71B-16 |
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S. H. Lee1, C. J. LEE2, T. W. Moon1, and K.-H. Park1. (1) Dept. of Food Science and Technology, Seoul National Univ., School of Agricultural Biotechnology, San 56-1. Silim-dong, Kwanak-gu, Seoul, 151-742, South Korea, (2) Dept. of Food Science and Technology, Seoul National Univ., School of Agricultural Biotechnology, San 56-1 Silim-dong, Kwanak-gu, Seoul, 151-742, South Korea Amylomaltase(4-a-glucanotransferase) catalyzes glucan transfer from one a -1,4-glucan to another a-1,4-glucan or to glucose. The enzyme action induces the changes of amylose contents, amylose-amylopectin ratio, the size of branched-chain of amylopectin and cycloamylose formation in starch. These changes influence the physical and structural properties of starch. In this study, sweet potato starch was treated with a-1,4-glucanotransferase from Thermus aquaticus (TAaGT) to change the physical, structural and rheological properties of starch. Enzymatically treated starch was produced by TAaGT treatment for 16 hrs at 70°É. They showed lower levels of amylose content than raw starch, and the pattern of wave-scanning indicated less amylose. The molecular weight (Mw) distribution obtained by gel permeation chromatography displayed that Mw of amylopectin was lower and more variable than that of raw starch. The chain length distribution using a high-performance anion exchange chromatography showed that the number of short side chains (DP<10) increased and cycloamylose was formed. In gelatinization parameters, enzymatically treated starch reduced the gelatinization enthalpy, and melting range was broader as compared to raw starch. The X-ray diffraction of enzymatically treated starch showed a weak V-type pattern. In microscopic observation, enzymatically treated starches showed very big holes on the surface and lost the granular structure. In rheological properties, the results of frequency sweep measurement revealed that the gel of enzymatically treated starch had higher storage modulus (G′) and loss modulus (G″) than those of raw starch. However, the structure of the enzyme treated starch gels was collapsed during temperature sweep measurement. The results of dynamic viscoelasticity during heating and cooling cycle showed that enzymatically treated starch changed reversible structure. These results show that TAaGT induces conformational and rheological change in sweet potato starch. Treatment TAaGT can improve retrograding properties of starches by reducing their molecular weight, suggesting their utilization in starch based products.
Session 71B, Food Chemistry: Proteins and enzymes
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |