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Table of Content

25 December 2019, Volume 40 Issue 24
Food Chemistry
Effects of Salt Ions on the Properties of Peanut Protein Isolate Nanoparticles and Pickering Emulsion Stabilized with the Nanoparticles
ZHANG Yazhen, XIONG Wenfei, PEI Yaqiong, LI Yan, LI Bin, WANG Ling
2019, 40(24):  1-7.  doi:10.7506/spkx1002-6630-20180910-092
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In this experiment, peanut protein isolate (PPI) nanoparticles were prepared and used to stabilize Pickering emulsion. The effects of salt ions on the transmittance (solubility), surface zeta potential of PPI nanoparticles solution and on the properties of Pickering emulsion stabilized with PPI nanoparticles were investigated. The results manifested that when salt ions were added to the solution of PPI nanoparticles, the surface zeta potential decreased, while the solubility lowered firstly and then heightened with the increase of salt concentration. The properties of the Pickering emulsion stabilized with the PPI nanoparticles exhibited that the emulsion had more uniform distribution of particle size and better storage stability with different salt ions. The emulsion particle size increased slightly at different concentrations of NaCl, but it rose significantly at different concentrations of CaCl2. As a consequence, PPI nanoparticles stabilized-Pickering emulsion has better resistance to NaCl.
Effects of Fatty Acids on Taste Quality of Cooked Rice
BI Xue, Sailimuhan·ASIMI, ZHANG Min, ZHOU Qi, YANG Zaishan
2019, 40(24):  8-14.  doi:10.7506/spkx1002-6630-20190121-242
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This work was conducted to study the effect of fatty acids (oleic acid and linoleic acid) on the taste quality of cooked rice from the cultivar ‘Kenyu 38’. Its texture, volatile flavor compounds and starch gelatinization characteristics were measured by using a cooked rice hardness viscometer, gas chromatography-mass spectrometry (GC-MS) and a rapid viscosity analyzer, respectively. The results showed that the amount of complexes formed by oleic acid, linoleic acid and rice starch increased with increasing addition of fatty acids from 1% to 3%. The hardness of cooked rice increased by 9.02%–30.97% and 12.45%–29.10% with addition of oleic acid and linoleic acid, respectively, while the viscosity decreased by 23.28%–53.44% and 11.64%–30.17%, respectively. Compared with linoleic acid, oleic acid molecules were more likely to form a complex with rice starch, leading to a more significant reduction in the viscosity of cooked rice. The addition of oleic acid and linoleic acid significantly increased the final viscosity (from 198.88 RVU to 232.21 and 237.96 RVU, respectively) and retrogradation value (from 59.04 RVU to 126.96 and 90.96 RVU, respectively) of rice starch. Compared with linoleic acid, oleic acid contributed more to the gelatinization properties of rice starch and to the formation of volatile flavor components in cooked rice.
Purification and Mechanism of Action of a Prolyl Endopeptidase Inhibitor from the Skeletal Muscle of Blue Scad (Decapterus maruadsi)
ZHONG Chan, XIE Xueqiong, SUN Lechang, ZHANG Lingjing, LIU Guangming, CAO Minjie
2019, 40(24):  15-20.  doi:10.7506/spkx1002-6630-20181210-117
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In the present study, an endogenous prolyl endopeptidase inhibitor (PEPI) was purified from the skeletal muscle of the marine fish blue scad (Decapterus maruadsi) by thermal precipitation, ammonium sulfate fractionation and a series of column chromatographies on DEAE-Sepharose, Sephacryl S-200 HRand HiTrap Q HP. Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Tricine-SDS-PAGE) showed that the molecular mass of PEPI was about 10 kDa. It was thermally stable and displayed tolerance to pH change. PEPI was a specific inhibitor to serine proteinase PEP and it worked in a reversible competitive manner with an inhibitory constant (Ki) of 0.34 μmol/L. A significant increase in α-helix and random coil and decrease in β-sheet were detected after formation of the PEP-PEPI complex. Quite possibly, the conformational change of PEP was the major reason for enzymatic activity inhibition.
Effect of Moisture Content on Quality of Frozen Nemipterus virgatus Sausages
ZHANG Shiwen, YI Shumin, Lü Keming, LI Xuepeng, LI Yuanzhao, DING Haochen, XU Yongxia, MI Hongbo, ZHU Wenhui, LI Jianrong
2019, 40(24):  21-26.  doi:10.7506/spkx1002-6630-20190122-266
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In order to investigate the effect of moisture content on the quality of frozen Nemipterus virgatu sausages, the fish sausages with moisture contents of 76%, 78%, 80%, 82% and 84% were frozen at –20 ℃ and then thawed at 4 ℃, while their counterparts maintained at 4 ℃ served as control. The freezing curve, thawing drip loss, water-holding capacity, moisture distribution and state, texture, microstructure and sensory evaluation were measured. The results showed that the freezing point and thawing drip loss increased with increasing moisture content of sausages, while the opposite was true for the water-holding capacity, texture and sensory evaluation. The immobilized water was transformed into free water. The gel microstructure became more loose and the ability to bind moisture was weakened. The quality indices of N. virgatus sausages frozen at –20 ℃ were lower than those of the controls. In summary, the quality of frozen N. virgatus sausages can be improved by reducing the moisture content.
Purification, Structural Identification and Effect on Cell Viability of RAW264.7 Macrophages of Polysaccharides from Psoralea corylifolia L. Fruits
YIN Zhenhua, ZHANG Juanjuan, CHEN Lin, GUO Qingfeng, ZHANG Wei, KANG Wenyi
2019, 40(24):  27-32.  doi:10.7506/spkx1002-6630-20190520-223
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In this study, purified polysaccharides from the fruits of Psoralea corylifolia L. (PPs) were investigated for their general physicochemical properties, monosaccharide composition, molecular mass, infrared spectroscopic characteristics, nuclear magnetic resonance (1H-NMR and 13C-NMR) characteristics and microstructure together with their effects on the cell viability of RAW264.7 macrophages. The crude polysaccharides, obtained by hot water extraction and ethanol precipitation, were deproteinized by Sevag’s method and then fractionated into two polysaccharides (PPs-1-1 and PPs-2-1) by DEAE-52 with 0.05 mol/L NaCl as the eluent and Sephadex G-100 column chromatography. Both PPs-1-1 and PPs-2-1 were dried into a white flocculent powder, soluble in water but insoluble in ethanol, n-butanol, acetone, chloroform, petroleum ether and other organic solvents. They were negative to Coomassie brilliant blue staining, and reaction with Fehling reagent, ferric chloride and iodine-potassium iodide, and their total sugar contents were (94.35 ± 0.23)% and (95.27 ± 0.42)%, respectively. Both polysaccharides were composed of rhamnose, arabinose, xylose, mannose, glucose and galactose with different molar ratios, and their average molecular masses were 3.98 × 106 and 4.47 × 106 g/mol, respectively. PPs-1-1, showing a three-dimensional laminar structure with a smooth and dense surface, contained α-/β-furanosides. PPs-2-1, having β-pyranosides, exhibited a multilayer lamellar structure with loose and porous surface morphology. PPs-1-1 and PPs-2-1 at concentrations lower than 0.16 and 0.01 μg/mL, respectively could significantly activate RAW264.7 macrophages.
Effects of Konjac Glucomannan on the Structural and Functional Properties of Gluten in Frozen Wheat Dough
GUO Jinying, HE Yijie, HAN Sihai, REN Guoyan, WU Ying, LUO Denglin, LIU Jianxue
2019, 40(24):  33-39.  doi:10.7506/spkx1002-6603-20181225-294
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This investigation studied the effects of konjac glucomannan (KGM) on the molecular mass, free sulfhydryl content, secondary structure, microstructure and functional properties (water-binding capacity, rheological properties and thermal properties) of gluten from frozen wheat dough. SDS-PAGE, a rheometer, a differential scanning calorimeter, an ultraviolet (UV) spectrophotometer, Fourier transform infrared spectroscopy and scanning electron microscopy (SEM) were used to analyze the structural and functional properties. The results showed that added KGM significantly enhanced the water-binding capacity and improved the viscoelasticity, the denaturation temperature (Tp) and denaturation enthalpy (ΔH) of gluten. In the presence of KGM, the contents of gluten α-helix and β-sheet increased, but the contents of β-turn and random coil decreased, improving the freeze stability of gluten. SEM image analysis showed that the microstructure of gluten added with 1.5% KGM had a distinct spongy structure with larger pores. KGM has a significant effect on gluten in frozen wheat dough and can act as a cryoprotectant for gluten.
