Table of Content

01 January 2023, Volume 46 Issue 1

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Basic Research

Nootropic, Antifatigue and Antioxidant Effects of Two Commercial Milk Fat Globule Membranes in Mice

WEN Xinyi, ZOU Xiaoxiao, LUO Yongkang, TAN Yuqing

2023, 46(1):  1-8.  DOI: 10.7506/rykxyjs1671-5187-20221209-070

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In this study, the nootropic, antifatigue and antioxidant effects of two commercial milk fat globule membranes (MFGM) in BALB/c male mice were evaluated and the possible mechanisms were elucidated. Normal saline was used a control. The experimental results showed that MFGM could improve learning and cognitive ability spatial memory ability in mice, extend exhaustive swimming time, significantly increase glycogen levels, and greatly improve fatigue- and oxidative stress-related indicators, indicating its nootropic, antifatigue and antioxidant effects. However, the effects of the two MFGMs, which are produced by different methods and have different compositions, were different.

Identification and Biological Characteristics of Hafnia alvei Isolated from Raw Milk

YU Lumin, LIU Zhixuan, WANG Pan, YIN Yikai, ZHAO Yixuan

2023, 46(1):  9-15.  DOI: 10.7506/rykxyjs1671-5187-20221227-075

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Strain HY-1, isolated from raw milk, was identified as Hafnia alvei by morphological, physiological and biochemical characterization and 16S rRNA sequence analysis, and its biological properties such as resistance to antibiotic, salt, acid and alkali, swimming motility and biofilm formation capacity were evaluated. Results showed that HY-1 was resistant to a wide range of antibiotics, which was moderately susceptible to tetracycline, erythromycin, penicillin G, ceftazidime, and cefuroxime axetil, and was resistant to midecamycin, clindamycin, clarithromycin, oxacillin, cephalothin, and cefazolin. HY-1 could grow in media at pH 5.0–8.0 containing 0.2–0.5 g/mL of sodium chloride at 4–37 ℃, and showed swimming motility as evidenced by the halo on the surface of the swimming plate. In addition, HY-1 could form biofilms, and milk at 2 mg/mL had the potential to facilitate biofilm formation by HY-1 and consequently increase its transmission and contamination, which may cause food quality and safety problems. However, when the concentration of NaCl equaled or exceeded 0.4 g/mL, the biofilm formation ability of HY-1 was significantly inhibited, indicating that the transmission and contamination of HY-1 could be intercepted by appropriate concentrations of NaCl.

Processing Technology

Preparation and Quality Evaluation of Fermented Milk with Added Insoluble Dietary Fiber from Auricularia auricula

LIU Lin, ZHU Wenjuan, HAN Xiaoyun, KONG Jing, LI Mengyang, SUN Qingshen

2023, 46(1):  16-23.  DOI: 10.7506/rykxyjs1671-5187-20221115-068

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In this study, the effect of addition of water-insoluble dietary fiber (IDF) enzymatically extracted from Auricularia auricula on the acidity and viable bacterial count of fermented milk was explored. One-factor-at-a-time method combined with orthogonal array design was used to optimize the formulation (concentrations of IDF, skim milk powder and sodium carboxymethyl cellulose) of fermented milk with added IDF based on sensory evaluation score. The nutrient composition and texture characteristics of the fermented milk prepared using optimized formulation were determined. The results showed that IDF from Auricularia auricula could promote the proliferation of lactic acid bacteria. The optimum formulation consisted of 7% IDF (converted into 0.78% freeze-dried powder) 1.5% sodium carboxymethylcellulose and 2.0% skim milk powder. The prepared fermented milk contained (3.53 ± 0.08)% protein, (3.12 ± 0.03)% fat, (0.78 ± 0.12)% ash, and (19.35 ± 0.49)% solids. Addition of IDF improved the water-holding capacity, hardness, chewiness and viscosity of fermented milk during storage and at the same time showed a protective effect on the starter culture.

