Health Benefits of Quercetin

Abstract

p>Flavonoids are natural antioxidants derived from plant pigments and commonly found in agricultural produce such as fruits, vegetables, and also in beverages like tea and wine. Quercetin is the most important flavonoid which belongs to the class of flavonol. Quercetin is a vital biologically active compound, which is present in many products, such as onion ( Allium cepa ), black tea ( Camellia sinensis ), Broccoli ( Brassica oleracea var . italic ), and also in red wine and green tea, It is widely used in medicine and pharmaceutics. In particular, it is used for cancer treatment; as it restrains the growth of cancer cells. Earlier some of computational investigations of this molecule were reported in literature, but they were made at low theory level. Quercetin provided many health promoting benefits, like cardiovascular properties, cancer reducing agent, Anti-inflammatory, asthma and many more. That is why the further investigation of this molecule is important. The main important of this review is to understanding of the structure of quercetin and corresponding biological properties of quercetin expressed in vitro studies, absorption is critical, but in vivo studies, better absorbed antioxidant were observed like vitamin C, further reported studies on effect of food processing, health benefits, storage effects, and evaluate its safety and dosage.</p

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1. INTRODUCTION
Flavonoids involve an important group of naturally
occurring, bioactive polyphenolics, popular in plants of
higher generation1. Currently, the interest and awareness on
avonoids have largely focused on two different benecial
aspects. First, for their biological activities, and second for its
anti carcinogenic properties. The anti carcinogenic property of
avonoids is most frequently attributed to their anti oxidant
activity.
Flavonoids are said to be highly effective as an anti-
proliferative agent against lymphoid, colorectal, ovarian, and
breast cancer cells. Similarly, they are identied to induce
chromatin condensation and apoptosis in some cancer cells.
The mechanisms of avonoid induced cytotoxicity are not yet
established, but it is said to inuence the sequential occurrence
of apoptosis2.
Quercetin is a most abundant poly phenolic bioavonoid or
avonoid, which is generally classied as a avonol. Quercetin
is also classied as water-soluble pigments, which cannot be
produced by human. It is also known as a phytoestrogens.
Quercetin, comprising 3 rings and 5 hydroxyl groups, has
many health benecial effects, including improvement of
cardiovascular health and reducing the risk for cancer.
Quercetin, present in fruits and vegetables, is identied
to occur in various forms of glycosides; although its skin
is found to posses quercetin aglycone structure and are in
higher concentration. It is also naturally present as glycone
or carbohydrate conjugates in plants. It is one of the most
profusely present dietary avonoids that are present in apples
(Malus domestica); black and green tea (Camellia sinensis)
onions (Allium cepa) (predominantly in the outer rings);
broccoli (Brassica oleracea).
Quercetin glycosides in the onion extracts were converted
to quercetin and sugars by thermo-stable β-glucosidase enzyme.
It is found to posses several benecial biological activities,
like antioxidant, anti-inammatory, anti-cancer, and anti-
viral properties. The benecial effects of quercetin are limited
due to its sparingly soluble nature in water, which makes its
absorption limited.
2. CHEMISTRY OF QUERCETIN
2.1 Structure
The International Union of Pure and Applied Chemistry
(IUPAC)) nomenclature for quercetin is 3,3’,4’,5,7-
pentahydroxyavanone (or) 3,3’,4’,5,7-pentahydroxy-2-
phenylchromen-4-one with a molecular formula C15H10O7. The
presence of ve hydroxyl groups, at positions 3, 5, 7, 3’, and 4’
in quercetin molecule as shown in Fig. 1, leads to the formation
of and pentamethyl derivatives. It is also commonly termed as
quercetine, sophretin, meletin3.
Quercetin is acts as a building block for other avonoids.
Quercetin is commonly present as an aglycone in food. On
hydrolysis with acid, quercitrin is converted to quercetin and
rhamnose as shown in Fig. 2.
