phenolic compounds (nhom hop chat phenol)

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/263571005 Phenolic compounds in fruits – an overview Article in International Journal of Food Science & Technology · October 2012 DOI: 10.1111/j.1365-2621.2012.03067.x CITATIONS READS 55 557 4 authors, including: Charles Haminiuk Giselle Maria Maciel Federal Technological University of Paraná … Federal Technological University of Paraná … 75 PUBLICATIONS 446 CITATIONS 27 PUBLICATIONS 248 CITATIONS SEE PROFILE SEE PROFILE Rosane Marina Peralta Universidade Estadual de Maringá 171 PUBLICATIONS 2,034 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Biosorption of bioactive compounds in Saccharomyces cerevisiae View project Biosorption of bioactive compounds in Saccharomyces cerevisiae View project All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately Available from: Charles Haminiuk Retrieved on: 15 October 2016 International Journal of Food Science and Technology 2012 Invited review Phenolic compounds in fruits – an overview Charles W I Haminiuk,1* Giselle M Maciel,2 Manuel S V Plata-Oviedo1 & Rosane M Peralta2 Programa de Po´s-Graduac¸a˜o em Tecnologia de Alimentos (PPGTA), Universidade Tecnolo´gica Federal Parana´, Campus Campo Moura˜o, Parana´, Brasil Departamento de Bioquı´ mica, Laborato´rio de Bioquı´ mica de Microorganismos, Universidade Estadual de Maringa´, Maringa´, Parana´, Brasil (Received 23 January 2012; Accepted in revised form April 2012) Summary Phenolic compounds are secondary metabolites widely found in fruits, mostly represented by flavonoids and phenolic acids The growing interest in these substances is mainly because of their antioxidant potential and the association between their consumption and the prevention of some diseases The health benefits of these phytochemicals are directly linked to a regular intake and their bioavailability Studies have shown the importance of the regular consumption of fruits, especially for preventing diseases associated with oxidative stress In the present review, the most recent articles dealing with polyphenols in fruits are reviewed, focusing on their occurrence, main methods of extraction, quantification and antioxidant assays In addition, the health benefits and bioaccessibility ⁄ bioavailability of phenolic compounds in fruits are addressed Keywords Bioaccessibility, bioavailability, extraction, fruits, health benefits, high-performance liquid chromatography, phenolic compounds Introduction Phenolic compounds comprise a diverse group of molecules classified as secondary metabolites in plants that have a large range of structures and functions They can be classified into water-soluble compounds (phenolic acids, phenylpropanoids, flavonoids and quinones) and water-insoluble compounds (condensed tannins, lignins and cell-wall bound hydroxycinammic acids) (Rispail et al., 2005) Phenolic compounds have been considered the most important, numerous and ubiquitous groups of compounds in the plant kingdom (Naczk & Shahidi, 2004) These substances are synthesised during the normal development of the plant, as well as in response to different situations, such as stress and UV radiation, among others (Naczk & Shahidi, 2004) Phenolic compounds have an aromatic ring bearing one or more hydroxyl groups and their structure may vary from that of a simple phenolic molecule to that of a complex high-molecular mass polymer (Balasundram et al., 2006) These antioxidant compounds donate an electron to the free radical and convert it into an innocuous molecule Oxidative stress can cause a series of degenerative illnesses in humans, such as cancer, multiple sclerosis, autoimmune disease and Parkinson’s disease, to name a *Correspondent: Fax: +554435181405; e-mail: haminiuk@utfpr.edu.br few (Theriault et al., 2006) Studies have suggested that a diet rich in phenolic compounds could avoid the oxidative damage that leads to ageing and age-related diseases by scavenging the free radicals from cell metabolism (Kurosumi et al., 2007) Regarding their biological effects (antioxidant, antiviral, antimicrobial, anti-tumour and antibacterial activities), polyphenols are known to participate in protection against the harmful actions of reactive oxygen species (Luo et al., 2011) The antioxidants present in fruits, such as phenolic acids, flavonoids, anthocyanins and tannins, among others, have been frequently associated with health benefits (Fu et al., 2011) Historically, ‘fruits have been considered a rich source of some essential dietary micronutrients and fibres, and more recently they were recognised as being an important source of a wide array of phytochemicals that individually, or in combination may benefit health’ (Yahia, 2009) This review focuses on presenting recent studies about phenolic compounds in fruits A brief overview of the research on polyphenols in fruits is presented Their occurrence, their main methods of analyses and an evaluation of their antioxidant properties using different in vitro and in vivo techniques are addressed Finally, the health benefits and the bioavailability ⁄ bioaccessibility of the phenolic compounds in the human body are discussed doi:10.1111/j.1365-2621.2012.03067.x Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology Phenolic compounds in fruits C W I Haminiuk et al Research on phenolic compounds in fruits The research on phenolic compounds in fruits has evolved considerably over the last 20 years (Fig 1) The role of phenolic compounds in foods, especially in fruits, has drawn the attention of researchers all over the world, and a large number of reviews and books have been published about this topic (Robards et al., 1999; Kaur & Kapoor, 2001; Balasundram et al., 2006; Andre´s-Lacueva et al., 2009; Belitz et al., 2009; El Gharras, 2009; Ignat et al., 2011) Approximately, 3244 articles on the topic of phenolic compounds in fruits were published from 1991 to 2011 The progressive increase in the number of publications (40-fold from 1991 to 2011) evaluating polyphenols in fruits as the main topic mostly reflects the great interest in studying these compounds worldwide The United States, Spain, Italy, China and Brazil stand out as the top five countries around the world where research on polyphenols in fruits has become prominent (Fig 2) The research is mainly focused on: (i) determination of total phenolic, flavonoid and anthocyanin contents, (ii) evaluation of different types of extraction (liquid–liquid, solid–liquid and supercritical fluid, (iii) investigation of the biological activity of polyphenols against some key diseases and microorganisms, (iv) evaluation of their total antioxidant capacity using several different chemical methods: (1,1-diphenyl-2-picrylhydrazyl radical (DPPHd), oxygen radical absorbance capacity (ORAC), 2,2¢-Azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), ferric reducing antioxidant power (FRAP), trolox equivalent antioxidant capacity (TEAC), b-carotene ⁄ linoleic acid, etc.), (v) the quantification and identification of polyphenols by spectrophotometric methods and high efficiency liquid chromatography (HPLC) using different detectors (UV ⁄ Vis, MS, ELSD, etc.), and (iv) study of bioaccessibility and bioavailability of polyphenols Classification and chemical structure of phenolic compounds Phenolic compounds make up a large and fascinating family of substances (Vermerris & Nicholson, 2006) Fruits contain considerable levels of bioactive compounds that impart health benefits beyond basic nutrition (Kaur & Kapoor, 2001) The amount of phenolic compounds in fruits is strongly dependent on the degree of ripeness, variety, climate, soil composition, geographic location and storage conditions, among other factors (Belitz et al., 2009) They are mainly classified according to the number of phenol rings they contain (phenolic acids, stilbenes, flavonoids, lignans and tannins) All these substances have one or more hydroxyl groups directly linked to an aromatic ring characterising thus the phenolic structure (Vermerris & Nicholson, 2006) International Journal of Food Science and Technology 2012 Figure Number of publications on the topic of phenolic compounds in fruits produced in two decades (database searched 20 February 2012) Data Source: certain data included herein are derived from the Web of ScienceÒ prepared by Thomson ReutersÒ, Inc (ThomsonÒ), Philadelphia, PA, USA: ÓCopyright Thomson ReutersÒ 2012 All rights reserved (out of a total of 3244 articles) Figure Share of publications about phenolic compounds in fruits among the top ten countries to publish such studies (database searched 20 February 2012) Data Source: certain data included herein are derived from the Web of ScienceÒ prepared by Thomson ReutersÒ, Inc (ThomsonÒ), Philadelphia, PA, USA: ÓCopyright Thomson ReutersÒ 2012 All rights reserved In the case of the flavonoids group, when they are linked to one or more sugar molecules they are known as