Table of Content

25 September 2019, Volume 40 Issue 18
Food Chemistry
Relationship between Soluble Solid and Soluble Sugar Contents and Optical Properties of Apple Flesh
WEI Kangli, LIU Chang, DING Haizhen, YANG Mingzhe, HAO Yajing, MA Chen, TU Kang, PAN Leiqing
2019, 40(18):  1-7.  doi:10.7506/spkx1002-6630-20190118-218
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In order to gain a deep understanding of the principle of an optimal method for the determination of soluble solid contents in fruits, we quantified the relationships between the contents of soluble solid, total soluble sugar, fructose, glucose and sucrose and absorption and scattering properties of apple flesh during storage (150 d at 0 ℃) using the single intergrating sphere technology. Besides, predictive models were established by partial least squares regression. The results showed that the contents of soluble solids and soluble sugars decreased during storage, and so did the absorption coefficient (μa) and reduced scattering coefficient (μ’s); highly significant positive correlations occurred between the two groups of parameters (r = 0.768–0.992). In particularly, the correlations between these soluble components and μa were higher. Among the three soluble sugars, soluble solids were the most correlated with sucrose (r = 0.961). The average correlations of soluble solids and sucrose with μa and μ’s (r = 0.890–0.963) were higher than those of fructose and glucose (r = 0.813–0.910). Furthemore, the prediction models for soluble solids and sucrose were better, with determination coefficient for prediction (Rp) of 0.886–0.893 and 0.864–0.906, respectively. The results showed that the high correlations between soluble sugars (especially sucrose) and optical properties may provide evidence that optical properties could be used to predict soluble solid contents. This study provides a theoretical rationale for optical detection of fruit quality.
Effect of Fat Addition on Lipid and Protein Oxidation and Volatile Compound Formation in Fermented Sausages
Hu Yingying, Wang Yan, Yu Jing, Jiang Peiyu, Kong Baohua, Chen Qian
2019, 40(18):  8-14.  doi:10.7506/spkx1002-6630-20181022-233
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The effect of addition of different amounts of fat (5%, 10%, 15% and 20%) on protein and lipid oxidation in fermented sausages was investigated in this study. Meanwhile, the volatile compounds were analyzed before and after fermentation for 15 days and sensory evaluation was performed. The results showed that the thiobarbituric acid reactive substances (TBARS) value and carbonyl content significantly increased with increasing added fat. In contrast, there was a significant decrease in total sulfhydryl content (P < 0.05), evidencing that lipid and protein oxidation in fermented sausages were enhanced with increasing fat addition. The higher contents of volatile compounds formed as a result of lipid oxidation, such as aldehydes, ketones, alcohols, acids, esters and hydrocarbons, were observed in fermented sausages with higher amounts of added fat (P < 0.05). Finally, the sensory evaluation results showed that fermented sausages with 15% fat addition had significantly higher acceptability scores than those with other addition levels (P < 0.05).
Changes in Phenloic Components and Antioxidant Activity of Barley before and after Malting
LI Weizhou, LI Fuxiang, HE Xiaoqin, LI Fuhua, ZHAO Jichun, LEI Lin, MING Jian
2019, 40(18):  15-21.  doi:10.7506/spkx1002-6630-20181227-319
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Free and bound phenolic extracts were obtained from eight varieties of barley and corresponding malts. Their components were analyzed and their antioxidant activities were evaluated. The results showed significant differences in the types and amounts of phenolics before and after malting for each barley variety. The total phenolic content of barley was significantly increased after malting (P < 0.05). Among the eight varieties, Hindmarsh displayed the highest percentage increase in total phenolics as well as free gallic acid, vanillin and ferulic acid, and the contents of feculic acid and orientin were increased significantly after malting; Metcalf had the highest percentage increase in bound ferulic acid and orientin. The results of antioxidant assay in vitro showed that the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and oxygen radical absorbance capacity were increased after malting for all the varieties, among which the free phenolics of Scope malt had the strongest DPPH radical scavenging capacity, while the bound phenolics of Baudin malt had the highest oxygen radical absorbance capacity (ORAC) value.
Effect of Protein Oxidation on Biochemical Properties of Coregonus peled Sarcoplasmic Proteins
DENG Xiaorong, LEI Yongdong, LU Shiling, LIU Juan, ZHANG Jian
2019, 40(18):  22-27.  doi:10.7506/spkx1002-6630-20181009-068
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Coregonus peled from Sayram Lake in Xinjiang, China was used to study the changes in the biochemical properties of muscle proteins after protein oxidation using a FeCl3/H2O2/ascorbic acid (Asc) hydroxyl radical-generating system (HRGS). The results showed that oxidant concentration (1–20 mmol/L) and oxidation time (1–5 h) were positively correlated with the carbonyl content, dityrosine content and surface hydrophobicity of C. peled sarcoplasmic proteins (SP), but negatively correlated with the total sulfhydryl content, free amino content and Ca2+-ATPase activity. Statistically significant changes were observed for all the indexes (P < 0.05). After 5 h oxidation with the oxidant H2O2 (20 mmol/L), the contents of carbonyl groups and dityrosine and the surface hydrophobicity increased by 41.28%, 39.5% and 37.5%, respectively, while the total sulfhydryl content, Ca2+-ATPase activity and free amino group content decreased by 65.9%, 60.2% and 22.5%, respectively compared with the unoxidized group. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns demonstrated the formation of protein polymers and protein degradation caused by H2O2 oxidation at the molecular level. Our findings indicate that protein oxidation and biochemical alterations of C. peled SP have an influence on the quality of C. peled.
Emulsifying Properties of Glyceryl Monolaurate Grafted Gum Arabic
XIE Yanping, ZHANG Xiuqi, CAI Zhixiang, ZHANG Hongbin
2019, 40(18):  28-34.  doi:10.7506/spkx1002-6630-20181031-375
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In order to improve the emulsification performance of gum arabic (GA), in the present work, glyceryl monolaurate (GML) was grafted with GA. The emulsifying properties and the effect on the stability of oil-in-water emulsions of various grafted products (GML-GA) prepared at different mass ratios of GML to GA of 0%, 5%, 10% and 20% were contrastively investigated. Bulk rheological results indicated that both GA and GML-GA aqueous solutions behaved as Newtonian fluids. The emulsifying properties of GML-GA and the stability of oil-in-water emulsions with GML-GA were significantly enhanced in comparison with GA. The emulsifying properties of GML-GA were improved and then decreased with increasing the GML content, and the best emulsification performance was obtained at a GML to GA ratio of 10%. The emulsification activity of GA was attributed to its content of arabinogalactan protein (AGP). As GML molecules were probably mainly grafted onto AG, the most abundant component in GA, the improved emulsification of the GML-GA products was due to the presence of both AGP and GML-grafted AG.
Effect of Natural Fermentation on Molecular Structure and Retrogradation Properties of Sorghum Starch
GE Yunfei, KANG Ziyue, SHEN Meng, WANG Juan, QUAN Zhigang, XIAO Jinling, WANG Weihao, CAO Longkui
2019, 40(18):  35-40.  doi:10.7506/spkx1002-6630-20180923-254
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This study aimed to clarify the influence of natural fermentation on the molecular structure and retrogradation properties of sorghum starch. The surface morphology, functional groups, molecular mass and chain length distribution of starch prepared by alkaline extraction of naturally fermented sorghum were measured versus fermentation time. The results showed that after natural fermentation, the surface of sorghum starch granules exhibited some traces of erosion; no new chemical groups were formed during the fermentation process, and the peak position of each functional group remained unchanged. The weight average molecular mass of the starch was reduced after fermentation, and the percentage of low-molecular-mass starch was increased from 74.2% to 78.5%, while the percentage of high-molecular-mass starch decreased from 5.4% to 2.5%; the percentage of short-chain branch of amylopectin decreased by 1.8%–3.89%, whereas the percentage of long-chain branch increased by 2.01%. After fermentation, and the setback value increased by 466 mPa·s, and the peak viscosity also increased. Fermented sorghum starch was more likely to form gel. The findings of this study provide a theoretical basis and supporting data for the regulation of natural fermentation of sorghum and the processing of foods with retrogradated starch.
Preparation and Stability of Soybean Lipophilic Protein-Hydroxypropyl Methylcellulose Emulsion
Zhong Mingming, Qi Baokun, Zhao Tian, Sun Yufan, Wang Diqiong, Fang Lin, Xie Fengying, Zhang Shuang, Yang Shuchang, Li Yang
2019, 40(18):  41-47.  doi:10.7506/spkx1002-6630-20181018-195
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This work studied the effect of high pressure treatment (60, 100 and 140 MPa) on the formation of composite emulsions of 0.5% soybean lipophilic protein (LP) and different concentrations (0%, 0.01%, 0.05%, 0.1% and 0.2%) of hydroxypropyl methylcellulose (HPMC) at different homogenization pressures, and it also revealed the relationship between the structural changes of LP and emulsion stability. Dynamic laser scattering (DLS), contact angle measurement and infrared spectroscopy were employed to investigate the hydrodynamic radius and interfacial adsorption characteristics of the composite emulsions as well as the changes in protein secondary structures. The results showed that the emulsions had lower emulsifying capacity, storage stability and interfacial adsorption capacity at 60 MPa than at other pressures. As the pressure increased, the particle size of the emulsions became smaller, the shape of the droplets was regularly and evenly distributed, and the negative charge on the emulsion surface increased. At 140 MPa and 0.1% cellulose concentration, the emulsification activity and emulsion stability were as high as 223.05 m2/g and 290.5 min, respectively. The high pressure treatments changed the secondary structures of LP, affecting its combination with HPMC and consequently the adsorption characteristics of the formed emulsion at the oil-water interface. The emulsion had the best hydrophilicity at 0.1% cellulose concentration.
