Production and Utilisation of Pectolytic Enzymes from some Agricultural Wastes
Twenty-one fungal strains – five foreign, sixteen local isolates were screened qualitatively and quantitatively for pectinase production. Six point strains among them were further studied to determine their nutritional requirements. The best two strains were Aspergillus niger (from Mysore, India) and Aspergillus repens (from Agege, Lagos). For mycelia growth and pectinase production, the optimum incubation period in static liquid media at ambient temperatures was 5 days and incubation at 24 ± 20C was found to be optimum for both strains; moreover, A. repens performed equally well when incubated at 35 ± 10C thereby indicating perfect ecological adaption to generally warm local environment of Lagos. Three locally available agro-industrial wastes – wheat bran, rice bran and peanut shell were analysed and studied for pectinase production as semi-solid media. They all contained water extractable nutrients such as reducing sugars (8-12mg/g); protein (1 – 2mg/g); starch (2 – 537mg/g; and pectin (0.4 – 6. 1%). The effect of acid concentration (0 – 0.3M HC1 solutions) as diluent on pectinase production by the media was found to be very critical. Generally, 0.5 – 0. 1m HC1 solutions were adequate in all cases resulting in maximum enzyme production in 1 to 3 days while lower or higher acidity drastically reduced the yield. Inoculation experiments A. repens showed that 1m1 spore suspense per 10g dry medium (about 2.2 x 105 spores per 1m) was adequate for rice bran and peanut shell, whereas 10mls inoculum per 10g dry medium was best for wheat bran. For A. niger with about 4.7 x 105 spores per m1, 1m1 spore suspension per 10g dry medium was adequate for each of the three media. Investigations on the effect of some nutrients on pectinase production showed that for A. repens, generally, soya flour (Glycine max) (whole and defatted) and the mixture of grapefruit peel (Citrus decumana), sucrose and soya flour increased pectinase production in the three media whereas plantain peel (Musa saplentun) and sucrose reduced it. For A. niger, plantain peel, glucose and sodium nitrate greatly reduced pectinase production in all three media. Studies on the effect of media depth (2-10cm) on enzyme production showed that for A. repens grown on wheat bran, 2cm was the best with rice bran 2 -4cm was quite good. For A. niger; 2 – 4cm was good in wheat bran; 2 – 6cm in rice bran and 2 – 10cm in peanut shell. The culture filtrates of both Aspergillus strains grown on the three semi-solid media contained mainly endo- and exo-polygalacturonases and relatively small amounts of pectinesterase and polymethylgalacturonate iyase. Apart from pectinase, they also had significant activities of cellulases, amylases and acid protease. Generally, the most significant activity in each enzyme group was the viscosity reducing action.