Renewable Utilization of Cassava Coat Solid Waste Using Fungal Enzyme Technology

Abstract

Utilization of cassava is mostly concerned with the efficiency of producing starch and converting starch to sugars or other products through enzyme hydrolysis or fermentation. Following starch manufacturing, a large amount of solid waste remains, especially the peeled-off coat obtained in the first step. This paper showed that the overall utilization of cassava coat-waste through enzyme technology resulted in the beneficial regaining of sugars and value-added products from the remaining fiber. The enzymes used were glucoamylase and polygalacturonase that were obtained from the fungi Aspergillus niger J8 and Rhizopus stolonifers 26R, respectively, isolated in Thailand. The two enzymes were tested for their efficiency in digesting uncooked cassava starch. The production of the enzymes could be undertaken using cheap agricultural substrates. The two fungal enzymes showed a synergistic effect on raw starch digestibility of cassava coat-solid waste and of the whole cassava tuber, whereas a combination of the fungal glucoamylase with a commercial pectinase showed no such effect. An optimum ratio of polygalacturonase and glucoamylase at only 3:2 resulted in 115 and 301 mg of reducing sugars being released from 1 g of solid waste in 8 and 72 h, respectively, which was 3.3 times higher than with a commercial pectinase. The remaining non-starch fiber was processed into two value-added biomaterials, a charcoal enzyme-digested cassava fiber (EDCF) and a composite board. The EDCF was a good source of alternative energy and had a calorific value of 3,555 cal/g, which was comparable to charcoal made from corncobs and rice straw. By introducing the renewable utilization of cassava solid waste with enzyme technology produced in Thailand, cassava manufacture may gain more benefit not only from the value-added products, but also from using domestic microbial enzymes and technology which involve low cost investment.