Table of Content

01 May 2025, Volume 48 Issue 3

Previous Issue   

Basic Research

Physicochemical Analysis of Antimicrobial Peptides Produced by Lactococcus lactis L-H410 and Optimization of Fermentation Conditions

HU Linghan, LI Pinglan, WANG Yu

2025, 48(3):  1-10.  DOI: 10.7506/rykxyjs1671-5187-20241223-111

Asbtract ( )   HTML ( )   PDF (3937KB) ( )  

Related Articles | Metrics

Antimicrobial peptides produced by Lactococcus lactis are natural and safe. The aim of this study was to investigate the physicochemical properties of antimicrobial peptides produced by L. lactis L-H410 and optimize the fermentation conditions for its production. The antimicrobial peptides exhibited broad-spectrum activity, and was stable against a broad pH range (2.0–9.5) and thermal treatment (at 80 ℃ for 30 min) and susceptible to proteases. The fermentation conditions (temperature, initial pH, and inoculum size) and medium components (carbon sources, nitrogen sources, stimulating factors, and divalent salt ions) were optimized by the combined use of one-factor-at-a-time method, Plackett-Burman design, path of steepest ascent, Box-Behnken design, and response surface methodology. The optimum fermentation conditions that provided maximum relative antibacterial potency of 378.7 AU/mL, which was 1.2 times of that before optimization (318.4 AU/mL), were determined as 3.32%, 2.5%, 0.2%, 0.02%, 29 ℃, 6.95, and 2.5% for sucrose, peptone, polyethylene glycol (PEG) 8000, manganese sulphate concentrations (m/m), temperature, initial pH, and initial inoculum, respectively.

Mutations at the N81 Site Modulate the Specificity of Bile Salt Hydrolase g1294 from Ligilactobacillus cholophilus BD7642

REN Quanlu

2025, 48(3):  11-17.  DOI: 10.7506/rykxyjs1671-5187-20241210-105

Asbtract ( )   HTML ( )   PDF (3827KB) ( )  

Related Articles | Metrics

This study aimed to analyze the effect of active site mutations on the specificity of bile salt hydrolase (BSH) g1294 from Ligilactobacillus cholophilus BD7642. Glycine scanning technology was used to investigate systematic mutations of BSH g1294’s active center, and the activity of mutants was assessed by the spot-plate method. High performance liquid chromatography was utilized to analyze the specificity of the mutants toward six bile salts. Additionally, saturation mutagenesis was conducted at the N81 site, followed by molecular docking simulations to analyze the differences between the mutants and the wild type. Results revealed that mutations at some sites led to the inactivation of the BSH activity. However, the N81G and N174G mutants exhibited enhanced substrate specificity, the former being superior to the latter. Among the mutants at the N81 site, significant variations in the enzymatic activity and hydrolytic capability were observed. Molecular docking simulations indicated that the N81G mutant acquired hydrolytic capability by reducing the steric hindrance between the catalytic site Cys2 and glycocholic acid. In conclusion, this mutant showed improved specificity than did the wild type. The molecular recognition of bile acids by BSH may not be simply based on amino acid recognition, which could provide new insights for rational design for BSH engineering.

Processing technology

Effects of Ultrasound-Treated Raw Milk on the Quality of Cheddar Cheese

JIAN Xiaoqing, ZHANG Shanshan, ZHANG Ziyi, LI Yanhui, MA Ling

2025, 48(3):  18-25.  DOI: 10.7506/rykxyjs1671-5187-20250120-005

Asbtract ( )   HTML ( )   PDF (2624KB) ( )  

Related Articles | Metrics

This study investigated the effects of ultrasound-treated raw milk on the quality of Cheddar cheese by applying ultrasound treatment at six different combinations of temperature (40, 50 and 60 ℃) and duration (15 and 30 min). Cheese made from pasteurized (63 ℃, 30 min) milk served as a control. The physicochemical properties, texture characteristics, rheological properties, yield, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns, and protein contents of cheese samples were measured. The results demonstrated that compared with the control group, ultrasonic treatment increased the water activity, elevated the pH value, and enhanced the thermal stability and texture properties. Ultrasonic treatment at 50 ℃ for 30 min resulted in the best texture, sensory and rheological properties of Cheddar cheese, while ultrasonic treatment at 40 ℃ for 30 min resulted in the highest cheese yield (12.34%). Cheese yield was not significantly affected by either ultrasonic temperature or time (P > 0.05). Moreover, ultrasonic treatment significantly increased the pH 4.6-soluble nitrogen content (P < 0.05), with the highest value of 1.54% being observed using ultrasonic treatment at 40 ℃ for 30 min. In summary, ultrasonic treatment at 50 ℃ promoted protein crosslinking and homogenization of fat globules to form compact networks, thereby improving cheese quality; however, ultrasonic treatment at 60 ℃ aggravated protein denaturation and consequently resulted in deterioration of cheese texture.

