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Plant Phenolics: Extraction, Analysis and Their Antioxidant and Anticancer Properties


Abstract and Figures

Phenolics are broadly distributed in the plant kingdom and are the most abundant secondary metabolites of plants. Plant polyphenols have drawn increasing attention due to their potent antioxidant properties and their marked effects in the prevention of various oxidative stress associated diseases such as cancer. In the last few years, the identification and development of phenolic compounds or extracts from different plants has become a major area of health- and medical-related research. This review provides an updated and comprehensive overview on phenolic extraction, purification, analysis and quantification as well as their antioxidant properties. Furthermore, the anticancer effects of phenolics in-vitro and in-vivo animal models are viewed, including recent human intervention studies. Finally, possible mechanisms of action involving antioxidant and pro-oxidant activity as well as interference with cellular functions are discussed.
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Molecules 2010, 15, 7313-7352; doi:10.3390/molecules15107313
ISSN 1420-3049
Plant Phenolics: Extraction, Analysis and Their Antioxidant and
Anticancer Properties
Jin Dai 1, 2 and Russell J. Mumper 3,*
1 Four Tigers LLC, 1501 Bull Lea Road, Suite 105, Lexington, Kentucky 40511 USA;
E-Mail: (J.D.)
2 Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington,
Kentucky 40536, USA
3 Division of Molecular Pharmaceutics, UNC Eshelman School of Pharmacy, University of North
Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
* Author to whom correspondence should be addressed; E-Mail:;
Tel.: +1-919-966-1271; Fax: +1-919-966-6919.
Received: 10 September 2010; in revised form: 15 October 2010 / Accepted: 19 October 2010/
Published: 21 October 2010
Abstract: Phenolics are broadly distributed in the plant kingdom and are the most abundant
secondary metabolites of plants. Plant polyphenols have drawn increasing attention due to
their potent antioxidant properties and their marked effects in the prevention of various
oxidative stress associated diseases such as cancer. In the last few years, the identification
and development of phenolic compounds or extracts from different plants has become a
major area of health- and medical-related research. This review provides an updated and
comprehensive overview on phenolic extraction, purification, analysis and quantification as
well as their antioxidant properties. Furthermore, the anticancer effects of phenolics in-vitro
and in-vivo animal models are viewed, including recent human intervention studies. Finally,
possible mechanisms of action involving antioxidant and pro-oxidant activity as well as
interference with cellular functions are discussed.
Keywords: plant phenolics; extraction; analysis; antioxidant; anticancer
Molecules 2010, 15
1. An Introduction to Natural Phenolics
Phenolics are compounds possessing one or more aromatic rings with one or more hydroxyl groups.
They are broadly distributed in the plant kingdom and are the most abundant secondary metabolites of
plants, with more than 8,000 phenolic structures currently known, ranging from simple molecules such
as phenolic acids to highly polymerized substances such as tannins. Plant phenolics are generally
involved in defense against ultraviolet radiation or aggression by pathogens, parasites and predators, as
well as contributing to plants’ colors. They are ubiquitous in all plant organs and are therefore an
integral part of the human diet. Phenolics are widespread constituents of plant foods (fruits, vegetables,
cereals, olive, legumes, chocolate, etc.) and beverages (tea, coffee, beer, wine, etc.), and partially
responsible for the overall organoleptic properties of plant foods. For example, phenolics contribute to
the bitterness and astringency of fruit and fruit juices, because of the interaction between phenolics,
mainly procyanidin, and the glycoprotein in saliva. Anthocyanins, one of the six subgroups of a large
group of plant polyphenol constituents known as flavonoids, are responsible for the orange, red, blue
and purple colors of many fruits and vegetables such as apples, berries, beets and onions. It is known that
phenolics are the most important compounds affecting flavor and color difference among white, pink and
red wines; they react with oxygen and are critical to the preservation, maturation and aging of the wine.
Plant phenolics include phenolics acids, flavonoids, tannins (Figure 1) and the less common
stilbenes and lignans (Figure 2). Flavonoids are the most abundant polyphenols in our diets. The basic
flavonoid structure is the flavan nucleus, containing 15 carbon atoms arranged in three rings (C6-C3-C6),
which are labeled as A, B and C. Flavonoid are themselves divided into six subgroups: flavones,
flavonols, flavanols, flavanones, isoflavones, and anthocyanins, according to the oxidation state of the
central C ring. Their structural variation in each subgroup is partly due to the degree and pattern of
hydroxylation, methoxylation, prenylation, or glycosylation. Some of the most common flavonoids
include quercetin, a flavonol abundant in onion, broccoli, and apple; catechin, a flavanol found in tea
and several fruits; naringenin, the main flavanone in grapefruit; cyanidin-glycoside, an anthocyanin
abundant in berry fruits (black currant, raspberry, blackberry, etc.); and daidzein, genistein and
glycitein, the main isoflavones in soybean [1].
Phenolic acids can be divided into two classes: derivatives of benzoic acid such as gallic acid, and
derivatives of cinnamic acid such as coumaric, caffeic and ferulic acid. Caffeic acid is the most
abundant phenolic acid in many fruits and vegetables, most often esterified with quinic acid as in
chlorogenic acid, which is the major phenolic compound in coffee. Another common phenolic acid is
ferulic acid, which is present in cereals and is esterified to hemicelluloses in the cell wall [1].
Tannins are another major group of polyphenols in our diets and usually subdivided into two groups:
(1) hydrolysable tannins and (2) condensed tannins. Hydrolysable tannins are compounds containing a
central core of glucose or another polyol esterified with gallic acid, also called gallotannins, or with
hexahydroxydiphenic acid, also called ellagitannins. The great variety in the structure of these
compounds is due to the many possibilities in forming oxidative linkage. Intermolecular oxidation
reactions give rise to many oligomeric compounds having a molecular weight between 2,000 and
5,000 Daltons [2]. Condensed tannins are oligomers or polymers of flavan-3-ol linked through an
interflavan carbon bond. They are also referred to as proanthocyanidins because they are decomposed
to anthocyanidins through acid-catalyzed oxidation reaction upon heating in acidic alcohol solutions.
Molecules 2010, 15
The structure diversity is a result of the variation in hydroxylation pattern, stereochemistry at the three
chiral centers, and the location and type of interflavan linkage, as well as the degree and pattern of
methoxylation, glycosylation and galloylation [3].
Figure 1. Structures of flavonoids, phenolic acids and tannins.
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Figure 2. Structures of stilbenes and lignan.
Despite their wide distribution, the health effects of dietary polyphenols have come to the attention
of nutritionists only in recent years. Researchers and food manufacturers have become more interested
in polyphenols due to their potent antioxidant properties, their abundance in the diet, and their credible
effects in the prevention of various oxidative stress associated diseases [4]. The preventive effects of
these second plant metabolites in terms of cardiovascular, neurodegenerative diseases and cancer are
deduced from epidemiologic data as well as in vitro and in vivo [5-8] and result in respective
nutritional recommendations. Furthermore, polyphenols were found to modulate the activity of a wide
range of enzyme and cell receptors. In this way, in addition to having antioxidant properties,
polyphenols have several other specific biological actions in preventing and or treating diseases.
2. Phenolic Sample Preparation and Characterization
2.1. Extraction
The extraction of bioactive compounds from plant materials is the first step in the utilization of
phytochemicals in the preparation of dietary supplements or nutraceuticals, food ingredients,
pharmaceutical, and cosmetic products. Phenolics can be extracted from fresh, frozen or dried plant
samples. Usually before extraction plant samples are treated by milling, grinding and homogenization,
which may be preceded by air-drying or freeze-drying. Generally, freeze-drying retains higher levels of
phenolics content in plant samples than air-drying [9]. For example, Asami et al. showed that freeze-
dried Marion berries, strawberries and corn consistently had a higher total phenolic content level
compared with those air-dried [10]. However, drying processes, including freeze-drying, can cause
undesirable effects on the constituent profiles of plant samples, therefore, caution should be taken
when planning and analyzing research studies on the medicinal properties of plants [9].
Solvent extractions are the most commonly used procedures to prepare extracts from plant materials
due to their ease of use, efficiency, and wide applicability. It is generally known that the yield of
chemical extraction depends on the type of solvents with varying polarities, extraction time and
temperature, sample-to-solvent ratio as well as on the chemical composition and physical
characteristics of the samples. The solubility of phenolics is governed by the chemical nature of the
plant sample, as well as the polarity of the solvents used. Plant materials may contain phenolics
varying from simple (e.g., phenolic acids, anthocyanins) to highly polymerized substances (e.g.,
Molecules 2010, 15
tannins) in different quantities. Moreover, phenolics may also be associated with other plant
components such as carbohydrates and proteins. Therefore, there is no universal extraction procedure
suitable for extraction of all plant phenolics. Depending on the solvent system used during exaction, a
mixture of phenolics soluble in the solvent will be extracted from plant materials. It may also contain
some non-phenolic substances such as sugar, organic acids and fats. As a result, additional steps may
be required to remove those unwanted components.
Solvents, such as methanol, ethanol, acetone, ethyl acetate, and their combinations have been used
for the extraction of phenolics from plant materials, often with different proportions of water. Selecting
the right solvent affects the amount and rate of polyphenols extracted [11]. In particular, methanol has
been generally found to be more efficient in extraction of lower molecular weight polyphenols while
the higher molecular weight flavanols are better extracted with aqueous acetone [12-15]. Ethanol is
another good solvent for polyphenol extraction and is safe for human consumption [16]. In preparing
anthocyanin-rich phenolic extracts from plant materials, an acidified organic solvent, most commonly
methanol or ethanol, is used. This solvent system denatures the cell membranes, simultaneously
dissolves the anthocyanins, and stabilizes them. However, care should be taken to avoid addition of
excess acid which can hydrolyze labile, acyl, and sugar residues during concentration steps. To obtain
the best yield of anthocyanin extraction, weak organic acids, such as formic acid, acetic acid, citric
acid, tartaric acid and phosphoric acid, and low concentrations of strong acids, such as 0.5-3.0% of
trifluoroacetic acid and < 1.0% of hydrochloric acid are recommended [17-19]. In addition, sulfured
water has also been used as extraction solvent in seeking a reduction of the use of organic solvents as
well as the cost of extraction [20].
