Table of Content

01 May 2021, Volume 44 Issue 3

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Basic Research

Protein Composition and Digestion Characteristics of Goats' Milk

CAI Junna, ZHANG Fuxin, LIU Yufang, XU Jinghui, ZHANG Yiting, WU Amin

2021, 44(3):  1-5.  DOI: 10.15922/j.cnki.jdst.2021.03.001

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The protein composition and digestion characteristics of goats’ milk were studied using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and in vitro simulated digestion. The results showed that goats’ milk proteins mainly included casein (αS1-casein, αS2-casein, β-casein and κ-casein, accounting for 23.10%, 30.39%, 38.09% and 8.42% of the total casein, respectively) and whey protein (α-lactalbumin, β-lactoglobulin, lactoferrin, serum albumin and immunoglobulin, accounting for 24.59%, 57.50%, 4.35%, 8.69% and 4.88% of the total whey protein, respectively). Casein was mainly digested in the intestinal juice, and the digestibility reached more than 99.00% after 120 min in the gastric juice, while it only took 2 min to reach more than 99.00% digestibility in the intestinal juice. The digestibility of lactoferrin, serum albumin and immunoglobulin in the gastric juice and intestinal juice was significantly higher than that of α-lactalbumin and β-lactoglobulin (P < 0.05), and α-lactalbumin and β-lactoglobulin were not easy to digest in the gastric and intestinal juice. The digestibility of α-lactalbumin and β-lactoglobulin was 67.53% and 50.82% in the gastric juice at 120 min, and 58.16% and 64.04% in the intestinal juice at 30 min, respectively. Gastrointestinal juice digestion also showed that casein in goats’ milk was more digestible than whey protein in goats’ milk.

Comparative Study on Secondary Structure and Function of Whey Protein in Bovine Milk and Donkey Milk

LIU Aicheng, LI Mohan, ZHANG Zhenghan, ZHANG Xiumin, LIU Yiming, CHEN Jiali, Rayhnigul, ZHENG Yan, YUE Xiqing

2021, 44(3):  6-11.  DOI: 10.15922/j.cnki.jdst.2021.03.002

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The secondary structure of whey proteins in donkey and bovine milk were investigated by Fourier transform infrared spectroscopy (FTIR), and comparative functional evaluation was carried out by gene ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Results showed that there were differences in the secondary structure of whey proteins between donkey and bovine milk. As the lactation period proceeded, the secondary structure content of whey proteins in both milks changed. Whey proteins in donkey colostrum and milk were involved in more biological functions and metabolic pathways compared with those in bovine colostrum and milk, especially in donkey milk, which could thus be more beneficial to the development and utilization of infant formula milk powder.

Processing Technology

Effect of Inonotus obliquus Polysaccharides on the Quality of Yak Yogurt

XU Yingrui, WU Shifang, YANG Xiaoli, XUE Yuantai, ZHU Yanli, ZHANG Weibing, ZHAO Jun, WEN Pengcheng

2021, 44(3):  12-18.  DOI: 10.15922/j.cnki.jdst.2021.03.003

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The impact of adding polysaccharides extracted from liquid-cultured mycelia of Inonotus obliquus into yak yogurt on its sensory evaluation score and titratable acidity was investigated to determine the optimal addition amount of the polysaccharides. The process parameters for producing yak yogurt with added Inonotus obliquus polysaccharides were optimized, and the quality of the yogurt prepared under optimized conditions was evaluated and compared with that of yogurt without added Inonotus obliquus polysaccharides as a control. The results showed that addition of 0.4% Inonotus obliquus polysaccharides to yak yogurt led to the highest sensory score together with a moderate acidity. Using orthogonal array design, the optimal process conditions were determined as follows: ratio of Streptococcus thermophilus G2 to Lactobacillus paracasei L9, 1:1; fermentation time, 14 h; temperature, 38 ℃; and sucrose concentration, 8 g/100 mL. Compared with the control, the as-prepared yogurt increased the number of viable lactic acid bacteria, titratable acidity and water-holding capacity by 34.1%, 11.0% and 16.8% respectively, and the pH value decreased accordingly. Addition of Inonotus obliquus polysaccharides into yak yogurt improved its firmness and viscosity as well as flavor.

