A study of the component glycerides of cow and buffalo milk fats with reference to the possible mechanism of their production during lactation

Abstract

Abstract The component glycerides of a cow and a buffalo milk fat have been studied quantitatively after resolving them by intensive crystallization from acetone or ether at temperatures between — 50 and 0°C into groups of glycerides which, although still complicated in fatty acid composition, contain much simplified mixtures of mixed glycerides as compared with the original fats. From the component acids of each separated glyceride group and of the trisaturated glycerides present therein, it has been possible to produce an approximately quantitative statement of the many individual mixed glycerides present in the original fats, and a more closely quantitative statement of the various glyceride categories (trisaturated, mono- or di-unsaturated, mono- or di-palmito, mono- or di-oleo, etc.) present. The bearing of the data so obtained on the question of the mechanism of the production of the characteristic short-chain acyl glycerides of ruminant milk fats is discussed. Evidence is collected which favours the view that the main source of milk fats is glycerides in the blood entering the lactating gland, the oleo- (or other unsaturated) groups in which are transformed in greater or less degree into acyl groups with shorter carbon chains (down to butyric, C4). It is shown that the alternative hypothesis of direct synthesis in the mammary gland of short-chain glycerides from carbohydrate or acetate is inconsistent with the quantitative com­position of the component acids of milk fats of a range of non-ruminant as well as ruminant mammals. On the other hand, it is considered that the maximal production of short-chain acyl glycerides observed in milk fats of the ruminant animals is clearly connected with the presence of unusual amounts of acetic and associated lower fatty acids in their blood, and that this causes conditions (pH range or other factor) in the lactating gland which favour the action of the enzyme system responsible for the conversion of oleo- into short-chain glycerides.