Table of Content

15 April 2020, Volume 41 Issue 7
Basic Research
Inhibitory Effect of Lactic Acid on Biofilm Formation of Enterobacter cloacae
LIU Yawen, JIN Panpan, XU Xiaoxi, LIU Fang, SUN Zhilan
2020, 41(7):  1-7.  doi:10.7506/spkx1002-6630-20190222-143
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The inhibitory activity of lactic acid against the biofilm formation of Enterobacter cloacae CY4 was evaluated by a crystal violet staining assay, and its potential molecular mechanism was explored by studying cell swimming and swarming motilities, exopolysaccharide production, biofilm microstructure and gene expression levels. The results showed that lactic acid at subinhibitory concentrations could significantly inhibit biofilm formation and decrease cell swimming and swarming motilities of E. cloacae CY4 (P < 0.05), as well as decrease biofilm polysaccharide production. Laser confocal microscopy and scanning electron microscopy showed that lactic acid at subinhibitory concentrations could greatly reduce the thickness of the biofilm and increase its surface roughness and porosity, as well as loosen the biofilm structure with greater cell length and wider gaps between cells. Lactic acid decreased the expression of genes involved in the synthesis of pili and polysaccharides as evaluated by real-time polymerase chain reaction (PCR). This study demonstrates that lactic acid has a significant inhibitory effect on biofilm formation of E. cloacae CY4, which may be related to its influence on cell adhesion and aggregation, and the production of extracellular polysaccharides.
Extraction and Antioxidant Activity of Different Polyphenols from ‘Changhei’ Hulless Barley
ZHU Yulin, YANG Shihua, HUANG Yonghua, LI Yongqiang, ZHANG Jianping, LI Qing, CHEN Bi, CHU Yajie, LI Chun, HUANG Aixiang
2020, 41(7):  8-13.  doi:10.7506/spkx1002-6630-20190408-083
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In this study, total soluble, free, esterified, etherified and insoluble bound polyphenols were extracted and separated from ‘Changhei’ hulless barley kernels. The contents of polyphenol and flavonoids and antioxidant activities in vitro were determined. Moreover, the composition of phenolic compounds was quantitatively and qualitatively analyzed by high performance liquid chromatography (HPLC). The results showed that the polyphenol contents of the total soluble, free, esterified, etherified and insoluble bound polyphenol-rich extracts ranged from (1.97 ± 0.06) to (16.97 ± 0.25) μmol/g and the flavonoids contents from (0.14 ± 0.04) to (1.08 ± 0.11) μmol/g. The contents of polyphenols and flavonoids in the total soluble polyphenol-rich extract were significantly higher than those in the other four polyphenol-rich extracts, and insoluble bound polyphenols were significantly more abundant than free, esterified and etherified polyphenols (P < 0.05). The ferric reducing antioxidant power, 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity and Trolox equivalent antioxidant capacity of the total soluble polyphenols were the highest among the 5 polyphenols, and the insoluble bound polyphenols were significantly stronger antioxidants than the free, esterified and etherified polyphenols. Similarly, the hydrogen peroxide scavenging activity of the insoluble bound polyphenols was significantly higher than that of the other four polyphenols (P < 0.05). There was a significantly positive correlation between the polyphenol contents and the antioxidant activity (R2 = 0.880–0.998). A total of 18 phenolic compounds were identified including hydroxybenzoic acid, hydroxycinnamic acid and flavonoids, with protocatechuic acid, ferulic acid and catechin being the most abundant ones. It can be concluded that hulless barley, with abundant phenolic compounds, can be regarded as a potential antioxidant value-added functional food ingredient.
Preparation and Characterization of Phytoglycogen-Quercetin Complex
WEI Qianqian, FAN Jinling, ZHU Wenxue, BAI Xiting, REN Guoyan
2020, 41(7):  14-22.  doi:10.7506/spkx1002-6630-20190307-096
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In this paper, phytoglycogen (PG) was used as a carrier to load quercetin (Qu) to prepare phytoglycogen-quercetin (PG-Qu) complex. The solubility enhancing effect of PG-Qu complex on Qu was studied. The antioxidant activity of PG-Qu complex and its inhibition on cancer cells were investigated. Dynamic laser light scattering, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to analyze the particle size characteristics, morphology and molecular interaction of the complex. The results showed that PG was a high-efficiency carrier of Qu, and the formed PG-Qu complex significantly improved the apparent solubility of Qu (P < 0.05). The loading efficiency was related to the concentration of PG and Qu. Alkaline condition was beneficial to the loading of PG onto Qu. The presence of NaCl and acetate did not affect the formation of complexes. PG-Qu complex was prepared from 5 mg/mL PG solution and ethanol solution containing 6 mg/mL of Qu at pH 8 without phosphate, which could be lyophilized and reconstituted. When the PG concentration was 50 mg/mL, the solubility of Qu was 509.46 μg/mL, loading capacity 9.68 μg/mg, and loading efficiency 79.88%. Compared with free Qu, the total reducing power, hydroxyl radical scavenging capacity of PG-Qu complex and its inhibitory activity against MCF-7 and A549 cells were significantly improved. Both PG and PG-Qu complex had a smooth spherical structure; the average particle size of the complex was 68–72 nm, and the particle size distribution was uniform. The zeta potential of PG decreased from ?4.12 to ?10 mV after being loaded with Qu. Qu existed in the amorphous form in PG-Qu complex; hydrogen bonding is the main driving force for the interaction between Qu and PG. Therefore, PG is a highly efficient carrier and the preparation of PG-Qu complex is simple, which can significantly improve the apparent solubility, antioxidant activity and anticancer activity of Qu. The preparation of PG-Qu complex is expected to be an important way to maintain the biological effects of Qu and broaden its application in the food industry.
Effects of Preparation Conditions on the Formation of Gellan Gum Fluid Gels
CHEN Qing, LI Rong, ZHOU Taotao, CHENG Hongmei, HAN Xiaoxiang
2020, 41(7):  23-29.  doi:10.7506/spkx1002-6630-20190306-060
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Low acyl gellan gum (LAG) fluid gels were prepared via heat-induced gelation of LAG solution under controlled temperature and shear conditions, and their properties were evaluated with respect to gellan gum concentration, cooling rate, shear rate, ion type and concentration, and glucono-δ-lactone (GDL). The microstructure of the gels was investigated as well. The results indicated that increased gellan gum concentration increased the transition temperature for the system, resulting in fluid gels with increased particle size, final viscosity and irregularity. When the cooling rate exceeded the critical value for the gel system, the transition temperature substantially remained unchanged. The critical cooling rate declined with increasing gellan gum concentration, decreasing from 9 to 4 ℃/min when gellan gum concentration increased from 0.005 to 0.015 g/mL. The transition temperature and the final viscosity and particle size of fluid gels increased with increasing ion concentration. Ca2+ led to a higher final viscosity than did Na+. The higher GDL concentration resulted in higher transition temperature and higher viscosity and looser texture of fluid gels.
Relationship between Soybean Protein and Qianye Tofu Quality
WANG Xibo, NIE Xin, LIAO Yi, LUO Jiaqian, Lü Xiuli, LIU Jishan, LIU Jun, WANG Zhongjiang, TENG Fei, LI Liang, LI Yang
2020, 41(7):  30-37.  doi:10.7506/spkx1002-6630-20190319-248
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In order to establish the relationship between soybean protein and the quality of Qianye tofu, this study used amino acid analysis, Fourier transform infrared spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis to analyze the amino acid composition, secondary structure and subunit composition of soybean proteins from 16 varieties. In addition, the texture properties, sensory properties and microstructure of Qianye tofu produced from each variety were tested by texture profile analysis, sensory evaluation and scanning electron microscope. The results indicated that high-quality Qianye tofu was produced from soybean protein varieties with higher values of sulfur-containing amino acids (methionine and cysteine), parallel β-sheet, and 11S/7S ratio, greater than (2.81 ± 0.02)%, (39.96 ± 0.57)% and 1.88 ± 0.16, respectively. This illustrated that the composition of soybean protein, especially sulfur-containing amino acids, parallel β-sheet and 11S/7S ratio could make critical contributions to Qianye tofu quality.
