Introduction: Aflatoxins are secondary hazardous fungal metabolites, that are produced by toxigenic strains of some Aspergillus species on food and feedstuffs. These toxins are mutagenic and carcinogenic compounds, and are capable of causing health hazard in human and animals. Prevention of aflatoxin production and their elimination from food products is a matter of importance for many researchers in the last decades. Neem plant is known as an inhibitor of aflatoxin biosynthesis in producing fungi. In this communication, we studied the effect of incubation time as an important parameter on growth and aflatoxin production by Aspergillus parasiticus in presence of different concentrations of Neem aqueous leaf extracts.

Materials and Methods: The toxigenic fungus (Aspergillus parasiticus NRRL 2999) was cultured on sucrose low salts (SLS) medium in presence of various concentrations of aqueous neem leaf extracts (0.2% , 0.8%, 3.12%, 12.5% and 50% v/v). After shaking incubation of culture for 2, 4, 6, 8, 10 and 12 days at 28oC, the fungal mycelia were collected and processed for determination of dry weight. A known amount of mycelia and also culture media were processed for aflatoxin B1(AFB1) determination by thin layer chromatography (TLC) method.

Results: The neem leaf extracts had not any obvious effect on fungal growth rate at different periods of time. AFB1 production in the control samples (without neem extract) increased to the maximum level in the 8th day of culture, and then remained in a constant status till 12th day. The inhibition of aflatoxin synthesis by aqueous neem extracts was found to be time- and dose-dependent with maximum of 80-90% in presence of 50% concentration. After 2 days, there wasn’t any change in AFB1 production in neem treated mycelia as compared with control samples. In the 4th day, at 12.5% and 50% concentrations, toxin production was reduced and this reduction at 50% concentration was significant after comparing with control samples (P<0.05).

Conclusion: The obtained results clearly show that inhibitory effects of aqueous neem leaf extracts on aflatoxin synthesis reported in this study is time-dependent without any obvious effect on fungal growth rate. Aflatoxin inhibition is mainly occured in primary stages of fungal growth where the genes involved in aflatoxin biosynthesis have the maximum activity within the fungal cells .

Hakim Research Journal 2005 8(2) 41-46.