Rutin Concentration and Characterization of Rutinosidase in Perennial Buckwheat (Fagopyrum cymosum) and Its Application in Foods

To evaluate the potential of perennial buckwheat (Fagopyrum cymosum; FC) as a food source, rutin concentration was investigated. FC contains more than 1% (w/w) rutin and 0.03% quercetin in the leaves, flowers, and seeds. In particular, rutin and quercetin concentrations were high in plant seeds. Therefore, FC is useful as a rutin- and quercetin-rich material. In contrast, the FC seed contained a large amount of rutinosidase. Purified rutinosidase in a homogenous mixture consisted of only one isozyme with M.W. of 58.4 KD and low K_m for rutin (0.367 mM). The rutin concentration in the FC dough decreased to almost zero, 10 min after the addition of water. Parallel to the decrease in rutin, quercetin was increased, and strong bitterness was generated, whereas steam-heated flour in which rutinosidase was inactivated did not have rutin hydrolysis and bitterness. These results indicate that rutinosidase is a major cause of rutin hydrolysis and bitterness. The in vitro rutinosidase is inactivated at pH 8.0 and 65 °C. Therefore, the control of dough pH and temperature should be useful in preventing rutinosidase activity.