Effect of Induced Electric Field Sterilization on the Physicochemical Properties of Raw Cow Milk

CHEN Xinwen, MENG Man, JIN Yamei, GAO Ying, JIANG Mingjun, YANG Na, XU Xueming

2025, 48(3):  26-31.  DOI: 10.7506/rykxyjs1671-5187-20241018-095

Asbtract ( )   HTML ( )   PDF (1896KB) ( )  

Related Articles | Metrics

In order to investigate the efficacy of induced electric field (IEF) in sterilizing raw milk and the effect on its physicochemical properties, milk samples were treated by IEF at different excitation voltages (300, 400, and 500 V) and evaluated for Staphylococcus aureus and Escherichia coli counts and physicochemical properties. Meanwhile, changes in acidity and total bacterial count were minored during storage. Results indicated that the outlet endpoint temperature of milk increased with the increase in excitation voltage, and so did the efficacy of IEF in inactivating S. aureus and E. coli. The efficacy of reducing the microbial level in raw milk was higher than that of traditional heat treatment and high-temperature short-time pasteurization. IEF had no significant effect on the pH, fat, soluble solids, casein, or lactoferrin content of milk (P > 0.05), nor did it destroy milk nutrients. Moreover, IEF effectively delayed the increase in acidity and extended the shelf-life of milk stored at 4 ℃ by about 6 days. This study provides a new solution for high-quality sterilization and shelf-life prolongation of raw milk.

Effect of Different Hot Stretching Temperatures in Whey on the Quality of Mozzarella Cheese

ZHANG Shanshan, JIAN Xiaoqing, YU Liya, LI Yanhui, ZHANG Ziyi, MA Ling

2025, 48(3):  32-37.  DOI: 10.7506/rykxyjs1671-5187-20250120-006

Asbtract ( )   HTML ( )   PDF (3210KB) ( )  

Related Articles | Metrics

Hot brine stretching of Mozzarella cheese can lead to the loss of protein and other components, while whey, which is rich in nutrients such as whey protein, has an important influence on the protein structure and functional characteristics of cheese. In this study, the effects of different stretching temperatures (65, 75, 85, and 95 ℃) in whey on the physiochemical and textural characteristics of Mozzarella cheese were investigated by using brine at 95 ℃ as a control. The results showed that the yield of stretched cheese in whey at 75 ℃ was as high as 7.38%, which was significantly higher than that of the other treatments (P < 0.05), and the cheese had good texture characteristics. In contrast, the stretched cheese in whey at 85 ℃ had the best sensory quality. Scanning electron microscopy analysis showed that at 75 ℃, the protein cross-linking was moderate and the cheese had an ideal balance of elasticity and hardness. Through sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis, it was found that stretching in whey at 75 ℃ more effectively retained the protein components in cheese. Additionally, rheological analysis indicated that the cheese subjected to hot stretching in whey exhibited better elastic properties.

Analysis & Detection

Simultaneous Determination of Five Major Proteins in Whey Protein Powder by Reversed-Phase High-Performance Liquid Chromatography

DAI Yuting, YANG Jinqing

2025, 48(3):  38-42.  DOI: 10.7506/rykxyjs1671-5187-20250113-002

Asbtract ( )   HTML ( )   PDF (2330KB) ( )  

Related Articles | Metrics

In this paper, a reversed-phase high-performance liquid chromatography method was proposed to determine five major proteins including α-lactalbumin, β-lactoglobulin, glycomacropeptide, bovine serum albumin, and immunoglobulin G in whey protein powder. After dissolution and ultrasonication, samples were separated on ChromCore 300 C4-T chromatographic column (4.6 mm × 150 mm, 5 μm) with gradient elution using a mobile phase consisting of 0.1% (V/V) aqueous trifluoroacetic acid (TFA) and 90% acetonitrile (containing 0.09% TFA). These analytes were detected using a diode array detector scanning in the wavelength range from 200 to 700 nm at 214 nm. Under the optimal experimental conditions, the five major bovine whey proteins were well separated within 30 min. The average recoveries from spiked samples were in the range of 83.5%–95.3% with relative standard deviations (RSDs) of 2.03%–7.49%. The limit of detection was 0.25% (m/m) for all analytes. The established method is rapid, accurate and sensitive that enables the simultaneous detection of the major bovine whey proteins in whey protein powder.

