Phenolic acid contents of kale (Brassica oleraceae L. var. acephala DC.) extracts and their antioxidant and antibacterial activities

Nine phenolic acids were identified and quantified by HPLC–MS in leaves and 10 in seeds of kale (black cabbage). The free, ester (methanol-soluble), glycoside and ester-bound (methanol-insoluble) phenolic acid contents of the leaves were 487, 532, 4989 and 6402 ng/g fresh weight, respectively. Ferulic and caffeic acids (total contents; 4269 and 4887 ng/g, respectively) were the most abundant. The seed contents of these fractions were 1993, 1477, 1231 and 4909 ng/g dry weight (DW), respectively, and sinapic acid was the most abundant (5037 ng/g DW). The fractions’ total phenolic contents, determined colorimetrically, were highly correlated with their DPPH scavenging capacity, and in antimicrobial activity assays, with nine test organisms representing a wide array of taxa, all of the fractions were effective against Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis and (most strongly) Moraxella catarrhalis. Antimicrobial and antioxidant activities of kale phenolics in free and conjugated forms are discussed.     

Free aromatic amino acids in egg yolk show antioxidant properties

Laying hens are known to be able to “bio-convert” health-promoting components from the diet into eggs. Wheat and corn are important sources of antioxidant phenolics in the human diet. Given the fact that wheat and corn are major feed ingredients of laying hens in Canada, the objectives of this study were to characterise the presence of novel phenolic compounds in egg yolk and to determine the effect of cooking methods on their content and activity. The total phenolic content of yolk extracts was 3.83 and 3.49 μmol gallic acid equivalents/g dry yolk for wheat-based and corn-based yolks, respectively. Antioxidant properties of yolk extracts were measured by the ORAC, DPPH and ABTS assays. ORAC values were 151.1 ± 26.1 and 155.9 ± 9.5 μmol TE/g for wheat-based and corn-based yolks, respectively. All cooking methods significantly reduced (p < 0.05) the antioxidant values. Ferulic acid was detected in trace amounts and no other phenolic compounds were found. However, tryptophan and tyrosine were found to be two main contributors to the antioxidant property of egg yolk. The contents of total free amino acids were 10081.0 and 10009.5 μg/g in wheat-based and corn-based yolks, respectively; cooking methods were found to reduce significantly the amount of free amino acids.     

Antioxidant and antiproliferative activities of common edible nut seeds

Frequent consumption of nuts has been linked to a lowered risk of cardiovascular disease. Phytochemicals, especially phenolics, in nuts may be considered to be the major bioactive compounds for health benefits. Nine types of tree nuts and peanuts commonly available in the United States were evaluated for total phenolic and flavonoid contents, antioxidant, and antiproliferative activities. The profiles of total phenolics and flavonoids, including both soluble free and bound forms, were investigated by utilizing solvent extraction, base digestion, and solid-phase extraction methods. Walnuts had the highest total phenolic and flavonoid contents (1580.5 ± 58.0 mg/100 g, 744.8 ± 93.3 mg/100 g, respectively). Walnuts also possessed the highest total antioxidant activity (458.1 ± 14.0 μmol of vitamin C equiv/g of nut). Both soluble phenolic and flavonoid contents were positively correlated with total antioxidant activity (R² = 0.9901, p < 0.05; and R² = 0.9749, p < 0.05, respectively). The proliferation of HepG₂ and Caco-2 cells was significantly inhibited in a dose-dependent pattern after exposure to the extracts of nuts, with walnuts and pecans exhibiting the highest antiproliferative activity. These results provide new knowledge about health functions of nuts and may influence consumers toward purchasing nuts exhibiting greater potential health benefits.     

