Antioxidant activity of extracts obtained from residues of different oilseeds

Residues of the oil-extracting process of oilseeds contain bioactive substances such as phenolic compounds, which could be used as natural antioxidants for the protection of fats and oils against oxidative deterioration. Thus, the extraction of such constituents from residual material can be considered to contribute to the added value of these residues, which could justify their isolation. In the present work the fat-free residues of eight different oilseeds whose oils are usable for nutritional applications, and also as renewable resources, were extracted with 70% methanol, 70% acetone, water, and ethyl acetate/water, respectively. The resulting extracts were investigated regarding their content of total phenolic compounds by the Folin-Ciocalteau assay, sinapine, flavanoids, and the UV-absorption spectra. Further, the antioxidant activity of the extracts was characterized by the DPPH method, the beta-carotene-linoleic acid assay, and ESR investigations. The fat-free residues of the different oilseeds contained considerable amounts of extractable substances. The yields decreased with decreasing polarity of the solvent in the order water, 70% methanol, 70% acetone, and ethyl acetate. The ratio of total phenolic compounds to the extractable compounds ranged from 3 to 19%. There was no significant correlation between the amount of total extractable compounds and the total phenolic compounds (p < 0.001). All extracts showed remarkable antioxidant activities determined with the different methods. The effects depended strongly on the solvent used for the extraction as well as on the extracted residue. A correlation between the methods used for the characterization of the antioxidant activity and the composition of the residues could not be shown.     

Avocado (Persea americana Mill.) phenolics, in vitro antioxidant and antimicrobial activities, and inhibition of lipid and protein oxidation in porcine patties

The first aim of the present work (study 1) was to analyze ethyl acetate, 70% acetone, and 70% methanol extracts of the peel, pulp, and seed from two avocado (Persea americana Mill.) varieties, namely, 'Hass' and 'Fuerte', for their phenolic composition and their in vitro antioxidant activity using the CUPRAC, DPPH, and ABTS assays. Their antimicrobial potential was also studied. Peels and seeds had higher amounts of phenolics and a more intense in vitro antioxidant potential than the pulp. Peels and seeds were rich in catechins, procyanidins, and hydroxycinnamic acids, whereas the pulp was particularly rich in hydroxybenzoic and hydroxycinnamic acids and procyanidins. The total phenolic content and antioxidant potential of avocado phenolics was affected by the extracting solvent and avocado variety. The avocado materials also displayed moderate antimicrobial effects against Gram-positive bacteria. Taking a step forward (study 2), extracts (70% acetone) from avocado peels and seeds were tested as inhibitors of oxidative reactions in meat patties. Avocado extracts protected meat lipids and proteins against oxidation with the effect on lipids being dependent on the avocado variety.     

On-line HPLC-DPPH screening method for evaluation of radical scavenging phenols extracted from apples (Malus domestica L.)

An on-line HPLC-DPPH screening method for phenolic antioxidants in apple methanol/water (80:20, v/v) extracts was applied. The determination of antioxidants was based on a decrease in absorbance at 515 nm after postcolumn reaction of HPLC-separated antioxidants with the 2,2'-diphenyl-1-picrylhydrazyl radicals (DPPH*). Each of the antioxidants separated by the HPLC column was observed as a negative peak corresponding to its antioxidative activity. The on-line method was applied for quantitative analysis of the antioxidants. A linear dependence of negative peak area on concentration of the reference antioxidants was observed. For validation of the on-line method the limit of detection, LOD (microg/mL), and the limit of quantification, LOQ (microg/mL), of the phenolic compounds were determined. Comparison of the UV and DPPH radical quenching chromatograms with authentic compounds identified catechin, chlorogenic acid, caffeic acid, epicatechin, and phloridzin in the apple cultivars (Lobo, Golden Delicious, and Boskoop), and the distribution of total antioxidant activity was calculated.     

Investigation of Australian olive mill waste for recovery of biophenols

Olive mill waste is a potential source for the recovery of phytochemicals with a wide array of biological activities. Phytochemical screening of hexane, methanol, and water extracts revealed a diversity of compounds, perhaps overlooked in previous studies through intensive cleanup procedures. Methanol and water extracts contained large amounts of biophenols, and further testing of polar extraction solvents, including ethyl acetate, ethanol, propanol, acetone, acetonitrile, and water/methanol mixtures, highlighted the latter as the solvent of choice for extraction of the widest array of phenolic compounds. Stabilization of the resulting extract was best achieved by addition of 2% (w/w) sodium metabisulfite. Quantitative data are reported for nine biophenols extracted using 60% (v/v) methanol in water with 2% (w/w) sodium metabisulfite. Six compounds had recoveries of greater than 1 g/kg of freeze-dried waste: hydroxytyrosol glucoside, hydroxytyrosol, tyrosol, verbascoside, and a derivative of oleuropein.     

