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25 March 2021, Volume 42 Issue 6
Food Chemistry
Effect of Non-Covalent Forces on Fish Gelatin-Pectin Composite Gel Systems
WANG Mengnan, TU Zongcai, HU Yueming, WANG Hui
2021, 42(6):  1-7.  doi:10.7506/spkx1002-6630-20191224-282
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This study aimed to explore the effects of changing the non-covalent interactions hydrogen bonds, hydrophobic interactions and electrostatic repulsion by adjusting pH (4, 5, 6, 7, 8, and 9) on the characteristics of fish gelatin-pectin composite gel systems. At pH 5, the composite gel system formed a supermolecular complex with the strongest hydrophobic interaction and there was a strong electrostatic attraction among the complexes. The composite gel system exhibited the strongest hydrogen bond at pH 7, and the strongest electrostatic repulsion at pH 9. The stability of the composite gel system dominated by hydrophobic interaction was poorer, but the melting and gelling temperature were relatively higher, while the composite gel system driven by electrostatic repulsion had higher gel strength and stability. The composite gel system dominated by hydrogen bonds formed a stronger and more stable gel network structure. Therefore, the different non-covalent interactions had different effects on the properties of fish gelatin-pectin complex systems, which would provide a foundation for developing protein-polysaccharide complex gel systems with desired properties.
Effects of Protein Oxidation Induced by Rice Bran Rancidity on the Interfacial Properties of Rice Bran Albumin
WU Xiaojuan, WU Wei
2021, 42(6):  8-15.  doi:10.7506/spkx1002-6630-20200325-369
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The effects of oxidative modification induced by rice bran rancidity on the interfacial properties of rice bran albumin were investigated. The results showed that carbonylation and sulfhydryl oxidation of rice bran albumin could be induced by rice bran rancidity. The emulsifying activity, emulsion stability, foaming capacity and foam stability of rice bran albumin were significantly (P < 0.01) negatively correlated with carbonyl content and α-helix/β-sheet proportions, while they were significantly (P < 0.01) positively correlated with free sulfhydryl content, surface hydrophobicity, and zeta potential. The oxidative rancidity products of rice bran induced rice bran albumin to form soluble and insoluble aggregates through protein-protein interactions via disulfide bond, non-disulfide covalent bond, and hydrophobic force, which led to a decrease in flexibility, surface hydrophobicity of protein molecule and electrostatic repulsion between molecules and consequently a negative impact on the interfacial properties of rice bran albumin.
L-Histidine Modifies the Structure and Heat-induced Gel Properties of Whey Protein
WANG Yaosong, MA Tianyi, HU Rongrong, ZHANG Weiwei, YING Ruifeng, HUANG Meigui, TANG Changbo
2021, 42(6):  16-23.  doi:10.7506/spkx1002-6630-20200128-282
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L-Histidine (L-His) was added as a functional enhancer of protein gels to whey protein isolate in aqueous solutions to prepare heat-induced gels. The effects of L-His on the structure and gel properties of whey protein were investigated. The results showed that aggregates with a diameter of about 1 700 nm and a very small specific surface area, which were found to be almost uncharged, were formed at the isoelectric point (pI 5.2) of whey protein. However, the aggregate size was ~400 nm at pH away from the pI. L-His inhibited whey protein aggregation, reduced the aggregate size but dramatically increased the specific surface area, promoted protein unfolding and increased the amount of charge carried by the protein molecule. Whey protein formed a heat-induced white gel with a low water-holding capacity (WHC) at the pI, whereas the gels formed at other pH values were yellow with higher WHC than at the pI and the yellowness was increased as pH was farther away from the pI. Despite having no obvious impact on the color, L-His significantly enhanced the WHC (P < 0.05) and improved the textural properties of gels. More notably, the elasticity and chewiness of the gels that were formed at pH 7.59 and 9.74 were significantly improved by L-His (P < 0.05). These changes in gel functional properties could be mainly attributed to the fact that L-His could impel the rearrangement of hydrogen bonds, disulfide bridges and hydrophobic interactions involved the gel matrix. Overall, L-His changed the structure of whey protein and improved the gel properties, and its effect was affected by pH.
Fabrication of Food-grade Pickering Emulsions Stabilized by Cyclodextrins
LIU Zhongbo, GENG Sheng, JIANG Zhaojing, YANG Wei, LIU Benguo
2021, 42(6):  24-30.  doi:10.7506/spkx1002-6630-20200214-145
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In this study, the effects of cyclodextrin (CD) structure, the amount of CD added, oil phase type and oil-to-aqueous phase ratio on the formation of oil-in-water (O/W) Pickering emulsions were investigated. The microstructures, microrheological properties and stabilities of medium-chain triglyceride (MCT)-based Pickering emulsions stabilized by α-, β- and γ-CD were systemically compared. In order to clarify the difference among CDs in emulsifying capacity, we simulated the formation of CD/MCT inclusion complexes using molecular docking. We found that both α- and β-CD exhibited good emulsion stability, which could be further enhanced with increasing the oil-to-water ratio and the amount of CD added and could also be obviously affected by oil phase type. Both α- and β-CD could reduce the O/W interfacial tension with similar effects. Thanks to its stronger interaction with MCT, α-CD could more easily form an amphiphilic supramolecule with MCT, thereby exhibiting higher emulsion stability than β-CD at a low addition amount (5 mg/mL). Although β-CD had slightly lower adsorption capacity at the O/W interface than α-CD, it could not only act as an emulsifier at the interface but also prevent the collision and coalescence of oil droplets through its participation in aggregation in the aqueous phase, which contributed to its stronger performance at high addition amounts (15 and 25 mg/mL). The obtained results are of reference significance to develop new food-grade Pickering emulsions and promote the application of CDs in foods.
Reaction Mechanism of Collagen Peptide with Four Aldehydes in Chinese Liquor
LIU Xian, HUANG Zhangjun, LI Xia, LIAO Xuepin, SHI Bi
2021, 42(6):  31-38.  doi:10.7506/spkx1002-6630-20191229-336
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In order to provide basic theoretical data for the healthy development of Chinese liquor (Baijiu), we studied the molecular mechanism of the interactions between collagen peptides and four aldehydes in Chinese liquor, furfural, benzaldehyde, acetaldehyde and isovaleraldehyde using ultraviolet-visible (UV-vis) spectroscopy, fluorescence spectroscopy and three-dimensional fluorescence spectroscopy. UV-vis absorption spectra indicated that the intensity of the absorption peak of collagen polypeptide at 198 nm was increased with increasing concentrations of furfural and benzaldehyde. Meanwhile, there was no significant change with acetaldehyde and isovaleraldehyde at lower concentrations. However, the absorption intensity was increased at higher concentrations of acetaldehyde and isovaleraldehyde, and new absorption peaks with increasing intensity were generated at wavelengths of about 280 nm and 290 nm respectively. Furthermore, fluorescence spectral analysis corroborated that all four aldehydes had obvious fluorescence quenching on collagen peptides, statically for furfural and benzaldehyde, and dynamically for acetaldehyde and isovaleraldehyde. Thermodynamic calculation revealed that furfural and benzaldehyde bound to collagen peptides predominately by hydrophobic interaction with about one binding site; the binding process was spontaneous. In addition, three-dimensional fluorescence spectral analysis suggested that the binding?strengths between the four aldehydes and collagen peptide decreased in the order of furfural > benzaldehyde > isovaleraldehyde > acetaldehyde. Finally, the results of headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) analysis showed that collagen peptide could reduce the content of aldehydic components in strong-flavor Chinese Baijiu.
Effect of Modified Wheat Bran on the Structure and Digestibility of Bread
XIAO Zhigang, LI Ruizhi, LUO Zhigang, DUAN Yumin, ZHANG Hongwei, LIU Lu, LÜ Chunyue, YANG Qingyu
2021, 42(6):  39-45.  doi:10.7506/spkx1002-6630-20200223-267
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Breads with wheat bran were prepared from high-gluten wheat flour with different amounts of added wheat bran modified by enzymatic hydrolysis followed by autoclaving. The aim was to investigate the effect of the modified wheat bran on the structure and digestibility of breads. The results revealed that the residual lipase activity in the modified wheat bran decreased to 0, the insoluble dietary fiber content decreased from 37.38% to 15.64%, and the water retention increased by 41.26%. Compared with the bread with the native wheat bran, the bread with the modified wheat bran had a stronger aroma, and exhibited an obvious improvement in the specific volume, hardness and elasticity. The aging degree, specific volume, elasticity and sensory quality of bread decreased and hardness increased with increasing level of the modified wheat bran. The content of resistant starch in bread added with the modified wheat bran increased and the hydrolysis rate of starch decreased. In addition, the modified wheat bran significantly reduced the glycemic index of bread.
