Growth of spoilage mould and aflatoxin B1 production in naturally contaminated or artificially inoculated maize as influenced by moisture content under ambient tropical condition

Maize (cv. TSZB) samples were re-moistened to different moisture contents (m.c.s) of 13, 15, 17, 20, 25, 30 or 35% and stored with the natural microflora or sterilized before artificial inoculation with either single or mixed moulds (Aspergillus flavus, A. niger, Penicilium purpurogenum and Fusarium moniliforme) and evaluated for initiation time for moulding, fungal populations and aflatoxin B1 production. Whereas the fungal populations of naturally contaminated maize of 13% m.c. decreased significantly with storage, 17 and 20% m.c. maize increased with the latter showing maximum of about log10 7 colony forming units (cfu g−1). Of the samples (13, 15, 17 or 20% m.c. maize), only those of ≥20% m.c. showed hazardous levels (>20 ppb) of aflatoxin B1 production. The 20% m.c. sample also showed a significant positive correlation (r = 0.92) between m.c. and fungal load but those of lower m.c.s exhibited poor correlations, probably reflecting the absence of changes in the m.c.s of the 13, 15 and 17% m.c. maize. Aflatoxin B1 content of 25% m.c. maize increased with increase in inoculum concentration of A. flavus. Mixed mould inoculation of maize samples resulted in a reduction in aflatoxin concentration with co-cultures of A. flavus and P. purpurogenum showing the lowest production, while that inoculated with A. flavus alone (control) exhibiting the maximum production. Initiation time for moulding was most rapid in ≥20% m.c. maize irrespective of inoculum type, with A. flavus being the most invasive in singly inoculated samples. However, A flavus was most competitive in 20–30% m.c. maize inoculated with mixed moulds, while F. moniliformewas most competitive in the 35% m.c. maize.