Analysis of Protein Subunit Composition and Quality Characteristics of Peanut Varieties (Lines) Grown in Xinjiang
YUAN Qiuyan, LIU Hongzhi, ZHANG Jian, LI Limin, WU Bin, WANG Qiang
2020, 41(7):  38-45.  doi:10.7506/spkx1002-6630-20190220-117
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The protein subunits from 36 peanut varieties grown in Xinjiang were analyzed by sodium dodecyl sulphate polyacrylamide gel electrophoresis and the quality characteristics of peanut protein isolates were also explored. The data obtained were subjected to correlation and cluster analysis. The results showed that there was a large genetic variability in the proportion of protein components among peanut varieties. The protein subunits were significantly different among peanut varieties, with the largest difference being observed in the 35.5 kDa subunit of arachin. Six (16.67%) of the 36 peanut varieties such as ‘Jihua 10’ were found to lack the 35.5 kDa subunit. The quality characteristics of peanut protein isolates varied among germplasm materials. The coefficient variations of water-holding capacity, solubility and other indicators but not of protein purity were greater than 10%, indicating considerable differences in protein quality characteristics among varieties. Correlation analysis showed that there was a significantly negative correlation between arachin and conarachin (r = ?1.000, P < 0.01), and protein solubility was significantly negatively correlated with gel hardness (r = ?0.498, P < 0.01). Cluster analysis showed that the 36 peanut varieties (lines) could be divided into five classes at the level of D2 = 5. Among them, the protein solubility of class II and the protein gel hardness and cohesiveness of class IV were better, making them worthy of popularization.
Action Mechanism of Oregano Essential Oil against Staphylococcus saprophyticus
CHEN Mengling, LAN Weiqing, LI Hanxiao, REN Zhichu, LU Zixuan, XIE Jing
2020, 41(7):  46-51.  doi:10.7506/spkx1002-6630-20190311-131
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The action mechanism of oregano essential oil (OEO) against Staphylococcus saprophyticus was investigated in this paper. The minimum inhibitory concentration (MIC) was determined by measuring inhibition zone diameter using the agar well diffusion method, and bacterial growth curve, electrical conductivity, alkaline phosphatase (AKP) activity, lactate dehydrogenase (LDH) activity, ultraviolet absorption and scanning electron microscopy (SEM) were used to evaluate the antimicrobial effect of OEO. The results showed that the MIC of OEO against Staphylococcus saprophyticus was 0.25%. When treated by OEO at MIC or 2 MIC, the logarithmic phase was delayed obviously, accompanied by the leakage of intracellular contents and increased significantly activities of AKP and LDH. The bacterial growth was concentration-dependently inhibited by OEO, with structural changes of the cell wall and membrane being observed. The SEM results revealed that the bacterial cells appeared morphologically deformed after being treated with OEO at MIC for 6 h, and OEO at 2 MIC caused cell surface disruption, outer membrane detachment and finally cell death. Our findings support that OEO exerts its bacteriostatic effect by destroying the integrity of the cell wall and membrane.
Structural Characterization and Hypoglycemic Activity in Vitro of Ulva pertusa Polysaccharides-Zinc Complex
TANG Chenpeng, Lü Feng, WANG Ronglin
2020, 41(7):  52-58.  doi:10.7506/spkx1002-6630-20190320-263
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The physicochemical properties and structure of Ulva pertusa polysaccharides before and after complexation with zinc ions were determined by gas chromatography-mass spectroscopy, gel permeation chromatography-multi-angle laser light scattering-refractive index detection, Congo-red test, ultraviolet-visible (UV-VIS) spectroscopy, infrared spectroscopy, X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy. The inhibitory effect of the polysaccharide-zinc complex on α-glucosidase and α-amylase was investigated. Results showed that Ulva pertusa polysaccharides were composed of rhamnose, fucose, xylose, mannose, glucose and galactose, with a molar ratio of 1.00:0.06:0.93:0.45:2.29:0.07. After the complexation reaction, the molecular mass and total sugar content of the polysaccharides were decreased, and the triple-helical structure disappeared. Zn2+ reacted with –COO-, –CH3, –OSO3- in the polysaccharides. The surface morphology of Ulva pertusa polysaccharides changed apparently, the molecular size was decreased, and the molecular aggregation ability was enhanced after complexation with zinc ions. The inhibitory effect of Ulva pertusa polysaccharides-zinc complex on α-glucosidase and α-amylase was stronger than that of the native polysaccharides. These results confirmed that the structure of Ulva pertusa polysaccharides changed obviously after complexation with zinc ions, and the hypoglycemic activity in vitro was enhanced.
Molecular Structure and Antimicrobial Mechanism of Mesenterocin ZLG85, a Bacteriocin Produced by Leuconstoc mesenteroides subsp. mesenteroides against Salmonella typhi
GAO Yurong, LI Dapeng, ZHANG Fengqin, SONG Junmei
2020, 41(7):  59-65.  doi:10.7506/spkx1002-6630-20190311-133
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Mesenterocin ZLG85 is a novel bacteriocin produced by Leuconstoc mesenteroides subsp. mesenteroides ZLG85, isolated from fermented cucumber. The molecular mass, amino acid sequences and secondary structure of mesenterocin ZLG85 were analyzed by liquid chromatography-mass spectrometry, the Edman method and circular dichroism (CD) spectroscopy. Some of its physicochemical properties were calculated by ProParam tool. The antimicrobial mechanism of mesenterocin ZLG85 against Salmonella typhi as a type strain was explored by evaluating its effects on the leakage of ultraviolet (UV)-absorbing materials, trans-membrane electrical potential and cell membrane permeability. Results showed that the molecular mass of mesenterocin ZLG85 was 2 522.5 Da, and its amino acid sequences differed from those of other reported bacteriocins. Anti-parallel structure, β-sheet and random coil were the major secondary structures of mesenterocin ZLG85, accounting for 32.70%, 20.70% and 36.40%, respectively. This bacteriocin had good stability. It could lead to the leakage of UV-absorbing materials at 260 and 280 nm from the bacterial cells, depolarization of trans-membrane electrical potential, and cause pore formation in the cell membrane and consequently increased cell membrane permeability.
Distribution of Substitution Groups in Acetylated and Hydroxypropylated Wheat Starch after Chemical Surface Gelatinization
ZHAO Kai, LIU Ning, LI Jun, LEI Ming, CHEN Wei, YANG Chunhua, CHEN Fenglian
2020, 41(7):  66-72.  doi:10.7506/spkx1002-6630-20190328-347
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Chemical surface gelatinization (CSG) technique was employed to unravel uncover the location of acylation and hydroxypropylation groups in wheat starch granules and the change of molecular mass of wheat starch. Granule properties, molecular mass and substitution group distribution were determined using scanning electron microscopy and gel permeation chromatography. The results indicated that: as theincrease in degree of surface gelatinization increased, the particle surface became rough and showed obvious peeling; the remaining part was still in the granular state. The total carbohydrate content and blue value were decreased after CSG and the remaining granules showed a decreased amylose content. The substitution degree of the remaining granules of mono and dual modified starches decreased with increasing duration of CSG treatment. The higher the gelatinization degree of the outer layer, the lower the degree of substitution of the remaining granules indicating that acetylation and hydroxypropylation modifications occur mainly in the outer part of the granule and the substitution groups primarily exist on the surface of both modified starch granules.
