Studies on rumen metabolism. IX. Contribution of plant lipases to the release of free fatty acids in the rumen

Abstract

Therole of plant lipases in the hydrolysis of dietary lipids in the rumen of pasturefed ruminants has been investigated by means of in vitro and in vivo experiments with rumen contents. Lipases present in the leaves of numerous pasture plants remained highly active for at least 5 h in the presence of metabolising rumen microorganisms, leading to the hydrolysis of triglyceride. Parallel experiments showed that the lipase activity of actively metabolising micro-organisms in rumen fluid was very low. A slight increase in lipolytic activity attributable to micro-organisms occurred after incubations of about 4 h with plant extract when the metabolic activity of the microbial population had passed its peak.In vivo experiments showed that the lipolytic activity of rumen fluid, obtained 0.5 to 5.0 h after feeding fresh grass, was about twice that of rumen fluid obtained after overnight fasting. Paired feeding experiments showed that lipase activity was higher in rumen fluid obtained from a pasture-fed, than from a hay-fed animal. Nevertheless, there was appreciable activity in the rumen contents obtained from the hay-fed twin, which is consistent with the presence of lipase activity in the extracts of dried grass.Multiple forms of plant esterases and phosphatases were present in the soluble fraction of rumen fluid several hours after feeding.It is concluded that the rapid release of free fatty acids which follows the ingestion of pasture is due mainly to the activity of plant enzymes and that rumen microorganisms have a subsidary role in hydrolysing ingested lipid.

The Rumen Microbial Ecosystem

“…Free fatty acids produced were rapidly hydrogenated, and at no stage in the hydrolysis of triglyceride was any mono-or diglyceride detected (Garton et aI., 1959(Garton et aI., , 1961. In contrast to the results of Faruque et al (1974), suggesting that the lipolysis of triglycerides and galactolipids in pasture-fed cows was due mainly to the activity of endogenous plant enzymes, it was concluded that the enzymes of rumen microorganisms are largely responsible for the degradation of plant lipids in the rumen . In view of the quantitative importance of galactolipids in the ruminant diet, it is surprising that the catabolic pathway for these lipids in the rumen was not established until somewhat later.…”

BOARD-INVITED REVIEW: Recent advances in biohydrogenation of unsaturated fatty acids within the rumen microbial ecosystem1

“…However, Faruque et al (1974) suggested that the hydrolysis of triglycerides and galactolipids from grass was due primarily to plant enzyme activity. Dawson et al (1977) autoclaved 14 C-labeled grass to inactivate plant lipolytic enzymes.…”

The role of microbes in rumen lipolysis and biohydrogenation and their manipulation

“…Forage plant tissues are rich in galacto-and phospholipases. These lipases remain active once ingested into the rumen for up to 5 h, suggesting that the plant material itself may contribute to ruminal lipolysis in grazing animals (Omar Faruque et al, 1974). Dawson et al (1977) challenged this idea and concluded that microbial lipases were more important than plant enzymes.…”