Evaluation of Useful Biological Activities of Hot-Water Extracts of Raw-Red Bean and Boiled-Red Bean (Phaseolus radiatus L.)

Abstract

Raw-red bean (RR) should be boiled in hot water, and only boiled-red bean (BR) has been used in the food industry. In the course of development of functional food using red- bean (Phaseolus radiatus L), hot- water extracts (HWEs) of RR and BR were prepared, respectively and their components and various biological activities were compared. The extraction yield at 100℃ of RR (16.2%) was higher than that of BR (14.8%), and contents of total polyphenols, total flavonoids and reducing sugars of HWE of RR were 2.5-fold, 2.1-fold and 1.5-fold higher than those of HWE of BR. In anti-oxidation activity assay, scavenging activities against DPPH anion and ABTS cation as well as reducing power of RR was higher than those of BR. The results suggest that the anti-oxidant compounds in red bean might be heat-liable or discarded during boiling in hot-water as a cooking drip. Unexpectedly, nitrite scavenging activity was stronger in HWE of BR than RR. In anti-microbial activity assay, HWE of RR (500 μg/disc) showed growth inhibition activity against gram-positive bacteria, whereas HWE of BR did not show any activity against any tested bacteria and fungi. Assay of in-vitro anti-diabetes and anti-thrombosis activities, which were previously reported in ethanol extract of red-bean, revealed that HWEs of RR and BR did not show significant activities against α-amylase, α-glucosidase, thrombin, prothrombin, or blood coagulation factors. Our results suggest that the anti-oxidation, anti-diabetes and anti-thrombosis activities of HWEs of RR and BR were lower than those of ethanol extracts of red bean, and bioactive substances in RR were destroyed during boiling or discarded after boiling. Further research on suitable boiling and re-use of cooking drip of red bean is necessary.