Analysis & Detection

Preparation and Characterization of Angiotensin Converting Enzyme Inhibitory Peptide from Sheep Casein

ZHANG Yan, GE Wupeng, SONG Yuxuan, XIE Yuxia, TANG Haixia, WANG Haiyan, WANG Shuangshuang

2021, 44(3):  19-23.  DOI: 10.15922/j.cnki.jdst.2021.03.004

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Bioactive peptides were prepared from sheep casein by neutral protease hydrolysis. The effect of hydrolysis time on the degree of hydrolysis and angiotensin converting enzyme (ACE) inhibitory activity of hydrolsates was investigated. The peptides were analyzed and identified by liquid chromatography-mass spectrometry (LC-MS) to select the ones with potential ACE inhibitory activity. The results showed that the highest degree of hydrolysis of 9.65% as well as a percentage of ACE inhibition of 84.55% was attained after 300 min, and the concentration of the peptide YYQQRP required for 50% ACE inhibition was 5–10 μmol/L. The sequence analysis of the peptides was performed by ultra-high pressure liquid chromatography-time of flight mass spectrometry (UPLC-TOF-MS). YYQQRP was identified as a new peptide with potential ACE inhibitory activity by comparison with the protein database. It was hypothesized that the structure of YYQQRP might be similar to that of the substrate and could reduce the catalytic activity of ACE by binding to the active site of ACE.

Enzymatic Preparation and Activity Evaluation of Angiotensin Converting Enzyme Inhibitory Peptide from Xinjiang Bactrian Camel Milk Casein

LIU Chen, WANG Xueqing, DOU Zhihua, WANG Jun, LI Rongrong, XU Zhaoyu, YANG Jie

2021, 44(3):  24-30.  DOI: 10.15922/j.cnki.jdst.2021.03.005

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The casein of the milk of bactrian camels in Xinjiang was hydrolyzed with pepsin and/or trypsin, and the angiotensin converting enzyme (ACE) inhibitory activity of the resulting hydrolysates was determined by measuring the production of hippuric acid (HA) by reversed-phase high performance liquid chromatography (RP-HPLC) using an external standard method. The competitive relationship between the casein hydrolysates and captopril was investigated by using the Michaelis-Menten equation. The ACE inhibitory activity of the retenates obtained after ultrafiltration of the hydrolysates through membranes with molecular mass cutoff of 50, 10 and 3 kDa was determined. The results showed that the degree of hydrolysis was 3.7% after 4 h hydrolysis with trypsin compared to 16.58% with pepsin. The percentage of ACE inhibition by the 2 h hydrolysate with trysin was 74.67% as opposed to 72.33% with pepsin. When the casein was hydrolyzed sequentially with pepsin for 2 h followed by trypsin for 4 h, the degree of hydrolysis increased in a linear manner with hydrolysis time. The percentage of ACE inhibition by the hydrolysate within 2 h reached 66.27%, which did not increase with hydrolysis time. Trypsin may act on the bioactive peptides, thus reducing the enzyme activity. At increasing substrate concentration, the hydrolysate could not counteract the ACE inhibitory effect of the polypeptides, which was characteristics of non-competitive inhibitors. The inhibitory constant Ki of the polypeptides was 0.25 mg/mL. The ACE inhibitory activity of the 3–10 kDa retenate was the highest, and the peptides LLVVYPWTR and VLPVPQQMVPYPQR were found to be structurally similar to the known ACE inhibitory peptides.

