Table of Content

01 October 2023, Volume 46 Issue 5

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Basic Research

Isolation and Identification of Lactobacillus plantarum and Its Effect on Pigment Production by Monascus

WU Zhongling, GAO Hongyan, LIU Zhenmin

2023, 46(5):  1-9.  DOI: 10.7506/rykxyjs1671-5187-20230920-047

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A lactic acid bacteria (LAB) strain BD-1 was isolated from red fermented bean curd, and the effect of BD-1 and its fermentation supernatant on the production of Monascus pigments (MPs) by Monascus purpureus ATCC 16365 was studied. The results showed that BD-1 was identified as Lactobacillus plantarum through Gram staining, physiological and biochemical profiles and 16S rRNA gene sequencing. Five different inoculum sizes of 0.2%, 0.4%, 0.6%, 0.8% and 1.0% were tested for strain BD-1 and ATCC 16365 was cultured for 0, 24 or 48 h. It was found that adding 0.6% BD-1 to the fermented medium with ATCC 16365 after culture for 24 h markedly increased the color value and synthesis of extracellular Monascus pigments (EMPs) and intracellular Monascus pigments (IMPs). Under this condition, the color values of EMPs and IMPs were (6.24 ± 0.05) and (288.14 ± 6.82) U/mL, and their synthesis was increased by (146.55 ± 7.84)% and (16.07 ± 0.30)% compared with the control group, respectively. In addition, adding the fermentation supernatant of BD-1 to ATCC 16365 also remarkably increased the color value and synthesis of EMPs, which were increased to 4.20 U/mL and by (29.85 ± 5.40) % compared to the control group, respectively. In summary, the optimal inoculum size of BD-1 for MPs production was 0.6%.

Effect of Wet Process on Nutrient Loss Rate and Mixing Uniformity of Infant Formula Milk Powder

LI Linyao, CHU Xiaojun, HUA Jiacai, GAO Chao, KANG Qiaojuan, ZHENG Huayan

2023, 46(5):  10-15.  DOI: 10.7506/rykxyjs1671-5187-20230725-036

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The wet process for producing infant formula milk powder requires multiple heating processes, which can cause some nutrient loss. Mixing uniformity is an important indicator for measuring the effectiveness of the mixing process, which is used to measure whether various nutrient indicators are evenly dispersed in infant formula milk powder. When designing infant formula milk powder, the loss rate and mixing uniformity of nutrients should be taken into account to ensure that the quality of products meets the requirements of the national food safety standards. This study analyzed nutrient loss rate and mixing uniformity in the wet processing of infant formula milk powder. The results showed that the nutrient that was most lost in the wet process was vitamins. Vitamin A (VA), vitamin B1 (VB1), vitamin B12 (VB12), and vitamin C (VC) were lost by 19.2%, 20.4%, 33.9%, and 20.3%, respectively, while the other vitamins were not significantly lost. Minerals were relatively stable in the wet process, and no significant loss of inositol, taurine or galactooligosaccharides was observed; the mixing uniformity of VB1 was less than 95%, while the mixing uniformity of the other nutrients was above 95%.

Effect of Secondary Homogenization on the Quality of Ultra-High Temperature Sterilized Whipped Cream

WANG Jidong, ZHENG Yuanrong, LIU Zhenmin

2023, 46(5):  16-21.  DOI: 10.7506/rykxyjs1671-5187-20231110-054

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In this research, the effect of different secondary homogenization pressures on the quality of ultra-high temperature instantaneous sterilized (UHT) whipped cream was analyzed. The results showed that secondary homogenization of whipped cream at pressures ranging from 4 to 8 MPa shifted the size distribution of the emulsion droplets toward smaller values, and increased the apparent viscosity, which improved the stability of the emulsion. However, too high homogenization pressure led to fat aggregation within the emulsion droplets, affecting the apparent viscosity and foam stability of whipped cream. With an increase in secondary homogenization pressure, whipping time of whipped cream was prolonged, whipping rate, foam stability and hardness was decreased, and even at 12 MPa, it could not be whipped into shape. Therefore, it is recommended that the secondary homogenizing pressure be controlled in the range of 4 to 6 MPa.