Determination and Analysis of Functional Characteristics of Alfalfa Stems and Leaves
LAI Sitong, CUI Qingliang, LIU Jinlong, LIU Junli, SUN Deng
2020, 41(7):  73-78.  doi:10.7506/spkx1002-6630-20190416-205
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The chemical components of stems and leaves from different positions were determined, and the functional characteristics, specific surface area, pore size, chemical groups and surface ultrastructure of alfalfa leaf powders with different particle sizes were measured. The results showed that the contents of soluble dietary fiber, protein, fat and ash in alfalfa leaves were higher than those in stems, with the highest values being found in upper leaves, which were 12.25%, 28.62%, 6.23% and 11.35%, respectively. As the particle size decreased in the range of 0.063–0.250 mm, water-holding capacity and swelling capacity first increase and then decrease, reaching their maximum values of 5.57 g/g and 4.40 mL/g, respectively when the particle size was 0.125–0.160 mm; oil-holding capacity decreased from 2.83 to 1.84 g/g; cation exchange capacity, cholesterol adsorption capacity and sodium nitrite adsorption capacity gradually increased. Specific surface area, cumulative pore volume and the number of some chemical groups increased, while the most probable pore diameter decreased. Alfalfa leaf powder with particle size of 0.125–0.160 mm had better water-holding capacity and expansibility and was therefore suitable for developing functional foods to improve intestinal functions and prevent obesity. In contrast, alfalfa leaf powder with particle size of 0.063–0.080 mm had better adsorption capacity for cholesterol and sodium nitrite and cation exchange capacity, making it suitable for use in functional foods to prevent hypertension, heart disease and cancer.
Food Engineering
Functional Characteristics of Oleosin Affected by Ultrasound-Assisted Alkali Treatment
SUN Yufan, QI Baokun, ZHONG Mingming, LIU Zhao, YANG Shuchang, LI Yang,
2020, 41(7):  79-85.  doi:10.7506/spkx1002-6630-20190408-075
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In order to improve the functional properties of oleosin, the effects of alkali and ultrasonic treatments alone and in combination on the structure, solubility and emulsifying properties of oleosin were studied. The mechanism of structural changes of protein aggregates under different treatment conditions was also discussed. The microstructure, hydrodynamic radius, internal structure and spatial structure of modified oleosin were studied by atomic force microscopy, dynamic laser scattering, fluorescence spectroscopy and circular dichroism microscopy. The results showed that ultrasonic treatment could promote the transformation of oleosin from insoluble aggregates to soluble ones, and the solubility of oleosin subjected to ultrasonic treatment alone or in combined with alkali treatment increased by 124% and 162% compared to the control, respectively (P < 0.05). Circular dichroism and fluorescence spectroscopy showed that both ultrasonic and alkali treatments could promote the unfolding of protein structure, thus promoting the exposure of more hydrophobic groups such as tyrosine and tryptophan. Compared with the control group, the α-helix content of oleosin increased by 17.7% and the β-folding content decreased by 9.2% after the combined treatment. At the same time, the particle size decreased (286.0 nm) and the emulsifying properties improved (emulsion stability index of 575.0 g/m2, and emulsifying activity index of 605.4 min). This study provides a reference for improved functions of oleosin.
Moisture Migration Properties and Quality Changes of Fresh In-Shell Peanuts during Hot Air Drying
LU Yingjie, REN Guangyue, DUAN Xu, ZHANG Ledao, LING Zhengzheng
2020, 41(7):  86-92.  doi:10.7506/spkx1002-6630-20190311-134
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In order to improve the quality of fresh in-shell peanut during hot air drying process, water migration characteristics and quality changes during hot air drying at different temperatures (40, 50 and 60 ℃) were investigated in the present study. The results showed that during the hot air drying process, the moisture content of fresh in-shell peanut changed significantly, and the content of weakly bound water decreased gradually. As the drying process progressed, the network structure of both peanut kernels and shells was deformed, and the porosity increased, which increased with increasing drying temperature. The drying process took place in the falling rate period. The drying time required to reach a moisture content within the safe limit was reduced by 45% when the drying temperature increased from 40 to 60 ℃, indicating that increasing temperature is helpful to accelerate the dehydration rate. In addition, under the influence of water content, the hardness of peanut kernels first increased, then decreased and finally increased once again at higher drying temperatures, and continuously increased at lower drying temperatures, while the hardness of peanut shells first decreased and then increased. According to the correlation analysis, the dry-basis moisture content was significantly positively correlated with the amplitude of low-field nuclear magnetic resonance signal (P < 0.01), negatively correlated with the porosity of peanut kernels and shells (P < 0.01) as well as the hardness of peanut kernels (P < 0.05). This paper provides a theoretical basis for the real-time monitoring of moisture during the hot air drying process of fresh in-shell peanuts and for high-quality drying.
Multi-Scale Structure and Physicochemical Properties of Highland Barley Starch Following Dry Heat Treatment
BIAN Huawei, ZHENG Bo, CHEN Ling, ZHU Huilian
2020, 41(7):  93-101.  doi:10.7506/spkx1002-6630-20181107-085
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In this study, changes in the multi-scale structure and physicochemical properties (digestibility and pasting properties) of highland barley starch before and after dry heat treatment (DHT) under alkaline conditions at different pH levels were explored by scanning electron microscopy, particle size and distribution analysis, small-angle X-ray scattering, X-ray diffraction and gel permeation chromatography. The results indicated that with the increase in pH value, DHT decreased the viscosity and retrogradation value but increased the paste stability of the starch paste. These changes resulted from an increase in starch highly-ordered structures and crystallinity and the rearrangement of degraded starch molecules. Moreover, the DHT starch possessed greater proportions of slowly digestible starch (SDS) and resistant starch (RS). The degraded starch with a molecular molar mass below 2 × 107 g/mol showed increased helix content, greater crystallinity with a more ordered crystalline lamellae, promoting SDS and RS formation. Overall, these results suggest that DHT is a promising approach for the regulation of starch digestibility with suitable pasting properties, which can provide valuable information for the rational design of highland barley starch-based products.
Comparative Experimental Study on Freeze Concentration and Vacuum Evaporation Concentration of Apple Juice
Frank G. F. QIN, DING Zhongxiang, YUAN Jiaojiao, JIANG Runhua, HUANG Simin, SHAO Youyuan
2020, 41(7):  102-109.  doi:10.7506/spkx1002-6630-20190129-376
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In this study, the freezing concentration and vacuum evaporation concentration of apple juice were compared and analyzed by using a prototype of a multi-pass intelligent freeze concentrator and a rotary vacuum evaporator. The freeze concentrator works in suspension crystallization mode and integrates the traditional separated unit operations: scraper heat exchanger, crystallizer and washing column to form a trinity compact structure. Its concentration ratio in a single pass was about 1.8. After three-pass freeze concentration, the concentration of apple juice increased from 10.5 to 34.5 °Brix. The retention rates of vitamin C and butyl acetate as an aromatic component were above 90%. At the same time, it had little effect on reducing sugar damage and the color of the juice. In addition, the distribution coefficients of soluble solids in ice crystals and mother liquor ranged from 0.008 1 to 0.067 0. The recovery yield of soluble solids was 98% and the loss of soluble solids was about 2% after three-pass freeze concentration. Parallel comparative experiments of apple juice concentration by vacuum evaporation showed that when the concentration of apple juice was 33.6 °Brix, the retention rates of vitamin C and butyl acetate were 84.5% and 43.9%, respectively. Therefore, freeze condensation was much better than evaporation concentration in terms of nutrition and flavor preservation.
Effect of Jet Cavitation on Physicochemical Properties and Structure of Soy Protein Isolate
BAI Yin, GAO Yue, WANG Zhongjiang, JIANG Zhongyang, MENG Fandi, JIANG Lianzhou
2020, 41(7):  110-116.  doi:10.7506/spkx1002-6630-20190304-028
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In this paper, the effects of different durations of jet cavitation treatment (2, 4, 6, 8 and 10 min) on the structure and physicochemical properties of soy protein isolate (SPI) was studied by Fourier transform infrared spectroscopy, fluorescence spectroscopy, the Lowry method, and the fluorescent probe 8-anilino-1-naphthalene sulfonate, and the underlying molecular mechanism was determined. The results showed that the secondary structure of SPI changed with the prolongation of jet cavitation time, and the β-sheet structure gradually transformed to α-helix, and the polarity of the microenvironment of tryptophan residues increased. The solubility, emulsifying capacity, oil-holding capacity and surface hydrophobicity were significantly increased with jet cavitation time (P < 0.05), while turbidity and water-holding capacity decreased gradually due to the over-treatment effect. Therefore, jet cavitation technology can effectively improve the physicochemical properties of SPI, and provide a new research direction for protein modification, which is beneficial to industrial utilization.
