Effects of rumen bacterial lipases on ruminal lipid metabolism

Abstract

With the world population set to increase to 9.6 billion in 2050 and increasing fatty food related diseases, it is paramount that a secure and nutritious food supply is available.
Despite the ruminant diet being rich in polyunsaturated fats (PUFA), ruminant products are high in saturated fat (SFA). This is due to lipolysis and subsequent biohydrogenation of PUFA in the rumen. Bacteria may biohydrogenate PUFA due to the toxicity of its double bonds upon incorporation into the bacterial membrane, so it is feasible that biohydrogenation could be inhibited using high concentrations of PUFA.
To test this hypothesis, a batch culture experiment was undertaken using 50% buffered rumen fluid and linoleic (LA) or linolenic acid (LNA) at 50μM, 250μM, 500μM, 750μM or 1mM. Lipids were extracted and analysed using FAME and gas chromatography. Total lipid profiles showed a decrease in 18:0 over 24 hours (250μM LNA) and at 4 hours reduced by 11.5% (250μM LA) and 16.7% (250μM LNA). Overall, data indicates that it is possible to inhibit biohydrogenation using PUFA to an extent, implying that lipolysis may be a suitable control point.
Another batch experiment was performed using increasing concentrations of the A1 phospholipase from Thermomyceslanuginosus(75 μM, 100 μM, 125 μM and 150 μM) with 50% buffered rumen fluid and phospholipid extract. Lipids were extracted and analysed using TLC (thin layer chromatography) and FAME (fatty acid methyl esters). There were slight decreases in C18 content (8.9%) suggesting partial inhibition of biohydrogenation.
Decreases in LNA (up to 25%), LA and C16 with in the polar lipid fraction following addition of 100, 125 and 150 μM concentrations of phospholipase A1, and particularly after 24h of incubation suggesting lipolysis was enhanced. In terms of biohydrogenation analysis of the fatty acids within the free fatty acid fraction showed that after addition of all concentrations of A1 phospholipase there were decreases in C18 content (8.9%) suggesting partial inhibition of biohydrogenation. Inhibition was achieved at a specific point resulting in an accumulation of the intermediate 18:1, trans-11 (up to 25% of total lipids) which is beneficial as it can be converted by Δ9-transferase in the bovine mammary gland to CLA, which is a human health beneficial fatty acid.
Whilst lipolysis enhancement shows potential, it is clear even higher concentrations of phospholipase are necessary to successfully inhibit biohydrogenation; the practicalities of which are questionable. Further research into lipolysis as a control point for biohydrogenation is also necessary, as well as into lipolytic bacteria and their lipases

Date of Award	2014
Original language	English
Awarding Institution	Aberystwyth University
Sponsors	Knowledge Economy Skills Scholarships & Hybu Cig Cymru | Meat Promotion Wales
Supervisor	Sharon Huws (Supervisor)