Analysis & Detection

Determination of 17 Mycotoxins in Milk and Dairy Products by High Performance Liquid Chromatography-Tandem Mass Spectrometry

LIU Ling, YE Pei, ZHANG Qiaoyan, SHEN Ying, DONG Yuying, JIANG Mengyuan, LI Wenting

2023, 46(5):  22-27.  DOI: 10.7506/rykxyjs1671-5187-20231011-050

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To establish a method for simultaneous detection of 17 mycotoxins in milk and dairy products based on high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Samples (5.000 0 g) were added to 20 μL of a mixed solution of isotope-labeled internal standards, extracted with 20 mL of acetonitrile-water-formic acid solution (70:29:1, V/V) by vortex shaking, salted out with 0.3 g of sodium chloride, and then centrifuged at high speed. The supernatant was passed through a 0.22 μm membrane filter, detected by triple quadrupole mass spectrometry in the multi-reaction detection mode and quantified by an internal standard method. Results: Under the optimized instrumental conditions, good linearity was observed for the 17 mycotoxins in the tested concentration ranges, with correlation coefficient (r) greater than 0.99. The limit of detection (LOD) was 0.05-6.20 μg/kg, and the limit of quantitation (LOQ) was 0.2-20.0 μg/kg. Good average recoveries (78.9%-119.5%) and precision (relative standard deviations (RSDs) 0.2%–8.4%) were achieved at three spiked levels. The method is convenient, stable, reliable and sensitive, can meet the requirements of qualitative and quantitative analysis of the 17 mycotoxins in milk and dairy products, and is suitable for laboratory monitoring of the contamination of these mycotoxins in milk and dairy products.

Determination of Steviol Glycosides in Fermented Milk by High Performance Liquid Chromatography

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

2023, 46(5):  28-34.  DOI: 10.7506/rykxyjs1671-5187-20230831-043

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A method for the determination of stevioside, rebaudioside A, rebaudioside B, rebaudioside C, rebaudioside F, dulcoside A, rubusoside and steviolbioside in fermented milk by high performance liquid chromatography (HPLC) was developed and validated. The chromatographic conditions and sample pretreatment conditions were optimized. Samples were ultrasonically extracted with water for 20 min and for another 10 min after addition of 30% acetonitrile in water bath at 45 ℃. Potassium ferrocyanide and zinc acetate were added to precipitate proteins. The chromatographic separation was achieved on a C18 with gradient elution using a mobile phase consisting of sodium phosphate buffer and acetonitrile, and the analytes were detected by an ultraviolet (UV) detector at 210 nm. The results showed that the method was linear in the concentration range of 1–50 μg/mL, the limit of detection (LOD, RS/N = 3) was 3.0 mg/kg, and the limit of quantitation (LOQ, RS/N = 10) was 10.0 mg/kg. The average recoveries of all analytes spiked at 15–200 mg/kg were between 92.0% and 103.1%, with relative standard deviation (RSDs) (n = 6) less than 3.0%. This method was rapid, accurate, stable, sensitive, and suitable for the analysis of the content of steviol glycosides in fermented milk.

