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Table of Content

15 April 2018, Volume 39 Issue 7
Basic Research
Fluorescence Labeling of Sea Cucumber Chondroitin Sulfate
WANG Jun, WU Fanxiu, CHANG Yaoguang, CHEN Feng, XU Xiaoqi
2018, 39(7):  1-6.  doi:10.7506/spkx1002-6630-201807001
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Sea cucumber chondroitin sulfate (CHS) is one of the important bioactive substancesins in sea cucumber body wall. Since its multiple bioactive functions have been validated, CHS is considered as a potential ingredient of novel functional foods. Similar to most carbohydrates, CHS lacks specific chromophores and fluorescence groups. Based on this background, the aim of this study was to construct fluorescence labelling of CHS. The polysaccharide was derivatized by hydrogen bromide activation method with 6-amino-fluorescein as the fluorescent dye. As a result, each molecule of the labelled product approximately contained 4.4 molecules of 6-amino-fluorescein. The optimal fluorescence excitation and emission wavelengths of the labelled CHS were 495 and 520 nm, respectively. Additionally, its molecular weight and sulfate content were determined. Infrared spectroscopy showed that the structural characteristics of the polysaccharide did not significantly change after labeling. The labelled CHS exhibited strong fluorescence intensity and stability in neutral and alkaline environments. The influence of NaCl in the solution environment on the labelled CHS was limited. The establishment of this fluorescence labeling method will facilitate further research on the absorption and metabolism, functions and underlying mechanisms of CHS and its interactions with other biomolecules.
Formation and Inhibition Mechanism of Harmful Cross-Linked Products Generated from Glycosylation of 11S Globulin
ZHANG Dingmin, LIU Guimei, LU Yongling, ZHENG Tiesong, Lü Lishuang
2018, 39(7):  7-13.  doi:10.7506/spkx1002-6630-201807002
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Purpose: The objective of this research is to identify the factors affecting the formation of advanced glycation end products (AGEs) in 11S globulin-sugar model system and to shed light on the inhibitory mechanism of flavonoids on AGEs formation. Methods: Fluorescence spectrometry (λex/λem = 340 nm/465 nm) was used to detect the effects of sugar type and concentration, temperature, pH and flavonoids on the formation of AGEs, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was employed to characterize the glycation process and investigate the inhibitory effect of flavonoids. Changes in the concentrations of quercetin and products during the reaction process were determined by liquid chromatograph-tandem mass spectrometry (LC-MS/MS). Results: The reaction between 11S globulin at 2 mg/mL and fructose at 8 mg/mL at pH 9.2, 121 ℃ formed the greatest amount of fluorescent AGEs. The formation of AGEs was inhibited by all four flavonoids (quercetin, luteolin, genistein, or rutin). LC-MS/MS analysis showed that quercetin inhibited the generation of fluorescent cross-linked AGEs by trapping methylglyoxal as an intermediate of glycolysis. SDS-PAGE analysis confirmed that quercetin at 1 mmol/L significantly reduced the generation of cross-linked macromolecules but did not influence sugar modification and resulted in significant improvement of emulsifying properties. Conclusion: Application of high-molecular weight sugars, reduced sugar concentration, pH and reaction temperature, and addition of flavonoids can effectively inhibit the formation of harmful products AGEs during the glycosylation process of soybean protein.
Textural and Rheological Properties of Oleogel-Based Margarine
HAN Lijuan, CHEN Hao, LIU Sheng, QI Yutang, ZHANG Weinong, HE Junbo, WANG Qi, QI Chuang
2018, 39(7):  14-19.  doi:10.7506/spkx1002-6630-201807003
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Interest in oleogel as a promising alternative to traditional hydrogenated vegetable oil has increasingly grown in recent years due to its low content of saturated fatty acids and zero trans fatty acids. In this research, refined soybean oil was used as base oil and added with a 1:1 mixture of β-sitosterol and lecithin as gelling agent, yielding oleogel-based margarine. The effect of gelling agent concentration and water content on textural and rheological properties, micro-network structure and crystallinity of oleogel-based margarine was studied. The results showed that a homogeneous margarine system could be formed at a lower gelling agent concentration with increasing water content. As gelling agent concentration and water content increased, so did the hardness, elasticity and crystallization degree of the margarine. Moreover, its three-dimensional network structure was more complete and the contact area between oil and water increased, thereby resulting in more uniform and stable system with higher hardness and elasticity.
Degradation of Protopanaxadiol-Type Ginsenosides with Aspartic Acid and Antioxidant Activity of Maillard Reaction Products
LIU Zhi, XIA Juan, LI Wei, ZHANG Jing, SUN Guangzhi, RUAN Changchun
2018, 39(7):  20-26.  doi:10.7506/spkx1002-6630-201807004
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The effect of aspartic acid as a catalyst on the transformation of protopanaxadiol-type ginsenosides (PDG) and Maillard reaction in high temperature steam was investigated. The antioxidant activity of the reaction products in vitro was also determined. The results showed that PDG was transformed into 20S-Rg3, 20R-Rg3, Rk1 and Rg5; the transformation pathway was as follows: PDG → 20S-Rg3/20R-Rg3 → Rk1/Rg5. The contents of 20R-Rg3 and Rg5 showed a gradual increase with increasing heating temperature, while the contents of 20S-Rg3 and Rk1 decreased. The 1,1-diphenyl-2- picrylhydrazyl radical scavenging capacity of the reaction products increased with increasing heating temperature, which was mainly attributed to the Maillard reaction products from aspartic acid and saccharides produced from PDG hydrolysis. This study can provide a basis for the development of green and environmental-friendly rare ginsenosides into health foods.
Modeling Moisture Absorption Isotherms of Hunan Raw Dark Tea and Evaluating Its Mildew Degree
XU Wei, ZHAO Renliang, JIANG Yihe, WU Dan, ZHU Qi
2018, 39(7):  27-32.  doi:10.7506/spkx1002-6630-201807005
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The aim of this paper was to discuss the aging characteristics of raw dark tea and the safety of dark tea during storage. The moisture absorption characteristics of Hunan raw dark tea at 20, 30 or 40 ℃ over the water activity range of 0.010 3–0.981 8 were evaluated using the static gravimetric method and response surface models were developed. Moisture absorption isotherm curves were plotted and fitted to a nonlinear model. Furthermore, the mildew degree was examined during storage under simulated storehouse conditions: 25 ℃ and 85%, 87% or 90% relative humidity. The results showed that the moisture absorption isotherms of raw dark tea exhibited the characteristics of a type II isotherm and the equilibrium time (14, 10 and 6 days) was shortened with increasing temperature (20, 30 and 40 ℃). Equilibrium moisture content was reduced with increasing temperature. The response surface models at all three temperatures showed regular patterns. Among 8 classical mathematical models, GAB and Oswin models were the best ones to describe the isothermal moisture absorption process. During 10 days of storage under simulated storehouse conditions, the dark tea did not mildew at 85% relative humidity (RH), mildewed partially at 87% RH, and mildewed seriously at 90% RH.
Synergistic Antioxidant Effect of Hexahydro-β-Acid-Cyclodextrin Inclusion Complex and Food Additives
XU Haining, LIU Yumei
2018, 39(7):  33-40.  doi:10.7506/spkx1002-6630-201807006
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In this study, hydroxyl and DPPH free radical scavenging assays were used to investigate the antioxidant capacity of novel inclusion complexes of hexahydro-β-acid, a hydrogenated derivative of resin in hops, with α, β and γ-cyclodextrin as well as 2-methyl, 2,6-bimethyl and 2,3,6-trimethyl-β-cyclodextrin. The results suggested that all inclusion complexes had antioxidant activity in varying degrees and their scavenging capacity against hydroxyl and DPPH free radicals was better than that of hexahydro-β-acid at the same concentration. On the basis of the above results, the synergistic antioxidant activity was evaluated on four inclusion complexes (2-methyl-β-cyclodextrin, hydroxypropyl-β-cyclodextrin, 2,3,6-trimethyl- β-cyclodextrin and γ-cyclodextrin), mixed with food additives (vitamin C, sodium chloride, citric acid and sucrose) in comparison with sodium benzoate. The results showed that all binary mixtures of inclusion complexes with citric acid and quaternary mixtures with vitamin C, NaCl and sucrose had no synergistic antioxidant activity in hydroxyl radical system, but the binary combinations of inclusion complexes with vitamin C, sodium chloride or sucrose were synergistic. Meanwhile, all binary/quaternary combinations except binary combination with sucrose had good synergistic antioxidant activity in DPPH free radical scavenging assay. However, sodium benzoate had no synergism with all four food additives in binary combinations.
Pasting Properties and Microstructure of Adzuki Beans during Cooking
BAI Jie, LIU Lisha, LI Yumei, PENG Yijiao, TIAN Xu, JIN Yang, ZHANG Qing, ZHANG Xiaofei, GUO Hong
2018, 39(7):  41-46.  doi:10.7506/spkx1002-6630-201807007
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The hardness, pasting properties and microstructure of adzuki beans during different cooking times were studied by using a texture analyzer, a rapid viscosity analyzer, a scanning electron microscope, X ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The correlation among basic components, hardness, crystallinity, gelatinization degree and pasting properties was also analyzed. The results showed that the contents of starch and protein, pasting properties, hardness and crystallinity showed a descending trend followed by leveling off with the increase of cooking time, while the gelatinization degree showed the opposite trend. However, there was no significant change in fat content (P < 0.05). During cooking, the cross-sectional microstructure of cotyledon cells in adzuki beans changed significantly. The starch granules were completely exposed and showed smooth and regular spherical particles as a result of wider cell gap and the disappearance of cell contour. The infrared spectra showed that cooking could decrease characteristic peak intensity in the sensitive regions, and some fingerprint regions also decreased or even disappeared. Both XRD and FTIR confirmed that structural changes of adzuki bean starch during cooking. Correlation analysis showed that starch, gelatinization degree, pasting properties, hardness and crystallinity had a very significant correlation with each other (P < 0.01).
Optimization of Key Sensory Attributes for Flavored Liquid Milk Based on Local Consumers’ Preference
ZHI Ruicong, ZHAO Lei, SU Yufang, YUN Zhanyou, GAO Haiyan
2018, 39(7):  47-55.  doi:10.7506/spkx1002-6630-201807008
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The refinement and personalization of product design has become a new trend in product development since the consumption level of Chinese residents has been upgraded. Consumers’ preference plays an important role in product design and development. In this paper, we focus on sensory evaluation of flavored liquid milk conducted by both sensory panel and consumers in various cities. The multivariate statistical analysis including partial correlation analysis and Penalty analysis were employed to analyze the relationship among sensory attributes. The preference map was utilized to comprehensively process both analytical sensory evaluation by a trained panel (sensory attribute intensity measurement) and emotional sensory evaluation by consumers (preference measurement), and to determine the improvement direction for specific sensory attributes based on the overall preference from different cities. The optimization results demonstrated that consumers in Shanghai prefer sweet samples, while those in Beijing and Chengdu prefer the samples with medium sweet and sour taste. All three cities have similar preference to fresh milk flavor, and like the samples with strong fresh milk flavor and smoothness. The preference of consumers in Beijing for thickness is not as strong as that of Chengdu and Shanghai consumers.
Changes in Physicochemical Properties, Microstructure and Protein Properties of Turbot (Scophthalmus maximus L.) Muscle during Steam Cooking
FU Xinxin, WANG Yao, LI Deyang, JIANG Pengfei, LIU Wentao, LIANG Jun, QI Libo, DONG Xiuping
2018, 39(7):  56-62.  doi:10.7506/spkx1002-6630-201807009
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In this study, the upper dorsal muscle of turbot was investigated for changes in fat content, moisture loss rate, mass loss rate, relatively extraction rate of myofibrillar protein, microstructure, shear force, hardness, chewiness and color. Besides, we also examined changes in the relative molecular mass of myofibrillar proteins in the fish muscle and proteins in the fish juice, Ca2+Mg2+-ATPase activity and total thiol group content. Results indicated that the moisture loss rate and mass loss rate increased, while fat content decreased with increasing cooking time. The extraction rate of myofibrillar protein decreased significantly in the first 2 min of cooking and then dropped to less than 10% by 4 min. Ca2+Mg2+-ATPase activity dropped to the lowest level at 2 min. Total thiol group content first increased and then declined during the first 1 min, followed by a leveling off. During cooking, the microstructure of turbot cubes was damaged; meanwhile, shear force, hardness and chewiness decreased significantly (P < 0.05). The L* value increased significantly to a plateau after 4 min. Myofibrillar proteins with different molecular weights continuously leaked out from fish muscle tissues, resulting in higher protein content in the exudate. In conclusion, turbot cubes (1.5 cm × 1.5 cm × 1.0 cm) cooked by steaming for 4 min had good quality.
Effects of Nutrient Solution Concentration on Growth, Quality and Storability of Tomato
CAO Yuxin, CAO Hongxia, WANG Ping, WU Xuanyi
2018, 39(7):  63-70.  doi:10.7506/spkx1002-6630-201807010
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In order to explore the suitable nutrient solution concentration for the growth of tomato, the tomato cultivar ‘Tianshuo308’ cultivated in buckets with perlite substrate was selected as an experimental crop throughout the growth stage. Hoagland nutrient solution at different concentrations (S1: 1/4S, S2: 2/4S, S3:3/4S, and S4: 4/4S; S represents the standard solution concentration) was used in this experiment to explore their effect on plant growth, postharvest fruit quality and storability. Results showed that the growth of tomato plants matched the Logistic curve over time, and the maximum plant height (124.367 cm) and the longest fast-growing period were achieved at S3 concentration. The chlorophyll content showed a single-peak curve at different growth stages, with the appearance of a peak at the blossom and fruit set stages. The contents of proline and malonaldehyde presented initial decrease and subsequent increase with the increase of nutrient solution concentration. In addition, the nutritional quality (total soluble sugar, lycopene, and VC content) of fruit first increased and then decreased. The total soluble sugar, lycopene, and VC content in tomato subjected to S3 treatment increased by 40.51%, 38.70% and 12.72%, respectively, when compared with S1 treatment. For all treatments, the contents of lycopene, soluble sugars, vitamin C and malondialdehyde increased first and then decreased during storage. In summary pre-harvest treatment with suitable nutrient solution concentration could inhibit the decrease in fruit hardness; after 16-day storage, the hardness of fruits in four treatment groups followed the decreasing order of S3 (3.593 kg/cm2) > S4 (2.843 kg/cm2) > S2 (2.740 kg/cm2) > S1 (2.300 kg/cm2). In conclusion, Hoagland nutrient solution at 3/4S concentration was found to be optimal for the growth of tomato, thereby improving fruit quality and the prolonging storage life.
Collagen Membrane Strengthened by Sodium Polyacrylate Based on Electrostatic Interaction
WANG Yabin, WANG Wenhang
2018, 39(7):  71-77.  doi:10.7506/spkx1002-6630-201807011
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In order to improve the properties of collagen films, based on the electrostatic interaction between electronegative sodium polyacrylate and electropositive turgid collagen fibers, we evaluated the impact of adding different amounts of sodium polyacrylate (0.1%–1.0%) on membrane properties. The results showed that Zeta potential of the film-forming suspension significantly changed with the increase of sodium polyacrylate concentration (P < 0.05) suggesting enhanced electrostatic interaction. Sodium polyacrylate addition decreased the elongation at break, light transparency and water vapor permeability (the minimum value reached 1.30 × 10-12 g/(cm?s?Pa)) of the films and increased the thermal stability (up to 1.50 folds higher than that of pure films), but it had no impact on film thickness. Scanning electron microscopic analysis showed that the composite films were more compact. Addition of 0.3% sodium polyacrylate showed better film properties: tensile strength, elongation at break, light transparency and water vapor permeability were 37.60 MPa, 14.20%, 48.70% and 1.30 × 10-12 g/(cm?s?Pa), respectively. In addition, the conformational changes of the composite films were confirmed by Fourier transform infrared spectroscopy. The enhanced effect of sodium polyacrylate and collagen due to electrostatic interaction showed that appropriate addition of sodium polyacrylate could effectively improve collagen membrane properties.
Nitrate Content, Activities of Key Enzymes for Nitrogen Metabolism, and Expression and Subcellular Localization of NRT1 in Different Nitrate-Enriched Varieties of Pakchoi (Brassica chinensis L.)
