Some Amino Acids, Peptides and Amines in Milk, Concentrated Milks and Cheese

The Amino Acid Composition of the Proteins of Cow's Milk and of Cheddar CheeseThe importance of milk and cheese proteins as sources for amino acids in the American diet warrants investigation on the effects of preparation and of storage on these food proteins (4).Hodson and Krueger (10) have determined the essential amino acid content of casein and of fresh, dried and evaporated cow's milk.They also studied the changes which these amino acids undergo on prolonged storage of dry skimmilk (11).The first portion of this paper describes the essential amino acid composition of the proteins of cheddar cheese, dried skimmilk and of both freshly prepared and stored evaporated milk. EXPERIIV~ENTAL -The proteins from commercial samples of spray-dried milk, evaporated milk and cheddar cheese were isolated after precipitation with trichloracetic acid and analyzed for nitrogen, amino nitrogen and amino acids by the methods previously described (3, 5).Whenever two or more proteins were to be compared, the analyses were carried out simultaneously. RESULTSThe analytical results are given in table 1 together with comparable data from the publications of Hodson and Krueger (10,11).It appears that in spite of the different kinds of milk used or the length of the curing period, the amino acid patterns of the proteins of raw milk cheddar cheese cured 90 days and pasteurized milk cheddar cheese, fresh or cured, are essentially the same and similar to casein.Likewise, the amino acid content of the proteins of spraydried milk, evaporated milk and fresh milk do not appear to be significantly different.Storage of the evaporated milk 2 for 6 too.under the conditions ree-Received for publication July 2, 1950. 1 These investigations were aided in part by grants from the American Dairy Association, Chicago, and from The Borden Co., New York City.Hodson (12) has compared the amounts of seventeen amino acids in evaporated milk, freshly prepared and stored for 5 yr.Of these amino acids, significant losses were observed for only lysine (17 per eent), histidine (17 per cent) and arginine (11 per cent).The customary storage period is less than 15 mos., yet even during this period the losses of the basic amino acids were net greater than 4 per cent in any case.1