Table of Content

30 December 2015, Volume 38 Issue 6

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Basic Research

Quantitative Polymerase Chain Reaction Analysis of Predominant Species of Lactic Acid Bacteria from Traditional Fermented Dairy Products from Ordos in Inner Mongolia

ZHANG Donglei, CHEN Hongxia, DE Liangliang, LIU Wenjun, SUN Tiansong

2015, 38(6):  1-5.  DOI: 10.15922/j.cnki.jdst.2015.06.001

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In this study, real-time quantitative polymerase chain reaction (q-PCR) was used to compare and quantitatively analyze the predominant species Lactobacillus helveticus, Leuconostoc mesenteroides and Lactococcus lactis subsp. lactis isolated from 28 samples of traditional fermented dairy products（including 7 samples of fermented sheep milk, 8 samples of fermented goat milk and 13 samples of fermented cow milk）from Ordos in Inner Mongolia. The results showed that the order of the number of three predominant species in fermented goat milk and fermented cow milk was Leu.mesenteroides＞L.helveticus＞Lac. lactis subsp. lactis whereas that of fermented sheep milk was L.helveticus > Leu.mesenteroides > Lac. lactis subsp. lactis.

Processing Technology

Optimization of Fermentation Conditions for the Production of a Fermented Dairy Beverage Fortified with Dendrobium officinale Polysaccharide

LI Xiaoyan, CHEN Gang, JIAN Suping

2015, 38(6):  6-9.  DOI: 10.15922/j.cnki.jdst.2015.06.002

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The fermentation conditions for producing a fermented dairy beverage from skim milk added with the polysaccharide extract from Dendrobium officinale were optimized in the present study. Beverage with the best flavor was obtained when skim milk added with 50% Dendrobium officinale polysaccharide and sugar at levels of 10% and 7% (by mass), respectively was fermented at 42 ℃ for 6 h after inoculation with the starter culture (Lactobacillus bulgaricus:Streptococcus thermophilus = 1: 1) at a level of 0.10%.

Optimization of Process Conditions for the Production of Fermented Milk Beverage with Added Juice of "Milpa Alta" Cactus Stems (Opuntia ficus-indica Mill.)

YAN Ying, CHEN Gang, JIAN Suping

2015, 38(6):  10-14.  DOI: 10.15922/j.cnki.jdst.2015.06.003

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Response surface methodology based on Box-Behnken design was employed to optimize the fermentation conditions of juice of “Milpa Alta” cactus stems (Opuntia ficus-indica Mill.) added with skimmed milk powder for producing fermented milk beverage. The optimal fermentation parameters were determined as follows: the concentrations of cactus stem juice, sucrose and starter culture (Lactobacillus bulgaricus:Streptococcus thermophilus = 1:1) were 15.3%, 9.4% and 0.16%, respectively; the fermentation was proceeded at 42 ℃ for 6.8 h. The acidity value of fermented beverage produced under these conditions was 93.2 °T, and it had a distinctive flavor and abundant nutrients.

Package & Storage

Charaterization of Aluminum-Free Composite Sealing Films for Yoghourt Cups

ZHANG Yu, LIU Xianghong, ZHANG Weirong

2015, 38(6):  15-18.  DOI: 10.15922/j.cnki.jdst.2015.06.004

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Three kinds of aluminum-free composite sealing film: F1, polyethylene/low density polyethylene/ethylenevinyl acetate copolymer (PE/LDPE/EVA); F2, polyethylene terephthalate (PET)/PE/EVA; and F3, PET/cast polypropylene (CPP)/ EVA were selected to package yoghurt in polystyrene (PS) cups. Comparison of material characteristics and packaging performance of composite films and the storage life of packaged yoghurt was carried out with respect to fim oxygen permeability, opening force and puncture resistance, and yoghurt sensory evaluation, acidity and storage life. The storage life of yoghurts packaged with F1, F2 and F3 was tested at (30.0 ± 1.5), (25.0 ± 1.5) and (4.0 ± 1.5) ℃, respectively. The results showed that oxygen permeability of F3 was the lowest, 46.602 cm3/(m2·24 h·0.1 MPa), among three kinds of films at the same temperature and humidity, and it had the best oxygen barrier property, while oxygen barrier property of F1 was the lowest. The storage temperature of (4.0 ± 1.5）℃ had less significant impact on the sensory evaluation, acidity or storage life of yoghurt than (30.0 ± 1.5) and (25.0 ± 1.5) ℃ and gave the longest storage life of 7 to 8 days, yielding an acidity higher than 87 °T at the end of the storage life. Under the same storage conditiuons (time and temperature), yoghurt packaged with F3 had the lowest acidity and exhibited the loweest growth rate of acidity and the best sensory evaluation results. In terms of opening force, only F2 and F3 met the packaing requirements for yoghurt. F1 had very high puncture resistance while F3 was the easiest to puncture with an ease level of 85%. Together, the above fingdings demonstrate that PET/CPP/EVA film is the most suitable sealing film for packaging yoghurt in cups, which achieves the longest storage life of 8 days at (4.0 ± 1.5) ℃ and meets the packaging requirements for yoghurt.

