Table of Content

01 January 2019, Volume 42 Issue 1

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Basic Research

Effects of Different Milk Protein Components on the Rennet Coagulation Properties of Bovine Milk

ZHAO Xiao, ZHAO Aimei, ZHENG Zhe, LUO Tianqi, YANG Zhennai

2019, 42(1):  1-7.  DOI: 10.15922/j.cnki.jdst.2019.01.001

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In this study, the relationship between milk clotting characteristics by rennet and different protein components was discussed. Addition of whey protein concentrate (WPC), κ-casein (κ-CN), β-lactoglobulin A (β-LgA) and β-lactoglobulin B (β-LgB) to skim milk could reduce the milk clotting time, increase the viscosity after coagulation and result in a more compact microstructure, while the formation of curds was inhibited by the addition of α-La, α-CN, β-CN and total CN and the microstructure of the formed curds was relatively loose. Dynamic light scattering method was applied to determine the particle size distribution of casein micelles during coagulation. The results showed that molecular radius distribution in casein solutions added with WPC, κ-CN, β-LgA and β-LgB changed quickly, indicating rapid aggregation of the protein molecules in solutions. Bidirectional electrophoresis and mass spectrometry identification of raw milk samples with significantly differential milk-clotting properties indicated that the differential protein components related to the rennet coagulation characteristics of bovine milk were mostly bioactive trace proteins affecting breast cell metabolism.

Effect of Test Conditions on the Determination of Textural Properties of Stirred Yoghurt

WU Weidu, ZHU Hui, OU Kai, LI Yanjun

2019, 42(1):  8-12.  DOI: 10.15922/j.cnki.jdst.2019.01.002

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In this paper, we investigated the effect of test conditions such as probe diameter, compression distance, trigger force, container volume, pre-test speed, test speed, post-test speed on the textural properties of stirred yoghurt, and we also evaluated the effect of pre-test speed, test speed, post-test speed on the firmness, elasticity and viscosity of yoghurt with an orthogonal experimental design L9(34). In addition, the textural properties, viscosity and elastic modulus of 8 kinds of popular commercial yogurt were in situ determined without destroying the original packaging. The results showed that all test conditions affected the textural properties of stirred yoghurt. The appropriate test conditions were as follows: 1 mm/s of pre-test speed and test speed, 10 mm/s of post-test speed, 30 mm of compression distance, 35 mm of probe diameter, 5 g of trigger force, and 100 mL of container volume. At the confidence level of α = 0.05, test speed had a significant effect on the firmness and elasticity, while post-test speed was a significant factor influencing the adhesive force. Moreover, there existed obvious differences in the textural properties of different kinds of yoghurt. Elastic modulus was correlated with firmness, consistency, adhesiveness, adhesive force and elasticity, and viscosity was correlated with firmness, consistency, adhesiveness and adhesive force.

Processing Technology

Response Surface Methodology for Optimization of Fermentation Conditions for α-Glucosidase Inhibitor Production by Paenibacillus polymyxa BD3736 from Skim Milk

FENG Huafeng

2019, 42(1):  13-18.  DOI: 10.15922/j.cnki.jdst.2019.01.003

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The aim of this study was the optimization of the fermentation conditions for the production of α-glucosidase inhibitors (AGIs) by Paenibacillus polymyxa BD3736 from skim milk. Using one-factor-at-a-time method, we investigated the effect of inoculum size, fermentation temperature, skim milk concentration and fermenation time on the activity of AGIs and and identified the main factors for optimization by response surface methodology with a three-factor and threelevel Box-Behnken design. The optimized fermentation conditions were determined as follows: fermentation temperature 31.5 ℃, inoculum amount 3.5% and 4 days of incubation time. The half maximal inhibitory concentration (IC50) of the fermentation supernatant obtained under these conditions against α-glucosidase was 30.5 mg/mL.

Analysis & Detection

Rehydration Process of Whole Milk Powder Investigated by Particle Size Analysis

JIA Hongxin, ZHOU Jiaying

2019, 42(1):  19-22.  DOI: 10.15922/j.cnki.jdst.2019.01.004

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The change in the particle size of whole milk powder during rehydration was studied by particle size analysis. This study also determined the effect of rehydration temperature (30, 40 and 50 ℃) and milk powder particle size on the rehydration process. Results showed that the rehydration of whole milk powder was affected by both temperature and its particle size. The rehydration time at 50 ℃ was 50% and less than 7.5% as compared to that at 40 ℃ and 30 ℃, respectively. For whole milk powder prepared using the same process, the larger the particle size, the shorter the rehydration time, and after rehydration under the same conditions whole milk powders with different particle size distributions exhibited different particle size distributions.

