Development of the Bacillus subtilis-S499 biocontrol of mould during red sorghum malting

RESUME

Bacillus subtilis exerts an inhibitory effect on moulds isolated from red sorghum raw grain. The total fungal count reduction time course, affected by the dilution of B. subtilis culture, follows a sigmoidal function type. Therefore, one can distinguish three zones: a first zone of high inhibition, where the dilution of B. subtilis culture does not greatly affect the steeping treatment on reducing mould growth (DF > minID); a second zone of dilution where the inhibitory effect of the steeping treatment is almost proportional to the dilution of the B. subtilis culture (MaxID < DF < minID); and a third zone of dilution where treatment is simply ineffective i.e., no significant reduction in total fungal count upon increasing the concentration of B. subtilis (DF < MaxID). Steeping in the biocontrol allows malt production with a low level of fungal contamination, relatively low malting losses and high β-glucanase levels. When compared with dilute alkaline steeping, the biocontrol treatments result in malts with low α- and β-amylase activities and a relatively high content of total phenolic compounds and condensed tannins. Bacillus subtilis dilution has been found to significantly affect kilned malt enzyme activities depending on the type of enzyme studied.

Keywords : Bacillus-subtilis-based biocontrol, mould growth inhibition, red sorghum malting

Jean-Claude Bwanganga Tawaba, François Béra, Philippe Thonart