Effects of Radio Frequency Treatment on Short- and Medium-Wavelength Infrared Drying Kinetics and Quality Characteristics of Red Jujubes
WANG Kunhua, LI Jiamei, PENG Fei, LIU Yudi, MA Qi, LI Mei, XU Huaide
2020, 41(7):  117-123.  doi:10.7506/spkx1002-6630-20190403-045
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Radio frequency (RF) technology was applied as a pretreatment for drying to shorten the drying process and improve the quality of dried red jujubes. Specifically, short- and medium-wavelength infrared drying was performed at 50, 60 or 70 ℃ to explore the drying kinetics and the quality characteristics of the dried red jujubes. In addition, the experimental results were fitted to eight common thin-layer drying models by nonlinear regression analysis and the optimum model was selected from these models. The results indicated that the drying time was shortened by 21.2%-29.3%; the effective diffusion coefficient of moisture was increased by 16.7%-49.6%; the activation energy of drying was reduced by 13.13% after RF treatment. In terms of correlation coefficient (R2), root-mean-square error (RMSE), and chi-square values (χ2), Weibull distribution was found to be the best model for describing and forecasting the short- and medium-wave infrared drying process following RF treatment of red jujubes. Comparatively, the color difference (ΔE) of dried jujubes after RF treatment decreased by 19.3%-31.4%, total phenol content increased by 14.9%-19.1%, and cyclic adenosine monophosphate content increased by 27.5%-31.9%. Compared with untreated jujubes, RF treated jujubes showed higher drying efficiency and better quality of dried products, indicating that RF is a promising pretreatment for dried jujube processing.
Effect of Different Sterilization Methods on Isoflavone Profile and Quality Characteristics of Ready-to-Eat Dried Soybean Curd (Tofu)
YE Tao, CHEN Zhina, YE Qianwen, LIU Huiqian, WANG Yun, LU Jianfeng
2020, 41(7):  124-130.  doi:10.7506/spkx1002-6630-20190304-040
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In order to explore the effects of different sterilization methods on the quality characteristics of ready-to-eat dried soybean curd (RTE-DSC), the impact of pasteurization (95 ℃ for 30 min), high-temperature sterilization (HTS; 121 ℃ for 15 min), high hydrostatic pressure (HHP; 400 MPa and 25 ℃ for 20 min) and pressure-assisted thermal sterilization (PATS; 400 MPa and 60 ℃ for 20 min) on the microbial load (total viable and coliform counts), texture, color, sensory quality, water-holding capacity and major soy isoflavone components of RTE-DSC coagulated with magnesium chloride was investigated. Total viable counts of RTE-DSC decreased to 420, 130, 180 and 120 CFU/g, respectively after pasteurization, HTS, HHP and PATS treatments, and no coliform bacteria were detected in all samples. Pasteurization had no significant effect on the texture of RTE-DSC (P > 0.05), but HTS, HHP and PATS could significantly increase the hardness by 68.04%, 36.51% and 43.02%, respectively (P < 0.05). The L value of RTE-DSC decreased from 80.99 to 74.76, and the a value increased from 3.24 to 3.70 after HTS; however, the other sterilization methods had no significant effect. In terms of sensory score, pasteurization and PATS had no significant effect on RTE-DSC (P > 0.05). The content of total isoflavones in unsterilized soybean curd was 1 031.8 μg/g (on dry basis). After pasteurization, HTS and PATS treatment, this value decreased significantly to 882.3, 846.1 and 893.8 μg/g (P < 0.05), respectively, but the effect of HHP (979.3 μg/g) was not significant (P > 0.05). Moreover, all treatments resulted in a decrease in total aglycone isoflavones, and heat treatment (pasteurization and HTS) resulted in greater losses. Therefore, PATS needs further research.
Nutrition & Hygiene
Protective Effect and Underlying Mechanism of Aplysin on Ethanol-Induced Liver Injury in Rats
CHANG Zhishang, LIU Ying, SU Ai, WANG Wencheng, XU Hongwei, JIANG Yushan, LIANG Hui
2020, 41(7):  131-139.  doi:10.7506/spkx1002-6630-20190227-215
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This study aimed to explore the protective effect of aplysin on ethanol-induced liver injury in rats and to explore the possible underlying mechanism from the perspective of the Toll-like receptor 4 (TLR4) signaling pathway. Male Wistar rats were randomly assigned into three groups: normal control, model control and aplysin-treated groups. The rats in the model control and aplysin-treated groups were given ethanol orally at 8 g/(kg·d) for two weeks, and then at 12 g/(kg·d) for another six weeks. The rats in the aplysin-treated group were administered with aplysin at 150 mg/(kg·d) via gavage one hour before ethanol for 8 weeks. After the last administration, all the animals were fasted with free access to water for 12 h and subsequently sacrificed; liver tissues were collected for histological and biochemical assessments; the levels of serum biomarkers for liver damage and endotoxin levels were detected with biochemical assay kits; primary rat Kupffer cells were cultured for assessment of their phagocytic activity with ink phagocytosis test. The mRNA expression levels of CD14, TLR4 and nuclear factor-kappa B (NF-κB) in Kupffer cells were assessed via reversed transcription polymerase chain reaction; the protein expression levels of TLR4, MyD88, NF-κB p65 and tumor necrosis factor-α (TNF-α) in Kupffer cells were assessed via western blotting; the levels of TNF-α and interleukin-1β (IL-1β) in Kupffer cells were measured by enzyme-linked immunosorbent assay. Aplysin relieved alcohol-induced hepatic histopathological changes, decreased plasma endotoxin levels and suppressed the elevation of liver damage biomarkers. Aplysin treatment effectively restored the phagocytic activity of Kupffer cells. Moreover, aplysin significantly decreased the expression levels of CD14, TLR4, MyD88, NF-κB p65 and TNF-α and the concentrations of TNF-α and IL-1β. These findings showed that aplysin exerted a potent hepatoprotective effect, which might be associated with the inhibition of the TLR4 signaling pathway.
Immunoregulatory Effect of Glycated Casein Digest in Normal Mice
SHI Jia, ZHAO Xinhuai
2020, 41(7):  140-145.  doi:10.7506/spkx1002-6630-20190318-216
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The Maillard reaction, also known as glycation, causes changes to the functional properties of proteins, but the impact of digests of the modified proteins on the immune status of normal mice has not been evaluated yet. In this study, glycated casein was prepared via the Maillard reaction between casein and lactose, and glycated and native casein were separately digested with trypsin. Normal mice were administered with either digest at doses of 100, 200, and 400 mg/kg mb for 28 days. At 24 h after the last administration, the mice in each group were sacrificed for measurement of immune indices such as spleen and thymus indices, hematological parameters, serum immunoglobulin (Ig) M, IgA, and IgG concentrations, lymphocyte proliferation, and natural killer (NK) cell activity. The results showed that the mice administered with the two digests had increased values of all evaluated indices compared with those mice administered with physiological saline (P < 0.05), indicating that the digests were able to improve the immune statue of the mice. Furthermore, the immuno-enhancing efficacy of native casein digest was higher than that of glycated casein digest. It is thus concluded that the Maillard reaction can weaken the enhancing effect of casein digest on the immune status of mice.
Improvement Effect of Mulberry Leaf Alkaloids on Hepatic Fibrosis Induced by Carbon Tetrachloride Combined with High-Fat Diet in Mice
WANG Zuwen, YANG Zhongmin, HUANG Xianzhi, DING Xiaowen
2020, 41(7):  146-152.  doi:10.7506/spkx1002-6630-20190314-181
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Objective: To study the improvement effect of mulberry leaf alkaloids on hepatic fibrosis induced by carbon tetrachloride (CCl4) combined with a high-fat diet in mice. Methods: Sixty male Kunming mice were randomly divided into six groups, normal control, model, positive control (100 mg/kg mb of silibinin), and gavage administration of mulberry leaf alkaloids at low, medium and high doses (50, 100 and 200 mg/kg mb). A mouse model of hepatic fibrosis was established by intraperitoneal injection of 10% CCl4 in olive oil combined with feeding of a high-fat diet for 8 weeks. After administration for 45 days, body mass and liver index were observed, and blood lipids, liver function-related indicators and fibrosis markers in plasma were measured. The histopathological characteristics of liver tissues were observed by hematoxylin-eosin staining. Results: Compared with the model group, liver index, the activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and the concentrations of total bilirubin (TBil) and direct bilirubin (DBil), total cholesterol (TC) and triglycerides (TG) and hepatic fibrosis markers such as hyaluronicacid (HA), laminin (LN), type IV collagen (IV-C) and type III precollagen (PC-III) in plasma were significantly decreased, and the levels of total protein (TP) and albumin (ALB) were significantly increased in the positive control group and the three treatment groups (P < 0.05). Body mass increased but not significantly in the above four groups (P > 0.05). Moreover, there was no significant difference between the high-dose group (200 mg/kg mb) and the positive drug group, and but neither restored the parameters investigated to normal levels. The histopathological examination showed that the degree of liver lesions in the positive control group and the three treatment groups was significantly reduced. Conclusion: Mulberry leaf alkaloids may improve hepatic fibrosis induced by CCl4 combined with high-fat diet as effectively as silibinin.