Isolation, Purification and Structural Identification of Antioxidant Peptides Derived from Enzymatic Hydrolysis of Pine Nut Kernel (Pinus koraiensis Sieb. et Zucc.) Albumin
LU Hongyan, YANG Hang, FANG Li, LIU Shimeng, MIN Weihong
2019, 40(24):  40-45.  doi:10.7506/spkx1002-6630-20181114-164
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Two peptides with strong antioxidant activity were seprate and purified from the alkaline protease of pine nut kernel albumin hydrolysate by by ultrafiltration, column chromatographies on Sephadex G-25, and Sephadex G-15 and reversed-phase high-performance liquid chromatography, and their structure was identified by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The peptides were found to be Phe-Phe-Pro-Tyr (FFPY) and Tyr-Leu-Pro-Phe (YLPF) with molecular masses were 572.67 and 538.65 Da, respectively. Solid phase synthesis of FFPY and YLPF was performed with a purity of 99.16% and 99.91%. It was proved that the oxygen radical absorbance capacity (ORAC) values of FFPY and YLPF were 7 329.63 and 2 835.47 μmol/g, respectively.
Impacts of Calcium Ion Addition on Rheological, Gel and Textural Properties of Apple Pectin-Apple Polyphenol Compound
WANG Hanchen, CHOU Shurui, CUI Huijun, ZHANG Shuyi, LIU Xuan, LI Bin
2019, 40(24):  46-52.  doi:10.7506/spkx1002-6630-20190122-275
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In this experiment, we investigated the impacts of calcium chloride addition at different levels (0.1%, 0.2%, 0.3% and 0.4%) on rheological, gel and texture properties of apple pectin-apple polyphenol compound so as to determine the optimal concentration of added calcium ions in calcium-fortified foods produced from apple pectin and apple polyphenols. The results showed that addition of calcium chloride had a notable influence on both rheological, gel and textural properties. Gel strength increased with calcium chloride addition up to 0.3% and then decreased. In addition, the gel formation rate gradually accelerated, the gel structure became more stable, leading to good gel properties, with increasing calcium chloride addition to 0.3%. But when further increasing the amount of added calcium chloride, the gel stability continued to decrease, and the gel formation rate became slower, prolonging the gel formation process. Moreover, texture properties of apple pectin-apple polyphenol compound were also greatly influenced by addition of calcium ion. Compound hardness, elasticity, viscosity, cohesiveness and chewiness increased to the maximum values with increasing addition of calcium ion to 0.3%, and then decreased with further increase in calcium ion addition. Therefore, in order to ensure the optimal rheological, gel and textural properties of calcium-fortified foods containing apple pectin-apple polyphenol compound system, the calcium ion concentration should be set as 0.3%.
Identification and Metal Chelation Activity of a Copper-Binding Peptide from Rice Globulin Hydrolysate
XING Changrui, CHU Chenlu, ZHANG Xiaoyun, WANG Jinyan, JU Xingrong, YUAN Jian
2019, 40(24):  53-59.  doi:10.7506/spkx1002-6630-20190521-240
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Four rice proteins were obtained by sequential extraction, and their metal element contents were determined. Rice globulin was selected from these proteins for hydrolysis by pepsin, and the hydrolysate was purified by ultrafiltration. The fraction containing polypeptides was collected and detected by mass spectrometry (MS). A total of 23 polypeptides with molecular mass ranging from 725 to 1 409 Da were obtained through software analysis. Based on the data reported in the literature, the polypeptides QGWSSSSE and YYGGEGSSSEQGY may have potential metal chelation activity. The Cu2+ chelation activity of the two synthetic polypeptides was compared with that of EDTA, citric acid and metallothionein. It was found that YYGGEGSSSEQGY had a better Cu2+ chelation activity than QGWSSSSE. The IC20 of YYGGEGSSSEQGY was 5.40 mmol/L, which was comparable to that of citric acid in a low concentration range, but was worse than EDTA and metallothionein. Furthermore, these two polypeptides could more strongly bind Fe2+ than other metal ions. Amino acid composition analysis showed that continuous serine SS, SSS, and SSSS may be associated with the copper-binding activity.
Preparation and Physicochemical Stability of Perilla Seed Oil Double-Layer Emulsions
YU Youqiang, GAO Yaxin, ZHU Qiaosha, MOU Dehua, DUAN Shenglin, HOU Zhanqun
2019, 40(24):  60-65.  doi:10.7506/spkx1002-6630-20180828-307
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In this paper, perilla seed oil single-layer and double-layer emulsions were prepared using perilla seed oil as the core material and soybean polysaccharides and chitosan as the wall material, respectively. The particle size, zeta potential, physical stability and chemical stability of the emulsions were analyzed. Results showed that with the increase in core-to-wall ratio (m/m), the particle size of single-layer emulsions increased and the physical stability became worse and that the optimum core-wall-ratio was 2:1. With the increase in chitosan concentration, the zeta potential of double-layer emulsions increased gradually, changing from negative and positive values. When the chitosan concentration was 0.2%, the minimum absolute value of zeta potential of 3.6 mV was obtained compared to 43 mV when increasing the chitosan concentration to 0.4%, indicating that the rate of increase in potential slowed with increasing chitosan concentration. Moreover, the particle size decreased first, then increased, and finally decreased again. When the chitosan concentration was 0.2%, the maximum particle size of 5.21 μm was observed, and it decreased to the minimum value of 1.185 μm when increasing the chitosan concentration to 0.4%. The physical stability of emulsions increased with the increase in chitosan concentration, and the chemical stability was significantly influenced by chitosan concentration (p < 0.05). The emulsions with 0.4% chitosan had the highest oxidation stability, followed by those with 0.6% and 0.2% chitosan.
Effects of Three Functional Sweeteners on Cooking Quality and Digestion Characteristics of Rice
PEI Fei, NI Xiaolei, ZHONG Lei, YANG Wenjian, YAO Yijun, MA Ning, FANG Yong, HU Qiuhui
2019, 40(24):  66-72.  doi:10.7506/spkx1002-6630-20190511-116
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In order to improve the cooking quality of rice, to retard the retrogradation of cooked rice and to improve the digestibility of cooked rice, we evaluated the effects of three low-energy sweeteners of fructo-oligosaccharide, sorbitol and maltitol at different concentrations on the water absorption rate and the proportion of amylase in raw rice, as well as the hardness, microstructure, thermal characteristics and digestibility of cooked rice. The results showed that all the three sweeteners could improve the water absorption capacity of raw rice and reduce the hardness and digestibility in vitro of cooked rice. The water absorption rate after 25 min immersion was 11.18% higher in 1.6% fructo-oligosaccharide solution than in blank control, and the proportion of amylose, gelatinization enthalpy and hardness after 24 h decreased by 7.36%, 22.91% and 21.79%, respectively. Compared with the other treatments, 1.6% fructo-oligosaccharide treatment significantly reduced gelatinization enthalpy and crystallinity, and showed better microstructure and anti-retrogradation ability. This study provides a basis for deep processing of rice and the development of instant rice products.
Structural Characterization of Translutaminase Cross-linked Soy Protein Isolate
ZANG Xueli, CHEN Guang
2019, 40(24):  73-78.  doi:10.7506/spkx1002-6630-20190722-282
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This study aimed to examine the effect of translutaminase (TGase) cross-linking on the molecular structure of soybean protein isolate (SPI). The structural changes of SPI before and after cross linking were analyzed by differential scanning calorimetry (DSC), scanning electron microscopy, X-ray, infrared spectroscopy and circular dichroism spectroscopy. The results showed that after being cross-linked, the surface hydrophobicity of SPI increased, and the content of free amino groups reduced. The structure and microcrystal structure changed from spherical to concave, with the polypeptide chains stretched adequately, the spatial structure changed and the crystallinity decreased; the β-fold content increased, the structure becoming more ordered, while the random coil content decreased. Finally, we found that the content of essential amino acids increased by 5.5% and the content of hydrophobic amino acids by 14.5%, indicating that the nutritional value and surface hydrophobicity of SPI was improved after cross linking, as analyzed by an amino acid automatic analyzer.
Cryoprotective Mechanism of Epigallocatechin Gallate on Frozen Nile Tilapia (Orechromis niloticus) Surimi
YUAN Yue, ZHAO Yongqiang, YANG Xianqing, LI Laihao, WU Yanyan, WEI Ya, CEN Jianwei
2019, 40(24):  79-85.  doi:10.7506/spkx1002-6630-20180927-298
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The cryoprotective effect and underlying mechanism of epigallocatechin gallate (EGCG) on frozen tilapia surimi were investigated by assaying gel properties and physicochemical indicators of myofibrillar protein as well as using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results showed that addition of EGCG had a cryoprotective effect on tilapia surimi, with a significant difference being observed compared to the blank control group. After freezing, the salt solubility and total sulfydryl content of myofibrillar protein in the control group decreased by 68.2% and 62.9% compared to 54.5% and 49.2% with the addition of 0.01% EGCG, respectively. EGCG could significantly delay the generation of protein carbonyl. In addition, the gel strength and water-holding capacity of surimi in both the presence and absence of EGCG decreased gradually with the prolongation of storage time, and excess EGCG accelerated gel degradation. SDS-PAGE showed that EGCG could effectively inhibit the degradation of myofibrillar protein, and that it was the most effective when added at a level of 0.01%. EGCG, which can delay the denaturation and degradation of myofibrillar protein and the oxidative degradation of surimi, is expected to be a new antifreezing agent for surimi.
