Determination of the Optimum Inoculum Concentration and Fermentation Period and their Effect on Nutrient Composition of Brewers’ Dried Grains.

Abstract

Brewers dried grains (BDG) a by-product of fermentation, was procured dried and subjected to a second stage fermentation using rumen liquor as inoculums. Five different concentrations of substrate (BDG) to inoculums ratios (10:1, 10:2, 10:3, 10:4, and 10:5 (w/w)) were used. The five inoculated samples were subjected to four periods of fermentation (2, 4, 6 and 8 days). Twenty (20) bottles of equal volume were arranged in five (5) sets (4-bottles each). The five sets of bottle were used to carry the same inoculated BDG sample. The four bottles of each set of the 5-inoculated BDG samples were buried under soil to maintain anaerobic condition and fermented for between 2 to 8 days. The refermented BDG samples were subjected to analyses for proximate nutrient composition and laboratory bacteria population count. The rumen liquor was microscopically examined for bacteria organism. Results in terms of dry matter (DM) percentage showed all BDG samples with substrate to inoculum concentration of 10:1. 10:2, 10:3 and 10:4 to be similar (P>0.05). The fermentation of all BDG samples generally resulted in increased crude protein (CP) and decreased crude fibre contents. The BDG sample on 2-day fermentation and 10:2 inoculum concentrations resulted in the highest crude protein. While the sample on 8 day fermentation with 10:4 concentration was least in CP content. The CP content of BDG samples on 2, 6, and 8 day fermentation did not differ significantly (P>0.05). The CP content of sample on 4 day fermentation was statistically similar (P>0.05) to those on 2 and 8 days fermentation but significantly lower (P<0.05) than those on 6-day fermentation. The crude fibre (CF) decreased from 37.90% to 14.16% on fermentation. BDG sample on 10:1 was significantly lower (P<0.05) compared to those on 10:2, 10:3 and 10:4 treatments. The ash content of samples on 10:2, 10:2, 10:3 and 10:4 were similar but significantly lower (P<0.05) than those on 10:5 fermentation. There were no definite trends observed in the bacteria population between samples in the different periods of fermentation. Rumen liquor contained Streptococcus bovis and Ruminococcus albus on microscopic observation. Second stage fermentation of BDG resulted in increased CP and decreased CF composition. For higher CP content, the optimum period of fermentation between 2, 4, 6 and 8 day is 2-day and the best substrate to inoculum ratio is 10:2.