Comparative Protective Effect of Lipoic Acid and Resveratrol on Acetaminophen-Induced Cellular Oxidative Damage in HepG2 Cells
ZHAO Liyun, LIU Ailian, LIU Meiyu, REN Xiaofeng
2020, 41(7):  153-158.  doi:10.7506/spkx1002-6630-20190311-137
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Lipoic acid (LA) and resveratrol (RES) are two important natural antioxidant agents. Acetaminophen (APAP) is a common analgesic drug. However, excess administration of APAP may cause oxidative stress and liver damage. In this paper, an in vitro cell model was used to compare the antioxidant effects of RES and LA on APAP-induced oxidative damage in HepG2 cells, and to explore the underlying mechanisms. The aim of this study was to provide a technical basis for the prevention and treatment of liver damage caused by acetaminophen. The effects of different concentrations of LA and RES on APAP-induced apoptosis in HepG2 cells were detected by Cell Counting Kit-8 (CCK-8) method. The antioxidant activities of LA and RES were comparatively evaluated using cellular antioxidant activity (CAA) method. Flow cytometry was used to detect apoptosis. The content of malondialdehyde (MDA) and the activity of glutathione (GSH) and superoxide dismutase (SOD) were detected by enzyme labeling method. Quantitative real-time polymerase chain reaction (qPCR) and Western blot were used to detect the expression of the apoptosis-related genes Bax, Bcl-2 and caspase-3. Cytotoxicity test results showed that both resveratrol and lipoic acid could increase the viability of cells, and LA was more effective than RES. CAA results showed that LA inhibited dichlorofluorescein (DCF) production more strongly than did RES. The results of flow cytometry showed that both LA and RES could inhibit apoptosis induced by oxidative stress, and the effect of LA was stronger than that of RES. The results of enzyme labeling, qPCR and Western blot showed that LA and RES inhibited APAP-induced apoptosis by decreasing MDA content, increasing GSH and SOD activity, up-regulating Bcl-2 expression, and down-regulating Bax and caspase-3 expression, with LA being more effective than RES. To sum up, compared with RES, LA had a more protective effect on APAP-induced liver injury, and the underlying mechanism may be related to reducing oxidative stress and inhibiting apoptosis.
Effects of Wheat Oligopeptides on Antioxidant Function of Mice with Acute Alcoholism
YU Lanlan, LIU Wei, ZHOU Yalin, LI Yong, QIN Yong, LI Ruijun, XU Yajun
2020, 41(7):  159-163.  doi:10.7506/spkx1002-6630-20190321-285
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The effects of wheat oligopeptides on ethanol-induced oxidative damage and antioxidant indexes in serum and liver tissues of mice were evaluated to preliminarily determine whether wheat oligopeptides can improve the antioxidant status of mice with acute alcoholism. Sixty healthy male ICR mice were randomly divided into five groups by body mass: blank control group, model group, and low-, medium- and high-dose wheat oligopeptides intervention groups (0.4, 0.8 and 1.6 g/kg mb), and all these animals were administered by gavage for 30 days. After the last gavage, the mice in the model group and the three wheat oligopeptides intervention groups were fasted for 26 h and then re-gavaged with 50% ethanol aqueous solution at a dose of 12 mL/kg mb, while those in the blank group were not treated. The activity of total superoxide dismutase (T-SOD), and the levels of glutathione (GSH), malondialdehyde (MDA) and protein carbonyl (PC) in the serum and liver of all mice were determined after 6 hours. The results showed that compared with the model control group, the activity of T-SOD in liver was significantly increased in each intervention group (P < 0.01). In the low-dose wheat oligopeptide group, the contents of GSH in serum (P < 0.05) and liver (P < 0.01) were both significantly increased, and the content of PC in liver was significantly decreased (P < 0.05). Wheat oligopeptides at high dose could significantly reduce the content of MDA in serum (P < 0.05). These results suggest that wheat oligopeptides can enhance the antioxidant capacity in mice with acute alcoholism and have a protective effect on acute alcoholic liver injury in mice.
Protective Effect of Agaricus blazei Protein Peptides on D-Galactose-Induced Aging Model in Mice
FENG Qingxia, YAN Yuning, YANG Yi, ZHOU Jianing, LI Lebin, LU Xuechun, AN Liping
2020, 41(7):  164-170.  doi:10.7506/spkx1002-6630-20190319-249
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Objective: To explore the protective effect of peptides purified from an enzymatic protein hydrolysate from Agaricus blazei on D-galactose (D-gal)-induced aging in mice. Methods: The peptides were separated by ammonium sulfate precipitation and purified by Sephadex G-50 column chromatography. ICR mice were randomly divided into four groups: blank, model, positive control (piracetam) and Agaricus blazei protein peptide (ABPP) treatment. The aging model was established by injecting D-gal at a dose of 300 mg/(kg mb·d). Morris water maze and step-through tests were used to evaluate the learning and memory ability of mice. The serum levels of total antioxidant capacity (T-AOC), malondialdehyde (MDA), catalase (CAT) and reactive oxygen species (ROS) were detected. The structural changes of hippocampal neurons were observed by hematoxylin-eosin (HE) staining. The mRNA expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2), NAD(P)H:quinone oxidoreductase 1 (NQO1) and glutamate-cysteine ligase (GCLM) in brain tissues were detected by reverse transcription polymerase chain reaction (RT-PCR). Results: A significant chromatographic fraction from Sephadex G-50 was identified corresponding to a peptide. Compared with the model group, ABPP could significantly shorten the step-through latency and improve learning and memory capacity (P < 0.05 or P < 0.01), accompanied by a significant increase in the serum levels of CAT and T-AOC and a significant reduction in ROS and MDA levels (P < 0.05 or P < 0.01). HE staining results showed that the hippocampal neuron was closely arranged in the ABPP treatment group, and the number of cells with nuclear pyknosis was significantly reduced. The expression mRNA levels of Nrf2, NQO1 and GCLM in the ABPP treatment group were significantly increased (P < 0.05). Conclusion: ABPP can delay the aging process of mice, which may be associated with its anti-oxidation effect.
