Summary Different colors, such as purple, brown, red and white, occur in the pericarp of rice. Here, two genes affecting proanthocyanidin synthesis in red‐ and brown‐colored rice were elucidated. Genetic segregation analysis suggested that the Rd and A loci are identical, and both encode dihydroflavonol‐4‐reductase (DFR). The introduction of the DFR gene into an Rcrd mutant resulted in red‐colored rice, which was brown in the original mutant, demonstrating that the Rd locus encodes the DFR protein. Accumulation of proanthocyanidins was observed in the transformants by the introduction of the Rd gene into the rice Rcrd line. Protein blot analysis showed that the DFR gene was translated in seeds with alternative translation initiation. A search for the Rc gene, which encodes a transacting regulatory factor, was conducted using available DNA markers and the Rice Genome Automated Annotation System program. Three candidate genes were identified and cloned from a rice RcRd line and subsequently introduced into a rice rcrd line. Brown‐colored seeds were obtained from transgenic plants by the introduction of a gene containing the basic helix–loop–helix (bHLH) motif, demonstrating that the Rc gene encodes a bHLH protein. Comparison of the Rc locus among rice accessions showed that a 14‐bp deletion occurred only in the rc locus.

alpha-Glucosidase (AGH) inhibitory study by natural anthocyanin extracts was done. As the result of a free AGH assay system, 12 anthocyanin extracts were found to have a potent AGH inhibitory activity; in particular, Pharbitis nil (SOA) extract showed the strongest maltase inhibitory activity, with an IC(50) value of 0.35 mg/mL, as great as that of Ipomoea batatas (YGM) extract (IC(50) = 0.36 mg/mL). Interestingly, neither extract inhibited the sucrase activity at all. For the immobilized assay system, which may reflect the pharmacokinetics of AGH at the small intestine, SOA and YGM extracts gave more potent maltase inhibitory activities than those of the free AGH assay, with IC(50) values of 0.17 and 0.26 mg/mL, respectively. Both extracts also inhibited alpha-amylase action, indicating that anthocyanins would have a potential function to suppress the increase in postprandial glucose level from starch.

The 80% ethanol extracts of 5 purple-fleshed sweet potato cultivars were separated into 2 fractions, anthocyanins-and phenolic compounds-rich fractions, to clarify the contribution of these constituents to the radical-scavenging activity. The separation was accomplished with an ethyl acetate liquid/liquid extraction. 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity in each fraction and the contributors varied according to the cultivars. The dominant DPPH radical-scavengers in "Ayamurasaki" and "Kyushu-132" were anthocyanins rather than phenolic compounds, while those in "Miyanou-36" and "Bise" were phenolic compounds, such as chlorogenic acid. Furthermore, the high-performance liquid chromatography analysis of anthocyanins showed that "Ayamurasaki" and "Kyushu-132" were rich in anthocyanins with peonidin aglycon, whereas "Miyanou-36," "Bise," and "Tanegashimamurasaki" contained cyanidin aglycon.

The extracts from white-, black-, and red-hulled rice were prepared by sequential extraction with six different polar solvents, and their radical-scavenging activities were measured by methods using 1,1-diphenyl-2-picrylhydrazyl radical (DPPH*) and tert-butyl hydroperoxyl radical (t-BuOO*). The extracts prepared with highly polar solvents, methanol and deionized water, exhibited higher DPPH* and t-BuOO* scavenging activities in all three cultivars. In addition, the acetone extract from red-hulled rice exhibited a high DPPH* and t-BuOO* scavenging activity, while no such activity was detected for the acetone extracts from white- and black-hulled rice. The major components responsible for the radical scavenging in the acetone extract from red-hulled rice were identified as procyanidins by acidic hydrolysis, vanillin assay, and Sephadex LH-20 chromatography. GPC analysis of the acetylated procyanidins revealed that the average molecular weight is about 5000, in a range of about 500-18,000.

The inhibitory effect of alpha-glucosidase (AGH) inhibitors against its origins (baker's yeast and rat, rabbit, and pig small intestines) was investigated. All inhibitors used in this study showed quite different inhibitory activities according to AGH origins. Voglibose, acarbose and glucono-1,5-lactone strongly inhibited mammalian AGHs, whereas no or less inhibition was observed in yeast AGH. On the contrary, (+)-catechin, a good inhibitor against yeast AGH (IC(50) = 1.3 x 10(-)(1) mM) as well as voglibose (IC(50) = 2.6 x 10(-)(2) mM), did not retard the mammalian AGH activity. Subsequent inhibition study with various food components revealed that all of foods except for green (IC(50) = 0.735 mg/mL) and oolong teas (IC(50) = 1.34 mg/mL) showed no inhibitory activity against rat AGH, whereas they inhibited yeast AGH. Consequently, the magnitude of AGH inhibition was greatly affected by its origin, and more attention relating to AGH origin would be needed to evaluate in vitro AGH inhibitory effect.