Effect of Flavonoids from Gordon Euryale Seeds on the Structure of Heat-treated Myofibrillar Proteins
HE Wenjie, WU Binbin, XU Wei, WANG Hongxun, YI Yang, LEI Feifei
2021, 42(6):  46-52.  doi:10.7506/spkx1002-6630-20200325-367
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In this paper, the effect of flavonoids from gordon euryale seeds on the structure of heat-treated myofibrillar proteins extracted from duck thigh meat was investigated by molecular fluorescence spectroscopy, near-infrared spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and changes in the sensory quality of marinated duck thighs with different mass ratios of flavonoids to myofibrillar proteins were explored. It was shown that when the mass ratio of myofibrillar proteins and flavonoids was 1 : 9, and the heat treatment time was 30 min, the highest sensory score (85 out of 100 points) was obtained, together with the lowest β-turn proportion (12.24%); the proportion of random coil structure was 9.02%, lower than that in the control group (11.56%). Moreover, the protein components were not significantly degraded. To sum up, adding appropriate amounts of flavonoids from gordon euryale seeds effectively prevented the secondary structures of myofibrillar proteins from being damaged by heat treatment and maintained the structural integrity thereby improving the sensory quality of marinated duck thighs.
Effect of Ethanol Extract of Tea on the Retrogradation of Waxy Corn Starch
WANG Cuntang, GAO Zengming, JIANG Chenhao, KONG Baohua
2021, 42(6):  53-60.  doi:10.7506/spkx1002-6630-20200212-109
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The research was designed to investigate the interactions of waxy corn starch (WCS) with ethanol extract of tea (EET) at different levels (1.0%, 2.5%, 5.0%, and 10.0%) during gelatinization and their effects on starch light transmittance, aging degree, solubility and swelling degree, gel strength, gelatinization and retrogradation properties, crystal structure, microstructure and in vitro digestibility. The results showed that the addition of EET had significant effects on the physicochemical properties, retrogradation properties and in vitro digestibility of WCS. With the addition of EET, the solubility and swelling degree of WCS increased gradually, while the gel strength decreased gradually. Compared with the control group, the aging degree, gelatinization enthalpy, retrogradation enthalpy, retrogradation rate, ratio of 1047/1022 and relative crystallinity of WCS with 2.5% EET added decreased, indicating significant inhibition of the retrogradation of WCS. The addition of EET to WCS decreased the digestibility of WCS, reduced the content of rapid digestible starch (RDS) and increased the content of resistant starch (RS). Therefore, adding a proper amount of EET to starchy foods can reduce the degree of starch retrogradation, improve the sensory quality and prolong the shelf life.
Carboxymethylation and Physicochemical Characterization of Wheat Bran Arabinoxylan
LU Zhenjie, LI Juan, CHEN Zhengxing, LI Cheng, LI Yanan
2021, 42(6):  61-67.  doi:10.7506/spkx1002-6630-20200210-078
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This study aimed to explore the effect of carboxymethylation modification of wheat bran arabinoxylan (AX), prepared by alkaline extraction, on its physicochemical properties. The effects of NaOH concentration, molar ratio of AX to sodium chloroacetate (SMCA) to NaOH, reaction temperature, and reaction time on the degree of substitution of carboxymethylated AX were investigated through single-factor experiments. The structures, monosaccharide compositions, molecular masses, viscosities and thermal stabilities of carboxymethylated AX with different degrees of substitution were studied. The results showed that when NaOH concentration, AX-SMCA-NaOH ratio, reaction temperature and reaction time were respectively 100 mg/mL, 1:2:2, 65 ℃ and 4 h, the highest degree of substitution of 0.66 was obtained. Infrared spectroscopy analysis proved the success of the carboxymethylation reaction. The total content of xylose and arabinose in carboxymethylated AX with the highest degree of substitution was 14.72%, and the molecular mass was 4.18 × 105 Da, both of which were lower than those (88.72% and 6.07 × 105 Da) of the unmodified arabinoxylan. In addition, when the degree of substitution was increased, the shear viscosity of carboxymethylated AX showed a significant decrease, while the thermal stability was increased obviously, as demonstrated by an increase in the temperature for the maximum thermal decomposition rate from 285 to 306 ℃. The results of this study indicated that the physicochemical properties of carboxymethylated wheat bran AX were quite different from those of the original form. This paper can provide a theoretical basis for studies on the carboxymethylation of wheat bran arabinoxylan and its application.
Bioengineering
Acid Tolerance Response of Salmonella in Beef and Its Formation Mechanism during Chilled Storage
LANG Chenxiao, ZHANG Yimin, ZHU Lixian, LIANG Rongrong, MAO Yanwei, YANG Xiaoyin, HAN Guangxing, LUO Xin, DONG Pengcheng
2021, 42(6):  68-74.  doi:10.7506/spkx1002-6630-20191128-287
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The influence of acid induction, two-component regulatory systems and long-term low-temperature storage on the formation of acid tolerance response (ATR) was evaluated, and the mechanism of ATR formation was elucidated by using the λRed recombination system, real-time polymerase chain reaction (real-time PCR) and amino acid addition experiments. The results showed that mild acid induction significantly enhanced the acid tolerance of Salmonella (P < 0.05), and once induced, it could be maintained for at least 1 week at 4 ℃, posing a great threat to food safety. As a mildly acidic incubation medium, beef did not induce ATR at 4 ℃, indicating that low-temperature treatment may be an important method to inhibit ATR in Salmonella typhimurium. Real-time PCR and amino acid addition experiments showed that PhoP/PhoQ and PmrA/PmrB were involved in the perception of the acidic environment, improving bacterial acid resistance by regulating the arginine decarboxylation and lysine decarboxylation systems. This explains the mechanism of ATR formation from the perspective of amino acid metabolism, which may also reveal an explanation of why food substrates can enhance the acid resistance of some bacteria.
Prokaryotic Expression and Purification of PurR and PurL from Lactobacillus plantarum KLDS1.0391 and Their Interaction with Bacteriocin Synthesis Promoter
LI Xinrui, ZHAO An, FAN Xiaopiao, GAO Wenwen, SHANG Jiacui, ZHAO Penghao, ZHAO Le, ZHOU Xue, MENG Xiangchen
2021, 42(6):  75-81.  doi:10.7506/spkx1002-6630-20191219-230
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The purpose of this study was to investigate whether purR and purL directly regulate the synthesis of bacteriocin by Lactobacillus plantarum KLDS1.0391 through in vitro experiments. Based on the whole genome sequence of L. plantarum KLDS1.0391, we obtained the genes encoding PurR and PurL proteins by PCR amplification. The genes were separately cloned into the pQE-30 vector to construct recombinant expression vectors. Then the recombinant vectors were transformed into Escherichia coli M15 for protein expression. The expressed proteins were puri?ed by Ni af?nity chromatography. After dialysis and ultrafiltration concentration, we studied whether the two proteins bind to the bacteriocin synthesis regulatory region of the strain by using the gel retardation assay and biolayer interferometry. The results showed that the recombinant proteins were successfully expressed, PurR was present in a soluble form while PurL was present as an inclusion body. The purified proteins showed a single band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). After being concentrated, the PurR concentration was 0.74 mg/mL and the PurL concentration was 3.8 mg/mL. The results of gel retardation assay and biolayer interferometry showed that the two recombinant proteins did not directly bind to the promoter of the bacteriocin synthesis gene of the strain. Further studies are needed to clarify whether and how bacteriocin synthesis is indirectly regulated by the two proteins.
Characterization of Recombinant Phenylalanine Aminomutase from Taxus chinensis and Its Application for Synthesis of R-β-Arylalanine
FENG Guoqiang, XU Wenliang, SONG Ping, LI Wanzhen, TAO Yugui, GE Fei, ZHU Longbao
2021, 42(6):  82-87.  doi:10.7506/spkx1002-6630-20191212-126
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In order to synthesize high value-added β-phenylalanine, the gene encoding phenylalanine aminomutase from Taxus chinensis was cloned and expressed in Escherichia coli. The expression vector Pet-sumo-Tcpam was successfully constructed and transferred into E. coli BL21 to express the recombinant enzyme (TcPAM). Electrophoretically pure TcPAM was obtained using affinity chromatography. The results of mass spectrometry (MS) and circular dichroism (CD) spectroscopy showed that TcPAM could catalyze isomerization of α-phenylalanine to R-β-phenylalanine. Its activity was 4.11 U/mg under the optimum conditions of 30 ℃ and pH 9. The metal ions K+, Fe2+ and Ca2+ as well as the surfactants cetrimonium bromide (CTAB), sodium dodecyl sulphate (SDS), Triton X-100, and Tween 80 had little effect on its activity, resulting in retention of about 90% of the initial activity, while Cu2+ and Zn2+ had strong inhibitory effect on TcPAM, Furthermore, when TcPAM was used to catalyze isomerization of α-arylalanines with different groups on the benzene ring to R-β-phenylalanine, the presence of electron-donating groups on the benzene ring promoted transfer of the α-amino group to the β site as compared to the presence of electron-withdrawing groups, improving the substrate conversion rate and the highest value of 45% was obtained when the R group was 4-MeO or 4-Me. This study provides the basis for enzymatic synthesis of β-arylalanine.
