Isolation and structure elucidation of flavonoid and phenolic acid glycosides from pericarp of hot pepper fruit Capsicum annuum L

Effects of structure on radical-scavenging abilities and antioxidative activities of tea polyphenols: NMR analytical approach using 1,1-diphenyl-2-picrylhydrazyl radicals

Tea (Camellia sinensis) leaves contain various antioxidants such as ascorbic acid (1) and polyphenols. This study tries to clarify the molecular mechanisms underlying the antioxidative and radical-scavenging activities of these antioxidants, and the reactivities of each antioxidant have been compared against that of the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH, 2) using nuclear magnetic resonance (NMR) analysis. Catechol (3) and (+)-taxifolin (4) were oxidized to o-quinone by 2. However, ethyl protocatechuate (5) and quercetin (6) were not oxidized to o-quinone, even though they possess a catechol structure. The radical-scavenging ability of o-dihydroxyl phenolic compounds with a conjugated olefinic double bond (e.g., 6) was superior to that of compounds without this bond (e.g., 4), whereas the ability of o-dihydroxyl phenolic compounds possessing a conjugated carbonyl bond (5) was inferior to that of compounds lacking this bond (3). Vicinal trihydroxyl phenolic compounds with a conjugated olefinic double bond [e.g., myricetin (7)] had an inferior scavenging ability as compared with compounds lacking this bond [e.g., pyrogallol (8)], but 7 was a better scavenger than compounds with a conjugated carbonyl double bond [e.g., ethyl gallate (9)]. In addition, vicinal trihydroxyl phenolic compounds (e.g., 9) were superior to o-dihydroxyl phenolic compounds (e.g., 6). Finally, 1 scavenged radicals more quickly than 8.

Antioxidant activity of the main phenolic compounds isolated from hot pepper fruit (Capsicum annuum L)

Four cultivars (Bronowicka Ostra, Cyklon, Tornado, and Tajfun) of pepper fruit Capsicum annuum L. were studied for phenolics contents and antioxidant activity. Two fractions of phenolics, flavonoids (with phenolic acids) and capsaicinoids, were isolated from the pericarp of pepper fruit at two growth stages (green and red) and were studied for their antioxidant capacity. Both fractions from red fruits had higher activities than those from green fruits. A comparison of the capsaicinoid fraction with the flavonoid and phenolic acid fraction from red fruit with respect to their antioxidant activity gave similar results. Phenolic compounds were separated and quantified by LC and HPLC. Contents of nine compounds were determined in the flavonoid and phenolic acid fraction: trans-p-feruloyl-beta-d-glucopyranoside, trans-p-sinapoyl-beta-d-glucopyranoside, quercetin 3-O-alpha-l-rhamnopyranoside-7-O-beta-d-glucopyranoside, trans-p-ferulyl alcohol-4-O-[6-(2-methyl-3-hydroxypropionyl] glucopyranoside, luteolin 6-C-beta-d-glucopyranoside-8-C-alpha-l-arabinopyranoside, apigenin 6-C-beta-d-glucopyranoside-8-C-alpha-l-arabinopyranoside, lutoeolin 7-O-[2-(beta-d-apiofuranosyl)-beta-d-glucopyranoside], quercetin 3-O-alpha-l-rhamnopyranoside, and luteolin 7-O-[2-(beta-d-apiofuranosyl)-4-(beta-d-glucopyranosyl)-6-malonyl]-beta-d-glucopyranoside. The main compounds of this fraction isolated from red pepper were sinapoyl and feruloyl glycosides, and the main compound from green pepper was quercetin-3-O-l-rhamnoside. Capsaicin and dihydrocapsaicin were the main components of the capsaicinoid fraction. A high correlation was found between the content of these compounds and the antioxidant activity of both fractions. Their antioxidant activities were elucidated by heat-induced oxidation in the beta-carotene-linoleic acid system and the antiradical activity by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) decoloration test. The highest antioxidant activity in the beta-carotene-linoleic acid system was found for trans-p-sinapoyl-beta-d-glucopyranoside, which was lower than the activity of free sinapic acid. Quercetin 3-O-alpha-l-rhamnopyranoside had the highest antiradical activity in the DPPH system, which was comparable to the activity of quercetin. The activities of capsaicin and dihydrocapsaicin were similar to that of trans-p-feruloyl-beta-d-glucopyranoside in the DPPH model system.

Characterization and quantitation of antioxidant constituents of sweet pepper (Capsicum annuum L.)

Sweet peppers (Capsicum annuum L.) cv. Vergasa have been studied at four maturity stages (immature green, green, immature red, and red). The individual phenolics (hydroxycinnamic acids and flavonoids), vitamin C (ascorbic acid and dehydroascorbic acid), and individual carotenoids were characterized and quantified. Five hydroxycinnamic derivatives and 23 flavonoids were characterized and quantified from the pericarp of sweet pepper by high-performance liquid chromatography-diode array detection-electrospray ionization-mass spectrometry. Identification was carried out by their UV spectra, chromatographic comparisons with authentic markers, identification of hydrolysis products, and tandem mass spectrometry analysis. Hydroxycinnamic derivatives, O-glycosides of quercetin, luteolin, and chrysoeriol, and a large number of C-glycosyl flavones have been characterized. Some of these compounds were found for the first time in nature. Clear differences in the individual and total phenolic content were detected between the different maturity stages. Immature green pepper had a very high phenolic content while green, immature red, and red ripe peppers showed a 4-5-fold reduction. Ascorbic acid was the main form of vitamin C, and its content increased as the pepper reached maturity. The red ripe stage had a relevant impact on the carotenoids content. Thus, immature green peppers showed the highest content of polyphenols, while red ripe fruits had the highest content of vitamin C and provitamin A.