The inhibitory effect of neem (Azadirachta indica) leaf extracts on aflatoxin synthesis inAspergillus parasiticus

The effect of neem (Azadirachta indica) leaf extracts onAspergillus parasiticus growth and aflatoxin biosynthesis was investigated. The extracts were prepared by blending 50 g (wet weight) of fresh leaves in one 1 of 10 mM potassium phosphate (pH 7.0) or by boiling the leaves in the buffer. Extracts were added to fungal growth media at 1, 5, 10, 20 and 50% (vol/vol) concentrations prior to inoculation. The formulations did not affect fungal growth (i.e., mycelial dry weight) but essentially blocked (>98%) aflatoxin biosynthesis at concentrations greater than 10% (vol/vol). The inhibitory effect was somewhat diminished (60–70%) inhibition) in heated leaf extracts. Volatile components of the extracts were analyzed using capillary gas chromatography/mass spectrometry; the major volatile component was 3‐methyl 2‐buten‐1‐ol. However, volatiles from blended leaf extracts did not affect either aflatoxin synthesis or fungal growth. The neem‐mediated inhibition appears to involve regulation of secondary metabolism, because once secondary biosynthesis was initiated the inhibitory effect of the neem leaf constituents was lost.