The recovery of phenolic compounds from plant materials is also influenced by the extraction time
and temperature, which reflects the conflicting actions of solubilization and analyte degradation by
oxidation [21]. An increase in the extraction temperature can promote higher analyte solubility by
increasing both solubility and mass transfer rate. In addition, the viscosity and the surface tension of
the solvents are decreased at higher temperature, which helps the solvents to reach the sample
matrices, improving the extraction rate. However, many phenolic compounds are easily hydrolyzed
and oxidized. Long extraction times and high temperature increase the chance of oxidation of phenolics
which decrease the yield of phenolics in the extracts. For example, conventional extraction and
concentration of anthocyanins is typically conducted at temperatures ranging from 20 to 50°C [18],
because temperatures > 70°C have been shown to cause rapid anthocyanin degradation [22]. Therefore,
it is of critical importance to select efficient extraction procedure/method and maintain the stability of
phenolic compounds. The conventional extraction methods such as maceration and soxhlet extraction
have shown low efficiency and potential environmental pollution due to large volumes of organic
solvent used and long extraction time required in those methods. A number of methods have been
developed in recent years such as microwave, ultrasound-assisted extractions, and techniques based on
use of compressed fluids as extracting agents, such as subcritical water extraction (SWE), supercritical
fluid extraction (SFE), pressurized fluid extraction (PFE) or accelerated solvent extraction (ASE) were
also applied in the extraction of phenolic compounds from plant materials.
Ultrasound-assisted extraction (UAE) is a potentially useful technology as it does not require
complex instruments and is relatively low-cost. It can be used both on a small and large scale in the
phytopharmaceutical extraction industry [23]. The mechanism for ultrasonic enhancement involves the
Molecules 2010, 15
shear force created by implosion of cavitation bubbles upon the propagation of the acoustic waves in
the kHz range [24]. Collapse of bubbles can produce physical, chemical and mechanical effects [25],
which resulted in the disruption of biological membranes to facilitate the release of extractable
compounds and enhance penetration of solvent into cellular materials and improve mass transfer [23,26].
Recently, UAE has been widely used in the extraction of various phenolic compounds from different
parts of plants such as leaves [27], stalks [28], fruits [29,30] and plant seeds [31]. A comparison study
showed that UAE caused less degradation of phenolics and was a much faster extraction process in
extraction of phenolic compounds from strawberries compared with other extraction methods
including solid-liquid, subcritical water and microwave-assisted method [32].
Pressurized liquid extraction (PLE), also known under the trade name of accelerated solvent
extraction (ASE), is a relative new technology for extraction of phytochemicals under high
temperature and pressure. Benthin et al. [33] were among the first to conduct a comprehensive study
on the feasibility of applying PLE to medicinal herbs after its emergence in the mid-1990s. In PLE,
pressure is applied to allow the use as extraction solvents of liquids at temperatures greater than their
normal boiling point. The combined use of high pressures (3.3-20.3 MPa) and temperatures (40-200°C)
provides faster extraction processes that require small amounts of solvents (e.g., 20 min using 10–50 mL
of solvent in PLE can be compared with a traditional extraction step in which 10–48 h and up to 200 mL
are required) [34]. High temperature and pressure improves analyte solubility and the desorption
kinetics from the matrices [35]. Therefore, extraction solvents including water which show low
efficiency in extracting phytochemicals at low temperatures may be much more efficient at elevated
PLE temperatures,. The use of water as an extraction solvent in PLE is the so-called subcritical water
extraction (SWE). In SWE, water is heated up to 200°C and the change in the dielectric constant of the
water with the temperature leads water to behave like an organic solvent. For example, the dielectric
constant of water at 200°C is equal to 36 which is close to methanol [34]. Ju et al. showed that PLE
(80–100°C) using acidified water was as effective as acidified 60% methanol in extracting anthocyanins
from grape skins [36]. However, phenolic compounds are easily oxidized at high temperature so it is
very important to prove that they will not degrade under the proposed PLE conditions [37]. In recent
years, PLE has been successfully applied to the extraction of phenolic compounds from different plant
materials such as grape seeds and skin [36,38,39], apples [40], spinach [41], eggplants [42] and barley
flours [43]. Another technology using carbon dioxide as compressed fluid as extraction solvent is
called supercritical and subcritical fluid extraction. Organic modifiers were added to increase the
polarity of the fluid for extraction of phenolic compounds [44-46]. SFE is performed in the absence of
both light and air; degradation and oxidation processes are significantly reduced in comparison with
other extraction techniques. In general, all these compressed fluid-base extraction techniques are more
environmental friendly procedures than other methods in reducing use of organic solvents (e.g., PLE),
allowing extraction performed with nonpolluting, nontoxic solvents, such as water (e.g., SWE),
supercritical CO2 fluid (e.g., SFE). However, due to the application of high pressure in these
techniques, the requirements of instrumentation are high and the cost of these methods on the
industrial scale is high which often outweigh the technical benefits.
Microwave-assisted extraction (MAE) is a process utilizing microwave energy to facilitate partition
analytes from the sample matrix into the solvent. The main advantage of this technique is the reduced
extraction time and solvent volume as compared to conventional extraction techniques [47]. It has
Molecules 2010, 15
been used for the extractions of some small-molecule phenolic compounds such as phenolic acids
(e.g., gallic acid, ellagic acid) [48], quercetin [49], isoflavone [50] and trans-resveratrol [51] which
were shown to be stable under microwave-assisted heating conditions at temperature up to 100°C for
20 min [52]. Phenolic compounds having a higher number of hydroxyl-type substituents (e.g., tannins)
and those that are sensitive to elevated temperature (e.g., anthocyanins) may not suitable to be
extracted by MAE due to degradation under MAE extraction conditions [52].
The extraction of phenolic compounds from plant materials may also be influenced by other factors
such as solvent-to-solid ratio and the particle size of the sample. Increasing solvent-to-solid ratio was
found to work positively for enhancing phenol yields [53,54]. However, an equilibrium between the use
of high and low solvent-to-solid ratios, involving a balance between high costs and solvent wastes and
avoidance of saturation effects, respectively, has to be found to obtain an optimized value [55]. Lowering
particle size also enhances the yield of phenolic compounds [56,57]. To increase the release of bound
phenolics, a number of enzymatic procedures involving the use of various mixed pectinolytic and cell
wall polysaccharide degrading enzyme preparation in phenolic extraction have been described [58-60].
The particle size of the mashed samples was found to be a main factor to increase the enzyme action and
extraction efficiency of phenolic compounds from samples in these enzyme-assisted extractions [61].
Besides enzymatic procedures, acid and alkaline treatments were found to be effective in releasing bound
phenolics in phenolic extractions [62,63].
2.2. Purification and Fractionation
Plant crude extracts usually contain large amounts of carbohydrates and/or lipoidal material and the
concentration of the phenolics in the crude extract may be low. To concentrate and obtain polyphenol-
rich fractions before analysis, strategies including sequential extraction or liquid-liquid partitioning
and/or solid phase extraction (SPE) based on polarity and acidity have been commonly used. In
general, elimination of lipoidal material can be achieved by washing the crude extract with non-polar
solvents such as hexane [64], dichloromethane [65], or chloroform [66]. To remove polar non-phenolic
compounds such as sugars, organic acids, a SPE process is usually carried out. SPE is becoming
popular since it is rapid, economical, and sensitive and because different cartridges and discs with a
great variety of sorbents can be used. In addition, this technique can now be automated. C18 cartridges
have been the most widely used in phenolic compound separation. After the aqueous sample is passed
through preconditioned C18 cartridges, the cartridges are washed with acidified water to remove sugar,
organic acids and other water-soluble constituents. The polyphenols are then eluted with absolute
methanol [67] or aqueous acetone [64]. Further separation of phenolic compounds can be achieved by
adjusting the pH of the sample as well as the pH and polarity of eluents. For example, Pinelo et al.
adjusted the pH of dealcoholic wine sample to 7.0 and eluted phenolic acids with water in the first
fraction [68]. Following this step, the C18 cartridge was acidified with 0.01 M HCl and nonpolymeric
phenols such as catechins, anthocyanins, and flavonols were eluted with ethyl acetate. Finally, a
mixture of water, acetone and methanol was used to elute the polymeric phenols. Other sorbents such
as Amberlite XAD-2 [69], XAD-7 [70,71], XAD-16 [66], Oasis HLB [72,73] have also successfully
been used to purify phenolic compounds in crude extracts or wine samples. A comparison of several
SPE cartridge including Amberlite, silica-based C8, copolymer-based HLB, PH, ENV+ and MCX with
silica-based C18 for the isolation of phenolic compounds in wine at low concentration showed that the
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proposed SPE method with HLB cartridge has a higher sensitivity, reproducibility and loading
capacity than with C18 cartridge and HLB cartridge may be a good alternative for the C18 cartridge
for the isolation of wine phenolic compounds [74].
Column chromatography has been also employed for fractionation of phenolic extracts. Although
this method is often labor-intensive and solvent-consuming, it provides greater amounts of fractions
for subsequent isolation and identification of pure substances. Typically-utilized column sorbents are
RP-C18 [75], Toyopearl [76,77], LH-20 [76,77] and to a less extent polyamide resin [78]. Ethanol,
methanol, acetone, and water and their combinations are commonly used as eluents. In particular, the
isolation of proanthocyanidins (condensed tannins) is routinely carried out by employing Sephadex
LH-20 column chromatography [79,80]. The crude extract was applied to the column which was
washed with methanol or ethanol to elute the non-tannin substances followed by elution with acetone-
water or alcohol-water to obtain proanthocyanidins. Using LH-20 column chromatography, methanol
is more commonly used than ethanol to elute non-tannin compounds. Acetone-water is a much better
solvent than ethanol-water to elute procyanidins from the column, especially polymeric procyanidins.
In some cases, preparative-scale HPLC has also been used in polyphenol sample purification [81,82].
The classical liquid-liquid extraction procedure has been less commonly used because it is a
tedious, highly time-consuming process with high solvent costs and low recoveries [83]. An example
of sequential extraction was provided by extraction of phenolic compounds from tissues of cider
apples [84]. The freeze-dried apple tissue powder was extracted sequentially with hexane (to remove
lipids, carotenoids and chlorophyll), methanol (sugars, organic acids and phenolic compounds with
low molecular weight) and aqueous acetone (polymerized polyphenols). As an alternative to liquid
chromatography, Countercurrent Chromatography (CCC) has been developed as an effective technique
for fractionation of various classes of phenolic compounds. CCC is a preparative all-liquid
chromatographic technique based on partitioning of compounds between two immiscible liquid phases,
a liquid stationary phase and a liquid mobile phase. Solutes are separated according to their partition
coefficients between the two solvent phases based on their hydrophobicity. The big advantage of CCC
is that it uses no solid matrix and the role of two liquid phases, namely, liquid stationary phase and
mobile phase, can be switched during a run. Thus, there is no irreversible sample adsorption and the
recovery is 100% [85]. Degenhardt et al. used high-speed countercurrent chromatography (HSCCC) for
separation of anthocyanins in the pigment mixtures extracted from red cabbage, black currant, black
chokeberry and roselle [86]. Anthocyanins were successfully fractionated based on their polarities into
the biphasic mixture of tert-butyl methyl ether/n-butanol/acetonitrile/water (2:2:1:5, v/v/v/v) acidified
with trifluoroacetic acid (TFA). Yanagida et al. demonstrated that HSCCC could be used for isolation
of tea catechins and other food-related polyphenols such as procyanidins, phenolic acids and flavonol
glycosides using tert-butyl methyl ether/acetonitrile/0.1% aqueous TFA (2:2:3, v/v/v) [87]. In addition,
Krafczyk and Glomb employed Multilayer Countercurrent Chromatography (MLCCC) coupled with
preparative High-Performance Liquid Chromatography (HPLC) to obtain pure flavonoids from
Rooibos tea [88]. This method was able to isolate up to gram of material and to verify known
polyphenol structures and discover previously unpublished ones [88].
