Lysine residues in milk proteins become "blocked" when they react with reducing sugars, particularly lactose, in the Maillard reaction. The blocked or glycated lysines reduce the biological availability of the lysine to metabolic processes and also hinder hydrolysis of the parent protein by digestive enzymes. Heating and storage of milk and milk products are the major promotants of the Maillard reaction and resulting chemical damage to the proteins. Several methods have been proposed to estimate the extent of this protein damage. Two major compounds, furosine, a product of acid hydrolysis of lactulosyl-lysine, the 1st stable product of the Maillard reaction, and carboxymethyl-lysine are used for assessing the early and advanced stages of the Maillard reaction, respectively. In addition, several methods are used for assessing the bioavailability of lysine in a protein; these include chemical, enzymic, and animal-based methods. This review discusses the Maillard reaction and its significance in milk and dairy products, methods of assessing the extent of the reaction and of the bioavailability of lysine, and the nutritional significance of blocked lysines and associated Maillard reaction products in milk proteins.

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Aim:The study was undertaken to find out the gross composition, nitrogen distribution, and selected mineral content in Surti goat milk, and its comparison was made between cow and buffalo milk.Materials and Methods:Goat milk samples of Surti breed and buffalo milk samples were collected during the period from July to January 2014 at Reproductive Biology Research Unit, Anand Agricultural University (AAU), Anand. Cow milk samples of Kankrej breed were collected from Livestock Research Station, AAU, Anand. Samples were analyzed for gross composition such as total solids (TS), fat, solid not fat (SNF), protein, lactose, and ash. Samples were also analyzed for nitrogen distribution such as total nitrogen (TN), non-casein nitrogen (NCN), non-protein nitrogen (NPN), and selected minerals content such as calcium, magnesium, phosphorous, and chloride. Total five replications were carried out.Results:Goat milk had the lowest TS, fat, protein, and lactose content among all three types of milk studied in the present investigation. On the other hand, the highest TS, fat, protein, and lactose content were found in buffalo milk. Buffalo milk had the highest SNF, calcium, magnesium, and phosphorous content, which was followed by goat milk and lowest in cow milk. The SNF, protein, TN, and calcium content of goat milk were statistically non-significant (p<0.05) with cow milk. The lactose content of goat milk was significantly lower (p>0.05) than that of the cow milk as well as buffalo milk. The goat milk had the highest ash and NCN content, which were followed by buffalo milk and lowest in cow milk. However, the differences in ash, NPN, and phosphorous content of three types of milk studied, viz., goat milk, cow milk, and buffalo milk were found statistically non-significant (p<0.05). The NCN content of buffalo milk was statistically non-significant (p<0.05) with cow milk as well as goat milk. The NCN and magnesium content of goat milk were significantly higher (p>0.05) than that of the cow milk. The magnesium content of goat milk was statistically non-significant (p<0.05) with buffalo milk. The chloride content of goat milk was significantly higher (p>0.05) than that of the buffalo milk as well as cow milk.Conclusion:It can be concluded from the study that the goat milk has lower TS, fat, lactose, protein content, TN as well as NPN but higher ash and NCN content compared to cow milk and buffalo milk. The goat milk has lower calcium, phosphorous compared to buffalo milk while it has higher calcium, phosphorous compared to cow milk, and it has higher magnesium, chloride content compared to cow milk and buffalo milk.

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