Evaluation of the Quality of Frankfurters Prepared with Highly Stable Vegetable Oil-in-Water Pre-Emulsion as a Partial Replacer of Pork Back Fat
CHEN Yichun, JIANG Shuai, CAO Chuan’ai, CHEN Jiaxin, KONG Baohua, LIU Qian
2019, 40(24):  86-93.  doi:10.7506/spkx1002-6630-20180906-060
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In the present study, a highly stable oil-in-water pre-emulsion was prepared using porcine plasma protein hydrolysate (PPPH) with 1 g/100 mL of added oxidized chlorogenic acid as the emulsifier, and the effect of partial replacement of pork back fat with it (15%, 30%, 45% and 60%) on quality attributes of frankfurters. The cooking loss, texture characteristics, color and water distribution profile of frankfurters were determined, as well as the emulsion stability and rheological properties of meat batter. The results showed that with increasing replacement ratio, the cooking loss of frankfurters significantly decreased (P < 0.05) while the hardness, chewiness, L* value and b* value significantly increased (P < 0.05). However, the springiness, cohesiveness and sensory evaluation did not change significantly (P > 0.05). Moreover, low-field nuclear magnetic resonance (LF-NMR) analysis showed that with increasing replacement ratio, the relaxation time was significantly shortened (P < 0.05), indicating that the pre-emulsion could enhance the water-holding capacity of meat protein matrix. Furthermore, the emulsion stability of meat batter significantly increased with increasing replacement ratio (P < 0.05). Dynamic rheological tests indicated that the storage modulus (G′) and loss modulus (G′′) of meat batter significantly increased with increasing replacement ratio (P < 0.05), and the phase angle tanδ decreased (P < 0.05). Therefore, our results reveal that pork back fat can be partially replaced by the oil-in-water pre-emulsion without considerably affecting the overall sensory properties of frankfurters, and that 45% was considered as the optimal replacement ratio.
Effect of Lactoferrin-Epigallocatechin Gallate Covalent Complex on the Stability and Digestion Characteristics of Fish Oil Emulsions
LIU Runhua, LIANG Xiuping, YAN Xiaojia, LIU Fuguo
2019, 40(24):  94-100.  doi:10.7506/spkx1002-6630-20180906-064
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The effects of lactoferrin (LF)-epigallocatechin gallate (EGCG) covalent complex, prepared by alkaline treatment, and their physical mixture on the rheological properties, oxidative stability and in vitro digestion characteristics of fish oil emulsions were studied. As the molecular mass of LF increased after combining with EGCG, the emulsion viscosity was 2.74 and 1.42 times higher with the complex than with single LF or the physical mixture, respectively, and the complex remarkably enhanced the physical stability and maintained good fluidity of emulsions for 15 d at 55 ℃ consistently in the dark. The complex and the physical mixture were more effective at inhibiting fish oil oxidation than single LF; the thiobarbituric acid reactive substances (TBARS) values of lipids in fish oil emulsions stabilized by single LF, the physical mixture and the covalent complex were 2.25, 0.75 and 0.70 nmol/g, respectively on the 15th day of storage. During the in vitro digestion process, the covalent complex-stabilized fish oil emulsion showed better inhibition of aggregation and delayed release of fatty acids to some extent. This study provides a basis for the rational design of fish oil delivery systems.
Bioengineering
Isolation, Purification and Characterization of Membrane-Bound Gluconate Dehydrogenase from Serratia marcescens
WANG Beibei, LI Haocong, SUN Wenjing, CUI Fengjie, WANG Daming,, QIAN Jingya, QI Xianghui
2019, 40(24):  101-109.  doi:10.7506/spkx1002-6630-20181110-121
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An intracellular membrane-bound gluconate dehydrogenase (GADH) with specific activity of 91.43 U/mg and purification fold of 160.4 was purified from Serratia marcescens JUIM03, a 2-ketogluconic acid (2KGA)-producing strain, using a five-step procedure, including ultrasonication, Triton X-114 phase separation, ammonium sulfate fractionation, DEAE-sepharose fast flow and hydroxyapatite column chromatography. The results showed that the membrane-bound GADH consisted of three subunits with molecular masses of 65.0, 45.0 and 23.0 kDa respectively. It was a flavin protein-containing cytochrome C catalyzing the oxidation of gluconic acid to 2KGA. The optimum reaction temperature and pH were 40 ℃ and 5.0 kDa, respectively. It was stable below 30 ℃ and in the pH range of 5.0–6.0, and exhibited strict substrate specificity for D-gluconate with a Km of 1.33 mmol/L. Several metal ions including Fe3+, Cu2+ and Zn2+, organic solvents including ethanol, isopropanol, methanol and acetone, denaturants including SDS and mercaptoethanol, and organic acids including oxamic acid and oxalic acid had significant inhibitory effects on the enzyme activity. This study provides a theoretical basis for the optimization and control of 2KGA biosynthesis in Serratia marcescens.
Microbial Diversity and Gene Function Analysis in Traditional Hand-Made Cheese from Pastoral Areas of Yili in Xinjiang
WANG Chunyan, LI Yuhui, LI Yingbiao, LI Baokun, WANG Tengbin, SHI Xiuru
2019, 40(24):  110-118.  doi:10.7506/spkx1002-6630-20190611-110
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This study aimed to explore the diversity of culturable lactic acid bacteria and bacteria in traditional hand-made cheese from different pastoral areas of Yili in Xinjiang. Illumina MiSeq high-throughput sequencing technology was used to sequence the V1–V3 variable region of the bacterial 16S rRNA gene. The results showed that a total of 493 bacterial genera and 780 bacterial species were found in 14 cheese samples. Ralstonia spp. and Lactobacillus spp. were the dominant bacteria and lactic acid bacteria in cheese, respectively, and Lactobacillus helveticus was the dominant Lactobacillus species. Pathogenic bacteria also existed in cheese. Furthermore, a total of 68 culturable strains suspected to be lactic acid bacteria were selected from MRS medium by the traditional culture method and identified by physiological and biochemical tests and 16S rDNA sequence homology analysis. The 68 strains turned out to belong to Lactobacillus brevis, Weissella confusa, Enterococcus faecium, Enterococcus faecalis, Enterococcus durans, Enterococcus avium, Enterococcus raffinosus, Lactobacillus plantarum, and L. helveticus. W. confusa was found to be the dominant lactic acid bacterial species in cheese. The traditional culture method allowed more accurate species-level identification of lactic acid bacteria. Prediction of gene functions showed that the microorganisms in cheese were rich in genes related to amino acid transport and metabolism. We found that although the bacterial community composition of all samples was significantly different, their functional gene composition was highly similar.
Molecular Docking Analysis of the Interaction between Recombinant Laccase and Aflatoxin B1 and Structural Elucidation of Degradation Products of Aflatoxin B1
LIU Yingli, MAO Huijia, YANG Ziyan, WAN Zhen, WANG Jing, SUN Baoguo
2019, 40(24):  119-127.  doi:10.7506/spkx1002-6630-20190623-260
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In the present research, 3KW7 with the highest homology to the laccase lac3 gene was selected as a template for homology modeling, and molecular docking was used to predict the binding mode of the recombinant laccase to aflatoxin B1 (AFB1). The results showed that the laccase and AFB1 could interact via hydrogen bond as the key force, indicating that it can be used for the degradation of AFB1. Using response surface methodology, the optimal conditions for degradation of AFB1 by the laccase were established as follows: substrate amount 1 μg, reaction time 15 h, temperature 34 ℃, and enzyme activity 2 U, and the maximum degradation rate of AFB1 of 91.08% was obtained under the optimized conditions. Four compounds in the degradation products of AFB1 were detected by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). According to their secondary mass spectrometric information and exact molecular masses, the molecular formulas of the four compounds were postulated to be C16H22O4, C14H16N2O2, C7H12N6O and C24H30O6, respectively.
Structural Segregation of the Gut Microbiome between Chinese Han and Tibetan Infants
ZHANG Qiuxue, SHANG Jiacui, ZHU Dequan, ZHU Zongtao, WAN Feng, JIA Fangfang, SUN Sirui, MENG Xiangchen
2019, 40(24):  128-135.  doi:10.7506/spkx1002-6630-20180728-346
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Ethnicity is considered as one of the major driving forces to shape the human gut microbiota, but how the gut microbiota evolves in population with disparate ethnic backgrounds since infants are born remains still unclear. Thus, this study aimed to understand the impact of ethnicity on infants. We investigated the fecal microbiota of healthy infants (3–6 months old, with breast feeding) from the Chinese Han and Tibetan ethnic groups (n = 10 for each group). By using high-throughput 16S rRNA gene sequencing analyses, we found some differences in fecal microbiota composition between the two groups. At the phylum level, the Han infants harbored higher relative abundance of Actinobacteria, whereas Firmicutes was more predominant in the Tibetans. A significant difference at the phylum level existed in Firmicutes (P < 0.05) between the two groups. Bifidobacterium and Escherichia-Shigella were the first and second major genera in both groups, respectively. There was a clear separation between the groups by principal coordinates analysis (PCoA) based on unweighted and weighted UniFrac distance. Moreover, partial least squares-discriminant analysis (PLS-DA) showed that the infant gut microbiome was segregated according to ethnicity. Taken together, our findings suggest that the gut microbiota could be differentiated between infants from distinct ethnic origins, and this expanded our knowledge of the co-evolution of human hosts and their symbiotic gut microbiota.
