Table of Content

01 September 2025, Volume 48 Issue 5

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Basic Research

Effect of Dosage on the Coagulation Performance of Bacillus velezensis Rennet

YANG Wendi, ZHANG Yafeng, QIAO Haijun, ZHANG Zhongming, REN Yongqiang, ZHANG Weibing

2025, 48(5):  1-7.  DOI: 10.7506/rykxyjs1671-5187-20250409-031

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To study the coagulation performance of rennet from Bacillus velezensis DS-1, we evaluated the effect of its different dosages (9、12、15、18、21 and 24 U/mL) on the turbidity, viscosity, rheology, optical density at 500 nm (OD500 nm) and microstructure of curd. To this end, commercial rennet was used as control. The results showed that when the rennet dosage ranged from 9 to 21 U/mL, the viscosity of coagulated milk initially increased and then leveled off, and the turbidity increased with increasing curdling time. When the rennet dosage was 24 U/mL, the turbidity increased at first and then decreased with increasing curdling time. The rheological characteristics showed that peak storage modulus of milk coagulated with rennet from strain DS-1 at dosages below 18 U/mL was smaller than that with commercial rennet and it gradually increased with increasing dosage of DS-1 rennet. As the dosage rose from 9 to 21 U/mL, the water-holding capacity increased significantly (P < 0.05). The OD500 nm value declined first and then increased slightly with increasing rennet dosage. The microstructure analysis showed that casein particles were more densely with increasing rennet dosage, and milk curd formed by rennet from Bacillus velezensis DS-1 exhibited a more porous structure. The results of this study demonstrate that Bacillus velezensis DS-1 rennet has good coagulation performance, showing minimal differences in coagulation parameters compared with commercial rennet.

Effect of Different Protease Treatments on the Solubility of Milk Protein Concentrate

LI Yuting, GAO Da, GAN Yongxiang, ZHANG Fuke, CUI Qiang, ZHANG Zhiqing

2025, 48(5):  8-16.  DOI: 10.7506/rykxyjs1671-5187-20250609-040

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Milk protein concentrate (MPC) is a high-quality ingredient for food formulations, but the reduction of MPC solubility during storage can seriously affect its use in foods. This study explored the effects of enzymatic hydrolysis with different proteases, an exoprotease (Flavourzyme 500MG (F500)), endoproteases (Alcalase 2.4L FG (A2.4L), Formea CTL 300BG (F300) and Neutrase 5.0 BG (N5.0)) and proteases with both exoproteolytic and endoproteolytic activities (Protamex 1.6 (P1.6), ProteAXH (AXH) and Protease A 2SD (A2SD)), on MPC aggregates and solubility. The results showed that hydrolysis by different proteases improved MPC solubility differently. The solubility of all hydrolysates was higher than that of MPC (54%). The endoproteases were the most effective; the solubility of MPC hydrolyzed by A2.4L, F300 and N5.0 under optimal conditions was 88.93%, 91.91% and 62.39%, respectively. The exoprotease was the least effective; the solubility of MPC hydrolyzed by F500 was 59.98% and a large amount of protein precipitated after hydrolysis. The solubility of samples hydrolyzed by P1.6 and F500 firstly increased and then decreased with increasing hydrolysis time.

Screening for Cholesterol-Lowering Lactic Acid Bacteria from Calf Feces and Their Antioxidant Activity

YANG Lixin, XU Chunyue, SUN Qingshen

2025, 48(5):  17-26.  DOI: 10.7506/rykxyjs1671-5187-20250327-026

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The aim of this study was to screen for lactic acid bacteria (LAB) with cholesterol-lowering capacity and to evaluate their antioxidant activity. In total, 45 strains of LAB were isolated from fecal samples of Jersey and Jersey × Wagyu calves before and after colostrum intake. By 16S rDNA sequence analysis, these strains were identified to belong to five genera, including Lactococcus taiwanensis, Lactococcus lactis, Ligilactobacillus salivarius, Weissella cibaria and Weissella confusa. Due to their strong cholesterol-lowering ability, W. confusa JCM11 and JCF7 were selected for evaluation of their safety, acid and bile salt tolerance, and antioxidant capacity. The experimental results demonstrated that W. confusa JCM11 and JCF7 removed 43.8% and 43.4% of cholesterol, respectively. Safety assessments showed that both strains were non-hemolytic, exhibited significant antibacterial activity against Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes, and tested negative in nitrate reductase, indole, and gelatin liquefaction tests. W. confusa JCM11 and JCF7 were highly tolerant to low pH and high bile salt concentrations. The fermentation supernatants of both strains showed good antioxidant activity. In conclusion, W. confusa JCM11 and JCF7 possess remarkable cholesterol-lowering and antioxidant activity along with excellent safety and gastrointestinal tolerance, making them valuable microbial resources for the development of functional probiotic products.

