Effects of long-term deep-freeze storage on the condition of the fat in raw sheep's milk

Abstract

SummaryEffects of long-term deep-freeze storage on the stability of fat in raw sheep's milk were assessed by measuring free fatty acid (FFA) concentrations, lipoprotein lipase activity and the amount of solvent-extractable fat. Portions of milk from three herds were frozen and stored at – 12, – 20 and – 27 °C. There was a gradual increase in FFA during 6 months storage, the rate of lipolysis being affected by storage temperature and differences between herds. After 6 months storage the residual lipase activity was only 2% (– 12 °C), 11% (– 20 °C) and 24% (– 27 °C) of the initial activity in fresh milk. The potential for lipolysis in the stored samples, after they were removed from storage and allowed to thaw to 4 °C, gradually fell as storage time was prolonged. This may be due to the loss of lipase activity.