EFFECT OF DIFFERENT PROCESSING TECHNIQUES ON THE QUALITY OF COCOYAM AND HYDROLYTIC ENZYMES OF ISOLATED MICROORGANISMS

Abstract

An investigation to determine the nutritional quality of processed cocoyam (red and white varieties) flour and the hydrolytic enzymes of microorganisms isolated from the processed cocoyam samples was carried out. The microorganisms isolated were: Aspergillus niger, Rhizopus stolonifer, Penicillium italicum, Passalora bacilligera, Tetrachaetum elegans, Articulospora inflata, Aspergillus saprophyticus, Saccharomyces cerevisiae, Bacillus subtilis, Staphylococcus aureus, Klebsiella aerogenes, Lactobacillus plantarum, Leuconostoc mesenteroides, Pediococcus cerevisiae, Lactobacillus brevis and Bacillus licheniformis. The protein and crude fibre contents ranged from 6.48 to 8.08% and 0.39 to 0.79% respectively. The mineral compositions of the samples are sodium (2.49 mg/100g), potassium (70.79 mg/100g), phosphorus (14.09 mg/100g), magnesium (12.48 mg/100g) and calcium (21.46 mg/100g). Contents of anti nutrient factors are flavonoid (1.20%), saponin (8.58%), phytate (30.55mg/g), oxalate (0.62mg/g) and tannin (0.11mg/g). Of all the fungi isolates, A. niger had the highest amylolytic activity at 48hrs while, A. saprophyticus produced the least activity. Amylase production by B. subtilis and B. licheniformis increased with increase in fermentation period and reached maximum at 48hrs after inoculation. The optimum incubation period for A. saprohyticus and P. italicum was 24hrs, while A. niger produced cellulase enzyme maximally at 72hrs of fermentation. A. niger had highest pectinase activity at 48hrs. A. niger produced alpha amylase maximally at pH of 5. While starch and NaNO3 were selected as best carbon and nitrogen sources respectively. The physical properties of the alpha amylase from A. niger were: pH optimum 7.0, pH stability 5-7, temperature optimum 60oC, temperature stability 50-60oC. This study provides useful information on the nutritional quality of processed cocoyam sample and physico-chemical properties of alpha amylase produced by A. niger. The optimum temperature (60oC) of alpha amylase suggests that the enzyme can be employed in food and beverage industries to convert starch into maltose. However, fermentation coupled with blanching with boiling water and cooking with peels are the best processing techniques for cocoyam and mineral content of the samples demonstrated that red cultivar is nutritionally superior to the white variety.