Pancreatin-induced liberation of starch/cyanidin 3-O-glucoside complexes from rice cooked with black soybean that exhibit slow hydrolysis

Abstract

Cyanidin 3-O-glucoside (C3G), which has various health-promoting functions, is contained in black soybean (BSB). In Japan and Korea, BSB is cooked with rice and the cooked rice appears purplish in colour. In this study, BSB was cooked with glutinous rice, non-glutinous rice, and high-amylose rice. The amount of C3G detected in high-amylose rice was greater than that detected in glutinous rice, suggesting that C3G combined more efficiently with amylose than with amylopectin. Pancreatin induced the liberation of starch/C3G complexes from the purplish cooked rice, and rate of the liberation was in the following order; glutinous rice < non-glutinous rice < high-amylose rice. The amylose/C3G complexes liberated from high-amylose rice was hydrolysed slowly, while the amylopectin/C3G complexes liberated from glutinous rice were hydrolysed into smaller amylopectin/C3G complexes that were difficult to further hydrolysis. Thus, C3G may be useful for preparing foods whose starch hydrolysis is slow.

Keywords:

• Black soybean
• cyanidin 3-O-glucoside
• rice
• starch/cyanidin 3-O-glucoside complexes
• starch hydrolysis

Authors contributions

U. T. designed the research, collected experimental data, interpreted the results and drafted the manuscript. J. P. collected kinetic data, T. A. provided a space to perform the experiments in his laboratory, and S. H. reviewed and edited final draft.

Acknowledgements

U.T. would like to thank Kyushu Dental University for allowing him to use their facility.

Disclosure statement

The authors repot no conflict of interest.

Additional information

Funding

Part of this work was supported by the Ministry of Education, Science, and Culture in Japan (2020 − 2022) under Grants-in-Aid [20K05916]; the Tojuro Iijima Foundation for Food Science and Technology [2019]and the Kieikai Research Foundation [2018] to S. H.