu province gained the highest comprehensive score. The results of this study are meaningful for guiding the development and utilization of pumpkin seed resources.
Safety Detection
A Method for Speciation Analysis of Bromine in Cherries and Its Application for Traceability Analysis of Methyl Bromide Fumigation
WU Chiying, ZHANG Runhe, DENG Xiaojun, SHENG Yonggang, CAI Wenxuan, XIE Min, CHEN Zhongbing, YANG Xiaojun, ZHAO Chaomin, FAN Xiang
2022, 43(12):  290-294.  doi:10.7506/spkx1002-6630-20210421-302
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An analytical method for the speciation of bromine in cherries fumigated with methyl bromide was established and applied to compare the contents of methyl bromide and inorganic bromine in un-fumigated and fumigated cherries in order to explore the relationship between methyl bromide fumigation and bromine residue. The samples were ultrasonically extracted with water and the extract was separated on an anion exchange column using a mobile phase composed of 36 mmol/L nitric acid and 67 mmol/L aqueous ammonia before being analyzed by high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Total bromine was determined by ICP-MS and methyl bromide by headspace sampling-gas chromatography with an electron capture detector (HS-GC-ECD). The results showed that recovery of the spiked bromate ranged from 89.7% to 101.4% with relative standard deviations (RSDs) of 2.1%?3.5%. The recoveries of the spiked bromide ion were 85.5%?107.3% with RSDs of 4.4%?7.0%. The limit of quantification of the developed method was 0.10 mg/kg. Only bromide ions were found to exist in cherries fumigated with methyl bromide and the content of bromide ions was consistent with the content of total bromine. Methyl bromide residues in fumigated cherries decreased over time. The content of total bromine in fumigated cherries was significantly higher than that in un-fumigated cherries, and did not significantly change with storage time or conditions. Therefore, this method, which is useful to trace methyl bromide fumigation of cherries, provides a basis for risk monitoring and quality control of fruit import and export.
Characterization of parC and gyrA Mutations in Foodborne Salmonella Isolates by Whole-Genome Sequencing and Real-time PCR
BI Wanglai, ZHAO Weiwei, MA Da, LI Rui, ZHOU Min
2022, 43(12):  296-301.  doi:10.7506/spkx1002-6630-20210412-163
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A total of 45 quinolone-resistant foodborne Salmonella isolates were used to screen for mutations in the parC and gyrA genes by whole-genome sequencing (WGS) and real-time polymerase chain reaction (real-time PCR). The reliability of the detection methods was tested, and the mutation characteristics of the antibiotic-resistance genes were evaluated. Four strains were subjected to next-generation WGS, and according to the results obtained, a real-time PCR assay was developed to detect the mutation sites of Asp87Tyr and Asp87Asn in gyrA, and Thr57Ser and Ser80Ile in parC. The Salmonella isolates were subjected to PCR detection for the qnrS, qnrA and qnrB genes. Thirty-one strains which were not found to carry the qnr genes were screened for mutation sites by real-time PCR, revealing that mutations of parC Thr57Ser and gyrA Asp87Asn were found to be the most frequent mutations. In order to check the accuracy of real-time PCR, PCR amplification of the complete sequences of gyrA and parC was performed on 10 positive strains and the resulting amplicons were sequenced. The sequencing results were completely consistent with the real-time PCR results. The combination of WGS and real-time PCR, which can be used to detect new mutations in genes conferring quinolone resistance and rapidly screen for the main type of mutation in massive samples, is a rapid and reliable method for the identification of gyrA and parC mutations in Salmonella.
Error Analysis for Textural Measurement of Chilled Mutton Based on Data Visualization
ZHANG Guoxiang, ZHANG Haiyu, LUO Hailing
2022, 43(12):  303-307.  doi:10.7506/spkx1002-6630-20210413-186
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In this study, the texture profile analysis (TPA) process of chilled mutton was analyzed by a data visualization method. It was found that some factors such as slight instrumental vibrations could cause systematic errors such as abnormal peaks and curve fluctuations on the TPA curve and consequently deviations between the characteristic nodes on the TPA curve selected by the detection system and the actual ones, ultimately leading to significant errors in the measurement of TPA indexes. The results also showed that the systematic errors were affected by compression ratios, significant errors appearing at 20% compression ratio, and there were differences in and correlations between the influence on different TPA indexes. The error in the extracted TPA data was effectively reduced by correcting the position of the characteristic nodes on the TPA curve. The average correction level of adhesiveness was more than 20% at all compression ratios tested, and the correlation coefficients between the corrected adhesiveness at 50% compression ratio and total volatile base nitrogen (TVB-N), the logarithm of total viable count, and the logarithm of coliform count increased by 11.2%, 20.7% and 8.3%, respectively. Therefore, errors in the measurement of TPA indicators can be effectively reduced by modifying the position of the characteristic nodes on the TPA curve, improving the accuracy and reliability of the measured TPA indicators.