Effect of Chlorogenic Acid on Fermentation Characteristics of Saccharomyces cerevisiae
XIAO Mei, LI Min, ZHANG Han, PENG Bangzhu
2021, 42(6):  88-93.  doi:10.7506/spkx1002-6630-20191209-098
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The effect of different concentrations (0 (control), 0.01, 0.1, and 1.0 g/L) of chlorogenic acid on the fermentation characteristics of Saccharomyces cerevisiae CICC31084 in a model apple juice was investigated by measuring biomass, the consumption of glucose, the release of carbon dioxide, the formation of alcohol and the changes of key aroma substances in the fermentation process. The results showed that high concentrations of chlorogenic acid could promote the growth of yeast cells, accelerate the release of CO2 and the rate of glucose metabolism, and delay the rate of ethanol production in the early stage of fermentation. The most significant effect was observed at the concentration of 1.0 g/L, shortening the fermentation period by up to 2–3 days. Chlorogenic acid increased the contents of 2-phenylethanol, ethyl acetate and isoamyl acetate and decreased the contents of ethyl hexanoate and ethyl decanoate, while it had little effect on the content of ethyl octanoate.
Preparation and in vitro Evaluation of Goat Milk-FOS/GOS Pichia kudriavzevii DS8-1 Microcapsules
LIU Yue, GAO Yunyun, LI Shan, LI Wangqiang, LI Baokun, LU Shiling, JIANG Caihong, WANG Qingling, DONG Juan, LI Yuhui
2021, 42(6):  94-103.  doi:10.7506/spkx1002-6630-20200125-280
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To improve its in vitro environmental resistance, Pichia kudriavzevii DS8-1, a strain with probiotic potential previously prepared by our research group from traditional fermented camel milk in Xinjiang, was microencapsulated by a piercing-solidifying method. Three types of microcapsules coated with goat milk, SAM, SAMF and SAMG, were prepared using sodium alginate alone and with added fructooligosaccharides (FOS) or galactooligosaccharides (GOS) as the wall material, respectively. Uncoated microcapsules (SA) with sodium alginate as the wall material were used as the control. The microcapsules were characterized by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Their tolerance to simulated gastric juice, release characteristics in simulated digestive juice and storage stability were evaluated. Besides, the effect of freeze drying on the survival of microencapsulated yeast cells was investigated. Results showed that the viability of lyophilized SAM, SAMF, and SAMG microcapsules was 7.16–7.67 (lg(CFU/g)). Compared with SA microcapsules, SAMF microcapsules could delay the release of yeast cells, improve the survival rate, and have stronger inhibitory activities on α-amylase and α-glucosidase after continuous exposure to simulated digestive juice. After SAMG microcapsules were stored at ?20, 4 or 25 ℃ for 30 days, the cell viability was higher than 7 (lg(CFU/g)). In conclusion, addition of FOS or GOS to sodium alginate and goat milk coating can be used to microencapsulate Pichia kudriavzevii with improved viability. The prepared microcapsules show promise as a delivery system for functional foods.
Effects of Splicing of Accessory Protein Gene on Phospholipase A1 Activity
YANG Meng, XUE Zhenglian, GAN Yufei, ZHOU Jie, WANG Zhou, LIU Yan
2021, 42(6):  104-110.  doi:10.7506/spkx1002-6630-20200115-181
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This study aimed to explore the key regulatory region of the gene encoding phospholipase A1 accessory protein (PlaS) on the activity of phospholipase A1 (PlaA1). According to the structural characteristics of PlaS, truncated mutants were designed, the gene encoding plaS in the PlaA1 and PlaS co-expressed gene (plaB) was spliced by PCR, and the PlaA1 activity and properties of the truncated strains were analyzed. The results showed that PlaS belonged to the Ankyrin family, which was mainly composed of three parts: N-terminal domain, ANK domain, and C-terminal domain. The ANK domain contained 4 typical anchoring protein repeats (ANK repeat). Out of the five truncated strains, AN-3 and AN-4 were found to have relatively high extracellular PlaA1 activity. In contrast to the untruncated strain BP28, the specific activities of AN-3 and AN-4 were increased by 73% and 78%, respectively, and the catalytic efficiencies (Kcat/Km) by 216% and 211%, respectively, while the optimum temperature (45 ℃) and pH (6.0) were unchanged. AN had the lowest catalytic efficiency among all the truncated strains. The results of plaS splicing showed that at least three ANK repeats in the ANK domain of PlaS were required to promote the extracellular activity of PlaA1, and the C-terminal domain of PlaS played an important role in maintaining the structural stability of PlaA1. This study provides a theoretical basis for revealing the regulatory mechanism of PlaS on PlaA1.
Effect of High-yield Phytase Lactic Acid Bacteria Fermentation on Protein and Baking Quality of Black Bean Sourdough Bread
LUO Kun, CAO Weichao, MA Zilin, WU Meng, Omedi Jacob OJOBI, ZHENG Jianxian, HUANG Weining, LI Ning, Filip ARNAUT
2021, 42(6):  111-117.  doi:10.7506/spkx1002-6630-20191225-290
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Pediococcus acidilactici L-19, a strain capable of phytase with high yield, was used as a starter culture for black bean sourdough bread production. The effects of the starter culture on the protein nutritional quality and baking properties of black bean sourdough bread were studied by measuring amino acid composition, nutritional properties, in vitro protein digestibility (IVPD), textural characteristics, ultrastructure and sensory properties. The phytase negative strain K-12 was used as a control. The results showed that after addition of black bean sourdough fermented by lactic acid bacteria, both the protein nutritional quality and baking properties of bread were significantly improved, with the most significant effect being observed in black bean bread prepared using (L-19SDB). Compared with control black bean bread (BB), phytic acid content of L-19SDB was decreased by 60.68% while IVPD was increased from 64.70% to 73.93%, and total amino acid content was increased by 73%. Moreover, as compared with the other three groups, L-19SDB had a better amino acid profile in terms of the ratio of essential amino acids to total amino acids (E/T), essential amino acid index (EAAI) and biological value (BV). Compared with BB, L-19SDB and K-12SDB showed an increase in specific volume of 31.45% and 23.59% and a decrease in hardness of 68.79% and 56.59%, respectively. ImageJ analysis results showed that the stomatal distribution of L-19SDB crumb was more uniform and this bread had the highest overall acceptability (7.72 points out of 9).
Determination and Correlation Analysis of Flavor Components with Bacterial Community in Post-fermented Red Sufu
CHEN Zhuo, WU Xuefeng, MU Dongdong, HE Ying, ZHANG Mingzhu, CAI Jing, HOU Zhigang, ZHENG Zhi, LIANG Jin, ZHANG Yumeng, LI Xingjiang
2021, 42(6):  118-125.  doi:10.7506/spkx1002-6630-20191203-043
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In this experiment, we sought to explore the relationship between the change of flavor substances and bacterial community succession during the post-fermentation of red sufu. By using headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS), and reversed-phase high performance liquid chromatography (HPLC) following precolumn derivatization with o-phthalaldehyde (OPA), we detected the contents of volatile flavor compounds and amino acids in the sufu. A total of 50 volatile flavor substances were detected, mainly including 20 ester compounds and 9 alcohols. The main flavor substances identified by odor activity value (OAV) analysis were phenyl ethanol, 1-octene-3-alcohol, ethyl acetate, etc. The types and contents of most flavor compounds such as esters, terpenes and furans were increased with fermentation time, while those of alkanes and esters were not changed significantly. The total content of free amino acids (FAA) was similarly increased with fermentation time. The bacterial community was analyzed by high-throughput sequencing, and it was found that the dominant bacteria were Bacillus, Enterobacter, Acinetobacter, Tetragenococcus, etc. The diversity of bacterial community was increased significantly during fermentation. The abundance of Bacillus was decreased significantly, while the abundances of Lactococcus and Tetragenococcus were increased over the entire fermentation period. The abundance of Enterobacter was increased significantly in the early-mid part of the period and then decreased in the mid-late part. Pearson correlation analysis showed that the production of amino acids in the post-fermentation period of red sufu was positively correlated with Enterobacter, while the production of most aroma compounds was negatively correlated with Enterobacter. Bacillus was positively correlated with a variety of ester aroma compounds. Other strains, such as Lactococcus and Acinetobacter, also provided good flavor during the post-fermentation period.
