Abstract: In order to retain the rutin in tartary buckwheat to greatest extent, the effects of frying, steaming and superheated steaming on the distribution and transformation of flavonoids, with special reference to rutin, were explored. Results showed that the contents of bound polyphenols and flavonoids in all three treated samples (with a gelatinization degree of 11%) significantly decreased compared with untreated ones (P < 0.05). Although the content of free polyphenols and flavonoids in whole buckwheat flour also decreased, the content of free polyphenols and flavonoids in the endosperm flour, especially rutin, significantly increased (P < 0.05). The content of free rutin in whole tartary buckwheat flour was significantly reduced by frying but increased by superheated steaming and steaming (P < 0.05), indicating that high temperature-high humidity treatment not only promoted the transformation of rutin from a bound form to a free form, but also facilitated the migration of rutin from the outer layer of the shell and bran into the core kernel. As a high temperature-high humidity treatment that is characterized by higher heating efficiency and shorter duration and leads to a higher retention rate of rutin compared with steaming, superheated steaming provides an effective pretreatment to improve the eating quality and nutritional quality of tartary buckwheat.

Key words: heat treatment; tartary buckwheat with hulls; rutin; bound state; free state