Antioxidant capacity and phenolic content of spinach as affected by genetics and maturation

Spinach leaves harvested at three maturity stages from eight commercial cultivars (CC) and eight advanced breeding lines (ABL) were evaluated for oxygen radical absorbing capacity (ORAC), total phenolics, and flavonoid composition and content. ABL had higher levels of total phenolics, total flavonoids, and ORAC than CC. Midmaturity spinach leaves had higher levels of total phenolics, total flavonoids, and antioxidant capacity than immature and mature leaves. The contents of individual flavonoids varied in response to maturation, with the predominant glucuronated flavones decreasing and patuletin and spinacetin derivatives increasing. Both total phenolics and total flavonoids correlated well with ORAC (r(xy)() = 0.78 and 0.81, respectively) demonstrating that flavonoids were major contributors to antioxidant capacity. Our results indicate that spinach genotypes should be harvested at the midmaturity stage for consumers to benefit from elevated levels of health promoting flavonoids present in the leaves. Additionally, plant breeders can select for increased phenolic content to increase antioxidant capacity of spinach genotypes.     

Wounding stress increases the phenolic content and antioxidant capacity of purple-flesh potatoes (Solanum tuberosum L.)

Several abiotic stresses, including ethylene, methyl jasmonate, temperature, light, and wounding, were tested for their ability to induce accumulation of phenolic compounds and antioxidant capacity in purple-flesh potatoes (cv. All Blue). Results indicated that temperature, ethylene, methyl jasmonate, and light treatments did not significantly affect the accumulation of phenolic compounds compared to control samples. Only tubers with low initial anthocyanin levels treated with methyl jasmonate showed approximately 60% anthocyanin accumulation. Wounding induced the accumulation of phenolics compounds and an increase of PAL-activity in sliced tissue compared to the control. Total phenolics increased approximately 60% with a parallel 85% increase in antioxidant capacity. These results show that selection of appropriate abiotic stresses can enhance the nutritional and functional value of potatoes.     

Antioxidant capacity of 26 spice extracts and characterization of their phenolic constituents

Total equivalent antioxidant capacity (TEAC) and phenolic content of 26 common spice extracts from 12 botanical families were investigated. Qualitative and quantitative analyses of major phenolics in the spice extracts were systematically conducted by reversed-phase high-performance liquid chromatography (RP-HPLC). Many spices contained high levels of phenolics and demonstrated high antioxidant capacity. Wide variation in TEAC values (0.55-168.7 mmol/100 g) and total phenolic content (0.04-14.38 g of gallic acid equivalent/100 g) was observed. A highly positive linear relationship (R2= 0.95) obtained between TEAC values and total phenolic content showed that phenolic compounds in the tested spices contributed significantly to their antioxidant capacity. Major types of phenolic constituents identified in the spice extracts were phenolic acids, phenolic diterpenes, flavonoids, and volatile oils (e.g., aromatic compounds). Rosmarinic acid was the dominant phenolic compound in the six spices of the family Labiatae. Phenolic volatile oils were the principal active ingredients in most spices. The spices and related families with the highest antioxidant capacity were screened, e.g., clove in the Myrtaceae, cinnamon in the Lauraceae, oregano in the Labiatae, etc., representing potential sources of potent natural antioxidants for commercial exploitation. This study provides direct comparative data on antioxidant capacity and total and individual phenolics contents of the 26 spice extracts.     

Antioxidant capacity in cranberry is influenced by cultivar and storage temperature

Ten cranberry (Vaccinium macrocarpon Aiton) cultivars were evaluated for oxygen radical absorbance capacity (ORAC), anthocyanins, and total phenolics contents after three months of storage at 0, 5, 10, 15, and 20 degrees C. The antioxidant capacity of cranberry was affected by cultivars and storage temperatures. Among the 10 cranberry cultivars used in this study, Early Black, Crowley, and Franklin had higher antioxidant capacities than the other cultivars. ORAC values, anthocyanins, and total phenolics contents increased during storage. The highest increases in antioxidant activity, anthocyanin, and phenolics contents occurred at 15 degrees C storage. Fruit stored at 20 degrees C had lower ORAC values than those stored at 15 degrees C. A positive relationship existed between ORAC values and anthocyanin or phenolic content in all 10 cranberry cultivars at different storage temperatures.     

Antioxidant capacity and phenolic content in leaf extracts of tree spinach (Cnidoscolus spp.)