Expression of VmaH and PMA in Penicillium digitatum and Their Potentials as Antimicrobial Targets
FAN Ming, PENG Litao, YAN Deng, FAN Gang, YANG Shuzhen, LI Jie
2021, 42(6):  126-133.  doi:10.7506/spkx1002-6630-20191230-348
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Objective: In order to develop safe, efficient and fungicides with new targets for postharvest disease control of citrus fruit, bioinformatics and expression pattern analysis of the VmaH and PMA genes of Penicillium digitatum were carried out in this study, and we further explored the potentials of the genes as potential antimicrobial targets. Methods: Using various kinds of online software such as Pfam and MEGA 5.0, bioinformatics analysis was performed. Furthermore, the gene expression levels of were analyzed by real-time PCR. Results: It was predicted that there were two highly conserved domains in VmaH, located at the N- and C-terminal ends, respectively. There were three highly conserved domains in PMA, N-terminal, E1-E2 ATPase, and hydrolase domains. Sequences alignment revealed that 79% and 80% identities for VmaH and PMA among different fungi, respectively, which indicates high conservation of VmaH and PMA among different fungi. The obtained cladogram showed that P. digitatum VmaH and PMA were closely related to those of Penicillium and Aspergillus. Compared to PMA, the expression of VmaH was maintained at a higher level throughout the growth of P. digitatum. The expression of PMA was significantly down-regulated during the later stages of P. digitatum growth. Glucose starvation significantly reduced the expression levels of VmaH and PMA, which could be restored by glucose supplementation. In particular, the expression of VmaH was even significantly up-regulated. The expression levels of VmaH and PMA were significantly down-regulated under extreme acid and alkaline conditions. However, the expression of PMA was increased in weakly acidic and alkaline environments. Treatment with either oxidants or reducing agents could significantly reduce the expression levels of VmaH and PMA. Compared with VmaH, the down-regulation of PMA was more significant. The expression of PMA was decreased significantly by treatment with each of the evaluated fungicides, while the responses of VmaH to different fungicide treatments were different. Conclusion: The proteins encoded by VmaH and PMA have the potential to be used as fungicide targets in P. digitatum for further research.
Screening and Application of Bacillus spp. Promoting Moromi Fermentation
WU Bohua, JIANG Xuewei, ZHANG Jinyu, RUAN Zhiqiang, LIANG Shengnan, CHEN Yongfa, ZHOU Shangting
2021, 42(6):  134-141.  doi:10.7506/spkx1002-6630-20200106-076
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A total of 56 strains with high protease activity were isolated from high-salt liquid-state moromi (soy sauce mash) by the casein plate method. Among these, the strain CS1.11 with the highest amylase activity, CS1.13 with the highest protease activity and CS1.17 with the highest cellulase activity were selected by the Oxford-cup method. According to the 16S rRNA gene sequence analysis and morphology, CS1.11, CS1.13, and CS1.17 were identified as B. velezensis, B. methylotrophicus and B. subtilis, respectively. The three strains and the control strain B. subtilis CS1.03 were separately subjected to salt brine fermentation after koji-making. It was found that the fermented soy sauce inoculated with CS1.13 had the highest ammonia nitrogen content (5.12 g/L), and the fermented soy sauce inoculated with CS1.11 had the highest reducing sugar content (27.20 g/L). The results were consistent with the strains’ enzymatic activities. In addition, the four strains had little effect on the total acid content of soy sauce. All the fermented soy sauce samples were qualitatively and quantitatively analyzed by solid-phase microextraction-coupled to gas chromatography-mass spectrometry (SPME-GC-MS) using the internal standard method. It was found that all four strains were advantageous for producing pyrazines and their precursors (acetoin and 2,3-butanediol), the three test strains being superior to the control strain. Pyrazines could impart a good flavor and health factors to soy sauce, and were the characteristic flavor substances of fermented soy sauce inoculated with Bacillus spp. Bacillus strains CS1.11, CS1.13, and CS1.17, thanks to their potential to promote moromi fermentation, enrich the flavor of soy sauce and increase health factors, will hold great promise for application in soy sauce production.
Fermentation Characteristics for Flavor Compounds Production by Quality Yeast Strains Isolated from Rice Wine Starters
CHEN Lihua, REN Lixia, LI Dongna, MA Xia
2021, 42(6):  142-149.  doi:10.7506/spkx1002-6630-20191212-134
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In order to improve the aroma quality of traditional rice wine and to realize its standardized production, six yeast strains with excellent fermentation characteristics for aroma production were isolated from several local characteristic rice wine starters in China and were identified by 26S rDNA sequence analysis. A phylogenetic tree was constructed for the strains, and the aroma characteristics of rice koji juice fermented with each of the strains separately were analyzed. The results showed that strains CMY001, CMY003 and NBY003 were identified as Saccharomyces cerevisiae, CMY002 and NBY002 as Wickerhamomyces anomalus and YCY001 as Candida glabrata. YCY001 was well tolerant to alcohol contents lower than 10%, while CMY002 could tolerate alcohol contents higher than 10%. NBY002 was well tolerant to temperature. All the strains could grow at pH 3–11; NBY003 had the strongest fermentation ability, and NBY002 exhibited the highest ester production up to 5.125 g/L. In the rice koji medium, the β-phenylethanol producing ability of NBY002 was significantly higher than that of the other strains, producing a strong floral aroma. The diversity and relative content of esters produced by YCY001 were significantly higher than those produced by the other strains, giving a rich ester aroma. CMY001 produced fatty, wine-like and grass-like aromas, while CMY002 and CMY003 gave a strong fruity aroma. In general, significant differences were found among the aroma profiles produced by the six strains. Octyl acrylate, phenylethyl acetate, ethyl acetate, isoamyl formate, β-phenylethanol, caprylic acid and ethyl benzoate were the key aroma compounds contributing to the discrimination of the fermentation products of the six strains.
Transcriptomic Analysis of Cordyceps militaris and Mining of Genes Involved in Carotenoid Biosynthesis
LOU Haiwei, ZHAO Yu, ZHAO Yi, LIN Junfang, ZHAO Renyong, YE Zhiwei, GUO Liqiong
2021, 42(6):  150-156.  doi:10.7506/spkx1002-6630-20200125-269
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Culture medium composition significantly affects carotenoid biosynthesis in Cordyceps militaris. In this study, high-throughput sequencing technology was used to investigate the transcriptomic differences of C. militaris mycelia (CM10_RL and CM10_WL) cultured with different media. The genes related to the biosynthesis of carotenoids in C. militaris were identified by bioinformatics analysis. The results showed that the carotenoid content of CM10_WL was significantly higher than that of CM10_RL. A total of 318 up-regulated genes and 618 down-regulated genes were found in CM10_WL compared with CM10_RL. Gene Ontology (GO) analysis indicated that the differentially expressed genes (DEGs) were mainly classified into the “metabolic process”, “membrane” or “catalytic activity” terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis suggested that these DEGs were mainly enriched in “metabolic pathways”. Therefore, all the transcripts derived from RNA-seq data were searched against the carotenoid biosynthetic pathway in the KEGG database, and the results showed that the CCM_06728 and CCM_09155 genes were involved in the biosynthesis of carotenoids. This study lay a foundation for further elucidating the biosynthetic pathway of carotenoids in C. militaris.
Fungal Community Succession and Flavor Compounds Metabolism during Pomegranate Wine Fermentation
PENG Xiao, ZOU Wenjing, SHAO Qingqing, SUN Zhongguan, ZHANG Lihua, LI Hehe, WANG Xueshan
2021, 42(6):  157-163.  doi:10.7506/spkx1002-6630-20200114-163
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In this study, we analyzed fungal community succession during pomegranate wine fermentation by applying high throughput sequencing. By applying gas chromatography-mass spectrometry (GC-MS), we also analyzed the change of volatile flavor compounds. Results showed that the dominant fungal genera during pomegranate wine fermentation were Saccharomyces, Hanseniaspora, Pichia, Candida and Aspergillus. Among these, Hanseniaspora was dominant and its relative abundance accounted for 57.84%–60.13% of the total fungal community. From day 4 to day 8 of fermentation, Saccharomyces was dominant and its relative abundance accounted for 90.00%–97.26% of the total fungal community. Moreover, Granger causality analysis showed Saccharomyces was the main factor that led to the high contents of isobutanol and isopentanol. The non-Saccharomyces yeasts Hanseniaspora and Pichia played an important role in the production of ethyl laurate and ethyl acetate in pomegranate wine. This study provides the theoretical basis for improving the quality pomegranate wine and controlling the fermentation process.
Characterization of a Wide Host-Range Cronobacter sakazakii Bacteriophage and Its Application in Milk Products
LI Hongjiao, HUANG Zicong, WU Xiyang, DING Yu, TANG Shuze
2021, 42(6):  164-170.  doi:10.7506/spkx1002-6630-20191209-094
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Bacteriophage TBC-1 was isolated from sewage using Cronobacter sakazakii ATCC25944 as the host. Observation under electron microscope revealed that TBC-1 displayed a contractile tail; the shape of its capsid was an icosahedron. It had a wide host range. The multiplicity of infection (MOI) of the bacteriophage was 0.001. The one-step growth curve showed that its latent time was 20 min; the outbreak period was 50 min; the number of outbreak was 100 PFU/cell. TBC-1 maintained its high titer at 40–50 ℃ and pH 4–10. In addition, C. sakazakii showed stronger lytic ability at higher MOI. The complete genome was 85 313 bp in length and the content of GC was 40.65%. It had 118 protein coding sequences (CDSs) and 24 tRNAs. The bacteriostatic effect of the bacteriophage on C. sakazakii ATCC25944 and ATCCBAA894 in milk products was investigated. It turned out that after incubation at 25 ℃ for 3 h with MOI = 106, both strains at 102 CFU/mL in milk were inhibited to below the detection limit. After incubation at 25 or 37 ℃ for 3 h, ATCCBAA894 was inhibited to below the detection limit; after incubation at 25 ℃ for 3–12 h, ATCC25944 was inhibited to below the detection limit. The results showed that the phage exhibited a wide host range against C. sakazakii and had good bacteriostatic efficacy in both milk and milk powder, demonstrating its potential to be a bio-control agent against C. sakazakii in foods.