2.2 Chemical and Physical Properties of Quercetin
Quercetin with its high molecular weight (302.24),
Health Benets of Quercetin
R. Kumar*, S. Vijayalakshmi, and S. Nadanasabapathi
Food Engineering and Packaging Division, Defence Food Research Laboratory, Mysuru – 570 011, India
*E-mail: kumardfrl@gmail.com
ABSTRACT
Flavonoids are natural antioxidants derived from plant pigments and commonly found in agricultural produce
such as fruits, vegetables, and also in beverages like tea and wine. Quercetin is the most important avonoid
which belongs to the class of avonol. Quercetin is a vital biologically active compound, which is present in many
products, such as onion (Allium cepa), black tea (Camellia sinensis), Broccoli (Brassica oleracea var. italic), and
also in red wine and green tea, It is widely used in medicine and pharmaceutics. In particular, it is used for cancer
treatment; as it restrains the growth of cancer cells. Earlier some of computational investigations of this molecule
were reported in literature, but they were made at low theory level. Quercetin provided many health promoting
benets, like cardiovascular properties, cancer reducing agent, Anti-inammatory, asthma and many more. That is
why the further investigation of this molecule is important. The main important of this review is to understanding of
the structure of quercetin and corresponding biological properties of quercetin expressed in vitro studies, absorption
is critical, but in vivo studies, better absorbed antioxidant were observed like vitamin C, further reported studies on
effect of food processing, health benets, storage effects, and evaluate its safety and dosage.
Keywords: Quercetin; Flavonoids; Health benets; Food processing; Safety
Defence Life Science Journal, Vol. 2, No. 2, April 2017, pp. 142-151, DOI : 10.14429/dlsj.2.11359
 2017, DESIDOC
Received : 16 February 2017, Revised : 13 March 2017
Accepted : 21 April 2017, Online published : 12 May 2017
REVIEW PAPER

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melting point (316.5 °C) and poor water-solubility makes
it a big challenge for being available for biologically. The
presence of ve hydroxyl groups in the quercetin molecule
makes it lipophilic nature. The Table 1 represents the physical
properties of quercetin. Quercetin derivatives can be lipophilic
or hydrophilic in nature based on the type of substituents in
the molecule. In general, O-methyl, C-methyl and prenyl
derivatives of quercetin are lipophilic in character. They are
synthesised by the glands present on the surface of leaves,
owers and fruits. They can be easily isolated by immersing
the plant tissue in acetone4. The structural decomposition of
quercetin occurs when heated at higher temperatures, wherein
it emits acrid smoke and irritating fumes5.
4-OH-3-methoxy-phenylacetic acid; thereby nally quercetin
formed is absorbed from the small intestine to colon6.
From various studies it was found that 0.07 per cent
to 17.4 per cent of the amount of quercetin consumed was
excreted as quercetin or its conjugates. But the quercetin in
form glycosides was reported to absorb in the rat stomach.
Walgren7, et al, established from his study with invitro studies
of Caco-2 cells, that lack of absorption of the quercetin
glucosides, happens primarily due to the effective efux by
the multi-drug resistance protein 2 transporters. In succeeding
studies conducted with human subjects, it was observed that
the quercetin glucosides were hydrolysed by bacterial enzymes
in the small intestine.
In another study, it was reported that the absorption of
quercetin and quercetin aglycone ranged from 36 per cent to
53 per cent and 65-81 per cent respectively. It was found that
absorption of quercetin in ileostomists, as quercetin glucosides,
quercetin rutinoside and quercetin aglycone was 52±5%, 17
±15% and 24±9%, respectively8-13.
3. EFFECT OF FOOD PROCESSING OF
QUERCETIN
3.1 Thermal Processes on Quercetin
Thermal processes have a great inuence on the
availability of avonoid from foods, based on their magnitude
and duration of exposure. Various thermal processes like
drying, microwaving, heating by an autoclave, roasting,
pasteurisation, blanching have been used and their respective
impact on the avanoid was analysed. The Table 2 listed a few
studies where the effect of heat treatment on the degradation of
quercetin in foods was reported. The authors have reported that
Figure 1. Structure of quercetin (pubchem).
Figure 3. Proposed pathways of quercetin absorption (Source: Wu
et al, 2002) extraction and analysis of quercetin.
C21H20O11 + H2O HCl C15H10O7 + CH3 (CHOH) 4 CHO
Quercetin Quercetin Rhamnose
Figure 2. Hydrolysis of quercetin.
