Effect of Dilute Alkaline Steeping on the Microbial Contamination, Toxicity and Diastatic Power of Sorghum Malt
Mathoto L. Lefyedi1,2 and John R.N. Taylor1,3
1 Department of Food Science, University of Pretoria, 0002, Pretoria,South Africa.
2 Current address: South African Agency for Science and Technol-ogy Development, P.O. Box 1758, Pretoria 0001, South Africa.
3 Corresponding author: E-mail: jtaylor@postino.up.ac.za
J. Inst. Brew. 112(2), 108–116, 2006 | VIEW ARTICLE
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, deoxy-nivalenol 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 micro-flora on the malt. Steeping both grain cultivars with 0.2% NaOH resulted in malts with the moulds and coliforms reduced to ap-proximately 3.5 and 2.0 log colony forming units/g, respectively and the percentages of some mould species to very low or un-detectable levels. The DP of the 0.2% NaOH steeped malts in-creased 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.
Key words:
Bacteria, diastatic power, moulds, mycotoxins, so-dium hydroxide, sorghum malt, steeping.
Publication no. G-2006-0629-410 ©2006 The Institute & Guild of Brewing