Table of Content

01 December 2022, Volume 45 Issue 6

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Basic Research

Isolation, Identification and Heat Resistance of Bacillus from Raw Milk

HOU Xiaxia, WANG Yunxia, LIU Lijun, LI Cuizhi, LÜ Zhiyong

2022, 45(6):  1-6.  DOI: 10.7506/rykxyjs1671-5187-20220913-057

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A small amount of bacterial spores with strong tolerance still exist in raw milk after sterilization and can multiply under certain conditions, causing a serious impact on product quality and consumer health. In this study, raw milk samples containing Bacillus were collected to isolate aerobic Bacillus and thermophilic aerobic Bacillus. The isolates obtained were identified based on their morphological, physiological, biochemical and molecular biological characteristics, and the heat resistance of the isolated thermophilic aerobic Bacillus was studied. Results showed that 10 strains of Bacillus were isolated from the milk samples, of which three were thermophilic aerobic Bacillus and seven were aerobic Bacillus. Among them, Bacillus coagulans and Bacillus clausii could tolerate heat treatment at 115 ℃ for 15 min. All Bacillus in raw milk could be killed by heat treatment at 121 ℃ for 20 min which decreased the number of spores by four orders of magnitude. The dominant Bacillus species in raw milk were Bacillus subtilis, Bacillus cereus, Bacillus pumilus, Bacillus licheniformis, Bacillus circulans, Bacillus gelatini, Bacillus amyloliquefaciens, Bacillus coagulans, and Bacillus clausii. Bacillus coagulans and Bacillus clausii had stronger heat resistance and could tolerate heat treatment at 115 ℃ for 15 min.

Monosaccharide Composition and Antioxidant Activity of Exopolysaccharides of Lactobacillus plantarum

ZHU Yuting, WEN Xin, XIANG Jun, GUO Jincai, JIN Huihua, LI Can, CHEN Tongqiang

2022, 45(6):  7-11.  DOI: 10.7506/rykxyjs1671-5187-20220510-030

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The monosaccharide composition and antioxidant activity of extracellular polysaccharides from Lactobacillus plantarum were analyzed. Crude polysaccharides were obtained from the fermentation broth of Lactobacillus plantarum by water extraction and alcohol precipitation and were fractionated into two fractions (DZ-1 and DZ-2) by DEAE-52 cellulose column chromatography. The monosaccharide components of DZ-1 and DZ-2 were analyzed by gas chromatography, and their antioxidant activity was tested using 1,1-diphenyl-2-picrylhy drazyl (DPPH), hydroxyl radical, and 2,2’-diazo bis-3-ethyl benzothiazoline-6-sulfonic acid (ABTS) cation radical scavenging assays. DZ-1 was a homopolysaccharide composed of only glucose units, while DZ-2 was a heteropolysaccharide composed of arabinose and galactose with a content ratio of 46.03:53.89. Both DZ-1 and DZ-2 had the ability to scavenge DPPH, hydroxyl and ABTS cation radicals.

Processing Technology

Effect of Coconut Milk Content on the Quality of Coconut Yogurt

LI Wei

2022, 45(6):  12-17.  DOI: 10.7506/rykxyjs1671-5187-20220930-062

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Coconut milk contains a lot of fat, so addition of coconut milk will have a great influence on the texture, flavor and stability of fermented products. The effects of different amounts of coconut milk (20%–60%) on the quality of coconut yogurt were studied in terms of its fermentation rate, texture properties, rheological properties and shelf life stability. The results showed that the fermentation rate was faster when more than 40% coconut milk was added. The centrifugation test and the Lumisizer stability analysis showed that coconut yogurt with more than 40% coconut milk had a good stability without syneresis or precipitation. Yogurt with 40%–50% coconut milk had moderate hardness, slightly pasty and smooth mouthfeel. After stirring, the viscosity of the product decreased, making it convenient to be drunk. Therefore, yogurt with 40%–50% coconut milk (containing 12%–15% fat) had good quality.

Analysis & Detection

Determination of Ethyl Carbamate in Fermented Milk by Gas Chromatography-Mass Spectrometry

CHEN Tongqiang, LIANG Feng, WU Haizhi, XIANG Jun, SONG Yang, JING Huihua, YUAN Liejiang, LI Can, LI Kailong

2022, 45(6):  18-21.  DOI: 10.7506/rykxyjs1671-5187-20220510-029

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An analytical method for the determination of ethyl carbamate in fermented milk was established by gas chromatography-mass spectrometry (GC-MS). Sample pretreatment conditions were optimized. The analytical figures of merit of the proposed method including linear relationship, precision, spiked recovery, detection limit and quantitation limit were evaluated. Ethyl carbamate was quantitated using an external standard. The linearity of this method was good in the range of 0–200 ng/mL (r > 0.999), and the detection limit and quantitation limit of ethyl carbamate were 2.0 and 5.0 μg/kg, respectively. The recovery of the added ethyl carbamate ranged from 89.9% to 105.2%, with relative standard deviation (RSD) less than 10%. This method is sensitive, accurate and repeatable, and can meet the requirements for the determination of ethyl carbamate in fermented milk.