Packaging & Storage
Conversion of Lipid Metabolism Pathways during Storage of Tan Sheep Fat Evaluated by GC-MS and LC-MS
YUAN Yudong, LI Zixin, LUO Ruiming, JU Ning, YOU Liqin
2020, 41(7):  171-176.  doi:10.7506/spkx1002-6630-20181210-115
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The dynamic evolution of lipid metabolism in intramuscular fat of Ningxia Tan sheep during chilled storage for 12 days was investigated by combined use of gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) with the OmicsBean cloud platform. The results showed that the types of metabolism pathways increased at the beginning of storage, and then decreased. The metabolism pathways related to the flavor precursors oleic acid, palmitic acid and stearic acid were not different from day 0 to day 4, while the fatty acid biosynthesis pathways (P = 6.65 × 10-3 < 0.05) and the gonadotropin-releasing hormone (GnRH) signaling pathway (P = 4.67 × 10-2 < 0.05) were significantly different from day 4 to day 8; the biosynthesis pathways of unsaturated fatty acids pathway significantly differed from day 4 to day 8 (P = 5.87 × 10-5) but not from day 0 to day 4 (P = 3.24 × 10-1). From day 8 onward, the fatty acid biosynthesis pathways and the GnRH signaling pathway were not different, and the biosynthesis pathways of unsaturated fatty acids were not significantly different (P = 1.57 × 10-1). At the early stage of storage, no difference in the biosynthesis pathways of fatty acids was observed, but the relative contents of short carbon chain compounds as precursors for the biosynthesis of palmitic acid such as 3-hydroxybutyric acid and 3-oxohexadecanoic acid. Their relative contents were significantly different from day 0 to day 4; from day 4 to day 8, the palmitic acid decomposition and fatty acid β oxidation pathways were activated, and consequently, the relative content of palmitic acid decreased significantly. The initiation of the fatty acid biosynthesis pathways could be ascribed to the activation of a variety of oxoylases, fatty acid synthases and acetyl-CoA. These enzymes catalyzed the formation of 3-hydroxybutyrate and 3-oxohexadecanoic acid as precursors for the formation of palmitic acid during the first 4 days of storage at 0–4 ℃. Therefore, it seems that metabolism does not stop immediately postmortem despite oxygen deficiency, and cells are still able to maintain their normal energy level. As the chilled storage time prolongs, the energy metabolism pathways in the body alternately work for energy supply. During the metabolic process, the relative contents of flavor precursors such as oleic acid, stearic acid, and palmitic acid change accordingly.
Effect of Near Freezing Temperature Storage on Chilling Injury and Active Oxygen Metabolism of Apricot Fruit
LI Yaling, CUI Kuanbo, SHI Ling, ZHU Zhaoshuai, LI Ling, LIU Yan, ZHU Xuan
2020, 41(7):  177-183.  doi:10.7506/spkx1002-6630-20190426-350
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The purpose of this work was to investigate the effect of near freezing temperature (NFT) storage on chilling injury and active oxygen metabolism of apricot fruit. ‘Xiaobaixing’ apricots from Kuche, Xinjiang were stored separately at near freezing temperature (?1 to ?1.5 ℃) and low temperature (4–6 or 1–2 ℃) for 49 days. Chilling injury incidence, chilling injury index, the activities of catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD), superoxide anion radical (O2-·) production rate and the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA), as well as cell membrane permeability were measured at every seven days. The results showed that compared with low temperature storage, NFT storage effectively delayed the onset of chilling injury, reduced the incidence of chilling injury, significantly increased the activity of SOD (P < 0.05), delayed the decline of POD and CAT activity, inhibited the content of H2O2 and O2-· generation rate, retarded the increase in MDA content and membrane permeability. Therefore, NFT storage could improve the cold resistance and storability of apricot fruit.
Effects of Cold Shock Combined with Glycine Betaine Treatment on Chilling Injury and Energy Metabolism of Zucchini
ZHANG Miao, JIANG Yu, TANG Jing, JIN Peng, ZHENG Yonghua
2020, 41(7):  184-190.  doi:10.7506/spkx1002-6630-20190716-212
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In order to explore the attenuating effect and mechanism of cold shock combined with glycine betaine treatment on chilling injury of zucchini, the effects of cold shock (ice-water mixture at 0 ℃), glycine betaine (10 mmol/L) and their combination on chilling injury index, relative electric conductivity, malondialdehyde (MDA) content, chlorophyll content, energy metabolism-related enzyme activities in zucchini stored at low temperature ((4 ± 1) ℃) were investigated. The results showed that all three treatments could inhibit the increase in chilling injury index, relative conductivity and MDA content, and delay the decrease in chlorophyll content and the increase in a* and b* values. Moreover, the treatments could maintain high activities of Ca2+-ATPase, H+-ATPase, succinate dehydrogenase (SDH) and cytochrome c oxidase (CCO), retard the decrease in ATP and ADP content, inhibit the increase in AMP content, and maintain high levels of energy charge in zucchini during storage. In conclusion, these treatments could effectively inhibit chilling injury of zucchini fruit, among which the combined treatment was the most effective, which may be related to maintaining high levels of energy charge in zucchini by regulating energy metabolism and consequently maintaining cell membrane integrity. This study provides a scientific basis for the application of cold shock combined with glycine betaine treatment in quality preservation of zucchini during low temperature storage and transportation.
Inhibitory Effect and Mechanism of trans-2-Hexenal against Inoculated Alternaria alternata on Pear Fruit
DONG Yupeng, SUN Ping, LI Yongcai, BI Yang, ZHANG Miao, HUANG Yi, ZHANG Tingting
2020, 41(7):  191-197.  doi:10.7506/spkx1002-6630-20190326-328
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The inhibitory effects of trans-2-hexenal, a plant-derived volatile substance, on the growth of Alternaria alternata and black spot development in pear fruit inoculated with this fungal pathogen were studied, and its underlying mechanism was also evaluated by examining cell membrane integrity. Results showed that trans-2-hexenal significantly inhibited the spore germination and mycelium growth of A. alternata in a concentration-dependent manner. The spore germination rate and colony diameter of A. alternata after treatment with 2.0 μL/mL were only 13.9% and 36.67% when compared with the control. At the same time, trans-2-hexenal fumigation treatment effectively reduced the development of pear black spot. Further research showed that the trans-2-hexenal treatment severely destroyed A. alternata cell integrity and significantly increased membrane conductivity and nucleic acid leakage rate (P < 0.05). Additionally, trans-2-hexenal treatment reduced the production of four mycotoxins in A. alternate including monomethyl ether, alternariol, altenuene and tentoxin to different extents. These findings suggested that the trans-2-hexenal might effectively reduce the growth and pathogenicity of A. alternata through damaging cell membrane integrity and decreasing mycotoxin production.
Correlation between Lipid Oxidation and the Activity of Endogenous Enzymes during Egg Storage
LIU Yu, ZHAO Mengbin, YU Haokun, YANG Li, Lü Bing, WANG Qingling
2020, 41(7):  198-202.  doi:10.7506/spkx1002-6630-20190325-317
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In order to illustrate the correlation between lipid oxidation and the activity of endogenous enzymes in egg yolk during egg storage, lipid oxidation was evaluated by measuring the total protein concentration, malondialdehyde (MDA) content and peroxide value (POV), and the activity of the endogenous enzymes lipase, glutathione peroxidase (GSH-Px), catalase (CAT), and total superoxide dismutase (T-SOD) was dynamically monitored. The results showed that during the entire storage period of 60 days, the degree of lipid oxidation in eggs continued to increase, POV rose rapidly and then reached a plateau, MDA content increased from 0.22 to 2.70 nmol/mg, and total protein concentration showed a downward trend. Over this period, lipase activity decreased from 1.78 to 0.29 U/g, both GSH-Px and CAT activity showed an overall downward trend, while T-SOD activity increased significantly from day 20 to 50 (from 0.20 to 2.87 U/mg) (P < 0.05). Correlation analysis showed that the lipid oxidation indexes were significantly negatively correlated with GSH-Px, lipase and CAT activity, but positively correlated with T-SOD activity, indicating antioxidant properties.
Effect of Combined Treatment with Ice Water and Lysozyme on Spinach Quality and Nitrate Content
LI Cuihong, WEI Lijuan, MU Yuwen, FENG Yuqin
2020, 41(7):  203-209.  doi:10.7506/spkx1002-6630-20190318-228
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In order to improve the storage quality of highland-grown spinach harvested in summer in Lanzhou, Gansu, we investigated the effects of different preservative treatments, water at ambient temperature (control), 1 g/L lysozyme, 2.3 mg/L ozone water and ice water combined with lysozyme, on spinach quality and nitrate content during storage at 4 ℃. Results indicated that combined treatment with ice water and lysozyme maintained higher levels of VC, chlorophyll, soluble sugar, soluble protein, folic acid, nitrate reductase (NR) and peroxidase (POD) activity in spinach during stroage, thus delaying the formation of oxalic acid, nitrate and nitrite and resulted in an increase of 14%, 17% and 30% in average color difference (?E) when compared with 1 g/L lysozyme, 2.3 mg/L O3 and control, respectivley. Moreover, the contents of chlorophyll and VC were 66% and 35% lower in the control group than in the combined treatment group on the eighth and tenth day of storage, respectively, and percenage folic acid loss in the combined treatment group was only half of that in the control group. The accumulation of nitrate and nitrite in the combined treatment group were significantly lower than those in the three other groups (P < 0.05). Overall, it could be concluded that combined treatment with ice water and lysozyme can maintain the quality of spinach during storage and extend the shelf period so that it can be of great commocial importance.