LI Yanhua, YANG Yun, XU Weihong, ZHOU Xinbin, WANG Weizhong, CHI Sunlin, LI Tao, ZHANG Chunlai, ZHAO Wanyi, QIN Yuli, WANG Zhengyin, XIE Deti
2018, 39(7):  78-84.  doi:10.7506/spkx1002-6630-201807012
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Solution culture experiments were conducted to investigate the effect of nitrate/ammonium ratio (50:50, 75:25 and 100:0) on nitrate content, the activities of key enzymes for nitrogen metabolism in pakchoi, and the expression and subcellular localization of nitrate transporter gene in two pakchoi varieties (low-nitrate variety ‘JN4’ and high-nitrate variety ‘HKTX’). The results showed that nitrate contents in leaves of ‘HKTX’ and JN4 subjected to treatment at NO3 - / NH4 + ratio of 100:0 increased respectively by 13.2% and 30.4% compared with treatment at NO3 - / NH4 + ratio of 150:50; nitrate contents in petioles of ‘HKTX’ and ‘JN4’ were increased respectively by 14.3% and 4.9% compared with treatment at NO3 - / NH4 + ratio of 50:50. With the increase of NO3 - / NH4 + ratio, the activities of nitrate reductase (NR) and glutamate synthase (GOGAT) in pakchoi decreased, the activity of nitrite reductase (NiR) increased, and the activity of glutamate dehydrogenase (GDH) initially increased and then decreased. Significant differences in NR, GOGAT, NiR, and GDH were observed between the two varieties. Significant expression of low affinity transporter gene (NRT1) was detected in both varieties, and a higher expression level was observed in ‘JN4’ than in ‘HKTX’. NRT1 was a low affinity nitrate transporter located in the plant cell membrane.
Effect of Heat Treatments on the Relationship between Flexibility and Structure of Soy Protein
WANG Jian, XU Yeye, YU Jie, ZHANG Xu, WANG Xibo, JIANG Lianzhou
2018, 39(7):  85-90.  doi:10.7506/spkx1002-6630-201807013
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The effects of different heat treatment conditions (60–121 ℃ for 5, 10 and 30 min) on the flexibility of soy protein isolate (SPI) as characterized by its sensitivity to trypsin and the relationship between flexibility and structure were investigated. The results suggested that heating at temperature below 80 ℃ had no significant impact on the flexibility of SPI, while the flexibility of SPI increased with increase in temperature (above 80 ℃) and heating time. Flexibility was very significantly correlated with turbidity, free sulfhydryl group content and surface hydrophobicity under heating conditions at 60–100 ℃, with correlation coefficients of 0.956, 0.954 and 0.954, respectively. Turbidity and surface hydrophobicity declined with increase in flexibility, while the content of free sulfhydryl group increased when heating temperature was higher than 100 ℃. The content of free sulfhydryl group reached the maximum level at 5 min of heating at 121 ℃, and then decreased. Ultraviolet absorption spectroscopy and endogenous tryptophan fluorescence spectroscopy suggested that the structure of SPI was more stretched with increase in SPI flexibility under heating conditions at 80–100 ℃.
Antioxidant Property of Soy Glycoprotein
XIA Xiufang, WANG Bo, ZHENG Xingzi, DENG Siyang, PAN Nan, WANG Hao
2018, 39(7):  91-97.  doi:10.7506/spkx1002-6630-201807014
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Soy glycoprotein was prepared from soy protein isolate (SPI) and glucose (m/m = 1:1) by Maillard reaction at 70, 80 or 90 ℃ for 0, 1, 2, 3, 4, 5, 6 h respectively. The reducing power, and hydroxyl radical and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity of products at different reaction times were determined. Moreover, browning degree, ultraviolet (UV) spectroscopic analysis, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were studied to explore the antioxidant mechanism of soy glycoprotein. The results showed that the antioxidant effect and browning degree of soy glycoprotein was significantly increased, and free amino group content was remarkably increased with an increase in reaction temperature and time. It was proved that soy glycoprotein obtained after reaction for 6 h at 90 ℃ had the maximum reducing power, which was 5.6 times higher than SPI. Soy glycoprotein obtained after reaction at 90 ℃ for 5 h exhibited the highest hydroxyl radical scavenging (a 1.69-fold increase over SPI) and DPPH radical scavenging activity (scavenging activity of 68.55%, a 3.68-fold enhancement over SPI). Through analysis of the secondary derivative ultraviolet spectrum, tryptophan migration in the protein occurred during the Maillard reaction. Meanwhile, SDS-PAGE illustrated that SPI and glucose formed high molecular weight conjugates. All in all, these results suggest that soy glycoprotein has antioxidant properties, which has a close relationship with the changes of protein structure.
Effect of Canopy Micro-Environment on Anthocyanins of ‘Moldova’ Grape
LIU Xiaohong, GUO Shuhua, XIAO Qiuhong, DU Yuanpeng, ZHAI Heng
2018, 39(7):  98-106.  doi:10.7506/spkx1002-6630-201807015
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The purpose of this study is to investigate the effects of vertical canopy and horizontal canopy on the anthocyanin composition of ‘Moldova’ grapes. Vertical trellis system and pergola were conducted to represent vertical canopy and horizontal canopy for two consecutive years, respectively. The temperature and relative humidity around the clusters of two canopy types were recorded by temperature and humidity recorder from the berry expansion stage. Grapes were picked from 9 to 15 weeks after blossom to quantify individual anthocyanins in the skin by HPLC-MS, and the enzyme activities and their gene expression levels involved in the anthocyanin metabolic pathway were measured as well. Finally, the grape quality of different canopy types was compared. The results showed that compared with vertical canopy, horizontal canopy decreased the proportion of high temperature and humidity fluctuation around the cluster, and improved mature fruit quality. In 2015, reducing sugar content, 100-berry weight, anthocyanin and flavonoids of horizontal canopy grapes increased respectively by 2.39%, 5.48%, 27.11% and 44.89% compared with vertical canopy grapes. In 2016, the contents of total phenols, anthocyanin and flavanols increased respectively by 5.09%, 6.45%, and 13.67% compared with vertical canopy. The relative expression of Vitis vinifera UDP-glucoseflavonoid 3-O-glucosyltransferase (VvUFGT), Vitis vinifera O-methyltransferase (VvOMT), Vitis vinifera polyphenol oxidase (VvPPO) genes in horizontal canopy was significantly upregulated from 11 to 13 weeks after blossom, and the enzyme activities of UFGT, OMT and anthocyanin 5-O-glucosyltransferase (5GT) were maintained at high levels from 13 to 15 weeks. From 9 to 13 weeks after blossom, the relative gene expression and enzyme activities of UFGT, leucoanthocyanin dioxygenase, OMT, 5GT and PPO in vertical canopy grapes showed similar trends. The analysis of individual anthocyanins indicated that 13 of 21 individual anthocyanins detected in horizontal canopy grapes were more abundant than in vertical canopy grapes. Meanwhile, the modification degree of anthocyanin was increased, but the type of anthocyanin did not significantly change.
Inactivation of Cronobacter sakazakii in Reconstituted Infant Formula by Trans-Cinnamaldehyde Treatment Coupled with Mild Heating
SHI Chao, GUO Du, ZHANG Wenting, GUO Kailun, WEN Qiwu, LIU Zhiyuan, SUN Huihui, CHEN Shan, SUN Zheng, GUO Xiao, YIN Shuhua, XIA Xiaodong
2018, 39(7):  107-112.  doi:10.7506/spkx1002-6630-201807016
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The objective of this study was to determine the bactericidal effect of trans-cinnamaldehyde (TC) combined with mild heating on Cronobacter sakazakii in reconstituted infant formula. Reconstituted infant formula samples with various concentrations of TC (0, 0.1%, 0.2%, 0.3% and 0.4%) were inoculated with a mixture of three C. sakazakii strains (approximately 6.6(lg (CFU/ mL))) followed by incubation at 25, 45, 50 or 55 ℃. The surviving bacteria at different sampling times were enumerated. In order to elucidate the mode of action of the combined treatment, the cell membrane integrity and cell morphology were examined using a LIVE/DEAD? bacterial viability kit and a field emission scanning electron microscope, respectively. TC at 0.4% combined with heat treatment at 25 ℃ for 90 min, at 45 ℃ for 20 min, at 50 ℃ for 10 min or at 55 ℃ for 10 min reduced all pathogens to undetectable levels. Our results demonstrated that the combination of TC and heat treatment significantly reduced (P < 0.05) the number of C. sakazakii compared with either treatment alone, and this effect was dependent on both temperature and TC concentration. The combined treatment inactivated the pathogens partly by damaging cell membrane integrity, leading to cell disruption. These findings suggested that TC combined with mild heating may have potential application to control C. sakazakii infection during reconstitution of infant formula.