Molecules 2010, 15
2.3. Analysis and Quantification of Phenolics
Natural phenolics are of interest from many viewpoints (antioxidants, astringency, bitterness,
browning reactions, color, etc.). Selection of the proper analytical strategy for studying phenolics in plant
materials depends on the purpose of the study as well as the nature of the sample and the analyte [21].
The assays used for the analysis of phenolics are usually classified as either those measuring total
phenolics content, or those quantifying a specific group or class of phenolic compounds.
Quantification of phenolic compounds in plant extract is influenced by the chemical nature of the
analyte, as well as assay method, selection of standards and presence of interfering substances [89].
Because of the heterogeneity of natural phenolics and the possible interference from other readily
oxidized substances in the plant materials, it is not surprising that several methods have been used for
determination of total phenolics and none are perfect [90]. Among such methods are the Folin-Denis
method (FD), Folin-Ciocalteu method (F-C), permanganate titration, colorimetry with iron salts, and
ultraviolet absorbance. In most cases, F-C has been found preferable as compared to the other
methods [90]. The F-C assay relies on the transfer of electrons in alkaline medium from phenolic
compounds to phosphomolybdic/phosphotungstic acid complexes to form blue complexes (possibly
(PMoW11O40)4) that are determined spectroscopically at approximately 760 nm [90,91]. Gallic acid is
widely used as the comparison standard and values are usually compared as milligram of gallic acid
equivalent per kilogram or liter of extract among samples. Owing to the general nature of the F-C
chemistry, it is indeed a measure of total phenolics and other oxidation substrates. The other oxidation
substrate present in a given extract sample can interfere the total phenolics measurement in an
inhibitory, additive or enhancing manner [90,91]. The inhibitory effects could be due to the oxidants
competing with F-C reagent and/or air oxidation after the sample is made alkaline. For this reason, the F-
C reagent is added ahead of alkali [90]. Additive effects occur from unanticipated phenols, aromatic
amines, high sugar levels or ascorbic acid in the samples. The additive effects can be measured before
adding the alkali or by a more specific assay of a known interference and then subtracted from the F-C
value [90]. Sulfites and sulfur dioxide which is a common additive for wine can cause enhancing effect
[90]. Singleton et al. [90] discussed the effects of potential interference compounds and methods for
correcting these factors. However, despite these disadvantages, the F-C assay is simple and reproducible
and has been widely used for quantification of phenolic compounds in plant materials and extracts.
Anthocyanins are one of the six subgroups of the large and widespread group of plant phenolics
known as flavonoids. While there are six common anthocyanidins, more than 540 anthocyanin
pigments have been identified in nature [92]. The simplest assay for the quantification of anthocyanins
as a group is based on the measurement of absorption at a wavelength between 490 nm and 550 nm,
where all anthocyanins show a maximum. This band is far from the absorption bands of other
phenolics, which have spectral maxima in the UV range [93]. However, by this method, anthocyanin
polymerized degradation products produced by browning reactions are co-determined and lead to an
overestimation of anthocyanin content. Therefore, an approach that differentiates anthocyanins from
their degradation products is preferable. The pH differential method takes the advantage of the
structural transformations of anthocyanin chromophore as a function of pH. By this method the
absorption of the sample is measured at pH 1 (anthocyanins as colored oxonium salts) as well as at pH
4.5 (anthocyanins as colorless hemiketals). The anthocyanin degradation pigments do not exhibit
Molecules 2010, 15
reversible behavior with pH, and are thus excluded from the absorbance calculation [94]. In this
method, calculation of monomeric anthocyanin concentration is usually based on the molecular weight
(MW) and the molar extinction coefficient (ε) of either the main anthocyanin in the sample or
cyanidin-3-glucoside, the most common anthocyanin in nature. For all quantification the MW and ε
underlying the calculation should be given because the differences in the MW of the anthocyanins and
the influence of the solvent on ε considerably distort the results [95]. For example, quantification as
cyanidin-3-glucoside equivalents gave markedly lower results for berries containing mainly
delphinidin and malvidin glycosides as compared with “real” values quantified based on corresponding
standard compounds [71].
In a study of 20 food supplements containing extracts of blueberry, elderberry, cranberry and
chokeberry, the total anthocyanin content (as determined as the cyanidin-3-glucoside equivalent)
obtained with pH differential method were in good agreement with those obtained with an HPLC
method [96]. In addition, a collaborative study where 11 collaborators representing academic,
government and industrial laboratories analyzed seven fruit juice, beverage, natural colorants and wine
samples demonstrated that total anthocyanin content can be measured with excellent agreement
between laboratories using the pH differential method and the method has been approved as a First
Action Official Method [97].
Anthocyanins are labile compounds and easily oxidized and condensed with other phenolics to form
brown polymeric pigments. Somers and Evans developed a method based on the use of sodium sulfite,
a bleaching reagent to determine the polymeric color and browning in wines [96]. Monomeric
anthocyanins will combine with bisulfite to form a colorless sulfonic acid addition adduct while the
polymeric anthocyanin degradation products are resistant to bleaching by bisulfite, as the 4-position is
not available, being covalently linked to another phenolic compound. This method has been applied to
a variety of anthocyanin-rich products and found to be extremely useful for monitoring the
anthocyanin degradation and browning during processing and storage [95].
Different colorimetric methods are used to measure total proanthocyanidin (condensed tannin) content
in plant samples. The proanthocyanidin assay is carried out in a butanol and concentrated hydrochloric
acid (95:5, v/v) solution, where proanthocyanidins are autoxidized and cleaved to colored anthocyanidin
monomer [98]. In the vanillin assay, condensation of resorcin- or phloroglucin- partial structure of
flavonols with vanillin in acidic medium leads to the formation of colored carbonium ions [99].
Catechin, a monomeric flavanol, is often used as a standard. The same reaction mechanism as in the
vanillin assay is used in the dimethylaminocinnamaldehyde (DMCA) assay, in which only the terminal
units of the proanthocyanidins react with DMCA [100]. These methods of quantification are
susceptible to the structure of the analytes as well as various external factors such as temperature,
concomitant substances, solvent, presence of oxidants, etc. [101]. Thus, adaptation and validation of
methods for different sample material are required. In addition, purification of proanthocyanidins
before quantification has proven to be very supportive to minimize the interference and obtain
reproducible results [101,102]. Over and above, these colorimetric methods for quantification of total
proanthocyanidins are limited due to low yield because of the formation of side reaction products such
as phlobatannins. Recently, a simple and robust method was developed and validated for the
quantification of condensed tannins in grape extracts and red wine by precipitation with methyl
cellulose, referred to as methyl cellulose precipitable tannin assay [103,104]. In this assay, condensed
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tannins are precipitated out in the sample by forming insoluble polymer-tannin complex with methyl
cellulose and its concentration is determined by subtraction of phenolics contents in the sample
monitored by measuring the absorbance at 280 nm before and after methyl cellulose treatment [103].
Hydrolysable tannins can be quantified by a number of approaches including the potassium iodate
method, rhodanine method and sodium nitrite method. Of these, the potassium iodate method is most
widely used. It is based on the reaction of methyl gallate, formed upon methanolysis of hydrolysable
tannins in the presence of strong acids, with potassium iodate to produce a red chromophore with a
maximum absorbance between 500 nm and 550 nm [105]. Similar as assays for proanthocyanidin
quantification, the yield of this reaction also influenced by a number of factors such as the structure of
the hydrolysable tannins, reaction time, temperature, other phenolics present in the sample, etc. The
rhodanine method can be used for estimation of gallotannins and is based on determination of gallic
acid in a sample subject to acid hydrolysis under conditions that must be anaerobic to avoid oxidation
of the product [106]. On the other hand, the sodium nitrite assay is developed for quantification of
ellagic acid in sample hydrolysate [107]. However, this assay requires large quantities of pyridine as a
solvent which introduces a toxicity risk in the analysis procedure.
Since the characteristic reaction of tannins is their ability to precipitate protein, there are many
methods developed to quantify tannins (both condensed and hydrolysable tannins) via protein binding.
For example, tannins can be precipitated by a standard protein such as bovine serum albumin and the
amount of tannin precipitated is assessed based on the formation of colored iron-phenolate complex in
alkaline, detergent-containing solution. Detailed discussions on protein binding methods can be found
in reviews by Hagerman and Butler [108,109].
In general, traditional spectrophotometric assays provide simple and fast screening methods to
quantify classes of phenolic compounds in crude plant samples. However, due to the complexity of the
plant phenolics and different reactivity of phenols toward assay reagents, a broad spectrum of methods
is used for assay of the constituents, leading to differing and often non-comparable results. In addition
to that, the methods are quite prone to interferences and consequently often result in over- or
underestimation of the contents. Modern high-performance chromatographic techniques combined
with instrumental analysis are the “state of art” for the profiling and quantification of phenolic
compounds. Gas chromatographic (GC) techniques have been widely used especially for separation
and quantification of phenolic acids and flavonoids. The major concern with this technique is the low
volatility of phenolic compounds. Prior to chromatography, phenolics are usually transformed into more
volatile derivatives by methylation, conversion into trimethylsilyl derivatives, etc. A detailed discussion
on application of GC on analysis of phenolic acids and flavonoids was provided by Stalicas [110].
HPLC currently represents the most popular and reliable technique for analysis of phenolic
compounds. Various supports and mobile phases are available for the analysis of phenolics including
anthocyanins, proanthocyanidins, hydrolysable tannins, flavonols, flavan-3-ols, flavanones, flavones,
and phenolic acids in different plant extract and food samples [13,111-120]. Moreover, HPLC
techniques offer a unique chance to analyze simultaneously all components of interest together with
their possible derivatives or degradation products [121,122]. The introduction of reversed-phase (RP)
columns has considerably enhanced HPLC separation of different classes of phenolic compounds and
RP C18 columns are almost exclusively employed. It was found that column temperature may affect
the separation of phenolics such as individual anthocyanin [123] and constant column temperature is
Molecules 2010, 15
recommended for reproducibility [110]. Acetonitrile and methanol are the most commonly used
organic modifiers. In many cases, the mobile phase was acidified with a modifier such as acetic,
formic, and phosphoric acid to minimize peak tailing. Both isocratic and gradient elution are applied to
separate phenolic compounds. The choice depends on the number and type of the analyte and the
nature of the matrix. Several reviews have been published on application of HPLC methodologies for
the analysis of phenolics [110,124-126].
