The Microbial Contamination, Toxicity and Quality of Turned and Unturned Outdoor Floor Malted Sorghum
Mathoto L. Lefyedi1,4, Gert J. Marais2, Michael F. Dutton3, and John R.N. Taylor1
1 Department of Food Science, University of Pretoria, 0002, Pretoria, South Africa.
2 Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, 0002, Pretoria, South Africa.
3 Faculty of Health Sciences, Technikon Witwatersrand, PO Box 17011, Doornfontein, 2028, South Africa.
4 Corresponding author. E-mail: mathoto.lefyedi@up.ac.za
J. Inst. Brew. 111(2), 190–196, 2005 | VIEW ARTICLE
ABSTRACT
Turned and unturned outdoor floor malted sorghum were studied for their total microbial contamination, nature and extent of contamination by moulds, cytotoxicity (IC50) and quality in terms of diastatic power (DP). The presence of aflatoxins, fumonisins, deoxynivalenol and zearalenone were also investigated. Total microbial counts were high (107–108 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 (IC50 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.
Key words:
Cytotoxicity, mycoflora, mycotoxins, sorghum malt.
Publication no. G-2005-0725-279 ©2005 The Institute & Guild of Brewing