Microwave-assisted extraction of phenolics with maximal antioxidant activities in tomatoes

Microwave-assisted extraction (MAE) was investigated for extraction of phenolic compounds from tomato with maximised antioxidant activities using response surface methodology (RSM) coupled with a central composite design, and in vitro antioxidant assays (FRAP and ORAC). MAE was more efficient for greater antioxidant activities and higher total phenolic contents than solvent extraction. The optimal MAE processing parameters were 96.5 °C, 2.06 min, 66.2% ethanol for FRAP, and 96.5 °C, 1.66 min, 61.1% ethanol for ORAC. The models were successfully applied to 20 tomato cultivars, whose total phenolic contents (TPC) and indexes (TPI) were 489.30–997.45 mg gallic acid equivalent/100 g dry weight (DW) and 281.34–468.52 mg/100 g DW, respectively. Eight phenolic compounds were identified. Individual phenolics were 6.10–42.73 mg/100 g DW. The FRAP, but not the ORAC value showed good correlation with the TPC or TPI. The methodologies developed and the knowledge acquired in this study will provide useful information to tomato breeders and food processors.     

Phenolic acid analysis and antioxidant activity assessment of oil palm (E. guineensis) fruit extracts

Phenolic compounds in oil palm fruit (E. guineensis) were extracted in soluble free (SFP), insoluble-bound (ISBP) and esterified (EFP) forms. The total phenolic content (TPC) of the oil palm fruit extracts was determined using the Folin–Ciocalteu method and found to range from 5.03 to 9.04 g/L per g of dried weight (DW). The antioxidant activities of oil palm phenolic extracts were analysed using free radical scavenging assays and results showed that oil palm phenolic extracts contained antioxidant activities in the order of ISBP > EFP > SFP. Eight different phenolic acids were identified and quantified using a simple reversed-phase high performance liquid chromatography (HPLC) with a diode array detector (DAD) and liquid chromatography/tandem mass spectrometry (LC/MS/MS). Ferulic, p-hydroxybenzoic and p-coumaric acid were the dominant phenolic acids found in oil palm fruit extracts and ranged from 55 to 376 μg/g of DW.     

Antioxidant and radical scavenging activities of the pyroligneous acid from a mangrove plant, Rhizophora apiculata

Total phenolics content, free radical scavenging activity, reducing power, and antioxidant activity of the pyroligenous acid from a mangrove plant, Rhizophora apiculata were evaluated. Dichloromethane extraction of the raw pyroligneous acid successfully yield 2 extracts, i.e. concentrated pyroligneous acid (CPA) and concentrated pyroligneous acid extract (CPAE). Phenolic contents in CPAE and CPA, expressed as (±)-catechin equivalents/g of the sample were 5465 ± 367 mg and 2502 ± 152 mg, and expressed as gallic acid equivalents/g of the sample were 2919 ± 209 mg and 1348 ± 90 mg, respectively. CPAE exhibited superior free radical scavenging activity with EC₅₀ value = 0.1235 mg/ml, or 80.96% of free radical scavenging capability. The ferric reducing power of CPAE was approximately 3.7, 5.1, 6.1, and 21.3 times higher than that of ascorbic acid, BHA, BHT and alpha-tocopherol. In phosphomolybdenum assay, CPAE showed the greatest antioxidant efficacy (A₆₉₅ = 1.278) compared to those of CPA and different standards. In addition, the free radical scavenging activity, ferric reducing power and total antioxidative activity of CPAE and CPA showed positive correlation with their total phenolic content with R² values ranging from 0.9624 to 0.9979.     