Figure 3. Strategies for preparation and characterization of phenolic samples from plant
materials. Abbreviations: MAE, microwave-assisted extraction; UAE, ultrasound-assisted
extraction; PFE, pressurized fluid extraction; PLE, pressurized liquid extraction; ASE,
accelerated solvent extraction; SWE, subcritical water extraction; SFE, supercritical fluid
extraction; SPE, solid phase extraction; CCC, countercurrent chromatography; FD, Folin-
Denis method (FD), F-C, Folin-Ciocalteu method; GC, gas chromatography; LC, Liquid
chromatography; FLU, fluorescence; PDA, photodiode array; EAD, electro-array
detection; ECD, electrochemical detection; MS, mass spectrometric; NMR, nuclear
magnetic resonance.
Given the intrinsic existence of conjugated double and aromatic bonds, every phenol exhibits a
higher or lower absorption in ultraviolet (UV) or ultraviolet/visible (UV/VIS) region. Thus, the most
common means of detection, coupled to LC, are UV/VIS, photodiode array (PDA), and UV-
fluorescence detectors. PDA is the most prevalent method since it allows for scanning real time
Molecules 2010, 15
UV/VIS spectra of all solutes passing through the detector, giving more information of compounds in
complex mixtures such as a plant crude extract. Other methods employed for detection of phenolic
compounds include electrochemical detection (ECD) [127], voltammetry technique [128], on-line
connected PDA and electro-array detection (EAD) [129], chemical reaction detection techniques [130],
mass spectrometric (MS) [117,123,131] and nuclear magnetic resonance (NMR) detection [120,132].
MS and NMR detections are more of structure confirmation means than quantification methods.
Electromigration techniques including capillary electrophoresis (CE), capillary zone electrophoresis
(CZE), and micellar electrokinetic chromatography coupled with UV, and to a less extent EC and MS
detection are also employed for phenolics analysis [133].
3. Antioxidant Properties of Phenolic Compounds
Antioxidants are defined as compounds that can delay, inhibit, or prevent the oxidation of
oxidizable materials by scavenging free radicals and diminishing oxidative stress. Oxidative stress is
an imbalanced state where excessive quantities of reactive oxygen and/or nitrogen species (ROS/RNS,
e.g., superoxide anion, hydrogen peroxide, hydroxyl radical, peroxynitrite) overcome endogenous anti-
oxidant capacity, leading to oxidation of a varieties of biomacromolecules, such as enzymes, proteins,
DNA and lipids. Oxidative stress is important in the development of chronic degenerative diseases
including coronary heart disease, cancer and aging [134].
Recently, phenolics have been considered powerful antioxidants in vitro and proved to be more
potent antioxidants than Vitamin C and E and carotenoids [135,136]. The inverse relationship between
fruit and vegetable intake and the risk of oxidative stress associated diseases such as cardiovascular
diseases, cancer or osteoporosis has been partially ascribed to phenolics [137,138]. It has been
proposed that the antioxidant properties of phenolic compounds can be mediated by the following
mechanisms: (1) scavenging radical species such as ROS/RNS; (2) suppressing ROS/RNS formation
by inhibiting some enzymes or chelating trace metals involved in free radical production; (3) up-
regulating or protecting antioxidant defense [139].
3.1. Phenolics as Free Radical Scavengers and Metal Chelators
Phenolic compounds (POH) act as free radical acceptors and chain breakers. They interfere with the
oxidation of lipids and other molecules by rapid donation of a hydrogen atom to radicals (R):
R + POH RH + PO· (1)
The phenoxy radical intermediates (PO·) are relatively stable due to resonance and therefore a new
chain reaction is not easily initiated. Moreover, the phenoxy radical intermediates also act as
terminators of propagation route by reacting with other free radicals:
PO· + R· POR (2)
Phenolic compounds possess ideal structure chemistry for free radical scavenging activities because
they have: (1) phenolic hydroxyl groups that are prone to donate a hydrogen atom or an electron to a
free radical; (2) extended conjugated aromatic system to delocalize an unpaired electron. Several
relationships between structure and reduction potential have been established as follows:
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(1) For phenolic acids and their esters, the reduction activity depends on the number of free
hydroxyl groups in the molecule, which would be strengthened by steric hindrance [140].
Hydroxycinnamic acids were found to be more effective than their hydroxybenzoic acid counterparts,
possibly due to the aryloxy-radical stabilizing effect of the –CH=CH–COOH linked to the phenyl ring
by resonance [136].
(2) For flavonoids, the major factors that determine the radical-scavenging capability [141,142] are:
(i) the ortho-dihydroxy structure on the B ring, which has the best electron-donating properties and
confers higher stability to the radical form and participates in electron delocalization.
(ii) the 2,3-double bond with a 4-oxo function in the C ring, which is responsible for electron
delocalization from the B ring.
(iii) the 3- and 5-hydroxyl groups with the 4-oxo function in A and C rings, which are essential for
maximum radical scavenging potential.
(iv) the 3-hydroxyl group is important for antioxidant activity. The 3-glycosylation reduces their
activity when compared with corresponding aglycones.
Quercetin is a flavonol that possess all of the factors described in (2). Anthocyanins are particularly
reactive toward ROS/RNS because of their peculiar chemical structure of electron deficiency.
As an alternative antioxidant property, some phenolic compounds with dihydroxy groups can
conjugate transition metals, preventing metal-induced free radical formation. The redox active metal ions
such as Cu+ or Fe2+ interact with hydrogen peroxide (H2O2) through Fenton chemistry (as shown in
reaction 3 below) to form hydroxyl radicals (·OH), which is the most reactive ROS known, being able to
initiate free radical chain reactions by abstracting hydrogen from almost any molecule. Phenolic
compounds with catecholate and gallate groups can inhibit metal-induced oxygen radical formation
either by coordination with Fe2+ and enhancing autoxidation of Fe2+ (as shown in reaction 4 below), or
the formation of inactive complex with Cu2+, Fe2+, or Cu+ with relatively weaker interaction [143, 144].
The attachment of metal ions to the flavonoid molecule can be 3’,4’-o-diphenolic groups in the B ring,
3,4 or 3,5-o-diphenolic groups, and the ketol structures 4-keto,3-hydroxy or 4-keto,5-hydroxy groups
in the C ring [145,146]. It was also proposed that optimum metal-binding and antioxidant activity is
associated with the structures which contain hydroxy-keto group (a 3-OH or 5-OH plus a 4-C = O), as
well as a large number of catechol/gallol groups [145, 147].
H2O2 + Cu+ or Fe2+ Cu2+ or Fe3+ + OH + ·OH- (3)
(4) [137]
Theoretically, these two antioxidant actions can cause a reduction of the steady state concentrations
of free radicals and oxidant species. As a result, the subsequent oxidation of target molecules such as
lipids, proteins and nucleic acids is diminished. Based on these potential capacities, extensive studies
have demonstrated the antioxidant activities of natural phenolics, in general, in a myriad of
biochemical and ex vivo systems [148], for example, in isolated low density lipoproteins (LDL),
synthetic membrane, ex vivo human plasma, and cells in culture. In addition, mutual synergistic effects
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were also observed between different phenolic compounds or with other non-phenolic antioxidants [149]
and it is generally accepted that a combination of phenolic or other antioxidants exert better
antioxidant effect than pure individual compound.
3.2. Prooxidant Activity of Phenolic Compounds
It is worth noting that some phenolic antioxidants can initiate an autoxidation process and behave
like prooxidants [141] under certain conditions. Instead of terminating a free radical chain reaction by
reacting with a second radical, the phenoxy radical may also interact with oxygen and produce
quinones (P = O) and superoxide anion (O2·) as shown below [139]:
PO· + O2 P=O + O2· - (5)
Nevertheless, transition metal ions could also induce prooxidant activity of phenolic antioxidants as
demonstrated by the following reactions [150]:
Cu2+ or Fe3+ + POH Cu+ or Fe2+ + PO· + H+ (6)
PO· + RH POH + R· (7)
R· + O2 ROO· (8)
ROO· + RH ROOH + R· (9)
ROOH + Cu+ or Fe2+ Cu2+ or Fe3+ + RO· + OH- (10)
It was found that phenolic antioxidants behave like prooxidants under the conditions that favor their
autoxidation, for example, at high pH with high concentrations of transition metal ions and oxygen
molecule present. Small phenolics which are easily oxidized, such as quercetin, gallic acid, possess
prooxidant activity; while high molecular weight phenolics, such as condensed and hydrolysable
tannins, have little or no prooxidant activity [151]. It is necessary to consider the possible prooxidant
effects of phenolics for in vitro antioxidant tests where great care should be taken in the design of
experimental conditions. Moreover, because the biological conditions in vivo may differ dramatically
from in vitro experiment, great caution must be taken when interpreting in vitro results and
extrapolating to in vivo conditions.
3.3. Determination of Total Antioxidant Capacity (TAC) of Phenolic Extracts
Due to the chemical diversity of phenolic compounds and the complexity of composition in plant
samples, it is costly and inefficient to separate each phenolic antioxidant and study it individually.
Moreover, an integrated total antioxidant power of a complex sample is often more meaningful to
evaluate the health benefits because of the cooperative action of antioxidants. Therefore, it is desirable to
establish convenient screening methods for quick quantification of antioxidant effectiveness of phenolic
extract samples. A variety of antioxidant assays such as Trolox equivalent antioxidant capacity (TEAC),
oxygen radical absorbance capacity (ORAC), total radical-trapping antioxidant parameter (TRAP), ferric
ion reducing antioxidant power (FRAP) and cupric ion reducing antioxidant capacity (CUPRAC) assays
have been widely used for quantification of antioxidant capacity of phenolic samples from fruits and
Molecules 2010, 15
vegetables. The Folin-Ciocalteu antioxidant capacity assay (F-C assay, or total phenolics assay) is also
considered as another antioxidant capacity assay because its basic mechanism is as oxidation/reduction
reaction although it have been used as a measurement of total phenolics content for many years. On the
basis of the chemical reaction involved, major antioxidant assays can be roughly classified as hydrogen
atom transfer (HAT) and electron transfer (ET) reaction based assays although these two reaction
mechanisms can be difficult to distinguish in some cases [150].
