The Microbial Contamination, Toxicity and Quality of Turned and Unturned Outdoor Floor Malted Sorghum

Abstract

Turned and unturned outdoor floor malted sorghum were studied for their total microbial contamination, nature and extent of contamination by moulds, cytotoxicity (IC 50 ) and quality in terms of diastatic power (DP). The presence of aflatoxins, fumonisins, deoxynivalenol and zearalenone were also investigated. Total microbial counts were high (10 7 -10 8 cfu /g) in both turned and unturned samples. All samples showed contamination by different moulds, with the dominant being Mucor species, Rhizopus oryzae, Fusarium moniliforme and Phoma sorghina as well as Aspergillus flavus and Alternaria alternata. The latter four are known for producing mycotoxins. Malt samples had very low cytotoxicity (IC 50 from 62.5 to >1000 kg/kg), though all contained fumonisins, deoxynivalenol and zearalenone at levels of < 0.25-2 µg/g, 15-20 and 10-15 µg/kg, respectively. Malt DP was generally lower in turned samples compared to unturned samples probably because the heat conserved in the latter ensured better germination conditions. Overall, turning during germination did not affect the microbial load, mould population and levels of deoxynivalenol and zearalenone in sorghum malt but decreased sorghum malt DP. Thus, alternative methods of controlling the sorghum malt microbial load should be sought.

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

“…This is in apparent contradiction to the results in our previous work 8 . However, in that case the steep water was not changed, whereas it was changed twice during malting in this work.…”

“…Therefore, there is a need for efficient and safe ways to control microbial growth during sorghum malting. As shown in our previous work 8 , the physical measure of turning germinating grains did not result in inhibited microbial growth. Steeping is probably the most critical stage at which microbial proliferation begins 10 .…”

“…Other analyses. The dried malts were assayed for the following as described in our previous work 8 . Microbial population: total aerobic plate counts (APC), lactic acid bacteria (LAB), yeasts, moulds and coliforms by standard plating methods.…”

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

“…Two condensed tannin-free red sorghum cultivars, NK 283 and PAN 8546 were used as described in our previous work 16,17 .…”

“…Traditional outdoor floor malted sorghum can be contaminated with high levels of coliform bacteria and moulds that can potentially produce mycotoxins 17 . Recently we have shown that these undesirable sorghum malt microflora can be controlled by steeping in dilute NaOH 16 .…”