Abstract
Cassava peels are generated as waste on soils during cassava processing in many tropical countries. This work set out to isolate some microorganisms associated with cassava peel degradation and characterize amylase enzymes responsible for the degradation under some physiological conditions. A total of 30 bacteria was isolated from the peels with Bacillus species occurring the most (46.5%) and Enterobacter species (13.3%) being the next. Frequencies of fungal isolations was Rhizopus sp. (35%); Aspergillus niger (25%); Aspegillus flavus (20%) and Penicillium species (20%). Bacillus cereus, Bacillus substilis Bacillus pumillus, Aspergillus niger and Apergillus flavus were selected and screened for their abilities to produce amylase. Amylase activity was highest at day 4 for B. substilis (39.4 units/ml) and A. flavus (66.1 units/ml); at day 3 for B. cereus (55.6 units/ml) and A. niger (44.6 units/ ml). While maximum amylase activity was obtained at day 6 for B. pumilus (80.2 units/ml). Optimum pH for amylases from the two fungal isolate was 6.0 (A. niger = 53.5 units/ml and A. flavus = 65.4 units/ml). While optimum pH for B.cereus (51.7 units/ ml) and B. pumilus (44.6 units/ml) was 6.5 and for B. substilis (56.1 units/ml) at pH 7.0. Amylase activities increased from 20°C to 40°C for amylase from Bacillus sp. and 20°C to 50°C for amylase from the Aspergillus sp. after which there was a decline in activities as temperature increased to 80°C. Effect of heating duration (at 70°C for 5 minutes) on the amylase showed that A. niger has the highest activity of 127 units/ml. Effect of substrate concentration on amylase activity showed that amylase form A. flavus had the highest activity of 72.2 units/ml at 0.4% substrate concentration. The implications of the findings were discussed.
Highlights
Amylases are derived from several sources such as plants, animals, bacteria and fungi
In this study we investigated the abilities and some characteristics of amylase produced by some Bacillus and Aspergillus species isolated from cassava waste peels
Four different species were the major ones isolated with Rhizopus sp. (35%) being mostly occurring; folllwoed by Aspegillus niger (25%) and Aspergillus flavus & Penicillium sp each having an occurrence of 20%
Summary
Amylases are derived from several sources such as plants, animals, bacteria and fungi. Cheap and readily available agricultural waste such as cassava peels, which presently constitutes a menace to solid waste management, may be a rich source of amylase producing microorganisms [2]. Plants and animals produce amylases, enzymes from microbial sources are generally used in industrial processes. This is due to a number of factors including productivity, thermostability of the enzyme as well as ease of cultivating microorganisms [4] [5]. Microorganisms that produce amylases could be assayed in the immediate environment especially in places such as soil around mills, cassava farms and processing factories as well as flour markets [7]
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