61A-9 |
Structural characteristics of slowly digestible waxy sorghum starch as affected by modification process |
H. J. CHOI1, S. I. Shin1, K. M. Chung2, B. R. Hamaker3, and T. W. Moon1. (1) Department of Food Science & Technologly, School of Agricultural Biotechnology, Seoul National University, Suwon 441-744, KOREA, South Korea, (2) Department of Food Science,College of Natural Sciences, Andong National University, 388 Songchon-dong,Andong,Kyungbuk,Korea, South Korea, (3) Department of Food Science, Purdue nuiversity, West Lafayette, IN
There
is much evidence to suggest that slowly digestible starch (SDS) is preferable
to rapidly digestive starch (RDS) not only in diabetics but also in healthy
individuals as it possesses a lower glycemic index. However, the formation of
SDS and its structural properties are not fully understood, yet. The objective of this study was to investigate the
structural characteristics of SDS fraction formed in waxy sorghum by several
modification treatments. SDS content was increased in cooked waxy sorghum
starch debranched with isoamylase followed by heating and storage at 1oC
for 3 days. The structure of SDS
was deduced by comparing the fraction of SDS mixed with RS and the RS fraction using
differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and
X-ray diffraction (XRD). SEM showed that the
SDS-RS mixture had crystallites with smooth plate-like
surface. In the RS fraction formed by a-amylase treatment, it was found that the edges of
the crystallites were digested away and that the crystallites were extensively
pitted at their surfaces. In DSC themograms, the SDS-RS mixture and the RS showed melting temperature of 94oC and 88oC,
respectively. Tp, Tc , Tc-To and enthalpy of the mixture were higher than those of the RS. For the XRD
pattern, the crystallinity of RS was estimated to be higher than that of SDS-RS mixture. The crystallinity also increased with increasing a-amylase treatment time. These results suggest that the RDS, SDS and RS fractions are reformed into a single crystallite by low temperature storage following debranching. RDS had amorphous structure and appeared to locate outside. SDS was intermediate, between RDS and RS which consisted of mostly amorphous region and a small portion of ordered double helix structure. RS had ordered double helix structure and located inside.
Session 61A, Carbohydrate
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