Screening for and Identification for Bacteriocin-producing Enterococcus faecium and Its Antibacterial Properties
ZHANG Ming, LUO Qiang, WEI Jie, LIU Qiao, LUO Fan
2021, 42(6):  171-177.  doi:10.7506/spkx1002-6630-20191213-147
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A total of 308 strains suspected of being Lactobacillus were isolated from traditional fermented yoghurt collected from Hongyuan, Sichuan province, and were screened by 96-well plate method and agar well diffusion method. Among these strains, SC-Y112 was selected for its obvious antibacterial effect. It was identified as Enterococcus faecium by morphological observation, 16S rDNA and ropA housekeeping gene sequencing analysis, and physiological and biochemical tests. After removing the influence of organic acid and hydrogen peroxide, the fermentation supernatant of the strain still had considerable antibacterial activity. The antibacterial effect decreased and even disappeared after being treated with protease, which indicated that the antibacterial components in the fermentation supernatant were proteins. Further, the biological characteristics, genetic stability and bacteriostatic characteristics of the bacteriocin produced by the strain were investigated, which showed that the bacteriocin was produced at 6 h and reached the maximum at 12?h after inoculation; the bacteriocin production ability was relatively stable within 86 consecutive generations; the bacteriocin was stable under the condition of pH 3.0-7.0 and heat-treatment at 100 ℃ for 30 min. The bacteriocin had a wide antibacterial spectrum, especially against Listeria monocytogenes.
Analysis of Microbial Community Diversity in Traditional Fermented Vegetables in Zhejiang Using High-throughput Sequencing
BAO Wei, HAN Jiaojiao, ZHANG Zhixuan, LU Chenyang, ZHOU Jun, MING Tinghong, LI Ye, SU Xiurong
2021, 42(6):  178-185.  doi:10.7506/spkx1002-6630-20191205-061
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The structure and diversity of the bacterial and fungal communities in juices, solids and microbial cultures from the traditional fermented vegetables in Zhejiang, stinky white gourd, stinky edible amaranth stalks, sour bamboo shoots and sour water bamboo (Zizania latifolia) shoots were analyzed by Illumina MiSeq high-throughput sequencing, and the difference in the microbial community composition of stinky and sour fermented vegetables was evaluated. The results showed that the sequencing coverage rates of bacteria and fungi in the 14 samples were 0.97 and 0.99, respectively. The number of bacterial operational taxonomic units (OTUs) and Shannon’s diversity index were the largest in stinky edible amaranth stalk solids, and were the smallest in sour bamboo shoot solids and juice, respectively. The structure of bacterial community was similar among stinky edible amaranth stalk juice and solids, and sour bamboo shoot solids and culture. The number of fungal OTUs was the largest in stinky white gourd culture and sour water bamboo shoot solids, and smallest in stinky edible amaranth stalk culture, while fungi were not detected in sour water bamboo shoot juice. The largest and smallest Shannon’s diversity index for fungi were found in sour bamboo shoot juice and stinky edible amaranth stalk culture, respectively. The composition of fungal community was similar among all samples except brine, stinky edible amaranth stem juice, and juice, solids and sour bamboo shoot culture. At the genus level, the dominant bacteria in stinky white gourd culture, sour bamboo shoot juice, sour bamboo shoot solids, and sour water bamboo shoot juice included Desulfovibrio, Klebsiella, Escherichia and Caproiciproducens; the dominant bacteria in brine culture, sour water bamboo shoot solids and culture were Clostridium; the dominant bacteria in stinky edible amaranth stem juice, solids and culture were Bacteroides; the dominant bacteria in brine, stinky white gourd juice and solids were Lactobacillus. Kodamaea was the dominant fungal genus in brine, Candida in stinky edible amaranth stem juice, solids and culture, and Leptospora in the other samples.
Analysis of Bacterial Diversity and Its Effect on Flavor of Chinese Sausage during Fermentation
GUO Zhuang, WANG Yurong, GE Dongying, SHANG Xuejiao, ZHANG Zhendong, ZHAO Huijun
2021, 42(6):  186-192.  doi:10.7506/spkx1002-6630-20191121-255
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In this study, electronic nose was used to evaluate the flavor of Chinese sausage at different fermentation times, MiSeq high-throughput sequencing technique was used to analyze the diversity of bacterial flora, and the metabolic function of bacteria was predicted. Finally, the correlation between bacterial diversity, sausage flavor and metabolic pathways was studied. The results showed that the flavor of sausage changed significantly on about day 10 of fermentation. The initial fermentation period was the key period for the formation of sausage flavor. At this time, at the phylum level, the sum of the average relative contents of Firmicutes and Proteobacteria was 96.00%. At the genus level, the dominant bacteria were mainly lactic acid bacteria such as Lactobacillus, Staphylococcus and Weissella. Through gene function prediction and correlation analysis, it was found that lactic acid bacteria in sausages played a crucial role in the fermentation and ripening as well as flavor formation of sausages. Besides, the study showed that the best sausage quality was achieved on about day 10 of fermentation.
Transcriptome Analysis of Hansenula polymorpha DL-1 with Sodium Selenite-Induced Biosynthesis and Accumulation of Glutathione
WANG Ting, LIU Chanchan, REN Juan, JING Rongrong, QIAN Weidong
2021, 42(6):  193-199.  doi:10.7506/spkx1002-6630-20200121-252
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To elucidate the mechanism of glutathione (GSH) biosynthesis by Hansenula polymorpha DL-1 (HP-DL-1) exposed to Na2SeO3, we examined the differentially expressed genes (DEGs) in yeast cells treated and not treated with Na2SeO3 using a combination of transcriptomic sequencing and bioinformatic methods. The results showed that 60 μmol/L Na2SeO3 was found to be able to increase the GSH yield of yeast cells up to (530.22 ± 9.6) mg/L after 48 h fermentation. A total of 1 254 DEGs was identified in the Na2SeO3-induced group, of which 630 genes were up-regulated, whereas the remaining 624 genes were down-regulated. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses indicated that these DEGs were involved in the cell cycle, mitosis, amino acid biosynthesis, glycolysis, ribosome components and methane, fat, nucleic acid, GSH metabolism pathways. This study provides adequate information for a better understanding of the physiological mechanism of GSH biosynthesis by H. polymorpha, which will provide theoretical support for subsequent molecular improvement for over-production of GSH by engineered strains.
Component Analysis
Effect of Carrier Gas Types on Separation of Cis-trans Fatty Acid Isomers by Gas Chromatography
PEI Ziwei, YANG Jie, ZHANG Lei, ZHOU Shuang, ZHAO Yunfeng, CHEN Dawei, MIAO Hong, FANG Congrong
2021, 42(6):  200-205.  doi:10.7506/spkx1002-6630-20200811-138
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Using gas chromatography-flame ionization detector (GC-FID) fitted with a CP-Sil88 capillary column as the analytical column, we investigated the effects of different carrier gases (helium and nitrogen) on the resolution and quantitative accuracy of C18:1 cis-trans fatty acid isomers in shortening, butter, biscuit and cake, as well as C18:2 and C18:3 cis-trans fatty acid isomers in vegetable oil under isothermal or rising temperature conditions. With helium as carrier gas, the resolution (R) of C18:1 13t,14t(6-8c) and C18:1 9c was greater than 1.0, which could clearly distinguish and separate 4t–13t,14t isomers at different concentrations, and accurate quantification was achieved without underestimating the total amount of C18:1 trans fatty acid isomers. The carrier gas had no effects on the resolution or content of C18:2 cis-trans isomers in vegetable oil. Compared with nitrogen, helium had a slight advantage in the separation of C18:3 trans isomer in vegetable oil, while no significant difference was noted between the values obtained using them as carrier gases. Compared with nitrogen, helium was more suitable for use as carrier gas for simultaneous determination of trans fatty acids, saturated fatty acids, monounsaturated fatty acids and polyunsaturated fatty acids in foods with higher quantitative accuracy and wider versatility.
