EFFECTS OF STORAGE MOULDS ON THE NUTRITIONAL QUALITY OF COCOA BEANS AND THEIR CONTROL IN SOUTH-WEST NIGERIA

Abstract

Apparently healthy and infected stored cocoa beans were obtained from three randomly selected cocoa stores in each of the five cocoa producing states of Oyo, Ondo, Osun, Ekiti and Ogun in South-West Nigeria. The samples were subjected to microbiological and proximate analyses. Aqueous (hot and cold) extracts as well as powdered forms of Aframomum danielli (seeds), Aframomum melegueta (seeds) and Tetrapleura tetraptera (fruits) were tested against pure cultures of the most occurring fungal isolates. The storage moulds isolated from both the healthy and infected samples were Aspergillus flavus, A. ochraceous, A. versicolor, Rhizopus sp., Pythium sp., Fusarium solani, A. terreus, A. niger, A. fumigatus, Lasiodiplodia theobromae and Penicillium digitatum. Proximate analysis conducted on the beans revealed that there was no significant difference (P ≤ 0.05) in the amount of fat, which ranged between 44.41 - 47.31% (in healthy beans) and 45.04 - 47.20% (in infected beans) across the five south-western states. However, there were significant differences (P ≤ 0.05) in the crude fibre contents of both the healthy and infected beans obtained from most of the states across the region. The study also showed that, except for the fat, iron and carbohydrate, the implicated storage moulds were able to reduce the organic and mineral contents of the stored cocoa beans, and thus lower their nutritional quality. The average percent inhibitions exhibited against the three test fungi (A. flavus, A. versicolor and A. ochraceous) by hot water extracts of A. danielli, A. melegueta and T. tetraptera ranged between 22.95 – 29.64%, 34.42 – 41.38% and 3.43 – 14.89% respectively. Cold water extracts of A. danielli induced the highest inhibition (10.18 – 33.94%) against the organisms while T. tetraptera (0.79 – 10.71%) produced the least. Powdered forms of A. danielli exhibited the highest inhibition (56.24 – 72.60%) against the three test fungi, followed by those of A. melegueta (33.23 – 55.07%), while T. tetraptera gave the least inhibition. Findings from this study have revealed that hot water extracts of A. melegueta were more effective against A. flavus, A.versicolor and A. ochraceous than their cold water extracts, while the reverse was the case for A. danielli with the exception of A. versicolor. The combinations of at least two of the powdered botanicals, though not synergistic, were also able to effect some appreciable degree of control against the fungi. In addition to proper handling of cocoa beans before and during storage, powdered forms of A. danielli and A. melegueta can therefore be used to effectively control the associated cocoa beans storage moulds.