New qualitative approach in the characterization of antioxidants in white wines by antioxidant free radical scavenging and NMR techniques

The aim of this study was to obtain new information on antioxidant compounds in white wines. For this purpose, white wine degradation was promoted by a forced aged protocol, and six normally aged white wines from different vintages were analyzed. Both normal and forced aged wines were sequentially extracted using hexane and ethyl acetate. Apolar antioxidants were removed using hexane, and polar antioxidants were extracted with ethyl acetate. This last residue was subject to partial re-extraction with hexane and acetone. The antioxidant capacity of the wines and of each fraction was evaluated by two free radical methods, ABTS and DPPH. Normal aging provides a decrease in the total antioxidant capacity of wines. The antioxidant activity of ethyl acetate/acetone extracts was approximately 95% higher than that found for the hexane extracts. Concerning the forced aged wines, results showed that the wine submitted to a temperature of 60 degrees C for 21 days had higher antioxidant activity than that submitted to a temperature of 20 degrees C. With regard to the ethyl acetate/acetone extracts, oxygen and temperature treatment leads to a decrease in their antioxidant activity. NMR analysis was performed in the highest antioxidant capacity organic fractions (ethyl acetate/acetone extracts) and in the aqueous fraction of the control wine (T = 20 degrees C), in order to attempt the characterization of species involved in oxygen protection. Possible structures of antioxidant compounds in white wines were proposed. Two of these are tyrosol-like structures. This molecule is a well-known phenolic compound in wine, and it is reported to have antioxidative effects.     

Radical scavenging activities of peels and pulps from cv. Golden Delicious apples as related to their phenolic composition

The relationship between phenolic composition and radical scavenging activity of apple peel and pulp was investigated in fruit produced according to both organic and integrated agricultural methods. Apple tissue extracts were subjected to high-performance liquid chromatography separation, which showed that as compared with pulps, peels are richer in almost all of the quantified phenolics. Flavonols, flavanols, procyanidins, dihydrochalcones, and hydroxycinnamates were the identified phenolic classes in peel tissue, and the most abundant compounds were epicatechin, procyanidin B2, and phloridzin. Pulps were poorer in phytochemicals. Their major phenolics were procyanidins and hydroxycinnamates. Flavonols in amounts <20 mg kg(-1) fresh weight (fw) were also found. In both peels and pulps, integrated production samples were richer in polyphenols. Among the 14 compounds identified, only phloridzin had a tendency to appear higher in organic peels. The total antioxidant capacities (TAC) of extracts were evaluated using the 1,1-diphenyl-2-picrylhydrazyl radical assay and were expressed as Trolox equivalents. Integrated peels gave the highest TAC (18.56 mM kg(-1) fw), followed by organic peels (TAC = 14.96), integrated pulps (TAC = 7.12), and organic pulps (TAC = 6.28). In peels, the top contributors to the antioxidant activity were found to be flavonols, flavanols, and procyanidins, which accounted for about 90% of the total calculated activity whereas in pulps, the TAC was primarily derived from flavanols (monomers and polymers) together with hydroxycinnamates. A good correlation between the sum of polyphenols and the radical scavenging activities was found. Among the single classes of compounds, procyanidins (in peels and pulps) and flavonols (in peels) were statistically correlated to the TAC.     

Antioxidant and antiradical activities in extracts of hazelnut kernel (Corylus avellana L.) and hazelnut green leafy cover

Phenolic compounds in the aqueous systems were extracted, from hazelnut kernel (HK) and hazelnut green leafy cover (HGLC), with 80% (v/v) ethanol (HKe and HGLCe) or 80% (v/v) acetone (HKa and HGLCa). The extracts were examined for their phenolic and condensed tannin contents and phenolic acid profiles (free and esterified fractions) as well as antioxidant and antiradical activities by total antioxidant activity (TAA), antioxidant activity in a beta-carotene-linoleate model system, scavenging of DPPH (2,2-diphenyl-1-picrylhydrazyl) radical, and reducing power. Significant differences (p < 0.05) in the contents of total phenolics, condensed tannins, and TAA existed among the extracts that were examined. HGLCa extract had the highest content of total phenolics (201 mg of catechin equivalents/g of extract), condensed tannins (542 mg of catechin equivalents/g of extract), and TAA (1.29 mmol of Trolox equivalents/g of extract) followed by HGLCe, HKa, and HKe extracts, respectively. Five phenolic acids (gallic acid, caffeic acid, p-coumaric acid, ferulic acid, and sinapic acid) were tentatively identified and quantified, among which gallic acid was the most abundant in both free and esterified forms. The order of antioxidant activity in a beta-carotene-linoleate model system, the scavenging effect on DPPH radical, and the reducing power in all extracts were in the following order: HGLCa > HGLCe > HKa > HKe. These results suggest that both 80% ethanol and acetone are capable of extracting phenolics, but 80% acetone was a more effective solvent for the extraction process. HGLC exhibited stronger antioxidant and antiradical activities than HK itself in both extracts and could potentially be considered as an inexpensive source of natural antioxidants.     

Analysis of nonextractable phenolic compounds in foods: the current state of the art

More than 500 phenolic compounds have been reported as present in foodstuffs, and their intake has been related to the prevention of several chronic diseases. Most of the literature on phenolic compounds focuses on those present in the supernatant of aqueous-organic extractions: extractable phenolics. Nevertheless, significant amounts of phenolic compounds remain in the solid residues after such extractions. These nonextractable phenolics are mostly proanthocyanidins, phenolic acids, and hydrolyzable tannins that are closely associated with the food matrix. Studies of this fraction of dietary phenolic compounds are scarce, and the few there are usually refer to particular types of phenolics rather than to the fraction as a whole. The present review reports the state-of-the-art methods that currently exist for analyzing nonextractable phenolic compounds in foods.     

Castanea sativa Mill. leaves as new sources of natural antioxidant: an electronic spin resonance study

The antioxidant potential of Castanea sativa Mill. leaf (sweet chestnut) was explored as a new source of active extracts. The capacity of the different fractions issued from aqueous, methanol, and ethyl acetate extracts to inhibit the stable free radical 2,2-diphenyl-1-pycryl-hydrazyl, superoxide anion, and hydroxyl radical was measured by electronic spin resonance. Their scavenging potential was analyzed versus their amount of phenolic compounds. Among the active fractions, the most effective one was A6, an ethyl acetate fraction, which contained a high level of total phenolic compounds (29.1 g/100 g). Thus, a different extraction procedure was performed to concentrate the active compounds of A6 in the new C. sativa leaf extract (CSLE). Compared to reference antioxidants (quercetin and vitamin E) and standard extracts (Pycnogenol, from French Pinus maritima bark, and grape marc extract), it was observed that A6 and CSLE have high antioxidant potentials, equivalent to at least those of reference compounds.     

Comparison of accelerated methods for the extraction of phenolic compounds from different vine-shoot cultivars

Most research on the extraction of high-priced compounds from vineyard/wine byproducts has traditionally been focused on grape seeds and skins as raw materials. Vine-shoots can represent an additional source to those materials, the characteristics of which could depend on the cultivar. A comparative study of hydroalcoholic extracts from 18 different vineyard cultivars obtained by superheated liquid extraction (SHLE), microwave-assisted extraction (MAE), and ultrasound-assisted extraction (USAE) is here presented. The optimal working conditions for each type of extraction have been investigated by using multivariate experimental designs to maximize the yield of total phenolic compounds, measured by the Folin-Ciocalteu method, and control hydroxymethylfurfural because of the organoleptic properties of furanic derivatives and toxicity at given levels. The best values found for the influential variables on each extraction method were 80% (v/v) aqueous ethanol at pH 3, 180 °C, and 60 min for SHLE; 140 W and 5 min microwave irradiation for MAE; and 280 W, 50% duty cycle, and 7.5 min extraction for USAE. SHLE reported better extraction efficiencies as compared to the other two approaches, supporting the utility of SHLE for scaling-up the process. The extracts were dried in a rotary evaporator, reconstituted in 5 mL of methanol, and finally subjected to liquid-liquid extraction with n-hexane to remove nonpolar compounds that could complicate chromatographic separation. The methanolic fractions were analyzed by both LC-DAD and LC-TOF/MS, and the differences in composition according to the extraction conditions were studied. Compounds usually present in commercial wood extracts (mainly benzoic and hydroxycinnamic acids and aldehydes) were detected in vine-shoot extracts.     