Boiling point Sublimes
Melting point 316.5 °C
Solubility
(a) Very soluble
(b) Soluble
(c) Water
Less than 1 mg/mL at 70 °C
Ether, methanol
Ethanol, acetone pyridine, acetic acid
60 mg/mL at 16 °C
Table 1. Physical properties of quercetin
2.3 Absorption and Metabolism of Quercetin
Initially it was assumed that quercetin is absorbed in
the small intestine following the cleavage of ß-glucoside
linkage by colonic micro ora found in humans, but later on it
was concluded that its absorption was improved by conjugation
with glucose as shown in Fig. 3. It is proposed that quercetin-
3-glucoside on reacting with bacterial enzyme results in the
formation quercetin, which further reacts with colon and tissues
to give 3,4-diOH-phenylacetic acid and isorhamnetin. 3,4-
diOH-phenylacetic acid which is produced, further interacts
with colon and tissues to give 3-OH-phenylacetic acid and
Table 2. Effect of heat treatment on quercetin content
Heat treatment
Food product/avonoids Processing conditions Impact on avonoids content
Grapefruit juices Pasteurisation (95 °C, 80 s) Decrease of quercetin
Bean (quercetin) Atmospheric (100 °C) and pressure boiling (121 °C) with and without
soaking and draining Increases of 1-90% of quercetin
Strawberry juices (quercetin) High intensity pulsed electric elds Pasteurisation (90 °C, 60 s) Stability of quercetin

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that quercetin was labile to heat degradation.
Ranilla14, et al, reported that boiling and
soaking of Brazilian beans at 100 °C along with
or without draining, induced a loss percentage
of 1-90 per cent of quercetin. Thermal
pasteurisation of strawberry juices when
performed at 90 °C for 60 s was reported to
have no effect on detrimental effect on quercetin
contents15, whereas it was proved to reduce
quercetin content in grapefruit juices16,17. The
avonoids in aqueous solutions have showed
to posses different degrees of sensitivity to
heat treatment based on their structures. The degradation of
avonoids may also be inuenced by other parameters such as
pH, phytochemicals and their structure and also by the presence
or absence of oxygen18.
3.2 Mechanical Processes on Quercetin
The commonly processes like peeling, trimming, and
cutting has been studied for its effect on bioactive compounds in
avonoid-rich foods; which is expected to inuence the content,
activity and availability of those bioactive compounds19. High
proportions of avonoids are lost during the pre-processing
step when undesired parts of the product was removed or cut
off. For instance, during peeling and trimming of onions it said
to result in 39 per cent of avonoids to lose20 and great losses
were noticed while peeling and dicing of tomatoes21. However,
in another study, it was reported that cutting increased avonol
content in fresh-cut potatoes22 and onions23.
3.3 Domestic Processes on Quercetin
Several studies were investigated to nd out the effects on
avonoid degradation under simulated home food preparation
conditions as shown in Table 3. Common domestic processes
methods like boiling, frying, baking, sautéing were performed.
Boiling was reported to result in avonoids losses of 43.9 per
cent for asparagus spears and 20.5 per cent for onions, due
to leaching of avanoids into the cooking water24. Similarly,
avanoid losses in onions were reported25-27. Lombard28, et al.
reported that sautéing resulted in a 25 per cent increase in the
avonoid content of onion. But the frying process was reported
to decrease about 25-33 per cent of avonoid content in
onion25,27. Conversely, baking was found to increase the amount
of quercetin conjugate and total avonol content (7 per cent)
in onions, due to the loss of water and other volatiles during
cooking and thereby making these compounds concentrated in
the tissues25,26.
4. EFFECT OF STORAGE ON QUERCETIN
The effect of storage conditions on the nutritional quality
of food can be a limiting step28. The degradation of avanoid is
inuenced by the storage duration, temperature and the presence
and intensity of light. The inuence of storage temperature and
time need to be controlled to reduce the effect on the avanoid
degradation. The quality degradation has been found to vary
with state of food (fresh or processed) when evaluated for the
effect of storage temperature (0 °C and 20 °C) under dark or
light exposure conditions as shown in Table 4.