Isolation and Screening for γ-Aminobutyric Acid-Producing Lactic Acid Bacteria from Traditional Fermented Foods in Kashgar

MARYANGU·Yasheng, ZHANG Tian, TUHANGULI·Tuoheti

2025, 48(5):  27-32.  DOI: 10.7506/rykxyjs1671-5187-20250617-043

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γ-aminobutyric acid (GABA) has many physiological benefits, such as lowering blood pressure, alleviating anxiety, and enhancing sleep quality. Lactic acid bacteria, generally regarded as safe, enjoy advantages in the production of GABA. This study aimed to explore probiotics that produce GABA from traditional fermented foods in Kashgar. Altogether, 38 bacterial strains were isolated from three types of fermented foods. Lactic acid bacteria were preliminarily selected using the calcium-solubilizing zone method and Gram staining, identifying Gram-positive bacteria capable of producing calcium-solubilizing zones. These selected strains were then fermented in a medium supplemented with 1 000 mg/L monosodium glutamate (MSG). Through primary screening by paper chromatography and secondary screening with high-performance liquid chromatography, we obtained ten strains that produced GABA at high yield (616.27–774.47 mg/L) with substrate conversion rates of 37.48%–51.79% in the MSG-supplemented medium. Based on morphological, colonial, physiological, biochemical, and molecular biological characteristics as well as comparison with relevant sequences from GenBank, strains JR5, JR10, JR11, and JR19 were identified as Lactobacillus sanfranciscensis, strains MN4, MN11, MN18, and MN24 as Lacticaseibacillus paracasei, and strains Y13 and Y15 as Limosilactobacillus fermentum. This study provides a theoretical foundation and practical basis for the production of GABA using microbial resources from traditional fermented foods Kashgar.

Identification and Control of Heat-Resistant Bacteria in Raw Milk

LI Fei, ZHANG Yanhui, XIA Zhaotian, CHEN Keliang, YUE Xiao’an, QU Yali

2025, 48(5):  33-39.  DOI: 10.7506/rykxyjs1671-5187-20241217-108

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With the increasing demand for liquid milk, it is particularly important to ensure its quality and safety. The presence of heat-resistant microorganisms in liquid milk is a non-negligible cause of its quality defects. Therefore, this study employed high-throughput sequencing to explore the microbial diversity of raw milk. Heat-resistant microorganisms were isolated in pure culture and identified by 16S rDNA sequencing and their biological diversity and morphological characteristics were analyzed. Subsequently, the identified bacteria were inoculated into normal sterilized milk and skim milk to simulate the spoilage process of products contaminated by them, and their tolerance was examined to provide ideas to screen and control abnormal milk products. The results showed that the heat-resistant microorganisms in raw milk are mainly of the genus Bacillus, and three colony forms were found by Gram staining. Particle precipitation and delamination after inoculation of different types of Bacillus into sterilized milk; yellow color and bitter taste after inoculation into skim milk. All three Bacillus species had strong temperature tolerance but poor tolerance to peracetic acid. Milk enterprises can combine peracetic acid-based disinfectants with Clean-in-Place cleaning to effectively kill residual heat-resistant microorganisms on the production line.

Effect of Combined Modification with Xanthan Gum and Docosahexaenoic Acid on the Antigenicity and Structural Characteristics of β-Lactoglobulin

WANG Jing, XU Yizhou, ZHENG Xinyue, WANG Jialing, ZHU Zhipeng, JI Yaya, SUN Yufei, CHEN Daichang, ZHAO Qian, LIANG Xiaona

2025, 48(5):  40-48.  DOI: 10.7506/rykxyjs1671-5187-20250313-018

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β-lactoglobulin (β-LG) can cause severe allergic reactions. In this study, the effects of combined modification of β-LG with xanthan gum (XG) and docosahexaenoic acid (DHA) on its antigenicity and structural characteristics were investigated. DHA-β-LG and DHA-β-LG-XG complexes were obtained through non-covalent binding. Their antigenicity and structural characterization were carried out using indirect competitive enzyme linked immunosorbent assay, particle size analysis, three-dimensional fluorescence spectroscopy, Fourier transform infrared (FTIR) spectroscopy, simultaneous fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy and molecular docking. The results showed that the antigenicity of the ternary complex was significantly reduced compared with those of β-LG and the binary complex (P < 0.05). The highest inhibition rate, (24.81 ± 0.27)%, of immunoglobulin G (IgG) binding capacity was observed at 2.5 mg/mL XG concentration. The ternary complex was more stable than the binary complex. As the concentration of XG increased, the particle size of the ternary complex increased and then decreased. Under the coexistence of XG and DHA, the relative contents of β-sheet and β-turn increased, and the relative contents of α-helix and random coil decreased. Furthermore, the exposure levels of both fluorophores and peptide bonds in β-LG showed a linear positive correlation with XG concentration. XG was inserted into the only hydrophobic cavity of β-LG, and DHA bound to the hydrophobic pocket on the surface of β-LG. Both XG and DHA formed the ternary complex with β-LG through hydrogen bonding, electrostatic interactions, and hydrophobic interactions. These structural changes affect the antigen binding epitopes of β-LG, thereby reducing its antigenicity.

