Compatibility of food grade antioxidants and natural phytochemicals with Purpureocillium lilacinum, a potential entomopathogenic fungus of insect vectors of aflatoxigenic fungi in stored maize

BARRA, P.; NESCI, A.; ETCHEVERRY, M.

Rotterdam

Conferencia; 7th conference of the World Mycotoxin Forum and XIIIth IUPAC International Symposium on Mycotoxins and Phycotoxins; 2012

Maize can be colonized by fungal communities at harvest and storage. This contamination reduces the quality and quantity of grain and can contaminate the cereal with mycotoxins, such as aflatoxins. On the other hand, insect contamination in food commodities in addition to damage the storage grain, contribute to the dispersal of viable fungal spores of Aspergillus Section Flavi. To avoid mycotoxin contamination, stored products can be treated with food grade antioxidants and natural phytochemicals. These substances also produce insecticide effect and decrease the dispersion of aflatoxigenic Aspergillus during storage. It is also believed that another alternative that deserves to be under investigation is the biological control of insects, by using of entomopathogenic fungi. We have isolated and identified potential entomopathogenic fungi from maize agroecosystem. Strategies have been employed to increase efficiency and accelerate insect mortality by combining entomopathogenic fungi with sublethal doses of antioxidants and phytochemicals insecticides. So, tolerance of entomopathogenic fungi to sublethal doses of these substances will allow us to select the appropriate compounds doses and schedule chemical treatments accordingly to minimize any deleterious effects on entomopathogenic efficacy. The purpose of this study was to determine the compatibility of 21 Purpureocillium lilacinum strains with the food grade antioxidants 2(3)-tert-butyl-4 hydroxyanisole (BHA) and 2,6-di tert-butyl-p-cresol (BHT) and natural phytochemicals trans-cinnamic acid (3-phenyl-2-propenoic acid) (CA) and ferulic acid (trans-4-hydroxy-3-methoxycinnamic acid) (FA). Studies were carried out in vitro, in 3 % maize meal extract agar (MMEA) over the aw range 0.99-0.95. The solutions of food grade antioxidants or natural phytochemicals alone (BHA 1 mM; BHT 7 mM; CA 1 mM; FA 7 mM) or their mixtures (BHA + BHT, 0.7 + 6 mM; CA + FA, 0.6 + 2 mM) were added to sterilize MMEA in an adequate volume to achieve the desired concentration. Entomopathogenic fungi were grown on potato dextrose agar (PDA) for 7 days at 25°C to obtain heavily sporulating cultures. Each plate of MMEA was inoculated with 100 µl of 107 spores ml-1 of the fungal strain assayed. Petri plates were incubated at 25 °C for 25 days. The fungal count was determined as CFU ml-1 in each treatment. The antioxidants BHA, BHT, BHA + BHT mixture and CA did not significantly influence the viable spores count when compared with control treatments. Furthermore, in some treatments there were higher counts than in controls. All strains showed compatibility percentages above 80 % when grown in the presence of BHT, BHA + BHT mixture and CA. Three strains showed compatibility percentages between 80 and 90 % in some treatments. The remaining 18 showed compatibility percentages between 90 and 100 %, and in some cases compatibility percentages above 100 %. BHT, BHA + BHT mixture and CA did not affect spores viability of P. lilacinum strains evaluated.