Table of Content

01 July 2023, Volume 46 Issue 4

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Basic Research

Effects of Heat Treatment Conditions on Physicochemical Properties and Functionality of Camel Whey Protein

CHEN Qi, ZHANG Xiurong, HE Jing, JI Rimutu

2023, 46(4):  1-9.  DOI: 10.7506/rykxyjs1671-5187-20230213-010

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Whey protein is an important component of milk, but heat treatment during sterilization has a certain impact on the structure and properties of whey protein. Therefore, this study investigated the effect of different heat treatments on the denaturation degree, physicochemical properties and functionality of camel whey protein, which was separated from camel milk heat-treated under different conditions, 65 ℃/30 min, 85 ℃/15 s, 125 ℃/4 s and 135 ℃/4 s, after milk fat and casein precipitation. The results showed that whey protein treated at 65 ℃ for 30 min had the highest turbidity (0.14), particle size (0.24 μm), zeta potential (?9.54 mV), solubility (24.57 mg/mL), and relative content of α-helix (31%) as well as the lowest relative contents of β-turn (13%) and random coil (19%); the water-holding capacity (WHC), foaming capacity and emulsifying capacity were significantly increased by the heat treatment, which indicated that 65 ℃/30 min treatment resulted in the smallest denaturation degree of whey protein and improvements in its functional properties such as emulsifying capacity, foaming capacity, WHC and oil-holding capacity (OHC) without significantly changing its physicochemical properties. With an increase in the heating temperature, the particle size of whey protein under 85 ℃/15 s treatment was increased to 0.32 μm, and the solubility was reduced to 22.34 mg/mL, but its functionality was improved compared with that of raw milk whey protein. Treatment at 125 ℃ for 4 s or 135 ℃for 4 s led to a large number of whey protein denaturation, destroyed the secondary structure, increased the particle size and turbidity, decreased the solubility, and worsened the functional properties.

Effect of Protease Treatment on Linear Allergenic Epitopes of Bovine Whey Proteins

WANG Zongzhou, CUI Chunlan, LI Qin, TIAN Qiying, ZHANG Lifang, SHAO Hu, LIANG Xiaona, YUE Xiqing

2023, 46(4):  10-15.  DOI: 10.7506/rykxyjs1671-5187-20230719-035

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In this study, the bioinformatics software DNAStar and Geneious and multiple reaction monitoring mass spectrometry (MRM-MS) were used to predict the linear epitope parameters, secondary structure content and epitope regions of bovine whey proteins. Meanwhile, relative quantification of linear allergenic epitopes was carried out. The results indicated that α-lactalbumin (α-LA) and β-lactoglobulin (β-LG) had 7 and 10 linear epitope regions, respectively. The secondary structure of α-LA and β-LG mainly consisted of α-helix, followed by β-turn, β-sheet and random curling, indicating that the structure of α-LA and β-LG made them more likely to become epitopes. Alkaline, protamex and flavourzyme treatment effectively reduced the linear allergenic epitopes of α-LA and β-LG by 50.0%–80.0%, with this effect being more pronounced for β-LG. The relative quantitation results showed that the content of 95.0% of linear epitope peptides was significantly reduced.

Analysis & Detection

Analysis of Reasons for Protein Coagulation in Ultra-High Temperature Milk at the End of Shelf-life

WANG Chuanbao, HE Xiong, LI Jiaxin, LIN Lin

2023, 46(4):  16-21.  DOI: 10.7506/rykxyjs1671-5187-20230630-033

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The protein content, pH, color, colonies number, average particle size, zeta potential, degree of proteolysis and proteinase activity of ultra-high temperature (UHT) milk with and without protein coagulation and commercial pure milk samples were determined to analyze the reasons for protein coagulation in UHT milk at the end of self-life. The results showed that the total protein content of coagulated milk samples was 2.9 g/100 g, which was not significantly different from that of milk samples without protein coagulation, but the pH decreased slightly. The total color difference (ΔE) and brightness value (L*) decreased to 68.05 and 67.56, respectively, indicating that the color became dark, and the total bacterial count increased to 1.92 (lg(CFU/mL)). The proteinase activity was 2 565.33 U/L, the degree of proteolysis was 17.07%, the average particle size was 685.8 nm, and the zeta potential increased to ?19.97 mV; these data were all significantly higher than those of milk samples without protein coagulation and commercial pure milk. The trend of changes in proteinase activity was basically consistent with that of the degree of proteolysis, particle size and zeta potential for all samples tested. Protein coagulation in UHT milk at the end of shelf life may be attributed to protein hydrolysis due to increased protease activity and physical deposition caused by the enlargement of casein micelles during long-term storage at ambient temperature.

