Physicochemical Basis of Eating Quality of Rice

The wide varietal difference in the eating quality of rice has been intensively Studied in several laboratories around the world since the 1950s. The Voluminous data initially suggested that the amylose starch content of rice was the single largest determinant of its end-use quality; yet amylose was not enough, additional factors seemed to be involved, among them possibly insoluble amylose, Brabender breakdown, gel consistency, and gelatinization temperature (GT). Still. the meaning of it all was not clear. A paradigm shift Occurred in the mid-1980s. A Study showed that amylopectin of rice varieties bound varying amounts of iodine, which con-elated positively with rice texture. It was then found that chain lengths of rice amylopectin varied and, more important, the proportions of the long chains differed greatly among varieties. The relative abundance of extra long chains of amylopectin strongly correlated (positively) with the cooked-rice texture. Rheological and microscopical studies suggested that abundant long chains in amylopectin resulted in a strong and resilient starch granule, while their absence led to a weak and fragile granule, which explained the difference in textures of cooked rice. Thus after half a century of extensive research, the end-use quality of rice has now been firmly attributed mostly to its amylopectin chain structure. although the protein content probably plays some minor role.