flavonoid glycosides, and when they are not connected to a sugar molecule they are called aglycones (Williamson, 2004) The degree of glycosylation directly affects the antioxidant capacity of flavonoids Usually, the aglycone forms of myricetin and quercetin are more active than the glycoside form (Hopia & Heinonen, 1999; Kaur & Kapoor, 2001) The flavonoids are the main bioactive compounds found in fruits and are Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology Phenolic compounds in fruits C W I Haminiuk et al distributed into six subclasses: flavonols, flavanones, isoflavones, flavan-3-ols, flavones and anthocyanins Flavonoids account for approximately two-thirds of the dietary phenols (Robbins, 2003) and they are mostly present as glycosides, and partly as esters, rather than as free compounds (Vermerris & Nicholson, 2006; Belitz et al., 2009) The per capita consumption of the six flavonoid subclasses in the United States is estimated to be 189.7 mg day)1, being mainly flavan-3-ols (Chun et al., 2007) Flavonoids or bioflavonoids are widely distributed in fruits and they are recognised as being natural antioxidants; over 5000 flavonoids have been identified to date (Lampila et al., 2009) These substances have apparent roles in plant stress defence, such as in the protection against damage caused by pathogens, wounding or excess UV light (Winkel-Shirley, 2002) The term flavonoid is usually used to describe a broad collection of natural products that include a C6-C3-C6 carbon framework or, more precisely, phenylbenzopyran functionality (Marais et al., 2006), and they constitute most of the yellow, red and blue colours in fruits (Lampila et al., 2009) These phytochemicals were found to be very effective scavengers of free radicals in in vitro tests and they are important antioxidants because of their high redox potential and their ability to chelate metals (Tsao & Yang, 2003; El Gharras, 2009; Ignat et al., 2011) The second most important group of phytochemicals comprises the phenolic acids, which account for almost the remaining third of the dietary polyphenols, and which are present in fruits in a bound form These substances are divided into two subgroups: hydroxybenzoic and hydroxycinnamic acids In contrast to other phenolic compounds, the hydroxybenzoic and hydroxycinnamic acids present an acidic character owing to the presence of one carboxylic group in the molecule (Annie & Jean-Jacques, 2003) Hydroxycinnamic acid compounds are mainly present as derivatives, having a C6C3 skeleton Ferulic acid, p-coumaric acid and caffeic acid are some examples of this class Hydroxybenzoic acids (C6-C1) are found in various fruits and mostly occur as esters The most common phenolic acids found in fruits in this category are gallic, vanillic, ellagic and syringic acids Tannins are the third class of polyphenols that are found in fruits and are mostly present as phenolic polymers Tannins are astringent and bitter substances of different molecular weights, and some of them, especially the hydrolysable tannins, are soluble in water They are a group of polyhydroxy-flavan-3-ol oligomers and polymers with carbon–carbon linkages between flavanol subunits (Schofield et al., 2001) Tannins have the ability to precipitate proteins The two main types of tannins are condensed and hydrolysable Gallotannin or tannic acid is a type of hydrolysable tannin found in fruits Condensed tannins (proanthocyanidins) are the major phenolic compounds found in grapes Proanthocyanidins, when in contact with salivary proteins, are responsible for the astringency of fruits (El Gharras, 2009) Stilbenes are a group of phenylpropanoid-derived compounds characterised by a 1,2-diphenylethylene backbone (C6-C2-C6) (Goyal et al., 2012) Low quantities of stilbenes are present in the human diet, and their main representative is resveratrol, mostly in the glycosylated form (Delmas et al., 2006; Ignat et al., 2011) Resveratrol is a phytoalexin This substance is mainly produced in grapevines in response to injury and fungal infection (Atanackovic´ et al., 2012), and the main dietary source of resveratrol in fruits is found in red grape skins Several studies have indicated that resveratrol has the ability to prevent cancer and coronary, neurological and degenerative diseases (Anekonda, 2006; Saiko et al., 2008; Das & Das, 2010; Gresele et al., 2011) Resveratrol present in red wine is directly linked to the French paradox, in which French people suffer a relatively low incidence of coronary heart disease even though they have a diet relatively rich in saturated fats (Ferrie`res, 2004) Furthermore, the incidence of heart infarction in France is about 40% lower than in the rest of Europe (Renaud & Delorgeril, 1992; Saiko et al., 2008) It is believed that the continuous and moderated ingestion of grape-derived products, especially red wine, plays a key role in preventing heart disease The fifth group of polyphenols comprises the lignans, a large variety of individual structures mostly consisting of two phenylpropanoid moieties connected via their side chain C8 carbons (Davin & Lewis, 2003; Aehle et al., 2011), usually occurring as glycosides Lignans are one of the major classes of phytoestrogens, which are oestrogen-like chemicals In the gastrointestinal tract, these molecules are converted into compounds (enterodiol and enterolactone) that have both oestrogenic and anti-oestrogenic properties (Meagher & Beecher, 2000) Fruits are not the main dietary source of lignans in food and low concentrations are found in strawberries and cranberries (Meagher & Beecher, 2000) The highest amount of these chemical compounds is found in flaxseed According to data from the Food Composition Panel of the Spanish Ministry of Environment and Rural and Marine Affairs, the average intake of lignans from fruits and vegetables is estimated to be 233.6 lg day)1 (Moreno-Franco et al., 2011) The composition of phenolic compounds in fruits varies considerably Fruits are a particularly rich source of flavonoids (especially flavonols, flavan-3-ols and anthocyanins) and hydroxycinnamic and hydroxybenzoic acids As previously stated, a large amount of scientific evidence shows that the regular consumption of fruit is directly linked to the prevention of various diseases, and the majority of polyphenols that might account for this are shown in Table Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology International Journal of Food Science and Technology 2012 Phenolic compounds in fruits C W I Haminiuk et al Table Main dietary source of polyphenols in fruits Main class Sub-class Name Phenolic acids Hydroxycinnamic acids Hydroxybenzoic acids Flavonoids Flavonols Chemical structure Fruit material References p-Coumaric acid Orange, Black currant Kelebek & Selli (2011a) and Gavrilova et al (2011) Caffeic acid Star fruit, Papaya, Peach, Avocado Fu et al (2011) and Golukcu & Ozdemir (2010) Chlorogenic acid Blueberry, Pear, Kiwifruit, Passion fruit, Peach Gavrilova et al (2011) and Fu et al (2011) Ferulic acid Mango, Red Arac¸a´, Orange, Papaya, Pineapple Poovarodom et al.(2010), Vidal et al (2006), Medina et al (2011) and Fu et al (2011) Gallic acid Banana, Pitaya, Avocado Fu et al (2011) and Golukcu & Ozdemir (2010) Vanillic acid Avocado, Strawberry Poovarodom et al (2010) and Russell et al (2009b) Syringic acid Strawberry, Black grape Russell et al (2009b) and Obo´n et al (2011) Quercetin Passion fruit, Jackfruit, Pomegranate, Camu-camu Fu et al (2011) and Akter et al (2011) Kaempferol Fig, Cambuci Vallejo et al (2012) and Goncalves et al (2010) International Journal of Food Science and Technology 2012 Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology Phenolic compounds in fruits C W I Haminiuk et al Table (Continued) Main class Sub-class Flavanones Flavan-3-ols Flavones Anthocyanins Name Chemical structure Fruit material References Myricetin Apple, Papaya Medoua & Oldewage-Theron (2011), Rinaldo et al (2010) and Lako et al (2007) Rutin Red Grape, Prune, Bluberry Fu et al (2011) and Gavrilova et al (2011) Hesperetin Grapefruit, Orange Zhang et al (2011) and Plaza et al (2011) Naringenin Grapefruit, Orange Ribeiro & Ribeiro (2008), Goulas & Manganaris (2012) and Zhang et al (2011) Epicatechin Avocado, Yellow Arac¸a´ Golukcu & Ozdemir (2010) and Medina et al (2011) Catechin Red grape, Sweet cherry Iacopini et al (2008) and Kelebek & Selli (2011b) Apigenin Mango, Durian, Bilimbi fuit Poovarodom et al (2010) and Miean & Mohamed (2001) Luteolin Lemon, Pineapple, Plum, Watermelon, Orange Fu et al (2011) and Fuzfai & Molnar-Perl (2007) Delphinidin Grapefruit, Blackcurrant, Blueberry Fu et al (2011) and Obo´n et al (2011) Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology International Journal of Food Science and Technology 2012 Phenolic compounds in fruits C W I Haminiuk et al Table (Continued) Main class Stilbenes Sub-class – Name Chemical structure Fruit material References Cyanidin