Antioxidant activity and phenolics of an endophytic Xylaria sp. from Ginkgo biloba

The objective of this study was to evaluate the antioxidant activity of cultivated fruiting bodies of an endophytic Xylaria sp. (strain number YX-28), from Ginkgo biloba. The results indicated that the methanol extract exhibited strong antioxidant capacity in both 2,2-diphenyl-1-picrylhydrazyl (DPPH) analysis and β-carotene–linoleic acid model system. Total phenolic and flavonoid contents extracted by different solvents were determined using Folin–Ciocalteu procedure and the flavonoid–aluminium method. The results showed that total phenolic and flavonoid contents were the highest in methanol extract (54.51 ± 1.05 mg gallic acid equivalent/g dry weight and 86.76 ± 0.58 mg rutin equivalent/g dry weight), while the hexane extract was the lowest (9.71 ± 0.57 mg GAE/g dw and 10.14 ± 0.76 mg RE/g dw, respectively). The correlation coefficients from regression analysis showed a positive relationship between total phenolic content in the extracts and DPPH activity (R² = 0.7336), as well as between total flavonoid content and DPPH activity (R² = 0.9392). Furthermore, GC/MS method was used to confirm the presence of phenolics with antioxidant activity in the methanol extract and resulted in the identification of 41 compounds, esters, phenolics, alkanes, carboxylates and alcohols being the main components. In conclusion, cultivated fruiting bodies of Xylaria sp.YX-28 may have potential as natural antioxidant.     

Antioxidant activity and phenolic content of 16 raisin grape (Vitis vinifera L.) cultivars and selections

Six raisin grape cultivars and 10 new raisin grape selections were analyzed for antioxidant activity (ABTS assay) and for total and individual phenolic compounds. Samples were freeze–dried and values are reported on a dry weight basis. Antioxidant activity across the 16 samples ranged from 7.7 to 60.9 μmol Trolox/g DW, with A95-27 exhibiting the greatest activity. Total phenolic content, determined in gallic acid equivalents using the Folin–Ciocalteau assay, ranged from 316.3 to 1141.3 mg gallic acid/100 g DW and was strongly correlated (r = 0.990) with antioxidant results. Concentrations of individual phenolics were determined by HPLC. trans-Caftaric acid was the predominant compound in all samples. A95-15 contained the lowest concentration (153.5 μg/g DW) of caftaric acid, while Fiesta contained the highest concentration (598.7 μg/g DW). Selections A56-66, A95-15, and A95-27 had much higher levels of catechin (86.5–209.1 μg/g DW) and epicatechin (126.5–365.7 μg/g DW) than the other samples.     

Systematic evaluation of natural phenolic antioxidants from 133 Indian medicinal plants

Total antioxidant capacities of 133 Indian medicinal plant species sampled from 64 families were assessed by ABTS, DPPH and FRAP assays, and their total phenolic contents measured by Folin–Ciocalteu assay. These species exhibited a broad range of antioxidant activities, varying from 0.16 to 500.70 mmol TEAC/100 g DW in the ABTS assay. The antioxidant activity values similarly varied with the DPPH and FRAP assays. Significant and positive linear correlations were found between total antioxidant capacities and phenolic contents (R = 0.89–0.97), indicating that phenolics were the dominant antioxidant constituents in the tested medicinal plants. Preliminary identification of the major phenolic compounds from 83 selected medicinal plants by reversed-phase HPLC revealed phenolic acids, tannins, flavonoids, curcuminoids, coumarins, lignans, and quinines. The fruit of Terminalia chebula, pericarp of Punica granatum and gall of Rhus succedanea showed very high levels of hydrolysable tannins, and the gum of Acacia catechu presented very high levels of catechin and epicatechin in addition to tannins. Major phenolics in many of the medicinal plants were identified for the first time (e.g., Euphorbia lathyrus, Ipomoea turpethum, and Picrorrhiza kurroa). This systematic investigation of a large number of Indian medicinal plants proved important for understanding their chemical constituents and functionality in Ayurvedic medicine, and contributes to the search for natural sources of potent antioxidants.     