Total phenolic content and antioxidant capacity of two tree spinach species (Cnidoscolus chayamansa McVaugh and C. aconitifolius Miller.) were determined in raw and cooked leaf extracts. Antioxidant capacity was assessed by the oxygen radical absorbance capacity (ORAC) assay, and flavonoid glycoside composition was quantified by HPLC and identified by GC. Total phenolics and antioxidant capacity were higher in raw than in cooked leaf extracts. The ORAC values were strongly correlated with total phenolic content (r = 0.926) in all leaf extracts. The major flavonoids isolated from the leaf extracts were kaempferol-3-O-glycosides and quercetin-3-O-glycosides. C. aconitifolius leaves contained more varieties of the flavonoid glycosides than C. chayamansa. Cooking reduced antioxidant activity and phenolic content and resulted in losses of some kaempferol glycoside and quercetin glycoside residues in leaf extracts. The results of this study indicate that tree spinach leaves are a rich source of natural antioxidants for foods.     

Polyphenols and antioxidant capacity of seed coat and cotyledon from Brazilian and Peruvian bean cultivars (Phaseolus vulgaris L.)

Seed coats and cotyledons from 25 Brazilian and 3 Peruvian bean cultivars were investigated in relation to their phenolic profiles and antioxidant capacity. Condensed tannins, anthocyanins, and flavonols such as kaempferol and quercetin glycosides were mostly found in seed coats. Cotyledons were rich in phenolic acids, such as ferulic, sinapic, chlorogenic, and other hydroxycinnamic acids. In general, the seed coat color pattern and the type of cultivar showed an important influence on the variability of phenolic profiles and levels, respectively. Total phenolics and antioxidant capacity assessed by the DPPH method were higher in seed coats than in cotyledons. The antioxidant capacity had a significant correlation with condensed tannins for all samples and with total anthocyanins in black and red seed coats, whereas in cotyledons, it was more related to the total phenolic content.     

Content and profile of flavanoid and phenolic acid compounds in conjunction with the antioxidant capacity for a variety of northwest Vaccinium berries

This investigation evaluated the content and profile of flavanoid and phenolic acid compounds present in nine Vaccinium species that included domestic blueberry cultivars and sample collections from undomesticated colonies. The study was focused in two areas of inquiry. The first involved extracting and analyzing the berries for total phenolics (TPH), total anthocyanins (ACY), and the antioxidant capacity. Vaccinium species differ in their polyphenolic content, and these high TPH and ACY levels are correlated to their antioxidant capacity. Second, berry extracts were analyzed by high-performance liquid chromatography equipped with photodiode array and mass spectrometric detectors to determine the content and profile of selected bioactive compounds. The flavanoid analytes of interest included the anthocyanidins, flavan-3-ols, and flavonol aglycons, as well as specific phenolic acid components. This semicomprehensive analysis begins to characterize the phytochemical profiles and illustrates the differences in the content of polyphenolic compounds present within these Vaccinium species.     

Antioxidant and cytotoxic activities of carob tree fruit pulps are strongly influenced by gender and cultivar

Extracts from fruit pulps of six female cultivars and two hermaphrodite Portuguese carob trees [(Ceratonia siliqua L., Fabaceae)] exhibited strong antioxidant activity and were rich in phenolic compounds. The extracts decreased the viability of different human cancer cell lines on a dose- and time-dependent manner. Gender and cultivar significantly influenced the chemical content and the biological activities of the extracts. Extracts from hermaphrodite trees had a higher content of phenolic compounds, and exhibited higher antioxidant and cytotoxic activities. Among females, cv. Aida had the highest radical scavenging activity and total content of phenolics, Mulata the highest capacity to inhibit lipid oxidation and Gasparinha the strongest cytotoxic activity on HeLa cells. The decrease in cell viability was associated with apoptosis on HeLa and MDA-MB-231 lines. (+)-Catechin and gallic acid (GA) were the main compounds identified in the extracts, and GA contributed to the antioxidant activity. Our results show that the antioxidant and cytotoxic activities of carob tree fruit pulps are strongly influenced by gender and cultivar, and provide new knowledge about the advantages of hermaphrodite trees over female cultivars, namely, as a source of compounds with biological interest, which may represent an increase of their agronomic interest.     

Great differences in antioxidant properties exist between 56 apple cultivars and vegetation seasons

The contents of ascorbate, thiols, and phenolic compounds and antioxidative enzyme activity were measured in the apple peel of 56 genotypes after harvest in two vegetation seasons, 2003 and 2004. The main reason of great interest in these bioactive compounds is their well-established physiological role in all living systems. The biggest differences between tested genotypes were noted for ascorbate peroxidase and glutathione reductase (GR) activity, followed by total ascorbate, phenolics, and glutathione concentration; the least difference was observed in the case of catalase. A large cultivar variation was noted in the anthocyanins and flavonols contents. Distinguishing the cultivars with the lowest, highest, relatively stable or those in which antioxidant content greatly differed depending on growing seasons was attempted. The GR activity is proposed as an environmental stress marker of apple fruit.     