Predicting and Identifying Linear B-Cell Epitopes of Wheat Allergen CM16
LI Xuejiao, LI Xinrui, FAN Zhuoyan, ZHANG Yani, CHE Huilian
2019, 40(24):  136-141.  doi:10.7506/spkx1002-6630-20181023-251
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Objective: To explore the feasibility and applicability of bioinformatics analysis in the identification of allergen linear B-cell epitopes. Methods: Fragments of the α-amylase/trypsin inhibitor wheat allergenic protein CM16 with digestive resistance were obtained by subjecting crude wheat protein extract (WPE) to simulated gastrointestinal digestion in vitro. The amino acid sequence and secondary structure of CM16 were analyzed by bioinformatics method, and its tertiary structure was determined by homology modeling. Results: Four linear B-cell epitopes of CM16 were predicted and compared with the digestion-resistant peptides identified by mass spectrometry (MS). It was found that two of the peptides partially overlapped, proving the feasibility and applicability of bioinformatics for identifying allergen linear B cell epitopes. Conclusion: The prediction of the linear B-cell epitopes of wheat allergen CM16 by bioinformatics will help us to gain further understanding of wheat allergens and more broadly provide an important basis for the identification and detection of wheat allergens.
Preparation and In Vitro Evaluation of Marine Oligosaccharide Coated Microcapsules Containing Probiotics and Their Regulatory Effect on Animal Intestinal Flora
CHANG Liuyi, ZHUANG Jingyun, MENG Fei, WANG Chun, SHEN Zhaopeng, JIANG Xiaolu
2019, 40(24):  142-150.  doi:10.7506/spkx1002-6630-20181127-311
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In order to solve the intolerance of probiotics to low pH and oxygen, Bifidobacterium longum was microencapsulated using alginate as the wall material in this study. Microcapsules were prepared with alginate alone or with alginate + alginate oligosaccharides (AOS) by emulsification method and then coated with chitosan oligosaccharides (COS) yielding COS-microcapsules and AOS-COS-microcapsules, respectively. In vitro experiments showed that the two marine oligosaccharide coated microcapsules could greatly improve the survival rate of B. longum in simulated digestive juice or during storage at 4 ℃. AOS-COS-microcapsules could maintain a viable cell count of more than 106 CFU/g after simulated gastric digestion. After simulated gastrointestinal digestion, the viable cell count of AOS-COS-microcapsules was about 1 000 times as high as that of the uncoated microcapsules. The two marine oligosaccharide coated microcapsules could maintain a viable cell count of greater than 108 CFU/g after storage for 28 days at 4 ℃. In vivo experiments showed that compared with free B. longum and the bare microcapsules, the coated microcapsules could significantly increase the content of probiotics and reduce the content of opportunistic pathogenic bacteria, and were more effective in regulating the intestinal flora. Therefore, marine oligosaccharide coated microcapsules containing probiotics have a great potential as a new type of functional food.
Comparative Study on the Stability of Five Strains of Lactic Acid Bacteria Adsorbing Acrylamide
ZHao Sijia, li Rui, LIU Tong, sun Hongyang, shen Yu, zhao Xiaoduo, SHANG Jiaqi, shao Meili
2019, 40(24):  151-156.  doi:10.7506/spkx1002-6630-20181225-288
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This study compared the acrylamide (AA) adsorption capacities of living and heat-inactivated cells of five strains of lactic acid bacteria (LAB) including Lactobacillus plantarum ATCC8014, L. plantarum 1.0665, L. plantarum 806, L. casei ATCC393 and L. acidopilus KLDS 1.0307. At the same time, the stability of the lactic acid bacteria-acrylamide (LAB-AA) complexes was evaluated in sterile deionized water, different organic solvents (methanol, acetonitrile/water and ketone), or in-vitro simulated gastrointestinal environment. The AA adsorption ability of heat-inactivated cells of each of the strains was found to be higher than that of their living counterparts. Heat-inactivated cells of L. plantarum ATCC8014 exhibited the highest AA adsorption rate of 96.53%. All the five LAB-AA complexes were stable in the three organic solvents, but when they were kept in sterile deionized water, a small amount of AA was released. In the simulated gastrointestinal environment, pH, bile salt, trypsin and incubation time affected the stability of LAB-AA complexes, resulting in the release of a small amount of AA. In conclusion, the complex between heat-inactivated L. plantarum ATCC8014 and AA had very good stability in the above-mentioned environments. These results provide a new idea to inhibit the toxicity of acrylamide in foods to humans when consumed.
Enzymatic Preparation of Peptone from Cold-Pressed Peanut Meal and Its Application in Microbial Culture
XIAO Huaiqiu, LI Yuzhen, LIN Qinlu, LIU Jun, LAN Lixin
2019, 40(24):  157-166.  doi:10.7506/spkx1002-6630-20181209-103
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In this study, cold-pressed peanut meal hydrolysate (also named as cold-pressed peanut meal peptone, CPMP) was prepared by sequential enzymatic hydrolysis using pepsin and alkali proteinase. The molecular mass distribution, proximate analysis and amino acid composition of CPMP were determined. Furthermore, its potential as an alternative to the commercial peptone in microbial culture was evaluated. CPMP was mainly composed of < 5.0 kDa peptide fractions. CPMP was rich in Ala, Arg, Asp, and Cys, especially Glu. Escherichia coli grew better for 8 h in CPMP medium than in beef peptone yeast medium. Bacillus subtilis exhibited a longer lag phase in CPMP medium than in Luria-Bertani medium and possessed a better growth behavior after 8 h incubation. The pH of CPMP medium inoculated with E. coli or B. subtilis displayed no statistically significant difference compared with the control medium (P > 0.05). Lactobacillus casei exhibited a different growth behavior in CPMP medium from that in MRS medium (P < 0.05). Staphylococcus aureus grew well in CPMP medium with no significant difference from the control. Saccharomyces cerevisiae in CPMP showed similar growth behavior and pH trend to those in the control. Aspergillus oryzae grew well in CPMP, similar to that in Czapek-Dox medium. Our evidence demonstrated that CPMP has a good potential as a commercial peptone alternative for microbial growth.
Identification of Dominant Postharvest Pathogens of Blueberry Fruit and Antifungal Activity of Cinnamon Oil against Them
WANG Dan, ZHANG Jing, JIA Xiaoman, XIN Li, ZHAI Hao
2019, 40(24):  167-172.  doi:10.7506/spkx1002-6630-20181029-338
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This study aimed to identify the main postharvest pathogens of blueberry fruit grown in Taian, Shandong province. The pathogenic strains were isolated and purified from naturally rotten fruit of the ‘Wanfeng’ cultivar, and they were identified by traditional fungal morphology and rDNA-ITS sequence analysis. Besides, the in vitro antifungal activity of cinnamon oil was assessed against the strains. The results showed that these strains were identified as Fusarium oxysporum, Alternaria alternate and Botrytis cinerea, respectively. Cinnamon oil exhibited obvious antifungal effects on the strains with minimal inhibitory concentrations of 60, 30 and 30 μL/L, respectively. Moreover, scanning electron microscopic observation showed that the mycelial morphology of all the strains was seriously damaged after being treated with cinnamon oil and the cell surface became sunken, shrunk and uneven compared to the untreated control.
Probiotic Characteristics of Lactobacillus plantarum UL-4, Able to Produce γ-Aminobutyric Acid at High Yield in Chickpea Milk
LI Wen, WANG Tao, DONG Yuwei, LI Tongxiang
2019, 40(24):  173-178.  doi:10.7506/spkx1002-6630-20181030-363
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Chickpea milk fermented with Lactobacillus plantarum UL-4 was found to be enriched in γ-aminobutyric acid (GABA). Moreover, the probiotic characteristics of strain UL-4 were evaluated by measuring its acid and salt tolerance, cell surface properties, antibacterial activity, and cholesterol and triglyceride degradation activity. Results showed that the viable cell count was 7.81 (lg(CFU/mL)) after 48 h fermentation and the GABA yield was 371.14 mg/L. The survival rates of the strain were respectively 46.67%, 91.81%, and 174.21% at pH 2, 3, and 4; 382.83%, 91.81%, and 56.28% at bile salt concentrations of 0.03%, 0.15%, and 0.3%, demonstrating strong acid and salt resistance. Its cell surface hydrophobicity and auto-aggregation were 52.49% and 61.50%, respectively, and it had adhesion and colonization ability in the intestine. The strain had potent antimicrobial activity, which inhibited the growth of Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium with inhibition zone diameters of 14.40, 15.77, and 13.36 mm, respectively. Furthermore, the strain could degrade cholesterol and triglyceride with degradation rates of 73.23% and 19.11%, respectively. In summary, L. plantarum UL-4 could ferment chickpea milk enriched in GABA, and also showed good probiotic characteristics, making it a candidate for developing functional foods.