Analysis of the Difference in the Quality Acceptance of Various Culture Media for the Detection of Coliform Bacteria in Raw Milk Using Different Standard Strains

LIU Shuai, XU Miaomiao, CHEN Yiwen, ZHANG Jie, WANG Hui, LI Xian, LIU Yumeng, CUI Shenghui, ZHANG Yalun

2023, 46(4):  22-27.  DOI: 10.7506/rykxyjs1671-5187-20230801-037

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In order to ensure the quality of raw milk and enrich quality control strains for the acceptance evaluation of culture media for the detection of coliform bacteria in raw milk, three brands of violet red bile agar (VRBA), violet red bile agar with 4-methylumbelliferyl-β-D-glucuronidehydrate (VRBA-MUG), lauryl tryptose broth (LST) and brilliant green lactose bile broth (BGLB) were selected and evaluated for their physical indicators such as appearance, pH and moisture content as well as microbial indicators such as growth rate and selectivity using the methods specified in China’s national standard for quality requirements for culture media and reagents in food microbiological examination (GB 4789.28-2013). Besides, using Citrobacter freundii ATCC 43864 as a reference strain, seven strains of C. freundii were selected for acceptance evaluation of the four media. The results showed that the color of all three brands of dry powdered media was normal. Their moisture content was 5%–6%, and their pH was in line with the national standard. The growth rate of the seven tested strains of C. freundii was greater than 0.7 on the three brands of VRBA and VRBA-MUG, while only CMCC 48098 and CICC 22910 achieved turbidity of 2 on the three brands of LST and BGLB, and produced gas in the catheter; the same results were obtained with ATCC 43864. In summary, the three brands of VRBA, VRBA-MUG, LST and BGLB all comply with GB 4789.28-2013, and CMCC 48098 and CICC 22910 can be recommended as supplements to quality control strains for the acceptance evaluation of the four media.

Contamination Status and Sources of Chlorate and Perchlorate in Infant Formula Milk Powder

LI Linyao, GAO Chao, CHU Xiaojun, LIU Xiaoping, HUA Jiacai, ZHENG Huayan

2023, 46(4):  28-34.  DOI: 10.7506/rykxyjs1671-5187-20230602-030

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Our aim was to understand the pollution levels and sources of chlorate and perchlorate in infant formula milk powder and to evaluate the risk of dietary exposure to chlorate and perchlorate in infants and young children. A total of 165 batches of samples were collected from the water, cow milk, and ingredients used, as well as 131 batches of infant formula milk powder. Chlorate and perchlorate in each sample were detected using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the data obtained were statistically analyzed. The results showed that chlorate and perchlorate were undetectable in the water samples. Cow milk was more severely polluted by perchlorate than by chlorate. Some ingredients were also found to contain chlorate and perchlorate. Infant formula milk powder was contaminated with chlorate and perchlorate, with average contents of 34.3 and 14.5 μg/kg, respectively. The average dietary exposure levels to chlorate and perchlorate for infants aged 0–6 months were 0.71 and 0.28 μg/(kg·d), respectively, which were at an acceptable level. Infant formula milk powder and the raw materials used were found to be contaminated by chlorate and perchlorate.

Determination of 6S-5-Methyltetrahydrofolate Calcium in Milk Powder by Reversed-Phase High Performance Liquid Chromatography

LIU Lijun, CHEN Jing, DUAN Guoxia, LI Cuizhi*, LÜ Zhiyong

2023, 46(4):  35-39.  DOI: 10.7506/rykxyjs1671-5187-20230417-019

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A reversed-phase high performance liquid chromatography (RP-HPLC) method was established for the determination of 6S-5-methyltetrahydrofolate calcium in milk powder. After protein precipitation with trichloroacetic acid solution, samples were extracted with ascorbic acid solution in a hot water bath, and the extract was separated on a C18 reversed-phase column by gradient elution using a mobile phase composed of 0.1% trifluoroacetic acid solution and methanol, and the detection wavelength was set at 280 nm. Quantitative analysis was carried out by the single standard method. The results showed that the limit of quantification and detection of 6S-5-methyltetrahydrofolate calcium in milk powder samples were 150 and 50 μg/100 g, respectively. The recoveries for samples spiked at levels ranging from 150 to 600 μg/100 g were 95.0%–109.1% with relative standard deviations (RSDs) between 1.26% and 4.04%. This method is simple, accurate, with high recovery and reproducibility, and suitable for the determination of 6S-5-methyltetrahydrofolate calcium in milk powder.