Reviews

Advances in Understanding the Functional Activities of the Milk of Non-Bovine Mammals

FAN Xiaoxue, WEI Haitao, GAO Xingming, CHEN Pinghua, WANG Cunfang, JIANG Hua

2021, 44(3):  31-36.  DOI: 10.15922/j.cnki.jdst.2021.03.006

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Compared with cow’s milk, the milks of minor dairy animal species are know to be richer in nutrients and have a variety of bioactivities such as antibacterial, anticancer activity and antifatigue activity. However, consumers have little knowledge about the nutritional value of the milks of minor species and their production volume, market share and consumption are all low. Current studies regarding the milks of minor dairy species primarily concentrate on nutrient composition and single functional activities but often neglect the overall activity of all functional components. Systematic studies on the functional components, physiological effects and mechanisms of action of the milks of minor dairy species are lacking. In this paper, recent progress in studying the functional activities of donkey milk, buffalo milk, camel milk and goat milk is reviewed, and an outlook on future trends is given. This review hopes to provide a scientific basis for future research and development of high-quality, health dairy products from minor dairy species.

Present Status and Future Trends of Cheese Industry in China

QIN Bozhi, SUN Wancheng

2021, 44(3):  37-42.  DOI: 10.15922/j.cnki.jdst.2021.03.007

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In recent years, consumers have shown a rising demand for a healthy and nutritious diet, and cheese has become a new favorite of Chinese consumers because of its good nutritional and health-promoting characteristics. In 2005, the sales and import volume of cheese in China increased by 27.08% and 27.4% year-on-year compared with those in 2016, respectively. China’s cheese market size has maintained an upward trend. At present, the production of cheese in China is mainly concentrated in Xinjiang, Tibet and other ethnic minority areas, where different ethnic groups use sheep milk, yak milk or buffalo milk to produce cheese according to their own living habits and regional characteristics. However, the production of these ethnic cheeses have not been standardized and industrialized, resulting in high production cost. In addition, the quality is highly variable and the taste is generally poor. Therefore, improvements should be made according to the market demands.

Review of Research on Nutritional Components and Functional Characteristics of Yak Milk

GAO Yu, WANG Jiaqi, DAI Zhiyong, PAN Lina, PENG Xiaoyu, MA Ying, GU Ruixia

2021, 44(3):  43-49.  DOI: 10.15922/j.cnki.jdst.2021.03.008

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The yak is a rare animal that predominantly lives on the Qinghai-Tibet Plateau. The production volume of yak milk is low, but it is rich in nutrients, containing higher contents of protein, fat and lactose compared with Holstein milk, as well as abundant amounts of other nutrients. Furthermore, it is found that yak milk has anti-hypoxia, anti-fatigue and antioxidant activities, among other, which may be attributed to the unique habitat of yaks. In this article, the lactation performance of yaks, as well as the nutritional components and functional characteristics of yak milk is reviewed, with a view to providing a theoretical reference for the development and utilization of yak milk.

A Review on the Major Nutritional Components in Milks of Humans and Domesticated Mammals

QIU Ji, MENG Yang, ZHAO Yi, SI Chenyu, LI Chun

2021, 44(3):  50-54.  DOI: 10.15922/j.cnki.jdst.2021.03.009

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Milk is a specialized substance secreted by the mammalian mammary gland and is the material basis for the survival and development of mammals. Understanding the similarities and differences in the milk composition of humans and domesticated mammals and gaining deeper insights into the characteristics of different mammalian milks will help in the targeted development and promotion of different mammalian dairy products. In this review, we summarize the main nutritional components in different mammalian milks and compare the composition and content of protein, fat and lactose, finding that there are large differences in these milk components. Besides, we review the functions and applications of different mammalian dairy products according to the conclusions drawn from the comparison.

Overview of Research and Development of Buffalo Milk in Guangxi, China

ZHANG Xiyu, LI Quanyang

2021, 44(3):  55-59.  DOI: 10.15922/j.cnki.jdst.2021.03.010

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Buffalo milk is nutritious, richer in protein, fat, dry matter and minerals than cow’s milk. Buffalo milk has a high economic value, so there are currently many commercially available buffalo milk products on the Chinese market. As the climate and environment in Guangxi, China are suitable for the growth and reproduction of buffaloes. Herein is reviewed the history of the introduction of buffalo into Guangxi, the milk quality of improved hybrids of buffalo and the compositional characteristics of buffalo milk. Meanwhile, this paper compares the differences in the nutritional composition of buffalo and bovine milk, and presents an overview of the development of buffalo milk products.