Suppressive Effect of Polyphenols from the Seed Coat of Scarlet Runner Beans on Blood Glucose Levels

Zhaohong Ci,Michiyuki Kojima,Chengyu Jiang

doi:10.12691/jfnr-6-3-7

Abstract

Scarlet runner beans (SRB) are a valuable source of many nutrients, including proteins, starch, dietary fiber, and oligosaccharides, and are used in various foods in Japan. In this study, we analyzed their polyphenol and procyanidin contents, DPPH radical scavenging activity, and reducing power. SRB (purple) had a higher polyphenol content and DPPH radical scavenging activity than those of SRB (black). The reducing power of SRB (black) (5.1 mg/g) was greater than that of SRB (purple) (4.1 mg/g). Both SRB (purple) and SRB (black) had greater levels of polymeric polyphenols (total Fra.II and Fra.III) than monomeric polyphenols (Fra.I), and inhibited the activity of Î±-glucosidase in a dose-dependent manner. SRB (black) showed higher Î±-glucosidase inhibitory activity (IC50, 26.4 µg/mL) than that of SRB (purple) (IC50, 39.7 µg/mL), and a mixed pattern of inhibition (non-competitive and uncompetitive). The Î±-glucosidase inhibitory activity was greater for polyphenols from the seed coat (>91%) than from the cotyledon (<0.1%) for SRB (purple) and SRB (black). Both 250 mg/kg and 750 mg/kg polyphenols from the coat of SRB (purple) effectively suppressed the elevation of blood glucose levels after the oral administration of starch in mice. These results suggest that the seed coat of SRB has useful properties and, in particular, has potential applications for the treatment of diabetes.

Highlights

Diabetes has received considerable attention owing to the increasing number of people suffering from this chronic disease [1]
All dietary carbohydrates are hydrolyzed by enzymes to yield simple sugars, which can improve blood glucose levels [4]. α-Glucosidase is an intestinal cell membrane enzyme that can hydrolyze polysaccharides; inhibiting the activity of αglucosidase may be an effective way to treat pre-diabetes and slow the progression of diabetes [5]
It has been reported that polyphenolic compounds from legumes [7,8] could inhibit α-glucosidase activity, few studies have examined the inhibitory activity of these polyphenolic compounds on both α-glucosidase and blood glucose levels

Summary

Introduction

Diabetes has received considerable attention owing to the increasing number of people suffering from this chronic disease [1]. Controlling the blood glucose level is the most effective method for preventing diabetes deterioration and hyperglycemia [3]. All dietary carbohydrates are hydrolyzed by enzymes to yield simple sugars, which can improve blood glucose levels [4]. Α-Glucosidase is an intestinal cell membrane enzyme that can hydrolyze polysaccharides; inhibiting the activity of αglucosidase may be an effective way to treat pre-diabetes and slow the progression of diabetes [5]. Several synthetic α-glucosidase inhibitors, such as acarbose and voglibose, have been developed, but these have various side effects, such as digestion disorders, flatulence, and liver function disorders [6]. It has been reported that polyphenolic compounds from legumes [7,8] could inhibit α-glucosidase activity, few studies have examined the inhibitory activity of these polyphenolic compounds on both α-glucosidase and blood glucose levels

Methods

Results

Conclusion