Effect of Autoxidation on the Nutritive Value of Acidulated Soybean Soapstock in Chicks

ACIDULATED soybean-oil soapstock (ASS) has recently become the main fat supplement for poultry feeds in Israel. This by-product of the edible oil industry is obtained from the alkali-neutralization of the crude oil in the form of raw soapstock (a mixture of soaps, neutral oil, water, sterols, pigments and other minor constituents). This rather unstable product is converted to acidulated soapstock by treatment with an excess of hot aqueous sulfuric acid. Most of the “impurities” which are removed from the crude oil by alkali-refining accumulate in the acidulated soapstock. Compared to crude soybean oil (CSO), ASS contains high levels of free fatty acid (over 50%), unsaponifiable matter and oxy-fatty acids (Bornstein and Lipstein, 1963), and is also rich in carotenoids (Budowski et al., 1964). Previous work of this labortory (Bornstein and Lipstein, 1961, 1963), as well as that of Sibbald et al. (1962), has shown that ASS is comparable to tallow…