Elucidation of the Mechanism by Which the Filtrate of Naturally Fermented Coconut Water Promotes Bacterial Cellulose Synthesis
FU Meijuan, DENG Jian, LUO Jiaxi, LIN Xue, LI Congfa, LIU Sixin
2019, 40(24):  179-184.  doi:10.7506/spkx1002-6630-20190620-242
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Komagataeibacter nataicola Y19 was statically cultured at 30 ℃ for 7 days in media with either cell-free filtrate or cell residue of naturally fermented coconut water (FCW). As a result, the production of bacterial cellulose (BC) in the medium with the filtrate was 5.65 g/L, which was 10 times as high as that in natural coconut water (NCW) compared to 2.8 times for the medium with the cell residue, suggesting that the filtrate of FCW significantly promotes BC synthesis. Changes in organic acid contents in the filtrate during the fermentation of coconut water were analyzed by gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). The total amount of volatile compounds in the filtrate was about 5 times as high as that in NCW. Alcohols were the major volatile components in the filtrate, accounting for approximately 62% of the total amount, and the contents of ethanol and acetic acid were 4.5 and 48 times as high as those in NCW, respectively. The contents of acetic and lactic acid gradually increased during the fermentation process, while the contents of all other organic acids except gluconic acid, significantly decreasing from day 1 to 3, did not significantly change. Hence, it was deduced that microbial metabolites generated during the fermentation of coconut water make an important contribution to BC synthesis, and that the alcohols and acids greatly changing after the fermentation may affect BC synthesis by participating in regulating the metabolism of K. nataicola Y19.
Whole-Genome Sequencing and Analysis of Paecilomyces variotii MTDF-01, Isolated during Maotai-Flavor Liquor Brewing
WANG Heyu, LIU Yanfeng, ZHANG Qiaoling, DU Guocheng, YANG Fan, LI Jianghua
2019, 40(24):  185-192.  doi:10.7506/spkx1002-6630-20181008-036
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This study aimed to gain insight into the metabolic mechanism of Paecilomyces variotii in the production of Maotai-flavor liquor for the purpose of providing an essential bioinformatic basis for further understanding and regulating the metabolism of this strain. The whole-genome sequencing of P. variotii MTDF-01, a strain isolated during the brewing of Maotai-flavor liquor, was carried out on the PacBio RS II platform. The sequencing reads were assembled and annotated via gene prediction and functional annotation. In the whole genome, 19 scaffolds and 19 contigs were obtained. The total length was 30 833 540 bp and the average GC content was 47.46%. A total of 8 815 genes, 5 044 simple sequence repeats (SSR), 221 tRNA and 49 rRNAs were predicted. The number of annotated genes was 8 662. The genome contained 60 starch hydrolase-coding genes and 165 cellulose hydrolase-coding genes, as well as 23 secondary metabolite biosynthetic gene clusters. The genome rearrangement of MTDF-01 was different from that of P. variotii No.5, a formaldehyde-resistant strain isolated from soil. Synteny analysis indicated that genome rearrangement and translocation occurred among these genomes. A total of 16 414 single nucleotide base mutations were found in the genomes of the two strains, including 525 base deletions, 335 base insertions and 15 554 single base substitutions. The high-quality whole-genome sequence and potential function of P. variotii MTDF-01 obtained in this study are of great significance for future studies on the regulation of the flavor and health-benefiting substances of Maotai-flavor liquor.
Component Analysis
Enantiomeric Distribution of Volatile Terpenoids in Different Types of Fuding White Teas
YAN Han, ZHU Yin, MU Bing, Lü Haipeng, KANG Suyoung, ZHANG Yue, LIN Zhi
2019, 40(24):  193-200.  doi:10.7506/spkx1002-6630-20181229-350
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In this work, the enantiomeric distribution of 14 volatile terpenoids in different types of Fuding white teas were analyzed by headspace-solid-phase microextraction (HS-SPME) and enantioselective gas chromatography-mass spectrometry (GC-MS). The relative quantitative analysis results showed that S-linalool, S-Z-nerolidol and (2S,5R)-linalool oxide B were relatively more abundant in most white teas, while the contents of four enantiomers of theaspirane were extremely low. The enantiomeric analysis results indicated that S-limonene, (2S,5S)-linalool oxide A, (2S,5R)-linalool oxide B, S-linalool, (2R,5R)-theaspirane A, (2R,5S)-theaspirane B, R-terpinen-4-ol, S-α-terpineol, S-citronellol, S-α-ionone, S-Z-nerolidol, S-E-nerolidol, (1R,2R)-methyl jasmonate and (1R,2S)-methyl epijasmonate were the major absolute configurations of terpenes in most white teas, and that the enantiomeric ratios (ERs) of linalool, linalool oxide B, terpinen-4-ol, citronellol, α-ionone, linalool oxide A and Z-nerolidol were related to the plucking standard of white teas. Moreover, multivariate statistical analysis exhibited that a significant difference in the contents of 12 volatile terpenoid enantiomers existed among the three different types of Fuding white teas. R-Linalool, (2R,5S)-theaspirane B, S-α-terpineol, R-E-nerolidol, R-Z-nerolidol, S-limonene and S-E-nerolidol presented the highest levels in Silver Needle tea samples, while the opposite was true for (2R,5R)-linalool oxide A and (2S,5R)-theaspirane B. S-Z-Nerolidol and (1S,2S)-methyl epijasmonate showed higher contents in White Peony tea samples, and the content of R-α-ionone was higher in Shou Mei tea samples than in the other types. The above studies provide the theoretical foundation for further understanding the formation mechanism of the aroma quality of, discriminating the types and grades of and establishing a fingerprint for white teas.
Molecular Compositions and Structural Properties of Proteins in Millet
GUO Liandong, XU Li, OU Caizhi, DING Yangyue, ZHANG Gaopeng, NI Chunlei, CHENG Jianjun
2019, 40(24):  201-206.  doi:10.7506/spkx1002-6630-20181225-293
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The structures of 4 protein components in millet were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), scanning electron microscopy, differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). This study showed that millet gliadin was composed of low-molecular-mass subunits (11–25 kDa), while albumin, globulin and glutenin subunits were widely distributed (11–180 kDa). Albumin contained the largest number of subunits. The prolamin, albumin and globulin molecules were closely linked and existed in an aggregated state, while the gluten molecules were loosely connected and had a smooth surface. The globulin was denatured at 71.33 ℃, and the prolamin had the highest denaturation temperature of 110.67 ℃. FTIR study showed that the secondary structures of the prolamin, gluten and globulin were mainly composed of β-sheet, accounting for 37.72%, 43.39%、42.23% of the total amount, respectively. The prolamin contained the most abundant structures of β-turn and antiparallel β-sheet, accounting for 16.64% and 12.73% of the total amount, respectively. However, the secondary structure contents of the four protein components were significantly different (P < 0.05).
Effects of Feeding Patterns on Volatile Flavor Components and Fatty Acid Composition of Sunit Sheep Meat
LI Wenbo, LUO Yulong, LIU Chang, DOU Lu, ZHAO Lihua, SU Lin, JIN Ye
2019, 40(24):  207-213.  doi:10.7506/spkx1002-6630-20190107-095
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The volatile flavor and fatty acid components of the Longissimus dorsi of twelve 12-month-old Sunit sheep subjected to two feeding patterns (grazing and forage supplemented with a concentrate mixture) were analyzed by gas chromatography-mass spectrometry (GC-MS), and then the expression levels of lipid metabolism-related genes were determined by quantitative real-time polymerase chain reaction (qRT-PCR) in order to explore the effect of feeding methods on the volatile flavor components and fatty acid contents of mutton. The results showed that hexanal, nonanal, 1-octen-3-ol and 2,3-octanedione were the main volatile compounds in Sunit sheep meat, and nonanal content in the meat of forage plus concentrate-fed sheep was significantly higher than in the meat of grazed sheep (P < 0.05), but the opposite was true for the contents of 1-octen-3-ol and 2,3-octanedione (P < 0.05). The contents of C16:0, C18:0 and C18:1 n9c were higher than those of the other detected fatty acids, and C18:0 was significantly more abundant in the meat of grazed sheep than in forage plus concentrate-fed sheep (P < 0.05). The expression level of lipoxygenase (LOX) gene in grazed sheep was significantly higher than in forage plus concentrate-fed sheep (P < 0.05), and the expression levels of acetyl-CoA carboxylase (ACC) and peroxisome proliferator-activated receptor (PPARγ) genes were higher but not significantly than in forage plus concentrate-fed sheep (P > 0.05). On the whole, the higher expression levels of PPARγ and ACC genes led to the synthesis and deposition of more fatty acids in the meat of grazed sheep and consequently activated expression of LOX, thereby promoting the oxidation of fatty acids to produce a large amount of volatiles like aldehydes and alcohols imparting a better flavor quality to the meat of grazed sheep.
