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KMID : 0903519920350050430
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Journal of the Korean Society of Agricultural Chemistry and Biotechnology
1992 Volume.35 No. 5 p.430 ~ p.431
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The structural analysis of rice starch : Ⅱ
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Kim, Hyo Jin
Nahm, Baek Hie/Kang, Mi Young/Choi, Hae Choon
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Abstract
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The polymeric structure of amylopectin as well as the composition of amylose are the most important factors to determine the functional properties of starch. To relate the structural characteristics and its functional properties of starch in rice, the degree of branch in amylopectin has been estimated by determining the level of size fractionated debranched starch on convertional gel filtration. However, the method using Sephadex-G75 is laborious and is difficult to dstinguish the long chain of amylopectin backbone from amylose due to the low exclusion limit and the low resolution. To estimate the degree of branch and polymerization of debranched starch, we developed a rapid, sensitive reproducible method using high performance gel filtration. Starch was isolated from mature seeds of various rice cultivars, debranched with isoamylase after gelatinization, and fractionated with high performance gel filtration system using Suprose-12 column with differential refractive index detector. The debranched starch polymers were fractionated into 4 distinct peaks, FractionⅠ, Ⅱ, Ⅲ and Ⅳ, depending on their molecular weight. The degree of polymerization (DP) of the FractionⅠ, regaraded as amylose of starch was measured to be higher than 200, and their levels were estimated from 6 to 16% of total sugar depending on the amylose contents. The DPs of Fraction Ⅱ, Ⅲ and Ⅳ containing linear polymers of different length were ranged 200∼100, 100∼50 and $lt;50, and their levels in the range of 8∼14%, 25∼37%, and 37∼52%, respectively. The ratios of each fraction were analyzed to estimate the degree of branch of amylopectin. The ratio of Fraction Ⅲ to Ⅱ (B ratio) were estimated to be from 2.2 to 5.0, while that of Fraction Ⅳ to Ⅱ(A ratio) from 3.2 to 5.7. These ratios can be suggested to represent the degree of branch with different length. As an another parameter, the ratios of Fraction Ⅱ and Ⅳ to Ⅱ (T ratio) describing the total degree of branch were from 5.4 to 10.2. The T ratio as well as A and B ratios did not show any relationship with amylose contents showed no relation with amylose contents in contrast the one observed in conventional gel filtration. The A, B and T ratios obtained by high performance gel filteration, the complexity of amylopectin in starch can be described to relate the functional properties of starch. Also from the analysis results of rice starch, we can suggest the degree of branch in amylose of rice starch be independent of the amylose contents.
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