Analysis & Detection

Determination of Ethylene Oxide and 2-Chloroethanol in Milk and Dairy Products

ZHOU Jing, XU Hongbin, ZHOU Zelin, ZHOU Yaobin, FU Changyu, LIU Yang

2023, 46(1):  24-29.  DOI: 10.7506/rykxyjs1671-5187-20221107-066

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In this study, headspace gas chromatography-mass spectrometry (HS-GC-MS) was used to accurately identify and quantify ethylene oxide and 2-chloroethanol in milk and dairy products (liquid milk, fermented milk, infant formula milk powder, and ice cream). The sample was diluted to a constant volume in a headspace bottle and balanced at 90 ℃ for 20 min, and the extract was separated on a DB-624 capillary column (60 m × 0.32 mm, 1.8 μm) with temperature programming. Ethylene oxide and 2-chloroethanol were detected using an electrospray ionization (ESI) source in the selected ion monitoring (SIM) mode. Quantitation was carried out using matrix-matched calibration curves. Good linearity was obtained in the range of 0.1–10.0 mg/L (R2 ≥ 0.99). The limits of detection of ethylene oxide and 2-chloropropanol in milk, fermented milk and ice cream were 0.12 and 0.60 mg/kg, respectively. At three spiked levels, the average recoveries of the two compounds were between 75.9% and 101.6%, with relative standard deviations (RSD) less than 10%. This method is precise and accurate, and can meet the requirements for the detection of milk and dairy products with a complex matrix.

Establishment of a Helicase-Dependent Isothermal DNA Amplification Method for Rapid Detection of Lactobacillus plantarum in Fermented Milk

ZHANG Yalun, LI Yongbo, ZHANG Tao, CHEN Chen, ZHANG Jie, ZHOU Wei, ZHANG Yan

2023, 46(1):  30-34.  DOI: 10.7506/rykxyjs1671-5187-20220908-056

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A rapid detection method based on helicase-dependent isothermal DNA amplification (HDA) was established for Lactobacillus plantarum in fermented milk. Specific primers were designed according to the scrB gene sequence of Lactobacillus plantarum (Genbank Accession NO. AJ579541.1), and the optimal concentrations of UvrD helicase and T4 gp32 in the reaction system were determined through experiments. The limit of detection (LOD), specificity, consistency and stability of the proposed method were evaluated by use of L. plantarum-spiked samples, amplification of various strains, and electrophoresis of amplified products and sequence alignment analysis, respectively. The results showed that the optimized of UvrD helicase and T4 gp32 in the reaction system were found to be 0.15 and 5.0 μg, respectively. The HDA method had high specificity with no amplification of other strains tested. The detection limit was 2.8 × 101 CFU/g. The amplified product was consistent with the designed sequence length (273 bp) and the sequence homology was 100%. In conclusion: this method is rapid, simple, sensitive and suitable for the detection of Lactobacillus plantarum in fermented milk.

Development of a Gas Chromatographic Method for the Determination of Iodine Content in Milk Powder and Homogeneity and Stability Assessment of Iodine Reference Material

BAI Xiaoyun, SU Yuncong, ZHANG Yaoguang, LI Xingjia, LI Fei, HUANG Yafang

2023, 46(1):  35-40.  DOI: 10.7506/rykxyjs1671-5187-20220920-060

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A gas chromatographic method for determining the iodine content in milk powder was established, and the homogeneity and stability of iodine reference material were evaluated. Butanone derivative with iodine produced under acidic conditions was detected by gas chromatography (GC) with an electron capture detector and quantified by an external standard method. The proposed method showed a good linear relationship (R2 = 0.999 6), the recoveries from spiled samples were between 95.3% and 101.3%, and the relative standard deviation (RSD) was 2.3% (n = 6). This method had high accuracy and could be used for the determination of the iodine content in milk powder.