Simultaneous Detection of Harmful Fungi and Mycotoxin Contamination in Peanuts by Electronic Nose
WANG Bei, SHEN Fei, HE Xueming, JIANG Xuesong, YUAN Jian, FANG Yong, HU Qiuhui, QIU Weifen, MAMO Firew Tafesse
2022, 43(12):  310-314.  doi:10.7506/spkx1002-6630-20210322-275
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In this study, electronic nose technology was used to establish a method for the simultaneous detection of fungal and mycotoxin contamination in peanuts infected with different strains. Peanuts were irradiated, inoculated with five common mold strains (three toxigenic strains and two non-toxic strains), and cultured in an incubator (26 ℃ and 80% RH) for six days. Samples were taken every day to collect electronic nose signals, and to measure the number of colonies and aflatoxin B1 (AFB1) content. Qualitative discriminant models for fungal and mycotoxin contamination levels were established. The results of principal component analysis (PCA) showed that the samples contaminated with different molds tended to be clustered, and they were located above the acceptable samples. The overall accuracy of linear discriminant analysis and partial least squares-discriminant analysis was more than 80%; the classification accuracy based on toxigenic and non-toxic strains was higher than 95.7%, the classification accuracy based on AFB1 content was more than 90%, while the classification accuracy based on the number of colonies was lower. False negative percentages were lower than 17% for all models. Electronic nose technology is feasible to determine fungal and mycotoxin contamination levels in peanuts infected with different strains. In order to improve the accuracy and stability of the models, peanut samples infected with more strains and different peanut varieties should be considered in further research.
Rapid Determination of Typical Alternaria Toxins in Wheat by Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry
WU Xi, XING Jiali, ZHENG Ruixing, ZHANG Aizhi, MAO Lingyan, XU Xiaorong, LOU Yongjiang, MU Yinghua
2022, 43(12):  317-321.  doi:10.7506/spkx1002-6630-20211201-011
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A dispersion liquid-liquid microextraction (DLLM) combined with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the simultaneous determination of seven Alternaria toxins (alternariol, alternariol monomethyl ether, altenuene, tenuazonic acid, altertoxin I, tentoxin and altenusin) in wheat. The samples were extracted with 3 mL of first-grade water and 10 mL of 1.5% formic acid acetonitrile-methanol (4:1, V/V), dehydrated with 2 g of MgSO4 and salted out with 1 g of NaCl, and then the mixture was shaken for 15 min followed by centrifugation for 10 min. One mililiter of the supernatant and 100 μL of trichloromethane were used for DLLM. The seven Alternaria toxins were separated on a BEH C18 (50 mm × 2.1 mm, 1.7 μm) column, and detected using an electrospray ionization source in the multiple reaction monitoring mode with positive and negative ions. The chromatographic separation was completed within five minutes. The limits of detection and quantification of this method were in the range of 0.11–0.16 μg/kg and 0.42–0.49 μg/kg, respectively. Good linearity was observed in the concentration range of 0.5–100 μg/L with coefficients of determination (R2) of greater than 0.987 277. In wheat matrix spiked at three levels, the average recoveries of the seven Alternaria toxins were 70.7%–101.3%, with relative standard deviations of 1.22%–4.11%. This method was used to analyze the contamination status of the seven Alternaria toxins in rye, buckwheat, naked oat, barley, oat, and wheat. The results showed that tentoxin and tenuazonic acid were detected in the six cereal species at levels of 0.6–10.7 μg/kg and none detected to 31 μg/kg, respectively. The detection rate of altenusin was lower than that of tenuazonic acid and tentoxin, but its highest content (37.3 μg/kg) was comparable to tenuazonic acid. This method proved to be stable, accurate, sensitive and fast, and could meet the requirements for the analysis of multiple Alternaria toxin residues in a variety of cereal.
