Table of Content

01 July 2020, Volume 43 Issue 4

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Basic Research

Screening and Fermentation Characteristics of Antimicrobial Lactic Acid Bacteria Isolated from Kefir Grains

SUN Min, SUN Yue, LI Bo, MEI Jun

2020, 43(4):  1-6.  DOI: 10.15922/j.cnki.jdst.2020.04.001

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Escherichia coli ATCC25922 and Staphylococcus aureus ATCC25923 were used as test strains for screening of antimicrobial lactic acid bacteria from kefir grains. The fermentation supernatant of the selected isolate was processed into a freeze-dried powder. When used at a concentration greater than 6.250 mg/mL, the unpurified antimicrobial peptides had a strong bacteriostatic effect. The strain was identified as Lactobacillus casei by 16S rDNA gene sequencing. Raw whole milk was fermented by inoculating this strain at 2, 3 or 4 g/100 mL, and stored at 4 ℃ for 30 days. The pH and syneresis of fermented milk decreased with increasing inoculum size, whereas the titratable acidity, hardness, viscosity and water-holding capacity increased. The fermented milks with inoculum amounts of 3 and 4 g/100 mL did not significantly differ in sensory evaluation scores, both higher than that inoculated at 2 g/100 mL.

Variations in the Metabolism of Lactose and Galactose in Leuconstoc mesenteroides Strains

AN Dongni, ZHANG Lan, ZHANG Chunxue, TAN Dongmei, WU Yi, LIU Xiaoming, ZHAO Jianxin, ZHANG Hao, CHEN Wei

2020, 43(4):  7-12.  DOI: 10.15922/j.cnki.jdst.2020.04.002

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The growth, acid production and changes in viable cell count of 8 strains of Leuconstoc mesenteroides were measured in chemically defined medium (CDM) with different carbon sources or skim milk. The results showed that there were significant differences in the growth of these strains in CDM with lactose or galactose as the single carbon source. Strains LM1, LM2, LM4 and LM8 grew well in CDM with lactose as the single carbon source. Strains LM2, LM3, LM5 and LM8 had stronger vitality in CDM with galactose as the single carbon source, but their growth was weaker than that in the presence of lactose. In skim milk, the viable cell count of all experimental strains increased obviously in the early fermentation stage. After 8 h, their growth entered the stable phase, and the pH value at the end of fermentation was above 6.0. While the differences in genes related to lactose and galactose metabolism were preliminarily compared among the strains in this study, the correlation between genes and phenotypes needs to be further analyzed based on lactose hydrolase activity and lactose and galactose residues.

Processing Technology

Optimization of Formulation and Processing Conditions of Milk Drink Added with Whole Oat Kernels

YU Peng

2020, 43(4):  13-17.  DOI: 10.15922/j.cnki.jdst.2020.04.003

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The formulation and processing conditions of milk drink added with whole oat kernels were optimized for improved stability. The centrifugal sedimentation rate, viscosity and sensory evaluation score were considered as response variables. The optimal combination of stabilizers obtained was 0.04% gellan gum, 0.020% carrageenan, 0.020% sodium carboxymethylcellulose, and 0.20% microcrystalline cellulose. By using single factor experiments followed by orthogonal array design, the optimal processing conditions that provided the best stability as well as good taste were determined as follows: bathing temperature 50 ℃, hydration time 40 min, homogenization pressure 30 MPa, and filling temperature 15 ℃.

Analysis & Detection

Comparative Analysis of Fatty Acid Contents between Ultra-High Temperature Sterilized Milk and Reconstituted Milk Based on 1H Nuclear Magnetic Resonance Spectroscopy

SU Meicheng, JIA Man, ZHANG Xia, TAN Dongfei, ZHANG Qingyang, YIN Zenghao, WANG Shaolei, CHEN Gang

2020, 43(4):  18-22.  DOI: 10.15922/j.cnki.jdst.2020.04.004

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A comparative analysis of fatty acid contents between ultra-high temperature (UHT) milk and reconstituted milk was carried out using 1H nuclear magnetic resonance (1H NMR) spectroscopy. The results showed that the relative contents of linolenic acid, linoleic acid, oleic acid and saturated fatty acid in UHT milk and reconstituted milk were (0.98 ± 0.11)% and (0.90 ± 0.04)%, (1.15 ± 0.36)% and (1.11 ± 0.36)%, (27.30 ± 0.56)% and (26.78 ± 0.78)%, and (43.26 ± 1.56)% and (43.81 ± 2.34)%, respectively. Orthogonal partial least squares discriminant (OPLS-DA) analysis and independent sample t test were performed on the 1H NMR spectrum peaks and fatty acid contents of the two milks. It was found that the relative content of linolenic acid was significantly different (P < 0.05) between the two milks. Nutritional assessment showed that UHT milk was more suitable than reconstituted milk for people with hyperlipidemia and/or high cholesterol, while the nutritional value of other fatty acids was similar between both milks.

