Partial swelling of granules enables high conversion of normal maize starch to glucose catalyzed by granular starch hydrolyzing enzyme

Tong, Z.; Tong, Y.; Shi, Y.-C.

Industrial Crops and Products 140: 111626

2019


ISSN/ISBN: 0926-6690
DOI: 10.1016/j.indcrop.2019.111626
Accession: 070961024

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Abstract
Maize starch is an abundant renewable biopolymer that can be processed into sugars and ethanol, or other fermented chemicals. The objectives of this study were to examine how partial swelling of starch granules enhanced the starch saccharification process, characterize the indigestible residues, and determine the optimal conditions for glucose production. Normal maize starch (2.0% in 50 mM citrate butter) was partially swollen by heating at 62, 65, and 70 degrees C for 30 min, and the preswollen starch hydrolyzed by addition of a granular starch hydrolyzing enzyme (GSHE). After preswelling at 70 degrees C, enzyme kinetics study of the release of glucose showed a 54% reduction in the Michaelis-Menten constant (K-m), suggesting that preswelling increased the complexing of GSHE with the starch granules. Preswelling the starch at 62, 65, and 70 degrees C followed by digestion with 1.0% GSHE (starch basis) at 62 degrees C for 24 h in 50 mM citrate buffer (pH 4.5) resulted in 61.3, 76.0, and 94.5% conversion to glucose. The indigestible fraction, compared to the untreated starch, had a lower A-type crystallinity and probably less amylose-lipid complex, was more highly branched, contained a higher proportion of short chains, and showed a higher gelatinization temperature but lower enthalpy of gelatinization. The indigestible fraction, after preswelling at 100 degrees C in citrate buffer, was converted practically quantitatively to glucose. Partial swelling of granules offers great potentials in converting starches to sugars by GSHE.