Effect of the use of dilute alkaline prior to Bacillus subtilis-based biocontrol steeping and germination conditions on red sorghum malt beta-glucanase activities and residual beta-glucans.

摘要

Malting is the ideal stage to deal with beta-glucans. Their hydrolysis is very important as the diffusion of both hormones and hydrolytic enzymes in the endosperm of germinated grain depend on it. A high malt beta-glucanase activity is not a guarantee of an extensive hydrolysis of beta-glucans. When Bacillus subtilis is used to control mould growth, red sorghum malt beta-glucanase activity (measured using carboxymethylcellulose as the substrate) was improved without significantly affecting the hydrolysis of malt beta-glucans. Thus, in order to reduce the residual beta-glucans content, soaking in 0.2% NaOH was combined with a biocontrol. Soaking in 0.2% NaOH is recognized as capable of improving grain hydration by opening-up the endosperm cell walls. The combined use of 0.2% NaOH with B. subtilis-based biocontrol treatments during red sorghum malting, leads to malt with increased beta-glucanase activity and a significant reduction of residual beta-glucans when compared with the 16 h biocontrol steeping without prior steeping in 0.2% NaOH. beta-glucanase activity increases with increased germination temperature and time while, conversely, the residual beta-glucans content of the malts decreases. Indeed, while the level of beta-glucanase was not vastly different between the malts obtained after steeping in distilled water and those obtained after 8 h steeping in 0.2% NaOH followed by 8 h resteeping in distilled water (NaOH + H₂O treatment), their residual beta-glucans levels differ significantly. B. subtilis-based treatment leads to malt with improved beta-(1-3)- and beta-(1-4)-glucanase activities without significantly improved malt beta-(1-3),(1-4)-glucanase activity. While malts obtained after 84 h germination weren't significantly different in terms of malt beta-(1-3),(1-4)-glucanase activities for all steeping treatments, the use of 0.2% NaOH steeping prior to resteeping led to malts with improved beta-glucans content. Combining the steeping in dilute alkaline and biocontrol enables taking advantage of the dilute alkaline effect on residual beta-glucans content, due probably to the opening-up of the cell walls and the improvement of water uptake, and that of the biocontrol (improvement of beta-glucanase synthesis).