Properties and stability of butter oil obtained from milk and yoghurt.

The physical and chemical characteristics and thermal stability of butter oil produced from cow's milk by two different methods were studied. Butter oil samples from cow's milk were made (i) directly from milk and (ii) from yoghurt. Samples were autoxidized at 60, 70 and 80 degrees C in the dark and the reaction monitored by peroxide, thiobarbituric acid and free fatty acid values. Peroxide and thiobarbituric acid values increased as the temperature increased. The increase of the acid value was not significant. The thermal stability was highest in butter oil produced from yoghurt. Oxidative changes compared to hydrolytic changes are of greater significance in the thermal stability of butter oil samples. Arrhenius parameters and activation energies were calculated for the peroxide value data. The percent loss of linolenic acid was about 3 times faster than that of linoleic acid.