Chemical composition and antioxidant properties of extracts of fresh fruiting bodies of Pleurotus sajor-caju (Fr.) Singer

The chemical composition and in vitro antioxidant activity of aqueous butanol and ethyl acetate extracts of Pleurotus sajor-caju were investigated in this study. Twenty-two compounds comprising methyl esters, hydrocarbon fatty acids, ethyl esters, and sterols were identified in ethyl acetate extracts, while cinnamic acid, nicotinamide, benzeneacetamide, and 4-hydroxybenzaldyhde were identified in butanol extracts by gas chromatography-mass spectrometry and NMR analysis. The antioxidant activity was determined by a β-carotene bleaching method, ferric reducing antioxidant power, trolox equivalent antioxidant capacity, and lipid peroxidation assays, while the total phenolic content in P. sajor-caju was assessed by Folin-Ciocalteau's method. The aqueous and butanol extracts exhibited the highest antioxidant activity, corresponding to the total phenolic content. The subfractions from the ethyl acetate extract (EP1, EP2, EP3, and EP4), however, showed moderate antioxidant activity. The regular consumption of P. sajor-caju as a part of our diet may render nutritional and nutraceuticals benefits for good health.     

Phenolic, flavonoid, and lutein ester content and antioxidant activity of 11 cultivars of chinese marigold

This study analyzed 11 Chinese cultivars of marigold to determine their major phytochemical contents and antioxidant activities. Dried marigold flowers were extracted with ethanol, ethyl acetate, and n-hexane and the extracts were analyzed by high-performance liquid chromatography-mass spectrometry and chemical methods to determine their lutein esters, phenolic and flavonoid contents, and antioxidant activity, respectively. The different cultivars of marigold showed considerable variations in their lutein ester contents, ranging from 161.0 to 611.0 mg/100 g of flower (dry basis). The lutein esters in marigolds consisted predominantly of six all trans-diesters, but small amounts of cis isomers of the respective diesters were also present. The different cultivars of marigold also showed marked variations in total phenols and flavonoids, as well as antioxidant and radical-scavenging activities. Ethanol was confirmed to be the best solvent for extracting both phenols and flavonoids from marigold flowers, while n-hexane was the worst. The ethanolic extracts also exhibited the highest antioxidant and radical-scavenging activities. The cultivar Xinhong had the highest phenolic and flavonoid contents and radical-scavenging activity, as well as one of the highest lutein contents and antioxidant activities.     

Phenolic profile, antioxidant property, and anti-influenza viral activity of Chinese quince (Pseudocydonia sinensis Schneid.), quince (Cydonia oblonga Mill.), and apple (Malus domestica Mill.) fruits

To evaluate the phenolic extracts of Chinese quince, quince, and apple fruits, their phenolic profiles, antioxidant properties, and anti-influenza viral activities were investigated. Chinese quince had the largest amount of phenolics consisting mainly of high polymeric procyanidins. Quince had considerable amounts of hydroxycinnamic derivatives mainly composed of 3-caffeoylquinic acid and 5-caffeoylquinic acid and polymeric procyanidins. Apple (cv. Fuji) had the lowest amount of phenolics, mainly 5-caffeoylquinic acid and monomeric and oligomeric procyanidins. The antioxidant functions of Chinese quince and quince phenolic extracts were superior to that of chlorogenic acid standard or ascorbic acid evaluated in both the linoleic acid peroxidation system and the DPPH radical scavenging system. However, those extracts were less effective than apple phenolics or (-)-epicatechin in linoleic acid peroxidation system. On the other hand, Chinese quince phenolics showed the strongest anti-influenza viral activity on the hemagglutination inhibition test.     

Critical assessment of various techniques for the extraction of carotenoids and co-enzyme Q10 from the Thraustochytrid strain ONC-T18

A variety of techniques for extracting carotenoids from the marine Thraustochytrium sp. ONC-T18 was compared. Specifically, the organic solvents acetone, ethyl acetate, and petroleum ether were tested, along with direct and indirect ultrasonic assisted extraction (probe vs bath) methods. Techniques that used petroleum ether/acetone/water (15:75:10, v/v/v) with 3 h of agitation, or 5 min in an ultrasonic bath, produced the highest extraction yields of total carotenoids (29-30.5 microg g-1). Concentrations up to 11.5 microg g-1 of canthaxanthin and 17.5 microg g-1 of beta;-carotene were detected in extracts stored for 6 weeks. Astaxanthin and echinenone were also detected as minor compounds. Extracts with and without antioxidants showed similar carotenoid concentration profiles. However, total carotenoid concentrations were approximately 8% higher when antioxidants were used. Finally, an easy-to-perform and inexpensive method to detect co-enzymes in ONC-T18 was also developed using silica gel TLC plates. Five percent methanol in toluene as a mobile phase consistently eluted co-enzyme Q10 standards and could separate the co-enzyme fractions present in ONC-T18.     

