Takuro Koga

Inhibitory Effect of an Ellagic Acid-Rich Pomegranate Extract on Tyrosinase Activity and Ultraviolet-Induced Pigmentation

A pomegranate extract (PE) from the rind containing 90% ellagic acid was tested for its skin-whitening effect. PE showed inhibitory activity against mushroom tyrosinase in vitro, and the inhibition by the extract was comparable to that of arbutin, which is a known whitening agent. PE, when administered orally, also inhibited UV-induced skin pigmentation on the back of brownish guinea pigs. The intensity of the skin-whitening effect was similar between guinea pigs fed with PE and those fed with L-ascorbic acid. PE reduced the number of DOPA-positive melanocytes in the epidermis of UV-irradiated guinea pigs, but L-ascorbic acid did not. These results suggest that the skin-whitening effect of PE was probably due to inhibition of the proliferation of melanocytes and melanin synthesis by tyrosinase in melanocytes. PE, when taken orally, may be used as an effective whitening agent for the skin.

Enzymatic synthesis of stable, odorless, and powdered furanone glucosides by sucrose phosphorylase.

Sucrose phosphorylase from Leuconostoc mesenteroides catalyzed transglucosylation from sucrose to 4-hydroxy-3(2H)-furanone derivatives. When 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) and 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone or 5-ethyl-4-hydroxy-2-methyl-3(2H)-furanone (EHMF) were used as acceptors, their transfer ratios were more than 45%. In the case of glucosylation of HDMF, the major transfer product was identified as 2,5-dimethyl-3(2H)-furanone 4-O-α-D-glucopyranoside (DMF-G). In the case of glucosylation of EHMF, two major transfer products were obtained, and their structures were identified as 2-ethyl-5-methyl-3(2H)-furanone 4-O-α-D-glucopyranoside (2E5MF-G) and 5-ethyl-2-methyl-3(2H)-furanone 4-O-α-D-glucopyranoside (5E2MF-G) on the bases of spectrometric investigations. These glucosides were more stable than each aglycone. The glucosylated HDMF, DMF-G, was an odorless chemical, on the other hand, HDMF had a pineapple flavor. The glucosylated EHMF (EMF-G) were white odorless powders, though aglycone EHMF was a pale yellow syrup like a caramel with an intense sweet odor. Although DMF-G and EMF-G showed little radical-scavenging activity, hydrolyzates of these glucosides by an intestinal acetone powder from pigs had antioxidative activity as well as their aglycones. It was suggested that these glucosides improved some physical properties and may become prodrugs by glucosylation.

KINETIC STUDIES ON THE FORMATION OF PHOSPHATIDYLCHOLINE HYDROPEROXIDES IN LARGE UNILAMELLAR VESICLES BY AZO COMPOUNDS

Abstract Peroxidation of phosphatidylcholine (PC) in large unilamellar vesicles (LUV) was studied by measuring PC-hydroperoxides (PC-OOH) formed by azo compound-initiated radical chain reaction. When the peroxidation was induced by a water-soluble azo compound, the rate of PC-OOH formation in LUV comprising of egg yolk PC was larger than that in multilamellar vesicles (MLV) of the same origin. On the other hand the opposite trend was observed when a lipid-soluble azo compound was used. The kinetic parameters of free radical oxidation of egg yolk PC were compared with those of soybean PC in LUV with a water-soluble azo compound or a lipid-soluble azo compound and in tert-butyl alcohol solution with a lipid-soluble azo compound. In LUV, the oxidizability per molecule and the kinetic chain length of egg yolk PC were much lower than those of soybean PC independent of the azo-compounds. In solution, the difference in these parameters between the two PC species was small. The oxidizability per bis-allylic hydrogen of egg yolk PC was also lower than that of soybean PC in spite of the same values from both PCs in solution. These data strongly suggest that molecular species substantially affect the oxidation kinetics of PC in unilamellar vesicles, as compared with those in solution.

Effect of dung beetle, Onthophagus lenzii H. on nitrogen transformation in cow dung and dung balls

Abstract A significant part of potentially mineralizable organic nitrogen (N) in soil comprises microbial cells (Bonde et al. 1988). Since the major part of organic N in cow dung also consists of microbial biomass N (Marsh and Campling 1970), it may be worth comparing the origin and the successive processes of N mineralisation in cow dung with those in soil. We studied the effect of the dung beetle, Onthophagus lenzii H., on the decomposition of cow dung and found that the dung beetle played a significant role in this process (Yokoyama et al. 1990). We employed, here, the acid hydrolysis method to analyze the effect of the dung beetle on N transformation in dung balls and residual cow dung.