Stability of butter oils

ABSTRACT STABILITY OF BUTTER OILS ÖZBAYRAM, Oya M.Sc. in Food Engineering Supervisor: Assoc. Prof.Dr. Ahmet KAYA August 2000, 65 pages The physical and chemical characteristics and thermal stability of butter oils produced from sheep's and cow's milk by using different production methods were studied. Thermal stability of samples was estimated by using Accelerated Shelf-life Testing Method. Results were compared for sheep's butter oils produced from (i) pasteurized and nonpasteurized milk, (ii) pasteurized milk and sweet yogurt and (iii) sweet and sour yogurt, and for cow's butter oils produced from (i) pasteurized milk and sweet yogurt, (ii) sweet and sour yogurt, and(iii) sweet yogurt using 3 and 6 h of melting. Samples were stored at 60, 70 and 80°C in the dark and the reaction was monitored by measuring peroxide, thiobarbituric acid and free fatty acid values. The peroxide. and thiobarbituric acid values increased as the temperature increased. The increase of the acid value of all samples was not significant. A slight increase in free fatty acid value showed that hydrolytic reaction was not responsible for the deterioration of butter oil samples in thermal stability studies. Oxidative changes compared to hydrolytic changes was of greater significance in thermal stability of butter oil samples. Thermal stability was highest in butter oil produced from sweet yogurt (27.0 days at 60°C) using sheep's milk. Butter oil produced from sweet yogurt using 6 h of melting time had higher thermal stability (37. 1 days at 60°C) when it was compared to the other butter oils prepared from cow's milk. Butter oil produced from cow's milk had higherthermal stability than that sheep's milk. Thermal stabilities were highest in butter oils produced in November and December. Activation energies were estimated from PV data using Arrhenius equation. Keywords: butter oil, thermal stability, accelerated shelf-life testing, peroxide value, thiobarbituric acid value, free fatty acid value. m