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

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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. nig&r 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.