Determination of Ethephon Residue in Milk by Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry

BAI Yanmei, ZHANG Lijia, WANG Yang, LIU Lijun, MO Nan, GAO Yujie, LI Peizhen, HU Xue, WU Xiaoli

2025, 48(3):  43-48.  DOI: 10.7506/rykxyjs1671-5187-20241223-112

Asbtract ( )   HTML ( )   PDF (2535KB) ( )  

Related Articles | Metrics

An ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method with solid phase extraction (SPE) was established for the detection of ethephon residue in milk. In the sample pretreatment stage, formic acid solution was selected as the extraction solvent, and the extract was purified on an amino SPE column. The target compound was separated on a Waters Anionic Polar Pesticide column (150 mm × 2.1 mm, 5 μm) using gradient elution with a mobile phase consisting of 0.1% formic acid containing 50 mmol/L ammonium formate and acetonitrile. The detection was performed using electrospray?ionization in the negative ion mode with multiple reaction monitoring, and the matrix-matched external standard method was used for quantification. The calibration curve for ethephon showed an excellent linearity (r2 > 0.99) in the concentration range of 2 to 100 ng/mL, and the limit of detection and limit of quantification of this method were 0.5 and 1.0 μg/kg, respectively. At spiked concentration levels of 1.0, 2.0 and 10.0 μg/kg, the recoveries were between 92.50% and 113.76%, and the precision, expressed as relative standard deviation, ranged from 3.04% to 4.60%. In conclusion, the UPLC-MS/MS method has the advantages of high accuracy, specificity, and repeatability, and is very suitable for the determination of ethphon in milk.

Development and Evaluation of Standard Reference Material for Iodine Analysis in Milk-Based Infant Formula Food for Special Medical Purposes

LI Qingqing, LIU Junyao, YAN Jing

2025, 48(3):  49-46.  DOI: 10.7506/rykxyjs1671-5187-20250223-012

Asbtract ( )   HTML ( )   PDF (2202KB) ( )  

Related Articles | Metrics

To address the need for iodine quantification in infant formula food for special medical purposes, a reference material for iodine analysis was developed. Powered infant formula milk for special medical purposes (containing partially hydrolyzed milk protein) was used as the matrix and added with dietary supplement of potassium iodide initially diluted with whey protein powder to establish a stable preparation system using stepwise dry dilution. The homogeneity and stability of the prepared reference material were verified using alkaline extraction combined with inductively coupled plasma mass spectrometry, and characteristic value assignment was conducted through a multi-laboratory collaborative approach. Results demonstrated excellent homogeneity and stability of the material, showing a characteristic value for iodine of (67.8 ± 4.6) μg/100 g (k = 2). This reference material could be useful for method validation, laboratory quality control, and instrument calibration for iodine determination in infant formula food for special medical purposes, providing technical support for ensuring accurate measurement of iodine content in this specialized food product.

Quality & Safety

Characteristics of a Protease-Producing Strain of Bacillus cereus Isolated from Raw Milk

QU Yali, ZHANG Yanhui, XIA Zhaotian, CHEN Keliang, ZHOU Ting, CHU Zhenzhen, LI Fei

2025, 48(3):  55-59.  DOI: 10.7506/rykxyjs1671-5187-20241217-110

Asbtract ( )   HTML ( )   PDF (4724KB) ( )  

Related Articles | Metrics

Eight Bacillus cereus strains were isolated from 10 batches of raw milk and identified through 16S rDNA sequencing and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Out of these strains, one was selected on the basis of higher protease production and identified as B. cereus LY-6. We inoculated this strain back into skim milk and observed the resulting spoilage process. It was found that the milk turned to yellow, and had a bitter taste and an unpleasant odor. Moreover, the pH decreased and large amounts of proteases were found, indicating that the spoilage process is closely related to microbial protease production. Strain LY-6 was intolerant to ultra-high temperature sterilization. A distribution map of B. cereus in the dairy was drawn to control its spread. It was found that this bacterium mainly existed in places where milk stains are difficult to clean such as pasture bedding, towels, milk trucks, workshop floors, personnel shoe soles, and equipment surfaces. Therefore, special attention should be paid to the cleaning effect of the backend pipeline after the sterilization process to prevent potential food safety hazards caused by secondary contamination of B. cereus.

Reviews

Progress in Application of Omics in Species Identification of Dairy Products

FAN Yujiao, CAO Meirong, FAN Sufang, WEI Zhengchao, ZHANG Yan

2025, 48(3):  63-70.  DOI: 10.7506/rykxyjs1671-5187-20241217-109

Asbtract ( )   HTML ( )   PDF (1700KB) ( )  

Related Articles | Metrics

Dairy products are rich in protein, fat, oligosaccharides, and micronutrients, and the global demand for these products is steadily increasing. However, in the processing of dairy products, there may be some problems such as adulteration with inferior milk or passing off low-quality milk products as high-quality ones. Therefore, establishing a robust method to identify the species composition of dairy products is crucial for quality supervision in the dairy industry. Omics technologies, characterized by their high throughput nature, broad applicability, and ability to accurately reflect food status, have increasingly been utilized for species identification in dairy products. This paper reviews the concepts of genomics, proteomics, and metabolomics, highlighting the current status and future prospects of these omics approaches in species identification in dairy products. The integration of multiple omics technologies will provide more reliable support for accurate, rapid, and comprehensive identification of dairy products.