Strategies to Reduce Acrylicamide Formation in Fried Dough Twists
ZHANG Yunhuan, FENG Yajing, LI Shuguo
2018, 39(7):  113-118.  doi:10.7506/spkx1002-6630-201807017
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Acrylamide, a potential carcinogen and neurotoxin recognized by the International Agency for Research on Cancer, is formed mainly in high temperature processed starch-rich foods. This study systematically investigated the effect of processing conditions and ingredients on acrylamide formation during the production of fried dough twists and developed strategies to reduce acrylamide formation. Results showed that the frying temperature and time should be controlled as low as possible and their optimal values were determined as 160 ℃ and 180 s, respectively. Frying in peanut oil, corn oil and soybean oil reduced the formation of acrylamide compared with palm oil. The formation of acrylamide was inhibited by addition of VC and ferulic acid inhibited but slightly increased by addition of tertiary butylhydroquinone. The non-reducing sugars β-cyclodextrin, mannitol, sorbitol and erythritol had inhibitory effects in decreasing order. The effect of β-glucan was negligible, but sucrose had a promoting effect. In addition, cysteine, glutamate, lysine and glycine could effectively reduce the formation of acrylamide in fried dough twists. Glycine showed the best inhibitory effect at an addition level lower than 0.2%, and the inhibitory effect of glutamate added at 0.3%–0.5% was better than other three amino acids. Four amino acids added at 0.5% provided optimal inhibition of acrylamide inhibition.
Effect of Chicoric Acid on Oxidative Protein Damage
XIAO Haifang, YANG Shuqing, WANG Xuguang, WANG Jing, SONG Yuanda
2018, 39(7):  119-124.  doi:10.7506/spkx1002-6630-201807018
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The effect of chicoric acid on free radical-induced oxidative damage to proteins was evaluated in this paper. Two different paradigms including metal-catalyzed oxidation induced by Cu2+/H2O2 and alkylperoxyl radicals formed by azo initiator 2, 2’-azobis (2-amidinopropane) hydrochloride (AAPH) were used to induce oxidative damage to proteins including bovine serum albumin (BSA) and mouse liver and brain proteins. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot were applied to determine the level of oxidative protein damage. Results showed that chicoric acid in the range of 100–1 000 μmol/L significantly inhibited oxidative protein damage induced by Cu2+/H2O2. However, chicoric acid at high concentration could induce oxidative damage to mouse tissue proteins. Chicoric acid protected the proteins against oxidative damage induced by AAPH-derived alkylperoxyl radicals in a dose-dependent manner. In conclusion, chicoric acid has different protective effects on oxidative protein damage in both paradigms.
Comparative Studies on Physical and Chemical Properties of Traditional Brown Sugar and Refined Brown Granulated Sugar
XU Lingjun, YUAN Yiming, FENG Aiguo, DENG Jian, HU Xiaoping
2018, 39(7):  125-130.  doi:10.7506/spkx1002-6630-201807019
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The physical and chemical properties (water activity (aw), color, crystal structure, main components, minerals and amino acids) and sulfur dioxide contents of traditional brown sugar and refined brown granulated sugar were studied and compared. In this paper, three brown sugars and two brown granulated sugars were chosen. The results showed that aw values of both brown sugar and brown granulated sugar were less than 0.7 and did not significantly differ from each other. The color of these two kinds of sugar was characterized by a combination of red and yellow tones, and a value could be an indicator to discriminate between brown sugar and brown granulated sugar. While the crystal structure of brown sugar was regular and showed approximate rectangles, the angle of each crystal surface of brown granulated sugar, being almost oval, was not constant. The reducing sugar content of brown sugar was significantly higher than that of brown granulated sugar, while the ash and sucrose contents were significantly lower than those of brown granulated sugar. Minerals were more abundant in brown sugar, and the contents of K, Mg and Fe were significantly higher than those in brown granulated sugar. Brown sugar contained a much higher proportion of essential amino acids than brown granulated sugar. Compared with brown sugar, sulfur dioxide content of brown granulated sugar was higher, and both of them meet the industrial standards.
Analysis of Cuticle Components and Microstructure of Satsuma Mandarin (Citrus unshiu Marc.) and Bingtang Sweet Orange (Citrus sinensis Osbeck)
ZHANG Jing, DING Shenghua, XIE Qiutao, FU Fuhua, WANG Rongrong, LI Gaoyang, SHAN Yang
2018, 39(7):  131-138.  doi:10.7506/spkx1002-6630-201807020
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The surface of citrus peel is covered with a layer of wax, exerting multiple important physiological functions. The qualitative and quantitative analysis of cuticular components in the fruit peel of Satsuma mandarin (Citrus unshiu Marc.) and Bingtang sweet orange (Citrus sinensis Osbeck) were carried out by gas chromatography-mass spectrometry (GC-MS). Scanning electron microscopy (SEM) was used to observe the difference in the cuticle microstructure of Satsuma mandarin and Bingtang sweet orange. GC-MS results showed that the epicuticular wax contents of Satsuma mandarin and Bingtang sweet orange were 3.7 and 2.2 μg/cm2, respectively, and the intracuticular wax contents were 13.9 and 18.4 μg/cm2, respectively. The major aliphatic components of epicuticular and intracuticular wax in two citrus cultivars were identical, including alkanes, fatty acids, and primary alcohols, but their proportions and carbon number distribution were dependent on cultivars. Farnesol was found to be exclusively present in the epicuticular wax of Bingtang sweet orange. Moreover, triterpenoid compounds were detected only in the intracuticular wax. The cutin contents of Satsuma mandarin and Bingtang sweet orange were 44.00 and 70.00 μg/cm2, respectively, being significantly different. SEM showed irregular platelet flattened platelet waxes to be deposited on the surface of Satsuma mandarin and Bingtang sweet orange, respectively. The removal of epicuticular wax could cause a significant increase of water loss rate in Satsuma mandarin and Bingtang sweet orange (P < 0.05). Compared with fatty acids, alkanes played a more significant role in water retention in fruits. The differences in the chemical composition and microstructure of cuticle between citrus varieties may contribute to the differences in postharvest storage characteristics, which will provide important evidence for improving the storage quality of different citrus varieties.
Changes in Active Components and Antioxidant Activity of Hawthorn during Simulated Gastrointestinal Digestion in Vitro
FENG Yicheng, MOU Dehua
2018, 39(7):  139-145.  doi:10.7506/spkx1002-6630-201807021
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This study investigated the changes in the active components and antioxidant activity of hawthorn during simulated digestion in vitro. The contents of flavonoids, polyphenols, polysaccharides and organic acids in simulated salivary, gastric, intestinal digests and intestinal dialysate of hawthorn and hawthorn extract were determined, and their 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulphonate (ABTS) radical scavenging activity, hydroxyl radical (?OH) scavenging capacity and ferric ion reducing power were evaluated as well. The results showed that all four groups of active substances in five samples had similar trends during the digestion process, and polysaccharides and organic acids were significantly increased after oral and gastric digestion. All antioxidant properties except ?OH radical scavenging capacity showed similar trends during the entire digestion process. Both the salivary and gastric digests presented the highest antioxidant activity, while the intestinal dialysate exhibited the lowest. Therefore, hawthorn seemed to maintain good antioxidant activity during in vivo digestion.
Interaction of AG9/AB9 with BSA: Analysis by Debye-Hückel Limiting Law and Observation of Enthalpy-Entropy Compensation
CAO Lijun, CHENG Zhengjun, JIANG Xiaohui
2018, 39(7):  146-152.  doi:10.7506/spkx1002-6630-201807022
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Multispectral techniques were employed to detect salt concentration (i.e. ionic strength)-modulated interaction of acid green 9 (AG9) and acid blue 9 (AB9) with bovine serum albumin (BSA). The Debye-Hückel limiting law was applied to quantitative analysis to calculate the true Gibbs free energy change (ΔG0I→0) and effective charge (ZB) in the anion receptor pocket of BSA. The sign of ZC value for AG9/AB9 was negative and the ZB values were positive. These results indicated the formation of ion-pair between opposite charges; for example, the negatively charged AG9/AB9 bound to the net positively charged binding pocket (site-I) of BSA, suggesting that the local charge rather than the overall or surface charge of BSA played a key role in dominating the interaction strength of BSA-AG9/AB9 system. Moreover, with the increase of salt concentration, the entropy gradually varied from positive to negative and the exothermic enthalpy term increased so that the ΔG0 was almost invariant, namely enthalpy-entropy compensation. Finally, the thermodynamic parameters changed from ΔH0 < 0, ΔS0 > 0 (electrostatic force) to ΔH0 < 0, ΔS0 < 0 (non-electrostatic force) at high salt concentration. These results showed that the mobility/local motion of AG9/AB9 complexed with protein was retarded due to the transformation of dominant force.
