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Journal of Zhejiang University-SCIENCE B

, Volume 19, Issue 8, pp 630–642 | Cite as

Spoilage potential of psychrotrophic bacteria isolated from raw milk and the thermo-stability of their enzymes

  • Lei Yuan
  • Faizan A. Sadiq
  • Tong-jie Liu
  • Yang Li
  • Jing-si Gu
  • Huan-yi Yang
  • Guo-qing He
Article

Abstract

The storage and transportation of raw milk at low temperatures promote the growth of psychrotrophic bacteria and the production of thermo-stable enzymes, which pose great threats to the quality and shelf-life of dairy products. Though many studies have been carried out on the spoilage potential of psychrotrophic bacteria and the thermo-stabilities of the enzymes they produce, further detailed studies are needed to devise an effective strategy to avoid dairy spoilage. The purpose of this study was to explore the spoilage potential of psychrotrophic bacteria from Chinese raw milk samples at both room temperature (28 °C) and refrigerated temperature (7 °C). Species of Yersinia, Pseudomonas, Serratia, and Chryseobacterium showed high proteolytic activity. The highest proteolytic activity was shown by Yersinia intermedia followed by Pseudomonas fluorescens (d). Lipolytic activity was high in isolates of Acinetobacter, and the highest in Acinetobacter guillouiae. Certain isolates showed positive β-galactosidase and phospholipase activity. Strains belonging to the same species sometimes showed markedly different phenotypic characteristics. Proteases and lipases produced by psychrotrophic bacteria retained activity after heat treatment at 70, 80, or 90 °C, and proteases appeared to be more heat-stable than lipases. For these reasons, thermo-stable spoilage enzymes produced by a high number of psychrotrophic bacterial isolates from raw milk are of major concern to the dairy industry. The results of this study provide valuable data about the spoilage potential of bacterial strains in raw milk and the thermal resistance of the enzymes they produce.

Key words

Spoilage enzyme Psychrotrophic bacteria Raw milk Thermo-stability 

原料奶中嗜冷菌产腐败酶的能力及腐败酶的热稳定性研究

中文概要

目的

探究从原料奶样品中分离到的480 株嗜冷菌(鉴定为24 个属、74 个种,并根据随机扩增多态性DNA(RAPD)图谱特征聚类为85 组)在室温和低温下产腐败酶的能力,以及这些腐败酶的耐热性。

创新点

系统地分析和比较不同种类的嗜冷菌在室温和低温下产腐败酶的能力,并探究这些腐败酶的耐热性,为控制乳制品和其它低温储藏食品的腐败变质提供理论基础。

方法

采用不同的筛选培养基评估480 株嗜冷菌在室温(28 °C)和低温(7 °C)产蛋白酶、脂肪酶、磷脂酶及β-半乳糖苷酶的能力;根据初筛的结果分别以偶氮酪蛋白和对硝基苯酚棕榈酸酯为底物定量测定蛋白酶和脂肪酶的酶活力;挑选酶活力高的蛋白酶和脂肪酶,分别测定经70、80 和90 °C 条件下处理一段时间后的残留酶活计算出热稳定性,并根据热动力学公式计算相关的热力学参数。

结论

PseudomonasSerratiaChryseobacterium 产蛋白酶的能力强,而Yersinia intermedia 产蛋白酶的活力最高;Acinetobacter 产脂肪酶的能力强,其中Acinetobacter guillouiae 产脂肪酶的活力最高;而一些特定的属能产生β-半乳糖苷酶及磷脂酶。细菌产腐败酶的能力在种水平上表现出差异性(如Pseudomonas fluorescensPseudomonas fragi)。大量的蛋白酶及脂肪酶即使经高温热处理后仍有酶活残留,且所得的热灭活动力学的参数证实这些腐败酶经常规方法灭菌后仍对乳制品的品质及货架期有潜在的危害。

关键词

腐败酶 嗜冷菌 原料奶 热稳定性 

CLC number

TS201.3 

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Copyright information

© Zhejiang University and Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.College of Biosystems Engineering and Food ScienceZhejiang UniversityHangzhouChina

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