343. Studies of the Biological Value of the Proteins (Nitrogen) of Dried Skim Milk: Value As An Addition to Bread; Tests With Young and Olderrats; Effects of Storage

Abstract

1. A sample of roller-dried skim-milk powder, found to possess the very low biological value of 55.2, supplemented slightly but definitely the proteins of national wheatmeal bread when it supplied 23% of the total nitrogen. No such effect was observed with another sample of milk with a biological value of 71.1 when it supplied 17 % of the total nitrogen, or with a further sample of milk with a biological value of 81.3 when added to bread at a 6 % level supplying about 15 % of the total nitrogen. On the first two occasions the biological value for two different samples of national wheatmeal bread was 48.9 and 55.0 respectively for young rats; for the same rats when mature the values were 55.8 and 64.6. No differences attributable to age were found with milk. Baking did not affect the biological value of the proteins of the milk added to the flour.2. The biological value of a sample of spray.dried skim milk declined from a value of 88.5, observed 18 months after manufacture, to 71.1 some 36 months later. The true digestibility remained unchanged.3. Commercial samples of spray.dried and roller.dried skim milk of good quality, and of over.neutralized and overheated roller.dried skim milk, yielded biological values of 78.6, 80.9, 78.2 and 76.2 respectively and true digestibilities of 90.5, 90.1, 89.4 and 88.8 respectively.