Changes in fungal community and aflatoxin levels during peanut butter production and storage.

Abstract

Most peanut butter brands on the Zambian market have been reported to contain high levels of aflatoxins (AFs). It is not clear whether these high levels are from the use of contaminated raw peanuts, proliferation during processing or storage. The changes in fungal community and AF levels during production and three months storage of peanut butter were monitored. The AF producing ability of isolated Aspergillus species was also assessed. The investigation was carried out on two peanut varieties: Chalimbana and Kadononga, both varieties obtained from a market and farm. Peanut butter was processed from sorted peanuts and stored at room temperature. Room temperature was recorded daily during storage. The raw peanuts were evaluated for moisture content, water activity, fungal and AF content, using established procedures. Changes in fungal and AF content of peanuts from various stages of the processing line including: roasting, blanching and grinding, as well as peanut butter samples under storage were assessed. The isolated fungi were identified by sequencing the ITS gene fragment and AF levels were assessed using lateral flow immunochromatography. The AF producing ability of isolated Aspergillus species from all peanut samples was also done. The following nine fungal genera were isolated from raw peanuts: Cladosporium, Aspergillus, Fusarium, Penicillium, Epicoccum, Alternaria, Talaromyces, Curvularia and Xenocamarosporium. A reduction in fungal diversity was observed during processing. Only three fungal genera were isolated from peanuts from the processing line: Cladosporium, Penicillium and Talaromyces. Fungal growth in peanut butter stored in a temperature range of 18.3 - 31.8 C was minimal but changes in fungal diversity were observed during storage. The AF producing potential of four isolates of Aspergillus indicated that out of the four, three were atoxigenic and only one strain was toxigenic. Sorting of raw peanuts reduced AF levels by 38 - 92%. Further reduction was observed after processing and there was no significant change in AF levels during storage. The present study concludes that processing of peanuts into peanut butter reduces fungal diversity as well as AF levels and no significant changes occur in AF levels during three months of storage when peanut butter is stored in a temperature range of 18.3 - 31.8 C. Therefore, high levels of AF in peanut butter are most likely due to the use of contaminated peanuts. Sorting is therefore recommended prior to processing. Keywords: Peanut butter, storage, Aspergillus, aflatoxin, sorting