Changes of Bound Aroma Compounds and Their Relationship between Soluble Sugars in Nectarines during Postharvest Storage
ZHANG Qin, ZHOU Dandan, PENG Jing, PAN Leiqing, TU Kang
2021, 42(6):  206-214.  doi:10.7506/spkx1002-6630-20200317-261
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Changes of free and glycosidically bound aroma compounds in ‘Ruiguang 1’ nectarines were investigated during postharvest storage at room temperature (20 ℃) or low temperature (1 ℃). Enzymatic hydrolysis was used to release the bound aroma compounds. Headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) was used for qualitative and quantitative analysis of the free and bound aroma compounds in nectarines. The correlation between bound aroma compounds and soluble sugars was studied. Results showed that the compositions of free and bound aroma compounds were significantly different in nectarines stored at 20 ℃ and 1 ℃. In nectarines storage at 20 ℃, a total of 37 free aroma compounds and 30 bound ones were identified, of which, 8 compounds were detected in both free and bound forms. The free aromas decreased until day 4 and then increased until day 6 but decreased again on day 8. The bound aromas decreased to the minimum on day 6 then increased on day 8. In nectarines stored at 1 ℃, a total of 21 free aroma compounds and 32 bound ones were identified, of which, 7 compounds existed in both free and bound forms. The free aromas decreased with storage time, while the bound aromas increased at the beginning and then decreased. Correlation analysis showed a significant correlation between the bound aromas and the soluble sugars, especially sucrose, showing the highest correlation coefficient.
Optimization of Solid Phase Microextraction for GC-MS Analysis of Nine Flavor Compounds in Lichuan Hong Tea and Flavor Discrimination by Partial Least Squares-Discriminant Analysis
CHENG Chao, XIA Lanxin, DU Fenni, LI Wei, TIAN Cheng
2021, 42(6):  215-222.  doi:10.7506/spkx1002-6630-20200324-353
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The solid phase microextraction (SPME) conditions for the analysis of flavor compounds in Lichuan Hong tea by gas chromatography-mass spectrometry (GC-MS) were optimized using response surface methodology (RSM). The composition of flavor compounds in Lichuan Hong tea was compared with that in Yihong and Dianhong tea. The results showed that the optimal extraction conditions were as follows: solid-to-liquid ratio 1:4.11 (g/mL), extraction time 50.15 min, and extraction temperature, 71.75 ℃. Under these conditions, a total of 73 flavor substances were identified in Lichuan Hong tea, mainly including furans, aldehydes, alkanes and esters, accounting for 21.202%, 20.11%, 13.751% and 11.662% of the total amount, respectively. A total of 59 flavor components were identified in Yihong tea, including furan, alcohol, aldehyde and alkane, accounting for 23.445%, 21.04%, 19.816% and 18.070% of the total amount, respectively. A total of 66 flavor components were identified in Dianhong tea, including alcohol, aldehydes and furans, accounting for 35.587%, 15.103% and 12.229% of the total amount, respectively. Partial least squares-discriminant analysis (PLS-DA) was performed on all flavor substances and nine selected flavor substances in the three black teas. The flavor types of black tea could be predicted based on the selected flavor substances, and even the prediction ability was better than that based on all flavor substances. In addition, variable importance in projection (VIP) analysis indicated that linalool, cis-linalool oxide, geraniol and 2-hexenaldehyde had the greatest influence on the flavor of the three black teas, and that these flavor components could be used as the main characteristic markers for distinguishing the three black teas. The results of this study enrich the basic theory of the flavor quality of Lichuan Hong tea and provide the basis for aroma quality control of Lichuan Hong tea.
Analysis of Flavor Differences among Three Brands of Lager Beer Based on Untargeted Flavoromics
CHEN Hualei, HUANG Kexing, ZHENG Min, YANG Zhaoxia
2021, 42(6):  223-228.  doi:10.7506/spkx1002-6630-20200319-294
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The volatiles in Lager beer were identified by headspace solid phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) and the flavor differences among three brands of Lager beer were discriminated by principal component analysis (PCA), partial least squares-discriminant analysis (PLS-DA) and random forest classifier (RFC). Using divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) SPME fibers, we extracted the samples for 5 min at room temperature, then desorbed the analytes at the GC inlet and analyzed them. Among the identified flavor compounds, ethyl octanoate and ethyl decanoate were the key components to discriminate the brands. In the established PLS-DA and RFC models, both giving a prediction accuracy of 100%, the two components contributed the most to the difference in beer flavor. This strategy could play a positive role in the establishment of a flavor-based method for beer classification.
Analysis of Differential Composition between Not from Concentrate and from Concentrate Orange Juices Using UPLC-QTOF-MS-Based Metabolomics
LIU Hanlu, ZHANG Jiukai, HAN Jianxun, SUN Ruixue, CHEN Ying, LIU Bing
2021, 42(6):  229-237.  doi:10.7506/spkx1002-6630-20191014-106
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This study analyzed the differential composition between not from concentrate (NFC) and from concentrate (FC) orange juices using non-targeted metabolomics. Metabolite information from the samples was acquired in both the positive ion and negative ion modes by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). NFC and FC orange juice were distinguished from each other by orthogonal partial least squares discriminant analysis (OPLS-DA), and 16 compounds that significantly differed (P < 0.05) in abundance between them were selected and identified according to the importance in projection values and t-test analysis, including flavonoids, organic acids and alkaloids. The contents of these components in FC orange juice were significantly lower than in NFC orange juice. The results of this study provide theoretical reference for the quality evaluation and identification of NFC juice.
Effects of Three Loading Treatments on Quality Attributes in Spine Grape (Vitis davidii Foex.) Cultivar Tianputao
YUE Xiaofeng, CAO Jianhong, ZHAO Yameng, YIN Chunxiao, JU Yanlun, ZHANG Zhenwen
2021, 42(6):  238-243.  doi:10.7506/spkx1002-6630-20200316-241
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In this study, the spine grape cultivar Tianputao (Vitis davidii Foex.) from Huaihua, Hunan province was used as the experimental material. Three loading levels were set as follows: 1 300 kg/667 m2 (L1), 1 900 kg/667 m2 (L2) and 2 500 kg/667 m2 (L3). The main quality indicators of mature grapes such as total acid, reducing sugar, anthocyanins and non-anthocyanin monomeric phenolics were determined. Principal component analysis (PCA) was carried out on the fruit quality attributes. The results showed that: (1) total acid content increased with loading level for the two crop years 2014 and 2015, while the reducing sugar content decreased; (2) total anthocyanin content was the highest at L1 and L2 for 2014 and 2015, respectively, and the total content of basic anthocyanins was the lowest at L3 for both years; (3) for the two years, the total content of non-anthocyanin monomeric phenolic compounds and total flavonol content were both the highest at L2, followed by those at L1, and L3 gave the lowest values. Furthermore, principal component analysis (PCA) showed that the distribution of Tianputao under the three loading levels was consistent but there was clear discrimination in fruit quality between the two years. For both years, the content of phenols was the highest at L2.
Evaluation and Analysis of Fatty Acid Composition and Contents in Safflower Oil
LIANG Huizhen, XU Lanjie, YU Yongliang, TAN Zhengwei, YANG Hongqi, DONG Wei, LI Lei, LI Chunming, LIU Xinmei, ZHANG Shouliang
2021, 42(6):  244-249.  doi:10.7506/spkx1002-6630-20200218-183
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To establish an effective evaluation method for safflower seed quality and, more broadly, provide a theoretical basis for the breeding and quality improvement of safflower. The total fatty acid contents and the relative contents of nine fatty acids in safflower oils extracted from 82 safflower seed samples from different habitats were analyzed using gas chromatography. Membership function transformation and principal component analysis (PCA) were applied to comprehensively evaluated the main nutritional quality characteristics of safflower oil. The total fatty acid contents and the relative contents of nine fatty acids were different in the 82 safflower oil samples, with coefficients of variation of 0.98%–111.99%. The average contents of total fatty acid were 22.16–27.23 mg/100 g, and the average contents of linoleic acid ranged between 78.54% and 82.45%. The correlation analysis showed that the total fatty acids were positively correlated with linoleic acid (C18:2) and palmitic acid (C16:0), and negatively correlated with oleic acid (C18:1n12 and C18:1n9). By PCA, we classified the nine fatty acids into three PCA factors. PC1, including linoleic acid (C18:2), oleic acid (C18:1n9), stearic acid (C18:0) and tetracycline acid (C24:0); PC2, including palmitic acid (C16:0) and linolenic acid (C18:3); and PC3, including oleic acid (C18:1n12), eicosanoic acid (C20:0) and eicosaenoic acid (C20:1). The three principal components explained 42.721%, 30.426% and 16.435% of the total variation, respectively, and 89.852% together. According to the membership function value and weight of each factor, we conducted comprehensive evaluation and ranking of safflower oils by the main nutritional quality indicators. The top ten safflower germplasms with the highest comprehensive quality evaluation scores were sample 09 from Xinjiang, sample 24 from Yunnan, sample 05 from Sichuan, sample 41 from Liaoning, sample 66 from Fengqiu, sample 55 from Weihui, sample 32 from Hebei, sample 71 from Bozhou safflower, sample 22 from Yanjin, and sample 78 from Jiangsu.
