Procyanidins in rice cooked with adzuki bean and their contribution to the reduction of nitrite to nitric oxide (^•NO) in artificial gastric juice

Abstract

In Japan, adzuki bean is cooked with rice. During the cooking, the colour of rice becomes pale red. It is postulated that the red pigment is produced from procyanidins and that the ingestion of red rice causes the production of nitric oxide (^•NO) in the stomach by reacting with salivary nitrite. The increase in colour intensity accompanied the decrease in the amounts of procyanidins, suggesting the conversion of procyanidins into the red pigment during the cooking. In addition, the red pigment combined with rice strongly. The red-coloured rice produced ^•NO by reacting with nitrite in artificial gastric juice, and the amounts were dependent on the contents of procyanidins and the equivalents. It is suggested that although adzuki procyanidins were oxidised during cooking with rice, procyanidins and the equivalents bound to rice still have the ability to produce bioactive ^•NO in the stomach using nitrite in mixed whole saliva.

Keywords:

• Adzuki bean
• binding of procyanidins to rice
• nitrite
• nitric oxide (^•NO)
• oxidation of procyanidins
• rice cooked with adzuki bean

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Part of this work was supported by the Grants-in-Aid [16K00836] from the Ministry of Education, Science, and Culture in Japan (2016 − 2018), and the Kieikai Research Foundation (2018). F. M. was partly supported by the Ministry of Education of the Czechia with co-financing from the EU [Grant KOROLID, CZ.02.1.01/0.0/0.0/15_003/0000336].