Investigation of organic bases in the specific odour of casein and coprecipitate during storage

Casein and coprecipitate (milk protein concentrate) are rational to use in food technology. In that case sensory properties of milk protein concentrates are very important. During storage of casein and coprecipitate a specific unpleasant odour is developed and accumulated. This fact restricts an application of milk proteins in food. Development of off‐flavour are explained earlier by increasing of carbonyl compounds being produced during oxidative destruction of lipids and Maillard reaction. In 1976 we began to search milk protein off‐flavours. It was found that the cause of the development of off‐flavours during 3, 6 and 12‐months of storage is connected with the volatile organic bases. GC‐fractions with typical off‐flavours were described by retention indices. 43 organic bases were identified. It was found that pyrazines are accumulated in casein and pyridines in coprecipitate. Nutritional value of protein in 12‐month stored casein is reduced on 16% and for 12‐month stored coprecipitates on 46% (using test‐culture Tetrahymena Pyriformis W.). At the same time insignificant changes in amino‐acid compositions were observed. The reasons of decrease nutritional value of milk proteins are discussed.