Determination of Nonylphenol in Milk Powder by High Performance Liquid Chromatography-Tandem Mass Spectrometry

BAI Yanmei, ZHANG Lijia, WANG Yang, LIU Lijun, XIE Ruilong, DUAN Jianhua, LI Cuizhi

2022, 45(6):  22-26.  DOI: 10.7506/rykxyjs1671-5187-20220804-048

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A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was established for the determination of nonylphenol in milk powder. Samples were extracted with acetonitrile and cleaned up with a solid phase extraction column. The analytes were separated on a Waters ACQUITY UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 μm), detected by electrospray ionization in the multiple reaction monitoring (MRM) mode, and quantified by an external standard method. The results showed that good linearity was observed in the concentration range of 1–200 ng/mL (R2 > 0.99). The limit of detection（LOD, RS/N = 3）was 2 μg/kg and the limit of quantitation (LOQ, RS/N = 10）was 5 μg/kg. The recoveries at different spiked levels were between 81.10% and 107.39% with relative standard deviation (RSD) ranging from 1.97% to 9.73%. This method has the advantages of accurate results, small background interference, simple operation, good stability and short pretreatment time, and is useful for the detection of nonylphenol in milk powder.

Development of Quality Control Samples for Qualitative Analysis of Listeria monocytogenes by Time-of-Flight Mass Spectrometry

ZHANG Yalun, YANG Fan, ZHANG Tao, ZHANG Rui, LI Xian, ZHOU Wei, ZHANG Yan

2022, 45(6):  27-32.  DOI: 10.7506/rykxyjs1671-5187-20220920-061

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A quality control sample for the qualitative analysis of Listeria monocytogenes was developed by vacuum freezing drying technology, and the homogeneity and stability of the quality control sample were systematically analyzed. By optimizing the type of lyophilized matrix, the optimal conditions for the development of quality control samples were obtained. The homogeneity and stability of the developed quality control sample were verified by counting the number of cells as well as using matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The quality control sample was white in color, spherical in shape and uniform in size. The results of cell counting for uniformity validation showed F = 0.567, which was less than the critical value, indicating good uniformity. In the transportation stability test, the quality control sample remained stable at 37 and 25 ℃. In the storage stability test, the resurrection rate of the quality control sample was 101.5% after 28 days of storage at ?20 ℃, and 99.6% after 28 days of storage at 4 ℃, indicating that the sample has good uniformity and stability, and can be used as a positive quality control sample for the detection and quality control of Listeria monocytogenes.

Uncertainty Evaluation for the Determination of 1-Oleic Acid-2-Palmitic Acid-3-Linoleic Acid Triglyceride Content in Milk Powder by Gas Chromatography

LIU Chunxia, DUAN Guoxia, LIU Lijun, LI Cuizhi, LÜ Zhiyong, CHEN Jing, GONG Huili, WU Lunwei

2022, 45(6):  33-36.  DOI: 10.7506/rykxyjs1671-5187-20220815-049

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The measurement uncertainty was estimated for the determination of 1-oleic-2-palmitic-3-linoleic acid triglyceride (OPL) content in milk powder by gas chromatography (GC). According to the Measurement and Expression of Uncertainty in Measurement (JJF 1059.1—2012) and the Guidance on Quantifying Uncertainty in Chemical Analysis (CNAS-GL 006: 2019), a mathematical model was established to analyze the sources of measurement uncertainty. The major factors affecting the measurement uncertainty were evaluated. Results showed that the average OPL content of six milk powder samples was measured to be 1.172 g/100 g. The relative expanded uncertainty (urel) was 0.023 6 with a coverage probability of approximately 95%. The standard uncertainty arising from sample preparation was the main source of uncertainty.

Reviews

Advances in Detection of Steroid Hormones in Dairy Products

XING Qianqian, LIU Zhenmin, YOU Chunping,

2022, 45(6):  37-41.  DOI: 10.7506/rykxyjs1671-5187-20220919-058

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Steroid hormones, small lipophilic substances, are often illegally used as growth-promoting agents in the animal husbandry and breeding industry. Residual hormones in dairy products can enter the human body through the food chain causing a series of health hazards. Residues of steroid hormones in dairy products have become the focus of worldwide concern about veterinary drug residues. Regulations have been issued to limit the content of steroid hormones in dairy products in China. This paper discusses the structure, classification and functions of steroid hormones, and summarizes the maximum residue limits, detection methods, contents and health risks of steroid hormones in dairy products, aiming to provide a reference for further research of steroid hormones in dairy products.

Progress in Research on the Nutritional Components of Donkey Milk

LI Mohan, LIU Aicheng, ZHAO Shanshan, ZHAO Huiwen, ZHANG Juan, SONG Wanying, YUE Xiqing, ZHENG Yan

2022, 45(6):  42-49.  DOI: 10.7506/rykxyjs1671-5187-20220819-051

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Donkey milk is considered as an ideal substitute for human milk because of its high contents of whey protein, lactose, lysozyme, unsaturated fatty acids and vitamin C, and low contents of casein and fat. Additionally, donkey milk has various physiological functions, including hypoallergenic, bacteriostatic and anticancer activity. Thus, this review introduces readers to the nutritional composition of donkey milk, including proteins, amino acids, fats, minerals, vitamins., and compares it with that of human milk, bovine milk, buffalo milk, goat milk, and camel milk, in order to provide useful information for the comprehensive processing and utilization of donkey milk.

Advances in Sterilization Techniques for Dairy Products

HONG Qing, LIU Zhenmin

2022, 45(6):  50-54.  DOI: 10.7506/rykxyjs1671-5187-20211222-012

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Milk and dairy products are foods with high nutritional values. Sterilization techniques that can ensure the safety, long shelf life and stable nutritional value of milk and dairy products are of great interest to researchers. In this paper, we review recent progress in research on sterilization techniques in the dairy industry, illustrates the mechanism of thermal and non-thermal sterilization techniques, and discuss the effect of different sterilization techniques such as pasteurization, ultra-high temperature instantaneous sterilization, ultra-high pressure, ultrasonic and pulsed electric field on the microbial load, nutritional bioactives, flavor compounds, texture and chemical reactions of milk and dairy products. We hope that this review can provide useful information for the development and application highly bioactive dairy products.