Dihydroferulic acid (DFA) and dihydrosinapic acid (DSA) were isolated from Kurosu (unpolished rice vinegar) as the major constituents responsible for Kurosu's radical scavenging activity. The levels of antioxidative activity of DFA and DSA in DPPH radical scavenging were higher than those of their respective structurally related compounds, ferulic acid and sinapic acid. The concentrations of DFA and DSA were low in common rice vinegar (polished rice vinegar), suggesting that Kurosu is more advantageous than rice vinegars as an antioxidative food item. As the concentrations of DFA and DSA were low in unpolished rice, too, these acids are thought to be produced in Kurosu through the process of the fermentation from ferulic acid and sinapic acid, respectively.

Bacterial strains were isolated from samples of Japanese rice vinegar (komesu) and unpolished rice vinegar (kurosu) fermented by the traditional static method. Fermentations have never been inoculated with a pure culture since they were started in 1907. A total of 178 isolates were divided into groups A and B on the basis of enterobacterial repetitive intergenic consensus-PCR and random amplified polymorphic DNA fingerprinting analyses. The 16S ribosomal DNA sequences of strains belonging to each group showed similarities of more than 99% with Acetobacter pasteurianus. Group A strains overwhelmingly dominated all stages of fermentation of both types of vinegar. Our results indicate that appropriate strains of acetic acid bacteria have spontaneously established almost pure cultures during nearly a century of komesu and kurosu fermentation.

S-modulin in frog or its bovine homologue, recoverin, is a 23-kDa EF-hand Ca 2؉ -binding protein found in rod photoreceptors. The Ca 2؉ -bound form of S-modulin binds to rhodopsin kinase (Rk) and inhibits its activity. Through this regulation, S-modulin is thought to modulate the light sensitivity of a rod. In the present study, we tried to identify the interaction site of the Ca 2؉ -bound form of S-modulin to Rk. First, we mapped roughly the interaction regions by using partial peptides of S-modulin. The result suggested that a specific region near the amino terminus is the interaction site of S-modulin. We then identified the essential amino acid residues in this region by using S-modulin mutant proteins: four amino acid residues (Phe 22 , Glu 26 , Phe 55 , and Thr 92 ) were suggested to interact with Rk. These residues are located in a small closed pocket in the Ca 2؉ -free, inactive form of S-modulin, but exposed to the surface of the molecule in the Ca 2؉ -bound, active form of S-modulin. Two additional amino acid residues (Tyr 108 and Arg 150 ) were found to be crucial for the Ca 2؉ -dependent conformational changes of S-modulin.

The modifying effects of administering an ethyl acetate extract of Kurosu (EK), a vinegar made from unpolished rice, in drinking water on the development of azoxymethane (AOM)-induced colon carcinogenesis were investigated in male F344 rats. Animals were given 2 weekly subcutaneous injections of AOM (20 mg/kg body weight). They also received drinking water containing 0%, 0.05%, or 0.1% EK for 35 wk, starting 1 wk after the last dosing of AOM. EK administration significantly inhibited the incidence and multiplicity of colon adenocarcinoma (P < 0.05), compared with those in the AOM alone group. These findings suggest that EK may be effective for inhibiting colon carcinogenesis.