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In this study, we explored the hydrolytic mechanism of glucan 1,4-α-maltotiohydrolase (AMTS). Kinetic parameters analysis of AMTS were performed using the amylopectin with different external chain lengths (ECL). Then, the waxy maize starch was gelatinized and hydrolyzed by AMTS to various degrees; retrogradation of starch hydrolysates were determined. Michaelis constant ( K m ) of the β -dextrin-3 (ECL 2.3) was eight folds than the amylopectin (ECL 17.8), but its catalytic efficiency ( k cat / K m ) was only 6.5% of amylopectin. AMTS preferred the external chains to the internal chains for hydrolysis, and amylopectin was hydrolyzed by AMTS through combined exo- and endo-action. In the initial hydrolysis stage, the exo-action of AMTS was predominant with slow reduction in M w and little changes in the internal chains of amylopection. The percentage of maltotriose in the soluble oligosaccharides (PM) was 90.5% at 2.1% degree of hydrolysis (DH), and gradually decreased from 90.5% to 71.2% at 35.4% DH. The PM decreased could be partially attributed to the increased transglycosylation reactions of AMTS. Complete inhibition of amylopectin retrogradation was observed with >15.9% hydrolysis for the increased shorter outer chains and low molecular weight dextrins. These results indicate that AMTS may be effective in retarding starch retrogradation in baked products. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine 1-buatnol–hydrochloric acid (1-butanol–HCl) hydrolysis process of starch. Normal rice starch was hydrolyzed by 0.36% HCl in anhydrous 1-butanol at 40 °C from 4 h to 7 days. The changes in starch granule, crystalline, and molecular weight during the 1-butanol–HCl hydrolysis were determined using SEM, particle size analyzer, XRD, HPSEC–MALLS–RI, and iodine staining. SEM and particle size analyzer analysis showed that the granule morphology significantly changed and the granule size decreased from 5.47 μm to 5.07 μm after the hydrolysis by 1-butanol–HCl for 7 days. XRD results indicated that amorphous areas of normal rice starch were firstly hydrolyzed followed by the ordered areas during 1-butanol–HCl hydrolysis. The peak (2θ) of V-type crystallinity was detected at around 20° in the XRD curves of 1-butanol–HCl-hydrolyzed starches. This peak confirmed the formation of amylose–1-butanol complex. HPSEC–MALLS–RI and iodine staining analysis demonstrated that the weight-average molecular weight of normal rice starch sharply decreased from 2.4 × 107 Da to 4.9 × 105 Da after 1-butanol–HCl hydrolysis for 4 h, then gradually decreased, and finally stabilized at about 2.6 × 104 Da after hydrolysis for 4 days. These results suggest that the attack of 1-butanol–HCl on normal rice starch preferentially occurred in the amylopectin molecules of amorphous areas. [ABSTRACT FROM AUTHOR]