Effects of ageing on the properties of acid casein

Acid casein is manufactured in New Zealand as a dry (100—120 g moisture kg ) granular powder which is stored in 25 kg bags until transported overseas to a customer. During the late 1970s, queries were raised concerning the suitability for industrial use of acid casein that had been stored for a number of years. Earlier reports refer mainly to the microbiological quality and the physical deterioration of the casein after up to 10 years of storage due to beetle and moth infestation and subsequent web growth. Warth (1939) noted that caseins stored up to 18 months showed no change in composition but exhibited a decrease in viscosity and glue strength that could be restored by sifting out the fine casein dust resulting from the physical deterioration of the product. Spellacy (1953) also noted that casein stored in excess of 10 years had shown very little deterioration in quality, although viscosity was somewhat reduced. In order to further the available information regarding the storage stability of acid casein, a study was initiated to monitor some properties of an acid casein (relevant to industrial casein use) during prolonged storage. Tests, on a batch manufactured in 1972, were initially conducted in 1978 and then a further seven times intermittently until the casein was 20 years old.