Impact of cultivar, harvesting time, and seasonal variation on the content of biophenols in olive mill waste

Olive mill waste (OMW) contains substantial amounts of valuable antioxidant biophenols that can be recovered for possible applications in food, pharmaceutical, and cosmetic industries. However, the impact of cultivar, harvesting time, and seasonal variation on the phenolic composition of OMW has not yet been assessed. Total phenols, antioxidant activity, and phenol profiles of OMW extracts from five different Australian-grown cultivars (Barnea, Correggiola, Manzanillo, Mission, and Paragon) were studied at four different harvesting times in the 2004 season. The impact of seasonal variation was assessed by comparing total phenol content, antioxidant activity, and phenol profile of two cultivars (Correggiola and Mission) harvested in the 2004 and 2005 seasons. The phenol content and antioxidant activity at different harvesting times were mainly a function of the olive cultivar. Harvesting time had a quantitative effect rather than a qualitative effect on the phenol profile. Intercultivar and harvesting time variation accounted for a 2-5-fold change in the total phenol and antioxidant capacity, while levels of individual biophenols experienced up to 50-fold change. The phenol content and antioxidant capacity of OMW significantly changed between seasons with different variation patterns for different cultivars.     

Contribution of individual polyphenolics to total antioxidant capacity of plums

To study the effect of polyphenolics on antioxidant capacities of plums, the amounts of total phenolics, total flavonoids and individual phenolic compounds, and vitamin C equivalent antioxidant capacity (VCEAC) of eleven plum cultivars was determined. There was a good linear relationship between the amount of total phenolics and total antioxidant capacity (r2 = 0.9887). The amount of total flavonoids and total antioxidant capacity also showed a good correlation (r2 = 0.9653). Although the summation of individual antioxidant capacity was lower than the total antioxidant capacity of plum samples, there was a positive correlation (r2 = 0.9299) of total antioxidant capacity of plum samples with the sum of the VCEACs calculated from individual phenolics. Chlorogenic acids and glycosides of cyanidin, peonidin, and quercetin were major phenolics among eleven plum cultivars. The antioxidant capacity of chlorogenic acids and anthocyanins showed higher correlation (r2) of 0.7751 and 0.6616 to total VCEAC, respectively, than that of quercetin glycosides (r2 = 0.0279). Chlorogenic acids were a major source of antioxidant activity in plums, and the consumption of one serving (100 g) of plums can provide antioxidants equivalent to 144.4-889.6 mg of vitamin C.     

Comparison of phenolic acids profile and antioxidant potential of six varieties of spelt (Triticum spelta L.)

Phenolic acids profile and antioxidant activity of six diverse varieties of spelt are reported. Antioxidant activity was assessed using eight methods based on different mechanism of action. Phenolic acids composition of spelt differed significantly between varieties and ranged from 506.6 to 1257.4 μg/g DW. Ferulic and sinapinic acids were the predominant phenolic acids found in spelt. Total ferulic acid content ranged from 144.2 to 691.5 μg/g DW. All analyzed spelt varieties possessed high antioxidant potential. In spite of the fact that bound phenolic acids possessed higher antioxidant activities, analysis of antioxidant potential and their relationship with phenolic acid content showed that free phenolics were more effective. Eight antioxidant methods were integrated to obtain a total antioxidant capacity index that may be used for comparison of total antioxidant capacity of spelt varieties. Total antioxidant potential of spelt cultivars were ordered as follows: Ceralio > Spelt INZ ≈ Ostro > Oberkulmer Rotkorn > Schwabenspelz > Schwabenkorn.     

Effect of growing and drying conditions on the phenolic composition of mate teas (Ilex paraguariensis)

Mate tea ( Ilex paraguariensis) has been used for centuries and is widely consumed in Brazil, Argentina, Paraguay, and Uruguay. The aim of the present study was to determine how growing and drying conditions affect the phenolic concentration and antioxidant capacity of 15 Mate teas from forest or plantation cultivations, dried either with hot air or wood smoke. The total polyphenol concentration determined with Folin-Ciocalteu ranged from 100.3 +/- 5.5 to 179.7 +/- 3.6 mg equiv chlorogenic acid/g dry leaves. The antioxidant capacity according to the oxygen radical absorbance capacity assay ranged from 1.5 +/- 0.3 to 4.1 +/- 0.1 mmol Trolox equiv/g dry leaves. Ten phenolic compounds were identified and correlated with antioxidant capacity ( R (2) = 0.80). Principle component analysis and multivariate linear regression were conducted to assess the effect of growing and drying conditions. Sun-exposed (plantation grown) Mate teas exhibited higher levels of all polyphenols as compared to shaded (forest grown) Mate teas ( P < 0.05). Lower rainfall, temperature, and drying conditions had varying effects on the phenolics. On average, plantation grown Mate teas had a greater concentration of phenolics than forest grown teas. Thus, plantation grown Mate teas represent better potential sources for their commercial extraction.     