Synthesis and Characterization of High-Potency Dipeptide Sweetener
HU Nan, QIU Yun, GUO Dasan, MU Xiaoqing, TAN Qikun, HU Jing, YAN Ri’an
2019, 40(18):  48-54.  doi:10.7506/spkx1002-6630-20181008-038
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N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-α-aspartyl]-S-tert-butyl-L-cysteine-1-methyl ester, a high-potency dipeptide sweetener, is approximately 40 000 times sweeter than sucrose. 3-(3-Hydroxy-4-methoxyphenyl) propanal was synthesized from isovanillin through Wittig reaction, catalytic hydrogenation at room temperature and ambient pressure and reduction with diisobutylaluminium hydride (DIBAL-H). A dipeptide was synthesized from S-tert-butyl-L-cysteine-methyl ester and N-(tert-butoxycarbonyl)-L-aspartic acid-4-tert-butyl ester coupled with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI) and 1-hydroxybenzotriazole (HOBt) by condensation reaction. N-(L-α-aspartyl)-S-tert-butyl-L-cysteine-1-methyl ester was prepared by dissolving the dipeptide in hydrochloric acid (HCl)-dioxane solvent. Finally, 3-(3-hydroxy-4-methoxyphenyl)propanal was reacted with N-(L-α-aspartyl)-S-tert-butyl-L-cysteine-1-methyl ester through palladium on carbon (Pd/C)-catalyzed hydrogenation at room temperature and ambient pressure to obtain N-[N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-L-α-aspartyl]-S-tert-butyl-L-cysteine-1-methyl ester. The structure of the final product was identified by infrared spectroscopy, mass spectrometry and nuclear magnetic resonance.
Transcriptome Analysis of Cherry Tomato Fruit Treated with Cryptoccocus laurentii Using High-Throughput Next-Generation Sequencing Technology
TANG Qiong, ZHENG Xiaodong
2019, 40(18):  55-62.  doi:10.7506/spkx1002-6630-20180830-322
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As a biological elicitor, Cryptococcus laurentii can significantly induce resistance to Botrytis cinerea in cherry tomato but the underlying mechanism is still ambiguous. High-throughput sequencing on an Illumina HiSeqTM 4000 platform was used for transcriptome sequencing of cherry tomato fruit treated with C. laurentii or sterile water, and bioinformatic methods were used for gene function prediction. Then the expression levels of some defense-related genes were monitored by real time-quantitative polymerase chain reaction (RT-qPCR). By transcriptome sequencing, it was found that there were a total of 3 141 differentially expressed genes in tomato fruit treated with C. laurentii for 48 h, 1 689 of which were up-regulated while 1 452 were down-regulated. These differentially expressed genes were involved in multiple metabolic pathways, which implied that the inductive effect of C. laurentii on cherry tomato fruit was a collaborative process. Moreover, the RT-qPCR results were consistent with the transcriptome analysis.
Effect of Ethanol Stress on Membrane Physiology and Adhesion of Lactobacillus plantarum
WANG Tingting, LI Chun, LI Jiadong, DU Peng, LIU Libo, XU Zhanwen, YANG Yuze
2019, 40(18):  63-69.  doi:10.7506/spkx1002-6630-20181009-059
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Objective: To investigate the change in the adhesion capacity of Lactobacillus plantarum under ethanol stress and its physiological response against ethanol stress. Methods: L. plantarum was subjected to ethanol stress at different concentrations and its survival rate, cell membrane integrity and ultrastructural changes were determined. Human colon cancer HT-29 cells were used as an in vitro model to determine the adhesion capacity of this bacterium. The changes in cell membrane fatty acids were analyzed by gas chromatography-tandem mass spectrometry (GC-MS). Results: The survival rate of L. plantarum decreased gradually with the increase in ethanol concentration, and the cell membrane integrity and surface structure were damaged. In addition, the adhesion rate to HT-29 cells decreased, and the proportion of unsaturated fatty acids in the cell membrane increased. Conclusion: Ethanol stress can reduce the adhesion of L. plantarum to HT-29 cells. Fatty acids in the cell membrane and its integrity play an important role in the ethanol stress response of L. plantarum.
Identification and Characterization of Cross-Reactive Allergens between Cow Milk αS1-Casein and Soybean Proteins
CONG Yanjun, Lü Xiaozhe, LI Ye, LIU Di, LI Linfeng
2019, 40(18):  70-75.  doi:10.7506/spkx1002-6630-20181224-272
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In this paper, we firstly identified cross-reactive soybean allergens using sera from cow milk allergic infants and mouse monoclonal antibodies. Then, the amino acid sequence similarity between the cross-reactive allergens and cow milk αS1-casein was analyzed by using bioinformatics software. In addition, the stability of the cross-reactive allergens was examined to in vitro digestion in simulated gastric fluid and to heating. The results showed that α subunit of β-conglycinin (Gly m Bd 60K) was identified as cross-reactive allergen. SDS-PAGE analysis demonstrated that Gly m Bd 60K could be completely digested in 2 min. Heating did not change the cross-reactivity of Gly m Bd 60K with αS1-casein monoclonal antibodies.
Bacterial Community Structure and Spoilage Potential of Dominant Bacteria in Chilled Beef
GU Chuntao, BI Weiwei, ZHU Junli
2019, 40(18):  76-82.  doi:10.7506/spkx1002-6630-20180925-263
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To investigate the changes in the bacterial community and the dominant spoilage bacteria in chilled beef stored at 0 ℃, culture-dependent 16S rRNA gene sequencing and culture-independent high-throughput sequencing were carried out to detect the changes in bacterial diversity during the storage. The sensory score, protease activity, pH, and total volatile base nitrogen (TVB-N) in sterile beef extract inoculated with the isolates from spoiled beef were assessed for spoilage potential. The results showed that chilled beef maintained good sensory quality during the early period of storage, and it smelled unpleasant and rotten on the 15th and 18th day, respectively. Total viable count (TVC) rapidly increased during the first 15 days, reaching 8.73 (lg(CFU/g)), and then remained steady. The growth rates of Pseudomonas, Brochothrix thermosphacta, Enterobacter and lactic acid bacteria (LAB) exhibited similar trends to TVC, among which Pseudomonas grew fastest, while Enterobacter and LAB showed the slowest growth rate. The bacterial composition in chilled beef was complex and diverse, including B. thermosphacta, Acinetobacter spp., Aeromonas spp. and Pseudomonas spp., while it became simpler after spoilage. Pseudomonas especially P. fragi and B. thermosphacta were the dominant spoilage bacteria in spoiled beef stored at 0 ℃. Furthermore, these spoilage isolates, including 10 strains of Pseudomonas, 4 strains of B. thermosphacta and 1 strain of Hafnia alve, were separately inoculated to sterile beef juice. The samples inoculated with Pseudomonas and H. alvei exhibited higher sensory score, pH value and TVB-N content, revealing stronger spoilage potential, compared to B. thermosphacta. Moreover, Pseudomonas had stronger protease activity. Thus, the shelf-life of chilled beef was about 15 d based on sensory and microbial evaluation. During the storage, the microbial diversity decreased, and Pseudomonas and B. thermosphacta were the dominant spoilage bacteria in chilled beef. Pseudomonas presented stronger spoilage ability in vitro than B. thermosphacta.
High-Level Expression of Recombinant Acidic Pectin Lyase Gene from Aspergillus niger and Application of the Enzyme in Juice Clarification
HE Yulan, WANG Bin, PAN Li,
2019, 40(18):  83-88.  doi:10.7506/spkx1002-6630-20181005-024
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In this study, the overexpression of acidic pectin lyase D (PelD) in Aspergillus niger was achieved by using its own strong promoter PglaA (the glucoamylase gene promoter). The recombinant PelD (rePelD) was purified by Ni-affinity chromatography and the specificity of the purified protein was confirmed by Western blot. The enzymatic properties were also studied. The pectin lyase activity was up to 8 822.6 U/mL in shake flask culture. The crude enzyme was one-step purified to a specific activity of 8 522.7 U/mg with a 79.4% yield. The optimum temperature and pH of rePelD were 50 ℃ and 5.0, respectively. rePelD was stable over a wide pH range, retaining over 50% of its initial activity after treatment at pH 3.0–6.5 and 40 ℃ for 2 h. The purified enzyme was stable in the temperature range from 30 to 50 ℃. At a concentration of 1 mmol/L, Ca2+, Mg2+, Cu2+, Zn2+, Ni2+, Mn2+ and Ba2+ (especially Zn2+, Ni2+ and Ba2+) had an activating effect on rePelD, while sodium dodecyl sulfate (SDS) showed inhibition effect. rePelD showed high specific activity for highly esterified pectin. It showed maximum activity (31 248.0 U/mL) towards citrus pectin (esterification degree ≥ 85%). After treatment with rePelD, the light transmittance of orange, apple and grape juice was increased by 17.9, 11.5 and 5.7 folds, respectively, suggesting that rePelD was very effective in clarifying orange, apple and grape juice.