Preliminary characterisation of cornelian cherry (Cornusmas L.) genotypes for their physico-chemical properties

Fruit weight, antioxidant capacity, total anthocyanins, total phenolics, ascorbic acid, soluble solid content (SSC), reducing sugar and acidity of a number of selected cornelian cherry (Cornusmas L.) genotypes of varied pigmentation were investigated. Two methods, namely β-carotene bleaching and ferric reducing antioxidant power (FRAP) were used to determine total antioxidant capacity, while Folin–Ciocalteu reagent was used to determine total phenols. Fruit weight, SSC and ascorbic acid content of genotypes were 2.09–9.17; 12.53–21.17% and 29–112 mg/100 g, respectively. Antioxidant activity and total phenolic content varied among genotypes and 44-18 genotype had the highest antioxidant capacity using both methods. This genotype also had the highest total phenolic (74.8 mg GAE/g DW) and total anthocyanin (115 mg cyanidin-3-glucoside equivalents /100 g FW) content. There are linear relationships between antioxidant capacities and total phenols. The present study demonstrates the potential of certain cornelian cherry genotypes, notably 44-18, for improvement of nutritional value through germplasm enhancement programmes.     

Antioxidant potentials of buntan pumelo (Citrus grandis Osbeck) and its ethanolic and acetified fermentation products

The antioxidant potentials of buntan pumelo (Citrus grandis Osbeck) and its fermented products were determined. The essential oil from peel had higher total phenolic (214 mM) and flavonoid (134 mg QE/g of dried material) contents than those of different solvent extracts from fruit pulp. In addition, DPPH free radical-scavenging activity and ferric-reducing antioxidant power values determined for the essential oil were 26.1 ± 1.2% and 2.3 ± 0.3 mM, respectively, which were significantly higher than those of various fruit pulp extracts. The ethanol-fermented products of pumelo juice had higher total phenolic and flavonoid contents than those of fresh juice. For maintenance of the substantial antioxidant properties of pumelo products, ethanol-fermented juice rather than fresh or acetate-fermented juice is recommended. Through correlation analysis, the phenolic compounds in the fermented pumelo products were found to be the major contributors to the free radical-scavenging activity and ferric-reducing power.     

Fruit quality and bioactive compounds relevant to human health of sweet cherry (Prunus avium L.) cultivars grown in Italy

The fruit quality characteristics, phenolic compounds and antioxidant capacities of 24 sweet cherry (Prunus avium L.) cultivars grown on the mountainsides of the Etna volcano (Sicily, Italy) were evaluated. High-performance liquid chromatographic methods were used to identify and quantify sugars, organic acids and phenolics. A total of seven phenolic compounds were characterised as hydroxycinnamic acid derivatives (neochlorogenic acid, p-coumaroylquinic acid and chlorogenic acid) and anthocyanins (cyanidin 3-glucoside, cyanidin 3-rutinoside, pelargonidin 3-rutinoside and peonidin 3-rutinoside). The total anthocyanin content ranged from 6.21 to 94.20 mg cyanidin 3-glucoside equivalents/100 g fresh weight (FW), while the total phenol content ranged from 84.96 to 162.21 mg gallic acid equivalents/100 g FW. The oxygen radical absorbance capacity (ORAC) assay indicated that fruit of all genotypes possessed considerable antioxidant activity. The high level of phenolic compounds and antioxidant capacity of some sweet cherry fruits implied that they might be sources of bioactive compounds that are relevant to human health.     

Distribution of phenolic compounds in the graded flours milled from whole buckwheat grains and their antioxidant capacities

Whole buckwheat grains were milled into 16 flour fractions using the gradual milling system and the phenolic compounds and the antioxidant capacity of each flour fraction were investigated. The phenolic and flavonoid contents of both free and bound phenolic extracts of buckwheat flour fractions significantly increased in the order from the fraction number 1 (phenolics less rich fraction) to the fraction number 16 (phenolics rich fraction). The phenolic compounds in buckwheat existed primarily in free form, whereas the flavonoids existed in grain in insoluble bound forms, bound to cell wall materials. The amounts of ferulic acid and rutin increased from 2.5 and 2.5 μg/g flour of the phenolics less rich fraction to 609.5 and 389.9 μg/g flour of the phenolics rich fraction of grain, respectively. The higher phenolic contents in the phenolics rich fractions exhibited the stronger antioxidant capacity than the phenolics less rich fractions. As a result, the flour milled from the outer layers of buckwheat grains with large amount of phenolic compounds and antioxidant capacity are considered to have significant health benefits.     