Increased phloridzin content associated with russeting in apple (<Emphasis Type="Italic">Malus domestica</Emphasis> (Suckow) Borkh.) fruit

Phloridzin is a phenolic compound unique to apple (Malus domestica (Suckow) Borkh.) and its wild relatives. Since its discovery, phloridzin has been researched for its nutraceutical properties, including anti-diabetic, anti-cancer, and antioxidant activities, making phloridzin a potential target for nutritional improvement in new apple cultivars. However, phloridzin accumulates at significantly lower concentrations in fruit than in vegetative tissues and seeds. In ‘Golden Delicious’ and its sports, we observed higher phloridzin content in peels of sports with a cuticle disorder termed russet. In russeted apples, the smooth, waxy fruit cuticle is partially or entirely replaced by a corky layer, induced through environmental and genetic effects. To understand the variation of phloridzin content and fruit russet in apple fruit, we surveyed 108 accessions with variation in russeting from the USDA-ARS Malus germplasm collection in Geneva, NY. Russeting in apple fruit ranged from 0 to 100%, and phloridzin content ranged from 24.3 to 825.0 μg/g in peels. Mean phloridzin content varied significantly between russeting groups; in groups with light (0–5%), medium–high (70–80%), and high (90–100%) russeting mean phloridzin content was 115.2, 591.2, and 378.8 μg/g, respectively. We observed that genetic factors and russeting are strong predictors of phloridzin content in peels, but not fruit flesh or leaves. Conversely, other peel phenolics are negatively associated with russeting. We observed variable phloridzin content related to russet incidence during fruit development in ‘Golden Delicious’ (low to medium russet) and its sports, ‘Empress Spur’ (low russet), ‘Razor’ (complete russet), and ‘Sergeant Russet’ (medium to high russet).     

Polymeric procyanidins as radical-scavenging components in red-hulled rice

The extracts from white-, black-, and red-hulled rice were prepared by sequential extraction with six different polar solvents, and their radical-scavenging activities were measured by methods using 1,1-diphenyl-2-picrylhydrazyl radical (DPPH*) and tert-butyl hydroperoxyl radical (t-BuOO*). The extracts prepared with highly polar solvents, methanol and deionized water, exhibited higher DPPH* and t-BuOO* scavenging activities in all three cultivars. In addition, the acetone extract from red-hulled rice exhibited a high DPPH* and t-BuOO* scavenging activity, while no such activity was detected for the acetone extracts from white- and black-hulled rice. The major components responsible for the radical scavenging in the acetone extract from red-hulled rice were identified as procyanidins by acidic hydrolysis, vanillin assay, and Sephadex LH-20 chromatography. GPC analysis of the acetylated procyanidins revealed that the average molecular weight is about 5000, in a range of about 500-18,000.     

Organic and conventional kiwifruit, myths versus reality: antioxidant, antiproliferative, and health effects

Comparison between organic and conventional kiwifruit cultivars 'Hayward' and 'Bidan', which was done by four radical scavenging assays, ESI-MS, and DSC measurements, showed significant differences between the cultivars. Such results were not estimated in kiwifruit growing under organic and conventional conditions. The extraction of bioactive compounds was done by two different methods: sequential extraction with ethyl acetate followed by methanol and maceration with methanol and ethyl acetate. The highest yield of polyphenols was found in the new cultivar 'Bidan' in comparison with the classic 'Hayward', by direct extraction with methanol. This is the first investigation of 'Bidan' kiwifruit cultivar, grown under organic conditions and compared with 'Hayward' organic. High contents of bioactive compounds and antioxidant and antiproliferative properties of the two kiwifruit cultivars justify their use as sources of valuable antioxidants. It is necessary to continue this study as a long-term experiment to eliminate the influence of seasonality.     