Diversity of Lactobacillus Species in Breast Milk Samples from Uygur Mothers at Different Lactation Stages in Kashi, Xinjiang
LI Xiaojuan, NI Yongqing, ZHANG Yan
2019, 40(18):  89-94.  doi:10.7506/spkx1002-6630-20180901-003
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The Lactobacillus composition of breast milk samples from Uygur mothers at different stages of lactation in Kashi, Xinjiang was comparatively investigated by strain isolation using modified MRS medium, repetitive polymerase chain reaction (rep-PCR) fingerprinting, homology analysis of the 16S rRNA sequence, and construction of a phylogenetic tree by means of MEGA V5.0. The results showed that a total of 229 Lactobacillus strains were isolated from 45 breast milk samples and they were identified as Lactobacillus, Enterococcus and Streptococcus, respectively. Of these isolates, 96.1% belonged to Lactobacillus spp., including L. brevis (75 strains), L. fermentum (82 strains), L. ori (37 strains), L. vaginalis (4 strains) and L. gasseri (22 strains). L. vaginalis is a rare bacterial species. The obtained data showed that the composition of Lactobacillus in the breast milk samples was diverse and varied among lactation stages. The population structure of Lactobacillus in mature milk samples was more complex than that of colostrum and late milk, and it was the most complex in breast milk samples between day 5 and month 5. This study provides the basis for the development of probiotics resources from breast milk.
Characterization of Trypsin and Trypsin-like Serine Proteases from Sea Cucumber Stichopus japonicus and Their Roles in Autolysis
XU Jinhua, MENG Zeling, GE Shiqi, XUE Peng, ZHANG Gongliang, HOU Hongman, SUN Liming,
2019, 40(18):  95-100.  doi:10.7506/spkx1002-6630-20181004-019
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In this paper, serine protease in the body wall of sea cucumber (Stichopus japonicus) was investigated on its partial properties and role in the autolysis of sea cucumber. The serine protease was obtained after a series of processes including extraction with Tris-HCl buffer, (NH4)2SO4 precipitation, dialysis, and ultrafiltration. Results showed that the maximum protease activity was observed using Boc-Phe-Ser-Arg-MCA as substrate. Based on this substrate, the peak protease activity occurred at pH 6.2 and 8.5 and 50–55 ℃. The protease activity could be significantly inhibited by Cu2+, Fe3+, Pb2+ and Zn2+ but activated by Ca2+. The activity was partially inhibited by phenanthroline, EDTA, and cysteine-modifying reagents, while it together with the production of soluble proteins and trichloroacetic acid (TCA)-soluble peptides as a result of autolysis could be significantly inhibited by 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride (AEBSF), phenylmethanesulfonyl fluoride (PMSF), N-p-tosyl-L-phenylalanine chloromethyl ketone (TPCK), (3S)-1-chloro-3-tosylamido-7-amino-2-heptanone hydrochloride (TLCK), and soybean trypsin inhibitor (SBTI). The above results suggest that there are at least two metal ion-dependent trypsin/trypsin-like serine proteases in the body wall of S. japonicus, with cysteine being involved in the active center or substrate-identifying site, and these proteases may be involved in the autolysis of S. japonicus.
Screening and Identification of Heat-Resistant Xylanase-Producing Strain and Investigation of Fermentation Conditions
YANG Ran, ZHANG Xiaoyu, LIU Pengxiao, FAN Guangsen, LI Xiuting,
2019, 40(18):  101-107.  doi:10.7506/spkx1002-6630-20180903-017
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In this research, we isolated a thermostable xylanase-producing strain FSD0302 from Jiuqu (a traditional Chinese liquor fermentation starter) from Zibo, Shandong, and we identified it as Thermomyces lanuginosus. The fermentation conditions for the production of xylanase by this strain were investigated by one-factor-at-a-time method. The results showed that a higher xylanase activity of 5 357.1 U/mL was obtained under the following conditions: particle size of corncob xylan 20–40 mesh, xylan concentration 4 g/100 mL, initial medium pH 6.0, fermentation temperature 50 ℃, and rotational speed 200 r/min, which was 3.9 times as much as that before the optimization. The specific activity was calculated as 10 493.72 U/mg. Strain FSD0302 produced two xylanases with different molecular masses of about 20 and 60 kDa, respectively. The enzymatic properties showed that the optimum temperature was 75 ℃ for both xylanases, and the optimum pH was 5.5 and 7.5, respectively. Over 50% of the xylanase activity could be retained in the pH range of 3.5–9.0. To sum up, the thermostable xylanase from T. lanuginosus FSD0302 is promising for application in the production of xylooligosaccharides.
Oenological Potential of Indigenous Torulaspora delbrueckii for Winemaking
YANG Shini, YE Dongqing, JIA Hongshuai, ZHANG Wenjing, SONG Yuyang, LIU Yanlin
2019, 40(18):  108-115.  doi:10.7506/spkx1002-6630-20180914-142
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In this research, the physiological and fermentation characteristics of three indigenous strains of Torulaspora delbrueckii separated in the wine-producing region of Qilian Mountain, Gansu were evaluated. Cabernet Sauvignon dry red wines were co-fermented by simultaneous or sequential inoculation of T. delbrueckii R12 and Saccharomyces cerevisiae at different mixing ratios. The results obtained were as follows: 1) all of the three strains could tolerate 12% (V/V) ethanol, 400 mg/L SO2 and 400 g/L sugar; 2) all the strains could allow complete fermentation of a model must with 200 g/L sugar, producing 11% (V/V) ethanol, whereas at a sugar concentration of no less than 300 g/L, notable residual sugar was found in the wines; and 3) R12 showed colonization activity regardless of which inoculation method was used, and the proliferation capacity was higher in sequential inoculation than that in simultaneous inoculation. Additionally, volatile acid concentrations in the wines significantly decreased with the increase in R12 cell concentration. The indigenous strains of T. delbruecki are expected to be promisingly application in China’s winemaking industry.
Correlation between Changes in Microbial Proteome and Community Succession in Fresh Tan Sheep Meat during Chilled Storage
ZHAO Xiaoce, HU Qianqian, LUO Ruiming, ZHANG Heyu
2019, 40(18):  116-120.  doi:10.7506/spkx1002-6630-20180927-294
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The differential microbial proteins from fresh Tan sheep meat during chilled storage were studied by surface enhanced laser desorption ionization time-of-flight mass spectrometry, and the changes in the dominant bacterial community composition were analyzed by metagenomics. Meanwhile, the correlation between dominant bacteria and differential proteins was examined. The obtained results indicated that the number of Pseudomonas and Brochothrix thermosphacta increased from an initial level of 9.98% and 0% to 33.70% and 23.98% after storage, respectively. They were positively correlated with necrosis-inducing phytophthora protein, MT-ND4L, somatostatin-28, ATP synthase F(0) complex subunit C1 and prion proteins, but negatively correlated with Keratin associated protein 3-1. The number of Escherichia increased from 4.35% to 11.40%, and the number of Lactobacillus increased from 4.02% to 7.54%. They were positively correlated with keratin-associated protein 8-1, antimicrobial peptide and phosphor apolipoprotein C-II, but negatively correlated with growth hormone-releasing hormone, ATP synthase, and apolipoprotein E. An increase in the number of the dominant bacteria corresponded to an increase in the contents of bacterial proteins positively correlated with it, while those negatively correlated with it were gradually degraded, leading to slow growth of the dominant bacteria.
Physicochemical Properties of Exopolysaccharide from Tibet Kefir and Its Application in Cheddar Cheese
LUO Tianqi, GUO Ting, YU Zhijian, CHEN Chao, CAO Yongqiang, YANG Zhennai,
2019, 40(18):  121-129.  doi:10.7506/spkx1002-6630-20181018-192
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The exopolysaccharide (EPS) yield of Tibet kefir KW1 grown in SDM medium at 37 ℃ was 624.82 mg/L. The EPS was separated and purified, and it was determined to be composed of rhamnose, arabinose, mannose, glucose and galactose in a molar ratio of 1:3.02:2.12:1.59:3.04. Infrared spectroscopy showed that the EPS exhibited a typical absorption peak pattern of polysaccharides. Under scanning electron microscopy, the EPS exhibited spherical and flaky structures with a surface smooth. Observation by atomic force microscopy showed aggregates with membrane-like and cluster-like structures. When applied in milk fermentation and Cheddar cheese production, the EPS promoted the growth of the starter culture, and this effect initially increased and then decreased with increasing its concentration. Addition of the EPS increased the yield of cheese, the water-holding capacity and the number of viable bacteria during ripening. A total of 69 volatile flavor compounds were detected by gas chromatography-mass spectrometry (GC-MS). The calculation of odor activity value (OAV) showed that a total of 17 flavor substances contributed to the overall flavor of the cheese, among which ethyl butyrate, ethyl hexanoate and ethyl octanoate were the key flavor substances. The present research can provide a technical basis for the application of the EPS from Tibetan kefir in fermented milk products.
