INFLUENCE OF PH ON LIPOLYSIS AND BIOHYDROGENATION OF SOYBEAN OIL BY RUMEN CONTENTS IN-VITRO

The effect of different pH values on rumen lipolysis and biohydrogenat ion was investigated during incubations of the rumen contents with 40 or 80 mg of soybean oil as the sole substrate. Mean pH values studied were 6.8, 6.3, 6.0, 5.6 and 5.2. Lipolysis was calculated from the dec rease in fatty acids present in triacylglycerols (TAG), as well as fro m the accumulation of free fatty acids (FFA) during the incubation. At pH less than or equal to 6.0 lipolysis was low, and the inhibition be came greater with decreasing pH. At the same pH value, the inhibition in incubations with 80 mg of soybean oil was more pronounced than with 40 mg. Even at the lowest pH value, after incubation, no free linolen ic acid could be detected because of biohydrogenation, whereas linolei c acid hydrogenation was only partially inhibited at pH 5.2. This mean s that lipolysis is much more sensitive to low pH values than biohydro genation. Literature data indicate however that, besides pH, other fac tors must be involved in the decrease of both lipolysis and biohydroge nation in the rumen of animals fed highly concentrated diets.