Abstract
Somatic cells are an important component naturally present in milk, and somatic cell count is used as an indicator of udder health and milk quality. The role of somatic cells in dairy processes and products is ill-defined in most studies because the role of these cells combines also the concomitance of physicochemical modifications of milk, bacterial count, and the udder inflammation in the presence of high somatic cell count. The aim of this review is to focus on the role of somatic cells themselves and of endogenous enzymes from somatic cells in milk, in dairy transformation processes, and in characteristics of final products overcoming biases due to other factors. The immune function of somatic cells in the udder defense and their protective role in milk will be primarily considered. Different characteristics of milk induced by various somatic cell counts, types, and their endogenous enzymes influencing directly the technological properties of milk and the final quality of dairy products will be discussed as well. By comparing methods used in other studies and eliminating biases due to other factors not considered in these studies, a new approach has been suggested to evaluate the effective role of somatic cells on dairy processes and products. In addition, this new approach allows the characterization of somatic cells and their endogenous enzymes and, in future research, will allow the clarification of mechanisms involved in the release of these components from somatic cells during dairy processes, particularly in cheese technologies.
Highlights
Milk is known to be a high-value nutritional biological fluid composed of water, proteins, fat, sugars, minerals, etc
The amount of somatic cells (SCs), usually called somatic cell count (SCC), in milk is used as an important indicator of udder health since SCs are involved in protecting the mammary gland from infection as part of the innate immune system
This review focuses on the state of our knowledge of SCs in the dairy field and on their effective role in dairy processes and products
Summary
Milk is known to be a high-value nutritional biological fluid composed of water, proteins, fat, sugars, minerals, etc. Other important components existing naturally in raw milk are somatic cells (SCs), and the predominant cell type, besides shed epithelial cells, in most species is leucocytes, including macrophages, polymorphonuclear neutrophils cells (PMNs), and lymphocytes (Boutinaud and Jammes 2002). The amount of SCs, usually called somatic cell count (SCC), in milk is used as an important indicator of udder health since SCs are involved in protecting the mammary gland from infection as part of the innate immune system. Though SCC is subjected to variation, it is still used as an indicator of milk quality in several species, especially in ruminant and human (Hunt et al 2013; Sharma et al 2011). Taking cow milk as an example, when SCC >2×105 cells.mL−1, the udder is considered to be infected, and when SCC >4×105 cells.mL−1, the milk is deemed unfit for human consumption in the European Union (EU). For caprine and ovine milk, the cutoff value is 1×106 in the USA but is not yet defined in the EU (Council Directive 92/46/EEC 1992)
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