Table of Content

01 May 2024, Volume 47 Issue 3

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Basic Research

Metabolomics Analysis of Fermentation Characteristics of Lactococcus lactis subsp. lactis in Soymilk

HE Hai, YANG Yu, ZHOU Sisi, LIU Xiaoming

2024, 47(3):  1-8.  DOI: 10.7506/rykxyjs1671-5187-20240422-026

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Most current studies on Lactococcus lactis subsp. lactis are focused on its application in bovine milk, but few studies have been conducted on its application in soymilk. The fermentation characteristics of Lactococcus lactis subsp. lactis in soymilk were analyzed by metabolomics and sensory evaluation in the present study. The results showed that Lactococcus lactis subsp. lactis strains DYNDL21-2, DYNDL1-2 and FJNDD18M8 showed good sucrose metabolism capacity, growth and acid production ability. The abundance of hexanal and various heterocyclic compounds such as furan in fermented soymilk was significantly down-regulated by DYNDL21-2 and FJNDD18M8, which effectively reduced the intensity of beany odor. Fermentation with FJNDD18M8 significantly up-regulated the abundance of acetaldehyde, acetoin and 2,3-butanedione in soymilk, enhancing the milky aroma and creamy flavor and improving the overall flavor. In conclusion, Lactococcus lactis subsp. lactis has excellent fermentation characteristics and strong metabolic capacity during soymilk fermentation, but there are some differences among strains.

Analysis & Detection

Development of Quantitative Loop-Mediated Isothermal Amplification for Rapid Detection of Streptococcus thermophilus and Lactobacillus bulgaricus in Fermented Milk

ZHOU Shuaikang, HU Lianxia, WANG Mengyang, LI Miao, LU Han, WANG Shijie

2024, 47(3):  9-15.  DOI: 10.7506/rykxyjs1671-5187-20240505-033

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In this study, a rapid and quantitative method for the detection of viable bacterial counts of Streptococcus thermophilus and Lactobacillus bulgaricus in fermented milk was established using propidium monoazide (PMA) combined with quantitative loop-mediated isothermal amplification (PMA-qLAMP). The PMA treatment conditions for S. thermophilus and L. bulgaricus were optimized. A linear relationship was fitted between the logarithm of bacterial concentration and cycle threshold (Ct) value. The limit of quantification for S. thermophilus and L. bulgaricus was 7.2 × 103 and 5.6 × 104 CFU/g, respectively. The PMA-qLAMP method was applied to measure viable bacterial counts in commercial fermented milk, demonstrating good sensitivity and practicality.

Determination of 25 β-Receptor Agonist Residues in Milk and Dairy Products by PRiME MCX Solid Phase Extraction Column Combined with Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry

FAN Lixin, YANG Liqiong, REN Xiaowei, YANG Cengceng, MENG Zhijuan, FAN Sufang

2024, 47(3):  16-25.  DOI: 10.7506/rykxyjs1671-5187-20240606-041

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A method for the determination of 25 β-receptor agonist residues in milk and dairy products was established based on ultra-high performance liquid chromatography-tandem mass spectrometry. Samples were enzymatically hydrolyzed in 0.2 mol/L ammonium acetate solution at pH 5.2 for 16 h. After the removal of fat and protein through glass fiber filter paper, the filtrate was purified by solid phase extraction (SPE) using a PRiME MCX solid phase extraction column, and separated on a Waters BEH C18 column (100 mm × 2.1 mm, 1.7 μm) by gradient elution using a mobile phase composed of acetonitrile and 0.1% formic acid in water. Mass spectrometry was performed using an electrospray ionization source (ESI) in the positive ion mode with multiple reaction monitoring (MRM), and quantitative determination was performed using the internal standard method. The proposed method showed good linearity for all analytes in the concentration range of 0.2–50.0 ng/mL with coefficients of determination (R2) greater than 0.996; the recoveries ranged from 80.3% to 106.2% with relative standard deviations (RSDs) of 0.6%–8.5% (n = 6). The limits of detection (LOD) were 0.05–0.10 μg/kg, and the limits of quantification (LOQ) were 0.10–0.20 μg/kg. This method is simple, efficient and suitable for the determination of the 25 β-receptor agonist residues in milk and dairy products.

