Structural and thermodynamic properties of rice starches with different genetic background Part 1. Differentiation of amylopectin and amylose defects.

A combined DSC - HPAEC-PAD approach, gel permeation chromatography and mild long-term acidic hydrolysis were employed to study the effects of amylopectin chain-length distributional and amylose defects on the assembly structures of amylopectin (crystalline lamellae, amylopectin clusters) in A-type polymorphic starches extracted from 11 Thai cultivars of rice with different amylose level. Joint analysis of the data allowed determining the contributions of different populations of amylopectin chains to the thermodynamic melting parameters of crystalline lamellae. It was shown that amylopectin chains with DP 6-12 and 25<DP<36 as well as amylose-lipid complexes or V-type crystalline structures and apparently amylose "tie-chains" could be considered as defects in the assembly structures of rice starches. Contrary to the defects listed above, amylopectin chains with DP 13-24 and >or=37 could be related to chains stabilizing these structures. The total effect of amylose and amylopectin defects can be described by means of Thomson-Gibbs' equation. The increase of defects in the assembly structures is accompanied by rise of the rates of acidic hydrolysis of both amorphous and crystalline parts in starches.