Effects of Different Sterilization Treatments on the Quality of Puffer Fish (Takifugu obscurus) during Refrigerated Storage
FENG Haojie, LAN Weiqing, LIU Dayong, CONG Jianhua, ZANG Yiyu, TANG Shuwen, ZHOU Dapeng, XIE Jing
2020, 41(7):  210-217.  doi:10.7506/spkx1002-6630-20190324-308
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The effects of different sterilization treatments (slightly acidic electrolyzed water (SAEW), ozonated water (OW) and ethanol water (EW)) on the quality of Takifugu obscurus during refrigerated storage were studied in this paper. Fresh fish were immersed separately in SAEW, OW and EW for 10 min and then each sample was drained, packaged in a polyethylene bag and stored in a refrigerator at 4 ℃. Samples immersed in sterile water were designed as the control group. Microbial indices (total viable count (TVC) and psychrophilic bacterial count (PBC)), physiochemical parameters (pH, texture profile analysis (TPA), total volatile base nitrogen (TVB-N) content, thiobarbituric acid (TBA) value and color difference), and sensory qualities (color, odor, morphology and springiness) were measured at 2-day intervals during storage. The results showed that pH, TVB-N content, TBA, TVC value and PBC of the treatment groups were better than those of the control group. However, EW treatment could accelerate lipid oxidation, and more strongly influence color difference and sensory scores compared to the other treatment and control groups. SAEW and OW treatments could effectively inhibit lipid oxidation, maintain the sensory quality, and prolong the shelf life of Takifugu obscurus for 1–2 days as opposed to 2 days with EW treatment. Correlation analysis indicated that TVC and PBC were significantly negatively correlated with springiness, resilience, and color difference (ΔE*) (P < 0.01), but significantly positively correlated with TVB-N content and TBA values (P < 0.01). According to the results of each index, SAEW and OW can be used for the cold preservation of Takifugu obscurus to extend the shelf life.
Recent Progress in Synthesis of Gold Nanoparticles and Its Application in Detection of Heavy Metal Ions
LIU Fengyuan, XIN Jiaying, SUN Lirui, WANG Yan, XIA Chungu
2020, 41(7):  218-227.  doi:10.7506/spkx1002-6630-20190225-174
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Heavy metal ions can enter the human body through foods, air and drinking water. They are non-degradable and can accumulate in living organisms, posing a serious threat to the environment and human health. As the methods traditionally used for the detection of heavy metal ions are cumbersome, time consuming, costly, and poorly portable, it is of great significance to develop quick, convenient and on-site detection methods. In addition to the characteristics of general nano-materials such as specific surface effect and quantum size effect, gold nanoparticles (GNPs) also have good biocompatibility and unique optical properties, thereby showing great application prospects in the detection of heavy metal ions. In this paper, we summarize the methods for the synthesis of several typical GNPs, and we review recent progress in applying surface plasmon resonance (SPR), dynamic light scattering, surface-enhanced Raman scattering, surface-enhanced fluorescence, gold test strip and GNPs chiral sensing technology in the detection of heavy metal ions based on the optical properties of GNPs. The principles of these technologies as well as their advantages and drawbacks are analyzed in order to provide useful information for the detection of heavy metal ions in foods, the environment, drinking water and specific samples.
Recent Progress in Biosynthesis of 3-Methylbutanal and Its Contribution to Nutty Flavor in Cheese
CHEN Chen, ZHOU Wenya, YUAN Jiajie, YU Haiyan, TIAN Huaixiang
2020, 41(7):  228-233.  doi:10.7506/spkx1002-6630-20190401-001
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Nutty flavor is the unique flavor of many cheeses, and 3-methylbutanal makes a key contribution to the nutty flavor of cheese. In this article, the effects of 3-methylbutanal on the nutty flavor of cheese are reviewed, the biosynthesis and Strecker degradation pathways of 3-methylbutanal are summarized and some strategies are highlighted to regulate the content of this particular flavor compound in specific cheese types. Future research directions are presented as well. We expect that this review will provide a theoretical basis for the development of nutty-flavored cheese products that can cater to Chinese consumers’ preference.
Progress in the Knowledge of the Cuticle of Citrus Fruits and Its Effect on Postharvest Fruit Quality during Storage
YANG Lüzhu, WANG Xinyu, WANG Rongrong, SHAN Yang, ZHANG Qun, DING Shenghua
2020, 41(7):  234-244.  doi:10.7506/spkx1002-6630-20190324-300
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The seasonality of citrus fruits and their susceptibility to postharvest mold decay can cause huge economic losses to the citrus industry. The surface of citrus fruits is covered with a hydrophobic layer called the cuticle, which can prevent non-stomatal water loss, resist the invasion of pathogenic bacteria and control gas exchange, and plays an important role in postharvest storage. In this paper, the composition, structure and biosynthesis of the cuticle and its functions are reviewed, in order to provide a theoretical basis for basic research into the cuticle and the postharvest preservation of citrus fruits.
Recent Progress in Understanding the Correlation between Egg Consumption and Cholesterol Homeostasis
XU Yichi, PENG Shiyi, YANG Fang
2020, 41(7):  245-254.  doi:10.7506/spkx1002-6630-20190401-008
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Egg is a source of essential fats, amino acids and trace elements with high cholesterol (200-300 mg/egg). Whether an increase in the amount of eggs in the diet will lead to an increase in cholesterol absorption and destruction of cholesterol homeostasis is always the focus of debate. A growing number of studies have consistently concluded that?there is only a weak correlation or no correlation between?dietary cholesterol and/or egg intake and?the incidence of cardiovascular diseases (CVDs)?in the general population.?Functional ingredients in eggs may regulate the absorption, transport and metabolism of cholesterol. However, a new debate on whether phospholipid-rich eggs promote the occurrence and development of atherosclerosis by trimethylamine-N-oxide (TMAO), a metabolic product produced by microbial fermentation, has been triggered. This review aims to summarize the latest progress in dietary recommendation of cholesterol and eggs, the homeostasis of cholesterol metabolism, epidemiological studies on cholesterol and eggs, the relative mechanism of egg intake affecting cholesterol homeostasis, and the correlation between TMAO and CVDs.
Bioactive Constituents of Allium and Their Physiological Functions: A Review
YU Jing, WEN Rongxin, YAN Qingxin, CHEN Qian, QIN Ligang
2020, 41(7):  255-265.  doi:10.7506/spkx1002-6630-20190225-170
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Allium is a genus of plants with high medicinal and food value that contains a variety of bioactive constituents, including sulfur-containing compounds, steroidal saponins, flavonoids, polysaccharides, nitrogen-containing compounds. The physiological functions of bioactive constituents in Allium, including antioxidant, antitumor and antibacterial effects and preventing cerebrovascular and cardiovascular diseases are reviewed in this paper. Meanwhile, future directions in the study of Allium are discussed. It is expected that this review will provide a theoretical basis for further development and utilization of Allium.
Recent Progress in the Construction and Functional Application of Curcumin Membrane Delivery Systems
ZHOU Arong, LIN Yilin, QIU Jianqing, ZENG Shaoxiao, LIN Shaoling
2020, 41(7):  266-274.  doi:10.7506/spkx1002-6630-20190402-030
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Curcumin has attracted extensive research attention due to its various biological activities. However, its low water solubility and biochemical/structural degradation during physiological transport lead to a low bioavailability which largely limits its economic value. Therefore, a large number of curcumin-based drug delivery systems have been introduced. The inclusion of curcumin into a biopolymer-based membrane delivery system is considered to have broad prospects. Polysaccharides and proteins are widely used as the polymeric carriers for the delivery of a variety of biologically active natural compounds. In this article, the challenges in the process of curcumin delivery and the recent progress in the construction of curcumin membrane delivery systems are summarized. Special focus is placed on reviewing the application of curcumin membrane delivery systems in food antioxidant packaging, freshness monitoring and antibacterial preservation, aiming to provide a theoretical basis for further development and application of curcumin.
