Michiyuki Kojima

Antioxidant and α-Glucosidase Inhibitory Activity of Polyphenols in Peel and Core from Five Different Pear Varieties

This study was performed to compare polyphenol content, DPPH radical scavenging activity and α-glucosidase inhibitory activity in peel, core and pulp of five different pear cultivars. Oligomeric polyphenols were the main polyphenols in core, which exhibited greater polyphenols, DPPH radical scavenging activity, and α-glucosidase inhibitory activity, compared to peel and pulp. For the peel, Japanese pears including Yasato, 20-Seki and Shinko pear contained relatively more polyphenol content and α-glucosidase inhibitory activity, compared to European pears including Starkrimson and Purekosu pear. Monomeric polyphenols were the main polyphenols in the peel of European pears, in contrast, oligomeric polyphenols were the main polyphenols in those of Japanese pears. The peel of Yasato pear had high ratios of non-monomeric polyphenols, and showed highest DPPH radical scavenging activity and α-glucosidase inhibitory activity amongst five pear cultivars. Thus DPPH radical scavenging activity and α-glucosidase inhibitory activity may be related with non-monomeric polyphenols in pears. Moreover, as comparing with peel, pulp had lower polyphenol content, DPPH radical scavenging activity and α-glucosidase inhibitory activity. All of the observations suggested that peel and core of pear contained abundant polyphenols and possess potential the values of reusing.

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

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 α-glucosidase in a dose-dependent manner. SRB (black) showed higher α-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 α-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.

Antioxidant Activity, α-Glucosidase and Lipase Inhibitory Activity in Rice Miso with Kidney Bean

Rice miso is a traditional Japanese seasoning food which are not only prolonging the consumption term, but also has good sensory characteristics. So thus, rice miso is very popular in Japan. In the present study, in order to improve the potential functionality, we processed rice miso adding with kidney bean (RMKB), red bean (RMRB) and buckwheat (RMBW), respectively. DPPH radical-scavenging activity, melanoidin and polyphenol content, and enzyme inhibitory activity were detected in rice miso products at different fermentation period (0, 3, 6, 24, 36 months), respectively. The results showed the DPPH radical-scavenging activity of each rice miso product was increased with prolonging the fermentation period, and RMKB showed the highest DPPH radical-scavenging activity in different rice miso products at 6, 24, 36 months. Moreover, DPPH radical-scavenging activity, melanoidin and polyphenol content of rice miso with kidney bean (RMKB) were significantly higher than those of rice miso (RM; as control) in methanol fraction purified by Diaion HP-20 column. RMKB-24M showed the highest antioxidant activity which was a better process to produce high antioxidant profiles. Furthermore, the melanoidin content in rice miso products was approximately 6-folds higher than polyphenol content. Comparing with polyphenol, melanoidin was the main antioxidant material in the rice miso products. In addition, RMKB-24M showed stronger α-glucosidase and lipase inhibitions. These results suggest rice miso with kidney bean had useful components, in particular, potential applications for antioxidant, and the treatments of diabetes and anti-obesity.

DPPH Radical Scavenging Activity and Polyphenols in the Pods of 3 Common Beans

The pods of common beans (Phaseolus vulgaris) are rich in various nutrients, and they could therefore be important parts of the human diet. In the present study, we have analyzed the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and the contents of polyphenols, anthocyanin, vitamin C, and carotenoid in the pods of 3 varieties of common beans. French beans had the highest DPPH radical scavenging activity and polyphenol contents among the three varieties. The anthocyanin content was 3.93 mg/g D.W. in French beans, but not detected in bush beans and Romano beans. The vitamin C and carotenoid contents ranged from 0.45-1.96 and 0.31-0.60 mg/g D.W. in the pods of these common beans, respectively. Moreover, we found French beans contained monomeric (Fra.I), oligomeric (Fra.II), and polymeric (Fra.III) polyphenols (67%, 31%, and 2%, respectively). In contrast, monomeric polyphenols are the main polyphenols (Fra.I > 96%) in bush beans and Romano beans. Oligomeric polyphenols (Fra.II) show higher DPPH radical scavenging activity than monomeric ones (Fra.I) in French beans. Oligomeric polyphenols with both B-type and A-type bonds were present in Fra.II from French beans. We identified malvidin 3,5-diglucoside as the anthocyanin in French beans by HPLC-PDA/MS. In summary, as a vegetable, French beans have the highest antioxidant activity among the three varieties of common bean pods studied here.