Electronic Nose Based on Gas Chromatography for Analysis of Flavor Changes of Milk with Different Fat Contents during Storage

ZHANG Shan, LI Wen, ZHANG Yuting, WEI Xuetong, SUN Ying, XUE Lu, ZHAO Pei, NIU Tianjiao

2024, 47(3):  26-34.  DOI: 10.7506/rykxyjs1671-5187-20240422-028

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During storage, milk is prone to different degrees of oxidative degradation of fat with varying storage conditions, which changes the aroma components of milk. In this study, electronic nose based on gas chromatography (GC) and sensory evaluation were used to compare the changes in the composition of volatile flavor compounds and sensory properties of pasteurized whole milk, low-fat milk and skim milk (fat contents of 4, 1.4 and 0 g/100 mL) during storage at different temperatures. The results showed that all three milks maintained good flavor characteristics during storage at 4 ℃. The composition of flavor substances in whole milk was more complex, where 43 volatile compounds were identified, and no obvious stale flavor was perceived. The decreasing order of difficulty of fat oxidation was whole milk > low-fat milk > skim milk. Nonanal, a marker of lipid oxidation, was detected in both skim milk and low-fat milk. Methyl ketones derived from lipid oxidization such as 2-butanone, 2,3-butanedione, 2-hexanone, 2-heptanone and 2-undecanone were detected in skim milk during storage. The results of sensory evaluation were basically consistent with those of electronic nose. The sweetness and milky flavor of whole milk were more prominent, the flavor of low-fat milk was relatively bland, and skim milk tasted slightly bitter after 21 days of storage at 25 ℃. The findings of this study will provide a scientific basis for monitoring the flavor changes of milk products during storage and improving the quality of milk products.

Determination of Vitamin C in Formulas for Special Medical Purpose Intended for Infants by Liquid Chromatography

WU Xiuping, CHENG Baiyu, XU Xiaoqian, JIANG Ruiyu

2024, 47(3):  35-40.  DOI: 10.7506/rykxyjs1671-5187-20240521-036

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A liquid chromatography (LC) method for the determination of vitamin C in formulas for special medical purpose intended for infants was established and validated. The sample was reduced, purified using an HLB solid phase extraction (SPE) cartridge, filtered through a 0.45 μm filter, and analyzed by hydrophilic interaction liquid chromatography (HILIC). The calibration curve was found to be linear in the concentration range of 0–50 μg/mL with correlation coefficient over 0.999. The limit of quantitation (LOQ) was 3.0 mg/100 g. Recoveries of spiked samples ranged from 95.2% to 102.8% with relative standard deviation (RSD) between 1.22% and 3.62%. The method is characterized by simple operation, accurate results and good reproducibility and suitable to determine vitamin C in formulas for special medical purpose intended for infants.

Reviews

Present Situation and Challenges of Children’s Cheese Food in China: Cheese Nutrition and Children’s Health

HAO Xinyue, ZOU Junzhe, LIU Liang, REN Jing, LIN Kai, YI Huaxi, ZHANG Lanwei, GONG Pimin

2024, 47(3):  41-48.  DOI: 10.7506/rykxyjs1671-5187-20240606-040

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With the development of China, children’s cheese has garnered increasing attention in the dairy industry, which has become a new growth point of China’s dairy industry. However, children’s cheeses currently available on the market are uneven, which cannot be fortified completely according to children’s nutritional needs. Their tastes are similar and their selling points are the same, which causes the public’s sensory fatigue and also go against consumers’ pursuit of clean label. Thus, the development of the children’s cheese industry is facing new challenges. In this paper, from the perspectives of children’s health and cheese nutrition, we link the needs of children of different ages for nutrition, flavor and texture with the nutrition, flavor and texture of cheese. The present situation, challenges and possible development directions of children’s cheese food in China are summarized.