Recent Advances in Understanding the Antitumor Activity of Polysaccharides from Plants
BIAN Liang, CHEN Huaguo, ZHOU Xin
2020, 41(7):  275-282.  doi:10.7506/spkx1002-6630-20190330-392
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As a class of natural products with many biological activities, plant polysaccharides have become a research hotspot in the field of anti-tumor functional foods because of their advantages of high efficiency and low toxicity. Clinical anti-tumor trials have demons plant polysaccharides can alleviate immunosuppression, enhance immune response, and inhibit the growth, invasion and metastasis of tumors.?In this review, the anti-tumor plant polysaccharides that have been reported over the decade are summarized. The anti-tumor mechanisms of plant polysaccharides are elucidated from four perspectives: regulation of tumor microenvironment, targeted cancer cell therapy, iron metabolism and erythrocyte immunity. Finally, the structure-activity relationship of anti-tumor plant polysaccharides is also discussed, and future research directions are presented in order to promote in-depth studies of plant polysaccharides and provide a theoretical basis for the research and development of anti-cancer foods.
Recent Advances in Understanding Glutathione during Wine-Making Process
SU Jing, GONG Rong
2020, 41(7):  283-291.  doi:10.7506/spkx1002-6630-20190411-151
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Glutathione (GSH), an endogenous antioxidant in grapes, can prevent the oxidative spoilage of wine especially white wine. It affects the quality of wine directly or indirectly. In recent years, this important sulfhydryl compound in grapes, grape juice and wine has become a growing concern for researchers and wine producers. In this paper, the structure and properties of glutathione are described, and its existing forms and roles in grapes and grape juice are summarized as well as the effects of glutathione on aromatic substances, yeast and lactic acid bacteria and color in wine and the factors affecting the glutathione content in wine. Moreover, future research directions were also proposed.
A Review: Domain Fine Structure of Pectic Polysaccharides
YI Jianyong, BI Jinfeng, LIU Xuan, Lü Jian, ZHOU Mo, WU Xinye, ZHAO Yuanyuan, DU Qianqian
2020, 41(7):  292-299.  doi:10.7506/spkx1002-6630-20190328-356
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Pectic polysaccharides are a group of polysaccharides composed of D-galacturonic acid and neutral saccharides, and they widely exist in plant cell walls. Pectic polysaccharides are endowed with multifunctional properties such as direct effects on plant tissue integrity and firmness and the self-protection of plants against phytopathogens, gelling ability, emulsifying capacity and emulsion stability, thickening ability and health benefits including regulating the intestinal microbiota, alleviating hyperlipidemia and prevent colon cancer. The fine structures of pectic polysaccharides include pectic domains such as homogalacturonan, rhamnogalacturonan-I, rhamnogalacturonan-II and/or xylogalacturonan, which are covalently inter-linked to form pectin complexes. This review focuses on the depiction of the structural domains of pectic polysaccharides with the aim of providing the latest information on the structural models of pectic polysaccharides.
Vulnerability Assessment and Its Applications in Food Fraud: A Review
SONG Huaxin, ZHANG Xinglian, LU Baiyi
2020, 41(7):  300-305.  doi:10.7506/spkx1002-6630-20190328-379
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Vulnerability assessment is an important research tool for global change and sustainable development disciplines. It has developed into an independent discipline covering the spatial and temporal scale, and emphasizing the coupling of natural and socio-economic systems. The common vulnerability assessment methods and weight calculation methods are reviewed in this paper, recent progress in the application of vulnerability assessment in food fraud is summarized, and the problems to be solved are also discussed.
Recent Advances in Applying Lactic Acid Bacteria for Alleviating Alcoholic Liver Disease
LI Huizhen, SHI Jialu, ZHAN Meng, GUAN Jiaqi, YAN Fenfen, HUO Guicheng
2020, 41(7):  306-314.  doi:10.7506/spkx1002-6630-20190408-072
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Although various drugs have already been used in a large number of animal and clinical studies to prevent or treat alcoholic liver disease, so far the drug treatments still may cause some side effects at various stages of alcoholic liver disease. As it is increasingly recognized that the gut microbiota plays an important role in the development and progression of various diseases, the potential role of lactic acid bacteria in treating alcoholic liver disease is receiving growing interest from researchers. Recent worldwide studies have found that lactic acid bacteria can alleviate alcoholic liver disease in many aspects. This article reviews the absorption and metabolism of alcohol in the body and the pathogenesis of alcoholic liver disease, as well as the mechanism by which lactic acid bacteria can alleviate alcoholic liver disease, namely by regulating the intestinal microbiota, improving intestinal barrier function, reducing liver oxidative stress, regulating liver inflammation and inhibiting liver fat accumulation, so as to provide a theoretical basis for the prevention and treatment of alcoholic liver disease by lactic acid bacteria.
Recent Advances and Future Prospects of Food-Derived Dipeptidyl Peptidase IV Inhibitors
ZHAO Rui, YAO Xinmiao, ZHOU Ye, GUAN Lijun, ZHANG Yinglei, LI Zhebin, SHEN Huifang, CUI Yijuan, LU Shuwen
2020, 41(7):  315-321.  doi:10.7506/spkx1002-6630-20190211-044
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Diabetes is considered as one of the most serious metabolic diseases in the world. Inhibitors of dipeptidyl peptidase IV (DPP-IV) have been testified as an effective pharmaceutical approach for the management of type II diabetes. Food-derived peptides have been suggested as promising sources of DPP-IV inhibitors with the potential to help manage glycemic levels. This review summarizes recent progress in the production, conventional research approaches, structural characteristics and modes of action of food-derived DPP-IV inhibitors. The applications of bioinformatics analysis (i.e., peptide cutter, molecular docking and quantitative structure activity relationship (QSAR)) in the field of DPP-IV inhibitory peptides are reviewed herein and their limitations are outlined. Furthermore, further studies are proposed on the application of food-derived DPP-IV as a functional food ingredient to help manage glycemic levels.
Recent Progress in Functional Microbial Community and Quality Evaluation of Vinegar Daqu
HUANG Jing, YAN Weiwei, LIU Shuliang, LIU Aiping, AO Xiaolin, WANG Rui, YANG Yong, DU Dazhao, CHEN Fusheng
2020, 41(7):  322-328.  doi:10.7506/spkx1002-6630-20190408-073
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Daqu is a traditional natural fermentation starter in China. It plays an important role in the production and flavor formation of traditional vinegar due to its complex microbial communities, substances and enzymes. Intensive studies have been carried out to reveal the functional microbial community, enzymes and flavor substances in vinegar Daqu. Here, the functional microbial community and quality characterization of vinegar Daqu, the factors influencing vinegar Daqu quality and the relationship between Daqu quality and vinegar quality, as well as the current measures used to improve Daqu quality are reviewed. We expect that this review will provide valuable information for the production and quality improvement of vinegar Daqu.
Current Pollution Situation of Perfluorinated Compounds in Waters and Foodstuffs and Recent Progress in Understanding Their Interactions with Liver Fatty Acid Binding Protein
FANG Guokang, XU Jianming, LI Ruohui, JIANG Dan, HUANG Yingchun
2020, 41(7):  329-335.  doi:10.7506/spkx1002-6630-20190330-393
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Perfluorinated compounds (PFCs), a class of fluorine-containing hydrocarbon compounds, are widely used in food, pharmaceutical and agricultural industries for its relatively stable physicochemical properties. But its poor degradability could bring about unpredictable damages to the atmosphere, soil and even organisms. In this paper, the current pollution situation of PFCs in water, plants, fishery products, meat and eggs is summarized, and the interaction between PFCs and liver fatty acid binding protein (L-FABP), which interferes with lipid metabolism and consequently leads to obesity, insulin resistance, type 2 diabetes and hyperlipidemia is reviewed together with the binding characteristics of PFCs with L-FABP and the possible mechanisms for the bioaccumulation and hepatotoxicity of PFCs. It is of great significance to understand the distribution in vivo and physiological toxicity of PFCs. Thus, the binding of PFCs with nine types of FABPs needs further investigation.