Evaluation of whisky distillery by-products. VI. The reduction in digestibility of malt distiller's grains by fatty acids and the interaction with calcium and other reversal agents.

In vitro methods have been used to study the inhibitory effects of fat and fatty acids which reduce the digestibility of malt distiller's grains (MDG). Glycerol and individual fatty acids below C8 in the homologous series do not produce any measurable decrease in digestibility. Capric acid lowers digestibility appreciably and the depression is even greater with lauric acid. Myristic, palmitic and stearic acids are less active than lauric and the greatest depressions were recorded with the unsaturated acids which showed greater activity with increasing unsaturation. Calcium salts produced partial reversal of digestibility in the presence of saturated acids above C10 and substantially greater reversal with the C18 unsaturated acids. The reduction in digestibility of MDG and in steam volatile acid production in the digesta by the presence of native fat may be attributed to the high content of oleic and linoleic acids which can also account for the marked reversal of effects by calcium. Alkaline earth metals and iron were examined for reversibility but only calcium produced consistent effects. Addition of ergocalciferol produced reversal effects similar to calcium. The reversal by calcium was evident when the calcium was added to the digesta up to 8 h after the commencement of incubation which indicates that the fatty acids have a bacteriostatic effect. In in vivo digestibility trials sheep consumed increasing amounts of dried MDG when the level of calcium supplementation was increased. Rations containing fat levels similar to that of MDG should be supplemented with calcium at levels higher than normal requirements of the element.