Characterization and Screening of Lactic Acid Bacteria (LAB) and Yeast from Fermented Sorghum and Maize Products for use as Starter Culture

Abstract

This study focused on the isolation, Characterization and screening of lactic acid bacteria and yeast for use as starter culture in order to eradicate the problem of excessive microbial contamination and the presence of mycotoxins. Lactobacillus plantarum and Saccharomyces cerevisiae were the predominant microorganisms isolated from the samples collected. The isolates were screened for their ability to produce enzymes and metabolites. Lactic acid bacteria produce a variety of antimicrobial compounds such as lactic acid, hydrogen peroxide, diacetyl on them as a natural competitive means to overcome other microorganism sharing the same niche. They were also screened for their ability to withstand some physiological stress like acid tolerance, temperature, salt concentration and antibacterial activity; the isolates produced significant values of enzymes and, antimicrobial metabolites. The antimicrobial activity of Lactobacillus plantarum is mainly attributed to the low pH due to Lactic acid production. The antimicrobial activity of the Saccharomyces cerevisiae appears to be mainly due to the competition with the other microorganisms. In addition, depletion of Oxygen and production of CO2, competition for nutrients and the production of antimicrobial substances could have been responsible for the overall antimicrobial activity of both cultures. According to the results obtained, both lactic acid bacteria and yeast proved to be a good source of starter culture.