Development of microbial inocula for silage fermentations

Silage is the product formed by the fermentation process that occurs when grass is stored anaerobically. Microbial silage inoculants are often added to grass at ensiling in order to improve the silage fermentation. Inoculants normally contain strains of homofermentative lactic acid bacteria. In order to be effective 10 6 viable microorganisms must be added per gram grass ensiled. Literature reports have shown that there are a number of shortcomings associated with inoculants most notably a lack of viability and long lag phases. Therefore, the objective of the research was to improve the quality of silage inoculants. It was hoped to achieve this using Immobilised Cell Technology. Various Pediococci were selected by virtue of their capability to grow in and reduce the pH value of MRS broth. These strains were compared with microorganisms isolated from a commercial inoculant. The strains differed in their ability to reduce the pH value of MRS broth. These strains were compared with microorganisms isolated from a commercial inoculant. The strains differed in their ability to reduce the pH of MRS broth. They had variation in the length of their lag phases and their ability to grow at various temperatures. The ability of strains to inhibit organisms detrimental to silage was tested. Many strains were capable of non-specifically antagonising Clostridia spp., Bacillus cereus and Listeria monocytogenes. Selected strains were immobilised in Ca-alginate beads before freeze-drying. Survival rates for free and immobilised cells were compared. Lag phases and the acid producing capabilities of free and immobilized cells were investigated. In most instances, immobilization had not significant protective effect during freeze-drying or subsequent storage. Italian rye grass was inoculated with either a free or an immobilised inoculum. Mini-silos were setup and the fermentation monitored over a 60-day period. Aerobic stability of the silage was investigated. A more rapid fermentation occurred when silage was inoculated. There was no significant differences between the quality of silage inoculated with free or immobilized cells. Inoculation resulted in the production of higher quality silage but reduced the aerobic stability