Starch Biosynthesis-Related Genotype of Rice (Wx and Alk):

The influence of the genetic background of rice on its suitability for brewing shochu and sake (Japanese alcoholic beverages) has not been clarified. This study investigates the effects of starch biosynthesis-related genes (Wx and Alk) on the water absorption capacity of commercially available rice samples and thus examines the possibility of using rice genotype as a predictor of suitability for shochu and sake brewing. The 24 examined rice samples were classified into four genotypes: Alk/Wxa, alk/Wxa, alk/Wxb, and alk/wx. No significant differences were observed among these genotypes in terms of nonstarch properties such as grain morphology, as well as the water absorption ratio during the initial absorption phase. However, after 1 h of absorption, significant differences in terms of this ratio were observed (Alk/Wxa < alk/Wxa < alk/Wxb < alk/wx). Starch structural analysis revealed that amylose content increased in the order of alk/wx < alk/Wxb < alk/Wxa ≈ Alk/Wxa and the proportion of short amylopectin chains increased in the order of Alk/Wxa < alk/Wxa ≈ alk/Wxb. Correlation analysis revealed a significant negative correlation between the water absorption ratio at 20-120 min and amylose content. The Wx genotype, through its influence on amylose content, was found to play a major role in determining short-term and steamed-rice water absorption ratios regardless of rice type, thus being a promising descriptor of rice suitability for shochu and sake brewing. Thus, our work provides fundamental insights for cultivar breeding and developing brewing methods tailored to specific rice varieties.