Determination of Erythrosine Content in Fermented Milk by Reversed-Phase High Performance Liquid Chromatography

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

2023, 46(1):  41-46.  DOI: 10.7506/rykxyjs1671-5187-20221025-064

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A reversed-phase high performance liquid chromatographic (HPLC) method was established for the determination of erythrosine in fermented milk. After enzymatic hydrolysis, the sample was extracted with anhydrous ethanol, and purified by solid phase extraction using an HLB column under alkaline conditions. The separation was performed on a C18 reversephase column by gradient elution using a mobile phase comprising 20 mmol/L ammonium acetate buffer solution (pH 6.5) and methanol. The detection wavelength was set at 520 nm, and quantification was performed by the external standard method. The results showed that the linear range for erythrosine was 0.05–20.00 μg/mL. The limit of quantitation (LOQ) and the limit of detection (LOD) of erythrosine in fermented milk samples were 0.2 and 0.1 mg/kg, respectively. The recoveries from fermented milk samples spiked at levels of 0.2–2.0 mg/kg were 96.5%–105.6%, and the relative standard deviations (RSD) were 1.87%–2.21%. The method is simple and accurate, has high recovery and good repeatability, and is suitable for the determination of erythrosine in fermented milk.

Reviews

Research Progress on Secondary Metabolites in Monascus and Their Application in Dairy Products

WU Zhongling, LIU Zhenmin

2023, 46(1):  47-55.  DOI: 10.7506/rykxyjs1671-5187-20221212-071

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Monascus spp. is a filamentous fungus that can produce beneficial secondary metabolites including Monascus pigments (MPs), monacolin K and γ-aminobutyric acid (GABA), which possess the important biological activities such as acting as a colorant, anti-cancer and anti-inflammation agent. Therefore, Monascus is widely used in such industries such as foods, medicine and brewing. However, Monascus can produce citrinin with nephrotoxicity, which limits its application. In this review, we systematically summarize the latest research progress on the synthesis pathway, biological activity and synthesis regulation of MPs, monacolin K, GABA and citrinin，as well as the application of Monascus in dairy products. We hope that this review can provide new ideas for the safe development of dairy products fermented by Monascus.

Comparison of Safety Requirements of Raw Milk Standards in China, the EU and Japan

WU Jie, ZHAO Yankun, ZHENG Nan, WANG Jiaqi, MENG Lu

2023, 46(1):  56-61.  DOI: 10.7506/rykxyjs1671-5187-20221218-074

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In recent years, the safety of animal original food has become a growing public concern. In order to ensure food safety, China has continuously upgraded relevant standards. Milk is the ideal food for human beings, and raw milk determines the quality and safety of dairy product. In this context, this article reviews and compares the limits for contaminants, mycotoxins, microbial contamination, pesticide residues, and veterinary drug residues in raw milk in China, the European Union, and Japan, and proposes suggestions for improving the raw milk standards in China.

Progress in the Application of Techniques for Rapid Detection of Foodborne Pathogens in Milk and Dairy Products

ZHAO Shuhuan, WANG Yunxia, LIU Lijun, LI Cuizhi, LÜ Zhiyong

2023, 46(1):  62-67.  DOI: 10.7506/rykxyjs1671-5187-20220905-054

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Being rich in nutrients, dairy products provide a good environment for the growth of Staphylococcus aureus, Salmonella, Listeria monocytogenes, Cronobacter and other foodborne pathogens, which poses a serious threat to the safety of dairy products. Therefore, rapid and accurate detection of foodborne pathogens in dairy products is essential to the prevention of foodborne pathogens. In recent years, analytical techniques including molecular biology and immunoassays have rapidly developed and attracted much attention due to their advantages of high sensitivity, rapidity and simplicity compared with the traditional food pathogen detection methods, which are cumbersome and time-consuming. In this paper, recent developments and applications of foodborne pathogen detection techniques are reviewed, and future trends were discussed in order to provide a reference for the rapid detection of foodborne pathogens in dairy products.