Package & Storage

Application of Whey Protein Isolate/Bacterial Cellulose Nanofiber-Stabilized Essential Oil Nanoemulsion in Loquat Preservation

LI Guihong, TANG Anjun, TAN Qingqing, WEN Tingting, LI Ziming, ZHANG Xingzhong

2025, 48(5):  49-55.  DOI: 10.7506/rykxyjs1671-5187-20250421-034

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This study aimed to investigate the effect of essential oil nanoemulsions on the storage quality of loquats, oil-in-water nanoemulsions loaded with Zanthoxylum schinifolium essential oil (ZSEO) and cinnamaldehyde (CA) were prepared using a mixed emulsifier of whey isolate protein and bacterial cellulose nanofibers. The effect of ZSEO/CA ratio (m/m) on the performance and stability of nanoemulsions was investigated by macroscopic and microscopic observation and physicochemical characterization. The results showed that the nanoemulsion with a ZSEO/CA ratio of 7:1 had a uniform particle size distribution without obvious aggregation, and exhibited high shear viscosity and viscoelasticity. Coating with this nanoemulsion could significantly inhibit the increase in mass loss rate and decay incidence of loquats during storage, slow down the decrease in titratable acid content, soluble solid content and hardness, effectively delay postharvest quality deterioration, and extend the shelf life.

Analysis & Detection

Core-Shell Covalent Organic Framework Composite for Magnetic Solid-Phase Extraction of Avermectin in Milk

TU Xiaoke, CHEN Yanxin, CHENG Ting, ZHU Jiahui, LÜ Shengnan, WANG Luliang

2025, 48(5):  56-61.  DOI: 10.7506/rykxyjs1671-5187-20250421-035

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Avermectin, as a broad-spectrum and highly effective antiparasitic drug, is commonly used to treat diseases in dairy cows and prone to remain in the body and can enter the food chain through milk, posing a threat to human health. In this study, a core-shell covalent organic framework composite (Fe3O4@TabDmtp) was prepared by a solvothermal self-assembly method using 1,3,5-tris(4-aminophenyl)benzene (Tab) and 2,5-dimethoxyterephthalaldehyde (Dmtp) as organic monomers. Fe3O4@TabDmtp was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometer. Fe3O4@TabDmtp was used as an adsorbent for the magnetic solid-phase extraction (MSPE) of avermectin, and the effects of eluent type and volume, adsorbent dosage, extraction time, pH and ionic strength on the extraction efficiency were investigated. Under the optimal extraction conditions, a new fluorescence method for the determination of avermectin was established. The?calibration curve for avermectin exhibited good linearity in the concentration range of 0.02–10 μg/mL with a correlation coefficient of 0.998. The limit of?detection and limit of?quantification were 0.006 and 0.02 μg/mL at signal-to-noise ratio of 3 and 10, respectively. Recovery rates for spiked samples ranged from 98.36% to 114.76%. In conclusion, the pretreatment method is time saving and Fe3O4@TabDmtp can be reused, and the analytical method has high accuracy, strong stability and high resistance to matrix interference. It can be applied to the rapid detection of avermectin in whole, low-fat and skim milk samples.

Stability of Formula for Preterm/Low Birth Weight Infants

ZHENG Huayan, HUA Jiacai, JIANG Yanxi, GUAN Xueqing, CHU Xiaojun

2025, 48(5):  62-66.  DOI: 10.7506/rykxyjs1671-5187-20250327-025

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The nutritional stability of a commercial formula for special medical purposes intended for preterm/low birth weight infants was evaluated during 6 months of accelerated storage at (37 ± 2) ℃ and relative humidity of (75 ± 5)%. The results showed that 19.12% of folic acid in the formula was lost after 2 months, 14.52% of biotin, 24.68% of iodine and 28.12% of selenium were lost after 3 months, and 13.47% of chlorine was lost after 6 months. The loss rate of choline (21.85%) was the highest during accelerated storage. To sum up, the nutrients in the formula were relatively stable, and their levels met the requirements of the Chinese national food safety and labeling standards.

Uncertainty Evaluation for the Determination of Melamine Residue in Milk Powder by Gas Chromatography-Mass Spectrometry

ZHANG Ting, WANG Shuting, LI Jia, CHE Yanzhuo, LING Li, CHENG Yongbin

2025, 48(5):  67-71.  DOI: 10.7506/rykxyjs1671-5187-20250609-042

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Objective: To evaluate the uncertainty for the determination of melamine residue in milk powder by gas chromatography-mass spectrometry (GC-MS). Methods: Following the Guidance on quantifying uncertainty in chemical analysis (CNAS-GL006: 2019), a mathematical model was established to analyze and evaluate the sources of uncertainty in the determination of melamine residue in milk powder by GC-MS according to the Chinese National Standard Determination of melamine in raw milk and dairy products (GB/T 22238-2008). The combined standard uncertainty was calculated from the uncertainty components. Results: The melamine content of the milk powder sample was determined to be 2.090 mg/kg with an extended uncertainty of 0.182 mg/kg (k = 2). Conclusion: The uncertainty mainly came from sample volume adjustment, sample recovery, standard solution preparation and curve fitting.