Importance of insoluble-bound phenolics to antioxidant properties of wheat

Two commercial samples of soft (70% Canadian Eastern soft red spring and 30% Canadian Eastern soft white winter) and hard (90% Canadian western hard red spring and 10% Canadian Eastern hard red winter) wheats were used to obtain different milling fractions. Phenolics extracted belonged to free, soluble esters and insoluble-bound fractions. Soluble esters of phenolics and insoluble-bound phenolics were extracted into diethyl ether after alkaline hydrolysis of samples. The content of phenolics was determined using Folin-Ciocalteu's reagent and expressed as ferulic acid equivalents (FAE). The antioxidant activity of phenolic fractions was evaluated using Trolox equivalent antioxidant capacity, 2,2-diphenyl-1-picrylhydrazyl radical scavenging, reducing power, oxygen radical absorbance capacity, inhibition of oxidation of human low-density lipoprotein cholesterol and DNA, Rancimat, inhibition of photochemilumenescence, and iron(II) chelation activity. The bound phenolic content in the bran fraction was 11.3 +/- 0.13 and 12.2 +/- 0.15 mg FAE/g defatted material for hard and soft wheats, respectively. The corresponding values for flour were 0.33 +/- 0.01 and 0.46 +/- 0.02 mg FAE/g defatted sample. The bound phenolic content of hard and soft whole wheats was 2.1 (+/-0.004 or +/-0.005) mg FAE/g defatted material. The free phenolic content ranged from 0.14 +/- 0.004 to 0.98 +/- 0.05 mg FAE/g defatted milling fractions of hard and soft wheats examined. The contribution of bound phenolics to the total phenolic content was significantly higher than that of free and esterified fractions. In wheat, phenolic compounds were concentrated mainly in the bran tissues. In the numerous in vitro antioxidant assays carried out, the bound phenolic fraction demonstrated a significantly higher antioxidant capacity than free and esterified phenolics. Thus, inclusion of bound phenolics in studies related to quantification and antioxidant activity evaluation of grains and cereals is essential.     

Influence of fertilization, mulch color, early forcing, fruit order, planting date, shading, growing Environment, and genotype on the contents of selected phenolics in strawberry (Fragaria x ananassa Duch.) fruits

The influence of agricultural practices (fertilization, mulch color, early forcing, and planting date), environment (light and growing area), cultivar, and fruit order on the selected phenolic content and antioxidant activity in strawberry (Fragaria x ananassa Duch.) fruits was studied. Three different levels of fertilization were given to plants in the fertilization experiment. The lowest fertilization level increased the contents of flavonols and ellagic acid from 19 to 57%. Between cultivars, up to 4-fold differences were found in the flavonol content, and it also varied according to growing environment. Planting date in glasshouse production was important for the phenolic content, and a statistically significant interaction was found between planting date and fruit order. Fruit order caused at highest 1.5-2.0-fold differences in the contents of phenolics. Interestingly, compared with other phenolics, anthocyanins were affected differently by many factors. Thus, the findings show that minor cultivation changes can increase the content of phenolics, especially in under-glass production where conditions can be easily manipulated.     

Antioxidant capacity, vitamin C, phenolics, and anthocyanins after fresh storage of small fruits.

Fresh strawberries (Fragaria x ananassa Duch.), raspberries (Rubus idaeus Michx.), highbush blueberries (Vaccinium corymbosum L.), and lowbush blueberries (Vaccinium angustifolium Aiton) were stored at 0, 10, 20, and 30 degrees C for up to 8 days to determine the effects of storage temperature on whole fruit antioxidant capacity (as measured by the oxygen radical absorbing capacity assay, Cao et al., Clin. Chem. 1995, 41, 1738-1744) and total phenolic, anthocyanin, and ascorbate content. The four fruit varied markedly in their total antioxidant capacity, and antioxidant capacity was strongly correlated with the content of total phenolics (0.83) and anthocyanins (0.90). The antioxidant capacity of the two blueberry species was about 3-fold higher than either strawberries or raspberries. However, there was an increase in the antioxidant capacity of strawberries and raspberries during storage at temperatures >0 degrees C, which was accompanied by increases in anthocyanins in strawberries and increases in anthocyanins and total phenolics in raspberries. Ascorbate content differed more than 5-fold among the four fruit species; on average, strawberries and raspberries had almost 4-times more ascorbate than highbush and lowbush blueberries. There were no ascorbate losses in strawberries or highbush blueberries during 8 days of storage at the various temperatures, but there were losses in the other two fruit species. Ascorbate made only a small contribution (0.4-9.4%) to the total antioxidant capacity of the fruit. The increase observed in antioxidant capacity through postharvest phenolic synthesis and metabolism suggested that commercially feasible technologies may be developed to enhance the health functionality of small fruit crops.     

