Abstract
A lime pretreatment process, calcium capturing by carbonation at room temperature (RT-CaCCO) that is used for enzymatic saccharification, was applied in order to recover glucose from whole-crop rice powders whose starch content was 26.4% of the total dry weight. Only 39.6% of the total starch was saccharified by enzymatic saccharification with the standard RT-CaCCO process, indicating the need for further optimization of the process. The effects of Ca(OH)2 concentration, mild heat treatment (MHT), and enzyme supplementation were evaluated for improved glucose release. Gelatinization enthalpy showed that MHT after RT-CaCCO (RT-MHT-CaCCO) with increased addition of Ca(OH)2 from 10% to 30% of the whole dry sample weight was reasonable in promoting sufficient disruption of starch structure, because of the increased absorption of Ca(OH)2 by the straw. The addition of α-amylase from Bacillus sp. improved the total glucose release up to 79.8% of the theoretically recoverable glucose, in which 87.0% of the total starch was saccharified. Bacillus α-amylase was probably more favorable for hydrolyzing alkali-treated starch and for producing substrates for amyloglucosidase compared to α-amylase found in the enzyme preparation of the standard RT-CaCCO process. The thorough alkali-gelatinization of starch and an appropriate combination of enzymes is crucial to apply the RT-CaCCO process to starch-rich whole-crop samples for efficient glucose recovery.
