Effects of cell wall phenolics and fungal metabolites on methane and acetate production under in vitro rumen conditions.

Abstract

The effects of cell wall phenolics, lignins and fungal metabolites on end products of simulated rumen fermentations were studied. Monomeric phenolics, selected to represent the products of aerobic oxidation of lignin by fungi, slightly enhanced carbon dioxide output at low concentrations (0.05%) but had no stimulatory effect on acetate production. Higher concentrations (0.5%) of industrial and Klason lignin decreased carbon dioxide, methane, acetate and propionate production. Secondary metabolites from toxigenic strains of Aspergillus flavus, which were used to simulate the presence of contaminated feedstuff arising from non-sterile fungal bioconversion systems (fermentations), stimulated carbon dioxide, methane, acetate and propionate production but not when extracts were boiled or autoclaved. Acetate, propionate, methane and carbon dioxide production were only slightly reduced in the presence of purified aflatoxin. With spruce sawdusts pretreated with fungi, it was found that accumulation of soluble compounds from lignin and polysaccharide depolymerisations in rumen simulations were markedly higher with sawdusts pretreated with fungi under non-sterile conditions. It was concluded that fungal pretreatment of lignocellulosic substrates had no adverse effects on the end products of rumen fermentations.