{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,29]],"date-time":"2026-10-29T18:53:49Z","timestamp":1793300029869,"version":"4.5.0"},"reference-count":44,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2023,10,12]],"date-time":"2023-10-12T00:00:00Z","timestamp":1697068800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Center of Technology Innovation for Dairy (2021-National Center of Technology Innovation for Dairy-11)","award":["LBH-Z22081"],"award-info":[{"award-number":["LBH-Z22081"]}]},{"name":"Postdoctoral Project of Heilongjiang Province","award":["LBH-Z22081"],"award-info":[{"award-number":["LBH-Z22081"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Foods"],"abstract":"<jats:p>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.<\/jats:p>","DOI":"10.3390\/foods12203752","type":"journal-article","created":{"date-parts":[[2023,10,12]],"date-time":"2023-10-12T07:28:44Z","timestamp":1697095724000},"page":"3752","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":32,"title":["Effect of Thermostable Enzymes Produced by Psychrotrophic Bacteria in Raw Milk on the Quality of Ultra-High Temperature Sterilized Milk"],"prefix":"10.3390","volume":"12","author":[{"given":"Xue","family":"Qin","sequence":"first","affiliation":[{"name":"Key Laboratory of Dairy Science, Ministry of Education, College of Food Science and Engineering, Northeast Agricultural University, Harbin 150030, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jingqi","family":"Cheng","sequence":"additional","affiliation":[{"name":"Key Laboratory of Dairy Science, Ministry of Education, College of Food Science and Engineering, Northeast Agricultural University, Harbin 150030, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xuehe","family":"Qi","sequence":"additional","affiliation":[{"name":"Key Laboratory of Dairy Science, Ministry of Education, College of Food Science and Engineering, Northeast Agricultural University, Harbin 150030, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ning","family":"Guan","sequence":"additional","affiliation":[{"name":"Center for Dairy Safety and Quality, National Center of Technology Innovation for Dairy, No. 1 Jinshan Road, Jinshan Development Zone, Hohhot 010110, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Qing","family":"Chen","sequence":"additional","affiliation":[{"name":"Key Laboratory of Dairy Science, Ministry of Education, College of Food Science and Engineering, Northeast Agricultural University, Harbin 150030, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xiaoyan","family":"Pei","sequence":"additional","affiliation":[{"name":"Risk Assessment Department, Inner Mongolia Yili Industrial Group Co., Ltd., No. 1 Jinshan Road, Jinshan Development Zone, Hohhot 010110, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yujun","family":"Jiang","sequence":"additional","affiliation":[{"name":"Key Laboratory of Dairy Science, Ministry of Education, College of Food Science and Engineering, Northeast Agricultural University, Harbin 150030, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xinyan","family":"Yang","sequence":"additional","affiliation":[{"name":"Key Laboratory of Dairy Science, Ministry of Education, College of Food Science and Engineering, Northeast Agricultural University, Harbin 150030, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chaoxin","family":"Man","sequence":"additional","affiliation":[{"name":"Key Laboratory of Dairy Science, Ministry of Education, College of Food Science and Engineering, Northeast Agricultural University, Harbin 150030, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,10,12]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"413","DOI":"10.1007\/s13594-011-0019-4","article-title":"Proteolysis of casein micelles by Pseudomonas fluorescens CNRZ 798 contributes to the destabilisation of UHT milk during its storage","volume":"91","author":"Gaucher","year":"2011","journal-title":"Dairy Sci. 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