The HAT-based assays include ORAC and TRAP assays. These assays measure the capacity of an
antioxidant to quench free radicals by hydrogen atom donation. The majority of HAT-based assays
involve a competitive reaction scheme, in which antioxidant and substrate compete for thermally
generated peroxyl radicals through the decomposition of azo compounds [150]. As an example of
HAT-based assays, ORAC assay [152] employs a fluorescent probe (e.g., fluorescein) to compete with
sample antioxidant for peroxyl radicals generated by decomposition of 2,2’-azobis (2-amidinopropane)
dihydrochloride (AAPH). The fluorescence intensity is measured every minute at physiological
conditions (pH 7.4, 37°C) to obtain a kinetic curve of fluorescence decay. The net area under the curve
(AUC) calculated by subtracting the AUC of blank from that of the sample or standard (e.g., Trolox)
and the TAC of sample is calculated as the Trolox equivalent based on a standard curve [150]. The
ORAC method is considered to mimic antioxidant activity of phenols in biological systems better than
other methods since it uses biologically relevant free radicals and integrates both time and degree of
activity of antioxidants [153]. However, the method often requires the use of expensive equipment and
it is usually a time-consuming process.
TEAC, F-C, FRAP and CUPRAC assay are ET-based assays. These assays measure the capacity of
an antioxidant in reduction of an oxidant probe, which changes color when reduced [150]. The reaction
is completed when the color change stops. The degree of color change is proportional to the
concentration of antioxidant. The oxidant probes used are 2,2’-azinobis(3-ethylbenzothiazoline-6-
sulfonic acid) radical cation (ABTS·+) in TEAC, Fe3+(2,4,6-tripyridyl-s-triazine)2Cl3 in FRAP and
bis(neocuproine)Cu2+Cl2 in CUPRAC assays, respectively. The TEAC method is operationally simple,
reproducible, and cost effective [154]. Most importantly, it can be applied in multiple media to determine
both hydrophilic and hydrophobic antioxidant capacity of plant extracts since the reagent is soluble in
both aqueous and organic solvent media [155]. As opposed to TEAC assay, FRAP assay measures ferric-
to-ferrous reduction capacity of water-soluble antioxidants in acidic pH such as pH 3.6 [156].
It was proposed that procedures and applications for three assays, namely ORAC, F-C, and TEAC,
be considered for standardization at the First International Congress on Antioxidant Methods held in
Orlando, FL, in June 2004 [157]. It must be emphasized that these antioxidant assays measure the
capacity of a sample only under defined conditions prescribed by the given method and strictly based
on the chemical reaction in vitro, so the bioactivity of a sample cannot be reflected solely by these
assays. In another words, the “total antioxidant capacity” of a particular sample cannot be truly
measured by any of the assays because of the complexity of the chemistry of antioxidant compounds.
For example, the total antioxidant capacity has to be able to reflect both lipophilic and hydrophilic
capacity, and to reflect and distinguish hydrogen atom transfer, electron transfer, as well as transition
metal chelation [157]. It is also very important to develop methods specific for each radical source for
evaluating effectiveness of antioxidant compounds against various ROS/RNS such as O2·, HO·, and
ONOO to fully elucidate a full profile of antioxidant capacity [157].
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4. Natural Phenolics and Cancer
Cancer is a multi-step disease incorporating environmental, chemical, physical, metabolic, and
genetic factors which play a direct and/or indirect role in the induction and deterioration of cancers.
Strong and consistent epidemiology evidence indicates a diet with high consumption of antioxidant-
rich fruits and vegetables significantly reduces the risk of many cancers, suggesting that certain dietary
antioxidants could be effective agents for the prevention of cancer incidence and mortality. These
agents present in the diet are a very promising group of compounds because of their safety, low
toxicity, and general acceptance [158]. Consequently, in the last few years, the identification and
development of such agents has become a major area of experimental cancer research. Phenolic
compounds constitute one of the most numerous and ubiquitous group of plant metabolites, and are an
integral part of the human diet. It was found that in addition to their primary antioxidant activity, this
group of compounds displays a wide variety of biological functions which are mainly related to
modulation of carcinogenesis. Various in vitro and in vivo systems have been employed to determine
the anticarcinogenic and anticancer potential of these natural phenolic compounds or extracts.
4.1. In vitro effects of phenolics
Phenolic extracts or isolated polyphenols from different plant food have been studied in a number
of cancer cell lines representing different evolutionary stages of cancer. For example, berry extracts
prepared from blackberry, raspberry, blueberry, cranberry, strawberry and the isolated polyphenols
from strawberry including anthocyanins, kaempferol, quercetin, esters of coumaric acid and ellagic
acid, were shown to inhibit the growth of human oral (KB, CAL-27), breast (MCF-7), colon (HT-29,
HCT-116), and prostate (LNCaP, DU-145) tumor cell lines in a dose-dependent manner with different
sensitivity between cell lines [66,159]. Katsube et al. compared the antiproliferative activity of the
ethanol extracts of 10 edible berries on HL-60 human leukemia cells and HCT-116 cells and showed
that bilberry extract was the most effective [160]. Ross et al. showed that the antiproliferative activity
of raspberry extract in human cervical cancer (Hela) cells was predominantly associated with
ellagitannins [161]. By comparing the phytochemical diversity of the berry extracts with their
antiproliferative effectiveness, McDougall et al. suggested that the key component that related to the
inhibition of cancer cell growth could be ellagitannins from the Rubus family (raspberry, arctic bramble,
and cloudberry) and strawberry, whereas the antiproliferative activity of lingonberry was caused
predominantly by procyanidins [162]. Similar results have also been reported in several cell system with
wine extracts and isolated polyphenols (resveratrol, quercetin, catechin, and epicatechin) [163,164], tea
extract and major green tea polyphenols (epicatechin, epigallocatechin, epicatechin-3-gallate, and
epigallocatechin-gallate) [165-167], although the effective concentrations depend on the system and
the tested substances. Other phenolic extracts or compounds intensely studies are from olives, legumes,
citrus, apples, and also curcumin from spice turmeric. For example, soy isoflavone genistein can
inhibit the growth of various cancer cell lines including leukemia, lymphoma, prostate, breast, lung
and head and neck cancer cells [168]. Citrus flavonoids strongly inhibit the growth of HL-60 leukemia
cells [169]. McCann et al. utilized established cell models of: genotoxicity (HT-29), invasion and
metastatic potential (HT-115), and colonic barrier function (CaCo-2) to examine the effect of apple
phenolic extract on key stages of colorectal carcinogenesis and found apple extract exert beneficial
Molecules 2010, 15
influence on all three carcinogenesis stages [170]. In addition, growth inhibitory effects of a number of
polyphenols such as flavones (apigenin, baicalein, luteolin and rutin), flavanones (hesperidin and
naringin) and sesame lignans (sesaminol, sesamin, and episesamin), which are not so extensively studied
previously, have been examined in different cancer cell lines including colon [171], prostate [172,173],
leukemia [174], liver [175], stomach, cervix, pancreas and breast [176].
4.2. In vivo Effects of Phenolics
In addition to in vitro studies on cancer cell lines, numerous in vivo experiments have also been
performed to verify the antitumor efficacy of plant food-derived phenolic extracts or compounds with
tumor incidence and multiplicity (e.g., number of tumors per animal) as endpoints [177-180]. The animal
models commonly employed are either chemically, genetically, or ultraviolet light-induced tumor, as
well as xenograft models, including colon, lung, breast, liver, prostate, stomach, esophagus, small
intestine, pancreas mammary gland and skin tumors. As an example, Lala et al. investigated the
chemoprotective activity of anthocyanin-rich extracts (AREs) from bilberry, chokeberry, and grape in
Fischer 344 male rats treated with a colon carcinogen, azoxymethane (AOM) [181]. After 14 weeks,
rats on ARE diets had significantly fewer colonic aberrant crypt foci (ACF) when compared with the
control group. Moreover, rats fed bilberry ARE had 70% fewer large ACF compared with rats fed the
control diet, indicating significant chemoprevention. Chokeberry-fed rats had a 59% reduction in large
ACF, whereas the reduction was only 27% in rats fed grape ARE. The authors concluded that AREs
from bilberry, chokeberry, and grape significantly inhibited ACF formation induced by AOM.
In another study by Ding et al. [182], cyanidin-3-glucoside (C3G), the major anthocyanin in
blackberry, was investigated for the potential ability to inhibit 7,12-dimethylbenz[a]anthracene
(DMBA)-12-O-tetradecanolyphorbol-13-acetate (TPA)-induced skin papillomas in animal skin model.
Fourteen days following DMBA initiation, the dorsal skin of the mice was exposed to TPA in the
presence or absence of C3G twice per week to cause promotion. The results showed that treatment of
the animals with C3G (3.5 µM, topical application, twice/week) decreased the number of tumors per
mouse at all exposure times. After 20 weeks of TPA promotion, a greater than 53% inhibition of
papillomagenesis by C3G was observed. After 22 weeks, there were four tumors greater than 4–5 mm
in diameter in the TPA-treated group, whereas no large tumors were found in the C3G plus TPA-
treated group. In addition, they also tested the effects of C3G on human lung carcinoma (A549)
xenograft growth and metastasis in athymic male nude mice. The results showed that C3G reduced the
size of A549 tumor xenograft growth and significantly inhibited metastasis in nude mice. The authors
concluded that C3G exhibits chemoprevention and chemotherapeutic activities by inhibiting tumor
promoter-induced carcinogenesis and tumor metastasis in vivo.
The inhibition of tumorigenesis by tea preparations and its polyphenol constituents such as
epigallocatechin-gallate (EGCG) and theaflavin have also been demonstrated in various animal models.
However, caution must be taken when attributed the tumor inhibitory effect of tea to tea polyphenols in
some animal models. For example, caffeine, a nonphenol constituent of tea, was found to contribute to
the inhibitory effects of green and black tea on UVB-induced complete carcinogenesis [183], as well as
the inhibition effects of black tea on lung tumorigenesis in F344 rats [184] to a significant extent.
It is worth noting that the effectiveness of a phenolic extract in different organs is also dependent on
the amount of its active constituents that can reach the target tissue. Therefore, the administration route
Molecules 2010, 15
and bioavailability factors of these extract constituents should be carefully considered when comparing
their inhibition efficacy in different tumors.
4.3. Human Intervention Studies Using Phenolics
Human intervention studies on potential health promoting or cancer preventive activity of polyphenol-
rich food or food preparations have been conducted in healthy volunteers or individuals at high risk of
developing cancer. Most studies have employed biomarkers reflecting antioxidant status or oxidative
stress as endpoints, for example, plasma or serum antioxidant capacity, plasma malondialdehyde
concentration, glutathione status, oxidative DNA damage in mononuclear blood cells (MNBCs), urinary
8-epi-prostaglandin F2α (8-Iso-PGF2) and 8-hydroxy-2’-deoxyguanosine (8-OHdG) concentration, etc..
Improvement of antioxidant status and/or protection against oxidative stress was observed in short
term intervention studies (1 dose) with various polyphenol-rich food including fruit juices [185-189],
red wines [190,191], chocolates [192-194] and fruits such as strawberries [190], as well as food
preparations such as lyophilized blueberry powder [195], black currant anthocyanin concentrate [196],
grape seed concentrate [197], dealcoholized [198] and lyophilized [190,199] red wines.
