Table of Content

01 July 2017, Volume 40 Issue 4

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Basic Research

Selective Enumeration of Lactobacillus plantarum and Leuconostoc mesenteroides in Co-Culture

HAN Jin, FENG Huafeng, WU Zhengjun

2017, 40(4):  1-5.  DOI: 10.15922/j.cnki.jdst.2017.04.001

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Based on their distinctive colonial morphology when co-cultured in MRS agar containing different carbon sources, two selective enumeration methods, namely difference method and chromatic aberration method, were established for Lactobacillus plantarum ST-Ⅲ and Leuconostoc mesenteroides BD1710 in co-culture. The reliability of these two methods could meet the requirements for selective counting of individual strains. The difference method was more suitable for research with high precision requirement owing to its higher average detection rate (97.2％ vs 95.4％ for ST-Ⅲ, 96.4％ vs 94.0％ for BD1710) compared with the chromatic aberration method, whilst the chromatic aberration method was superior in operability and cost and could provide factories with a fast way to determine viable bacterial counts in related products.

Effect of Chitooligosaccharide Addition on Fermentation and Sensory Properties of Yogurt

JI Xiaomin, GE Jiahui, HAN Shuting, WANG Tingting, WANG Zongji, LI jinguo, MAO Xueying

2017, 40(4):  6-10.  DOI: 10.15922/j.cnki.jdst.2017.04.002

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The effect of chitooligoosaccharide on the fermentation and sensory properties of yogurt was investigated. The fermentation progress was assessed by measuring pH value, titratable acidity, lactic acid bacteria counts and rheological properties. The sensory quality was evaluated by flavor, taste, texture, and color. Results showed that the addition of 50 mg/mL chitooligosaccharide did not cause any significant difference in titratable acidity compared with the control group (P > 0.05). When chitooligosaccharide addition was lower than 100 mg/mL, there was no significant difference (P > 0.05) in pH value or sensory quality scores in comparison with the control group. Additionally, at the same fermentation time, lower titratable acidity and lactic acid bacteria counts and higher pH value were observed with increasing addition of chitooligosaccharide (P < 0.05). Chitooligosaccharide addition in the range of 0–100 mg/mL had no detrimental effect on the fermentation characterstics or quality of yoghurt and improved the flavor. Hence chitooligosaacharide can be used in the production of yogurt.

Analysis & Detection

Isolation, Identification and Antibiotic Resistance of Staphylococcus warneri from Yak Milk

WEI Chao, MAO Jianfei, DAI Xiaohang, GUO Lingan

2017, 40(4):  11-14.  DOI: 10.15922/j.cnki.jdst.2017.04.003

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Another bacterium, identified as Staphylococcus warneri by matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS), was obtained during the isolation of Staphylococcus aureus from yak milk by using Baird-Parker (BP) medium. The biochemical properties and antibiotic susceptibility of the Staphylococcus warneri strain were examined, and antibacterial experiments were carried out. Also, this study determined antibiotic residues in yak milk. The results showed that the biochemical properties of the obtained strain were consistent with those of Staphylococcus warneri. The strain was highly susceptible to most antibiotics except neomorphine, which had no inhibitory effect on it. Besides, all the yak milk samples were found to be negative for antibiotic residues. Although the opportunistic pathogen Staphylococcus warneri was detected in yak milk, it was sensitive to most antibiotics due to the pure environment of the milk source.

Evaluation of Bisphenols Residues in Infant Foods by High Performance Liquid Chromatography-Tandem Mass Spectrometry Using Stable Isotope Internal Standard

GENG Ning, LU Jian

2017, 40(4):  15-19.  DOI: 10.15922/j.cnki.jdst.2017.04.004

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An isotope internal standard coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was established for the simultaneous determination of four bisphenols (bisphenols A, B, F and S) in infant foods. Samples were extracted with a mixture of ethyl acetate and cyclohexane and detected by HPLC-MS/MS in the multi-reaction monitoring mode. Under the optimized conditions, the four bisphenols showed good linearity in the range of 5.0–200.0 μg/L with R2 larger than 0.9970. The detection limit of the method was 1.5 μg/kg. The mean recoveries of negative samples spiked at three concentration levels (5.0, 10.0 and 50.0 μg/L) were in the range of 84.0％–106.5％with relative standard deviations (RSDs, n = 6) ranging from 1.6％ to 6.4％. The proposed method had the advantages of high sensitivity, good purification efficiency and quantitative accuracy and it was suitable for the detection of bisphenols in infant foods.

