Preliminary study on the synthesis of bioethanol from tapioca starch using high gravity Simultaneous Saccharification and Fermentation (SSF) Method

Abstract

Tapioca starch is extracted from the root of cassava plant (Manihot esculenta). Currently, cassava root is produced mainly in African and Asian countries, with South East Asian countries being the major cassava root exporting countries. Tapioca starch is a potential raw material for food and non-food industries. Due to its high carbohydrate content (typically more than 70%), tapioca starch has the potentiality to be used for the preparation of bioethanol. In this research, a promising approach to synthesise highly concentrated ethanol from tapioca starch in one-pot process, i.e. High Gravity Simultaneous Sacharification and Fermentation (SSF) method, was investigated. High Gravity SSF was performed on liquefied tapioca starch suspensions (15% and 25%-w/v carbohydrate content). In the Liquefaction step, tapioca starch suspension was first gelatinised for two hours at 90°C and hydrolised at the same temperature for another two hours using comercial - amylase (Liquozyme Supra, 0.16%-v/ w starch). The pretreated mixture was sterilised, mixed with nitrogenous supplement (yeast extract/peptone or urea, N-content equivalent to 0.375 %-w/v), and used as fermentation substrate. After addition of Saccharomyces cereviseae NRRL Y-132 inoculum (10%-v/v; 3.9 x 109 cells/ ml) and commercial amyloglucosidase (Dextrozyme GA, 3%-w/v), High Gravity SSF was allowed to proceed for 5 days at 30°C with rotary shaker speed of 100 rpm. Total cell number during fermentation was determined by direct microscopic method, while concentration of glucose, maltose, and ethanol was monitored using HPLC. The experimental result shows that tapioca starch has been successfully converted to ethanol with concentration of 9.94-18.54%, which is corresponding to yield of 63.32-72.91% w ethanol/ w of initial carbohydrate. The use of simple nitrogeous supplement (urea) resulted in reduced ethanol yield when compared to yeast extract/ peptone. The result suggests that High Gravity SFS is a prospective method to synthesise bioethanol from tapioca starch.