Machado Solimar G, Baglinière François, Marchand Sophie, Van Coillie Els, Vanetti Maria C D, De Block Jan, Heyndrickx Marc
Instituto Federal do Norte de Minas Gerais - Campus Salinas Salinas, Brazil.
Department of Microbiology, Universidade Federal de Viçosa Viçosa, Brazil.
Front Microbiol. 2017 Mar 1;8:302. doi: 10.3389/fmicb.2017.00302. eCollection 2017.
Raw bovine milk is highly nutritious as well as pH-neutral, providing the ideal conditions for microbial growth. The microbiota of raw milk is diverse and originates from several sources of contamination including the external udder surface, milking equipment, air, water, feed, grass, feces, and soil. Many bacterial and fungal species can be found in raw milk. The autochthonous microbiota of raw milk immediately after milking generally comprises lactic acid bacteria such as , , , and species, which are technologically important for the dairy industry, although they do occasionally cause spoilage of dairy products. Differences in milking practices and storage conditions on each continent, country and region result in variable microbial population structures in raw milk. Raw milk is usually stored at cold temperatures, e.g., about 4°C before processing to reduce the growth of most bacteria. However, psychrotrophic bacteria can proliferate and contribute to spoilage of ultra-high temperature (UHT) treated and sterilized milk and other dairy products with a long shelf life due to their ability to produce extracellular heat resistant enzymes such as peptidases and lipases. Worldwide, species of , with the ability to produce these spoilage enzymes, are the most common contaminants isolated from cold raw milk although other genera such as are also reported as important milk spoilers, while for others more research is needed on the heat resistance of the spoilage enzymes produced. The residual activity of extracellular enzymes after high heat treatment may lead to technological problems (off flavors, physico-chemical instability) during the shelf life of milk and dairy products. This review covers the contamination patterns of cold raw milk in several parts of the world, the growth potential of psychrotrophic bacteria, their ability to produce extracellular heat-resistant enzymes and the consequences for dairy products with a long shelf life. This problem is of increasing importance because of the large worldwide trade in fluid milk and milk powder.
生牛乳营养丰富且pH值呈中性，为微生物生长提供了理想条件。生牛乳中的微生物群落多样，其污染源有多种，包括乳房外部表面、挤奶设备、空气、水、饲料、草、粪便和土壤。生牛乳中可发现许多细菌和真菌种类。刚挤完奶时，生牛乳中的原生微生物群落通常包括乳酸菌，如 、 、 和 等菌种，这些菌种对乳制品行业具有重要技术意义，尽管它们偶尔也会导致乳制品变质。各大洲、国家和地区在挤奶方式和储存条件上的差异导致生牛乳中微生物种群结构各不相同。生牛乳通常在低温下储存，例如在加工前储存于约4°C以减少大多数细菌的生长。然而，嗜冷菌能够增殖，并会导致超高温（UHT）处理和灭菌的牛奶以及其他保质期长的乳制品变质，因为它们能够产生胞外耐热酶，如肽酶和脂肪酶。在全球范围内，能够产生这些变质酶的 菌种是从冷藏生牛乳中分离出的最常见污染物，尽管也有报道称其他属，如 也是重要的牛奶变质菌，而对于其他一些菌种，还需要对其产生的变质酶的耐热性进行更多研究。高温处理后胞外酶的残留活性可能会在牛奶和乳制品的保质期内导致技术问题（异味、物理化学不稳定）。本综述涵盖了世界上几个地区冷藏生牛乳的污染模式、嗜冷菌的生长潜力、它们产生胞外耐热酶的能力以及对保质期长的乳制品的影响。由于全球范围内液态奶和奶粉的贸易量大，这个问题变得越来越重要。
