•The color of red rice sample changes according to the duration of storage.•The color change is attributed to chemical modifications of proanthocyanidins.•The color change phenomenon can be simulated via photooxidation.To elucidate the mechanism of the color deepening phenomenon involving aged red rice samples, the time-dependent changes in the color and chemical composition of four different samples (freshly harvested, as well as those stored for 1, 2, and 5 years) were studied. A detailed study of the color change was carried out by obtaining the reflectance spectra of the samples. To investigate the underlying chemical changes, each sample was extracted with an appropriate solvent and analyzed by high-performance liquid chromatography, Folin–Ciocalteu assay, phloroglucinolysis, and mass spectrometry. A similar color change was induced via the photoirradiation of a fresh red rice sample. It is suggested that the chemical modifications of proanthocyanidins are responsible for the color change observed in red rice.

The molecular mechanism by which tea polyphenols decrease the micellar solubility of cholesterol is not completely clear. To clarify this mechanism, this study investigated the interaction between tea polyphenols (catechins and oolongtheanins) and cholesterol micelles. A nuclear magnetic resonance (NMR) study was performed on a micellar solution containing taurocholic acid and epigallocatechin gallate (EGCg), and high-performance liquid chromatography (HPLC) analysis was carried out on the precipitate and the supernatant that formed when EGCg was added to a cholesterol–micelle solution. The data indicated a regiospecific interaction of EGCg with taurocholic acid. Therefore, the ability of EGCg to lower the solubility of phosphatidylcholine (PC) and cholesterol in micellar solutions can be attributed to their elimination from the micelles due to interaction between taurocholic acids and EGCg.

•The oolongtheanins isomerize in aqueous solutions.•In organic solvent, oolongtheanins exist as the structure revised.•In water, oolongtheanins exist as the mixture with originally reported structure.•The equilibrium mixture ratio varies with the type of oolongtheanins.Oolongtheanins, catechin dimers derived from oolong tea leaves, were isolated by Hashimoto et al. in 1988. Later, Tanaka et al. revised the oolongtheanin structure. In this study, it was clarified that oolongtheanins in organic solvent like acetone or methanol have the structures proposed by Tanaka et al. Based on the hydrogen/deuterium exchange reaction in aqueous solution, it was suggested that they exist as an equilibrium mixture of the structures proposed by Hashimoto and Tanaka.

The synthesis of oolongtheanins (1a–d) was accomplished from EGC and/or EGCg in three steps. Oolongtheanin-3′-O-gallate (1b) showed more potent inhibitory activity on micellar cholesterol solubility than did EGCg.

Phenolic compounds and total antioxidant capacity of eight leafy vegetables, namely Komatsuna, Mizuna, Pok choi, Mitsuba, Salad spinach, Lettuce, Red amaranth and Green amaranth were determined. The phenolic compounds were characterized as hydroxybenzoic acids, hydroxycinnamic acids and flavonoids. Salicylic acid was, by far, the most common hydroxybenzoic acid, ranging from 4.40 to 117.36 μg/g fresh frozen weight (ffw). Vanilic acid, gallic acid, caffeic acid, chlorogenic acid, p-coumaric acid, ferulic acid and m-coumaric acid were commonly found in all of these vegetables. Isoquercetin and rutin, the most common flavonoids, ranged from 3.70 to 19.26 and 1.60 to 7.89 μg/g ffw, respectively, and hyperoside was highest (38.72 μg/g ffw) in Mizuna. Total antioxidant capacity values varied widely between ABTS+ and DPPH assay methods, with values reported as equivalents to trolox, quercetin and ascorbic acid. Among these vegetables, total antioxidant capacity was found in the following order: Pok choi > Komatsuna > Mizuna > Mitsuba > Red amaranth > Lettuce > Green amaranth > Salad spinach.Highlights► Phenolics and antioxidant capacities were characterized in eight leafy vegetables. ► Salicylic acid, vanilic acid, sinapic acid and p-coumaric acid were prevalent as phenolic acids. ► Rutin and isoquercetin were detected as the most abundant flavonoids. ► Total antioxidant capacity was measured using ABTS+ and DPPH assays. ► Pok choi contained the highest antioxidant capacity among the selected vegetables.