The lower temperature storage of fresh has been reported
to result in minimal effect on the avanoid degradation. Price27,
et al. reported that nil effect was acquired in onion quercetin
conjugate content when stored under dark condition at 4°C
temperature for 6 months. Lopez-Rubira29, et al. reported
the effect on the antioxidant activity was insignicant in the
pomegranates stored at 1 °C for 13 days. In contrary to this,
Vina and Chaves30 reported 47 per cent loss in total avanoid
content of pre-cut celery, when stored at 0 °C for 21 days. An
increase in the avanoid content was reported22,31. The potato
strips when stored at 4 °C and exposed to light, was reported
to have a higher avanoid accumulation rate22. Wang31, et al.
reported that storage of raspberries 16 °C/24 °C for 4 days
induced an increase in it’s the phenolic content.
The quercetin content of strawberry juices was found to
decrease progressively on storage at 4 °C in darkness for 56
days15. In another study on raspberry jams, 40 per cent loss
of quercetin 3-glycoside was reported when it was stored in
dark at 20 °C for a period of 6 months32. Though the studies
have proved the effect of storage conditions such as time,
Table 3. Effects of domestic treatment on quercetin content
Domestic processes
Food product Processing condition Impact on avonoid content
Onions Sautéing (5 min),
baking (15 min, 176 °C) Increase of quercetin conjugates
Brown skinned
onions
Boiling (20 min) A 14.3% loss of quercetin conjugates
Frying (5 min, 15 min) 23-29% Losses of quercetin conjugates
Red skinned
onions
Boiling (20 min) A 21.9% loss of quercetin conjugates
Frying (5 min, 15 min) 23-29% Losses of quercetin conjugates
Effect of storage conditions
Food product/ avonoids Storage conditions Impact on avonoids content
Fresh foods pomegranate Storage (13 days, 1°C) No effect on antioxidant activity
Fresh-cut potatoes (avonols) onions
(quercetin conjugates)
Storage at 4 °C under light Long-term
storage in darkness (6 months,4 °C)
A 100% increase of avonol content
and no effect on quercetin conjugates
Enriched tea drink
Strawberry juice (quercetin)
Storage (6 months, 4 °C) Refrigeration in
darkness (56 days, 4 °C) Decrease of quercetin
Raspberry jams (quercetin 3-glycoside) Storage (6 months, 20 °C) 40% loss of quercetin3-glycoside
Table 4. Effect of storage conditions on quercetin

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temperature and lighting, on the degradation of the avanoids,
the effect cannot generalised, as the degree or type of inuence
varies with the type of product and its nature, and with storage
condition.
5. EFFECT OF LIGHT ON QUERCETIN
The photodegradation of avanoid has been investigated
earlier33-35. The photodegradative effect on the avanoids was
reported to either increase or decrease, based on the state of
the food (fresh or processed foods). The stress signal caused
by the light exposure enhances the avanols in fresh foods56
such as fresh-cut potatoes and onions22,25. In a study on the
effect of illumination on fresh cut onons, 8 per cent increase
in the quercetin was reported. The exposure of the blueberries
to UV-C increased the avonoid content and the antioxidant
activity as well. Wang31, et al. reported an increase in the
phenolic content of the raspberries when exposed light.
The effect of light, primarily on the photodegradation of
phenols was reported to be dependent on various variables like
wavelength of light, pH, concentration and its structure, based
which positive or negative effects were obtained.
According to Tommasini36, et al. structural rearrangement
of 3-hydroxyavone, occurred rapidly when irradiated at 254
nm than when it was exposed at 350 nm. It was also reported
to be highly inuenced by the physicochemical properties
of the solvent, which played a vital in determination of the
occurrence of a photo-oxidation or photo-induced molecular
rearrangement.
6. HEALTH BENEFITS OF QUERCETIN
The versatile nature of quercetin contributes too many
benecial biological properties such as antioxidant action,
canker sores, neurological effect, antiviral activity, anti-
inammatory, asthma, cardiovascular properties and as a
anticancer agent.
6.1 Antioxidant Action
The antioxidant property of the avanoids principally
neutralises the free radicals by donating hydrogen atoms to it.
Pietta37, et al. observed that difculty aroused on correlating
the structure of avonoids and their accountability for radical-
scavenging.
