Deterioration and spoilage of peanuts and desiccated coconuts from two sub-Saharan tropical East African countries due to the associated mycobiota and their degradative enzymes

Abstract

A broad variety of fungi (84 species belonging to 36 genera) were identified with more taxa infesting peanut seed samples from two tropical countries (29 genera and 61 species) compared to those found in desiccated coconuts (20 genera and 55 species) on both DRBC and DG18 media. This may be due to the higher moisture levels in peanuts (5.07-7.97%) compared with coconuts (1.5-4.17%). More taxa and propagules were recovered on DG18 in both cases. The dominant fungi from both substrates on both isolation media were Aspergillus and Penicillium, with other fungi from only one substrate/medium. The aflatoxigenic species (A. flavus) dominated Kenyan samples more so than Ugandan samples on both substrates. However only 71.5% and 87.5% of the peanut kernels, on DRBC and DG18, respectively, were found to be infested with fungi. The aflatoxigenic species (A. flavus/parasiticus) were found in 75% of the samples, however only 15.75% and 13% of the kernels analyzed were infested. The most frequently isolated species from peanuts were A. niger followed by A. flavus and M. phaseolina. E. repens, E. amstelodami, E. rubrum and E. chevalieri dominated peanut seeds on DG18, and R. stolonifer, A. parasiticus, F. solani, L. theobromae and P. chrysogenum on DRBC. The mean count of fungal propagules in coconut samples were approximately 0.7 x 10(3) and 0.8 x 10(3) on DRBC and DG18, respectively, with a high proportion of those propagules recorded for the aflatoxigenic species (about 0. 17 x 10(3) and 0.25 x 10(3) colonies/g). The mycobiota of desiccated coconut was dominated by A. niger, A. flavus and P. chrysogenum. Also A. ochraceus, P. waksmanii, Paecilomyces variotii, P. islandicum and R. mucilaginosa were more frequent on DRBC, while, species of Cladosporium. Chrysosporium and Eurotium were more frequent on DG18. Enzyme indices (or the activities) for each specific strain, when determined after 5 and 8 days of incubation, proved to be similar. A recommendation is given. The proteolytic and lipolytic potentialities of the most commonly encountered species from both peanuts and coconuts were studied. The most interesting observation is that most of the positive isolates, in both commodities had high enzymic activity compared to those reported earlier for isolates of the same species. Such capabilities suggest that these commodities are expected to deteriorate, since climatic conditions in tropical areas favour fungal proliferation. Emphasis on the proper harvesting, drying, handling, transportation and/or storage; and also education of the populace, especially those are dealing with these foods, should be taken into consideration by the relevant authorities. The contaminated foods constitute a health hazard for human consumption.