Biological Characteristics of a Lytic Short-Tailed Salmonella Phage T139 and Its Antibacterial Effect in Milk and Ground Beef
NIE Ruonan, LI Wanning, YANG Qile, WANG Xiaohong, WANG Jia
2019, 40(18):  130-136.  doi:10.7506/spkx1002-6630-20180828-304
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A double-layer plate method was used to isolate a virulent phage named T139 from sewage using Salmonella typhimurium (ATCC 13311) as the host strain, and the biological characteristics and antibacterial activity of phage T139 in milk and beef samples were studied. The results showed that phage T139 formed clear plaques; it could lyse its host bacterium and other Salmonella strains with a broad host spectrum. Transmission electron microscopic (TEM) observation showed that phage T139 belonged to the Podoviridae family with a head diameter of (43 ± 1) nm and a tail length of (11 ± 0.6) nm. The optimal multiplicity?of?infection (MOI) of this phage was 0.001, and the optimal adsorption rate was 66%. The one-step growth curve showed that the latent period was 5 min, the burst period was 60 min, and the average lysis amount was 54.54 PFU/cell. The phage was stable within 30–50 ℃ and pH 4–12. It had a good lytic effect on S. typhimurium cultured in vitro. The antibacterial effect of phage T139 on S. typhimurium in milk was not significant at 4 ℃, and the number of host cells decreased by 4.32 and 4.27 (lg (CFU/mL)) at MOI = 10 and 100 at 25 ℃, respectively. Similarly, it had no significant effect on S. typhimurium in beef at 4 ℃, MOI = 10, whereas at MOI = 100, the number of host cells decreased by 0.66 (lg (CFU/mL)). At 25 ℃, MOI = 10 and 100, the number of host cells decreased by 0.77 and 1.16 (lg (CFU/mL)), respectively. It was shown that phage T139 could effectively inactivate S. typhimurium in milk and beef.
Changes in Color and Texture of Shuidouchi, a Chinese Traditional Fermented Soybean Product, during Fermentation Process
LIANG Yexing, ZHANG Ling, LI Xue, ZHANG Huanhuan, XIONG Jiayan, ZHANG Xuemei, GAO Feihu, YANG Shixiong
2019, 40(18):  137-143.  doi:10.7506/spkx1002-6630-20180919-203
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The hardness, chewiness, elasticity, cohesiveness, color, amino acid nitrogen content and cellulose activity of naturally fermented Shuidouchi made from soybeans grown in southwestern China’s Chongqing and northeastern China were measured at different stages of the fermentation process. The relationship between amino acid nitrogen content and color parameters and hardness was determined using regression analysis. The results showed that during the fermentation process consistent changes were observed in hardness and chewiness. The largest decrease in hardness occurred during the soaking and cooking processes. The trends of cohesiveness and elasticity were consistent, both of which were only slightly changed during soaking and cooking. The elasticity decreased during post-fermentation process. The L value decreased first rapidly and then tended to be stable, and the color gradually became darker. The a and b values remarkably increased, and the color turned into yellow and red. As a result, Shuidouchi formed its unique yellow or yellowish-brown color. Regression analysis revealed that the content of amino acid nitrogen was negatively correlated with the L value but positively correlated with the a and b values. The L value was the most correlation with the content of amino acid nitrogen, and for Shuidouchi made from Chongqing-grown and northeastern China-grown soybeans, the correlations were 74.5% and 86.3%, respectively. Accordingly, it was suggested that the L and a values could be used to predict the amino acid nitrogen content of Shuidouchi. Chongqing-grown soybean was more suitable for the processing of Shuidouchi.
Fermentation Efficiency and Flavor Characteristics of Bayberry Wine with Mixed Starter Culture of Issatchenkio orientalis and Saccharomyces cerevisiae
ZHANG Wenwen, WENG Peifang, WU Zufang
2019, 40(18):  144-151.  doi:10.7506/spkx1002-6630-20180831-375
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In this paper, Issatchenkio orientalis (Io) and Saccharomyces cerevisiae (Sc) were used in combination to ferment Chinese bayberry juice. The fermentation period was determined and the volatile flavor compounds of the wine were compared. The results showed that the fermentation efficiency of the mixed starter culture was higher than that of Sc alone, and the primary fermentation was completed 3 days earlier. The types of volatile flavor compounds from the mixed starter culture were similar to those from pure Sc, but the concentrations of the unpleasant odorants octanoic acid and decanoic acid produced by Sc were reduced by 0.020 and 0.053 mg/L, respectively. The concentration of acetic acid produced by Io was also reduced. The concentrations of ethyl eaters (ethyl butyrate, ethyl isovalerate, ethyl hexanoate, ethyl heptanoate, ethyl nonanate, 3-nonenoic acid ethyl ester) and acetates (ethyl acetate, isomyl acetate and phenethyl acetate) in wine fermented with Sc-Io were increased by 18.52% and 57.34%, respectively compared to wine fermented with Sc alone, which enhanced the fruity flavor. Moreover, mixed-culture fermentation reduced the yeast flavor and the astringency of ethyl caprate produced by Sc, and gave a pleasant taste.
Effects of Citral on Environmental Stress Tolerance and Antibiotics Susceptibility of Cronobacter sakazakii
KANG Shenmin, LIU Zhiyuan, MENG Yujie, CHENG Xiaomeng, TU Junhong, WEN Qiwu, GUO Du, SHI Chao
2019, 40(18):  152-160.  doi:10.7506/spkx1002-6630-20181004-014
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In this study, the sub-inhibitory concentrations (SICs) of citral on Cronobacter sakazakii were firstly determined. Then, the effect of citral at its SICs on the tolerance of C. sakazakii to desiccation, heat, osmotic pressure, acid and bile salt was investigated. The E-test? method was also used to detect the changes in the susceptibility of C. sakazakii to ampicillin and cefoxitin. Finally, the effects of citral on C. sakazakii genes related to environmental stress tolerance were analyzed at the transcription level by real-time RT-PCR. The results indicated that 31.250 μg/L citral had no effect on C. sakazakii growth. Thus, 31.250 and 15.625 μg/L were selected as SICs of citral. Citral at its SICs could significantly reduce the desiccation, heat, osmotic pressure, acid, and bile salt tolerance of C. sakazakii in a concentration-dependent way. In addition, the sensitivity of the bacterial cells to ampicillin and cefoxitin was enhanced after treatment with the SICs of citral. RT-PCR results showed that citral reduced the transcription levels of multiple genes associated with environmental stress tolerance in C. sakazakii. In conclusion, the environmental stresses tolerance and antibiotics susceptibility of C. sakazakii can be reduced significantly by citral. Citral has the potential to control C. sakazakii in food production and processing. This study provides new ideas for the control of foodborne pathogens by natural active substances.
Production of Zhejiang Rosy Vinegar by Pneumatic Stirring and Its Effect on Product Flavor
FANG Guanyu, WU Guangzhong, JIANG Yujian
2019, 40(18):  161-172.  doi:10.7506/spkx1002-6630-20181013-106
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In this study, pneumatic stirring method was used instead of manual stirring for the production of Zhejiang rosy vinegar, and the effects of stirring method and frequency on the fermentation process and vinegar flavor were explored as well. The optimal airflow rate and ventilation time were determined to be 0.73 m3/min and 53 s, respectively. Excessively low stirring frequency could affect substance exchange in acetic acid bacteria, while excessively high stirring frequency was detrimental to the growth of acetic acid bacteria. Under both conditions, the fermentation speed and the final yield of vinegar were reduced. The concentrations of organic acids and non-volatile acids in rosy vinegar produced by pneumatic stirring were increased compared with the traditional method. The volatile component concentrations of rosy vinegar produced by pneumatic stirring method with stirring frequency of once every 5 and 7 d were 6 344.59 and 6 062.63 mg/L, respectively, higher compared to 5 505.83 mg/L for the traditional method. Principal component analysis (PCA) was performed on the volatile components. Rosy vinegar produced by pneumatic stirring was significantly different from that produced by the traditional method and rice vinegar produced using a self-priming fermentor.