Recent Progress in Research on the Physicochemical Properties and Microbial Metabolism of Yogurt Fermented by Lactic Acid Bacteria

LIU Huiyao, PENG Fei

2024, 47(3):  49-60.  DOI: 10.7506/rykxyjs1671-5187-20240505-029

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Lactic acid bacteria, a group of microorganisms that can ferment sugars into lactic acid, are widely used in the production of yogurt products. Different lactic acid bacteria exhibit different fermentation characteristics, which not only alter the physicochemical properties of yogurt but also have a significant impact on its nutritional value. This paper reviews the relationship between yoghurt products and microbial metabolism with a special focus on the role and influence of microorganisms in yoghurt making. The production of yogurt relies on the fermentation of specific microorganisms, such as lactic acid bacteria, which not only convert lactose to lactic acid, change the pH and texture of yogurt, but also synthesize a range of bioactive substances, such as vitamins, thereby having a positive impact on the health of consumers. This paper summarizes recent advances in understanding the fermentation mechanism of yoghurt, revealing the contribution of microbial diversity to product characteristics. In addition, this paper also discusses the health benefits of microbial metabolites in yogurt, including improving intestinal health and enhancing immunity. It is hoped that this review will provide a scientific basis and technical guidance for the research and development of yogurt products.

Research Progress on Isolation, Preparation and Functional Characteristics of Postbiotics and Their Applications in Dairy Products

LI Yue, REN Dayong

2024, 47(3):  61-70.  DOI: 10.7506/rykxyjs1671-5187-20240415-023

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Probiotics have been extensively researched for their health advantages, but their poor stability and viability prevent them from being used in foods and medicine on a larger scale. Compared with probiotics, postbiotics have the advantages of higher safety and stability in its existing form, which avoids the limitation of probiotics. In 2021, the International Scientific Association for Probiotics and Prebiotics defined postbiotics as preparation of inanimate microorganisms and/or their components that confers a health benefit on the host including bacterial components and metabolites, such as cell-free supernatant, cell lysate, extracellular polysaccharide, peptidoglycan, short-chain fatty acids, and organic acids. Postbiotic components exhibit varying beneficial effects on the host, such as regulating immunity and lipid metabolism, anti-inflammatory, antioxidant, anti-tumor, and antibacterial activities, and on product processing as an antibacterial, stabilizing and emulsifying agent. This paper provides an overview of the methods for separating, preparing and identifying postbiotics. It also summarizes the potential functional characteristics of probiotics, their processing characteristics in dairy products and their potential application value. This review provides a theoretical basis for the application of postbiotics as good raw materials in the medical and food fields.

Research Progress on Functional Properties Changes and Application of Processed Milk β-Lactoglobulin

NIU Jiaojiao, QIU Yu, LI Xin, CHEN Hongbing

2024, 47(3):  71-79.  DOI: 10.7506/rykxyjs1671-5187-20240415-024

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Milk β-lactoglobulin, the major protein in whey protein, possesses a unique molecular structure that provides binding sites for many ligands, endowing it with versatile functional properties including gelation, emulsification, and foaming. Hence, it has a broad application prospect. This paper first introduces the molecular structure, ligand binding sites, gelation, emulsification, and foaming properties of β-lactoglobulin. Then, it discusses the effect of several main processing methods including heat treatment, high-pressure processing, pulsed electric field treatment, and ultraviolet radiation induction on the properties of β-lactoglobulin. Finally, it elucidates the application of β-lactoglobulin in food processing, nanomaterials and basic research, aiming to provide a theoretical and scientific reference for promoting the industrial application of β-lactoglobulin in the food industry and other related industries.

Advances in Techniques for Protease Detection in Milk and Milk Products

LIANG Jianying, TANG Shuo, LIU Lijun, HUANG Xiaoyan, YUE Hong, HU Wenhui, LI Cuizhi

2024, 47(3):  80-85.  DOI: 10.7506/rykxyjs1671-5187-20240326-010

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The proteases in cow’s milk have a great influence on the flavor and quality, especially on the shelf life of dairy products, but there is no uniform reference standard for the detection of protease activity in dairy products. This paper elaborates the sources, types and characteristics of protease in cow’s milk, and summarizes recent progress in the detection of the activity of different types of protease in cow’s milk, pointing out that the precise detection of protease activity in milk has great significance for dairy production and quality assurance.