Control of the Growth of Coliforms and Moulds in Sorghum Malting by Bacterial and Yeast Cultures

Abstract

Traditional outdoor floor malted sorghum can be contaminated with high levels of coliform bacteria and moulds that can potentially produce mycotoxins. The effect of steeping with the addition of bacterial and yeast starter cultures on microbial contamination, toxicity and diastatic power (DP) of sorghum malt was investigated. Lactobacillus plantarum, Pedicococcus pentosaceus and Saccharomyces species were selected on the basis of inhibition of fungal species using the disc diffusion assay. Steeping the sorghum with the addition of these cultures at 107-108 cfu/mL reduced the level of moulds by one to two log cycles, with the Saccharomyces culture appearing to be the more effective and L. plantarum the least effective. Coliforms, where present in significant numbers, were reduced to levels of >101-102 by steeping with the cultures, with the P. pentosaceus culture appearing to be the most effective and Saccharomyces the least effective. There were no detectable amounts of mycotoxins and no significant cytotoxicity in the malts in either the controls or the culture-steeped malts. Steeping with the cultures did not affect malt DP. The use of such P. pentosaceus and Saccharomyces sp. cultures could be an alternative to chemical treatment for the control of microbial contamination in sorghum malt.