Screening and Cultivation of Pleurotus ostreatus: Optimization of Cultivation Conditions for Mycelial Ergosterol Production and Ultraviolet Light-Induced Conversion into Vitamin D2 in Fruit Body
XU Mingfang, CHEN Gengnan, SHEN Linyan, WANG Yangyang, LI Yan, HUANG Xiaojing
2019, 40(18):  173-181.  doi:10.7506/spkx1002-6630-20181010-085
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Five strains of Pleurotus ostreatus were screened for the production of ergosterol as a?vitamin D?precursor in shake flask culture. The optimization of medium components for higher ergosterol content in P. ostreatus mycelia in submerged culture was carried out using response surface methodology. The fruit body resulting from approximately 40-d culture of the mycelia was irradiated with ultraviolet light (280 nm). Then the contents of ergosterol and VD2 were synchronously detected by high performance liquid chromatography (HPLC) and the effect of the cellular structures of different fruit body tissues on ergosterol conversion to VD2 were also explored by field emission scanning electron microscope (FESEM). The results showed that the ergosterol content of strain P831 was up to 3.25 mg/g, higher than those of the other four strains. Therefore, it was used for the following experiments. The Plackett-Burman design indicated that peptone, sucrose, potassium phosphate dihydrogen were key medium constituents affecting the mycelial ergosterol content. Under the optimized conditions of peptone 0.35%, sucrose 3.48% and potassium phosphate dihydrogen 0.35%, the mycelial ergosterol content reached its maximum value of 3.64 mg/g, 12% higher than that before optimization. The contents of ergosterol and VD2 in the cap and lamella were higher than in the stipe. The results of FESEM showed that the cap contained plentiful amounts of mycelia, forming a clamp-like structure; the lamella was covered with large quantities of dense spores; and the stipe was dominated by a fiber-like tubular network structure with no spores being observed. As the mycelial clamp-like structure and spores in the fruit body of Pleurotus edodes are the main tissues with strong cell division ability and metabolism, we speculate that the differences in the contents of ergosterol and VD2 among fruit body tissues may be related to the morphological structure and cellular metabolism.
Wine Made from a Blend of Red Globe and Glutinous Rice: Optimization of Fermentation Process and Analysis of Aroma Components
YE Linlin, YANG Juan, CHEN Tong, LI Yuanyuan, WU Fenghua, LIU Xingquan, HE Zhiping
2019, 40(18):  182-188.  doi:10.7506/spkx1002-6630-20181017-182
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Objective: This study aimed to improve the quality of wine made from table grapes by addition of natural exogenous sugars for the fermentation process. Methods: Wine was prepared from red globe grapes with added saccharified glutinous rice. The fermentation process was optimized using one-factor-at-a-time method and response surface methodology based on a three-variable, three-level Box-Behnken design. The independent variables considered were fermentation temperature, substrate ratio, yeast inoculum size and SO2 addition. The responses were ethanol and anthocyanin concentration. Results: Using one-factor-at-a-time method, addition of 80 mg/L SO2, a fermentation temperature of 20 ℃, an inoculum size of 1 g/L and a saccharified glutinous rice/red globe grape ratio of 1:4 (V/V) were determined to be the optimal conditions. Using response surface methodology, the fermentation conditions were further optimized as follows: temperature 21 ℃, inoculum size 1.2 g/L, SO2 concentration 84 mg/L, and substrate ratio 1:4. After 7 d fermentation under these conditions, the alcohol concentration was 12.7%. A total of 39 volatile compounds were identified in the wine by gas chromatography-mass spectrometry (GC-MS), including 15 alcohols, 15 esters, 5 acids and 2 terpenes. Based on their odor activity value (OAV), 12 volatile compounds were identified as the major characteristic aromas including β-damascenone, ethyl caproate, ethyl caprylate, isoamyl acetate, ethyl caprate. Conclusion: Saccharified glutinous rice juice can be used as an exogenous sugar source to improve the alcohol concentration of red globe wine, and the wine has a good taste and typical wine flavor.
Component Analysis
Identi?cation and Quanti?cation of Major Carotenoids in Kumaiti Apricot
DU Binhua, AILA?Reheman, CHEN Qi, XIE Rui, HUANG Yadong, HUANG Wenshu,
2019, 40(18):  189-194.  doi:10.7506/spkx1002-6630-20181021-222
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In order to determine the composition and content of carotenoids in fresh Kumaiti apricot (Prunus armeniaca L.), the major carotenoids were analyzed by high performance liquid chromatography-diode array detection-atmospheric pressure chemical ionization-mass spectrometry (HPLC-DAD-APCI-MS) and were identi?ed by comparison of their chromatographic, spectroscopic and mass spectral data with those of reference standards or those reported in the literature. An external standard method was applied to quantify the carotenoids. Results: β-Carotene, α-carotene, β-cryptoxanthin and their cis isomers were found to be the main carotenoid components in Kumaiti apricot, and its β-carotene content was up to 114 μg/g dry sample. In conclusion, Kumati apricot is rich in β-carotene and is a good dietary source of β-carotene.
Differential Lipid Metabolite Profiles during Storage of Tan Sheep Meat Determined by Gas Chromatography-Mass Spectrometry and Liquid Chromatography-Mass Spectrometry
YUAN Yudong, YOU Liqin, LUO Ruiming, JU Ning, ZHAO Xiaoce
2019, 40(18):  195-202.  doi:10.7506/spkx1002-6630-20180724-297
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The differential lipid metabolites of chilled Ningxia Tan sheep meat stored 0, 4, 8 and 12 d were determined by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) based on the OmicsBean cloud platform, aiming to find out the precursors and intermediates of flavor substances. It was demonstrated that the number of differential metabolites generally showed a downward trend during the 12 d of storage. The number of free amino acids increased at the beginning of storage, and then decreased with prolonged storage duration. The contents of hypoxanthine, alanine and threonine increased significantly on day 8, indicating that the flavor precursors related to umami and bitterness were produced during storage. The contents of the flavor precursors derived from lipids such as oleic acid, palmitic acid and stearic acid decreased significantly, indicating that fatty acid metabolism was active during this period. Therefore, studying the postmortem changes in lipid metabolism could provide a theoretical guidance for improvement of the chilled Tan sheep meat production technology.
Aroma Characteristics of Aged ‘Cabernet Sauvignon’ Dry Red Wine from Eastern Foothill of Helan Mountain
ZHANG Zhong, LI Hui, ZHANG Jing, XUE Jie, ZHANG Junxiang
2019, 40(18):  203-209.  doi:10.7506/spkx1002-6630-20181026-318
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The aroma components of ‘Cabernet?Sauvignon’ dry red wines from 10 vertical vintages and the Eastern Foothill of Helan Mountain in Ningxia were determined quantitatively by head space-solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS). The cluster heat map analysis of aroma components was performed to reveal the differences in the main aroma components among different vintages. The sensory evaluation of wine aroma was carried out as well. The correlation matrix between aroma components and aroma quality was constructed. Results showed that the main aroma components identified were esters, followed by alcohols and acids. From the vintage 2015 to 2005, wine aroma changed from black fruit-like, vegetal and baked to red fruit-like, spice-like, animal-like, resin-like and earthy. Sensory analysis showed that aroma quality of wine aged for 7 and 8 years reached the highest level. The main aroma components of wines from different vintages were clustered into three groups according the cluster heat map. Correlation matrix analysis revealed that ethyl acetate, benzaldehyde, linalyl butyrate and ethyl lactate were the key aroma components in aged ‘Cabernet Sauvignon’ dry red wine.
Principal Component Analysis and Multiple Linear Regression Analysis of CIELAB Parameters and Anthocyanins in Red Wine
GUO Yaodong, WANG Fei, DONG Shaojie, WANG Shengyi, ZHANG Ang
2019, 40(18):  210-215.  doi:10.7506/spkx1002-6630-20190408-080
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A total of 119 red wine samples were analyzed for color parameters by using CIELAB color space, the contents of 16 different anthocyanin monomers by ultra-high performance liquid chromatography tandem mass spectrometry, and total anthocyanins content by the pH differential method. Principal component analysis, correlation analysis and multiple linear regression analysis were conducted to study the relationship between CIELAB color parameters (L*, a* and b* values) and the contents of total anthocyanins and anthocyanin monomers and pH in red wine. Three principal component factors reflecting the color in red wine samples were selected, which cumulatively accounted for 84.11% of the total variability. The color parameters were affected by different anthocyanin monomers. Among the 16 anthocyanin monomers, cyanidin-3-glucoside content had the?greatest?impact?on?L* and a* values, while malvidin content had the?greatest?impact on b* value. The content of total anthocyanins had a very significant effect on all color parameters. A significant negative correlation occurred between L* and?a* values.