Raspberry, Pomegranate, Acerola Fanali et al (2011) and Mamede et al (2009) Malvidin Blueberry, Myrtle fruit, Red Grape Wang et al (2008b), Messaoud & Boussaid (2011) and Lambert et al (2011) Peonidin Blueberry, Black Currant Obo´n et al (2011) and Bakowska-Barczak & Kolodziejczyk (2011) Pelargonidin Strawberry, Raspberry, Mangosteen Obo´n et al (2011) and Zarena & Udaya Sankar (2012) Petunidin Apple, Blueberry Kahle et al (2006) and Fanali et al (2011) Resveratrol Red Grape, Cranberry, Strawberry Granato et al (2011) and Huang & Mazza (2011) Extraction of polyphenols The extraction of phenolic compounds is influenced by several parameters, and the initial step of a preliminary experiment is to select the most appropriate extraction conditions Sample preparation plays an important role in the quantification of phytochemicals from plant material, and it is the first and usually the most important process, which greatly influences the repeatability and accuracy of the analysis (Zhao et al., 2011) To achieve maximum extraction, it is recommended that several different parameters are tested, such as the solvent, agitation, extraction time, solute ⁄ solvent ratio, temperature, efficiency of mass transfer and particle size, for example (Luthria, 2008; Hurtado-Fernandez et al., 2010; Haminiuk et al., 2011; Yang et al., 2011) Ideally, the extraction of polyphenols should be performed using fresh fruit samples However, because of seasonality, perishability, shelf-life and quality, many researchers International Journal of Food Science and Technology 2012 have used freezing and drying processes to preserve the plant material These processes are often a necessary step for preserving the fruit sample against different types of degradation, for avoiding microorganisms and for concentrating the antioxidant compounds Some authors have reported that the freezing process and long-term frozen storage cause important losses in the amount of phenolic compounds and vitamins found in fruits (de Ancos et al., 2000; Chaovanalikit & Wrolstad, 2004; Turkben et al., 2010) Different techniques are available to preserve plant material, and in the last few years, lyophilisation has been widely used Lyophilisation is a process that removes the water from materials such as foods, drugs and biological samples, and it has been recognised as an important and well-established technique for improving the long-term stability of a product (Kasper & Friess, 2011) In the literature, several authors have reported the use of lyophilisation as a drying technique for Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology Phenolic compounds in fruits C W I Haminiuk et al preserving fruit samples (Marques et al., 2007, 2009; Hurtado-Fernandez et al., 2010; de Torres et al., 2010; Ignat et al., 2011; Kotikova et al., 2011; Rockenbach et al., 2011) The utilisation of finely powdered plant material enhances the extraction of phenolic compounds by increasing the surface area of the sample and promoting disruption of the plant cell wall (Kim & Lee, 2001) When the fruit sample is obtained (fresh, frozen, dried or lyophilised), the next stage is extraction, per se The most commonly used step for extracting phenolic compounds in fruits is the use of organic solvents The choice of the most appropriate solvent depends on its selectivity, miscibility, density, recovery, price, vapour pressure, viscosity and chemical and thermal stability Various solvents and conditions have been used to achieve optimal extraction The application of acidified methanol, ethanol, acetone and ethyl acetate, and the combination of these solvents with water, has been widely reported in the literature (Luthria & PastorCorrales, 2006; Durling et al., 2007; Luthria, 2008; Wang et al., 2008a; Russell et al., 2009a; Annegowda et al., 2012; Haminiuk et al., 2011; Prasad et al., 2011; Ramful et al., 2011) Solid–liquid extraction (SLE) is an important, simple and efficient technique of mass transfer used for the recovery of polyphenols from fruit tissues It allows soluble components to be removed from the plant matrix and these compounds migrate into the solvent up to the point of equilibrium (Corrales et al., 2009) This process can be improved by changing the concentration gradients, the boundary layer and diffusion coefficients (Corrales et al., 2009; Ignat et al., 2011) In addition, to enhance the extraction process, some authors have combined the SLE technique with ultrasound This method has been successfully used to extract bioactive compounds (Herrera & de Castro, 2005; Ma et al., 2009; Casazza et al., 2010; Prasad et al., 2010; Wang & Zuo, 2011) Ultrasound-assisted extraction is a quick and efficient method for extracting phenolic compounds from fruits (Kim & Lee, 2001), being an effective way of extracting analytes from different matrices in a shorter time than other extraction techniques (Herrera & de Castro, 2005) The increase in polyphenol extraction by this technique is because of the disruption of cell walls, a reduction in particle size and enhancement of the mass transfer of cell contents to the solvent, caused by the collapse of the bubbles produced by cavitation (Paniwnyk et al., 2001; Rodrigues & Pinto, 2007) One of the disadvantages of the solid-extraction process is the co-extraction of substances such as proteins, sugars and organic acids (Ignat et al., 2011) that might interfere in the quantification of polyphenols, especially with the Folin-Ciocalteu method To remove these interferences, the use of C18 Sep-Pak cartridges is highly recommended This purification technique separates the non-polyphenolic substances from the polyphenolic extract of the fruit, producing more accurate results In the last decade, the use of supercritical fluid extraction (SFE) of bioactive compounds in fruits has been investigated and is gaining popularity Carbon dioxide is the most commonly used fluid in SFE (Quitain et al., 2006) This type of extraction is considered an emerging technology (Casas et al., 2009) and it presents some advantages over classic solvent extraction methods, because it is a more selective and less toxic technique (Alpendurada, 2003) Other advantages of SFE include free-solvent products and the prevention of oxidation during processing (Vatai et al., 2009; Herrero et al., 2010) One disadvantage of this technique is the need for expensive equipment and high pressures, which increase the costs compared with conventional liquid extraction Therefore, SFE will only be used when significant advantages overcome these disadvantages Vatai et al (2009) showed that the pre-treatment of fruit samples with carbon dioxide (CO2) removed the non-polar substances, making the polar polyphenols more accessible in grapes and elderberries However, the amount of extracted anthocyanins in these fruits was not significantly influenced by SFE In another study, SFE with CO2 ⁄ EtOH showed similar results for the total phenolic compounds (TPC) in guava seeds compared with the Soxhlet SLE method (Castro-Vargas et al., 2010) Supercritical carbon dioxide was successfully used to extract resveratrol from grape pomace by Casas et al (2010) In this study, SFE with CO2 ⁄ EtOH (400 bar and 35 °C) presented the highest resveratrol recovery (49.10 mg per 100 g of dry sample) when compared with conventional extraction [methanol ⁄ HCl (0.1%) for 30 in an ultrasonic bath], where 3.10 mg of resveratrol per 100 g of dry sample was obtained Quantification of phenolic compounds by spectrophotometric techniques Fruits are an important source of polyphenols in the human diet and the proper quantification of these substances is of fundamental importance The main methodologies used to quantify the bioactive compounds in fruits, which are widely described in the literature, are the colorimetric method of Folin-Ciocalteu that estimates the total polyphenols (TPC), the aluminium chloride colorimetric assay that quantifies the total flavonoids (TF) and total anthocyanins (TA) estimated by the pH differential method, which is based on the structural change of the anthocyanin chromophore between pH values of 1.0 and 4.5 (Granato et al., 2010; Haminiuk et al., 2011) Table shows a brief summary of the total polyphenols, total flavonoids and TA in different fruits The quantification of phenolic compounds is mainly carried out by spectrophotometric analysis Generally, Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology International Journal of Food Science and Technology 2012 Phenolic compounds in fruits C W I Haminiuk et al Table Summary of total phenolic compounds, flavonoids and anthocyanins of different fruits as quantified by spectrophotometric measurements Fruit material Ac¸aı´ Acerola Banana Blackberry Cambuci Fig Grape Kiwifruit Mulberry Orange Plum Raspberry Strawberry Uvaia Sample Fresh Fresh Fresh Fresh Fresh Fresh Fresh Fresh Lyophilised powder Fresh Fresh Fresh Lyophilised powder Fresh Solvent Methanol ⁄ acetone Methanol ⁄ acetone Acetone ⁄ water ⁄ acetic Phosphate buffer Ethanol Methanol ⁄ HCl Methanol ⁄ HCl Acetone ⁄ water ⁄ acetic Water Acetone ⁄ water ⁄ acetic Acetone ⁄ water ⁄ acetic Phosphate buffer Water Ethanol Total phenolics Total flavonoids a acid acid acid acid 454.00 1063.00a 475.00c 226.00a 3414.00e 463.00a 2348.00e 112.00c 1515.90a 243.00c 311.00c 267.00a 363.70a 373.40e Total anthocyanins b – 0.70d – 30.16d 45.60f – 0.40d 250.10d 6.10d 3.00d – 14.60d 58.72d 111.00 18.90b 0.00b 153.30b 19.44b 27.30b 99.08b 0.00b – 0.00b 102.00b 197.20b – 4.77b References Rufino et al (2010) Rufino et al (2010) Kevers et al (2007) Wang & Lin (2000) Haminiuk et al (2011) Solomon et al (2006) Orak (2007) Kevers et al (2007) Lin & Tang (2007) Kevers et al (2007) Kevers et al (2007) Wang & Lin (2000) Lin & Tang (2007) Haminiuk et al (2011) mg GAE 100 g)1 of fresh weight mg 100 g)1 of fresh weight (expressed as cyanidin 3-glucoside or malvidin-3-glucoside) c mg CAE 100 g)1 of fresh weight d mg of QE 100 g)1 of fresh weight e mg GAE l)1 of fresh weigh f mg CE 100 g)1 of fresh weight GAE, gallic acid equivalent; CAE, chlorogenic acid equivalent; QE, quercetin equivalent; CE, catechin equivalent a b the visible region of the spectrum is used to quantify total phenolics, flavonoids and tannins, among other substances The most common and widespread methodology used to quantify the total phenolic compounds in foodstuffs originated from the methodology developed in 1927 by Otto Folin and Vintila Ciocalteu for the measurement of tyrosine (Folin & Ciocalteu, 1927; Everette et al., 2010), and it was adapted in 1965 by Vernon Singleton and Joseph Rossi for the evaluation of total phenolics in wine (Singleton & Rossi, 1965) This methodology is based on chemical reduction by a mixture of tungsten and molybdenum oxides (Waterhouse, 2001) Upon reaction with phenols, a blue colour is produced, which absorbs light at 765 nm (Everette et al., 2010) The intensity of light absorption at this wavelength is proportional to the concentration of phenols (Waterhouse, 2001) It is noteworthy that this reagent does not only measure total phenols but it will react with any reducing substance For this reason, the total reducing capacity of a sample will be quantified and not only the level of phenolic compounds (Ikawa et al., 2003) The average time for this test is h; however, this time can be reduced by heating the sample The main disadvantage of heating is that it affects the reproducibility of the assay because heating causes instability of the blue colour over time (colour loss) Several articles reporting the total phenolic composition of fruits estimated using the Folin-Ciocalteu method (Singleton & Rossi, 1965; Singleton et al., 1999) are available in the scientific literature: kiwifruit International Journal of Food Science and Technology 2012 (Sun-Waterhouse et al., 2009), grape (Yang et al., 2009), mango (Prasad et al., 2011), pomegranate (Cristofori et al., 2011), cranberry (Coˆte´ et al., 2011), banana, guava, peach and pear (Contreras-Calderon et al., 2011), lemon, orange, passion fruit, pitaya, plum, avocado and papaya (Fu et al., 2011) and apple (Zheng et al., 2012) In a recent study, a wide variation in the contents of the total phenolic compounds of sixty-two Chinese fruits was found, where the total phenolic compounds ranged from 11.88 to 585.52 mg gallic acid equivalent (GAE) per 100 g, with a difference of 49-fold and a mean value of 71.80 mg GAE per 100 g (Fu et al., 2011) Pear (honey) and Chinese date presented the lowest and the highest amounts of total phenolic compounds, respectively (Fu et al., 2011) High contents of TPC can be found in fruits: 1063 mg GAE per 100 g of fresh weight (FW) in acerola (Rufino et al., 2010), 1365 mg GAE per 100 g of FW in cambuci (Haminiuk et al., 2011), 1797 mg GAE per 100 g of FW in camucamu (Genovese et al., 2008) and 2167 mg GAE per 100 g of FW in Andean blackberry (Vasco et al., 2008) Flavonoids are mainly accumulated in the outer tissue of fruits because their synthesis is stimulated by sunlight (Manach et al., 2004; Rosa et al., 2010) The total flavonoid content in fruits is mainly estimated using the colorimetric method with aluminium chloride In this methodology, the fruit extract is added in a methanolic solution of aluminium chloride at a determined concentration In some methodologies, the extract is mixed with NaNO2 before mixing with AlCl3 (Sun et al., 2011) After a short period of time, the absorbance is measured Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology Phenolic compounds in fruits C W I Haminiuk et al and compared with a flavonoid standard (catechin, quercetin or rutin) The disadvantage of this methodology is that it only gives an estimation of the total flavonoid content (Ignat et al., 2011) Nevertheless, this is a simple and efficient methodology for quantifying the total content of flavonoids in fruits and it can be very useful when more advanced equipment, such as HPLC, is not available The flavonoid concentration in fruits varies by many orders of magnitude and in most of fruits these compounds are present in the skin Berries are in the group that presents one of the highest values of total flavonoids among fruit (USDA, 2011) Blueberry, among another nineteen Bulgarian fruits, was found to contain the highest amount of total flavonoids with 190.3 mg of catechin equivalent (CE) per 100 g of FW, followed by sour cherry with 138.6 mg CE per 100 g of FW (Marinova et al., 2005) Anthocyanins are water-soluble glycosides of anthocyanidins (aglycones) (Vermerris & Nicholson, 2006) These compounds are benzopyrylium and flavylium salts (Belitz et al., 2009) They are divided into anthocyanidin aglycones (sugar free) and anthocyanin glycosides These substances are particularly evident in flowers and fruit tissues Anthocyanin is derived from two Greek words, anthos and kyanos, meaning flower and dark blue, respectively (He & Giusti, 2010) This class of phenolic compounds is recognised as being the most important group of pigments in nature and they contribute to the attractive colours of fruits Anthocyanins are pigments dissolved in the vacuolar sap of the epidermal tissues of fruits, to which they impart a pink, red, blue or purple colour, and they exist in different chemical forms, both coloured and non-coloured, according to the pH (Mouly et al., 1994; Manach et al., 2004) Over 635 anthocyanins have been identified in plants to date (Wallace, 2008; He & Giusti, 2010), although only six are commonly found: delphinidin, cyanidin, pelargonidin, malvidin, petunidin and peonidin The pH differential method is the most commonly and widely used assay for quantifying monomeric anthocyanins This methodology measures the absorbance at two different pH values, and it is based on the structural transformation of the anthocyanin chromophore as a function of pH (Giusti & Wrolstad, 2001) It was initially developed to evaluate pigments in strawberry jam (Sondheimer & Kertesz, 1948) The methodology has undergone some modifications over time (Fuleki & Francis, 1968; Wrolstad et al., 1982; Giusti & Wrolstad, 2001) In this methodology, basically the pigments reversibly change colour with a change in pH The samples are diluted with aqueous pH 1.0 and 4.5 buffers and absorbance measurements are made at the wavelength of the maximum absorbance of the pH 1.0 solution (Wrolstad et al., 2005) The pH differential method is based on this reaction and the difference in the absorbance of the pigments at 520 nm is proportional to the pigment concentration The results are mainly expressed on a cyanidin-3-glucoside basis The group of cherries and berries has been extensively reported in literature as containing the fruits with the highest levels of anthocyanins per serving Berries with red, blue or purple colours constitute one of the most important sources of these phytochemicals (Kahkonen et al., 2003) Grapes are one of the major dietary sources of anthocyanins (Munoz-Espada et al., 2004), being widely obtained from wine, juices and jams, for example Some hybrid grape cultivars can reach up to 603 mg of anthocyanins per 100 g of FW (Mazza, 1995; Yang et al., 2009) Raspberry, blackberry, blueberry, chokeberry and bilberry, among others, are very rich in anthocyanins Plum and elderberry are also among the richest sources of anthocyanins in fruits (USDA, 2011) Identification and quantification of phenolic compounds by HPLC Liquid chromatography is an important physical separation technique carried out in the liquid phase where a mixture of compounds can be easily and rapidly separated Reverse-phase high-performance liquid chromatography (RP-HPLC) is the main method used for the separation of phenolic compounds in plant-food material, in which the stationary phase is less polar than the mobile phase The stationary phase is generally made up of hydrophobic alkyl chains, where there are three common