Table of Content

04 December 2024, Volume 47 Issue 6

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Basic Research

Identification and Antioxidant Activity of Bioactive Peptides Derived from Zhongdian Yak Milk Casein

HE Jinze, CUI Haoran, LI Yufang, ZHENG Wentao, PENG Qingya, LI Li, HUANG Aixiang

2024, 47(6):  1-7.  DOI: 10.7506/rykxyjs1671-5187-20240814-075

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The enzymatic hydrolysate of Zhongdian yak milk casein was fractionated by ultrafiltration into two fractions: molecular mass > 3 kDa and < 3 kDa. The cell proliferation activity and antioxidant activity of the two fractions were determined. The bioactive peptides derived from yak milk casein were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), bioinformatics and molecular docking. The results showed that the proliferation rate of RAW264.7 cells was above 80% in the presence of either the molecular mass > 3 kDa or < 3 kDa fraction. Both fractions had the ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) cation radical. The cell proliferation and free radical scavenging activity of the molecular mass < 3 kDa fraction were better than those of the > 3 kDa fraction. A total of 895 peptides were identified from the molecular mass < 3 kDa fraction, of which 96 were known bioactive peptides, mainly antioxidant peptides (39.6%) and angiotensin-converting enzyme inhibitory peptides (30.2%), indicating that Zhongdian yak casein is an important source of bioactive peptides. Based on their activity and hydrophobicity, antioxidant peptides GYF and RPW were selected from the predicted 20 potential antioxidant peptides. The results of molecular docking showed that the binding energies of GYF and RPW with ABTS cation and DPPH radicals were all negative, indicating that they had binding potential and exerted antioxidant activity mainly by forming hydrogen bonds and hydrophobic interactions.

Correlation between Physicochemical Indexes and Acidity of Sheep Milk in Different Lactation Periods

SHEN Yufei, ZHANG Yan, TONG Fenfen, WANG Shuangshuang, HU Qisheng, XU Liqing, SONG Yuxuan, GE Wupeng

2024, 47(6):  8-14.  DOI: 10.7506/rykxyjs1671-5187-20240708-057

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This study explored changes in the acidity of sheep milk across different lactation periods and the key factors affecting the acidity of sheep milk. The pH, titratable acidity, fat content, protein content and composition, total sugar content, mineral content, density, lactose content, fatty acid composition and content were analyzed, and the correlation between physicochemical indexes and acidity was investigated. The results indicated that the acidity of raw sheep milk was closely related to lactation stages. The highest acidity was observed in the early lactation period, which then gradually decreased as lactation progressed. Acidity changes were primarily associated with the protein content, fat content, fatty acid composition, total sugar content, lactose content, mineral content, and density of the milk. Among these, the protein content showed the strongest correlation with acidity changes, whereas fatty acid content had a relatively low correlation with acidity variations.

Processing Technology

Effect of Polysaccharide Extract from Potentilla anserina L. on the Quality of Yak Yoghurt

ZHOU Wenjia, ZHAI Jianing, DU Peng, LIU Libo, LI Aili

2024, 47(6):  15-22.  DOI: 10.7506/rykxyjs1671-5187-20240809-074

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The optimal parameters for ultrasonic-assisted enzymatic extraction of polysaccharides from Potentilla anserina L. using a mixture of cellulase, pectinase and papain (2:1:0.5) were determined as follows: enzyme dosage 49 U/g, ultrasonic time 100 min and pH 4.4. Under these conditions, the maximum yield of polysaccharide extract from Potentilla anserina L. (PAPE) of (6.89 ± 0.08)% was obtained. Furthermore, the effect of PAPE on yak yoghurt fermentation was investigated. The results showed that PAPE could significantly enhance the viable count and acid-producing capacity of Streptococcus thermophilus CICC 6038, Lactobacillus bulgaricus CICC 20247 and Lactobacillus fermentum HY01 in a dose-dependent manner. Yoghurt added with PAPE at 2 g/100 mL concentration had a hardness of (163.0 ± 9.9) g, a viscosity of (?182.9 ± 1.6) g·s, a consistency of (69.7 ± 1.7) g·s, a cohesiveness of (410.0 ± 6.0) g and it had a good taste, with a sensory score of 7.78; its antioxidant capacity in terms of scavenging capacity against hydroxyl, superoxide anion and 2,2’-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) cation radicals increased significantly compared with the control group. This study provides new ideas for improving the quality and added value of yak yogurt.