Effects of Different Sterilization Methods on Fatty Acid Composition and Volatile Flavor Profile of Braised Goose in Brown Sauce
ZHOU Huijian,YUAN Jingyao, ZHU Dan, LI Cong, CHEN Chunmei, LIU Rui, WU Mangang, GE Qingfeng, YU Hai,
2019, 40(18):  216-222.  doi:10.7506/spkx1002-6630-20190119-223
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The purpose of this paper is to investigate the effects of three different sterilization methods of electron beam (0, 3, 6, 9 and 12 kGy), 60Co-γ ray (0, 3, 6, 9 and 12 kGy), and heat treatment (105 and 121 ℃) on thiobarbituric acid reactive substances (TBARS) value, fatty acid composition and volatile flavor profile of vacuum-packed braised goose in brown sauce. The results showed that high-dose electron beam, 60Co-γ ray and high-temperature treatments could promote lipid oxidation of braised goose in brown sauce. Among them, 9 kGy 60Co-γ ray treatment possessed the most significant effect on the TBARS value (P < 0.05). The contents of saturated fatty acids and monounsaturated fatty acids significantly increased along with increasing electron beam and 60Co-γ ray dose. The content of saturated fatty acids was significantly higher in the sample sterilized at 105 ℃ than at 121 ℃ (P < 0.05), while the reverse was found for the content of monounsaturated fatty acids (P < 0.05). The content of polyunsaturated fatty acids significantly decreased as the dose of electron beam and 60Co-γ ray irradiation increased (P < 0.05), and it was significantly higher in the sample treated at 105 ℃ than at 121 ℃ (P < 0.05). The electronic nose analysis indicated no significant difference in volatile flavor profile among the 3 kGy electron beam, 3 kGy 60Co-γ ray, 105 ℃ and control groups. Therefore, our data suggested that low-dose electron beam, 60Co-γ ray irradiation (< 6 kGy) and 105 ℃ treatments have slight effects on the fatty acid composition and volatile flavor profile and are thus promising candidates for the sterilization of braised goose in brown sauce.
Effect of Fermentation with Eurotium cristatum on Aroma Components of Tea Infusions
ZHENG Mengxia, LI Huijuan, CHEN Shuna, ZHAO Zhen, LIU Xinqiu, LI Xinghui, CHEN Xuan
2019, 40(18):  223-228.  doi:10.7506/spkx1002-6630-20181022-230
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The aroma components of green tea and black tea infusions were quantified by headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) before and after fermentation with Eurotium cristatum. It was found that benzoic acid methyl ester, isophorone, methoxy styrene, ethyl benzene, formaldehyde, sweet folic acid methyl ester, and 3,4-dimethyl methyl benzoic acid were detected in the fermented tea infusions, but not in the fresh ones. In the green tea infusion, the concentrations of linalool, linalool oxide I, linalool oxide II, methyl phenylacetate, α-terpineol, trans-2-decylolefine aldehyde, and α-ionone were elevated by 2.30, 3.15, 3.04, 1.29, 4.18, 1.10 and 3.08, respectively after the fermentation, and the number and amount of aroma components increased similarly. In contrast, for the black tea infusion, the majority of the aroma compounds decreased and phenethyl alcohol, trans-2-nonenal, 2-phenylcrotonaldehyde, cis-citral, 4-methyl-2-phenyl-2-pentenal, lauraldehyde and tetradecanal were undetectable after the fermentation, indicating a loss of the total amount of aroma components. Compared to black tea, low-end green tea was more suitable for the processing of fermented beverage with E. cristatum.
Establishment of Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry Method for Determination of 18 Individual Anthocyanins in Wine
JIN Gang, YANG Zhiwei, WANG Shengyi, WANG Changsen, MA Wen, ZHANG Jinjie, ZHANG Ang, ZHANG Junxiang,
2019, 40(18):  229-235.  doi:10.7506/spkx1002-6630-20181008-040
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Objective: To simultaneously determine 18 anthocyanin monomers in red wine using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Methods: Wine samples were diluted 500 times with acidified methanol solution containing 1% formic acid (V/V) before being filtrated. The filtrate was separated by gradient elution chromatography on a phenyl-hexyl column. Detection was carried out using an electrospray ionization source in the positive ion mode with multiple reaction monitoring (MRM). The mass spectrometric conditions were as follows: curtain gas 30 psi, ion spray (IS) voltage 5 500 V, and ion source temperature 500 ℃. The analysis took 20 min. Results: The recoveries of the analytes at spiked levels of 10.0, 20.0 and 50.0 μg/L were between 95% and 100%, and the calibration curve for each analyte exhibited a correlation coefficient (R2) of greater than 0.999. The precision, expressed as relative standard deviation (RSD), ranged between 1.71% and 2.87%. The limits of detection (LOD) were between 0.2 and 3.5 μg/L, and the limits of quantitation (LOQ) were between 0.4 and 11.5 μg/L. Conclusion: This method was characterized by simple pretreatment, high sensitivity, short analysis time, shorter time and good precision and accuracy and could be applied to detect individual anthocyanins in red wine.
Application of Electronic Tongue in the Evaluation of Sweet Taste Quality of Congou Black Tea
YAO Yuefeng, WANG Jiaqin, HUA Jinjie, XU Qi, ZHANG Mingming, JIANG Yongwen, YUAN Haibo, DONG Chunwang, LI Jia
2019, 40(18):  236-241.  doi:10.7506/spkx1002-6630-20181012-100
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The major purpose of this study was to evaluate the sweet taste quality of Congou black tea objectively, rapidly and accurately. According to sensory evaluation data obtained from experts, Congou black tea samples were divided into three categories, i.e., sweet, pure and with off-flavor. Next, the taste quality of tea infusions was comprehensively evaluated by using electronic tongue in combination with multivariate statistical analyses such as principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA) and one-way analysis of variance (ANOVA). A model was established for the discrimination of sweet taste from non-sweet taste based on analysis of electronic tongue data by using binary logistic regression. Finally, the obtained results were preliminarily validated using a separate set of black tea samples. Results: PCA and PLS-DA based on the responses of electronic tongue sensors provided clear discrimination between sweet and non-sweet (pure and with off-flavor) black tea samples. The key electronic tongue sensor for taste classification was identified as the sweet taste sensor SWS (P < 0.001, by one-way ANOVA). A predictive equation for the sweet taste was established based on binary logistic regression, with an overall predictive accuracy of 93.8%. Furthermore, we confirmed the effectiveness of electronic tongue analysis by applying it to the tea samples in the validation set. In summary, the electronic tongue is able to rapidly and accurately evaluate the sweet taste of Congou black tea, and it provides a theoretical foundation for further studies of key taste components in tea, and also offers a novel tool for objective and intelligent evaluation of tea taste.
Determination and Analysis of Bitter and Astringent Substances in Youxi Bitter Tea Resources
TANG Qin, SUN Weijiang, CHEN Zhidan, SHEN Shiyu, ZHOU Zhe, CHEN Jiajia, CHEN Cuicui
2019, 40(18):  242-247.  doi:10.7506/spkx1002-6630-20181030-362
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This study determined the bitter and astringent substances, such as anthocyanins, total flavonoids, alkaloids and catechins in 33 samples of Youxi bitter tea leaves by ultraviolet spectrophotometry and high performance liquid chromatography (HPLC). The results showed that all characteristic components tested varied among samples, and the variation coefficients of 20 of these indicators varied from 9.74% to 73.08%, indicating the rich diversity and high variability of bitter and astringent compounds in Youxi bitter tea. Compared with four control teas, the average values of anthocyanins, caffeine, theobromine, theophylline, epigallocatechingallicacid, total catechins and ester catechins were found to be higher in Youxi bitter tea, providing preliminary evidence that the distinct bitterness and astringency of Youxi bitter tea is related to the high contents of anthocyanins, caffeine and catechins and their synergistic effects. This study then screened out one anthocyanin-rich sample, one caffeine-rich sample, one theobromine-rich sample and 21 EGCG-rich samples. This study provides a good material basis for future research on cross-breeding, processing innovation, functional components and secondary metabolism of bitter tea.
Comparative Analysis of Volatile Profiles Orthodox Black Teas and CTC Black Teas Using HS-SPME-GC-MS
LIU Honglin, ZENG Yitao, ZHAO Xin
2019, 40(18):  248-252.  doi:10.7506/spkx1002-6630-20180927-308
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A total of 14 different commercial brands of black teas including orthodox (OTD) and crush, tear and curl (CTC) teas were collected from markets in six regions of China as well as Sri Lanka, and their volatile flavor compounds (VFC) were comparatively analyzed using headspace solid phase micro-extraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). In total, 59 volatiles were identified from these teas among which terpenes (10.38%–60.34%), ketones (1.1%–22.09%) and esters (3.18%–41.83%) represented the most abundant compounds. The results showed that CTC teas contained a lower number of volatile components and lower contents of aldehydes and alcohols but higher contents of esters than did OTD teas. The data presented in this study also suggested that terpene index might be used as an alternative approach for the determination of the geographical origin of teas, but the accuracy is not sufficient yet, and other parameters are needed to identify the origin of tea products.
Changes of Aroma-Active Components in High-Salt Liquid-State Fermented Soy Sauce before and after Sterilization
KANG Wenli, CHEN Liang, HE Bo, WU Can, ZHOU Shangting
2019, 40(18):  253-258.  doi:10.7506/spkx1002-6630-20181024-275
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In order to determine the changes of aroma-active compounds (AACs) in high-salt liquid-state fermented soy sauce before and after sterilization, we extracted volatile constituents from the samples by direct solvent extraction combined with solvent-assisted flavor evaporation and analyzed them by gas chromatography-olfactometry (GC-O). Twenty-four AACs were detected, and their structures were identified by comparing their odor characteristics, mass spectral data, and retention indices with those of authentic compounds. Their concentrations were determined with 2-octanol as an internal standard. Based on their concentrations and thresholds, the odor activity values (OAVs) of the AACs were calculated. By analyzing the OAVs obtained, the changes in the aroma of soy sauce before and after sterilization were mainly attributed to the changes in the concentrations of 3-methylthiopropanal, maltol, 4-hydroxy-5-ethyl-2-methyl-3(2H)-furanone, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, hexanal, vanillin, guaiacol and 4-ethylguaiacol. This result agreed well with the aroma evaluation.