chain lengths: C4, C8 and C18 (Guzzeta, 2011) Silica-bonded C18 columns are widely used to separate phenolic compounds In RP-HPLC, the retention time of phenolic compounds is higher for substances that are less polar (myricetin, quercetin, kaempferol); meanwhile, polar molecules are eluted more easily (gallic acid, protocatechuic acid, epigallocatechin) Owing to their chemical complexity and similarity, polyphenols in fruits are usually identified and quantified by RP-HPLC using a gradient elution instead of the isocratic mode, where the mobile phase is generally a binary system (Merken & Beecher, 2000; Kim & Lee, 2001) Usually, gradient elution is carried out with high quality ultrapure acidified water (phosphoric, acetic, formic acids) as the polar solvent; meanwhile, acetonitrile and methanol are usually used as less polar solvents (Kim & Lee, 2001) A small quantity of acid is added to the solvent system to suppress the ionisation of phenolic and carboxylic groups, which will improve certain parameters such as retention time and resolution (Ha¨kkinen, 2000) Polyphenols have a maximum absorbance (kmax) in either the ultraviolet or visible regions and, thus, determination of the optimum absorbance for each substance plays an important role in the identification, quantification and accuracy of the analysis The ultraviolet Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology International Journal of Food Science and Technology 2012 10 Phenolic compounds in fruits C W I Haminiuk et al spectrum in the region of maximum absorbance of gallic acid, resveratrol and quercetin is shown in Fig High-performance liquid chromatography systems can be equipped with a wide range of detectors (refractive index, fluorescence, electrochemical, lightscattering, mass spectrometric and UV ⁄ Vis) (Thompson & LoBrutto, 2006), which can be used to detect and quantify polyphenols with and without chromophore groups, depending on the methodology used Among the different detectors available, UV ⁄ Vis with a photodiode array is one of the most widely used to elucidate polyphenols in plant-based materials The main advantage of diode array detectors (DAD) is that several results can be obtained from a single run, mainly because of its collection of UV ⁄ Vis spectra (Kim & Lee, 2001), thereby increasing the throughput of the HPLC In addition, it is possible to determine the correct wavelength in one run, to detect multiple wavelengths and to evaluate peak purity, among others (Dionex, 2003) Sophisticated systems of liquid chromatography coupled with modern detectors such as UPLC-DADMS ⁄ MS (ultra-performance liquid chromatographyDAD-tandem mass spectrometry), UPLC-DAD ⁄ ESI-MS (ultra-performance liquid chromatography-DAD and electrospray ionisation-mass spectrometry), HPLCPDA-MS ⁄ ELSD (HPLC-photodiode array-mass spectrometry and evaporative light-scattering detector), UHPLC-MS ⁄ MS (ultra- HPLC–tandem mass spectrometry) and HPLC-ESI-TOF ⁄ MS (HPLC–electro- (a) spray ionisation-time of flight-mass spectrometry) are currently available, which are able to determine the chemical structure of a wide range of compounds However, these systems are still expensive, which generally limits access to these types of equipment by most researchers In this context, the system of liquid chromatography coupled with DAD-UV ⁄ Vis is the most utilised, especially in the identification of phenolic compounds, because of its low cost, sensitivity, separation efficiency, flexibility and identification potential A compilation of recent papers published about the separation and identification of phenolic compounds in fruits using RP-HPLC-DAD ⁄ UV-Vis is summarised in Table The methods of extraction, separation and the analysis of phenolic compounds in plant-food material were recently reviewed (Ignat et al., 2011) The applications and advances in the liquid chromatography analysis of polyphenols have evolved considerably over the years (Kalili & de Villiers, 2011); however, these advances are not considered in the present review Antioxidant activity of fruits Many methods have been used to evaluate and compare the antioxidant activity of fruits owing to the complexity of the substrate analysed (Kaur & Kapoor, 2001; Szabo et al., 2007) The antioxidant capacity is mainly evaluated through chemical tests and more recently through a cell antioxidant test The antioxidant activity using (b) (c) Figure Maximum absorbance of (a) gallic acid – 271.7 nm, (b) resveratrol – 306.2 nm and (c) quercetin – 370.6 nm International Journal of Food Science and Technology 2012 Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology A (5% formic acid in water), B (acetonitrile ⁄ solvent A 60:40), 1.0 A (2% acetic acid in water), B (methanol), 0.8 A (0.5% acetic acid in water), B (methanol), 0.8 A (0.1% formic acid in acetoni trile), (B) acetonitrile ⁄ water ⁄ formic acid (5:92:3), 1,5 A (4.5% formic acid in water), B (acetonitrile), 1.0 A (acetic acid in mM sodium acetate, final pH 2.55), B (acetonitrile), 1.0 A (0.1% formic acid in water), B (80% acetonitrile in water), 1.0 A (acetic acid in water pH 2.74), B (acetonitrile), 0.8 A (2% acetic acid in water), B (water ⁄ acetonitrile ⁄ acetic acid, 78:20:2), 1.0 Sweet cherry Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology Grape skin Guava Bayberry juice Apple juice Strawberry Kiwifruit waste Grape pomace Mango A (0.1% phosphoric acid in water), B (methanol), 0.8 Mobile phase (gradient) ⁄ flow rate (ml min)1) Raspberry Fruit material 278 Agilent Eclipse XDBÒ C18 (250 · 4.6 mm length, lm) ⁄ 30 Merck LichrospherÒ C18 (250 · 4.0 mm length, lm) ⁄ 40 PhenomenexÒ C18 (250 · 4.6 mm length, lm) ⁄ 45 DiamonsilÒ C18 (250 · 4.6 mm length, lm) ⁄ 30 Phenomex LunaÒ C18 (250 · 4.6 mm length, lm) ⁄ 38 Waters Nova PackÒ C18 (250 · 4.6 mm length, lm) ⁄ 20 PhenomexÒ C18 (250 · 4.6 mm length, lm) ⁄ 30 Agilent ZorbaxÒ SB C18 C18 (150 · 4.6 mm length, lm) ⁄ 37 280, 316, 365 and 520 Beckman UltrasphereÒ ODS C18 (250 · 4.6 mm length, lm) ⁄ 25 210–360 280, 320 and 370 360 and 520 280, 320 and 360 280,320, 360 and 520 280, 320 and 370 254, 280, 320 and 365 280, 360 and 520 Wavelength (k) nm Varian OmnisphereÒ C18 (250 · 4.6 mm length, lm) ⁄ 20 Column type and temperature (° C) Rutin, luteolin, apigenin and kaempferol Quercetin, kaempferol and myricetin Quercetin, kaempferol and cyanidin Proanthocyanidins, (+)-catechin, p-coumaric acid and pelargonidin Chlorogenic acid, caffeic acid, cinnamic acid Chlorogenic acid, gallic acid and (+)-catechin Gallic acid, p-coumaric acid, ellagic, mangiferin and rutin Caffeic acid, p-hydroxybenzoic acid and syringic acid Ellagic acid and (+)-catechin, ())-epicatechin, quercetin and cyanidin Neochlorogenic acid, ())-epicatechin, rutin and cyaniding Major compounds identified Table Summary of the methodologies used for the separation and identification of phenolic compounds in fruits by RP-HPLC-DAD ⁄ UV-Vis Obreque-Slier et al (2010) Kubola et al (2011) Fang et al (2009) Torres et al (2011) Oszmianski et al (2009) Sun-Waterhouse et al (2009) Hassan et al (2011) Sagdic et al (2011) Kelebek & Selli (2011b) Jakobek et al (2009) References Phenolic compounds in fruits C W I Haminiuk et al International Journal of Food Science and Technology 2012 11 12 Phenolic compounds in fruits C W I Haminiuk et al chemical methods is primarily evaluated through: (I) hydrogen atom transfer methods (HAT) or (II) electron transfer methods (ET) (Prior et al., 2005; Badarinath et al., 2010) ORAC, lipid peroxidation inhibition capacity, total radical-trapping antioxidant parameter (TRAP) and ABTS radical scavenging are the most commonly used hydrogen atom transfer methodologies, and TEAC, FRAP and DPPH• free radical scavenging are the main ET tests (Badarinath et al., 2010) These in vitro methodologies have been frequently used to estimate antioxidant activity in fruits As these antioxidant assays are based on different mechanisms using different radical or oxidant sources (USDA, 2010), the results obtained are expressed in different units and, therefore, cannot be directly compared (USDA, 2010) Antioxidants are molecules that are able to inactivate free radicals and their action (Halliwell, 1996; Devasagayam et al., 2004), providing an important role in the body defence system against reactive oxygen species (Noipa et al., 2011) Phenolic compounds are considered natural antioxidants, and fruits are very rich in these phytochemicals The DPPH• (1,1-diphenyl-2-picrylhydrazyl) assay is the one of the most popular methods used to evaluate antioxidant activity in fruits; it was originally introduced by Marsden Blois in 1958 (Blois, 1958) The principle behind this assay is based on scavenging of the stable DPPH• by an antioxidant (reduction of DPPH• to DPPH2) (Mishra et al., 2012) The absorbance is monitored in the range of 515-520 nm (Noipa et al., 2011), where the purple colour of the solution changes to yellow and a reduction in the absorbance