Biochemical Characterization of Crude α-Amylase of Aspergillus spp. Associated with the Spoilage of Cassava (Manihot esculenta) Tubers and Processed Products in Nigeria

Abstract

In this research, crude α-amylases associated with the spoilage of cassava (Manihot esculenta) tubers/ product (‘eba’) were biochemically characterized. They were isolated from five fungi: Aspergillus sp. CSA25, Aspergillus sp. CSA26, Aspergillus sp. CSA27, Aspergillus sp. CSA35 and Aspergillus sp. CSA38. The results of the analyses showed that the activities of α-amylase obtained from both sources (cassava tuber/ eba) were optimal at 45°C and pH 5.0. The maximum specific activity (Vmax) of the enzyme was found to be 10 U/mg protein, while its Michaelis-Menten constant (Km) was between 0.37 -1.25%w/v. The α-amylase is thermally stable for 1 - 2 h at optimum temperature and pH (45°C; pH 5.0). A broad range of substrate specificity was expressed by the enzyme for cassava starch-containing products (tapioca flour, garri flour, cassava flour, 1%, w/v); however, potato (Ipomoea batatas) starch, yam (Dioscorea rotundata) flour and cocoyam (Colocasia esculenta) flour were relatively minimally hydrolyzed by the crude α-amylases obtained from Aspergillus spp. that caused spoilage of cassava. Ethylenediamine tetraacetic acid (1 mM EDTA) and Mg2+ treatment had no significant (p > 0.05) effect on the activities of the amylase, but Na+, K+, Ca2+, Fe3+, thiourea and 5′,5′-dithiobis-2-nitrobenzoate (1 mM DTNB) enhanced its activities. The fungal α-amylases were most activated by K+ and had a salt tolerance of 1 - 2 M NaCl for 24 h. The fungal α-amylases reported in this study would find useful application in industries like food industry, detergent industry, paper industry, textile industry, pharmaceutical industry, etc where microbial α-amylases would be required for efficient and cost-effective hydrolysis of cassava starch, cassava flour and or its products.