Correlation Analysis of Volatile Flavor Components and Sensory Characteristics of Maillard Reaction Products Derived from Sipunculus nudus Protein Hydrolysate and Different Saccharides
YOU Gang, NIU Gaigai, DONG Qingliang, ZHANG Ziran, GUO Dejun
2019, 40(18):  259-265.  doi:10.7506/spkx1002-6630-20180803-022
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Headspace-solid phase micro-extraction coupled with gas chromatography-mass spectrometry and descriptive sensory analysis were conducted to investigate the changes in volatile compounds and sensory characteristics of the Maillard reaction products (MRPs) prepared from enzymatically hydrolyzed Sipunculus nudus protein with different saccharides (glucose, maltose, xylose and gum acacia) at 120 ℃ for 120 min. Principal component analysis (PCA), hierarchical cluster analysis and partial least squares regression were applied to explore the correlation of main volatile compounds with different MRPs and sensory characteristics. The results indicated that saccharide type affected the kinds and concentrations of volatile compounds, including aldehydes, alcohols and ketones. The Maillard reaction reduced the bitter and earthy taste of S. nudus enzymatic hydrolysate (SEH) and enhanced the aroma and caramel flavor; the reaction with xylose could significantly increase the kinds and concentrations of aldehydes improving the flavor characteristics. Further analysis suggested that the flavor characteristics of MRPs from SEH with glucose, maltose and gum acacia were not significantly different from each other, which were correlated with hexanal, hexadecanal and decene; MRPs from SEH with xylose were positively correlated with aldehydes, including 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, hexanal, heptaldehyde, methylthiopropanal, furfural, benzaldehyde, undecanal, phenylacetaldehyde, tridecanal, dodecanal, tetradecanal and pentadecal. Nevertheless, SEH showed positive correlations with 4-terpenol, 1-nonanol, 2-pentylfuran, 6-methyl-5-hepten-2-one, octyl formate and 2-acetylthiazole. Moreover, methylthiopropanal, phenylacetaldehyde, n-octanol and 2-pentylfuran were the main volatile compounds that contributed to the aroma and caramel flavor, while 4-terpenol, 2-pentylfuran and 6-methyl-5-hepten-2-one affected the formation of earthy taste. Different saccharides, therefore, remarkably affected the volatile compounds and sensory characteristics, where xylose indicated optimal improvement in the flavor and sensory characteristics. This study provides a theoretical basis for selecting better saccharides to improve the flavor and sensory characteristics of SEH.
Analysis of Characteristic Aroma Components of Flaxseed Oils Obtained by Different Processing Techniques by HS-SPME-GC-MS-O
YU Wenlong, HAO Nan, WU Kaijin, SANG Yaxin, SONG Chunli, WANG Xianghong
2019, 40(18):  266-272.  doi:10.7506/spkx1002-6630-20181009-073
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Abstract:In this study, volatile compounds from cold-pressed and hot-pressed flaxseed oils produced from flaxseeds grown in Zhangjiakou, Hebei province were separated by headspace solid-phase micro-extraction (HS-SPME) and were analyzed by means of gas chromatography-mass spectrometry (GC-MS). The key aroma components of the flaxseed oils were identified by gas chromatography-olfactometry (GC-O). A total of 16 characteristic aroma components of hot-pressed flaxseed oil were detected, including 7 aldehydes, 4 heterocyclic compounds, 3 alcohols, one acid and one ester. A total of 14 characteristic aroma components were identified from cold-pressed flaxseed oil, including 6 aldehydes, 4 alcohols, 3 acids and 1 ester. Seven aroma components were found to be present in both the cold-pressed and hot-pressed oils. 2,5-Dimethylpyrazine, 2,3,5-trimethylpyrazine and (E)-2-hexenoaldehyde were the unique aroma components of hot-pressed flaxseed oil as important contributors to the roasted and greasy aroma. Acetic acid was the unique aroma component of cold pressed flaxseed oil.
Determination of Flavonoids in the Supercritical CO2 Extract of Sea Buckthorn Fruit by Using Ultra-High Performance Liquid Chromatography-Mass Spectrometry
DING Lina, QIU Yiyi, SHU Tong, RUAN Hui
2019, 40(18):  273-280.  doi:10.7506/spkx1002-6630-20181015-138
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Sea buckthorn fruit oil was obtained by supercritical CO2 extraction, and its flavonoid components were analyzed by ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) through Peakview workstation matching followed by tandem mass spectrometric analysis and comparison of ultraviolet spectroscopic data and mass spectral data with those of reference standards as well as with literature data. A total of 18 flavonoid compounds were determined, including eight flavonol aglycones and flavonol glycosides, three dihydroflavonol aglycones and dihydroflavonol glycosides, five flavonoid aglycones and flavonoid glycosides, one dihydroflavonoid aglycon and one flavanol glycoside. To our knowledge, apigenin-6-C-glucoside-8-C-xyloside, catechin-7-glucopyranoside, alizarin, violet and locustin were found in sea buckthorn for the first time.
Purification, Preliminary Characterization and Antioxidant Activity of Polysaccharides from Green Husks of Walnut (Juglans regia L.) Grown in Changbai Mountain
XIE Dongxue, LU Juan, WANG Yue, WANG Chaoxue, CHEN Ruizhan, GAO Jiaxin
2019, 40(18):  281-286.  doi:10.7506/spkx1002-6630-20181017-177
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In this study, polysaccharides named as JPs were ultrasonically extracted from walnut green husks. After sequential treatments of ethanol precipitation, deproteinization and dialysis, JPs were fractionated by DEAE-Sepharose and Sephadex G-100 column chromatography into two homogenous fractions (JPs-1-1 and JPs-2-1). The molecular masses of JPs-1-1 and JPs-2-1 were measured to be 5.45 × 104 and 5.22 × 104 u by high performance gel filtration chromatography, respectively. Monosaccharide analysis by precolumn derivatization with 1-phenyl-3-methyl-5-pyrazolone (PMP) coupled to high performance liquid chromatography (HPLC) indicated that both polysaccharides were composed of rhamnose, glucuronic acid, galactose, glucose, galacturonic acid, xylose and arabinose, but in different molecular ratios. JPs and its fractions possessed a good antioxidant activity in terms of ferric-reducing antioxidant power and scavenging activities against hydroxyl and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals in a dose-dependent manner within a certain concentration range.
Processing Technology
Optimization of Preparation of Oligosaccharides by Enzymatic Hydrolysis of Pea Fiber Powder
WU Shuhua, ZHANG Zhehao, FAN Yuyan, MA Chengye,
2019, 40(18):  287-294.  doi:10.7506/spkx1002-6630-20181015-140
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In this study, pea fiber powder was used as a starting material to prepare oligosaccharides by enzymatic hydrolysis. In order to determine the optimal ranges of process parameters, the effects of solid-to-solid ratio, xylanase dosage, cellulase dosage and reaction temperature on the contents of oligosaccharides, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity and hydroxyl radical scavenging capacity were investigated using a quadratic rotatable composite design. The results indicated that a solid-to-solid ratio of 1:20.7–1:24.5 (g/mL), a xylanase dosage of 170.9–176.7 U/g, a cellulase dosage of 316.6–320.4 U/g and a reaction temperature of 52.1–57.6 ℃ were found to be the optimal conditions to obtain higher oligosaccharide content of 13.98%–15.02%, higher DPPH radical scavenging capacity of 30.56%–33.21% and higher hydroxyl radical scavenging capacity of 39.36%–42.44%. Analysis by liquid chromatography showed that the oligosaccharide prepared under the optimized conditions consisted mainly of arabinose, glucose, galactose, cellobiose, cellotriose and cellotetraose.
Optimization of Extraction Process for S-Adenosyl-L-Methionine from Saccharomyces cerevisiae by Response Surface Methodology
DU Jin, ZHANG Xiaoqing, ZHANG Aijun, SI Xiaoguang, WANG Shuxun, CAO Junrui
2019, 40(18):  295-301.  doi:10.7506/spkx1002-6630-20181010-075
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S-adenosyl-L-methionine (SAM) from Saccharomyces cerevisiae is usually extracted with a high concentration of perchloric acid or organic solvents. In order to reduce the use of organic solvents and potential operating risks during SAM extraction from S. cerevisiae, an ultrasonic-assisted extraction method using a low concentration of hydrochloric acid as the extraction solvent was proposed. First of all, dry yeast cells were used to compare the extraction efficiencies of various solvents including perchloric acid, ethyl acetate-sulfuric acid and hydrochloric acid at different concentrations in an effort to select the most efficient solvent for the extraction of SAM. Subsequently, the extraction process was optimized using one-factor-a-at-a-time method, Plackett-Burman design, steepest ascent design and response surface methodology. The results demonstrated that 0.01 mol/L hydrochloric acid was the solvent of choice. The effects of various factors on extraction efficiency decreased in the descending order of were in the descending order of solid-to-liquid ratio > ultrasonic power > irradiation time > irradiation interval. The optimal conditions obtained were as follows: ultrasonic power, 314 W; irradiation time, 4.1 min; and solid-to-liquid ratio, 1:27 (g/mL). Under the optimized conditions, the experimental extraction yield of SAM was 66.56 mg/g, 92.1% as compared to traditional perchloric acid extraction. The relative deviation between the experimental and predicted values was 0.98%. The optimized extraction procedure is applicable to the production of SAM.
