Causes of lumps in dairy products

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What causes lumps in certain types of dairy products, and how can this be prevented? Milk is a very complex food with over 100,000 different molecular species found. It is composed of approximately 87.3% water, 3.9% milk fat and 8.8% solids-not-fat.(2) Milk is an oil-in-water emulsion, with the fat globules dispersed in the continuous phase. It is a colloid suspension of casein micelles, globular proteins and lipoprotein particles, and a solution of lactose, soluble proteins, minerals, vitamins and other components.(5) Heating of milk products can cause lumps or grittiness. This is a major problem in the dairy industry as texture and flavour are major factors that influence the consumer. Heat treatment is used to greatly extend the normally short shelf life of milk products. Two major examples that display these problems are Ultra High Temperature treated milk and sweetened condensed milk. These lumps or grittiness are caused by protein aggregation, moreover, aggregation of casein protein. The casein content of milk represents about 80% of milk proteins. The principal casein fractions are alpha-s1 and alpha-s2 caseins, ßeta-casein, and kappa-casein. Most, but not all, of the casein proteins exist in a colloidal particle known as the casein micelle.(2) The exact structure of casein micelles is still under debate. Various models for casein micelle structure have been proposed. Most of the proposed models fall into three general categories, which are: coat-core, subunit (sub-micelles), and internal structure models. The coat-core model describes the micelle as an aggregate of caseins with outer layer differing in composition form the interior, and the structure of the inner part is not accurately identified. The subunit model is considered to be composed of roughly spherical uniform subunits, and the internal structure model specifys the mode of aggregation of

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