Growth of spoilage mould and aflatoxin B-1 production in naturally contaminated or artificially inoculated maize as influenced by moisture content under ambient tropical condition

Maize (cu. 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 microfl ora or sterilized before artificial inoculation with either single or mixed moulds (Aspergillus flavus, A. niger., Penicilium purpurogenum and Fusmari um moniliforme) and evaluated for initiation time for moulding, fungal popu lations and aflatoxin B-1 production. Whereas the fungal populations of nat urally contaminated maize of 13% m.c, decreased significantly with storage, 17 and 20% m.c. maize increased with the latter showing maximum of about l og(10) 7 colony forming units (cfu g(-1)). Of the samples (13, 15, 17 or 20 % m.c. maize), only those of greater than or equal to 20% m.c. showed hazar dous levels (> 20 ppb) of aflatoxin B-1 production. The 20% b m.c, sample a lso showed a significant positive correlation (r = 0.92) between m.c. and f ungal load but those of lower m.c.s exhibited poor correlations, probably r eflecting the absence of changes in the m.c.s of the 13, 15 and 17% m.c. ma ize. Aflatoxin BI content of 25% m.c. maize increased with increase in inoc ulum concentration of A. flavus Mixed mould inoculation of maize samples re sulted in a reduction in aflatoxin concentration with co-cultures of A. fla vus and P. purpurogenum showing the lowest production, while that inoculate d with A. flavus alone (control) exhibiting the maximum production. Initiat ion time for moulding was most rapid in greater than or equal to 20% m.c, m aize 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. moniliforme was most competitive in the 35%, b m.c. maize. (C) 2000 Published by Elsevier Scienc e Ltd. All rights reserved.