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KMID : 0903519920350050429
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Journal of the Korean Society of Agricultural Chemistry and Biotechnology
1992 Volume.35 No. 5 p.429 ~ p.430
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The structural analysis of rice starch : Ⅰ
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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 composition and polymeric structure of starch are the most important factors to determine the functional properties of rice. In an effort to relate the structural characteristics its functional properties of starch in rice, we analyzed the polymeric structure of starch from 24 rice cultivars. Starch was isolated from mature seeds, debrached with isoamylase after gelatinization, and fractionated with Sephadex-G 75 gel filtration. The amount of total sugar in each fraction was determined by phenol-sulfuric acid method and the maximum absorption carbohyrate complex. The size fractionated debrached starch was categorized into four groups such as Fraction Ⅰ, Ⅱ, Ⅲ and intermediate Fraction depending on their λ_(max). The fractions with the λ_(max) higher than 620 ㎚ were designated as Fraction Ⅰ, while those in the range of 600∼620 ㎚ and 540∼600 ㎚ as the intermediate Fraction and Fraction Ⅱ, respectively. The fractions with the λ_(max) lower than 540 were described as Fraction Ⅲ. The average degree of polymerization (DP) of the Fraction Ⅰ was estimated to be higher than 200, and those of other fraction, i.e. the intermediate Fraction Ⅰ, Fraction Ⅱ and Ⅲ were 150, 45 and 25, respectively. The levels of Fraction Ⅰ were varied from 11 to 35% of total sugar. The Fraction Ⅰ showed the linear relationship with the amylose contents, and therefore it could represent amylose fraction of starch. The levels of the intermediate Fraction, which might contain the mixture of short chain of amylose and debrached long chain of amylopectin, were measured to be in the range of 2.7∼8.4%. The levels of Fraction Ⅱ and Ⅲ, both to be considered as the branches of amylopectin, were ranged 14.5∼23.6% and 39.7%∼73.0%, respectively. The ratio of Fraction Ⅱ to Fraction Ⅱ describing the degree of branch or compactness of amylopectin was estimated to be around 4.0 for waxy varietied and around 2 for high amylose cultivars. With these results, it can be suggested that the degree of branch of the amylopectin may effect on amylose contents of starch or vice versa. The ratio Fraction Ⅲ to Ⅱ could be one of the important parameters in describing the compexity of structure related the functional properties of starch in rice.
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