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.
View full abstract