In a 6-month chemopreventive pilot study conducted by researchers from the Ohio State University,
patients with Barrett’s esophagus (BE) were treated with 32 or 45 g (female and male, respectively) of
freeze-dried black raspberries (FBRs) [200]. BE is a premalignant esophageal condition in which the
normal stratified squamous epithelium changes to a metaplastic columnar-lined epithelium and is
underscored by the fact that it increases the risk for the development of esophageal adenocarcinoma, a
rapidly increasing and extremely deadly malignancy by 30- to 40-fold [201]. Their results suggested
that daily consumption of FBRs reduced the urinary excretion of 8-Iso-PGF2 and 8-OHdG, among
patients with BE indicating reduced oxidative stress [200]. The same group of researchers also
investigated a novel mucoadhesive gel formulation for local delivery of FBRs to human oral mucosal
tissues [202]. The results indicated that a gel formulation was well-suited for absorption and
penetration of anthocyanins into the target oral mucosal tissue site as evidenced by detectable blood
levels within 5 min after gel application and the greater penetration of anthocyanins into tissue
explants was observed in berry gels with a final pH of 6.5 versus pH 3.5 [202]. Furthermore, the
effects of the 10% (w/w) FBR gel formulation was examined clinically on oral intraepithelial neoplasia
(IEN), a recognized precursor to oral squamous cell carcinoma [203,204]. It was found that topical
FBR gel application (0.5 g applied four times daily for six weeks) was well tolerated in all the 27 trial
participants [203]. Results from this clinical trial showed that FBR gel topical application significantly
reduced loss of heterozygosity (LOH) indices at chromosomal loci associated with tumor suppressor genes
[203], uniformly suppressed gene associated with RNA processing, growth factor recycling and inhibition of
apoptosis and significantly reduced epithelial COX-2 levels in human oral IEN lesions [204]. In addition, it
was found gel application also reduced microvascular density in the superficial connective tissues and
induced genes associated with keratinocyte terminal differentiation in a subset of patients [204].
A recent study evaluated the effects of anthocyanin/polyphenolic-rich fruit juice consumption on
antioxidant status in hemodialysis patients that are facing an elevated risk of cancer, arteriosclerosis,
and other diseases, ascribed in part to increased oxidative stress [205]. In this pilot intervention study,
21 hemodialysis patients consumed 200 mL/day of red fruit juice (3-week run-in; 4-week juice uptake;
3-week wash-out). Weekly blood sampling was done to monitor DNA damage (comet assay +/
Molecules 2010, 15
formamidopyrimidine-DNA glycosylase enzyme), glutathione, malondialdehyde, protein carbonyls,
Trolox equivalent antioxidant capacity, triglycerides, and DNA binding capacity of the transcription
factor nuclear factor-kappa B (NF-κB). Results show a significant decrease of DNA oxidation damage
(P < 0.0001), protein and lipid peroxidation (P < 0.0001 and P < 0.001, respectively), and NF-κB
binding activity (P < 0.01), and an increase of glutathione level and status (both P < 0.0001) during
juice uptake. The authors attributed this reduction in oxidative (cell) damage in hemodialysis patients
to the especially high anthocyanin/polyphenol content of the juice. The authors concluded that
consumption of antioxidant berry juices appears to be a promising preventive measure to reduce
chronic diseases such as cancer and cardiovascular disease in population subgroups exposed to
enhanced oxidative stress like hemodialysis patients [205].
4.4. Mechanism of Action of Phenolics
Cancer development is a multistage process that involves a series of individual steps including
initiation, promotion, progression, invasion and metastasis. Tumor initiation begins when DNA, in a
cell or population of cells, is damaged by exposure to carcinogens, which are derived from three major
sources: cigarette smoking, infection/inflammation, and nutrition/diet [206].
Figure 4. Potential anticancer mechanisms of plant phenolics during cancer development.
If the DNA damage escapes repair, it can lead to genetic mutation. The resulting somatic mutation
in a damaged cell can be reproduced during mitosis, which given rise to a clone of mutated cells.
Tumor promotion is a selective clonal expansion of the initiated cells to form an actively proliferating
multi-cellular premalignant tumor cell population. It is an interruptible or reversible and long term
process. During progression, premalignant cells developed into tumors through a process of clonal
expansion. In the late stages of cancer development, invasion and metastasis happens, where tumor
cells detach from the primary tumor mass, migrate through surrounding tissues toward blood vessels or
lymphatic vessels, and create a second lesion. Metastasis is the major cause of cancer mortality. It is
widely accepted that human cancer development does not occur through these discrete phases in a
predictable manner, rather it is best characterized as an accumulation of alteration in cancer regulating
Molecules 2010, 15
genes [207], such as oncogenes, tumor suppressor genes, resulting in altered cellular processes,
namely, decreased apoptosis, increased proliferation, and cell maturation and differentiation. The
inhibitory effect of natural phenolics in carcinogenesis and tumor growth may be through two main
mechanisms: 1) modifying the redox status and, 2) interfering with basic cellular functions (cell cycle,
apoptosis, inflammation, angiogenesis, invasion and metastasis) [208].
4.4.1. Antioxidant and prooxidant effect of phenolics on cellular redox status
ROS/RNS are constantly produced during normal cellular metabolism or by other exogenous means
including the metabolism of environmental toxins or carcinogens, by ionizing radiation and by
phagocytic cells involved in the inflammatory response. When the cellular concentration of oxidant
species is increased to an extent that overcome the endogenous antioxidant defense system, oxidative
stress occurs, leading to lipid, protein, and DNA damage. In addition, ROS, particularly H2O2, are
potent regulators of cell replication and play an important role in signal transduction [209]. Hence,
oxidative damage is considered a main factor contributing to carcinogenesis and evolution of cancer.
Due to their ability to scavenge and reduce the production of free radicals and act as transition metal
chelators, natural phenolic compounds can exert a major chemopreventive activity [208]. Indeed, it has
been shown that natural polyphenols can inhibit carcinogen/toxin-induced cellular oxidative damage.
For example, in nicotine-treated rat peripheral blood lymphocytes, ellagic acid effectively restored the
antioxidant status and reduced DNA damage as well as lipid peroxidation [210]. A phenolic apple
juice extract as well as its reconstituted polyphenol mixture (rutin, phloridzin, chlorogenic acid, caffeic
acid and epicatechin) were shown to effectively reduce menadione-induced oxidative DNA damage
and increasing of cellular ROS level [211]. Tea polyphenols [212] and other extensively studied
polyphenols such as resveratrol [163,213], quercetin [214-216] were also showed to exert protective
effects against cellular oxidative damage in different human cell lines.
UV radiation-induced ROS and oxidative stress is capable of oxidizing lipids, proteins, or DNA,
leading to the formation of oxidized products such as lipid hydroperoxides, protein carbonyls, or
8-OHdG, which have been implicated in the onset of skin diseases including skin cancers [217-219].
Phenolic extracts, such as pomegranate-derived extracts [220], tea [221] and wine [222] extracts have
been shown to reduce the oxidative damage of UV light in skin. Purified phenolic compounds such as
anthocyanins [223], proanthocyanidin [224] and EGCG [225] were found to inhibit the UV-radiation-
induced oxidative stress and cell damage in human keratinocytes.
On the other hand, in vitro studies also suggested that polyphenols may exert their inhibitory effects
by acting as prooxidants on cancer cells. It has been reported that many polyphenols including
flavonoids such as quercetin, rutin, apigenin, phenolics acids such as gallic acid, tannic acid, caffeic
acid, as well as delphinidin, resveratrol, curcumin, gallocatechin and EGCG can cause oxidative strand
breakage in DNA in vitro [226,227]. Furthermore, the cytotoxicity of quercetin and gallic acid on CaCo-2
cells and normal rat liver epithelial cells was partially reduced by antioxidant such as catalase [228].
Similar results have also been reported in oral carcinoma cell lines with EGCG [229]. These studies
suggested that the antiproliferative effects of some polyphenol antioxidants on cancer cells are
partially due to their prooxidant actions. However, it has been proposed that this oxidative property
depends on the amount of dissolved oxygen in the test medium [230]. The oxygen partial pressure in a
Molecules 2010, 15
cell culture system (160 mmHg) is much higher than that in the blood or tissues (< 40 mmHg). It is not
clear whether a similar mechanism could also occur in vivo.
4.4.2. Interference of basic cellular functions by phenolics
Natural phenolics can affect basic cell functions that related cancer development by many different
mechanisms. Firstly, in the initiation stage, phenolics may inhibit activation of procarcinogens by
inhibiting phase I metabolizing enzymes, such as cytochrome P450 [231] and also facilitate
detoxifying and elimination of the carcinogens by induction of phase II metabolizing enzymes such as
glutathione S-transferase (GST), NAD(P)H quinine oxidoreductase (NQO), and UDP-glucuronyl-
transferase (UGT) [232]. They may also limit the formation of the initiated cells by stimulating DNA
repair [233,234].
Secondly, phenolics may inhibit the formation and growth of tumors by induction of cell cycle
arrest and apoptosis. Malignant cells are characterized by excessive proliferation, inability to
terminally differentiate or perform apoptosis under normal conditions, and an extended or
immortalized life span. The regulation of cell cycle is altered in these cells. Thus, any perturbation of
cell cycle specific proteins by phenolics can potentially affect and/or block the continuous proliferation
of these tumorigenic cells. Natural phenolics have been reported induce cell cycle arrest at different
cell phases: G1, S, S-G2, and G2 by directly down-regulating cyclins and cyclins-dependent kinases
(CDKs) or indirectly inducing the expression of p21, p27 and p53 genes [158,235]. Moreover, some
studies have shown that natural phenolics exhibit differential effect in cancer versus normal cells. For
example, anthocyanin-rich extract from chokeberry was found to induce cell cycle block at G1/G0 and
G2/M phases in colon cancer HT-29 cells but not in NCW460 normal colonic cells [236].
Apoptosis has been reported to play an important role in elimination of seriously damaged cells or
tumor cells by chemopreventive or chemotherapeutic agents [232,237]. The cells that have undergone
apoptosis have typically shown chromatin condensation and DNA fragmentation. They are rapidly
recognized by macrophages before cell lysis, and then can be removed without inducing inflammation.
