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KMID : 1007519990080040221
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Food Science and Biotechnology
1999 Volume.8 No. 4 p.221 ~ p.226
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Aging of Waxy Rice Starch and Amylopectin Gels Isolated from Waxy and Nonwaxy Rice Starches
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Kim, Jeong Ok
Kim, Wan Soo/Shin, Mal Shick/Baek, Man Hee
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Abstract
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The pasting behaviors of waxy rice starch (WRS) and amylopectins isolated from waxy (AWRS) and nonwaxy (ANRS) rice starches were investigated using the Brabender Visco-Amylograph. The degree of retrogradation (DR) of those gels (50%, w/w) stored at 4℃ for up to 14 days were measured by the α-amylaseiodine method, DSC, and X-ray diffractometry. The initial pasting temperature of WRS was at 70℃, but those of AWRS and ANRS were not observed. While the amylogram of WRS showed a peak viscosity, those of AWRS and ANRS did not show a marked change in viscosity, as did that of WRS. The DRs of all gels increased rapidly for the first 2 days of storage and then either remained unchanged (for AWRS and ANRS gels), or increased slowly for the WRS gel thereafter. The DR of ANRS gel was the highest among all the aged gels. In DSC, the aged gels showed a single endotherm at 34.0-63.8℃ and the enthalpies of aged ANRS gels were 2 and 3-6 times higher for 1 and 7 days of storage, respectively, than those of aged WRS and AWRS gels. The X-ray diffractogram of WRS showed an A-type pattern, but those of AWRS and ANRS had no peak, supporting the conclusion that the crystallinities of the isolated amylopectins from rice starches were altered. With aging, the crystallinities of all gels were converted into B-types, similar to a retrograded starch.
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