Recently, the prevention of phenolic off-flavor ‘phénolé’ has become a focus in red winemaking. We first investigated the frequency of phénolé in samples of commercial red wines produced in Japan. Almost 80% of the samples contained phénolé at a concentration of less than 0.100mg/L. Thus, it was clarified that most of the red wines produced in Japan are of high quality and contain minimal phénolé. Yeast cells belonging to the genus Brettanomyces were present in some wine samples that contained high concentrations of phénolé. These wine samples also showed high pH values. Furthermore, screening, isolation and characterization of phenol-producing yeast strains were performed during the red wine production process in Japan. Some yeast isolates were isolated from red wine samples that were collected from barrels. Using standard morphological and biochemical tests, these isolates were identified as belonging to the genus Brettanomyces. The isolates were inhibited by 0.6mg/L molecular sulfur dioxide. Further studies focusing on the prevention of Brettanomyces contamination are expected.
Purple sweet potato rich in acylated anthocyanin (YGM) pigments was used to develop a vinegar with a deep color and high functionality. The addition of purple sweet potato to the acetic acid fermentation process, together with seed vinegar and pure ethanol, was more effective than the use of a saccharification source, utilized previously. Furthermore, use of concentrated pigment extract instead of purple sweet potato provided a brewing method for ‘red vinegar’ exhibiting twofold higher YGM concentration. This red vinegar was expected to have high functionality since it contains acetic acid, purple sweet potato-derived components, and brewing ingredients. Isolation and structural determination of the brewing components resulted in the identification of new acylated polyphenols. A two-step purification method using an adsorption resin column was established for the large-scale preparation of the major component, 6-O-caffeoylsophorose (CS). A single oral administration of CS to maltose-loaded SD rats caused an effective anti-hyperglycemic effect via the acute inhibition of α-glucosidase in the small intestine. In addition, CS was found to be transported across Caco-2 monolayers by the monocarboxylate transporter. Absorbed CS may promote glucose uptake into skeletal muscle cells. Taken together, CS or the brewed vinegar developed in this study could serve as new functional foods and help prevent lifestyle-related diseases, for example by exhibiting an anti-diabetic effect.