Therefore, apoptosis-inducing agents are expected to be ideal anticancer drugs. Polyphenols have been
found to affect cancer cell growth by inducing apoptosis in many cell lines such as the hepatoma
(HepG2), the colon (SW620, HT-29, CaCo-2, and HCT-116), the prostate (DU-145 and LNCaP), the
lung (A549), the breast (MCF-7), the melanoma (SK-MEL-28 and SK-MEL-1), the neuroblastoma
(SH-SY5Y) and the HL-60 leukemia cells [238,239]. In many cases, apoptosis induced by polyphenols
was caspase-3-dependent. The induction of apoptosis and/or inhibition of proliferation/survival by
polyphenols has been reported to result from a number of mechanisms including inducing cell cycle
arrest; blocking the extracellular regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and P38
mitogen-activated protein kinase (MAPK) pathway; inhibition of the activation of transcription factors,
NF-κB and activator protein-1 (AP1); suppression of protein kinase C (PKC); suppression of growth
factor-mediated pathways [158,235]. For example, Afaq et al. showed that pomegranate fruit extract,
rich in anthocyanins and hydrolysable tannins, protected against the adverse effect of both UVB-
radiation in normal human epidermal keratinocytes in vitro [240] and 12-O-tetradecanoylphorbol-13-
acetate (TPA) in CD-1 mouse skin in vivo [241], by inhibiting the activation of NF-κB and MAPK
pathway. In addition, green tea polyphenols was found to protect against pentachlorophenol (PCP)-
induced mouse hepatocarcinogenesis via its ability to prevent down-regulation of gap junctional
Molecules 2010, 15
intercellular communication (GJIC) which is strongly related to cell proliferation and differentiation [242].
Pure phenolic compound such as quercetin [243], resveratrol [244] were also found to block tumor
promoter such as TPA-induced inhibition of GJIC.
One important aspect of carcinogenesis is recognized to be the involvement of inflammation. For
instance, prostaglandins are mediators of inflammation and chronic inflammation predisposes to
carcinogenesis. The over-expression of inducible cyclooxygenases (COX-2), the enzyme which
catalyzes a critical step in the conversion of arachidonic acid to prostaglandins and is induced by
pro-inflammatory stimuli, including mitogens, cytokines and bacterial lipopolysaccharide (LPS), is
believed to be associated with colon, lung, breast and prostate carcinogenesis. Natural phenolics have
been reported to inhibit transcription factors closely linked to inflammation (e.g., NF-κB) [245,246],
pro-inflammatory cytokines release [245,247] and enzymes such as COX-2 [248, 249], lipoxygenases
(LOX) [250], inducible nitric oxide synthase (iNOS) [251] that mediate inflammatory processes, both
in vitro and in vivo [252]. In many cases, polyphenols exhibit anti-inflammatory properties through
blocking MAPK-mediated pathway. Furthermore, a few structure-activity studies have been
conducted. For example, Hou et al. examined the inhibitory effects of five kinds of green tea
proanthocyanidins on cyclooxygenase-2 (COX-2) expression and PGE-2 release in LPS-activated
murine macrophage RAW-264 cells [248]. It was revealed that the galloyl moiety of
proanthocyanidins appeared important to their inhibitory actions. Another study by Herath et al.
suggested that the double bond between carbon 2 and 3 and the ketone group at position 4 of
flavonoids are necessary for potent inhibitory effects on LPS-induced tumor necrosis factor-alpha
(TNF-α) production in mouse macrophages (J774.1) [253].
Finally, natural phenolics such as green tea polyphenols (EGCG, GCG), grape seeds
proanthocyanidins, hydrolysable tannins, genistein, curcumin, resveratrol, and anthocyanins, were
found to suppress malignant cell migration, invasion and metastasis in vitro and in vivo [254-259]. The
inhibition effect has been shown to be related to their ability to down-regulate the matrix
metalloproteases (MMPs), namely, MMP-2 and MMP-9, as well as urokinase-plasminogen activator
(uPA) and uPA receptor (uPAR) expression. In addition, phenolic compounds possess
antiangiogenesis effects [260], which is an important aspect in the inhibition of tumor growth, invasion
and metastasis. It has been reported that phenolic compounds such as ellagic acids, EGCG, genistein
and anthocyanin-rich berry extracts inhibit tumor angiogenesis through down-regulation of vascular
endothelial growth factor (VEGF), VEGF receptor-2 (VEGFR-2), platelet-derived growth factor
(PDGF), PDGF receptor (PDGFR), hypoxia-inducible factor 1α (HIF-1α) and MMPs, as well as
inhibition of phosphorylation of EGFR, VEGFR and PDGFR [235].
5. Conclusions
In summary, natural phenolics have been found to intervene at all stages of cancer development. In
addition to their antioxidant action, the inhibition of cancer development by phenolic compounds relies
on a number of basic cellular mechanisms, involving a spectrum of cellular basic machinery. Moreover,
the extensive studies of this class of compounds will provide clues about their possible pharmaceutical
exploration in the field of oncology.
Molecules 2010, 15
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... Studies of medicinal plants have demonstrated that the health-promoting properties and therapeutically beneficial qualities can often be attributed to specific polyphenols or iridoids, two of the most prevalent groups of bioactives in many plant extracts, and in the representatives of the Galium genus [9,11,16,17]. Polyphenols are the most abundant secondary metabolites in plants, notably characterised by their potent antioxidant properties [18]. Polyphenols also modulate the activity of many enzyme and cell receptors, scavenge free radicals, regulate nitric oxide, decrease leukocyte immobilization, induce apoptosis, and inhibit cell proliferation and angiogenesis [18][19][20][21][22][23]. ...
... Polyphenols are the most abundant secondary metabolites in plants, notably characterised by their potent antioxidant properties [18]. Polyphenols also modulate the activity of many enzyme and cell receptors, scavenge free radicals, regulate nitric oxide, decrease leukocyte immobilization, induce apoptosis, and inhibit cell proliferation and angiogenesis [18][19][20][21][22][23]. Therefore, polyphenols possess several mechanisms for preventing and treating illnesses. ...
... Phenolic acids include derivatives of benzoic acid such as gallic acid, and derivatives of cinnamic acid, such as coumaric, caffeic and ferulic acid. Flavonoids are the most prevalent polyphenols in the human diet [18], and possess a variety of pharmacological effects mainly tied to their free radical scavenging and antioxidative properties, such as hepatoprotective, antiatherosclerotic, anti-inflammatory, antithrombogenic, antitumor, antiosteoporotic, antibacterial, and antiviral effects [22,[28][29][30]. Some of the most common flavonoids include quercetin, catechin, naringenin, kaempferol, rutin, cyanidin-glycoside, daidzein, genistein, and glycitein [19,31]. ...
Full-text available
The aim of the present study was to examine three different Galium species from the native population of Estonia, Galium verum, Galium aparine, and Galium mollugo, to characterise their non-volatile and volatile phytochemical composition and antioxidant activity. The main groups of bioactive compounds in the plants were quantified by colorimetric tests, showing high concentrations of polyphenols (up to 27.2 ± 1.5 mg GAE/g), flavonoids (up to 7.3 ± 0.5 mg QE/g) and iridoids (up to 40.8 ± 2.9 mg AE/g). The species were compared using HPLC-DAD-MS/MS, revealing some key differences in the phytochemical makeup of the extracts. The most abundant compound in the extracts of Galium verum blossoms and herb was found to be asperuloside, in Galium aparine herb, asperulosidic acid, and in Galium mollugo herb, chlorogenic acid. Additionally, the composition of volatile compounds was analysed by SPME-GC-MS. The degree of variability between the samples was high, but three volatiles, hexanal, anethole, and β-caryophyllene, were quantified (≥1%) in all analysed samples. The antioxidative activity of all extracts was evaluated using the ORACFL method, demonstrating that the Galium species from Estonia all exhibit strong antioxidant capacity (up to 9.3 ± 1.2 mg TE/g). Out of the extracts studied, Galium verum blossoms contained the highest amounts of bioactives and had the strongest antioxidant capacity.
... This was expected, given that the leaves are described as the active plant parts in the ethnopharmacological usage of this plant. Furthermore, the obtained results can be attributed to phenolic and proanthocyanin compounds, which are well known for their antimicrobial activity [16,55,60,61]. Because of the slight discrepancy in results between antimicrobial activity and phenol composition (significant concentration in the roots but low antimicrobial activity), we can assume that other compounds, such as flavonoids (found in low concentrations in the leaf extract), play an important role in the antimicrobial effect of the tested extracts. ...
Full-text available
The present study investigated the antimicrobial activity, total phenolic content, and proanthocyanidin concentration of ethanolic extracts from fresh leaves of Sempervivum tectorum L. The extracts were phytochemically analyzed and evaluated for antimicrobial activity. The broth microdilution method was used to assess antimicrobial activity against pathogenic bacteria isolated from ear swabs taken from dogs with otitis externa. Many compounds were present in the ethanolic aqueous extracts, which exhibited a broad spectrum of antimicrobial activity. They showed strong antibacterial activity against standard clinical Gram-positive strains such as S. aureus and Gram-negative strains such as P. aeruginosa. In our study, the obtained quantity of total phenolic compounds in the ethanol:water extract of leaves was 126.17 mg GAE/g. The proanthocyanidin concentration in the tested Sempervivum tectorum L. extracts was 15.39 mg PAC/g material. The high contents of total phenolics and proanthocyanidin indicated that these compounds contribute to antimicrobial activity. The antimicrobial activity of the tested S. tectorum L. extracts ranged from 1.47 to 63.75 µg/mL, starting with 1.47 µg/mL and 1.75 µg/mL against S. aureus ATCC 25923 and P. aeruginosa ATCC 27853 strains, respectively. Likewise, S. tectorum L. ethanol extract demonstrated a bacteriostatic effect against S. aureus clinical isolate with a median MIC of 23.25 µg/mL and MBC of 37.23 µg/mL; and bactericidal against S. aureus ATCC 25923 with the median MIC of 20.33 µg/mL and MBC of 37.29 µg/mL. In the Gram-negative P. aeruginosa clinical and standard strains, the expressed MIC and MBC values were 24.234 and 20.53 µg/mL for MIC, and 37.30 and 37.02 µg/mL for MBC, respectively.
... The synthesis of these metabolites can be affected by pathogens, drought, and other external factors. Phenolic compounds are widely distributed in plants (Bravo, 1998) and provide ecological advantages to those plants, for example as protection against ultraviolet radiation, pathogens, and parasites (Pandley and Rizvi, 2009;Dai and Mumper, 2010). Phenolic compounds are involved in plant defense mechanisms to protect against herbivores, and in different plant growth processes. ...