High Performance Liquid Chromatography Determination of Deoxynivalenol and Its Acetyl Derivatives in Dairy Products, Cereal Flour and Dairy Cow Feed

WU Lunwei, YUE Hong, CHEN Jing, LIU Chunxia, LIU Lijun

2019, 42(1):  23-26.  DOI: 10.15922/j.cnki.jdst.2019.01.005

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A method for the determination of deoxynivalenol (DON) and its derivatives 3-acetyl-deoxynivalenol (3-ADON) and 15-acetyl-deoxynivalenol (15-ADON) in dairy products, cereal flour and dairy cow feed was developed using high performance liquid chromatography (HPLC). Samples were extracted with ultrapure water, and the extract was cleaned up by immunoaffinity column chromatography and detected by HPLC with ultraviolet detection (HPLC-UVD). The limit of quantitation of the method was 100 μg/kg for all three analytes in dairy products, cereal flour and feed. Recoveries from these three sample matrices spiked at concentration levels ranging from 100 to 500 μg/kg were higher than 90% for DON and higher than 80% for 3-ADON and 15-ADON. This method proved to be simple, fast, sensitive, highly selective, and suitable for the simultaneous analysis of DON, 3-ADON and 15-ADON in dairy products, cereal flour and feed.

Reviews

Advances in Studies on Phage-Host Interaction of Streptococcus thermophilus

ZHAO Huiying, LI Yanjun, CHEN Su, OU Kai, WANG Jian, HE Guoqing

2019, 42(1):  27-32.  DOI: 10.15922/j.cnki.jdst.2019.01.006

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Streptococcus thermophilus phages pose a major threat to the production of many fermented dairy products. As new Streptococcus thermophilus phages have been continuously discovered and isolated during dairy fermentation, knowledge of the physiological characteristics and infection mechanism of Streptococcus thermophilus phages has gradually been improved. Understanding their biodiversity and determining their interaction with the host can provide a theoretical basis for the control of phages in the dairy industrial environment. This review summarizes the classification of Streptococcus thermophilus phages, the adsorption receptor and receptor binding protein of Streptococcus thermophiles and the molecular mechanisms of phage infection in order to provide useful information for the study and control of other Lactobacillus phages.

Functional Characteristics and Application in Infant Formula of Alpha-lactalbumin

CHEN Wenliang, SU Miya, JIA Hongxin, QI Xiaoyan

2019, 42(1):  33-38.  DOI: 10.15922/j.cnki.jdst.2019.01.007

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Alpha-lactalbumin (α-LA) is a major protein component of breast milk. Therefore, humanization of α-LA from mammalian milk should be an important part of the study aimed to develop infant formula simulating the major protein components in breast milk. The structure of α-LA is described in terms of amino acid composition and stereostructure in this article. Moreover, the functional characteristics of α-LA and its application in infant formula are also discussed, which is expected to provide useful information for researchers in this field.

Advances in Research and Application of Probiotic in Obese Animal Models

HONG Qing, LIU Zhenmin, LI Nan

2019, 42(1):  39-43.  DOI: 10.15922/j.cnki.jdst.2019.01.008

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Obesity has become one of the most prevalent diseases worldwide that seriously threatens human health. Obesity is closely related to variations in the gut microbiota. Probiotics have potential for obesity treatment as they play an important role in regulating the balance of intestinal flora and improving the immunity of the body. This paper reviews the current status of research on the mechanisms of action of probiotics in animal models of obesity induced by different factors so as to provide useful information for clinical trials and applications of probiotics.

Recent Progress in the Development of Blood Lipid-Regulating Functional Dairy Products

WU Shang, LIANG Xiaona, WU Shangyi, HAN Hongjiao, KONG Fanhua, YUE Xiqing, YANG Mei

2019, 42(1):  44-50.  DOI: 10.15922/j.cnki.jdst.2019.01.009

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Dairy products are an important part of the dietary structure of Chinese residents. A wide variety of dairy products are commercially available, which are rich in nutrients and contain high-quality protein, various trace elements and functional ingredients including such active ingredients that are beneficial for lipid metabolism as milk calcium, whey, polar lipids and conjugated linoleic acid. Dairy products have the potential to regulate blood lipids and reduce the risk of cardiovascular disease. In addition, dairy products are high-quality carriers of active ingredients, and the active ingredients in milk can synergize with those added to milk to regulate blood lipids or to protect them. For this reason, milk is often used as an ingredient of functional dairy products. Hyperlipidemia is recognized worldwide as one of the risk factors for cardiovascular and cerebrovascular diseases such as atherosclerosis, coronary heart disease and hypertension. Studies have shown that functional milk can aid in regulating blood lipids. This paper reviews the current status of studies on dairy products and lipid metabolism-related health problems, aiming to provide a theoretical basis for the research of functional dairy products.

Recent Progress in Understanding Flavor Formation in Cheese

LI Zhiguo, ZONG Xuexing, YAN Qingquan, WANG Le, LI Lingyu, LIU Hao, BIAN Yanfei

2019, 42(1):  51-54.  DOI: 10.15922/j.cnki.jdst.2019.01.010

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In order to provide a deep understanding of flavor formation in cheese, this paper reviews the formation and metabolism of flavor compounds in cheese with respect to proteolysis, lipolysis, and lactase and citric acid fermentation. The focus of this review is on protein breakdown into short-chain peptides and amino acids by natural enzymes, chymotrylase, starter cultures, secondary starter cultures and non-starter microorganisms, the formation of lactone and butyric acid as metabolites during the enzymatic hydrolysis of fatty acids, the conversion of lactose into lactic acid by lactic acid bacteria, and the conversion of the intermediate pyruvate into diacetic acid and 3-hydroxy-butanone, acetaldehyde or acetic acid. Conclusively, the flavor substances of cheese mainly include fatty acids, esters, aldehydes, alcohols, ketones, sulfides, phenols and ethers.