The formation of reactive oxygen species (ROS) has
been reported to contribute to the diabetes, atherosclerosis,
hypertension, ischemic heart disease and heart failure. Quercetin
acts as an antioxidant by preventing oxidative stress, the major
cause for generation of ROS. The avonoids comprising 3-OH
and 3`, 4`-catechol were known to be ten times more effective
towards peroxynitrite than ebselen, a RNS scavenger38.
Quercetin is widely known for its antioxidant property that
is for its ability to scavenge free radicals and bind transition
metal ions. The ultimate effects on the humans by quercetin for
its antioxidant property need to streamline to obtain signicant
impact on the biomarkers/ indices to be measured. In a study, the
consumption of a test meal of fried onions was reported to have
signicantly increased the plasma quercetin levels. Though
an increase in the total antioxidant activity of the plasma was
noted, not much difference occurred in the oxidation of the
plasma or isolated low density lipoprotein (LDL) over the 48-h
period following the consumption of the fried onions. The
two weeks supplementation of quercetin in healthy subjects
(150 mg/day) was reported to have minimal inuence on the
plasma, its antioxidant capacity, oxidised LDL, or alpha- or
gamma-tocopherols.
6.2 Neurological Effects
Quercetin has been proved to be neuroprotective as well
as neurotoxic. Joseph34, et al. reported to be neuroprotector
in rat brain when used in combination to sh oil, where it
benecial effects against neurodegenerative diseases (e.g.
Alzheimer’s disease). Choi40, et al. showed inhibitory effects
against acetylcholinesterase. Quercetin was reported to have
decreased the 6-hydroxydopamine induced oxidative stress in
the neurons of brain striatum of rats56. In another study, it was
reported that the quercetin treatment affected the working of
the nervous system by depleting the intracellular glutathione
contents41. On the other hand, whether the prolonged usage
of antioxidant supplements can be considered safe for human
health is still a big question.
6.3 Antiviral Activity
Quercetin has been reported to be effective against viruses
i.e. it posses antiviral activity against enveloped viruses such
as herpes simplex type I, parainuenza type 3, respiratory
syncytial, pseudorabies, and Sindbis. It was also proved to
be protecting from the cardio virus42. The antiviral activity of
quercetin was due to its ability to bind to viral coat protein
and polymerases and also to damage DNA. The mutagenic,
carcinogenic, and anti carcinogenic activity of quercetin was
found to be related to its ability to impose or prevent damage
to DNA. It was reported that on stabilisation of Quercetin with
ascorbate it enhances its antiviral activity, which was similar
to the effect induced by ascorbate enhanced antiproliferative
effect on squamous cell carcinoma43. Quercetin was also proved
to have enhance the antiviral activity of agents like interferon
and 5°ethyl-2’-deoxyuridine.
6.4 Anticancer Agent
Quercetin and other avonoids, derived from fruits and
vegetables have been marked important compounds as it was
considered to positively help in preventing cancer. Various
studies has been performed to evaluate the anti-carcinogenic
effect of quercetin on cell cultures, where it was found that
slow the growth of cancer cells was effected and it also helped
to foster apoptosis. The induction of apoptosis in cancer cells
has been proved to be an vital step in the development of novel
anticancer drug44. Some animal studies conducted have shown
that quercetin helps in the protecting form certain type of
cancers, especially colon cancer45.
6.5 Canker Sores
Small and shallow lesions known as the canker sores
(aphthous ulcers), occur on the soft tissues in mouth or at the
base of gums. Sharma45, et al. proved that quercetin reduced
the occurrence of mouth sores and also helps to induce mild
symptomatic relief.

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6.6 Cardiovascular Properties
Heart diseases have been identied to be the primary and
leading cause of mortality in the developed countries. Though
the exact reason for the cause and the mechanism involved
in the occurrence of heart disease still remains a mystery,
oxidative stress and inammation has been identied to play
a vital role. Quercetin has been investigated for its possible
utilisation as a safe alternative to the antioxidant and anti-
inammatory drugs used for conditions like cardiovascular
disease. The studies have revealed that, both preclinical and
clinical study, quercetin positively reduced several of the risk
factors related with heart disease, including blood pressure and
cytokine-induced C-reactive protein (CRP) expression. It has
also been identied as a potent vasodilatory agent.