Determination of 19 β-Agonist Residues in Milk by Ultra-High Performance Liquid Chromatography Tandem Mass Spectrometry

GUAN Xuenong, ZHANG Min, SU Yuncong, WANG Yao, LI Fei, LI Xingjia, DU Liwei, ZHANG Yaoguang, CHAI Yanbing

2020, 43(4):  23-28.  DOI: 10.15922/j.cnki.jdst.2020.04.005

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This study established a method for the simultaneous detection of 19 β-agonist veterinary drug residues in milk samples. The samples were extracted with acidified acetonitrile solution, and the phospholipids were removed by using an Oasis PRiME HLB solid-phase extraction cartridge. The analytes were detected by ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Under optimized pretreatment and instrumental conditions, all analytes showed a good linear relationship in the concentration range of 0 to 10 ng/mL (R2 ≥ 0.995). The average recovery rates for milk samples spiked at levels of 0.2 to 1.0 μg/kg were between 70% and 110%, and the precision relative standard deviation (RSD) was less than 15%. The method had the advantages of simple and fast pretreatment, and high sensitivity and stability, and therefore could be used for the rapid detection of β-agonist veterinary drug residues in milk.

Reviews

Recent Progress in Understanding Bifidobacterium and Related Products in Alleviating Symptoms of Inflammatory Bowel Disease

SUN Qingshen, LUO Qinwen, XU Yanling

2020, 43(4):  29-33.  DOI: 10.15922/j.cnki.jdst.2020.04.006

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Bifidobacterium has the function of regulating intestinal flora and treating functional gastrointestinal diseases. It is one of the probiotics widely used to improve the human intestinal tract. Inflammatory bowel disease (IBD) is a chronic recurrent inflammatory disease that is accompanied by intestinal mucosal ulcers and cell death, and is prone to relapse. In recent years, there have been documents mentioning the probiotic effect of Bifidobacteria in enteritis treatment. This review outlines the alleviating effects of Bifidobacterium, related products and metabolites on IBD, which may open up a new research direction for the application of Bifidobacterium in the medical field.

Recent Advances in the Development of Methods for the Production of Lactulose

XU Zheng, ZHANG Qian, LI Kewen, XU Hong

2020, 43(4):  34-40.  DOI: 10.15922/j.cnki.jdst.2020.04.007

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Lactulose, also known as isomerized lactose, is a reducing disaccharide made from the dairy industry by-product lactose. Its concentrate is an important over-the-counter (OTC) drug that has a significant therapeutic effect on acute or chronic constipation and hepatic encephalopathy. The methods that have been developed to produce lactulose include the chemical method, β-galactosidase method and epimerase method. In recent years, the epimerase method has aroused extensive attention due to the high conversion rate it yields, which makes it a promising candidate for lactulose preparation although currently there exist some bottlenecks like the high proportion of epilactose as a by-product and the rather low enzyme activity. This article reviews the history and current status of research on the methods for lactulose production, in the hope of providing reference for basic theoretical research and industrialization in this field.

Recent Progress in Spray Drying of Lactic Acid Bacteria

WANG Ruixue, E Jingjing, YAO Caiqing, ZHANG Qiaoling, SUN Ruiyin, HE Zongbai, MA Rongze, CHEN Zichao, WANG Junguo

2020, 43(4):  41-46.  DOI: 10.15922/j.cnki.jdst.2020.04.008

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Lactic acid bacteria (LAB) are an important group of microorganisms used in the fermented food industry. Lactic acid and special flavor substances produced by the metabolism of LAB can impart fermented foods with unique qualities, and LAB have been widely used in the food industry, health care and clinical medicine. Therefore, the preparation and storage of LAB starter cultures are crucial. As the traditional method for producing dried agents, freeze-drying technology has the disadvantages of high cost, long time consumption and high energy consumption. In contrast, spray drying has the advantages of low cost, high efficiency and rapidity, and continuous production. It is a potential alternative to freeze-drying for the production of LAB powder. However, hot air generated during spray drying kills LAB, resulting in a low survival rate after drying. This paper reviews the current status of research on different spray drying process parameters, and it highlights the external and internal factors that may affect the quality and efficacy of spray-dried LAB starter cultures.

A Review of Recent Research on Milk Globule Size

HUANG Qixue, XING Zhiyang, ZHANG Menglu, ZHU Heshui, HAN Liqiang

2020, 43(4):  47-51.  DOI: 10.15922/j.cnki.jdst.2020.04.009

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Milk fat is secreted mainly in the form of fat globules (MFG) from the mammary glands of female mammals into the milk. The MFG particle size ranges from 0.2 to 15.0 μm. MFG sizes can affect the health of newborns and the physical and chemical properties of dairy products. As the size of MFG is determined by intracellular lipid droplets during the secretion of mammary epithelial cells, the regulation factors of lipid droplet size include intracellular triglyceride (TG) level and enzymes involved in the synthesis and hydrolysis of TG, enzyme, membrane phospholipid, and lipid droplet fusion, etc. This review mainly describes the synthesis and structure of MFG, the regulation of MFG particle size and its impact on human nutrition, dairy processing and lipid droplet size fusion, which will provide reference for the application of milk fat globule size.

Legal Application and Perfection of Food Safety Administrative Detention

LUO Jie

2020, 43(4):  52-56.  DOI: 10.15922/j.cnki.jdst.2020.04.010

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To normalize the newly established administrative detention system for the revised Food safety Law, starting with the concept and characteristics of the administrative detention system for food safety regulation, this paper analyzes the implementation situation and flaws of the existing administrative detention procedure by comparing with other forms of detention, and it puts forward some ideas and suggestions regarding the legislation and procedural normalization of administrative detention in food safety regulation. If serious violations of the Food Safety Law do not constitute a crime according to the types of administrative detention and penalty specified in the Legal Liability section of the law, the personal freedom of people involved in the violations will be restrained for a short period of time by the public security authority. In order to effectively implement the new legal requirements and maintain a good order of food safety, it is necessary to construct perfect and detailed procedural norms.