Abstract:

Starch and its pasting and retrogradation properties appear to be one of the key factors determining the qualities of wheat products. Amylopectin structure in starch granules can be described by a cluster model. The chain-length distribution of amylopectin has been focused in researches because of its relation to physicochemical properties of starch. The long B chains render the starch granule strong and resilient, thus leading to the firm texture of cooked rice, while the shortage of such chains leads to weak granules resulting in soft cooked rice. Now more and more researchers show their attentions to the relationship between the structure and physicochemical properties of starch. We mainly studied chain length distribution of amylopectin debranched by isoamylase in waxy and non-waxy wheat (Triticum aestivum L.) at Yangzhou University, also analyzed the relationships between starch structure and starch physicochemical properties, which would provide some information for producing wheat with good grain quality and high yield. The blue value (BV) and maximum absorption (λ_max) of amylose or amylopectin and the chain length distribution of debranched amylopectin were measured. The results showed that BV and λ_maxAM of amylose were higher than those of amylopectin. The order of BV and λ_max of amylopectin (λ_maxAP) was medium-gluten wheat>weak-gluten wheat>strong-gluten wheat>waxy wheat. There was a positive correlation between BV and λ_maxAP. Three kinds of components of debranched amylopectin molecular chain were got by Sephadex G75 from all different cultivars except waxy wheat cultivars. The weight percentage of long B-chain in debranched amylopectin was the lowest among three compositions, that of intermediate B-chain content was the second, that of short B-chain and A-chain contents accounting for about 65% were the highest. The order of long B-chain and intermediate B-chain percentage was weak-gluten wheat>strong-gluten wheat>medium-gluten wheat in normal types. Obvious differences among different cultivars in the same type were also observed. There was no long B-chain in amylopectin of waxy wheat. The proportion of long B-chain was highly significantly correlated with pasting parameters of RVA except breakdown (BD), and significantly correlated with crystalline degree. It might be assumed that physicochemical characteristics of starch in wheat grain were significantly affected by the long B-chain content.

Key words: Wheat (Triticum aestivum L.), Amylose content, Chain length distribution, Physicochemical characteristic