Food Engineering
Change in Intermolecular Force of Myosin from Litopenaeus vannamei Treated by Dense Phase Carbon Dioxide
LIU Shucheng, GUO Minghui, LIU Yuan, JI Hongwu, GAO Jing, MAO Weijie, DENG Chujin, HAO Jiming, LUO Shuai, DONG Andi
2018, 39(7):  153-159.  doi:10.7506/spkx1002-6630-201807023
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Dense phase carbon dioxide (DPCD) is a promising non-thermal food processing technology, which can induce protein denaturation and self-assembly leading to gel formation. In order to clarify the mechanism of gel formation of myosin induced by DPCD, we explored the effects of DPCD treatment at different pressures and temperatures on intermolecular force of myosin from Litopenaeus vannamei. The results showed that compared with the untreated samples, DPCD treatment decreased the contents of hydrogen bonds and ionic bonds in myosin (P < 0.05), and increased the contents of hydrophobic interaction, disulfide bonds and non-disulfide covalent bonds (P < 0.05). In the case of DPCD treatment at the same temperature, pressure (5–25 MPa) had no significant effect on intermolecular force of myosin (P > 0.05). In the case of DPCD treatment at the same pressure, with the increase in temperature (40–60 ℃), hydrogen bonds and disulfide bonds did not change significantly (P > 0.05), non-disulfide covalent bonds increased (P < 0.05), hydrophobic interaction decreased (P < 0.05), and ionic bonds initially decreased followed by an increase (P < 0.05). Therefore, hydrophobic interaction, disulfide bonds and non-disulfide covalent bonds but not hydrogen bonds and ionic bonds are the major intermolecular forces in myosin gelation induced by DPCD. These results will provide useful data for clarifying the mechanism of myosin gelation induced by DPCD.
Far-Infrared Radiation Drying and Quality Characteristics of Sweet Purple Potato
YI Jie, LIU Yunhong, LI Haideng, SI Shangfei, ZHOU Xianlong, TAN Xixi, MA Liting
2018, 39(7):  160-167.  doi:10.7506/spkx1002-6630-201807024
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In order to explore the drying characteristics and quality of sweet purple potato using a far-infrared dryer, the effects of radiation temperature and distance on drying characteristics and nutrients including total phenols, total flavonoids, total sugar and VC were investigated. The results showed that drying time decreased and average drying rate increased significantly with an increase in radiation temperature and a reduction in radiation distance. The whole process of drying took place in the rate-falling period, thereby being mainly controlled by internal diffusion. The effective moisture diffusivity coefficient ranged from 2.42 × 10-10 to 4.64 × 10-10 m2/s and increased with an increase in radiation temperature and a reduction in radiation distance. The retention of total phenolics, total flavonoids, total sugar and VC was influenced significantly by radiation temperature and distance. The nutrient contents were very differently affected by temperature at different radiation distances. The optimal processing parameters were determined as radiation temperature of 240 ℃ and radiation distance of 14 cm based on comprehensive weighted scores. Under these optimized conditions, the drying time, and the contents of total phenols, total flavonoids, VC and total sugar were 270 min, 359.62, 223.13, 11.81 mg/100 g and 30.71 g/100 g, respectively. The drying rate and quality of dried product were both improved effectively by using far-infrared radiation. This study can provide a basis for the application of far-infrared radiation in the drying of sweet purple potato and other agricultural products.
Encapsulation of Astaxanthin in Zein-Saccharide Graft Reaction Products
KANG Xuefan, LI Haiming, CHEN Danjie, ZHANG Hui, FENG Fengqin
2018, 39(7):  168-173.  doi:10.7506/spkx1002-6630-201807025
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In this study, zein was grafted with glucose or xylose, and grafted zein/astaxanthin particles were prepared to study the impact of glycosylation on the encapsulation of astaxanthin. The percentages of glucose and xylose grafted onto zein were 2.59% and 2.53%, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) using Coomassie staining and Schiff staining proved the existence of glycoprotein. Circular dichroism results showed that the secondary structure of zein was changed as evidenced by a decrease of alpha-helix and an increase of beta-sheet and beta-turn, indicating partial protein unfolding. The field emission scanning electron microscopy and differential scanning calorimetry measurements showed that the formed zein/astaxanthin particles were hollow with astaxanthin well dispersed around. Compared to the untreated zein, the encapsulation efficiency of astaxanthin was increased by 10% in the grafted zein. After dissolving in ethanol solution for 12 h, the release rate of pure astaxanthin was 99.8%, while in the case of zein/astaxanthin, zein-glucose/astaxanthin, zein-xylose/astaxanthin particles, the release rates were 49.7%, 31.7% and 30.2%, respectively. The thermal stability of astaxanthin was significantly improved in these particles. After heating treatment, the loss rate of pure astaxanthin was 75.29%, while only 25% of encapsulated astaxanthin was lost.
Effect of High Pressure Carbon Dioxide Processing on Microbial Population and Quality of Fresh-Cut Hami Melon (Cucumis melo var. saccharinus)
HOU Zhiqiang, HUANG Xuying, WANG Yongtao, LIAO Xiaojun
2018, 39(7):  174-180.  doi:10.7506/spkx1002-6630-201807026
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This study aimed to determine the most suitable cleaning process for Hami melon. The changes in microbial populations (total aerobic bacteria (TAB), and total yeast and mold counts), sensory (mass loss, texture and sensory score) and physicochemical properties (total soluble solid (TSS) content, pH, vitamin C and polyphenoloxidase and peroxidase activity) of high pressure carbon dioxide (HPCD)-treated Hami melon during storage at 4 ℃ for 8 days were investigated. Results showed that treatment with strong acid electrolyzed water for 25 min was the best cleaning process. It could reduce TAB of Hami melon by 0.81 (lg (CFU/g)). During the storage, the number of microorganisms of fresh-cut melon HPCDtreated at 2.5, 3.5, 4.5 MPa for 8 min increased significantly and PPO activity also increased. In addition, fruit mass, hardness and ascorbic acid content were decreased respectively by 16.45%–42.70%, 30.38%–48.97% and 96.25%–96.73% after 8 days of storage. This study can provide a theoretical basis for further exploration and application of HPCD on fresh-cut fruits and vegetables.
Effect of Micronization-Enzymatic Hydrolysis on Nutrition and Functional Properties of Silkworm (Bombyx mori) Pupa Protein
LI Shaohui, JIA Junqiang, GUI Zhongzheng
2018, 39(7):  181-187.  doi:10.7506/spkx1002-6630-201807027
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In this paper, the nutritional and functional properties of silkworm (Bombyx mori) pupa protein modified by micronization-enzymatic hydrolysis were studied. Results showed that the ratio of essential amino acids to non-essential amino acids and to total amino acids in the modified protein reached the Food and Agriculture Organization/World Health Organization (FAO/WHO) recommended pattern suggesting significantly improved nutritional value compared with the native protein (P < 0.05). The degree of hydrolysis was increased by 65.62%, and solubility, emulsifying capacity and foaming capacity by 402%, 187%, and 141%, respectively; the sulfhydryl group content was increased by 57% whereas disulfide content was decreased by 21%; the amount of random coil secondary structure was increased from 37.46% to 91.33% after the modification. The modified pupa protein at 25 μg/mL enhanced the proliferation of mouse splenocyte by 100%, suggesting a significant improvement of immunity (P < 0.01).
Nutrition & Hygiene
Tannic Acid Inhibits the Akt Signaling Pathway by Modulating TRAF6 Recruitment to Plasma Membrane
RUAN Haihua, HU Shuangyan, ZHANG Chunchen, CAO Hua, ZHANG Zhen
2018, 39(7):  188-194.  doi:10.7506/spkx1002-6630-201807028
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Purpose: Epidermal growth factor receptor (EGFR)/protein kinase B (PKB, also named Akt) signaling pathway is over-expressed and abnormally activated in most human solid tumors. EGFR/Akt signaling activation has been known to promote cell proliferation, which is a key factor for tumor survival. Tannins are a class of plant polyphenols, which have been reported for their antitumor activity. However, it remains unclear how tannic acid regulates EGFR/Akt signaling pathway in tumors. Methods: In the present study, human malignant glioma U87 cells with over-activated EGFR/Akt signaling pathway were used as a model to clarify the mechanism underlying the inhibitory effect of tannic acid on cell proliferation and EGFR/Akt signaling pathway. Results: Tannic acid significantly inhibited the phosphorylation of Akt and its two downstream effector proteins, 4EBP-1 and S6, whose phosphorylation are important for protein translation and tumor cells proliferation. Tannic acid also suppressed the proliferation of human glioma U87 cells. Further investigation revealed that tannic acid could block the recruitment of TRAF6 to plasma membrane and decrease the amount of Akt directly interacted with TRAF6, leading to the inhibition of Akt phosphorylation in human glioma U87 cells. In order to validate the role of tannic acid in TRAF6 recruitment, we expressed a constitutively activated EGFR vIII mutant in human glioma U87 cells and found that the inhibition of tannic acid on EGFR phosphorylation, leading to the decrease of TRAF6 plasma membrane recruitment, required the existence of 2-7 exons of EGFR extracellular domain; and the inhibition of tannic acid in EGFR phosphorylation. Conclusion: EGFR is the receptor of tannic acid in human glioma U87 cells. Tannic acid manipulates TRAF6 recruitment and inhibits Akt activation, thereby executing the signal transduction of tannic acid across the cell plasma membrane into tumor cells. These results provide a possible mechanism for the potential anti-tumor therapy with food-derived tannin.
