Effect of Dilute Alkaline Steeping on the Microbial Contamination, Toxicity and Diastatic Power of Sorghum Malt

Abstract

Steeping in dilute alkali was investigated with the primary aim of reducing the moulds, coliforms, and preventing toxicity of sorghum malt. Red tannin-free sorghum cultivars NK 283 and PAN 8546 were steeped in 0.1, 0.2 and 0.3% NaOH and 0.1, 0.3 and 0.5% Ca(OH)2. The effects of these solutions on aerobic plate count, lactic acid bacteria, yeasts, moulds, coliforms, the presence of some mycotoxins (aflatoxins, fumonisins, deoxynivalenol and zearalenone), the cytotoxicity and diastatic power (DP) of sorghum malt was evaluated. Steeping NK 283 in 0.1% Ca(OH)2 increased the DP from 10.5 to 16 Sorghum Diastatic Units (SDU)/g. However, it did not reduce the general levels of malt microflora. Steeping in dilute NaOH reduced the microflora on the malt. Steeping both grain cultivars with 0.2% NaOH resulted in malts with the moulds and coliforms reduced to approximately 3.5 and 2.0 log colony forming units/g, respectively and the percentages of some mould species to very low or undetectable levels. The DP of the 0.2% NaOH steeped malts increased to 16.2 and 26.9 SDU/g in the NK 283 and PAN 8546, respectively. There were no detectable amounts of mycotoxins and no indication of cytotoxicity in the 0.2% NaOH steeped samples. Steeping sorghum grains in food-grade 0.2% NaOH is recommended as a method for the control of bacterial and fungal contamination during sorghum malting.