The search for alternative naturally occurring antimicrobial agents will always continue, especially when emerging diseases like COVID-19 provide an urgency to identify and develop safe and effective ways to prevent or treat these infections. The purpose of this study was to evaluate the potential antimicrobial activity as well as antioxidant properties of commercial samples from four traditional medicinal plants used in Central America: Theobroma cacao, Bourreria huanita, Eriobotrya japonica, and Elettaria cardamomum. Ethanolic extracts were prepared from commercial products derived from the seeds or flowers of these plants. Total phenolics and antioxidant activity were assessed using commercial kits. The cytotoxicity and antiviral activity against severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) were evaluated using the XTT colorimetric assay and a SARS-CoV-2 delta pseudoviral model. The half-maximal cytotoxic concentration (CC50) and half-maximal effective concentration (EC50) were used to calculate the therapeutic index (TI). Additionally, the antibacterial activity against Escherichia coli and Staphylococcus epidermidis was tested using a spectrophotometric method. The extracts showed total phenolics in the range of 0.06 to 1.85 nM/µL catechin equivalents, with T. cacao bean extract showing the highest content. The antioxidant activity showed values between 0.02 and 0.44 mM Trolox equivalents. T. cacao bean extract showed the highest antioxidant activity. Most plant extracts showed zero to moderate selective antiviral activity; however, one T. cacao beans sample showed excellent antiviral activity against SARS-CoV-2 with a TI Cornejal et al.: Antimicrobial and Antioxidant Properties of Theobroma cacao, Bour 2 value of 30.3, and one sample of E. japonica showed selective antiviral activity with a TI value of 18.7. Significant inhibition of E. coli and S. epidermidis by an E. japonica ethanolic extract (p<0.001) was observed using a spectrophotometric method that monitors bacterial growth over time. Additionally, ethanolic extracts of E. cardamomum showed significant inhibition of S. epidermidis growth (p<0.001). The results warrant further investigation of the antimicrobial and antioxidant properties of these plant extracts.
... Bioactive plant products used in drugs are derived from secondary metabolites. These substances are classified as phenolic, including J o u r n a l P r e -p r o o f polyphenols, tannin, and quinone, and flavonoids are well-known for their antioxidant, cytotoxic, and antimicrobial properties [8][9][10] . Nevertheless, the underutilization of plants continues to hinder drug development. ...
... Reason why results are different from presented above is probably due to different method of extracting. Aim of this study was to compare results of three different extraction methods and of two types of samples, extracts of fresh and shade dried and to ease the process of choosing extraction technique. of each phenolic antioxidantan, total antioxidant power of a complex sample is often more meaningful to evaluate the health benefits, because of the cooperative action of antioxidants [39]. Extracts that were obtained by maceration had the lowest antioxidant capacity, while extracts obtained with Soxhlet extraction had the highest antioxidant capacity. ...
The samples of stinging nettle were collected during June in the Tuzla region. Aqueous extracts were prepared from fresh and dried leaves in order to determinate and compare content of bioactive components and antioxidant potential. Conventional soxhlet, ultrasound assisted extraction and traditional maceration extraction were used as extraction methods. Quantitative determination of phenols and flavonoids was carried out using spectrophotometric methods. Antioxidant activity of nettle aqueous extracts was determined using ferric reducing antioxidant power and DPPH free radical scavenging activity. Extracts obtained by Soxhlet extraction showed the highest total phenolic and flavonoid content and expected the highest antioxidant capacity, while extracts obtained by maceration gave the lowest results. KEYWORDS:stinging nettle extract;bioactive components;extraction;antioxidant
Plant extracts and essential oils have a wide variety of molecules with potential application in different fields such as medicine, the food industry, and cosmetics. Furthermore, these plant derivatives are widely interested in human and animal health, including potent antitumor, antifungal, anti-inflammatory, and bactericidal activity. Given this diversity, different methodologies were needed to optimize the extraction, purification, and characterization of each class of biomolecules. In addition, these plant products can still be used in the synthesis of nanomaterials to reduce the undesirable effects of conventional synthesis routes based on hazardous/toxic chemical reagents and associate the properties of nanomaterials with those present in extracts and essential oils. Vegetable oils and extracts are chemically complex, and although they are already used in the synthesis of nanomaterials, limited studies have examined which molecules are effectively acting in the synthesis and stabilization of these nanostructures. Similarly, few studies have investigated whether the molecules coating the nanomaterials derived from these extracts and essential oils would bring benefits or somehow reduce their potential activity. This synergistic effect presents a promising field to be further explored. Thus, in this review article, we conducted a comprehensive review addressing the main groups of molecules present in plant extracts and essential oils, their extraction capacity, and available methodologies for their characterization. Moreover, we highlighted the potential of these plant products in the synthesis of different metallic nanomaterials and their antimicrobial capacity. Furthermore, we correlated the extract’s role in antimicrobial activity, considering the potential synergy between molecules from the plant product and the different metallic forms associated with nanomaterials.
Cancer is a hard-to-treat disease with a high reoccurrence rate that affects health and lives globally. The condition has a high occurrence rate and is the second leading cause of mortality after cardiovascular disorders. Increased research and more profound knowledge of the mechanisms contributing to the disease’s onset and progression have led to drug discovery and development. Various drugs are on the market against cancer; however, the drugs face challenges of chemoresistance. The other major problem is the side effects of these drugs. Therefore, using complementary and additional medicines from natural sources is the best strategy to overcome these issues. The naturally occurring phytochemicals are a vast source of novel drugs against various ailments. The modes of action by which phytochemicals show their anti-cancer effects can be the induction of apoptosis, the onset of cell cycle arrest, kinase inhibition, and the blocking of carcinogens. This review aims to describe different phytochemicals, their classification, the role of phytochemicals as anti-cancer agents, the mode of action of phytochemicals, and their role in various types of cancer.
The burning of plastic trash contributes significantly to the problem of air pollution. Consequently, a wide variety of toxic gases get released into the atmosphere. It is of the utmost importance to develop biodegradable polymers that retain the same characteristics as those obtained from petroleum. In order to decrease the effect that these issues have on the world around us, we need to focus our attention on specific alternative sources capable of biodegrading in their natural environments. Biodegradable polymers have garnered much attention since they can break down through the processes carried out by living creatures. Biopolymers' applications are growing due to their non-toxic nature, biodegradability, biocompatibility, and environmental friendliness. In this regard, we examined numerous methods used to manufacture biopolymers and the critical components from which they get their functional properties. In recent years, economic and environmental concerns have reached a tipping point, increasing production based on sustainable biomaterials. This paper examines plant-based biopolymers as a good resource with potential applications in both biological and non-biological sectors. Scientists have devised various biopolymer synthesis and functionalization techniques to maximize its utility in various applications. In conclusion, recent developments in the functionalization of biopolymers through various plant products and their applications are discussed.
This collaborative study was conducted to determine the total monomeric anthocyanin concentration by the pH differential method, which is a rapid and simple spectrophotometric method based on the anthocyanin structural transformation that occurs with a change in pH (colored at pH 1.0 and colorless at pH 4.5). Eleven collaborators representing commercial laboratories, academic institutions, and government laboratories participated. Seven Youden pair materials representing fruit juices, beverages, natural colorants, and wines were tested. The repeatability relative standard deviation (RSDr) varied from 1.06 to 4.16%. The reproducibility relative standard deviation (RSDR) ranged from 2.69 to 10.12%. The HorRat values were ≤1.33 for all materials. The Study Director recommends that the method be adopted Official First Action.
Here, we examined the effect of black tea and caffeine on lung tumorigenesis in F344 rats induced by the nicotine-derived carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in a 2-year bioassay, NNK was administered s.c. at a dose of 1.5 mg/kg body weight three times weekly for 20 weeks. Animals were given either black tea as drinking water at concentrations of 2%, 1%, or 0.5%, or caffeine in drinking water at concentrations identical to those in 2% and 0.5% tea infusions for 22 weeks, The treatment period began 1 week before and ended 1 week after the NNK administration. The animals were sacrificed on week 101 for the examination of tumors in target organs, including lung, liver, nasal cavity, and other major organs. The NNK-treated group, given 2% black tea, showed a significant reduction of the total lung tumor (adenomas, adenocarcinomas, and adenosquamous carcinomas) incidence from 47% to 19%, whereas the group given 1% and 0.5% black tea showed no change. The 2% tea also reduced liver tumor incidence induced by NNK from 34% in the group given only deionized water to 12%, The tumor incidence in the nasal cavity, however, was not affected by either black tea or caffeine at any of the concentrations tested. The most unexpected finding was the remarkable reduction of the lung tumor incidence, from 47% to 10%, in the group treated with 680 ppm caffeine, a concentration equivalent to that found in the 2% tea. This incidence is comparable to background levels seen in the control group. This study demonstrated for the first time in a 2-year lifetime bioassay that black tea protects against lung tumorigenesis in F344 rats, and this effect appears to be attributed, to a significant extent, to caffeine as an active ingredient of tea.
A method for the screening of antioxidant activity is reported as a decolorization assay applicable to both lipophilic and hydrophilic antioxidants, including flavonoids, hydroxycinnamates, carotenoids, and plasma antioxidants. The pre-formed radical monocation of 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS*+) is generated by oxidation of ABTS with potassium persulfate and is reduced in the presence of such hydrogen-donating antioxidants. The influences of both the concentration of antioxidant and duration of reaction on the inhibition of the radical cation absorption are taken into account when determining the antioxidant activity. This assay clearly improves the original TEAC assay (the ferryl myoglobin/ABTS assay) for the determination of antioxidant activity in a number of ways. First, the chemistry involves the direct generation of the ABTS radical monocation with no involvement of an intermediary radical. Second, it is a decolorization assay; thus the radical cation is pre-formed prior to addition of antioxidant test systems, rather than the generation of the radical taking place continually in the presence of the antioxidant. Hence the results obtained with the improved system may not always be directly comparable with those obtained using the original TEAC assay. Third, it is applicable to both aqueous and lipophilic systems.
Folklore has long supported the role of cranberry juice in maintaining urinary tract health. Now, a significant body of scientific evidence supports this cranberry benefit. Recently, bioassay directed fractionation studies have identified cranberry proanthocyanidins as the compounds responsible for preventing the adhesion of certain E. Coli to the uroepithelial cells. Prior to this discovery, an established analytical method for determining the percentage of cranberry juice in a product has been used to standardize products to ensure the contained a minimum and consistent amount of cranberry. Now, with this evidence for the active component in urinary tract health, valid analytical methods are needed to assure product claims regarding proanthocyanidin content. The analytical methods and the issues faced in validating methods for cranberry proanthocyanidin quantification will be reviewed.
Systematic methods for identification of anthocyanin pigments and their quantitative measurement are well-established because of their importance in food color quality and their usefulness in chemotaxonomic investigations. Interest in their accurate analysis has heightened because of their importance in nutraceuticals and functional foods. Efficient extraction can be achieved with cryogenic milling and acetone extraction. Total anthocyanin content is easily measured with the pH differential spectrophotometric method while HPLC with external standard quantitation is an attractive alternative. Additional spectral procedures provide indices for polymeric color and browning. Reverse phase HPLC with uv-visible diode array detection is the method of choice for tracking qualitative changes. Methods for identification include acid hydrolysis and saponification reactions as well as NMR and electro-spray mass spectroscopy (ESMS).