Package & Storage

Influence of Dry Granulation on the Shelf Life and Quality of Milk Tablets

HUO Xiaoyan, WANG Zhenyu, LIU Baojun, LI Wei, LIU Biao

2017, 40(4):  20-25.  DOI: 10.15922/j.cnki.jdst.2017.04.005

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In order to ascertain the influence of dry granulation on the shelf-life and quality of milk tablets, the rate of lipid oxidation in milk tablets prepared with and without dry granulation was measured and the changes in physicochemical and sensory qualities were compared under accelerated oxidation and normal temperature conditions. The results showed that dry granulation slightly accelerated lipid oxidation and significantly increased surface lipid content compared with the directly prepared sample. During accelerated and normal storage, the changes in all other parameters were similar without significances between the two samples. Furthermore, dry granulation had no evident effect on the shelf life of milk tablets.

Effects of Secondary Pasteurization on the Quality of Long-Term Shelf-Stable Yoghurt

SHEN Ling

2017, 40(4):  26-29.  DOI: 10.15922/j.cnki.jdst.2017.04.006

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The viscosity, susceptibility to syneresis (STS) and sensory quality of long-term shelf-stable yoghurt subjected to secondary pasteurization were measured. Moreover, mold and yeast counts and total aerobic plate count were determined at regular intervals during storage at 25 and 37 ℃. Results indicated that viscosity decreased and STS increased with increasing temperature of pasteurization. The yoghurt produced by secondary pasteurization at 60 ℃ for 30 s was most liked, and the yoghurt produced by secondary pasteurization at 90 ℃ for 30 s was least liked by consumers. The residual molds and yeasts were inactivated by secondary pasteurization under the conditions selected in this study. Furthermore, total aerobic plate count declined with increasing temperature of pasteurization. At higher storage temperature the yoghurt was more susceptible to microbial contamination. Overall, we concluded that secondary pasteurization at 70 ℃ for 30 s was optimal.

Reviews

Advances in Research on Structure-Function Relationship of Exopolysaccharides from Lactic Acid Bacteria

JIANG Chenbo, HONG Qing, HANG Feng

2017, 40(4):  30-35.  DOI: 10.15922/j.cnki.jdst.2017.04.007

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Exopolysaccharides (EPS) produced by lactic acid bacteria (LAB), with a variety of physiological functions, play a significant role in the improvement of physical properties of fermented dairy products. The structures and functions of EPS synthesized by different LAB strains are highly diverse. Therefore, this review summarizes the progress that has been made in recent years in studying the structure of EPS from LAB and its effect on physical properties and health-beneficial functions of fermented dairy products, in order to lay a theoretical foundation for developing new fermented dairy products with stable quality and desired health-beneficial functions.

A Review on the Application of Magnetic Solid Phase Extraction for Detection of Antibiotic Residues in Milk

LI Longfei

2017, 40(4):  36-40.  DOI: 10.15922/j.cnki.jdst.2017.04.008

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The sample pretreatment is a critical step for the analysis of samples and has a direct impact on the analytical results. As a novel sample pretreatment technology, magnetic solid phase extraction (MSPE) is of great interest in the field of analytical testing because of its simple operation, low cost, time saving and low environmental pollution. The presence of antibiotic residues in milk is a long-standing problem, and antibiotic abuse can lead to allergies, drug resistance, secondary infection and other side effects on human health. In recent years, studies that introduce MSPE as a sample pretreatment method into antibiotic residue detection in milk have been published in large numbers. In this paper, the source and harm of antibiotic residues in milk are reviewed as well as the applications of MSPE in the detection of antibiotic residues in milk that have been reported over the past 5 years.