Simultaneous Determination of 10 Water-Soluble Vitamins in Infant Formula by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry

CHEN Xiumei, YAN Huijuan, ZHANG Xiaomin, LIN Tingjuan, MENG Genhua

2023, 46(4):  40-47.  DOI: 10.7506/rykxyjs1671-5187-20230616-032

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To develop a method for simultaneous determination of 10 water-soluble vitamins (nicotinic acid, nicotinamide, vitamin B2, pyridoxine, pyridoxal, pyridoxine, pantothenic acid, biotin, folic acid and vitamin B12) in infant milk by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Samples were dissolved in water, and adjusted to pH 1.7 with 5 mol/L HCl solution and then to pH 4.5 with 5 mol/L NaOH solution to precipitate proteins. The supernatant was added with a mixed solution of isotope internal standard, and separated on an ACQUITY UPLC HSS T3 column (2.1 mm × 50 mm, 1.8 μm) by gradient elution using a mobile phase composed of 10 mmol/L ammonium formate aqueous solution (containing 0.1% formic acid) and 10 mmol/L ammonium formate methanol solution (containing 0.1% formic acid). Detection was performed by electrospray ionization in the positive ion mode with multiple reaction monitoring (MRM). The external standard method was used for the quantification of pyridoxine, pyridoxal and pyridoxine, and the internal standard method for the other seven vitamins. Good linearity of the calibration curves for the 10 water-soluble vitamins was obtained in the range of 10–5 000 ng/mL with correlation coefficients (R2) above 0.99, and the recoveries for spiked samples ranged from 73.9% to 106.0%, with relative standard deviations (RSDs) of 0.9%–8.0%. The proposed method is simple, rapid, sensitive and accurate, and can meet the requirements for the determination of the 10 water-soluble vitamins in infant formula.

Determination of Sulfonamide and Quinolone Residues in Infant Formula Milk Powder by Ultra-Performance Liquid Chromatography Tandem Triple Quadrupole Mass Spectrometry

SUN Lei, ZHANG Chunlin, HE Liangna, FAN Lixin, ZHANG Xu, MA Junmei

2023, 46(4):  48-54.  DOI: 10.7506/rykxyjs1671-5187-20230517-024

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An analytical method was established for the determination of the residues of 11 sulfonamides and five quinolones in infant formula milk powder using ultra-performance liquid chromatography tandem triple quadrupole mass spectrometry (UPLC-MS/MS). Acidified acetonitrile was used for sample extraction and the extract was purified and concentrated by solid phase extraction (SPE) using a PRiME hydrophilic lipophilic balance (HLB) column, then separated on an XBridge BEH C18 column, detected in the positive ion mode using an electrospray ionization source, and quantified by the calibration curve method with matrix matching. The calibration curves of all analytes showed a good linear relationship in the concentration range of 2–100 ng/mL with correlation coefficients greater than 0.995 0. The limit of detection (LOD) and the limit of quantification (LOQ) were 0.1-0.2 and 0.3-0.5 μg/kg, respectively. Recoveries for spiked samples were between 84.8% and 108.0%, with relative standard deviations (RSDs) between 0.36% and 5.41%. The proposed method is simple, efficient, reliable and sensitive.

Reviews

Research Progress on DNA-based Technologies for Adulteration Detection in Non-bovine Milk

WANG Yue, ZHANG Yinan, YE Qing, LIU Yang

2023, 46(4):  55-60.  DOI: 10.7506/rykxyjs1671-5187-20230801-038

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In recent years, it has been often reported that non-nominal ingredients are found in milks from minor dairy species. Adulteration detection in milks from minor dairy species provides important technical support for market surveillance. DNA-based detection is a common and effective approach for food authentication, and also has advantages in milk adulteration detection. In order to provide a reference for the quality control of minor species milks, this article reviews the general aspects of minor species milks and the application of common DNA-based qualitative and quantitative techniques in adulteration detection in minor species milks in term of target gene selection, and their principles, sensitivities, application scenarios, advantages and limitations.

Research Progress on Chemical Pollutants in Dairy Products and Methods for Their Detection

OUYANG Xiaoyan, QIN Pei, HUANG Shan, FAN Yunyan, LIANG Shanfan

2023, 46(4):  61-67.  DOI: 10.7506/rykxyjs1671-5187-20230710-034

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The safety problem of dairy products is still a hot issue of concern to the general public, and chemical pollutants are an important hazardous factor for the quality and safety of dairy products. In order to guarantee the quality of dairy products, methods for the detection of chemical pollutants in dairy products has become a research hotspot in various countries. Developing new methods and techniques for the analysis and detection of chemical pollutants in dairy products, strengthening supervision, and raising dairy companies’ awareness of product quality are the key to ensuring the safety of dairy products to protect the health of consumers. In this paper, the classification and harms of chemical pollutants in dairy products, and the types of and the prevention and control approaches against chemical pollutants that commonly occur in dairy products are briefly reviewed.