Comparative moisture sorption, insect infestation and aflatoxin production by resident aspergillus flavus link spores in solar and sun dried cassava accessions before and after gamma irradiation

Abstract

Ten accessions of Solar and Sun dried cassava (Manihot esculenta Crantz) were studied for their comparative ability to absorb moisture and harbour insects under varying Environmental Relative Humidities, (l:--R1Fs) representative of the Ghanaian tropic conditions. The colour change during storage was also assessed by the Hunter's L * a* b* colour system. The production of aflatoxin (BJ Bl' Gh and G~ before and after gamma irradiation (0, 20KGy) by-resident Aspergillus flavus spores was also investigated. The.moisture sorption isotherms of both solar and sun dried cassava flours followed a near sigmoid curve and equilibration at ERJI's (55, 75, 95 %) was attained after 4-6 days at 32°C The drying method did not significantly (P>0.01) influence the sorption isotherms. A gamma irradiation dose of at least 5KGy eliminated the infesting insects predominated by Araecerus fascicuiatus and Lasioderma serricorne. Analysis of variance to determine the influence of incubation humidity (A) accession number (B) and radiation treatment (C) as well as the interaction of these factors showed that A, B, C significantly (P<O.01) influenced colour change of flours. Interaction. between AB, AC as well as BC and ABC·were significant. The natural uninoculated and unirradiated cassava flour (I22II, 03211, DMA030) did not contain aflatoxin .Gj• There was an apparent enhancedformation by A. flavus spores in the artificially inoculated cassava flour samples after irradiation with 20 KGy but this was not attributable to the irradiation treatment per se but rather to the tendency of reduced inoculum of A. flavus to produce more aflatoxins