Inhibitory role of neem seed kernel extracts and terpenoids on growth and aflatoxin production by Aspergillus parasiticus (NRRL 2999)

Abstract

The effect of neem seed kernel extracts and purified terpenoids on Aspergillus parasiticus in relation to fungal growth, ergosterol synthesis and aflatoxin elaboration was investigated in yeast extract sucrose (YES) liquid medium. Aqueous (0.05, 0.25, 0.5 and 1.0 %), hexane, methanolic, ethyl acetate and acid-methanolic extracts (0.01, 0.1, 0.5 and 1.0 %) of neem seed kernel were tested at 3, 5, 7, 9 and 12 days of incubation. Fungal growth was not affected by aqueous and hexane extracts, while it was inhibited by the methanolic, ethyl acetate and acid-methanolic extracts. The inhibition of ergosterol biosynthesis was 73 and 82 % by the aqueous extract at 0.5 and 1.0 % conc, while hexane and ethyl acetate inhibited in a dose dependent manner on day 7. The AFB₁/total toxin altered significantly (p<0.01) in the presence of various neem seed kernel extracts, except that of hexane extract. Purified terpenoids, azadirachtin, nimbin and salannin had no inhibitory effect on fungal biomass and aflatoxin elaboration at 0.01, 0.1, 0.25 and 0.5 % levels. Azadirachtin at 0.25 and 0.5 % level inhibited ergosterol biosynthesis by 30 and 34 %, respectively. Neem seed kernel extracts were inhibitive to the fungal growth, ergosterol biosynthesis and toxin elaboration as compared to purified neem terpenoids, suggesting anti-fungal and anti-aflatoxigenic properties.