Effect of Sodium Chloride Addition on Free Amino Acid Contents in Hard Yak Cheese during Maturation

SONG Xuemei, SONG Guoshun, LIANG Qi, ZHANG Yan

2024, 47(6):  23-30.  DOI: 10.7506/rykxyjs1671-5187-20240814-076

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Liquid chromatography-mass spectrometry was employed to determine the change of free amino acid contents in hard yak cheeses with different salt levels during 6 months of ripening. The results showed that a total of 23 free amino acids were detected, the major ones being aspartic acid, glutamic acid, isoleucine, leucine, phenylalanine, threonine and cysteine, together representing 94% to 95% of the total free amino acid content. The content of each free amino acid showed an increasing trend between months 1 and 6. In the late stage of maturation, the contents of threonine, asparaginate, aspartic acid, valine, proline and phenylalanine increased with increasing salt addition, the contents of alanine, histidine, arginine and tyrosine decreased, and the contents of leucine, isoleucine, serine, glycine and tryptophan first increased and then decreased. The contents of of glutamic acid, leucine, isoleucine, aromatic amino acid, cysteine, glycine and serine were significantly higher in long-ripened cheese with 1.3% salt addition than in those with higher salt contents. This study provides theoretical support for the development of low-salt hard yak cheese.

Analysis & Detection

Determination of 3-Monochloropropane-1,2-Diol Esters and Glycidyl Esters in Infant Formula Milk Powder by Gas Chromatography-Mass Spectrometry

WANG Shengjie, LIANG Lin

2024, 47(6):  31-36.  DOI: 10.7506/rykxyjs1671-5187-20240606-042

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An analytical method for the determination of 3-monochloropropane-1,2-diol esters (3-MCPDEs) and glycidyl esters (GEs) in infant formula milk powder was established using gas chromatography-mass spectrometry (GC-MS). Based on optimized lipid extraction and derivatization conditions, the method was evaluated for spiked recovery, linear relationship, precision, limit of detection (LOD) and limit of quantification (LOQ). Quantification was carried out using the internal standard method. The proposed method showed good linearity in the range of 5–500 ng (r > 0.999), with an LOD of 0.006 mg/kg and an LOQ of 0.015 mg/kg. The recovery rates at three spiked concentration levels of 10, 100 and 500 ng ranged from 95.6% to 100.9%, with relative standard deviations (RSDs) less than 5.03%. The results of GC-MS and gas chromatography-tandem mass spectrometry (GC-MS/MS) for 3-MCPDEs and GEs in several batches of infant formula samples did not significantly differ. In addition, compared with GC-MS/MS, the GC-MS method was simpler and easier to operate with lower cost and could be promoted in different levels of laboratories. Therefore, this method is suitable for determining the content of 3-MCPDEs and GEs in infant formula milk powder.

Performance Evaluation of Colloidal Gold Immunochromatographic Test Strips for Identification of Bovine-, Ovine- and Caprine-Derived Components in Dairy Products

XU Zhipeng, PAN Qiuli, XIAO Jing, ZHANG Shuang, SONG Jiasheng, WANG Jun

2024, 47(6):  37-42.  DOI: 10.7506/rykxyjs1671-5187-20240814-077

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According to the opinions of the state administration for market supervision on standardizing the use of rapid food detection, the performance of commercial colloidal gold immunochromatographic test strips for rapid in situ identification of bovine-, ovine- and caprine-derived ingredients in dairy products were evaluated in terms of application scope, detection limit, cross-reaction rate, sensitivity, false negative rate, false positive rate and coincidence rate with the results of the reference method. The results showed that the application scope of the test strip for bovine-derived ingredients was raw milk, and the detection limit was 5% (V/V); the application scope of the test strip for ovine- and caprine-derived ingredients was raw ovine and caprine milk, and the detection limit was 0.3% (V/V). Both test strips had no cross-reaction with enrofloxacin, sulfamethazine, dexamethasone, tetracycline or aflatoxin M1. The sensitivity, false positive rate and false negative rate of the test strips were 100%, 0% and 0%, respectively. The coincidence rate with the results of the reference method was high. In conclusion, the colloidal gold immunochromatographic test strips have high accuracy, and can be used for rapid in situ screening of adulterated milk.

