Breeding of Buckwheat to Reduce Bitterness and Rutin Hydrolysis

Buckwheat (Fagopyrum esculentum) is recognized as an important traditional crop in some regions, and its taste is an important characteristic. Of the three cultivated buckwheat species, Tartary buckwheat (Fagopyrum tataricum) and perennial buckwheat (Fagopyrum cymosum) have strong bitterness in their seeds, which has prevented the wider use of the seeds of these varieties. In Tartary buckwheat, some studies have focused on the cause of strong bitterness generation. Tartary buckwheat seeds contain large amounts of the functional compounds rutin and rutinosidase, and rutin hydrolysis by rutinosidase has been found to be the trigger of rutin hydrolysis. Therefore, a variety with only a trace of rutinosidase and with reduced bitterness is required. The rutinosidase in Tartary buckwheat seeds consists of two major isozymes with very similar enzymatic characteristics, which can hydrolyze flour rutin within several minutes after the addition of water. Recently, the trace-rutinosidase variety Manten-Kirari in Tartary buckwheat was developed. The trace-rutinosidase characteristics were dominated by a single recessive gene. In 'Manten-Kirari' dough and foods, such as breads, confectionaries, and noodles, the rutin residual ratio was higher and bitterness was reduced compared to that of the normal-rutinosidase variety. In this review, we summarize the detailed research on the breeding of buckwheat related to reducing bitterness and rutin hydrolysis.