Characterization of Critical Amino Acids in Linear Immunoglobulin G Epitopes of α-Lactalbumin in Cow Milk
CONG Yanjun, LI Ye, LIU Jiaqi, CHEN Shu, YU Xiaofeng, LI Linfeng
2018, 39(7):  195-200.  doi:10.7506/spkx1002-6630-201807029
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α-Lactalbumin is one of the major allergens in cow milk. Characterizing the critical amino acids in the epitopes of α-lactalbumin is of great significance for the understanding of the role of immunoglobulin G (IgG) in milk allergy and the development of hypoallergenic dairy products. In this study, the alanine scanning of immunodominant epitopes was used to identify the critical amino acids. First, a series of peptides based on the sequence of α-lactalbumin were identified with IgG in individual sera from cow milk-allergic patients by enzyme-linked immunosorbent assay (ELISA). Then, new peptides were synthesized by sequential replacement of the amino acids acting on the epitopes with alanine, and the critical amino acids were identified with serum pool from cow milk-allergic patients by ELISA. The results showed that IgG-binding epitopes were located in the sequences of aa 6–20, aa 21–35, aa 36–50 and aa 86–100. Our data revealed Phe9, Leu15, Pro24, Trp26 and His32 were the critical aa in the IgG-binding epitopes.
Immune Interaction of Bioactive Components in Ziziphus jujuba cv. Huizao Fruits from Aksu
ZOU Man, ZHANG Yuhuan, CHEN Yilun, MA Xinfeng, WANG Guixin, MA Chao, ZHU Fengtao
2018, 39(7):  201-206.  doi:10.7506/spkx1002-6630-201807030
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The effects of intragastric administration of bioactive components such as polysaccharides, polyphenols and triterpenoids extracted from Ziziphus jujuba cv. Huizao fruits grown in Aksu alone and their combinations on mouse immune organ indexes, phagocytic index, antibody-producing capacity and delayed type hypersensitivity (DTH) to sheep red blood cells (SRBC) were studied in this work. The results showed that the polysaccharides, polyphenols and triterpenoids could significantly improve immune organ indexes, serum half hemolysis value (HC50), phagocytic index and footpad thickness, and enhance cellular and humoral immune responses and nonspecific immune responses in mice. The polysaccharides had synergistic immunoregulatory effects with the polyphenols. Moreover, the polysaccharides had an antagonistic interaction with the triterpenoids, and their effects were additive.
Antihypertensive and Hepatoprotective Effects of Yogurt Containing Purple Sweet Potato Extract and Casein Hydrolysate
HU Zhihe, XIA Lei, LI Yanjun, WANG Lijuan, XUE Lu
2018, 39(7):  207-214.  doi:10.7506/spkx1002-6630-201807031
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The objective of this paper is to produce a new yogurt containing purple sweet potato extract (PSPE) rich in anthocyanins (PSPE-A) and casein hydrolysate rich in angiotensin converting enzyme (ACE) inhibitory peptides (CH-A) based on ordinary yoghurt processing, and to evaluate its anti-hypertensive and hepatoprotective effects using animal model. Spontaneously hypertensive rats (SHR) were orally administered with yogurts containing 3.0 g of CH-A and 1.5 g of PSPE-A (treatment 1) or 3.0 g of CH-A and 3.0 g of PSPE-A (treatment 2) at a dosage of 3.33 g/kg. Results showed that at 4 h after administration, systolic blood pressure (SBP) of SHR in treatments 1 and 2 was decreased by (23.13 ± 2.41) and (26.23 ± 1.44) mm Hg, respectively. The SHR were orally administered with the yoghurts at a dose of 3.33 g/kg for 30 days to evaluate their hepatoprotective effect against alcoholic liver damage. Results showed that among five tested indexes, namely aspartate transaminase (AST), alanine transaminase (ALT), triglyceride (TG), malondialdehyde (MDA) and reduced glutathione (GSH), at least three indexes such as AST, ALT and MDA were improved significantly (P < 0.05). Both yogurts improved the hepatic cells and fat metabolism as evidenced by histopathological examination. Therefore, yoghurt containing purple sweet potato extract rich in anthocyanins and casein hydrolysate rich in ACE exerts antihypertensive and hepatoprotective effects in the experimental dosage range.
Packaging & Storage
Changes in Physicochemical Properties and Proteins during Shelf Life of Cold Stored Swamp Eel (Monopterus albus)
ZHENG Hong, SU Xianbo, MA Liang, ZHANG Xiaojie, MA Mingsi, SUN Yi, ZHANG Yuhao
2018, 39(7):  215-220.  doi:10.7506/spkx1002-6630-201807032
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The purpose of this study was to investigate the quality changes of cold stored Monopterus albus during shelf life. The results showed that the shelf life of Monopterus albus was 4 days during cold storage as determined by measuring total volatile basic nitrogen (TVB-N) content, K value (freshness index) and thiobarbituric acid reactive substances (TBARS). pH decreased firstly and then increased with storage time, color turned from bright red to brown red, and water-holding capacity decreased continuously. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and trichloroacetic acid (TCA)-soluble nitrogen measurement showed that myosin and actin were degraded gradually during storage. Chemical analysis indicated that ionic bonds and hydrogen bonds decreased, whereas disulfide bonds and hydrophobic interactions showed a gradually increasing trend. Fourier transform infrared spectroscopy analysis indicated that amide A band moved to high wavenumber, which was consistent with the changes of hydrogen bonds. Curve fitting of amide ? band indicated that interconversion between β-sheet and β-turn was dominant during the early storage period, and then the protein structural components were transformed to α-helix and random coil, indicating increased structural disorderliness. Overall, these results showed that hydrogen bonds and ionic bonds may be the major forces to maintain the secondary structure of protein during the early storage period. The destruction of hydrogen bonds and ionic bonds can cause changes in protein conformation.
Effects of Modification Methods and Maleic Anhydride Content on the Properties of Starch/Polyhydroxyalkanoate Composite Films
SUN Shenglin, LIU Pengfei, QIN Yang, WANG Wentao, HOU Hanxue, DONG Haizhou
2018, 39(7):  221-229.  doi:10.7506/spkx1002-6630-201807033
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Hydroxypropyl distarch phosphate/polyhydroxyalkanoate (PHA) composite films were prepared by extrusion blowing using maleic anhydride (MAH) as a compatibilizer. MAH was added at 1%, 3% or 5% into the starch/PHA system by two different methods, viz., blending starch and PHA with MAH directly by extrusion (method 1) or blending PHA modified with MAH under dry conditions with starch by extrusion (method 2). The aim was to explore the effects of modification methods and MAH content on the properties of composite films were explored. The results showed that when PHA content was 12%, the films prepared by direct addition of 1% MAH exhibited higher tensile strength and light transmittance, as well as better moisture barrier property, heat stability and compatibility with a flat, smooth and uniform microstructure, while those prepared by method 2 with 5% MAH had higher elongation at break and a flat and smooth surface. The films prepared with 24% PHA and 3% MAH by the first method exhibited higher tensile strength, moisture barrier property and heat stability with a smooth and uniform microstructure. The films prepared by the second method with 24% PHA and 3% MAH had better mechanical properties, while films with higher light transmittance were obtained with 5% MAH when other conditions were kept the same. Fourier transform infrared spectroscopy suggested that addition of MAH could enhance the intermolecular interaction. These results suggested that the films prepared by direct addition of 1% MAH exhibited better properties when PHA content was 12%, whereas those prepared by direct addition 3% MAH showed better properties when PHA content was 24%.