HPLC Fingerprinting and Chemical Pattern Recognition of Brown Sugar, White Granulated Sugar, Red Granulated Sugar and Black Sugar
CAI Weiqi, ZUO Wenwen, LU Yang, HUANG Shengliang, LI Cunyu,, ZHENG Yunfeng,, PENG Guoping
2021, 42(6):  250-255.  doi:10.7506/spkx1002-6630-20200324-358
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In this study, high-performance liquid chromatography (HPLC) fingerprints of brown sugar, black sugar, red granulated sugar, and white granulated sugar were established, and pattern recognition was performed on them. A Durashell C18-AM hydrophilic column (250 mm × 4.6 mm, 5 μm) was used for the analysis. Acetonitrile-trifluoroacetic acid water was used as the mobile phase at a flow rate of 1.0 mL/min. The column temperature was set at 25 ℃. The injection volume was 10 μL. The detection wavelength was 210 nm. The obtained results were analyzed by cluster analysis (CA), principal component analysis (PCA), and orthogonal partial least squares-discriminant analysis (OPLS-DA). The results showed that 13 peaks were shared among the fingerprints of 10 batches of brown sugar samples, 1 peak among 7 batches of white granulated sugar samples, 7 peaks among 10 batches of red granulated sugar samples, and 17 peaks among 3 batches of black sugar samples. Six differential components were identified by OPLS-DA. In conclusion, the method is stable and reliable, and can clearly distinguish among brown sugar, black sugar, red granulated sugar and white granulated sugar, enabling it to be used for quality control and evaluation of these foods.
Combined Use of GC-MS, GC-O and Electronic Nose Technology to Evaluate the Aroma Characteristics of Passion Fruit Wine
CHENG Hongzhen, CAI Zhipeng, WANG Jing, SHEN Yonggen, LU Jianqing, LI Xiaoming, LIU Fuyuan, Xu Xian, AN Zhaoxiang
2021, 42(6):  256-264.  doi:10.7506/spkx1002-6630-20200319-286
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The aroma characteristics of wines made from whole passion fruits and its juice were evaluated by using headspace solid-phase microextraction coupled to gas chromatography-mass spectrometry (HS-SPME-GC-MS), gas chromatography-olfactometry (GC-O) and electronic nose technology. The results showed that a total of 78 aroma components, including 21 alcohols, 21 esters, 10 terpenes, 7 ketones, 4 aldehydes, 3 ether acids and 12 other substances, were identified in passion fruit juice and the two wines; a total of 27 characteristic aroma components were identified by GC-O combined with aroma intensity method, including 12 alcohols, 7 esters, 4 terpenes, 2 ketones, 1 acid and 1 aldehyde. There were significant differences in aroma intensity among the three samples (P < 0.05). In total, 15, 18 and 19 aroma components with odor-activity value (OAV) greater than 1 were found in the juice and wines made from passion fruit juice and whole fruits, respectively. Linalool, β-violone and ethyl hexanoate were the most important aroma components. Principal component analysis (PCA) showed clear discrimination among the three samples. Linear discriminant analysis (LDA) showed that there were overlaps in flavor between the wines, but they were distinct from the juice.
Analysis of Volatile Components in the Heartwood of Quercus liaotungensis Koidz and Q. mongolica Fisch
NIU Jianming, ZHANG Bo, WU Juandi, AN Shuangdi, MA Chaoling, SHI Xiao, HAN Shunyu
2021, 42(6):  265-273.  doi:10.7506/spkx1002-6630-20200228-315
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This study aimed to investigate the volatile components of the heartwood of Quercus liaotungensis Koidz and Q. mongolica Fisch, both originating in China, by liquid-liquid extraction combined with gas chromatography-mass spectrometry (LLE-GC-MS). Five kinds of components, including furans, volatile phenol, phenolics, lactones and others, were preliminarily identified. Q. liaotungensis Koidz contained the largest number and amount (88 and 75 113.03 μg/kg) of volatile components, followed by Q. acutissima Caruth produced in France (79 and 70 940.18 μg/kg), and the number and amount of volatile components in Q. mongolica Fisch (77 and 52 967.62 μg/kg) were the smallest. Furthermore, principal component analysis (PCA) and heat map analysis showed that the Q. liaotungensis Koidz exhibited a high correlation between guaiacol and its derivatives, vanillin and syringaldehyde, and obvious flowery and fruity aroma characteristics, showing good application potential. Thus, it may be an alternative to traditional oak.
Analysis of Flavor Compounds of Maotai-flavor Baijiu Produced in Different Regions of the Chishui River Basin
TANG Ping, LU Jun, BI Rongyu, SHAN Qimuge, WANG Li, WANG Fan, LI Changwen
2021, 42(6):  274-281.  doi:10.7506/spkx1002-6630-20200330-434
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This study aimed to explore the differences in the flavor compounds of Maotai-flavor Baijiu produced in different regions of the Chishui river basin. Headspace-solid-phase microextraction/liquid-liquid extraction combined with gas chromatography-mass spectrometry (HS-SPME/LLE-GC-MS) was used to detect and analyze volatile aroma components in 56 representative samples collected from 5 different regions. The results showed that a total of 85 aroma components were detected in all samples, including 45 esters, 11 alcohols, 7 ketones, 8 aldehydes, 3 acids, 3 alkanes and 8 other compounds. The main aroma components of Maotai-flavor Baijiu were basically similar while their contents largely differed among the producing regions. A partial least squares-discriminant analysis (PLS-DA) model for discriminating Maotai-flavor Baijiu from different regions was established with 57 important aroma compounds as the key classification factors, which exhibited good classification, and further 20 factors with variable importance in the projection (VIP) > 1 were identified. The distribution of aroma components in Maotai-flavor Baijiu from different regions was characterized by hierarchical cluster analysis (HCA) and heat map analysis.
Analysis of Sensory Characteristics and Flavor Components in Light-flavor Chinese Liquor (Baijiu) Made with Xiaoqu Starter by Modern and Traditional Technologies
SUN Xizhen, DU Jiawei, HUANG Pan, ZHANG Fan, LIU Yuancai
2021, 42(6):  282-290.  doi:10.7506/spkx1002-6630-20191129-297
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The flavor compounds and aroma profiles of light-flavor Baijius made with Xiaoqu starter by the modern and traditional technologies were analyzed by headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), gas chromatography-olfactometry-mass spectrometry (GC-O-MS) and sensory evaluation. A total of 116 compounds in the liquor made by the modern technology (JPXQL-M) and 121 compounds in that made by the traditional technology (JPXQL-T) were identified by comparison of their retention indices (RI) with those of reference standards. Among them, 49 odor-active compounds with flavor dilution (FD) factor ≥ 2 were further confirmed in the two liquors by aroma extract dilution analysis (AEDA). A total of 33 odor-active compounds in JPXQL-M and 34 odor-active compounds in JPXQL-T were identified according to odor activity value (OAV). According to the quantitative results, we performed aroma reconstruction experiments. Omission experiments was further performed, which revealed that the important odor-active compounds in JPXQL-M were ethyl octanoate, acetaldehyde, isoamyl acetate, 1,1-diethoxyethane, ethyl hexanoate, valeric acid, 1-octen-3-ol, ethyl acetate, isobutanol, ethyl isovalerate and that the important odor-active compounds in JPXQL-T were ethyl octoate, ethyl hexanoate, ethyl valerate, ethyl butyrate, acetaldehyde, isoamyl acetate, valeric acid, 1,1-diethoxyethane, isobutanol, ethyl acetate, n-propanol, and 1-octen-3-ol. The odor-active compounds in the liquors were basically similar. However, there was a marked difference in aroma intensity and OAV, and consequently in sensory evaluation and aroma characteristics.