Establishment of Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry Method for Determination of 29 Monophenols in Wine
YANG Zhiwei, WANG Shengyi, QI Pengyu, ZHANG Ang, LI Xiang, WANG Fei, ZHANG Jinjie
2019, 40(24):  214-219.  doi:10.7506/spkx1002-6630-20190110-126
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Purpose: To establish a rapid method for simultaneous determination of 29 phenols in wine by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Methods: The sample was diluted with acidified methanol-water, and centrifuged at high speed. The supernatant was taken for analysis. The chromatographic separation was implemented on an ACQUITY UPLC? BEH C18 column using a mobile phase consisting of 0.1% formic acid-acetonitrile and 0.1% formic acid water. The analytes were detected using an electrospray ion source with multiple reaction monitoring in the negative ion mode. The instrumental parameters were as follows: ion source temperature (TEM) 500 ℃, electrospray voltage ?4 500 V, air curtain gas (CUR) pressure, 40 psi, collision gas medium, atomized gas pressure 60 psi, auxiliary heating pressure, 50 psi. The analysis process took 17 min. Results: The limits of quantitation (LOQs) of 29 monomeric phenols were between 0.001 and 0.01 mg/L, and the linear correlation coefficients R2 were greater than 0.99. The recoveries for spiked samples ranged between 90.8% and 104.5%, with relative standard deviations (RSDs) of 0.26% to 7.54%. Conclusion: This method is characterized by simple pretreatment, high sensitivity and fast analysis as well as good precision and accuracy, and thuscan be applied to detect 29 monophenols in wine.
Effects of Different Smoking Materials on Volatile Flavor Compounds in Smoked Chicken Thighs
LIU Dengyong, ZHAO Zhinan, WU Jincheng, ZOU Yufeng, WANG Xiao, LI Mingqian
2019, 40(24):  220-227.  doi:10.7506/spkx1002-6630-20190104-062
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This study was conducted in order to explore the effects of different smoking materials (apple tree sawdust, black tea, and white sugar) on the volatile flavor compounds of smoked chicken thighs. Solid phase microextraction (SPME) combined with gas chromatography-mass spectrometry (GC-MS) was used to separate and identify the volatile compounds, and the main flavor components were determined by calculating the relative odor activity values (ROAV). Results showed that a total of 92 volatile flavor components were identified from the three smoked chicken thighs. Furfural and 5-methyl-2-furancarboxaldehyde were determined as the characteristic compounds of sugar-smoked flavor; 2-methoxyphenol, 2-methoxy-4-methyl-phenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-vinylphenol, furfural, and 5-methyl-2-furancarboxaldehyde as the characteristic compounds of wood-smoked flavor; 2,6-diethyl-pyrazine and 2-methoxyphenol as the characteristic compounds of tea-smoked flavor. Furans, pyrazines and phenoic compounds were typical compounds of smoked flavor.
A Rapid Method for the Discrimination of Different Varieties of Green Coffee Beans by Headspace-Gas Chromatography-Ion Mobility Spectrometry
DU Ping, CHEN Zhenjia, YANG Fang, LI Xiaolei, YANG Jun, LIU Chunxia, LIANG Jingsi, REN Fang
2019, 40(24):  228-233.  doi:10.7506/spkx1002-6630-20190429-386
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The volatile organic compounds (VOCs) of different varieties of green coffee beans from Yunnan province were analyzed nondestructively by headspace-gas chromatography-ion migration spectroscopy (HS-GC-IMS). According to the retention index in GC and the migration time, the VOCs were identified two-dimensionally and differential profiles were created. Principal component analysis (PCA) was performed on the VOCs data. The results showed that HS-GC-IMS could effectively separate the volatile components of green coffee beans, and that the information collection and analysis could be completed within 20 min. A total of 42 volatile substances were identified, mainly including aldehydes, esters, alcohols, ketones, pyrazines, acids and sulfur-containing compounds. PCA analysis of HS-GC-IMS spectra could accurately distinguish different varieties of green coffee beans. This method is rapid, sensitive and nondestructive, and it is of great significance for varietal identification, origin tracing and quality control of green coffee beans.
Analysis and Evaluation of Main Functional Components of Loquat Leaves at Different Positions from 6 Varieties
HUO Yuhang, LI Yantang, LIU Lili, ZHANG Yunyun, LU Zhoumin
2019, 40(24):  234-240.  doi:10.7506/spkx1002-6630-20190109-116
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Six varieties of loquat leaves picked from positions 1, 3, 5, 7 and 9 (from the top downward) on branches of the same age surrounding the tree crown were analyzed for their contents of 12 functional components. The results showed that the contents of the 12 components were different among leaf positions for each loquat cultivar, and their variation trends were likewise different. The contents of neochlorogenic acid and chlorogenic acid decreased rapidly with increasing leaf position, while the content of corosolic acid increased obviously. The contents of total phenols, flavonoids and triterpenic acid in ‘Dawuxing’, ‘Marc’ and ‘Jialing’ increased with the increase of leaf position, but they did not change significantly in the other three varieties. The mean values of total phenolics, flavonoids, total triterpenic acid, ursolic acid, oleanolic acid, catechin, neochlorogenic acid and isoquercetin in the leaves of ‘Dawuxing’ were significantly higher than in the other 5 varieties, and ‘Dawuxing’ scored higher in principal component evaluation.
Quantitative Determination and Nutritional Evaluation of Five Minerals in Banana
LIANG Shuilian, Lü Daizhu, ZHOU Ruohao, MA Chen, ZHANG Liqiang, JIU Yuanda, WANG Mingyue,
2019, 40(24):  241-245.  doi:10.7506/spkx1002-6630-20190830-335
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Bananas from four major cultivars grown in Guangdong, Guangxi, Hainan and Yunnan provinces were selected to determine the contents of 5 mineral elements including potassium, magnesium, zinc, iron and phosphorus and further to analyze and the differences among cultivars and producing areas. Moreover, the index of nutrient value (INQ) was used to evaluate the nutritional value of each of the mineral elements, and their contents in bananas were compared with those in five other tropical fruits and 3 berries. The results showed that the contents and INQ values of potassium and magnesium in bananas were high, 347.75 mg/100 g and 4.40 for potassium; and 27.42 mg/100 g and 2.10 for magnesium, respectively. In contrast, the contents of iron, phosphorus and zinc in bananas were low, and the INQ values were less than 1. The comparative analysis showed that the contents and INQs of potassium and magnesium in bananas were the highest among the 9 fruits tested, and the content of potassium in bananas was 2–3 times as high as that in litchi, pineapple and grape, and 2-4 times as high as that in mango, litchi and pineapple. The contents of potassium in the 4 banana varieties were relatively high and did not differ from each other, while no varietal differences were found in the contents of magnesium, iron and phosphorus. The contents of magnesium and iron in the four banana cultivars (Musa acuminata L. AAA Cavendish) were in following order: ‘Formosana’ > ‘Nan Tian Huang’ > ‘Brazil’ > ‘Williams B6’, whereas the phosphorus contents were in the decreased order: ‘Formosana’ > ‘Brazil’ > ‘Williams B6’ > ‘Nan Tian Huang’; yet there was no significant difference in zinc content, and the INQ values were all less than 1 in these banana cultivars. For all the producing areas, the INQs of potassium and magnesium in bananas were greater than 4 and 1, respectively, and the INQs of zinc, iron and phosphorus were all less than 1. The INQs of magnesium, iron and phosphorus in bananas from Yunnan and Hainan were higher than those in bananas from Guangdong and Guangxi, and the INQs of potassium and zinc in bananas from Yunnan and Guangxi were higher than those in bananas from Guangdong and Hainan. Accordingly, the nutritive value of potassium and magnesium minerals in bananas were high, providing a good mineral source for special populations. The experimental results provide a basis for reasonable nutritional matching and well-balanced nutritional structure.
Comparative Chemical Composition of Mycelium and Fruit Body of Phellinus igniarius
YE Yujie, SHI Guang, ZHOU Zhengyi, WANG Jiaqi, AN Liping, DU Peige
2019, 40(24):  246-251.  doi:10.7506/spkx1002-6630-20181218-206
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The fruit body and mycelium of Phellinus igniarius were analyzed for general nutrient composition and the contents and activities of the main functional compounds, aiming to lay a foundation for further exploitation and utilization of P. igniarius. The following bioactivities were evaluated: 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity and antitumor potential against SW620 and HepG2 tumor cells. The results showed that the mycelium and fruiting body of P. igniarius had basically similar nutrient composition including protein, polysaccharide, amino acid, fat, fiber and mineral elements. The contents of water and ash (P < 0.05) as well as crude fiber (P < 0.01) in the mycelium were significantly lower than in the fruit body, while the contents of crude protein and crude fat was significantly higher than in the fruit body (P < 0.01). The fruit body and mycelium had the same composition of the 17 amino acids tested, and their total amino acid contents were 25.11% and 4.69%, respectively. The contents of polysaccharides, flavonoids and triterpenoids in the fruit body were significantly higher than in the mycelium (P < 0.01). The highest percentages of DPPH radical scavenging by polysaccharides, flavonoids and triterpenes from the fruit body were 77.14%, 61.37% and 49.97%, respectively. The highest percentages of inhibition of tumor cells by polysaccharides from the mycelium and fruit body were 21.45% and 32.86% for SW620, and 37.91% and 51.29% for HepG2 cells, respectively. The results showed that the nutrient composition of the mycelium and fruit body of P. igniarius is basically the same, having high nutrient contents. The liquid-state fermentation mycelium can alleviate the shortage of wild P. igniarius fruit body, and it likewise has great potential for exploitation and application.
