Raw milk is an example of an environment that contains a diverse and complex microbial population (Quigley et al., 2011 Vacheyrou et al., 2011). Many microbial communities are complex that is, they are comprised of many different taxonomical groups of microorganisms. Methods employed to determine the microbial composition of milk The potential sources of the microorganisms that are present in raw milk and the role/significance that some of these have when present in milk. It also addresses their sources, their subsequent significance with respect to industrial applications and the contribution of specific populations to food quality and health. This review will highlight the various microbial populations found in raw milk and the methods employed for their detection. In contrast, it is claimed that other raw milk microorganisms can contribute to health by aiding digestion or by reducing the frequency of allergies, including asthma and atopic diseases, in individuals who consume raw milk during the early years of life (Debarry et al., 2007 Braun-Fahrländer & Von Mutius, 2011). The microbial composition of milk can also have health-related implications in that the consumption of raw milk contaminated with pathogens can lead to, in some cases, severe illness (Oliver et al., 2009). Microorganisms can also negatively impact on milk quality and shelf life for example, psychrotolerant bacteria can proliferate during refrigeration and, through the production of extracellular lipases and proteases, result in spoilage (Desmasures & Gueguen, 1997 Hantsis-Zacharov & Halpern, 2007). Microorganisms can bring about the fermentation of milk through the production of lactate and have a variety of different impacts on the sensory, texture, flavour and organoleptic properties of resultant products (Wouters et al., 2002). The specific composition of the milk microbiota directly impacts on the subsequent development of dairy products (Fig. Human milk on the other hand is typically dominated by Streptococcus, Staphylococcus, Lactobacillus and Bifidobacterium spp. Other strains of non-LAB genera are also encountered in milk, as well as various yeasts and moulds (Quigley et al., 2011). Psychrotrophic populations, which particularly establish themselves during cold storage, are also a major component and frequently include Pseudomonas and Acinetobacter spp. The most common LAB genera in milk include Lactococcus, Lactobacillus, Leuconostoc, Streptococcus and Enterococcus. It is generally accepted that the lactic acid bacteria (LAB), a group of bacteria that ferment lactose to lactate, are a dominant population in bovine, goat, sheep and buffalo milk, prior to pasteurisation. Some of these nutrients are directly available to all microorganisms, while others are provided following the metabolism of major components by specific populations to release components and metabolites that are used by others (Frank, 1997). However, the high nutrient content of these milks, which includes proteins, fats, carbohydrates, vitamins, minerals and essential amino acids (Supporting information, Table S1), all at a near neutral pH and at a high water activity, provides an ideal environment for the growth of many microorganisms. Milk is a highly nutritious food that can be obtained from a variety of animal sources such as cows, goats, sheep and buffalo, as well as humans, for human consumption. Here, we comprehensively review these topics, while comparing the approaches, both culture-dependent and culture-independent, which can be taken to investigate the microbial composition of milk.ĭairy, spoilage, safety, health, probiotic, milkborne pathogens Introduction There is also concern that the presence of antibiotic residues in milk leads to the development of resistance, particularly among pathogenic bacteria. Listeria, Salmonella, Escherichia coli, Campylobacter and mycotoxin-producing fungi). lactobacilli and bifidobacteria) or causing disease (e.g. Pseudomonas, Clostridium, Bacillus and other spore-forming or thermoduric microorganisms), promoting health (e.g. Lactococcus, Lactobacillus, Streptococcus, Propionibacterium and fungal populations), causing spoilage (e.g. These microorganisms enter milk from a variety of sources and, once in milk, can play a number of roles, such as facilitating dairy fermentations (e.g. Milk, due to its high nutritional content, can support a rich microbiota. Here, we review what is known about the microorganisms present in raw milk, including milk from cows, sheep, goats and humans.
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