Effect of Gamma Irradiation on Agricultural Waste-Decomposing and Fermentation Microorganisms in Ghana

Abstract

Maize production in Ghana between 1984 and 1990 exceeded 500,000 metric tonnes per year except in 1985 where there was a shortfall to 395,000 metric tonnes. The unfavourable years of drought between 1981-1983 were attended by a sharp decline in maize production ( 140,000-333,200 metric tonnes ). The bulk of the national maize production was contributed by Ashanti, Brong-Ahafo, Eastern and Northern Regions. Maize husk available after removing cobs was commensurate with the total maize harvest for each Region. As a raw material for fungal protein production, maize husk has a potential for sustainable use. Gamma irradiation ( 0-200 Krad ) was used as a mutagen to evaluate its effect on vegetative growth, cellulolytic, pectinase and amylase activity of AspergiI1 us niger. Rhisopus oryzae, Trichoderma. viride and Lactobacillus plantarum. Screened for use in the production of fungal protein on corn husk slurry by solid substrate fermentation. A dose of 20 Krad decreased vegetative growth of A. niger by 46.6 percent and further increases up to 50 Krads increased dry matter accumulation by the fungus. Vegetative growth of R. orysae was increased by about 30 percent by 50 Krad and remained nearly the same up to 200 Krad. There was no stastitical difference ( < 0.05, Student’s t-test ) between dry weight of mycelium obtained with 50, 100, 200 Krad of gamma irradiation. The best vegetative growth of T viride was obtained when 100 or 200 Krad of gamma irradiation was applied to spores prior to culturing. The best vegetative growth of the bacterium ( L . plantarum ) was attained when the culture was exposed to 50 Krads prior to incubation at 28 JC for 5 days. Optimum cellulase, amylase and pectinase activity was induced by 50 Krad of gamma irradiation in A. nig&T and L. pi an tar urn ; on the other hand, optimal cellulase activity in T. viride and R. oryzae was induced by a dose of 100 Krad whilst 50 Krad was optimal for maximal production of amylase and pectinase enzymes by the same fungi ( T. viride and R. oryzae ) . Generally, the gamma irradiation dose that induced optimal vegetative growth was also attended by optimal cellulase activity.The pH of the medium containing spores of T viride treated with 100 krad was between pH 5.0 - 6.5 corresponding to the best pH for cellulase activity in T viride. The potential for use of gamma irradiation as a mutagen for enzyme production is promising. Gamma irradiation up to 200 Krad linearly increase acid production by A. niger as pH shifted from 2.9 to 2.2. The culture medium containing gamma-irradiated ( i 50 Krad. ) R. oryzae sporangiospores also became more acidic ( pH 4.5 - 3.8 ) presumably indicating accumulation of acids. Hydrolysis of corn husk into a slurry was achieved by using either one percent or five percent sodium hydroxide or hydrochloric acid and heating at 80° , 100° or 120°C for 1-3 hours. The best treatment combination for corn husk hydrolysis was heating at 100 C fot at least 1 hr. in either one or five percent sodium hydroxide or 1 percent Hydrochloric acid. This gave good accessibility of cellulase for microbial enzyme attack leading to high crude fungal protein ( 20.0 percent ) produced by T. viride irradiated with 100 Krad of gamma irradiation prior to innoculation of the solid substrate. Irradiation caused morphological changes in T. viride and A. niger cultures. In T viride, as much as the conidiophores remained irregularly branched, the bright green colour development decreased progressively with increasing gamma irradiation dose ( eg. at 200 Krad there was no colour development ). Practical implications of these findings are discussed and future studies leading to commercial application of the technique suggested.