Optimization of Ultrasonic-Assisted Preparation and Structural Characterization of Potato Starch Nanocomposite Films
ZHANG Rongfei, WANG Xiangyou, CHENG Meng
2019, 40(18):  302-311.  doi:10.7506/spkx1002-6630-20180929-328
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In order to improve the dispersibility of nano-SiO2 in potato starch films and consequently to enhance the packaging and preservation properties, potato starch nanocomposite films were prepared by two cycles of ultrasonication. The optimization of the concentrations of nano-SiO2, potato starch and glycerin was conducted using the orthogonal array method. The prepared films were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and ultraviolet-visible (UV-vis) spectroscopy. The effect of packaging with the films on reactive oxygen metabolism in the white button mushroom Agaricus bisporus during storage at (4 ± 1) ℃ was determined. The results showed that ultrasonication resulted in uniform dispersion of nano-SiO2 in the films. The films with exhibited the optimal properties at a potato starch concentration of 3.5 g/100 mL, a glycerin concentration of 3 g/100 mL and a nano-SiO2 concentration of 0.3 g/100 mL. The XRD and FTIR analyses confirmed that the ultrasonic in-situ synthesis method could result in the formation of strong hydrogen bonding between nano-SiO2 and starch molecules. The composite films had outstanding anti-UV property. The properties of films were enhanced by ultrasonic in-situ synthesis compared to the routine method, as indicated by a reduction in water vapor transmission rate, oxygen permeability and water solubility of 30.22%, 71.16% and 39.61%, respectively, and an increase in tensile strength of 17.82%. The films prepared in this study could control reactive oxygen metabolism, thereby extending the shelf-life of Agaricus bisporus.
Safety Detection
Measurement of the Refining Degree of Sunflower Oil Based on Gas Chromatography-Ion Mobility Spectrometry
CHEN Tong, GU Hang, CHEN Mingjie, LU Daoli, CHEN Bin
2019, 40(18):  312-316.  doi:10.7506/spkx1002-6630-20181012-102
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In this study, we analyzed the volatile organic components of sunflower oils with different degrees of refining by using gas chromatography-ion mobility spectrometry (GC-IMS) and we constructed fingerprints. Our aim was to discriminate and classify the sunflower oils based on refining degree. A total of 22 effective characteristic peaks were selected by two-dimensional differential spectrometry as variables to characterize the changes in refining degree. Principal component analysis (PCA) and supervised pattern recognition methods such as the k-nearest neighbor (kNN) method, quadratic discriminant analysis (QDA), and Fisher linear discriminant analysis (FLDA) were used to carry out discriminant analysis. The results showed that all three supervised pattern recognition methods could effectively distinguish the sunflower oil samples with an accuracy rate of up to 97.30%. GC-IMS combined with chemometrics could accurately and visually distinguish sunflower oil samples with different refining degrees. This method facilitates the quality control of vegetable oils in enterprises and provides a new detection method for quality inspection technicians.
Highly Sensitive Detection of Streptomycin Residues by Ultraviolet-Absorbing Graphene Oxide-Based Aptasensor
LIU Zhenping, JIANG Rong, XIA Mingxing
2019, 40(18):  317-322.  doi:10.7506/spkx1002-6630-20190123-298
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Objective: Based on the protective effect of aptamers on the aggregation of graphene oxide (GO) aqueous solution, we established a highly sensitive and specific aptasensor for the detection of streptomycin (STR) residues. Methods: In saturated GO aqueous solution, a STR-specific aptamer could interact with the surface of GO via hydrophobic and π-π stacking interactions between the ring structures in the nucleo-bases and the hexagonal cells of GO to promote its dispersion. When STR entered the system, the aptamer was combines with STR and separated from GO, resulting in decreased GO dispersion and consequently aggregation. After centrifugation, the ultraviolet (UV) absorbance of the supernatant was determined at 230 nm. The linear relationship between the absorbance and STR concentration was established thereby allowing quantitative detection of STR. Results: Under the optimized conditions, the UV absorbance of GO decreased with the increase in STR concentration and had a good linear relationship with the logarithm of STR concentration in the range of 0.002 4–240 ng/mL, which was fitted as follows: A = -0.105 73lgCSTR + 0.471 5 (R2 = 0.994). The detection limit was 0.001 3 ng/mL. The average recoveries for spiked honey samples from two different sources were 89.3%–108.1% and 94.7%–110%, respectively. Conclusion: The aptasensor developed in this study can be used to rapidly detect STR residues with good repeatability and stability and high sensitivity.
Rapid Quantitative Detection of Escherichia coli O157:H7 in Milk Based on Catalytic Activity of Cobalt-Based Metal Organic Framework (ZIF-67)
WANG Shujuan, LIU Cheng, FANG Shuiqin, TIAN Yachen, DONG Qingli, WANG Xiang, XU Dongpo, LIU Qing,
2019, 40(18):  323-328.  doi:10.7506/spkx1002-6630-20190220-120
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The aim of this study was to establish a new method for the rapid quantitative detection of Escherichia coli O157:H7 (E. coli O157:H7) in milk samples based on the catalytic activity of metal-organic framework. A cobalt-based metal organic framework (ZIF-67) was synthesized by using 2-methylimidazole and cobalt chloride hexahydrate as starting materials with Bola amphiphilic surfactant as solvent. The catalytic performance of ZIF-67 was studied. It was found that ZIF-67 had similar catalytic activity to horseradish peroxidase (HRP) and could catalyze the chromogenic reaction of 3,3’,5,5’-tetramethylbenzidine (TMB) in the absence of hydrogen peroxide (H2O2). Based on this, we established a method for indirect detection of E. coli O157:H7 in milk by specific enrichment with magnetic microspheres and subsequent detection of ZIF-67 combined with the target. The detection range of this method was 17–1.7 × 108 CFU/mL, and the detection limit (LOD) was 17 CFU/mL. The detection took 1 h. This method could detect E. coli O157:H7 in milk quickly and simply with high sensitivity and selectivity. It has great potential for application in rapid screening of foodborne pathogens.
Determination and Stability of Titanium Acetylacetone in Printed Layer of Polyethylene Film
WANG Yini, LIN Qinbao, LI Zhong, ZHONG Huaining, PAN Jingjing
2019, 40(18):  329-334.  doi:10.7506/spkx1002-6630-20180727-320
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A gas chromatography mass spectrometry (GC-MS) method and a liquid chromatography-mass spectrometry (LC-MS) method were established and optimized for detecting titanium acetylacetone (TAA). The existing form of TAA standard was identified using the proposed methods. The acetylacetone (AA) and titanium contents in TAA standard, gloss oil, ink, and printed materials were detected using high performance liquid chromatography (HPLC) and inductively coupled plasma optical emission spectrometry (ICP-OES), respectively. Ultraviolet-treated and heat-treated TAA samples were studied using Fourier transform infrared (FTIR) spectroscopy. Results indicated that AA and titanium irons existed in TAA standard solution and therefore needed to be detected separately. Titanium was detected in all samples, while AA was detected in gloss oil and TAA standard but not in ink and printed materials. After heat treatment or ultraviolet (UV) irradiation, oxidation reaction occurred in the carbon-carbon double bond of TAA, which means that this substance was changed.
Quantum Dot-Based Assay for Rapid Simultaneous Detection of Lead and Cadmium
LIU Beibei , CAO Lin
2019, 40(18):  335-341.  doi:10.7506/spkx1002-6630-20181031-372
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The objective of this study was to establish a quantum dot-based fluorescence immunochromatographic assay for the rapid simultaneous detection of lead and cadmium. Mouse anti-Cd2+-IEDTA and anti-Pb2+-IEDTA monoclonal antibodies were separately coupled with CdSe/CdS core-shell quantum dots embedded in polystyrene microspheres. The optimum reaction time of the dual test strip was 5 min. Pb2+ concentrations of 1–500 ng/mL, and Cd2+ concentrations of 1–400 ng/mL were detectable using the proposed method with coefficients of variation of less than 10%. Moreover, there was no cross-reactivity with other metal ions. The results of this assay were correlated well with those of inductively coupled plasma-mass spectrometry (ICP-MS) for commercial meat samples. This dual fluorescence immunochromatographic assay provided an applicable method for the rapid and simultaneous quantitative detection of lead and cadmium in meat.