Effects of Temperature and Mechanical Vibration Conditions on Grape Quality during Storage and Transportation
ZHANG Zhe, ZHANG Zhiquan, HAO Junjie, ZHANG Ping, ZHU Zhiqiang, TIAN Jinjin, DING Hao, MAO Yiqiong
2018, 39(7):  230-235.  doi:10.7506/spkx1002-6630-201807034
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Based on the actual situation during storage and transportation, the effects of temperature fluctuations, and mechanical vibration frequency and acceleration rate on the storage quality of Kyoho grape were investigated. The experimental temperature conditions (?1, ?1 to 1, ?1 to 2, ?1 to 3 and ?1 to 5 ℃) and mechanical vibration conditions (three vibration acceleration rates of 2.5, 5.0 and 7.5 m/s2 and five vibration frequencies of 10, 20, 30, 40 and 50 Hz) were designed. The effects of temperature fluctuations and mechanical vibration conditions on hardness and titratable acid content, threshing percentage, decay incidence, and vitamin C content in grapes from each group were analyzed. The experimental results showed that temperature fluctuation had the largest effects on vitamin C content and hardness. Vibration frequency was not directly proportional to the rate of grape deterioration. At 20 Hz, however, the rate of quality deterioration was slowest during actual storage and transportation process. The greater vibration acceleration rate could result in more severe damage to grape quality during the early period of storage, and the effect of vibration acceleration rate on threshing percentage and hardness was greatest.
Effects of Extraction Temperature of Chum Salmon (Oncorhynchus keta) Skin Gelatin and Glycerol Content on Its Film-Forming Properties
LIU Yang, XIA Lining, JIA Hui, LI Qi, PAN Jinfeng
2018, 39(7):  236-242.  doi:10.7506/spkx1002-6630-201807035
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Extraction temperature and glycerol content are the critical factors affecting gelatin film properties. In the present study, chum salmon (Oncorhynchus keta) skin gelatin was extracted at different temperatures (40, 50, 60, 70, 80 and 90 ℃), and the effect of glycerol content (1.1, 1.2 and 1.5 g/100 mL) on gelatin film properties including thickness, mechanical properties, color, optical properties, microstructure and infrared absorption characteristics was explored. Results indicated that films of gelatin extracted at 40, 50 and 60 ℃ showed higher thickness than films of gelatin extracted at 70, 80 and 90 ℃ (P < 0.05). Mechanical analysis showed that tensile strength (TS) of films of gelatin extracted at 50 and 60 ℃ was higher than that of films of gelatin extracted at 70, 80 and 90 ℃ (P < 0.05). Elongation at break (EAB) of films with 1.5 g/100 mL glycerol increased with the increase of gelatin extraction temperature (P < 0.05). TS of films prepared from gelatin extracted at 50, 70 and 80 ℃ declined with the increase of glycerol content (P < 0.05). The a* value of films increased with the increase of gelatin extraction temperature (P < 0.05). Water vapor permeability (WVP) showed an increase with the increase of extraction temperature and glycerol content (P < 0.05). The light transmittance of films were 0.00% at wavelengths of 200 and 280 nm and 46.53%–74.57% in the range of 350–800 nm. The light transmittance of films prepared from gelatin extracted at 60 ℃ was lower than that of films prepared from gelatin extracted at 40 and 50 ℃ (P < 0.05). Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) analysis demonstrated that gelatin films exhibited the characteristic absorption regions of gelatin, including amide I, II and III bands and amide A and B bands. Among them, amide A shifted to lower wavelength with the increase of extraction temperature and its amplitude increased with increase of glycerol content. Scanning electronic microscopy showed no distinct crack or gaps on the surface and cross section of films. The results indicated that extraction temperature had a significant impact on mechanical properties, WVP and color of gelatin films. However, glycerol content only affected mechanical properties and WVP. Thus, the properties of films prepared from chum salmon skin gelatin can be improved by optimizing gelatin extraction temperature and glycerol content.
Preparation and Properties of Silver Carp Skin Gelatin-Sodium Alginate Composite Films
GUO Kaihong, ZHANG Leilei, WU Xiaocui, XIONG Shanbai, HU Xiaobo
2018, 39(7):  243-248.  doi:10.7506/spkx1002-6630-201807036
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Silver carp skin gelatin film has aroused wide attention due to its unique advantages including high safety and easy availability. However, the application of pure silver carp skin gelatin film in the food packaging industry is hampered due to its poor mechanical and barrier properties. In order to improve the properties of the film, the fish skin gelatin and sodium alginate were mixed to obtain composite films. The results showed that the composite films had a translucent appearance and could provide a shield against ultraviolet light and oil. The composite films with 20% sodium alginate had minimum water solubility and water vapor permeability and maximum tensile strength, suggesting that barrier properties and mechanical properties of the composite films were better than those of pure fish skin gelatin film. Fourier transform infrared (FT-IR) spectra and X ray diffraction results revealed a strong interaction between fish skin gelatin and sodium alginate, which may be the major cause of changes in the properties of the composite films.
Effect of Crude Extract Containing Antimicrobial Peptide Produced by Lactobacillus paracasei subsp. tolerans FX-6 on the Quality of Litchi during Storage
PENG Bo, FENG Konglong, MIAO Jianyin, CHEN Yunjiao, CHEN Feilong, CAO Yong
2018, 39(7):  249-255.  doi:10.7506/spkx1002-6630-201807037
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The inhibitory effect of crude extract containing antimicrobial peptide from Lactobacillus paracasei subsp. tolerans FX-6 on the growth of Phytophthora litchi was investigated in vitro, and the effect of two different concentrations of the extract on the quality of litchi during storage at 25 ℃ was also evaluated using prochloraz as a control. The results showed that the antimicrobial peptide could significantly inhibit the growth of Phytophora litchi, improve the storage quality of litchi fruits, inhibit mildewing and browning, and preserve the nutritional quality of litchi pulp. The antimicrobial peptide at 0.5 mg/mL had better effect than prochloraz at the same concentration but was less effective than at 1.0 mg/mL. It is clear that the antimicrobial peptide could prolong the storage period of litchi at normal temperature, thus having potential application value.
Effects of Flavonoids Extracted from Lycium barbarum Leaves on the Quality of Minced Mutton Mixture during Cold Storage
HAN Lina, SHEN Hao, TIAN Jianwen, FAN Yanli
2018, 39(7):  256-262.  doi:10.7506/spkx1002-6630-201807038
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Minced mutton mixture with high nutritional value was made from vegetable oils rich in n-3 polyunsaturated fatty acids and mutton. The effects of adding different amounts (0.5%, 1.0% and 1.5%) of flavonoids extracted from Lycium barbarum leaves on lipid peroxidation indexes and textural properties of minced mutton mixture were studied during refrigerated storage (4 ℃). The results showed that the flavonoids could significantly inhibit the increase of pH, acid value, peroxide value and total volatile basic nitrogen (TVB-N) content (P < 0.05) in a dose-dependent manner. Meanwhile, the flavonoids could also increase hardness, gumminess and chewiness (P < 0.05), and effectively control textural changes caused by spoilage. In addition, they could preserve the sensory quality of minced mutton during the whole storage period. These results indicated that the flavonoids extract from Lycium barbarum leaves could significantly inhibit lipid oxidation in minced mutton, which will provide a new direction and theoretical basis for the deep processing and utilization of Lycium barbarum leaves and the development of mutton products rich in n-3 polyunsaturated fatty acids.
Reviews
Progress in the Generation and Health Risks of Methylglyoxal in Foods and Methylglyoxal-Scavenging Agents from Natural Products
GUO Limin, ZHANG Wensheng, LI Shiming
2018, 39(7):  263-269.  doi:10.7506/spkx1002-6630-201807039
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Methylglyoxal (MG) is one of the most potent active carbonyl compounds harmful for human health. MG as an endogenous metabolite exists in foods, especially processed foods and beverages containing sugar or high fructose corn syrup. MG has a direct cytotoxicity and can participate in the glycation of proteins and nucleic acids, triggering carbonyl stress and consequently inducing pathological status and even exacerbateing the development of chronic degenerative diseases. Herein, we summarize the mechanism of MG generation during food processing and its pathological risks, especially the types, structure and reactivity of MG trapping agents from edible plants. The aim is to provide a theoretical evidence for finding natural, effective and efficacious MG scavenging agents for the development of functional foods.
A Review of the Application of Fourier Transform Infrared Spectroscopy for Quality and Safety Analysis of Edible Oils
CHEN Jia, YU Xiuzhu, LIU Xiaoli, XU Lirong, LI Mengjun, HUYAN Zongyao
2018, 39(7):  270-277.  doi:10.7506/spkx1002-6630-201807040
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In order to expand the application of Fourier transform infrared (FTIR) spectroscopy to analyze edible oils, we herein summarize recent advances in the application of FTIR spectroscopy for evaluating the quality and safety of edible oils. Oil quality has been evaluated in terms of physicochemical properties (peroxide value, trans fatty acid content, free fatty acid content, moisture content, iodine value, carbonyl value and multivariable analysis) and oxidative stability. The safety of edible oils has been tested by assessing their authenticity. This review is focused on the discussion of spectral acquisition, waveband selection, data processing and substrate effect elimination.