Rapid Determination of 54 Pesticide Residues in Fresh Milk by QuEChERS Pretreatment and Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry

YANG Qi, JIAO Xinzhe, MENG Hu, FANG Zhongfang, ZHANG Yaowu, ZHAO Lili, ZHANG Qianting

2024, 47(6):  43-50.  DOI: 10.7506/rykxyjs1671-5187-20240816-080

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A high-throughput method for the screening and quantitation of 54 pesticide residues in fresh milk was developed by quick, easy, cheap, effective, rugged, safe (QuEChERS) extraction followed by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The study optimized the composition of mobile phase, extraction solvent, extraction solvent volume, extraction salt packet formulation, and purification packet formulation. Furthermore, the matrix effect was evaluated and methodological evaluation were carried out. The results showed that the linear range was 5.0–100.0 μg/L for all 54 pesticides, with correlation coefficients (r) higher than 0.999. The limit of quantification (LOQ) was 10.0 μg/kg for all target analytes, and the average recoveries from spiked samples were 67.78%–119.38%, with relative standard deviations (RSDs) (n = 6) lower than 9%. The method is simple, rapid, sensitive, and accurate. It can meet the requirements of the simultaneous detection and analysis of 54 pesticide residues in fresh milk.

Reviews

Recent Advances in the Composition, Preparation and Functional Properties of Goat’s Milk Oligosaccharides

WANG Yuqi, YANG Liu, ZHANG Tong, WANG Pengyue, LIU Libo, ZHANG Guofang, LI Chun, CUI Xiuxiu

2024, 47(6):  51-59.  DOI: 10.7506/rykxyjs1671-5187-20240729-072

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Goat’s milk contains a rich variety of oligosaccharides with various physiological functions, and its content and structure are close to those of human milk oligosaccharides. Goat’s milk can be regarded as a natural alternative source of human milk oligosaccharides with potential applications in the food field. This paper briefly introduces the composition, content and structure of oligosaccharides in goat’s milk, analyzes the factors affecting the composition and content of oligosaccharides in goat’s milk, and focuses on the comparison of various preparation methods such as membrane separation, chromatography and biosynthesis. In addition, the pre-treatment methods for and the characteristics of different techniques for the detection of goat’s milk oligosaccharides are summarized, and finally, the probiotic functions of goat’s milk oligosaccharides as well as the prospects and challenges for their application in the future research are discussed. Finally, the probiotic functions of goat’s milk oligosaccharides and future prospects and challenges for their research and application are discussed.

Research Progress on the Composition and Bioactivity of Oligosaccharides in Minor Species Milks

YAN Siyu, SU Xinran, LIN Dawei, YUE Xiqing, GUAN Boyuan, CAO Xueyan

2024, 47(6):  60-69.  DOI: 10.7506/rykxyjs1671-5187-20240806-073

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China is blessed with minor species milk resources. Minor species milks from different sources have their own distinctive characteristics in terms of nutrient composition and content as well as functional activity. Oligosaccharides, as important bioactive ingredients in milk, have many significant biological functions. With the aim of providing theoretical reference for the development and utilization of oligosaccharides in minor species milk, this paper reviews recent progress in the research on the types, structures and contents of oligosaccharides in goat milk, donkey milk, buffalo milk, camel milk and horse milk, and it also summarizes the bioactive functions of milk oligosaccharides such as probiotic, antibacterial and anti-inflammatory properties as well as promoting brain development.

Research Progress on the Isolation, Identification and Biological Characteristics of Milk-Derived Extracellular Vesicles from Minor Dairy Animals

FU Shangchen, ZHANG Yan, TONG Fenfen, LIU Mengjia, DING Yi, HU Qisheng, GE Wupeng

2024, 47(6):  70-76.  DOI: 10.7506/rykxyjs1671-5187-20240713-061

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Milk-derived extracellular vesicles (MEVs), originating from mammary epithelial cells, are nanoscale double-layered membrane vesicles transporting bioactive molecules like proteins, nucleic acids, and lipids, being crucial for intercellular communication and immune regulation. Although milk from minor animal species is not commonly found in the market due to its lower production, it possesses unique nutritional value and potential health benefits and is therefore worth exploring. This review covers the isolation and identification techniques, morphological characteristics, composition and biological characteristics of MEVs from goat, camel, yak, donkey, buffalo, porcine and horse milk. It points out the challenges and future directions in studying MEVs from minor dairy species, aiming to provide a theoretical foundation and scientific guidance for further research and application of MEVs so as to foster the development of the minor species milk industry.