is observed (Mishra et al., 2012) This antioxidant assay has been modified over the years (Brand-Williams et al., 1995; Mensor et al., 2001; Chen et al., 2005; Chien et al., 2007) because the original methodology was somewhat oversimplified (Molyneux, 2004) This test was recently reviewed to standardise the protocols (Sharma & Bhat, 2009) The main findings refer to the use of a 50 lm DPPH• solution in methanol or buffered methanol, because of the accuracy of spectrophotometric measurements In addition, a time course of the inhibition process is also suggested A new approach for evaluating antioxidant capacity using the DPPH• test in aqueous solution using surfactant aggregates or micelles was recently proposed by Noipa et al (2011) It was found that the optimum micelle system for determining the antioxidant capacity is mm cethyltrimethylammonium bromide (CTAB) in 0.1 m acetate buffer (pH 4.6), and it was suggested that this new approach could be an alternative to the DPPH• assay using methanol Moreover, the test showed a shorter time of analysis because the rate constants observed in the micelle system were significantly faster than those in methanol Another important assay that is widely used to evaluate the antioxidant capacity of fruits is the ORAC International Journal of Food Science and Technology 2012 test The ORAC assay measures the ability of antioxidants to protect proteins from damage by free radicals (Awika et al., 2003), and it is the only chemical method that takes free radical action to completion (Wang et al., 2004) Furthermore, owing to its biological relevance to the in vivo antioxidant efficacy, the ORAC is the preferred technique of some researchers (USDA, 2010) This methodology was originally introduced by Glazer (1990) and it was modified by Cao et al (1993) In the original methodology, b-phycoerythrin is used as an indicator protein, 2,2¢-azobis(2-amidinopropane) dihydrochloride (AAPH) as a peroxyl radical generator, and trolox as a control standard, where the results are expressed as micromolar of trolox equivalent per litre or per gram of sample (Cao et al., 1993; Prior et al., 2005) The ORAC was improved in 2001 because of limitations of b-phycoerythrin, such as: inconsistency from lot to lot, photobleaching and interactions with polyphenols (Ou et al., 2001) The authors proposed the use of fluorescein as the fluorescent probe Water-soluble and fat-soluble antioxidant compounds can also be assayed by the method described by Prior et al (2003) for hydrophilic (H-ORAC) and lipophilic ORAC (LORAC), respectively One disadvantage of the ORAC method in comparison with other antioxidant tests is that it requires expensive apparatus (Awika et al., 2003) In a comprehensive study, over 100 different kinds of foods were evaluated using the ORAC test (Wu et al., 2004) Among the fruits assayed, the berries, plums and some varieties of apples gave higher values in the ORAC test; these data were also confirmed in the USDA database for ORAC of selected foods (USDA, 2010) In this database, higher values of micromolar of trolox equivalent per gram of fruit were found for different berries and some other fruits such as: chokeberry, elderberry, black raspberry juice, raisins, raspberry and rose hip Despite the great popularity of chemical tests, these methodologies fail to effectively predict the antioxidant capacity in vivo A more relevant method called ‘cellular antioxidant activity (CAA)’ was recently proposed to measure the cellular activity of antioxidants (Wolfe & Liu, 2007) This methodology considers important aspects such as uptake, metabolism and location of antioxidant compounds within cells (Song et al., 2010), which are not considered by traditional methods This technique is performed using a 2¢,7¢-dichlorofluorescin (DCFH) probe in human hepatocarcinoma cells (HepG2), which fluoresce when oxidised by peroxyl radicals to 2¢,7¢-dichlorofluorescein (Wolfe et al., 2008) The CAA methodology was used to evaluate the inhibition of peroxyl radical-induced DCFH oxidation by selected pure phytochemical compounds and fruits by measuring the EC50 values (Wolfe & Liu, 2007) Quercetin showed the highest CAA value among the pure compounds assayed, and blueberry was the most effective in preventing peroxyl radical-induced DCFH Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology Phenolic compounds in fruits C W I Haminiuk et al oxidation among the fruits The same research group published another cellular antioxidant study where twenty-five fruits commonly consumed in the United States were evaluated (Wolfe et al., 2008) The group of berries (mainly blackberry) and pomegranate showed the highest values of CAA On the other hand, bananas and melons showed the lowest values of CAA Health benefits of phenolic compounds Non-communicable diseases (NCDs) are diseases of a long duration and generally a slow progression Among NCDs, the four main types are: cancer, cardiovascular diseases (CVD), chronic respiratory diseases and diabetes (WHO, 2011) It is estimated that NCDs are accountable for more than 63% of annual deaths in the world (WHO, 2011) It has been speculated that phenolic compounds, especially the group of flavonoids, contribute towards lowering the incidence of NCDs During the last decade, the number of studies relating the beneficial effects of polyphenols in human health has significantly increased Epidemiological studies have shown that the daily intake of plant-derived foods possibly prevents some types of cancer, particularly cancers of the gastrointestinal tract, CVD and even lowers the incidence of diabetes (Liu et al., 2000; WHO, 2003, Bazzano et al., 2008; Wang et al., 2012) In vitro tests have shown that phenolic compounds inhibit cancer cell proliferation, protect neurons, improve insulin secretion, reduce vascularisation and stimulate vasodilation (Ferguson et al., 2004; Silva et al., 2008; George et al., 2009; Del Rio et al., 2010) Among the common modifiable risk factors, unhealthy diets play an important role in NCDs Several diseases are associated with unhealthy diets, which are characterised by a high intake of calories with absent or low nutritional value Fruits are of great interest as they are richer in phenolic compounds than vegetables (Scalbert & Williamson, 2000; Rinaldo et al., 2010) The protective effect from fruits can be attributed to multiple factors, including phytochemicals, micronutrients, fibre and other anti-carcinogenic substances (Campbell et al., 1999) Although there is evidence showing the beneficial effects of consuming fruits, data supporting a beneficial role of fruit and vegetable consumption against cancer are conflicting (Thompson, 2010) A recent study involving 500 000 people in Europe showed a very low association between the intake of fruits and vegetables and the reduction in cancer risk (Boffetta et al., 2010) Despite this, the American Heart Association recommends eating at least five servings of fruit and vegetables per day (Liu et al., 2000) This recommendation is reinforced by the World Health Organization (WHO), which recommends the intake of a minimum of 400 g of fruits and vegetables per day, excluding potatoes and starchy tubers (WHO, 2003) A wide range of studies has shown that the eating habits have an important impact on health, quality of life and longevity (Frazao, 1999) The interest in polyphenols of different fruits (natives or exotics) by different laboratories and research groups all over world has increased significantly during the last two decades Among the polyphenols, flavonoids are the group of phytochemicals that have received the majority of attention in research They are alleged to have healthpromoting effects because of their higher antioxidant activities (in vitro tests), despite the fact that inconclusive evidence of in vivo antioxidant effects of flavonoids (Halliwell et al., 2005) has been disclosed Polyphenols are extensively metabolized in the human body, resulting in a significant modification of the redox capacity of these substances (Williams et al., 2004) It has been reported that even after the extensive intake of flavonoids, the metabolites tend to have reduced antioxidant activity (Halliwell et al., 2005) The concentration of polyphenols can be 100–1000 times lower in the human body (LPI, 2011), rarely exceeding nm concentrations in plasma after normal dietary intake (Del Rio et al., 2010) In vivo tests have shown that these substances not act as conventional hydrogen-donating antioxidants but they may exert modulatory actions in cells (Williams et al., 2004) After an extensive literature review, British scientists concluded that the concentration of flavonoids usually found in vivo is high enough to have pharmacological activity at receptors and on enzymes and transcription factors (Williams et al., 2004) Despite all of the evidence presented, conflicting or not, it is common sense that the consumption of