Progress in Research on Hydroxyoctadecaenoic Acids as Oxidation Products of Linoleic Acid
JIANG Chunjiao, JIANG Yun, GENG Zhiming, ZHANG Muhan, SUN Chong, BIAN Huan, WANG Daoying, XU Weimin
2018, 39(7):  278-284.  doi:10.7506/spkx1002-6630-201807041
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Hydroxyoctadecaenoic acids (HODEs) are oxidation products of linoleic acid (LA). Existing studies indicate that endogenous HODEs exert pathophysiological roles in the development and progression of some human diseases, while exogenous HODEs may have the same effects and the potential health risk associated with them deserves the public’s concern. The present paper reviews the classification, formation mechanism, pathophysiological significance and analytical methods of HODEs. Moreover, prospects for future research in the field of food safety are also proposed.
Effects of Artificial Sweeteners on Human Health
GAO Yuting, ZHANG Peng, DU Gang, LI Shiming, ZHAO Hui
2018, 39(7):  285-290.  doi:10.7506/spkx1002-6630-201807042
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Artificial sweeteners (AS) are a class of food additives made by human beings. Because of their high sweetness, non-calorie and non-nutritional value, they are widely used in food and beverage processing. However, recent studies have shown that excessive intake of AS can cause changes in the structure and compositions of the gut microbiota, thereby leading to glucose intolerance and metabolic disorders and even giving rise to obesity and other health problems. These results suggest that attention should be paid to AS intake and ingestion time during their application, which will provide a theoretical basis for further development and rational application of AS.
Protective Effect of Cryoprotectants on Protein Denaturation in Frozen Fish Meat
SHAO Ying, YAO Jieyu, JIANG Yangyang, DING Tian, CHEN Shiguo, HU Yaqin
2018, 39(7):  291-297.  doi:10.7506/spkx1002-6630-201807043
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Frozen storage is a widely used method for long-term preservation of fish and fish products. Cryoprotectants can effectively inhibit protein denaturation and maintain the quality of fish meat during frozen storage. The mechanism of protein denaturation in frozen fish and the mechanisms of action of commonly used cryoprotectants including sugars, sugar alcohols, carbohydrate degradation products, polyphenols, protein hydrolysates, salts and antifreeze peptides are reviewed in this article. The factors influencing the efficacy of these cryoprotectants and their applications and limitations are discussed with the aim of providing a comprehensive reference for cryoprotection of frozen fish meat.
A Review of the Application of Matrix-Assisted Laser Desorption Ionization Mass Spectrometry Imaging in Food Analysis
YIN Xiaoyu, CHEN Qian, HAN Qi, KONG Baohua
2018, 39(7):  298-304.  doi:10.7506/spkx1002-6630-201807044
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Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI), a new analytical technique, is widely used in biological, medical and other fields due to its usefulness for the detection of compounds without extraction, purification, separation, or labeling. Although the methodology of MALDI-MSI in food science is not yet fully established, its application is expected to open up a new insight in food science. In this paper, the principle of MALDI-MSI imaging is described and its application in sample preparation and food analysis is reviewed. Future prospects for MALDI-MSI application are also discussed. We expect that this review which will provide a basis for the application and popularization of MALDI-MSI in food analysis.
Progress in Foodborne Pathogen Cross-Contamination and Risk Assessment during Meat Processing
JIANG Ronghua, WANG Wen, CAI Zheng, LIN Yuhai, DONG Qingli
2018, 39(7):  305-311.  doi:10.7506/spkx1002-6630-201807045
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Foodborne pathogen cross-contamination between food-contact surfaces and processing equipment surface readily occurs during meat processing, causing health risks upon consumption of the final products. Nowadays, the risks associated with the consumption of meat products have been assessed worldwide. This paper reviews studies published between 2000 and today on foodborne pathogen cross-contamination during meat processing and the models used to study this issue. The current status of foodborne pathogen cross-contamination during meat processing and the foodborne illnesses caused by pathogen cross-contamination are presented and some models available to describe foodborne pathogen cross-contamination during meat processing and their application in microbial risk assessment are briefly outlined. We also summarize current studies on the risk assessment of sausage and ham products. Finally, some suggestions and thoughts are put forward for further studies on foodborne pathogen cross-contamination during meat processing and quantitative microbial risk assessment. Our suggestions include: make more efforts to model foodborne pathogen cross-contamination during meat processing, reinforce the interaction between risk assessment and management, establish a perfect risk monitoring system and carry out further systematic studies on quantitative microbial risk assessment.
Aflatoxin B1 Contamination in Foods: A Review
ZHANG Muchen, ZHENG Nan, WANG Jiaqi
2018, 39(7):  312-320.  doi:10.7506/spkx1002-6630-201807046
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Crops including maize and wheat are easily contaminated by toxigenic fungi and mycotoxins during growth, harvest and storage, which will induce acute or chronic toxic reaction when humans consume processed grains and oils as well as livestock products containing these toxins. Among various types of mycotoxins, aflatoxin B1 (AFB1) is more commonly encountered and it is considered to more toxic. Excessive intake of AFB1 may cause cancer, teratogenesis or immunosuppression. This review summarizes previous studies on the sources of AFB1 contamination, the factors affecting it, the molecular structure, toxicity, pathogenesis, limit standard, risk assessment, and prevention and control of AFB1 in foods.
Biosynthesis, Metabolic Regulation and Bioactivity of Phenolic Acids in Plant Food Materials
CHEN Zhijie, WU Jiaqi, MA Yan, WANG Pei, GU Zhenxin, YANG Runqiang
2018, 39(7):  321-328.  doi:10.7506/spkx1002-6630-201807047
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Phenolic acids, a class of secondary metabolites containing phenolic hydroxyl and carboxyl groups, are widely distributed in higher plants. Phenolic acids are bound to structural components of the cell wall through ester and ether linkages in plant food materials, and have multiple bioactivities, such as antioxidant, antimicrobial and anticancer activity. Phenolic compounds have gained wide interest in recent years and become one of the hotspots in the field of food research. Through a series of biological regulation techniques, various phenolic acids can be enriched in plant food materials, thereby effectively improving their nutritional value. In this paper, the types, structures, biosynthesis, metabolic regulation and bioactivities of phenolic acids in plant food materials are summarized. In the end, the future directions are also discussed.
Progress in Mining of Microbial Lipase Resources
CAI Haiying, WANG Zhenzhen, ZHANG Ting, ZHAO Minjie, LI Yang, MAO Jianwei, FENG Fengqin
2018, 39(7):  329-337.  doi:10.7506/spkx1002-6630-201807048
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Lipases are ubiquitous in animals, plants and microorganisms, but industrial lipases are mainly produced by microorganisms. The industrial application of lipases is constrained by its high cost and enzymatic characteristics such as temperature and pH tolerance, specific activity, substrate specificity and solvent resistance. Despite the abundance of information regarding microbial lipase genes and proteins, there are currently very few commercial lipase preparations that are suitable for application in the food, pharmaceutical and energy industries. Accordingly, tremendous research efforts have been made to mine novel alternative lipase resources. This article mainly presents a review of the approaches used to mine microbial lipase resources including environmental screening and metagenomics screening for mining new lipases with good properties, genetic improvement of lipase-producing strains, recombinant expression of lipases in genetically engineered strains, lipase modification by protein engineering, lipase immobilization and optimization of reaction conditions of immobilized lipase.
Advances in the Application of Physical Methods in Preservation of Fresh-Cut Apples
WANG Zhirong, YANG Qi, Lü Xingang, ZHENG Lirong, GAO Hui
2018, 39(7):  338-343.  doi:10.7506/spkx1002-6630-201807049
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Fresh-cut apples are favored by consumers due to their freshness and convenience. However, mechanical damage during the processing of fresh-cut apples will destroy the structure of apple tissue, rendering it prone to browning, softening, rotting and other issues. Yet traditional chemical preservation methods have been unable to meet the desire of consumers for safe and high quality food products. In contrast, physical methods have been extensively used in the preservation of fruits and vegetables due to their easiness to control, high efficiency and good safety. This article reviews the application of photoelectric methods, high-pressure technology, modified atmosphere packaging, temperature control and other physical techniques for maintaining the storage quality of fresh cut apples. The possible mechanisms underlying these preservation technologies are elucidated with respect to enzyme inactivation, enzymatic browning inhibition and microbial inactivation. The storage quality of fresh-cut apples will be ensured with the development and application of these technologies.