Detection of Salmonella by G-quadruplex-Based PCR-RCA Double Amplification
LIU Jianhui, ZHANG Xianzhou, ZHANG Yunzhe, LI Lanru, WANG Hongjing, GAO Jie, GENG Fengzhen, TAN Jianxin
2022, 43(12):  325-328.  doi:10.7506/spkx1002-6630-20210304-060
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In this study, a method to detect Salmonella was developed using polymerase chain reaction (PCR) combined with rolling circle amplification (RCA) with a dumbbell ring-shaped template into which a G-quadruplex complementary sequence was inserted. This method was based on PCR-RCA double amplification and the fact that thioflavin T (ThT) can specifically bind to the G-quadruplex, enhancing the fluorescence signal. Under the optimized detection conditions, the logarithmic concentration of Salmonella genomic DNA (x) had a good linear relationship with the fluorescence signal intensity at 486 nm (y). The regression equation was y = 2.101x + 2.872 3 (R2 = 0.992 5) in a linear range of 17 fg/μL–1.7 ng/μL. The specificity of the method was evaluated, revealing that it was suitable for the detection of Salmonella with a detection limit of 4.28 CFU/mL for artificially contaminated milk samples. This method, which has several advantages such as strong specificity, high sensitivity and low detection limit, provides a new method for the rapid detection of foodborne pathogens.
Determination of Eight Antifungal Drug Residues in Meat by QuEChERS Extraction Coupled with UPLC-MS/MS
HUANG Yongqiao, SONG Guanglin, MAO Minxia, YANG Changbiao, MA Kai, GAO Liang
2022, 43(12):  334-335.  doi:10.7506/spkx1002-6630-20210408-100
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An analytical method was developed for the rapid determination of the residues of eight antifungal drugs (fluconazole, ketoconazole, naftifen, bifonazole, clotrimazole, econazole, griseofulvin, and miconazole) in pork, beef and mutton by quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction coupled with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). In this study, several important experimental parameters were effectively optimized using spiked samples, including the type of extraction solvent, extraction time, adsorbent type, adsorbent dosage and salt dosage. Under the optimum extraction and detection conditions, the detection process was completed within 7 minutes in the positive ion multiple reaction monitoring mode and quantification was performed by an external standard method. Good linearity was observed over the concentration range of 0.05–10.00 ng/mL (r > 0.998), the limit of detection (LOD) was 0.1 μg/kg, and the limit of quantitation (LOQ) was 0.3 μg/kg. When this method was used to detect meat samples spiked with the analytes, good repeatability and stability was obtained, with accuracy within 15%, average recoveries of 85.7%–113.6% for the intra-day assay (n = 6) and 87.6%–107.9% for the inter-day assay (n = 3) and coefficient of variation (CV) of 1.2%–14.8%. The QuEChERS-UPLC-MS/MS method is simple, rapid, efficient and accurate, and can be used for the rapid qualitative and quantitative analysis of the eight antifungal drug residues in meat.
Quantitative Analysis and Early Detection of Postharvest Gray Mold in Strawberry Fruit Using Electronic Nose
LIU Qiang, ZHANG Tingting, ZHOU Dandan, DING Haizhen, ZHANG Bin, CHEN Min, DING Chao, PAN Leiqing, TU Kang
2022, 43(12):  341-349.  doi:10.7506/spkx1002-6630-20210511-112
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A non-destructive method for the detection of gray mold in strawberry fruit based on odor information was proposed in order to monitor the decay process of strawberry fruit. A portable electoral nose (E-nose) was utilized to collect the odor information of samples every 24 h. Healthy strawberry fruit were taken as the control group. The volatile compounds of samples were then quantitatively detected by headspace solid phase micro-extraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS). Finally, a regression model for predicting the microbial load in artificially infected strawberry fruit was established based on E-nose datasets by partial least squares regression (PLSR). The results showed that after 120 h storage, the contents of esters, aldehydes and alcohols in infected strawberry fruit were significantly changed, and the content of alcohol (mainly ethanol) increased rapidly from 0.85 to 3.95 μg/g. Principal component analysis (PCA) showed a high correlation between the microbial load and the stable response of E-nose sensors. The optimal PLSR model for the microbial load showed a coefficient of determination for prediction (Rp2) of 0.815, and a relative percent deviation (RPD) of 2.270. Furthermore, the non-destructive detection method based on stable signals of E-nose sensors could identify early diseased strawberry fruit with an accuracy of 92.9%. These results can provide a reference for non-destructive monitoring and early detection of strawberry postharvest diseases.