Safety Detection
Isolation, Molecular Characteristics and Antimicrobial Susceptibility of Staphylococcus aureus inform the Production Chain of Goat Milk Powder
ZHANG Pengfei, FU Xueting, ZHAO Chunhua, LIU Xinyu, ZHANG Jie, ZHANG Meng, KOU Mingying, GE Wupeng, WANG Xin
2021, 42(6):  291-297.  doi:10.7506/spkx1002-6630-20191128-291
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To investigate the prevalence, molecular characteristics and antibiotic resistance of Staphylococcus aureus isolated from the key links in the goat milk powder processing chain, we collected samples from different production stages of a goat milk powder plant. The S. aureus isolates were identified by using selective culture as well as nuc gene amplification. Twenty-one virulence genes, 16 common antibiotics, staphylococcal protein A (SPA), multi-locus sequence typing (MLST) and pulsed field gel electrophoresis (PFGE) typing of the isolates were investigated. The results showed that among the 112 samples collected, 6 samples (5.4%) were contaminated by S. aureus, including processing equipment (2 samples), processing personnel (2 samples), tank milk (1 sample) and floor powder (1 sample). Each isolate carried at least one toxin gene, and the detection rate of the panton-valentine leukocidin (pvl) gene was the highest (100%, 6/6), followed by sea, sec, see, seh, sek and seq (50.0%, 3/6), seg, sej and ser (33.3%, 2/6) and sed, sei, sem and seo (16.7%, 1/6). All the isolates were resistant to at least four antibiotics, and the isolates were most commonly resistant to ampicillin, cefoperazone, trimethoprim/sulfamethoxazole and penicillin (100.0%, 6/6), followed by erythromycin and amoxicillin/clavulanic acid (83.3%, 5/6), tetracycline (50.0%, 3/6) and gentamycin (16.7%, 1/6). In addition, all the strains were sensitive to oxacillin, cefoxitin, vancomycin and linezolid. Four spa types and 3 ST types were detected in all the isolates, and ST1-t127 (50.0%, 3/6) was the most predominant clone, followed by ST5-t002, ST5-t548 and ST188-t189 (16.7%, 1/6). For PFGE typing, these strains could be divided into 3 large clusters (I, II and III) and 4 pulsotypes (A, B, C and D), among which the processing equipment and the floor powder shared the same PFGE typing. The results showed that there was S. aureus contaminations in the processing of goat milk powder. Moreover, the key links of contamination were tank milk, processing equipment, processing personnel and floor powder, and there were some cross-contaminations in different processing links. Although the contamination rate is relatively low, it is necessary to carry out a long-term investigation on microbial contamination in different processing links of goat milk plants. Investigation should be taken to confirm the key contamination links, which can provide us with useful information to effectively control the spread of S. aureus in goat milk powder products.
Rapid Determination of 17 Phthalate Acid Esters Residues in Vegetable Oils by Gas Chromatography-Electrostatic Field Orbitrap High Resolution Mass Spectrometry
MENG Zhijuan, HUANG Yunxia, LI Yan, SUN Wenyi, WANG Dong, LI Qiang, FAN Sufang, ZHANG Yan
2021, 42(6):  298-304.  doi:10.7506/spkx1002-6630-20191012-093
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A new method for simultaneous determination of the residues of 17 phthalate acid esters (PAEs) in vegetable oils by gas chromatography-electrostatic field orbitrap high resolution mass spectrometry (Orbitrap GC-MS) was developed. The oil samples were extracted by acetonitrile with a whirl instrument and the extracts were frozen at ?20 ℃ for 30 min, and then purified by dispersive solid phase extraction with ostade-cylsilane (C18) and primary secondary amine as sorbents (150 mg per 2.0 g of sample each). Accurate mass measurements of the target analytes in the full scan mode could eliminate matrix interference effectively. Four typical vegetable oils (soybean oil, peanut oil, olive oil and rapeseed oil) were evaluated by the developed method. Good linearity was observed for the 17 PAEs in the concentration range from 0.01 to 2.0 mg/L with correlation coefficients greater than 0.995 0. The limits of detection (LODs) were 0.005–0.010 mg/kg and the limits of quantification (LOQs) were 0.015–0.030 mg/kg. The average recoveries at spiked levels of 0.03, 0.20 and 0.50 mg/kg were in the range of 80.2%–109.5% in the four matrices, with relative standard deviations (RSDs) of 1.2%–9.8%. The contents of the 17 PAEs in 50 vegetable oil samples were determined by this method. The detection rates of diisobutyl phthalate (DIBP), dicyclohexyl phthalate (DCHP), dibutyl phthalate (DBP) and bis(2-ethylhexyl) phthalate (DEHP) were higher than those of the other compounds, and the detection rates in soybean oil and rapeseed oil were higher than those in the other samples. The method proved to be simple, sensitive and suitable for the rapid screening and confirmation of PAEs in vegetable oils.
Determination of Cyclamate in Pastries by Dual-Wavelength Rayleigh Light Scattering Technique
JIANG Hong, CHEN Minglang
2021, 42(6):  305-309.  doi:10.7506/spkx1002-6630-20191011-081
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A novel dual-wavelength Rayleigh light scattering (DWO-RLS) method for fast and accurate determination of the food additive cyclamate in cake, bread and biscuit was established. In the alkaline Tris-hydrochloric acid medium at pH 9.27, cyclamate reacted with brilliant green via electrostatic interaction to form an ionic association complex, leading to a distinctly enhanced RLS of the system, and producing a new RLS spectrum with two strong characteristic scattering peaks. The strong peak was located at 341 nm and the weak peak at 470 nm. There was a good linear relationship between the magnitude of enhanced RLS intensity (ΔIRLS) and cyclamate concentration in the range of 0.004 to 0.50 mg/L. The limits of detection (LOD) were 0.003 6 and 0.004 0 mg/L at 341 and 470 nm, respectively. The limits of quantitation (LOQ) of the DWO-RLS method were 1.05, 0.974 and 0.994 mg/100 g for cake, biscuit and bread, respectively. The recoveries of spiked samples were in the range from 97.3% to 103%, and the relative standard deviations (RSD, n = 5) ranged from 1.1% to 2.6%. The method was simple, rapid and highly sensitive, and it was applied to actual samples analysis with satisfactory results.
Determination of Multiple Organophosphorus Pesticide Residues in Fruits and Vegetables by Molecularly Imprinted Array Solid Phase Microextraction
CHU Yaojuan, ZHANG Xuena, XIANG Xiaozhe, LI Xiujuan
2021, 42(6):  310-315.  doi:10.7506/spkx1002-6630-20200327-398
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Two types of molecularly imprinted solid phase microextraction fibers were fabricated through sol-gel method using diazinon and isocarbophos as the templates, respectively, and were assembled together to constitute a molecularly imprinted array solid phase microextraction device. The device was then used in combination with gas chromatography for the determination of five organophosphorus pesticide residues in fruits and vegetables. The proposed method exhibited very low limits of detection, ranging from 0.002 8 to 0.043 6 μg/kg, lower than those obtained by using a single molecularly imprinted solid phase microextraction fiber. The recoveries of five analytes in spiked apple and potato samples were 78.7%–122.8%. The study showed that the molecularly imprinted array solid phase microextraction device had the advantages of high extraction efficiency, high sensitivity, good accuracy and selectivity, and high throughput, and could be suitable for simultaneous determination of multiple analytes in complex matrices.
Preparation and Application of Molecularly Imprinted Electrochemical Sensor for Rapid Detection of Quinoxaline Drug Residues
TIAN Jingsheng, LI Dongdong, ZHAO Lingyu, GAO Wenhui
2021, 42(6):  316-324.  doi:10.7506/spkx1002-6630-20200721-286
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A novel molecularly imprinted electrochemical sensor for rapid?detection of quinoxaline drugs was prepared using nanosized silver sol and graphene as electrode modification materials, olaquindox as template molecule, and o-aminophenol and resorcinol as composite functional monomers. Using ultraviolet (UV) absorption spectroscopy, we selected the optimal functional monomer, and studied the interaction between template molecule and functional monomer. The preparation conditions were optimized by electrochemical analysis and the analytical performance of the sensor was evaluated. The template molecules were efficiently eluted in 20 min with ethanol-0.4 mol/L NaOH aqueous solution (3:1, V/V). The contents of four quinoxaline growth promoters were indirectly determined by measuring changes in response current with K3[Fe(CN)6] as electroactive probe. The results showed that the sensor displayed high sensitivity and selectivity to olaquindox, and could also specifically adsorb its structural analogues; the recoveries of spiked samples were between 89.05% and 100.86% with relative standard deviations (RSDs) of 1.03%–3.11% (n = 5), and the sensor was successfully applied to sensitive and rapid detection of quinoxaline growth promoter residues in animal origin foods.
Isolation and Identification of Pathogenic Microorganisms Causing Postharvest Spoilage in Hami Melons
ZHAO Xinxin, NING Ming, ZHANG Qin, CAI Wenchao, SHAN Chunhui, TANG Fengxian
2021, 42(6):  325-335.  doi:10.7506/spkx1002-6630-20200102-023
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To investigate the relationship between microorganisms and postharvest spoilage of Hami melons, with traditional cultivation of microorganisms, we studied the dynamic changes of cultivatable microorganisms on Hami melons during storage at different temperatures. It was found that the main pathogenic bacteria causing postharvest spoilage of Hami melons were mycetes, including Fusarium, Alternaria, Penicillium, and Staphylococcus. The dominant pathogens causing spoilage in Hami melons during refrigerated transport and storage were Penicillium and Fusarium. This study indicated that postharvest spoilage in Hami melon was caused by single pathogenic bacteria and interactions among multiple pathogenic bacteria through a complicated mechanism. This study is conducive to a better understanding of the dynamics of microbial community during the storage of Hami melon fruit. Further study should be conducted to monitor characteristics of spoilage-related species isolated from Hami melons so as to restrict the growth of pathogens and extend the shelf-life of Hami melons, which will provide theoretical foundation for improvements in the existing post-harvest preservation technology.