Enhancing the Enzymatic Saccharification of Agricultural and Processing Residues of Cassava through Pretreatment Techniques

Purpose The aerial part of the cassava plant comprising stems, leaves and cassava peels are waste biomasses generated during the cultivation and processing of cassava. The potential of these biomasses as alternative substrates for the production of bioethanol was investigated. Methods The efficacy of three types of pretreatments such as (i) hydrothermal treatment, (ii) microwave exposure of acid slurry and (iii) dilute acid treatment (steam as well as under pressure) in enhancing the enzymatic degradability of agricultural residues of cassava was investigated. Results Whilst cassava stems and peels had 15.00 and 29.84 % starch along with 22.8 and 14 % cellulose respectively, dry leaves had only 2.43 % starch and 17.3 % cellulose. Hemicellulose ranged from 23 to 29 % in these biomasses. The pretreated biomasses were compared with the native samples for the fermentable sugar yield during enzyme saccharification by the cellulolytic enzyme complex, Accellerase (TM) 1000. Among the pretreatments, hydrothermal treatment (HT) of moist powders for 30 min was the most effective in giving the highest yield of reducing sugars, followed by microwave assisted dilute acid treatment for 20 min. Extending the exposure time for HT to 45 and 60 min reduced the sugar yield. Leaf was the most recalcitrant among the three biomasses. Ultrastructural studies using Scanning electron microscopy also supported the saccharification data. Very high extent of release of sugars during saccharification was noticed from cassava peels which also had Ca. 29.84 % starch. Optimal level of Accellerase required for saccharification was 500 mg enzyme protein. Conclusions It was concluded from the study that hydrothermal treatment of the powdered biomasses for 30 min was the most appropriate technique to enhance the biodegradation by cellulolytic enzymes.