A Study on Hot-water-insoluble Amylose Content in Rice (Oryza sativa L.)

Abstract

Amylopectin structure and its long B chain content in rice (Oryza sativa L.) regarded as an important eating quality determinant has gained acceptance since mid-1980s. Hot-water-insoluble amylose content (HISAC), an indirect measure of long B chain of amylopectin, has been proposed as a complementary criterion for evaluation of rice eating quality. However, little has been known of the distribution of HISAC in various rice accessions and its relationships with other quality characters, etc. By using 85 non-waxy rice accessions and breeding lines of indica, japonica and those with intermediate genetic background between indica and japonica, their HISAC were measured to analyze the correlation between HISAC and apparent amylose content (AAC) and pasting viscosity characters of RVA profiles. Great differences were found in the distribution of HISAC among various rice types, ranging from the lowest 8.0% in low AAC varieties, to the highest 17.9% in high AAC ones and with an average of 11.1% on the whole. The ratio of HISAC to AAC was often higher than 90% in low AAC rice, and decreased linearly with the increase of AAC upto 15%. For most rice varieties of AAC higher than 15%, the ratios remained around 50% to 70%. HISAC was significantly correlated to both AAC and HSAC, with coefficients of 0.8913** and 0.6100**, respectively. HISAC proved positively or negatively correlated to the values of setback and breakdown viscosity, the two most important values of RVA profile related to eating quality, with significant coefficients of 0.6083** and -0.5942**, respectively. However, these coefficients were smaller than coefficients between AAC and above mentioned characters of RVA profile. These results implied that HISAC alone could not perfectly reflect the importance of amylopectin in determination of eating quality of rice.