Index

With the introduction of lactic acid bacteria inoculants, the production of consistently high-quality silage has been greatly facilitated. This high-quality silage has proved to be susceptible to aerobic spoilage, which causes losses of around 5% of the final product. This work was initiated with the objective of producing a candidate for use as an inoculant capable of minimising aerobic spoilage.

Ancillary work was also conducted to ascertain the potential market for such an inoculant in England and Wales. In a survey of dairy farmers, it was found that aerobic spoilage is considered a problem by one-third of farms that currently use inoculants, suggesting that there is a definite market for an inoculant which addresses the problem.

149 LAB strains were screened for their capacity to inhibit the yeast primarily responsible for aerobic spoilage, and three strains with superior efficacy were found. They were investigated further using a variety of antifungal tests and one, Lactobacillus plantarum LPC-22, was found to have the widest and most consistent spectrum of activity. Sensitive to lipase I, it was observed against Candida holmii, Saccharomyces cerevisiae, Saccharomyces exiguus, and Acetobacter sp. Some activity was found in the sterile supernatant from LPC-22, and attempts to isolate an active agent were made using freeze drying, solvent extraction, precipitation, dialysis and ultrafiltration did not result in an active agent. Trials in laboratory scale silos proved ambiguous.

A second line of enquiry, the engineering of a currently-used inoculant to overproduce acetic acid, was also fruitless. Acetic acid, toxic to yeast, is produced by certain LAB in conditions of glucose limitation. This study investigated ways in which glucose-repression might be removed, but no satisfactory technique was found.

In conclusion, a strain of LAB has been isolated which is effective in laboratory conditions at inhibiting spoilage organisms, but further field trials are necessary.