Effect of Phospholipids and Unsaponifiable Matter on Oxidative Stability of Milk Fat

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Abstract
Stability of milk fat samples prepared by different methods was measured by determining the length of the induction period at 80[plus or minus] 0.5[degree] C. Fat extracted from cream or buttermilk with a 2:3 ether-pentane mixture had greater stability than churned fat. This was attributed to synergism between phospholipids and other antioxidants or synergists extracted from membrane material and plasma and was confirmed by the stabilizing effects of adding different levels of phospholipids and/ or unsaponifiable matter to churned fat. Churned fat contained no phospholipids. Unsaponifiable matter (free of acid) alone, added to churned and extracted fats, increased fat stability. Among the known constituents of the unsaponifiable matter, beta-carotene acted as a prooxidant, and cholesterol had no significant effect. Alpha-tocopherol was the only unsaponifiable matter constituent tested that acted synergistically with phospholipids in stabilizing churned fat. However, differences in the amounts of tocopherol could not entirely account for the differences in stability among different extracted fats. Oxidative deterioration was detected organoleptically in churned fat before the end of the induction period and at peroxide values less than 1.00.