Processing Technology
Effect of Nitrogen Deodorization on Peroxide Value of Evening Primrose Oil
YU Dianyu, YUAN Taizeng, WANG Hong, PEI Xingwu, JIANG Lianzhou, WANG Liqi, YU Wenbo
2019, 40(24):  252-257.  doi:10.7506/spkx1002-6630-20190510-097
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Nitrogen gas was used to deodorize decolorized evening primrose oil instead of conventional steam distillation. The operating conditions including temperature, time and gas flow rate were optimized by response surface methodology based on peroxide value. The results showed that the optimum process conditions were determined as follows: temperature 144 ℃, time 3.5 h, and gas flow rate 2.1 mL/min. Under these conditions, the peroxidate value of deodorized evening primrose oil was 0.321 mmol/kg, which was effectively reduced compared with that before deodorization. In addition, the solvent residue was 0.02 mg/kg, and linolenic acid was effectively retained in the oil. The quality of the evening primrose oil could meet the industrial requirements. This study provides a new process and theoretical basis for improving the stability of evening primrose oil.
Optimization of Extraction Conditions, Separation and Purification of Antifungal Peptides from Hot Pepper Seeds
HAN Yuzhu, LI Pinglan, HE Qin, ZHAO Zhanzhan, LIU Xuewen, YANG Yemei
2019, 40(24):  258-264.  doi:10.7506/spkx1002-6630-20181112-123
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Protein extracts from the seeds of different cultivars of hot pepper were screened for their antifungal activity against Aspergillus flavus in terms of inhibition zone diameter. The results showed that the seeds of all six cultivars investigated had inhibitory effects on the growth of A. flavus, and Guizhou lantern pepper seeds had the strongest antifungal effect of them. The conditions for extraction of antifungal proteins from the Guizhou Lantern cultivar were optimized as follows: EDTA buffer as the extraction solvent, solid-to-solvent ratio 1:5.05 (g/mL), extraction time 16.13 h, and ammonium sulfate saturation 81.15%, leading to an inhibitory zone diameter of 23.89 mm, which was 93.06% higher than that (12.34 mm) before optimization. In addition, the antifungal peptides from hot pepper seeds were separated and purified by dialysis, 10 kDa ultrafiltration and Sephadex gel chromatography. The purified antifungal peptide was found to be homogenous with a molecular mass of around 7.8 kDa by Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
Peptides from Tibetan Sheep Placental Protein: Optimization of Ultrasound-Assisted Enzymatic Preparation Using Response Surface Methodology and Antioxidant Activity Evaluation
REN Haiwei, SHI Jufen, CAI Yaling, FAN Wenguang, JIANG Qixing, LI Zhizhong, PEI Jiawen, WANG Yanrui
2019, 40(24):  265-273.  doi:10.7506/spkx1002-6630-20181101-009
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In this paper, we optimized the conditions for ultrasound-assisted enzymatic preparation of peptides from Tibetan sheep placental protein (TSPP) using a combination of one-factor-at-a-time method and response surface methodology (RSM). Degree of hydrolysis (DH), peptide yield (PY) and antioxidant capacity were considered as the response variables. Six proteases and their binary combinations were screened for their suitability for the hydrolysis of TSPP preceding the optimization. Furthermore, the amino acid composition and molecular mass distribution of the hydrolysate prepared under the optimized conditions were determined. The results indicated that the simultaneous addition of papain and neutral protease was found to be the best hydrolysis scheme. The effects of sonication time, temperature, hydrolysis time and ultrasonic power on DH decreased in that order. The optimal hydrolysis parameters were obtained as follows: sonication time 16.5 min, temperature 25.5 ℃, ultrasonic power 438 W, and hydrolysis time 4.9 h, resulting in DH, PY and antioxidant capacity of 55.22%, 18.52% and 1.08 mmol/L Trolox equivalent, respectively. The resulting hydrolysate was rich in glutamic acid, aspartic acid and glycine and peptides below 2 000 Da accounted for 95.02% of the total peptides, the majority of which were small oligopeptides. In conclusion, the ultrasound-assisted enzymatic hydrolysis process could not only had improved hydrolysis efficiency but also produce small peptides with excellent antioxidant activity.
Preparation of Bagasse-Nano Silver Oxide Preservative
MA Ruijia, CAI Chenchen, LEI Caiyu, WANG Youfa, LU Dengjun
2019, 40(24):  274-280.  doi:10.7506/spkx1002-6630-20181128-328
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In this research, bagasse was used as a carrier for nano silver oxide to prepare a new environmentally friendly preservative. Sucrose ester was used as a surfactant in the reaction between sodium hydroxide and silver nitrate. Nano silver oxide was adsorbed onto bagasse in an ultrasonic field. The optimal conditions for product formation were determined with respect to NaOH, AgNO3 and sucrose ester concentration, reaction time and ultrasonic power. The product was characterized by X-ray diffraction and scanning electron microscopy (SEM). Its antibacterial properties against Escherichia coli and Bacillus subtilis were examined by determining its minimum inhibitory concentration (MIC). The results showed that nano silver oxide with the lowest particle size of 63.38 nm was prepared under the conditions of 0.02 mol/L AgNO3, 0.03 mol/L NaOH, 1.4 g/L sucrose ester, temperature 40 ℃, reaction time 110 min, and ultrasonic power 400 W. The MICs were 289.662 5 and 579.325 μg/mL for E. coli and B. subtilis, respectively.
Optimization of Emulsifier Combinations to Stabilize Cooked Dajiang, a Fermented Soybean Paste in North China, by Response Surface Methodology
GAO Yawen, LI Hongmei, ZHENG Hongyan, SHI Junhua
2019, 40(24):  281-286.  doi:10.7506/spkx1002-6630-20181117-198
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According to their functional characteristics, six emulsifiers were selected to investigate the effects of different amounts of emulsifiers on the stability of cooked Dajiang. Three of these emulsifiers were found to the most effective in reducing oil separation after centrifugation and their combinations were optimized using response surface methodology. Besides, the effects of different amounts of oil and different ways of adding emulsifiers on the stability of cooked Dajiang were investigated. The optimized combination was obtained as follows: monoglyceride 0.4%, soybean phospholipid 0.6%, and sodium carboxymethyl cellulose 0.5%. The separation rate of oil from the cooked Dajiang with 25% added oil containing the emulsifiers was 2.72%. It had a shiny golden color as well as well-balanced strong oily and sauce-like flavor and was uniform and stable without oil separation.
Safety Detection
Fast Detection of Hami Melon Ripeness Based on Features Extracted from Acoustic Signals of Smartphone
Lü Jiguang, WU Jie
2019, 40(24):  287-293.  doi:10.7506/spkx1002-6630-20180918-191
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This work aimed to address the desire of both melon growers and consumers for convenient, rapid, low-cost and non-destructive detection of Hami melon ripeness. In this paper, a mobile phone was used to record acoustic signals generated by thumping Hami melons with different maturity levels. Then the raw signals were preprocessed to remove noises and segmented into thumping event frames. A series of extraction steps were performed on these acoustic signals, including the calculation of root mean square, start/end detection, extraction of thumping events, filtration with Butterworth filter and fast Fourier transform. As a result, eleven features including short-time energy (STE), frame energy (E), average amplitude difference function (AMDF), short-time energy ratios of four sub-bands (SSTE1, SSTE2, SSTE3 and SSTE4), zero crossing rate (ZCR), spectral centroid (wc), resonant frequency (f) and bandwidth (B) were extracted. The significant differences among these features were analyzed and the ripeness-related features were found. Eight features (i.e. STE, E, SSTE1, SSTE2, SSTE4, ZCR, wc and f) were selected to construct a ripe classifier-based support vector machine (SVM) for distinguishing between unripe and ripe melons. Also, seven features (i.e. AMDF, SSTE1, SSTE2, SSTE3, SSTE4, ZCR, and B) were selected to construct a proper ripe SVM classifier for distinguishing properly ripe from overripe melons. For both SVM classifiers, the algorithm used radial base kernel function to achieve better performance. Single or multiple selected ripeness-related features were used as vector to train the SVM classifiers. We measured the recall, precision, accuracy and F1-Measure by confusion matrix analysis for the two classifiers. The results showed that the classifier trained by the feature vectors wc, E and SSTE1 was the most suitable for disguising unripe from ripe melons. While the classifier trained by the feature vectors ZCR, SSTE2 and SSTE3 was the most suitable to discriminate properly ripe from overripe melons. Furthermore, a prediction model for the soluble solids content of melon was constructed by stepwise multiple regressions with wc, E, SSTE1, SSTE2 and SSTE. Finally, we developed an Android application on the mobile phone, which can correctly classify the melon maturities with an overall accuracy of 90.9%. Its classification performance can be improved by the user feedback. Additionally, it can be used to quantitatively detect the sugar content of melon with a high prediction accuracy.