Effects of extraction solvent mixtures on antioxidant activity evaluation and their extraction capacity and selectivity for free phenolic compounds in barley (Hordeum vulgare L.)

Four kinds of solvent extracts from three Chinese barley varieties (Ken-3, KA4B, and Gan-3) were used to examine the effects of extraction solvent mixtures on antioxidant activity evaluation and their extraction capacity and selectivity for free phenolic compounds in barley through free radical scavenging activity, reducing power and metal chelating activity, and individual and total phenolic contents. Results showed that extraction solvent mixtures had significant impacts on antioxidant activity estimation, as well as different extraction capacity and selectivity for free phenolic compounds in barley. The highest DPPH* and ABTS*+ scavenging activities and reducing power were found in 80% acetone extracts, whereas the strongest *OH scavenging activity, O2*- scavenging activity, and metal chelating activity were found in 80% ethanol, 80% methanol, and water extracts, respectively. Additionally, 80% acetone showed the highest extraction capacity for (+)-catechin and ferulic, caffeic, vanillic, and p-coumaric acids, 80% methanol for (-)-epicatechin and syringic acid, and water for protocatechuic and gallic acids. Furthermore, correlations analysis revealed that TPC, reducing power, DPPH* and ABTS*+ scavenging activities were well positively correlated with each other (p < 0.01). Thus, for routine screening of barley varieties with higher antioxidant activity, 80% acetone was recommended to extract free phenolic compounds from barley. DPPH* scavenging activity and ABTS*+ scavenging activity or reducing power could be used to assess barley antioxidant activity.     

Comparative analysis of polyphenolic profiles and antioxidant and antimicrobial activities of tunisian pome fruit pulp and peel aqueous acetone extracts

Pome trees, apple, pear, and quince, are classified into the subfamily Pomoideae, belonging to the Rosaceae family. Their autumnal fruits are consumed worldwide in different forms, that is, fresh or transformed into jams, jelly, juices, etc. Their well-established beneficial properties to human health were found mainly related to their phenolic content. Pulp and peel aqueous acetone extracts obtained from Tunisian fruits at commercial maturity were comparatively evaluated for their phenolic profiles and antioxidant and antimicrobial potentials. The phenolic compounds present in the extracts were identified and quantified using RP-HPLC-DAD and ESI-MS techniques. Significant differences in the chromatographic profiles among these fruits, as well as between pulp and peel extracts of each fruit, were observed. Quince, followed by 'Red Delicious', peel extracts showed the highest phenolic content (160.33 and 110.90 mg/100 g of fresh weight). The stronger inhibitory effect on DPPH radicals corresponded to those obtained from peel materials. A comparative analysis of the antimicrobial potential against a range of microorganism strains was also carried out. Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus cereus were the most sensitive to the active extracts. Among the examined phenolic extracts, 'Red Delicious' and quince peels showed the highest effects for inhibiting bacteria growth. Minimum inhibitory and bactericide concentrations ranged from 10(2) to 10(4) microg of polyphenol/mL. Red skin apple and quince peels could be of great interest as important antioxidant and antimicrobial polyphenol sources.     

Literature data may underestimate the actual antioxidant capacity of cereals

Several recent articles have reported a significant antioxidant capacity of cereal products, determined in methanolic and ethanolic extracts. The aim of this work was to conduct an assessment of the antioxidant capacity of cereals using both chemical and in vitro digestive enzymatic extraction of antioxidants. Ferric reducing power (FRAP) and free radical scavenging capacity (DPPH) methods were used to determine the antioxidant capacity in wheat flour, bread, raw and boiled rice, wheat bran, and oat bran. The most efficient antioxidant extraction was achieved by using successively acidic methanol/water (50:50 v/v, pH 2) and acetone/water (70:30 v/v). The antioxidant capacity in these extracts ranged from 1.1 to 4.4 micromol Trolox/g dw. A significant amount of hydrolyzable phenolics with a high antioxidant capacity (from 5 to 108 micromol Trolox/g dw) was found in the residues of this aqueous-organic extraction. The antioxidant capacities of these nonextractable polyphenols are usually ignored in the literature, although they may have an antioxidant role in the gastrointestinal tract, especially after colonic fermentation, and may be fermentated to active metabolites. On the other hand, in vitro digestive enzymatic extracts obtained by enzymatic treatments that mimic conditions in the gastrointestinal tract showed that the amount of antioxidants released by the cereal matrix into the human intestine may be higher than the one that can be expected from measurements in the usual aqueous-organic extracts.