Physicochemical Screening of Lactobacillus plantarum and its Effects on the Fermentation of Panicum maximum Grass for Silage Production

In this study, 20 different isolates of lactic acid bacteria (LAB) were physicochemically screened for the ability to grow at low pH and produce lactic acid. The best isolates were selected for fermentation of Panicum maximum in order to produce silage. The grass was harvested at 6 weeks re-growth and ensiled at 15, 30, 45 and 60 days. Samples were taken on each of these days for microbial changes, physical and chemical composition and acceptability by ruminants. Afterwards, silage was exposed to air at 45 and 60 days of ensiling and its effects on microbial succession were determined. Lactobacillus plantarum produced the highest concentration of lactic acid (18.72) in MRS broth and has the highest optical density of 0.949 when grown at pH 2 was selected. The LAB count in the inoculated silage increased to 10.26 log cfu/g on day 45 and 10.87 cfu/g on day 60 compared to an increase of 8.46 log cfu/g and 7.48 log cfu/g respectively on the same day for the uninoculated silage. Spoilage organisms like yeast decreased to 2.94 log cfu/g and 2.97 log cfu/g on days 45 and 60 respectively in the inoculated silage. The pH of the inoculated silage decreased to 3.97 within the first 30 days of ensiling and the crude protein content increased to 9.84 by the end of day 60. The NDF content of the inoculated silage also decreased to 55.00 on day 15 while that of the control had a value of 63.00 on this same day. When exposed to air on day 45, the inoculated silage was less stable having an increase of spoilage bacteria like mould from 2.04 log cfu/g on day 1 to 3.97 log cfu/g by day 2. The uninoculated silage was more preferred with coefficient of preference value of 1.04, 1.16 and 1.21 on days 15, 30 and 60 respectively. Therefore silage inoculation with L. plantarum can improve the fermentation process of silage but not aerobic stability of the silage.