Magnetic Beads-Based Electrochemical Aptasensor for the Detection of Ampicillin in Milk
ZHU Junya, LI Fang, ZHAO Lanxin, LI Xixi, LIU Yunhong
2019, 40(24):  294-299.  doi:10.7506/spkx1002-6630-20180923-236
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A novel electrochemical aptasensor using magnetic beads, based on the specific binding of aptamer to ampicillin, was developed for the detection of ampicillin in milk. Ampicillin functionalized magnetic beads were prepared and used to compete with ampicillin in samples for binding to its aptamers and horse radish peroxidase. Then a magnetic electrode was used to capture and focus the resulting magnetic beads on its surface. Under the optimal conditions, the net current response was linear with ampicillin concentration in the range of 1.0 × 10-12–1.0 × 10-8 mol/L, with a detection limit of 1.0 × 10-12 mol/L. The method was applied in the determination of ampicillin in milk samples with a satisfactory precision and acceptable recoveries.
Determination of Three Catecholamines in Livestock Meat by Solid Phase Extraction Combined with Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry
REN Nan, ZHAO Wentao, CHEN Chao, WU Yanchao, ZHANG Yingying, LI Yingying, GUO Wenping, FAN Wei, WANG Shouwei
2019, 40(24):  300-305.  doi:10.7506/spkx1002-6630-20190107-085
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This study aimed to establish a method for simultaneous qualitative and quantitative analysis of three catecholamines (CAs) in livestock meat by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were homogenized, extracted with perchloric acid solution, and purified on a PCX solid phase extraction cartridge. The chromatographic separation was achieved on an HILIC Plus column (4.6 mm × 100 mm, 3.5 μm) using a mobile phase consisting of acetonitrile and formic acid in water (1:99, V/V). The analytes were ionized by positive electrospray (ESI+), detected in the multiple reaction monitoring mode (MRM) and quantified by the external standard method. The results indicated that a good linearity over the concentration range of 40–1 000 ng/mL was observed for all the analytes with correlation coefficients greater than 0.99. The limits of detection (LOD) and quantification (LOQ) were 10 and 40 μg/kg, respectively. The average recoveries of the CAs ranged from 75.48% to 91.25% with relative standard deviations (RSDs) of 1.2%–4.6% (n = 6). The method is sensitive, simple, rapid and accurate and can meet the requirements for practical analysis.
Rapid Detection of Cronobacter sakazakii Using Recombinase Polymerase Amplification Combined with Lateral Flow Strip
CHEN Chunyang, ZHANG Chenning, SHI Aiying, DU Xinjun, WANG Shuo
2019, 40(24):  306-312.  doi:10.7506/spkx1002-6630-20190411-152
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In this study, recombinase polymerase isothermal amplification (RPA) combined with lateral flow test strips (LF) was developed to quickly and reliably detect Cronobacter sakazakii. RPA using the primers modified with biotin and digoxin produced large amounts of double-stranded DNA products labeled with biotin and digoxin at each end. The products could interact with gold-labeled anti-digoxin antibody and streptavidin fixed on the LF, giving visible results on the strip. The RPA-LF method showed a limit of detection (LOD) of 1.7 × 102 CFU/mL for C. sakazakii in pure culture with no cross-reactivity with other common pathogens. The LOD of the RPA-LF was 1.7 × 100 CFU/g after 4 or 6 h enrichment for different types of atrifically contaminated food samples. In order to further evaluate its performance, 20 real food samples were detected by the RPA-LF in comparison with the national standard method. The results obtained were consistent with each other.
Quality Detection of Turbot (Scophtalmus maximus) Treated with Electrostatic Field Using Gas Chromatography-Ion Mobility Spectrometry
CHEN Dongjie, ZHANG Minggang, NIE Xiaobao, JIANG Peihong, ZHANG Yuhua, ZHANG Changfeng, REN Fang
2019, 40(24):  313-319.  doi:10.7506/spkx1002-6630-20180904-044
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The effect of electrostatic field on the storage quality of turbot was studied by examining the changes in total bacterial count (TBC), Pseudomonas aeruginosa count, total volatile basic nitrogen (TVB-N) content and thiobarbituric acid (TBA) value under different storage conditions. The odor fingerprint information was collected by electronic nose and the volatile substances were analyzed and identified by gas chromatography-ion mobility spectrometry (GC-IMS). The results showed that electronic field could significantly preserve the quality of Scophthalmus maximus during storage by inhibiting the growth of TBC and the dominant spoilage bacteria and reducing the increase in TVB-N and TBA values, and suppressed lipid oxidation. The quality of turbot with different storage times and different treatments could be distinguished by using principal component analysis (PCA) and linear discriminant analysis (LDA). According to the GC-IMS fingerprints, the volatile substances of turbot with different storage times and different treatments could be distinguished by heatmap cluster analysis. With the characteristics of rapidity, accuracy and non-destructiveness, the combination of GC-IMS and electronic nose is feasible to detect the freshness and quality of S. maximus.
High Performance Liquid Chromatography-Tandem Mass Spectrometry Detection of Promethazine in Animal-Derived Foods
LI Zhigang, LI Huichen, MA Yanhong, WANG Shouwei, REN Nan, GUO Wenping, GUO Chao, LI Yingying
2019, 40(24):  320-324.  doi:10.7506/spkx1002-6630-20190115-166
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In this research, an analytical method for the determination of promethazine residues in livestock meat and viscera by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was established. Samples were extracted with formic acid-acetonitrile, and then the extract was purified on an HLB ion exchange extraction column before being quantitatively analyzed by using multi-reaction monitoring (MRM) mode. The results showed that the method had a good linear relationship in the concentration range of 0.5–50 ng/mL with a correlation coefficient of greater than 0.999. The limit of detection (LOD) and limit of quantitation (LOQ) were 0.1 and 0.3 μg/kg, respectively. The recoveries from spiked samples were 85.7%–102.0%, and the relative standard deviations for precision were 0.9%–7.4% (n = 6). This method is simple and rapid, and can be used for the determination of promethazine in animal-derived foods.
Residues and Dissipation Dynamics of Abamectin and β-Cypermethrin in Pitaya (Hylocereus undatus) Fruit
LU Qiqi, TANG Mingxin, LIU Yushan, QU Liwen, SU Jiangli, ZHONG Guohua, LIU Jie
2019, 40(24):  325-331.  doi:10.7506/spkx1002-6630-20181225-285
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In order to examine the residual levels and dissipation dynamics of abamectin and β-cypermethrin (β-CP) in pitaya fruit, the fruit were sprayed with 5.2% abamectin-β-CP emulsifiable concentrate (EC) at a recommended dose of 46.8 g/hm2 at different times before harvest. The two insecticides were extracted from the fruit samples using acetone, purified and then concentrated prior to analysis. Abamectin was detected by reversed-phase high performance liquid chromatography while β-CP by gas chromatography. The limits of detection (LODs) were 0.002 and 0.02 ng/μL, and the limits of quantification (LOQs) 0.005 and 0.1 mg/kg for abamectin and β-CP, respectively. The spiked recoveries ranged from 93.8% to 97.2% for abamectin and from 94.0% to 99.2% for β-CP with relative standard deviations (RSDs) less than 9.4%. The dissipation dynamics of abamectin and β-CP sprayed on pitaya fruit was fitted to a first-order kinetic model, and their half-lives were 2.76–4.20 and 3.09–6.08 d, respectively. The final minimum residue values of abamectin and β-CP were < 0.005 and < 0.1 mg/kg, respectively, and the maximum residue values 0.009 and 0.13 mg/kg, respectively. The results showed that the abamectin-β-CP EC could be fast degraded and the pre-harvest interval (PHI) was 14 d, so that it could be recommended for safe pest management. The present study provides basic data and a useful guidance for the use and safety evaluation of abamectin and β-CP on tropical fruits.
Changes and Control of Dimethyl Sulfide, S-Methylmethionine and Dimethyl Sulfoxide Contents during Beer Making
LIU Cheng, DU Jinhua, BAO Jiao
2019, 40(24):  332-337.  doi:10.7506/spkx1002-6630-20181224-276
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In order to control the content of dimethyl sulfide (DMS), a substantial contributor to the aroma and flavor of many commercial beers, 15 beer samples marketed in China were analyzed by gas chromatography with hydrogen flame ionization detection. Variations in the contents of DMS, S-methylmethionine (SMM), and dimethyl sulfoxide (DMSO) were traced during beer fermentation. The results showed that the content of DMS in 47% of the beers exceeded 60 μg/kg. Notably, 71% of the Ale-branded beer samples were found to contain DMS contents higher than 60 μg/kg (with the highest value of 105 μg/kg). Significant variation (up to 160%) was found among 10 commercial malts in the country in the contents of DMS and dimethyl sulfide precursor (DMSP). The contents of DMS and DMSP in most wheat malts were lower than those in Australian malts. After being boiled for 40 min at pH 5.6, the content of DMS in worts decreased by 92%, and the half-life of SMM was 31 min. Additionally, the content of DMS significantly decreased by up to 41% during the vigorous fermentation stage.