6.7 Anti-inflammatory
The normal biological process in response to injuries,
microbial infection or intoxication and chemical irritation
was known as inammation. Inammation was generally
considered to be initiated by the migration of immune cells
from blood vessels to the infected/ injured area and discharge
of mediators to combat the infection/injury.
Quercetin has been widely known for its anti-inammatory
activity. During a in vivo study conducted by Lin46, et al., when
the rats were treated with quercetin mixed with polysorbate 80,
it resulted in the inhibition of edema in the paw of the rats. The
applications of quercetin glycoside through the skin surface
were found to be ineffective against inammation due to low
absorption value. The quercetin pentamethylether formulation
was highly absorbed through the skin route in rat, and it was
found to be effective against inammation, therby proving it to
be a potent anti-inammatory agent.
6.8 Asthma
Asthma is a chronic lung-disease that swells and narrows
the airways, thereby causing difculty in breathing. Quercetin
was found to ease the symptoms of asthma. It was found to
induce reduction in the inammatory immune cells number
and activation, cuts off the histamine level and also eases the
airway smooth muscle. Rigolin47, et al. reported that even at
the minimum concentration, quercetin was effective against
asthma, in comparison to the standard asthma maintenance
medications and steroid inhalers that reduces the resistance to
air ow.
Quercetin was also reported to reduce pathologies of
asthma, such as eosinophil and neutrophil enrollment, bronchial
epithelial cell activation, mucus and collagen production and
airway hyperactivity. The dietary intake levels of quercetin
were reported to inuence the asthma symptoms. The clinical
studies performed revealed the possible application of quercetin
to prevent or treat asthma in human patients.
7. NEGATIVE EFFECTS OF QUERCETIN
Quercetin which was generally considered to be safe was
reported to result in few side effects like headache and discomfort
of stomach. A preliminary study conducted, suggested that the
byproduct of quercetin leads to the loss of protein function.
It has also been reported that very high doses of quercetin
may harm the kidneys and thereby it was suggested to take
intermittent breaks during the consumption of quercetin. It was
advised that pregnant and breastfeeding women and people
with kidney disorder should avoid quercetin. Consumption
of doses greater than 1 g per day, have been reported to have
caused damage to the kidneys.
In a four-week rat study performed by Azuma48, et al.
increase in the ratio of weight of liver and kidney to the body
weight ratios was observed when fed with more than 314 mg
and 157 mg quercetin/kg body weight/day, respectively. The
consumption of doses above 157 mg quercetin/kg body weight/
day resulted in a pro-oxidant effect.
In human studies, it was seen that the quercetin content has
commonly been well tolerated. It was proved that consumption
of doses up to 1,000 mg/day for several months have not
induced any adverse effects on blood parameters of liver and
kidney function, hematology, or serum electrolytes. At present,
the principal concern for toxicity was the co-administration of
high quercetin doses with digoxin. Though it has been proved
to be toxic, until more studies pertaining to the safe dosage
level determination, it suggested to avoid consumption of
quercetin along with digoxin31.
8. SAFETY AND DOSAGE OF QUERCETIN
Several studies, have shown that the higher doses of
quercetin more than 200 μm reduced the cell viability49; but
low doses of quercetin (<200 μm) was reported to increase the
cell viability and to be xed as therapeutic dose. It was reported
that a low dose of quercetin also resulted in the inhibition of
the proliferation of breast cancer cells, mild cytotoxic effect,
and also induce mild DNA damage. The fruit and vegetable
consumption was reported to contribute to an average of 15 mg
to 40 mg of quercetin per day from the diet. It was suggested
that an increase in quercetin intake could be accomplished
by increasing the consumption of more fruit and vegetables.
Therapeutic dosages of quercetin intake were denoted to range
from 250 mg to 500 mg three times per day. Quercetin was
generally available, in the form of capsules or tablets ranging
in doses from 50 mg to 500 mg, as dietary supplements. The
dosage of quercetin has been recommended based on the health
condition to be treated and no standard dose for quercetin has
been suggested. According to Werbach50, et al, for allergic
conditions and for chronic hives, a dose of 250 mg - 600 mg
per day and 200 mg - 400 mg has been recommended. It was
reported that a low dose of quercetin was sufcient to inhibit
the proliferation of breast cancer cells, mild cytotoxic effect,
and to induce mild DNA damage51.