Determination of Pyramid and Its Metabolite Melamine in Milk by High Performance Liquid Chromatography

DENG Xiaoqing, ZHENG Lijun, TANG Wanli, TANG Wenjie, CHEN Tongqiang

2023, 46(5):  35-39.  DOI: 10.7506/rykxyjs1671-5187-20231229-065

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A high performance liquid chromatography method was established to determine the content of cyromazine and its metabolite melamine in milk. The external standard method was used to quantify figures of merit such as linear relationship, precision, recovery, detection limit, and quantification limit. The results showed that the method had good linearity in the concentration range of 0.0–1.0 mg/L (R2 > 0.999), with detection limits of 0.003 and 0.004 mg/kg and quantification limits of 0.008 and 0.010 mg/kg for cyromazine and melamine, respectively. The average spiked recoveries were in the range of 84.4% to 89.5% and 83.9% to 91.2% for cyromazine and melamine, respectively, with relative standard deviations (RSDs) less than 10%. This method is characterized by high sensitivity, high accuracy, and good reproducibility, and can meet the requirement of the determination of cyromazine and its metabolite melamine in milk.

Packaging & Storage

Quality Change and Shelf Life Prediction of Yogurt at Different Storage Temperatures

YIN Xianhua, YIN Cheng, MENG Jingjing, QIAN Jing

2023, 46(5):  40-47.  DOI: 10.7506/rykxyjs1671-5187-20230914-045

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In order to better analyze the quality and predict the shelf life of yogurt, changes in the number of lactic acid bacteria, pH value and acidity in yogurt at different storage temperatures were analyzed, and the temperature dependence and shelf life of yogurt were studied by the combined use of kinetic analysis and the Arrhenius equation. The results showed that the number of lactic acid bacteria was maintained, and the decrease of pH value and the increase of acidity value were slowed down during storage at 9 ℃. The acidity value could well reflect the quality changes of yogurt, and the activation energy of yogurt was 67.5 kJ/mol as determined by chemical kinetics. Furthermore, a shelf-life model based on the acidity of yogurt was obtained.

Reviews

Research Progress in the Analysis of Whole-Chain Quality Traceability Information in Dairy Production

HUANG Run, YANG Xiaojian, SONG Xiaodong, LI Mei, LI Linchun, DONG Guanjun, LI Te, SHI Yongqiang, YANG Yong, XIE Xiaolong, HU Wei

2023, 46(5):  48-54.  DOI: 10.7506/rykxyjs1671-5187-20230927-049

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In recent years, consumer complaints about dairy products have been frequent, and dairy quality problems have become the focus of social and livelihood concerns. It is urgent to build a whole-chain quality traceability system for dairy production and improve the traceability system of dairy products. This paper deeply analyzes the whole quality information flow of dairy production, and reviews the traceability technologies currently used in dairy production. This review is expected to provide innovative control strategies for improving the dairy management system and help diary producers in reducing consumer complaints about quality problems.

Research Progress on Probiotics Assisting in Regulating Scalp Health

WU Jiang, DING Xinli, SHAO Li, JIA Hongxin

2023, 46(5):  55-60.  DOI: 10.7506/rykxyjs1671-5187-20231110-055

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The balance of scalp microecological environment is very important to scalp health. Some scalp disorders may be associated with the imbalance of microbial communities. As beneficial live microorganisms, probiotics can regulate the intestinal flora, and then affect the immune system of the scalp through the gut-skin axis, which have a positive impact on the health of the scalp. Studies have shown that probiotics have the potential to maintain scalp health. This paper summarizes the mechanism of action of probiotics on the skin and their auxiliary role in regulating hair loss and dander.

Analysis and Review of Element Detection Techniques for Milk and Dairy Products

HUANG Xiaoyan, TANG Shuo*, LIU Lijun, LI Cuizhi, NING Yuelian, YUE Hong

2023, 46(5):  61-67.  DOI: 10.7506/rykxyjs1671-5187-20230904-044

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Abnormal analysis of trace elements and heavy metal over-standard in dairy products are major concerns in the dairy industry, and how to detect elements of concern in dairy products quickly and accurately has become the focus of attention. Detection of elements in milk and dairy products is a prerequisite to ensure product quality and safety. Therefore, the pretreatment and detection methods specified in the Chinese and international standards for elements in milk and dairy products are reviewed. The principle, pros and cons of each method are elaborated so as to provide a reference for the detection of elements in the dairy industry.