plantderived foods, especially fruits, is of fundamental importance for keeping the body in good health, especially foods rich in polyphenols Studies have reported important health benefits of fruit consumption, including the anti-inflammatory effects of ac¸aı´ , citrus, bilberry, grape and pomegranate (Benavente-Garcia & Castillo, 2008; Terra et al., 2009, 2011; Mueller et al., 2010; Kang et al., 2011), the antitumor effects of pomegranate and cranberry (Yan et al., 2002; Neto et al., 2008; Sturgeon & Ronnenberg, 2010) and the anti-allergic properties of strawberry (Itoh et al., 2009), among other protective effects Bioaccessibility and bioavailability of antioxidant compounds in fruits A considerable number of studies describing the presence of many different types of bioactive compounds with antioxidant properties in fruits have been published over the last few years However, food scientists have only recently begun to evaluate the actual contribution of these bioactive compounds, such as active antioxidants, after their consumption Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology International Journal of Food Science and Technology 2012 13 14 Phenolic compounds in fruits C W I Haminiuk et al The ingestion of fruits containing a large amount of polyphenols is not usually correlated with highest concentrations of active metabolites of these polyphenols (capable of antioxidant effects) in the human body (Manach et al., 2004; Palafox-Carlos et al., 2011) This can generally be explained by differences in bioaccessibility and bioavailability of polyphenols from fruits and other foods, which directly influence antioxidant effects in vivo (Manach et al., 2004; Palafox-Carlos et al., 2011) The bioaccessibility and bioavailability of polyphenols from fruits and other foods can be defined as: (i) the amount of the antioxidant compound that is released from its food matrix after digestion, becoming available for intestinal absorption (Hedren et al., 2002; Manach et al., 2005) and, (ii) the proportion of the antioxidant compound that is absorbed (i.e reaches the bloodstream) and becomes available for metabolic utilisation and exerts its effects at the site of action (Shi & Le Maguer, 2000; Parada & Aguilera, 2007; Tagliazucchi et al., 2010; Palafox-Carlos et al., 2011; Rodrigo et al., 2011), respectively Therefore, bioaccessibility and bioavailability are distinct concepts and the bioavailability of polyphenols depends on their bioaccessibility from the food matrix (Manach et al., 2005; Parada & Aguilera, 2007; Tagliazucchi et al., 2010) Fruits contain complex mixtures of polyphenols that are not evenly distributed throughout the peel, pulp and seeds Furthermore, these polyphenols are not all absorbed with equal efficiency (Manach et al., 2004) Several factors can interfere with the release and ⁄ or absorption of polyphenols from fruits In summary, the main factors include the following: The chemical structure of polyphenols and their interactions with different macromolecules such as proteins and dietary fibres affect their assimilation and metabolic fate in vivo (Faulks & Southon, 2005; Parada & Aguilera, 2007; Yang et al., 2008; Palafox-Carlos et al., 2011) Most of the polyphenols in fruits exist as polymers or in glycosylated forms The content of hydrolysable tannins and proanthocyanidins associated with dietary fibre and proteins in some fruits is about fivefold that of free polyphenols (Vitaglione et al., 2008; Fogliano et al., 2011) Commonly, the aglycones, which only correspond to a small portion of the polyphenols in fruits, can be directly absorbed from the small intestine Most polyphenols in their native form (polymeric, glycosylated or esterified) must be enzymatically hydrolysed before absorption (Walle, 2004) The type of sugar linked to a polyphenol as well as the degree of glycosylation affects the rate and extent of intestinal absorption (Arts et al., 2004; D’Archivio et al., 2010) Acylation, conjugation, molecular size and solubility also determine the absorption and metabolism of fruit International Journal of Food Science and Technology 2012 phenolics (Scalbert & Williamson, 2000; Yang et al., 2008; Koli et al., 2010) Polyphenols with a high molecular weight are predicted to be poorly absorbed (Yang et al., 2008) The slow elimination of quercetin metabolites from the body can be explained by the existence of intermolecular bonds between the metabolites and serum albumin (Manach et al., 2004) The interactions of polyphenols with fibre (indigestible polysaccharides of plant cell walls) in the small intestine can lower their bioaccessibility and, consequently, bioavailability (Palafox-Carlos et al., 2011) However, these antioxidants may reach the large intestine and remain in the colonic lumen, where they could contribute to a healthy antioxidant environment (Saura-Calixto et al., 2010; Palafox-Carlos et al., 2011) In general, polyphenols associated with dietary fibre can be partially bioavailable, although the bioavailability of polyphenols is usually delayed by a high content of dietary fibre (Perez-Jimenez et al., 2009) Conversely, pectin might enhance the bioavailability of quercetin from rutin by altering the metabolic activity of the intestinal microflora or intestinal physiological functioning (Tamura et al., 2007) The role of dietary fibre in the absorption of antioxidants has been recently reviewed (PalafoxCarlos et al., 2011) Fruit processing affects polyphenol contents and alters fruit microstructure, resulting in the loss or enrichment of some polyphenols and influencing their access and availability (Scalbert & Williamson, 2000; Manach et al., 2004; Parada & Aguilera, 2007) Fruit peeling can result in the loss of a significant portion of some polyphenols Apple peels may present higher antioxidant and antiproliferative activities than the pulp (flesh) (Wolfe et al., 2003), and flavonols are not usually found in peeled apples (Burda et al., 1990) The peel of peach contains most of the flavonols and cyanidins in the fruit (Andreotti et al., 2008) Higher concentrations of resveratrol are found in red wines, which are fermented with the skin (peel), than in white wines (King et al., 2006) Industrial fruit juices usually present low flavonoid contents, because flavonoids are frequently removed during clarification or stabilization processes (Manach et al., 2004) The oxidative degradation of polyphenols can occur during fruit pulp processing as a result of the release and action of cytoplasmic polyphenol oxidase (Manach et al., 2004) Otherwise, the maceration or pressing of fruits can result in the diffusion of antioxidant compounds in the juice, including the solubilisation of polyphenols from unconsumed parts of the fruits, such as skins and seeds (Scalbert & Williamson, 2000; Gonzalez-Neves et al., 2004) Tannins from grapes are Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology Phenolic compounds in fruits C W I Haminiuk et al mainly extracted during winemaking by pressing the fruit and during fermentation (especially in red wines), where these polyphenols can be extracted from the insoluble matrix (Hazak et al., 2005; Parada & Aguilera, 2007) Suppression of the food matrix effect (reduction of the interaction between polyphenols and carbohydrate polymers) increases the bioavailability of polyphenols (Parada & Aguilera, 2007) The fermentation process in winemaking can result in the transformation of polyphenols from grapes or the formation of new structures (van de Wiel et al., 2001; Flamini, 2003), and the presence of ethanol in wine may contribute to their bioavailability (Duthie et al., 1998; Rodrigo et al., 2011) The biological interactions between polyphenols and cells, enzymes and proteins from the gastrointestinal system and colonic microflora play an essential role in their bioavailability Many polyphenols from fruits are only bioaccessible and bioavailable in the human body through the action of intestinal and hepatic enzymes and also via colonic microflora Approximately 48% of dietary polyphenols are bioaccessible in the small intestine and 42% become bioaccessible in the colon (large intestine) (Saura-Calixto et al., 2007) These polyphenols are then absorbed and metabolized Most of the biological activity of polyphenols from fruits is believed to be elicited in the human body by their secondary metabolites instead of the native compounds (Kroon et al., 2004; Donovan et al., 2006) Several enzymes in the human body are involved in the metabolism of polyphenols The specificity and location of the enzymes can regulate absorption of the polyphenols One of the first steps in the metabolism of most glycosylated antioxidant compounds is the removal of sugars by enzymes Polyphenols attached to glucose are potential substrates for human b-glucosidases, but those attached to rhamnose are not cleaved by b-glucosidases and depend upon the action of rhamnosidases produced by colonic