Chemical characterization, bioactive compounds, and antioxidant capacity of jussara (Euterpe edulis) fruit from the Atlantic Forest in southern Brazil

Samples of fruit from the jussara palm plant (Euterpe edulis), collected in different regions of the state of Santa Catarina, Brazil, were analyzed for chemical composition, phenolic acids, anthocyanins, flavonoids and fatty acids profile. Results indicated that the jussara fruit has a high lipid content (18.45-44.08%), oleic acid (44.17-55.61%) and linoleic acid (18.19-25.36%) are the fatty acids found in the highest proportion, and other components were proteins (5.13-8.21%), ash (1.55-3.32%) and moisture (34.95-42.47%). Significant differences were found in the total phenolic, total monomeric anthocyanins and other flavonoids for the samples from the five cultivation regions. The fruit from region E harvested in summer, with high temperatures and medium altitudes, had the highest contents of total phenolics (2610.86 ± 3.89 mg 100 g⁻¹ GAE) and monomeric anthocyanins (1080.54 ± 2.33 mg 100 g^− 1 cy-3-glu). The phenolic compound included ferulic, gallic, hydroxybenzoic and p-coumaric acids, as well as catechin, epicatechin and quercetin. The results show promising perspectives for the exploitation of this tropical fruit with a chemical composition comprising considerable phenolic acids and flavonoids compounds and showing activity antioxidant.     

Optimization of microwave-assisted extraction of phenolics from potato and its downstream waste using orthogonal array design

While other extraction methods have been tempted, a microwave-assisted extraction (MAE) method coupled with the orthogonal array design was investigated for efficient extraction of the phenolic compounds in potato downstream wastes. Four parameters were examined for the MAE of the total phenolic content (TPC) and optimized at 60% ethanol, 80 °C, 2 min, solid-to-solvent ratio 1:40 (g/ml). The MAE was proven more efficient than the conventional solvent extraction by refluxing. The optimized model showed that the downstream wastes, both the supernatant and the residue contained high TPC, particularly the former (11.0 ± 0.26 mg GAE/g DW). The antioxidant activities (DPPH and FRAP) closely correlated with the TPC of the samples (r = 0.92–0.97). Chlorogenic acid and caffeic acid were found to be the predominant phenolic acids. The extracts of the downstream wastes from potato processing can be a promising candidate for functional foods and nutraceutical ingredients.     

Phenolic composition of Flacourtia indica, Opuntia megacantha and Sclerocarya birrea

The phenolic acid composition of the peel and pulp of the fruits of Flacourtia indica (Burm. f.) Merr., Opuntia megacantha (L.) Mill and Sclerocarya birrea (A. Rich.) Hochst., from Zimbabwe, were analysed using traditional colorimetric as well as HPLC methods. The total phenolics, flavanoids and condensed tannin levels varied with species. Sclerocarya birrea pulp had the highest total phenolics, flavanoids and condensed tannins, i.e., 2262 μg GAE/g, 202 μg catechin/g and 6.0% condensed tannins, respectively. Flacourtia indica pulp contained the least total phenolics, flavanoids and condensed tannins 334 μg GAE/g, 41 μg catechin/g and 1.4%, respectively. There were no significant differences in the total phenolics between the peels and the pulps of the individual fruits. However, significant differences were noted in the flavanoids and the condensed tannins between the peels and pulps of the fruits assayed. Ferulic acid, caffeic acid and vanillic acid were the dominant phenolic acids in the three fruits. There were differences between the phenolic acids in the peels and the pulps of the fruits.     

