ABSTRACT
Sorghum is one of the important cereals consumed by humans, animals and also used for the production of mushroom spawns in Ghana. Aim: Identification of fungi present on sorghum grains before and after pretreatment (steam and gamma radiation) principally for mushroom cultivation Methodology: The total number of mycoflora (Log10 CFU g-1) of sorghum grains and their relative frequency (percentage occurrence) associated with the raw grains and the mycoflora present after subjecting the sorghum grains to gamma radiation doses of 0, 5, 10, 15, 20, 25 and 32 kGy at a dose rate of 1.7 kGy/h from a Cobalt-60 source (SLL-515, Hungary) and moist heat at a temperature of 100- 120ºC for 2- 2.5 hours was evaluated. Mycological analysis was done by direct plating method on Cooke’s and Dichloran Rose Bengal Chloramphenicol (DRBC) media. Results: Nine fungal species belonging to six genera were associated with the sorghum grains. Among these fungi were Cladosporium macrocarpum, Trichoderma harzianum, Fusarium oxysporum, Rhodotorula spp., Penicillium spp., Aspergillus niger, Aspergillus fumigatus, Aspergillus ochraceous and Aspergillus flavus. Comparatively higher fungal counts of 3.27 and 3.82 Log10 CFU g-1 were recorded for non-pretreated while lower counts of 0.5 Log10 CFU g-1 were recorded for pretreated sorghum grains. Gamma radiation and moist heat significantly (P<0.05) reduced total fungal populations by an average of 2.4 and 2.1 log cycles, respectively. Rhodotorula sp. (11.5%), Penicillium sp. (34.6%), Aspergillus fumigatus (29.9%) persisted on the moist heat sterilized while only Rhodotorula sp. (100%) persisted on gamma irradiated grains. Conclusion: These data indicate possible health hazards for humans and animals upon consumption of such contaminated food grain by toxigenic moulds and also reveal the sensitivity of fungal species to gamma radiation and moist heat as a selective substrate for oyster mushroom spawn preparation.
ABSTRACT
Effect of gamma irradiation on antibacterial activities of chitosan is described. Chitosan was prepared from crab shells via demineralization, deproteinization, decoloration and deacetylation. Chitosan solutions (2%) were prepared in 1% acetic acid and irradiated at 0, 5, 15 and 25 kGy. The degree of deacetylation and viscosity-average molecular weight of the chitosan were determined. Susceptibility tests of E. coli and S. parathyphi against the chitosan were determined. E. coli was more susceptible to lower concentrations of chitosan solutions. Irradiated chitosan in solutions exerted a slightly faster inhibition on both E. coli and S. parathyphi than the unirradiated chitosan solution, but there was no difference observed between irradiated and unirradiated chitosan in solutions after 48 hours of incubation. The degree of susceptibility of both E. coli and S. parathyphi to irradiated chitosan in solutions was not significantly affected by the irradiation dose.