microflora (Scalbert & Williamson, 2000) Polyphenols in the free form (aglycones) can be conjugated in the small intestine and later in the liver by glucuronidation, methylation, sulphation or a combination of these Conjugation ⁄ deconjugation reactions of polyphenols are mainly carried out by enzymes such as cytosolic b-glucosidase (CBG) and lactase phloridizin hydrolase (LPH), which are mainly located in the epithelial cells of the small intestine, and catechol-Omethyltransferase (COMT), UDP glucuronosyl transferase (UDPGT) and phenol sulphotransferases (P-PST), which are located in many different tissues (Scalbert & Williamson, 2000) The conjugation reac- tions significantly interfere with the metabolic fate of polyphenols (Manach et al., 1998; Scalbert & Williamson, 2000; Cano et al., 2002), either producing active metabolites or increasing the excretion rate of some polyphenols (D’Archivio et al., 2010) The aglycones are either absent in blood or present in low concentrations (Scalbert & Williamson, 2000) The polyphenols that are not absorbed in the small intestine can reach the colon where they can be metabolized by the colonic microflora (D’Archivio et al., 2010) The colonic microflora hydrolyses glycosides into aglycones and also degrades them into phenolic acids (Aura et al., 2005; D’Archivio et al., 2010) Esterified hydroxycinnamic acids require the action of esterases of the colonic microflora for the cleavage of ester bonds because there are no esterases in human tissues The metabolism of chlorogenic acid is dependent upon the action of enzymes produced by colonic microflora (Plumb et al., 1999; Scalbert & Williamson, 2000) The colonic biotransformation of polyphenols was recently reviewed by van Duynhoven et al (2011) Some experimental procedures used to predict and evaluate the bioaccessibility and ⁄ or bioavailability of polyphenols in vitro (digestive enzymes, Caco-2 cells, gastrointestinal and colonic model systems) and in vivo (either in humans or in animals) are reported in the studies conducted by Fogliano et al (2011), Tagliazucchi et al (2010), Cilla et al (2008, 2009), Saura-Calixto et al (2007), Bermudez-Soto et al (2007) and Koli et al (2010), and Serra et al (2010), Borges et al (2010), Perez-Jimenez et al (2009) and Vitaglione et al (2008), respectively Finally, to understand the real contribution to human health by ingesting polyphenols and also to develop food products with relevant antioxidant properties, it is important to consider the amount, the chemical structure and the source of polyphenols as well as the biological interactions that polyphenols might have with macromolecules, cells, enzymes and colonic microflora All of these factors affect the absorption, tissue concentration, metabolic fate and action of polyphenols as antioxidants in promoting health benefits Conclusions Phenolic compounds are a fascinating and unique class of bioactive compounds widely spread throughout nature Studies about polyphenols have increased exponentially over the last two decades, mainly because of the association between the consumption and health benefits of these substances Fruits are excellent sources of phenolic compounds, which impart health benefits beyond basic nutrition The extraction, isolation and quantification of polyphenols in fruits still present a Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology International Journal of Food Science and Technology 2012 15 16 Phenolic compounds in fruits C W I Haminiuk et al challenge Therefore, the search for new methodologies is essential for better understanding this class of phytochemicals In addition, the establishment and consolidation of databases of polyphenols are of great importance because they are key in assisting epidemiological investigations The absorption mechanisms of phenolic compounds are still not well established Further investigations are necessary to better understand the bioaccessibility ⁄ bioavailability of polyphenols, focusing on the action of colonic microflora on the metabolism and bioavailability of several polyphenols, the biological properties of conjugated polyphenols and active metabolites besides aglycones and parent compounds, the effect of dietary fibre on polyphenol absorption Acknowledgments The authors thank the National Council for Scientific and Technological Development (CNPq; Process Number 501535 ⁄ 2009-8) for financial support References Aehle, E., Mu¨ller, U., Eklund, P.C., Willfo¨r, S.M., Sippl, W & Dra¨ger, B (2011) Lignans as food constituents with estrogen and antiestrogen activity Phytochemistry, 72, 2396–2405 Akter, M.S., Oh, S., Eun, J.B & Ahmed, M (2011) Nutritional compositions and health promoting phytochemicals of camu-camu (Myrciaria dubia) fruit: a review Food Research International, 44, 1728–1732 Alpendurada, M.F (2003) Polynuclear aromatic 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Major compounds identified Table 3 Summary of the methodologies used for the separation and identification of phenolic compounds in fruits by RP-HPLC-DAD ⁄ UV-Vis Obreque-Slier et al (2010) Kubola et al (2011) Fang et al (2009) Torres et al (2011) Oszmianski et al (2009) Sun-Waterhouse et al (2009) Hassan et al (2011) Sagdic et al (2011) Kelebek & Selli (2011b) Jakobek et al (2009) References Phenolic compounds. .. promoting health benefits Conclusions Phenolic compounds are a fascinating and unique class of bioactive compounds widely spread throughout nature Studies about polyphenols have increased exponentially over the last two decades, mainly because of the association between the consumption and health benefits of these substances Fruits are excellent sources of phenolic compounds, which impart health benefits... 599–606 Rispail, N., Morris, P & Webb, K (2005) Phenolic compounds: extraction and analysis In: Lotus Japonicus Handbook (edited by A Ma´rquez) Pp 349–354 Berlin: Springer Robards, K., Prenzler, P.D., Tucker, G., Swatsitang, P & Glover, W (1999) Phenolic compounds and their role in oxidative processes in fruits Food Chemistry, 66, 401–436 Robbins, R.J (2003) Phenolic acids in foods: an overview of analytical... Marı´ n, J.G & Toma´s-Barbera´n, F.A (2012) Phenolic compound content of fresh and dried figs (Ficus carica L.) Food Chemistry, 130, 485–492 Vasco, C., Ruales, J & Kamal-Eldin, A (2008) Total phenolic compounds and antioxidant capacities of major fruits from Ecuador Food Chemistry, 111, 816–823 Vatai, T., Sˇkerget, M & Knez, Zˇ (2009) Extraction of phenolic compounds from elder berry and different grape... efficiency, flexibility and identification potential A compilation of recent papers published about the separation and identification of phenolic compounds in fruits using RP-HPLC-DAD ⁄ UV-Vis is summarised in Table 3 The methods of extraction, separation and the analysis of phenolic compounds in plant-food material were recently reviewed (Ignat et al., 2011) The applications and advances in the liquid chromatography... Technology 2012 15 16 Phenolic compounds in fruits C W I Haminiuk et al challenge Therefore, the search for new methodologies is essential for better understanding this class of phytochemicals In addition, the establishment and consolidation of databases of polyphenols are of great importance because they are key in assisting epidemiological investigations The absorption mechanisms of phenolic compounds are... Extraction of phenolics from Vitis vinifera wastes using non-conventional techniques Journal of Food Engineering, 100, 50– 55 Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology Phenolic compounds in fruits C W I Haminiuk et al Castro-Vargas, H.I., Rodrı´ guez-Varela, L.I., Ferreira, S.R.S & Parada-Alfonso, F (2010) Extraction of phenolic. .. International Journal of Food Science and Technology 2012 17 18 Phenolic compounds in fruits C W I Haminiuk et al Glazer, A.N (1990) Phycoerythrin fluorescence-based assay for reactive oxygen species Methods in Enzymology, 186, 161–168 Golukcu, M & Ozdemir, F (2010) Changes in phenolic composition of avocado cultivars during harvesting time Chemistry of Natural Compounds, 46, 112–115 Goncalves, A., Lajolo, F.M &... Antioxidant and antiproliferative capacities of phenolics purified from Phyllanthus emblica L fruit Food Chemistry, 126, 277–282 Luthria, D.L (2008) Influence of experimental conditions on the extraction of phenolic compounds from parsley (Petroselinum crispum) flakes using a pressurized liquid extractor Food Chemistry, 107, 745–752 Luthria, D.L & Pastor-Corrales, M.A (2006) Phenolic acids content of fifteen dry... selected pure phytochemical compounds and fruits by measuring the EC50 values (Wolfe & Liu, 2007) Quercetin showed the highest CAA value among the pure compounds assayed, and blueberry was the most effective in preventing peroxyl radical-induced DCFH Ó 2012 The Authors International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology Phenolic compounds in fruits C W I