Free radical scavenging activities and bioactive substances of Jerusalem artichoke (Helianthus tuberosus L.) leaves

The total phenolic content and radical scavenging activities of Jerusalem artichoke (Helianthus tuberosus L.) leaves were investigated. Results indicated that the ethyl acetate fraction contained the highest total phenolic content (266.69 ± 2.51 mg GAE/g dry extract) accompanied with strongest free radical scavenging abilities. Following an in vitro radical scavenging activity-guide fractionation procedure, six phenolic compounds which strongly quenched free radicals were separated from ethyl acetate fraction. Among them, 3-O-caffeoylquinic acid and 1,5-dicaffeoylquinic acid played a dominant role due to their strong free radical scavenging abilities and their high contents. The content of 3-O-caffeoylquinic acid in n-butanol fraction was 74.58 ± 1.05 mg/g, while 1,5-dicaffeoylquinic acid in ethyl acetate fraction was 104.51 ± 2.86 mg/g. The results imply that the leaves of Jerusalem artichoke might be a potential source of natural antioxidants.     

Antioxidant activity of the essential oil and various extracts of Nepeta flavida Hub.-Mor. from Turkey

This study was designed to examine the chemical composition and in vitro antioxidant activity of the essential oil and various extracts (hexane, dichloromethane and methanol sub-fractions) of Nepeta flavida. GC and GC–MS analyses of the essential oil resulted in the identification of 68 compounds, representing 96.4% of the oil; 1,8-cineole (38.9%) and linalool (25.1%) were the main components, comprising 64.0% of the total oil. The samples were subjected to a screening for their possible antioxidant activities by using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and β-carotene-linoleic acid assays. In the first case, the IC₅₀ value of the N. flavida essential oil was determined to be 42.8 ± 2.19 μg/ml. Among the extracts, the strongest activity was exhibited by the polar sub-fraction of the methanol extract with an IC₅₀ value of 63.2 ± 1.75 μg/ml. In the β-carotene-linoleic acid system, N. flavida essential oil exhibited 86.3% ± 1.69 inhibition against linoleic acid oxidation. Among the extracts prepared with various solvents, a correlation was observed between the polarity and antioxidant activity. The extracts exhibited the same activity pattern in this system the most active one is the polar sub-fraction, 79.7% ± 0.89. On the other hand, 1,8-cineole, a major compound of the essential oil, exhibited marked antioxidant activity in both systems, whereas the other compound, linalool, did not show any activity. The amount of total phenolics was highest in the polar and non-polar sub-fractions. Particularly, a positive correlation was observed between the total phenolic content and the antioxidant activity of the extracts. As estimated from the results, amounts of phenolic compounds were less in hexane and dichloromethane extracts than in the others. In conclusion, antioxidant potentials of polar and non-polar methanol sub-fractions could be attributed to their high phenolic contents. In both systems, antioxidant capacities of BHT, ascorbic acid, curcumin and α-tocopherol were also determined in parallel experiments.     

Determination of free phenolic acids and antioxidant activity of methanolic extracts obtained from fruits and leaves of Chenopodium album

In this study, determination of phenolic acids as well as investigation of antioxidant activity of methanolic extracts from the fruits and leaves of Chenopodium album is described. Extracts were subjected to acidic hydrolysis in order to obtain total free phenolic acids. However, some of phenolic acids were identified and quantified by HPLC-DAD. The results were confirmed by LC-MS equipped with MS-ESI. In addition, Folin–Ciocalteu method was applied to determine the total phenolic contents. The antioxidant activity of C. album extracts was examined by using DPPH and hydroxyl radical-scavenging activity assays. Results revealed that the leaves extract exhibits better performance in antioxidant assays and in the higher total phenolic contents (3066 mg of GAE/100 g) when compared to fruits extract (1385 mg of GAE/100 g). From these results it has been revealed that the methanolic extracts of C. album from fruits and leaves have great potential as a source for natural health products.