Survey of mycoflora counts, aflatoxin production and induced biochemical changes in walnut kernels

Fungal infection and mycotoxin contamination in fresh and stored kernels of walnut (Juglans regia) collected from different localities of Uttaranchal (India) were investigated. Fresh samples carry a combination of field as well as storage fungi. Species of Alternaria, Aspergillus and Penicillium were predominant. Thirty-nine percent of Aspergillus flavus isolates were toxigenic and produced up to 2170 μg/l of aflatoxin B1 in the liquid media. Aflatoxin B1 was the most common mycotoxin encountered as a natural contaminant in the stored samples. Twenty-one percent of fresh samples contained aflatoxin B1 in low concentrations. The concentration of aflatoxin B1 in fresh as well as stored samples was in the range of 140-1220 μg/kg. Characteristic rotting was observed in fresh as well as stored samples. The walnut kernels exhibited significant reductions in the levels of oil, starch and protein content during fungal infection.