Analysis & Detection

Detection of Thiocyanatein in Dairy Products by High-Performance Liquid Chromatography

ZHAO Zhen, L(U) Haiyan, LIU Lijun, WAN Peng, LI Cuizhi, SHAO Jianbo

2015, 38(6):  19-21.  DOI: 10.15922/j.cnki.jdst.2015.06.005

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A method for detecting thiocyanate in dairy products by high-performance liquid chromatography (HPLC) is described. The proteins in the samples were precipitated by the addition of acetonitrile, then the filtrate was separated on a strong anion exchange (SAX) column using a mobile phase made up of a mixture of sodium dihydrogen phosphate solution and methanol. The target compound was detected with a UV detector at 218 nm. The results showed that the calibration curve displayed a good linear relationship in the range of 0.2–100 mg/kg. The recovery rate of thiocyanate was 98.5%– 113.0%.The method is simple with good accuracy and stability for detecting thiocyanate in dairy products.

Reviews

A Review on the Anti-Phage Mechanism of Lactic Acid Bacteria

XI Yu, WANG Zhengyu, ZHANG Heping, CHEN Xia

2015, 38(6):  22-26.  DOI: 10.15922/j.cnki.jdst.2015.06.006

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The contamination of phage is considered as one of the major risks for food fermentation. It may cause the fermentation to slow down or even fail, and then cause huge economic loss. So, understanding the classification, morphology, and infection mechanism of phages and discussing the anti-phage mechanisms of lactic acid bacteria (LAB) are very important to the application of LAB and the production of related products. The aim of this paper is to describe the anti-phage mechanism of LAB, which may provide a certain theoretical support to the selection of anti-phage strains and prevention of phage contamination.

Advances in the Application of Rumen-Protected Choline in Periparturient Dairy Cows

LI Shengkai, LIU Yuqi, YE Tianmei, ZHANG Qin, YANG Yingbai

2015, 38(6):  27-30.  DOI: 10.15922/j.cnki.jdst.2015.06.007

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The periparturient period is one of the most important period in the process of dairy farming, implicating the transition from the dry period to lactation, during which cows may undergo physiological stress that results in a decrease of dry matter intake (DMI) and negative energy balance (NEB) during early lactation. Besides, the early-lactating cows have poorer milk production and reproductive performance, which are often accompanied by metabolic diseases such as fatty liver, ketosis, mastitis, etc. Choline contributes favorably to milk production and reproductive performance, participates in fat metabolism, reduces the incidence of fatty liver and strengthens immunity in dairy cows. Therefore, dietary rumen-protected choline (RPC) can improve metabolic functions and increase the supply of choline in the small intestine, consequently improving milk yield and milk composition, relieving fatty liver and reducing perinatal diseases. This paper summarizes the effects of feeding RPC to periparturient dairy cows on DMI, milk production performance, milk composition and health condition, aims to provide the theoretical basis for feeding of periparturient dairy cows.

Progress in Research on Staphylococcus aureus Exotoxins

CHEN Wanyi, YOU Chunping, LIU Zhenmin

2015, 38(6):  31-37.  DOI: 10.15922/j.cnki.jdst.2015.06.008

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Staphylococcus aureus (S. aureus) is a Gram positive bacterium that is carried by about one third of the general population and is responsible for common and serious diseases. These diseases include food poisoning and toxic shock syndrome, which are caused by exotoxins produced by S. aureus. Among the more than 20 staphylococcal enterotoxins (SEs), SEA and SEB are the best characterized and are also regarded as superantigens because of their ability to bind to class II MHC molecules on antigen presenting cells and stimulate large populations of T cells that share variable regions on the β chain of the T cell receptor. This article provides a detailed elaboration of the pathogenicity and underlying mechanism of SEs as well as the methods used to detect the exotoxins, which has a guiding significance for clinical treatment and food safety monitoring. Owing to the occurrence of multiple resistant strains of S. aureus, the health harm of S. aureus in food has become more and more serious, so we have to minimize the microbial load of this bacterium in food, and prevent cross contamination in food.