Lettuce and chicory byproducts as a source of antioxidant phenolic extracts

A process to obtain enriched antioxidant phenolic extracts from lettuce (baby, romaine, and iceberg cultivars) and chichory byproducts as a way to valorize these byproducts was developed. Two extraction protocols using water and methanol as solvent were used. Amberlite XAD-2 nonionic polymeric resin was used to purify the extracts. The extraction yield, phenolic content, and phenolic yield were evaluated as well as the antioxidant capacity of the extracts (DPPH, ABTS, and FRAP assays). Baby and romaine lettuce byproducts showed the highest water extract yields [27 and 26 g of freeze-dried extracts/kg of byproduct fresh weight (fw), respectively], whereas baby and iceberg lettuce showed highest methanol extract yields (31 and 23 g of freeze-dried extracts/kg of byproduct fw, respectively). Methanol extraction yielded a raw extract with a high phenolic content, the baby and chicory extracts being the richest with approximately 50 mg of phenolics/g of freeze-dried extract. Regarding the purified extracts, water extraction yielded a higher phenolic content, baby and chicory being also the highest with mean values of approximately 190 and 300 mg of phenolics/g of freeze-dried extract, respectively. Both raw and purified extracts from baby and chicory showed the higher antioxidant contents (DPPH, ABTS, and FRAP assays). The antioxidant capacity was linearly correlated with the phenolic content. The results obtained indicate that lettuce byproducts could be, from the industrial point of view, an interesting and cheap source of antioxidant phenolic extracts to funcionalize foodstuffs.     

Processing strawberries to different products alters contents of vitamin C, total phenolics, total anthocyanins, and antioxidant capacity

Strawberries were processed to juice, nectar, wine, and puree. For investigation of the antioxidant capacity as well as the contents of ascorbic acid, total phenolics and total anthocyanins, samples were taken after different stages of production to determine the effects of processing. The content of vitamin C was measured spectrophotometrically. The total phenolic content was analyzed by using the Folin-Ciocalteu method, and the amount of total anthocyanins was determined by using the pH-differential method. Two different methods-the trolox equivalent antioxidant capacity assay and the ferric reducing antioxidant power test-were used to determine the hydrophilic antioxidant capacity. This study showed the decrease of all investigated parameters within processing strawberries to different products. The content of ascorbic acid decreased with production time and processing steps, especially during heat treatment. The investigations on total phenolics in strawberry products proved fining to be a mild method to clarify berry juices and wines without removing high amounts of total phenolics. Fermentation did not lead to heavy losses of total phenolics, probably due to polymerization and condensation of monomer phenolics such as anthocyanins. Total anthocyanins and the hydrophilic antioxidant capacity decreased while using high temperatures. Anthocyanins also decreased considerably during the processing of wines, mainly caused by fermentation and pasteurization.     

Changes in antioxidant effects and their relationship to phytonutrients in fruits of sea buckthorn (Hippophae rhamnoides L.) during maturation

Different fractions of sea buckthorn fruits were investigated for antioxidant activity and its relationship to different phytonutrients. Capacity to scavenge radicals of the crude extract, like the phenolic and ascorbate extracts, decreased significantly with increased maturation. The changes were strongly correlated with the content of total phenolics and ascorbic acid. Antioxidant capacity of the lipophilic extract increased significantly and corresponded to the increase in total carotenoids. The phenolic fractions made a major contribution to the total antioxidant capacity due to the high content of total phenolics. The lipophilic fractions were most effective if the comparison was based on the ratio between antioxidant capacity and content of antioxidants. The crude extract of fruits showed the highest inhibitory effect in both 2,2-azobis(2,4-dimethylvaleronitrile) (AMVN) and ascorbate-iron induced lipid peroxidations. The aqueous and ascorbate-free extracts showed higher inhibition in the AMVN assay, but lower inhibition in ascorbate-iron induced peroxidation, than the lipophilic extract.