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Article

Effect of Thermostable Enzymes Produced by Psychrotrophic Bacteria in Raw Milk on the Quality of Ultra-High Temperature Sterilized Milk

by
Xue Qin
1,
Jingqi Cheng
1,
Xuehe Qi
1,
Ning Guan
2,
Qing Chen
1,
Xiaoyan Pei
3,
Yujun Jiang
1,
Xinyan Yang
1 and
Chaoxin Man
1,*
1
Key Laboratory of Dairy Science, Ministry of Education, College of Food Science and Engineering, Northeast Agricultural University, Harbin 150030, China
2
Center for Dairy Safety and Quality, National Center of Technology Innovation for Dairy, No. 1 Jinshan Road, Jinshan Development Zone, Hohhot 010110, China
3
Risk Assessment Department, Inner Mongolia Yili Industrial Group Co., Ltd., No. 1 Jinshan Road, Jinshan Development Zone, Hohhot 010110, China
*
Author to whom correspondence should be addressed.
Foods 2023, 12(20), 3752; https://doi.org/10.3390/foods12203752
Submission received: 19 September 2023 / Revised: 6 October 2023 / Accepted: 10 October 2023 / Published: 12 October 2023
(This article belongs to the Special Issue The Microbial Safety of Milk, Cheese and Dairy Products)
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Abstract

Ultra-high temperature sterilized milk (UHT) is a popular dairy product known for its long shelf life and convenience. However, protein gel aging and fat quality defects like creaming and flavor deterioration may arise during storage. These problems are primarily caused by thermostable enzymes produced by psychrotrophic bacteria. In this study, four representative psychrotrophic bacteria strains which can produce thermostable enzymes were selected to contaminate UHT milk artificially. After 11, 11, 13, and 17 weeks of storage, the milk samples, which were contaminated with Pseudomonas fluorescens, Chryseobacterium carnipullorum, Lactococcus raffinolactis and Acinetobacter guillouiae, respectively, demonstrated notable whey separation. The investigation included analyzing the protein and fat content in the upper and bottom layers of the milk, as well as examining the particle size, Zeta potential, and pH in four sample groups, indicating that the stability of UHT milk decreases over time. Moreover, the spoiled milk samples exhibited a bitter taste, with the dominant odor being attributed to ketones and acids. The metabolomics analysis revealed that three key metabolic pathways, namely ABC transporters, butanoate metabolism, and alanine, aspartate, and glutamate metabolism, were found to be involved in the production of thermostable enzymes by psychrotrophic bacteria. These enzymes greatly impact the taste and nutrient content of UHT milk. This finding provides a theoretical basis for further investigation into the mechanism of spoilage.
Keywords: psychrotrophic bacteria; UHT milk; thermostable enzymes; quality psychrotrophic bacteria; UHT milk; thermostable enzymes; quality
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MDPI and ACS Style

Qin, X.; Cheng, J.; Qi, X.; Guan, N.; Chen, Q.; Pei, X.; Jiang, Y.; Yang, X.; Man, C. Effect of Thermostable Enzymes Produced by Psychrotrophic Bacteria in Raw Milk on the Quality of Ultra-High Temperature Sterilized Milk. Foods 2023, 12, 3752. https://doi.org/10.3390/foods12203752

AMA Style

Qin X, Cheng J, Qi X, Guan N, Chen Q, Pei X, Jiang Y, Yang X, Man C. Effect of Thermostable Enzymes Produced by Psychrotrophic Bacteria in Raw Milk on the Quality of Ultra-High Temperature Sterilized Milk. Foods. 2023; 12(20):3752. https://doi.org/10.3390/foods12203752

Chicago/Turabian Style

Qin, Xue, Jingqi Cheng, Xuehe Qi, Ning Guan, Qing Chen, Xiaoyan Pei, Yujun Jiang, Xinyan Yang, and Chaoxin Man. 2023. "Effect of Thermostable Enzymes Produced by Psychrotrophic Bacteria in Raw Milk on the Quality of Ultra-High Temperature Sterilized Milk" Foods 12, no. 20: 3752. https://doi.org/10.3390/foods12203752

APA Style

Qin, X., Cheng, J., Qi, X., Guan, N., Chen, Q., Pei, X., Jiang, Y., Yang, X., & Man, C. (2023). Effect of Thermostable Enzymes Produced by Psychrotrophic Bacteria in Raw Milk on the Quality of Ultra-High Temperature Sterilized Milk. Foods, 12(20), 3752. https://doi.org/10.3390/foods12203752

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