9. DIETARY SOURCE OF QUERCETIN
Scientists have involved in the process of identication
and quantication of quercetin from various food sources.
It was reported that on comparing the quercetin content in
onion peel with that in its esh, the highest concentration was
found in the peels of onion52. It has been normally found in
a variety of foods like onions, apples, berries, tea, tomatoes,
grapes, shallots, brassica vegetables, many seeds, nuts,
owers, barks, leaves and also in some medical plants (ginkgo
biloba, cranberries and St. John’s wort). The aglycone form

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of quercetin was found in much lesser amounts in the diet
generally consumed. Hollman8, et al. analysed the glycoside
and aglycone form of quercetin extracted from plants, and
quantied using High-performance Liquid Chromatography
(HPLC). The Table 5 represents the list of items and their
quercetin content as reported by the United States Department
of Agriculture53.
11. CONCLUSIONS
Quercetin, a avonoid has been proved to be a powerful
antioxidant which can be derived from raw foods such as fruit
and vegetables, cocoa, tea, coffee, etc. Quercetin was also
known to provide various benecial properties for human health
as a anti-oxidant, anti-inammatory agent, antiviral activity,
cardiovascular properties and anticancer properties. The health
benets of quercetin can be preserved in the processed foods by
adapting less intense and non-aggressive processes. However,
providing the consumers, antioxidants enriched food products
may not be an easy task, despite the several studies conducted
on the effect of food processes on the degradation of quercetin
and their functional activities, it has been difcult to generalize
the results and adapt. Many factors such as:
(i) The type of raw food
(ii) Standardisation of processing and analytical methods
(iii) The inuence of the food matrix, affect the quercetin
content extraction, analysis and it properties as well.
The usage of quercetin for its anti-oxidative and anti-
inammatory property has been well established. Interestingly,
these were the two effects of quercetin which has been widely
dealt to combat the oxidative stress and inammation proving
it to be a major source of supplementation for those who have
been suffering from this problem.
The major toxicological work related to the quercetin and
its by product has been widely studied with the in vitro studies.
The formation of toxic compounds from quercetin upon
oxidation, during its ROS scavenging activities were likely
to occur. The primary oxidation product of quercetin formed
was found to be orthoquinone, which has been proved to be
toxic. As a result, the supplementation of quercetin during the
in vivo studies has to be done with utmost care, considering
the possibility of toxic compounds/ metabolite formation,
especially in the treatment of chronic ailments.
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CONTRIBUTORS
Dr R. Kumar, obtained his MSc (Food Science & Nutrition)
from Tamil Nadu Agricultural University, Coimbatore and
PhD (Food Science) from Bharathiyar University, Coimbatore.
Presently working as Scientist ‘F’ in DFRL, Mysuru. He has 65
research papers and 10 patents to his credit. He has received
many awards including DRDO Performance Excellence Award
and Thomson Edition Award. He has research experience in
thermal, non-thermal food processing technologies and food
packaging.
Contribution in the current study, he did collection of relevant
literature, preparation of manuscript and correction.

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KUMAR, et al.: DEF. LIFE SCI. J., VOL. 2, NO. 2, APRIL 2017, DOI : 10.14429/dlsj.2.11359
Ms S. Vijayalakshmi obtained her MSc (Food Science and
Technology) from Pondicherry University. Presently she is
working as Senior Research Fellow in DFRL, Mysuru. She
has published more than 10 research and review papers. Her
research interest includes: Reduction of Aflatoxin contamination
by the use o f pulsed e le ct rical field ( PE F) proce ss in g and
combination processing.
Contribution in the current study, she is involved in writing
of manuscript.
Dr S. Nadanasabapathi obtained his MSc (Chemistry) from
Annamalai University and PhD (Chemistry) from University
of Mysuru. Presently working as Scientist ‘G’ and Head,
Food Engineering & Packaging in DFRL, Mysuru. He has 95
research papers and 15 patents to his credit. He has received
DRDO Performance Excellence Award, Thomson Edition Award,
Technology Group Award, and Laboratory Scientist of the Year
Award. He has research experience in the : Food packaging,
thermal and non thermal food processing technologies.
Contribution in the current study, he is involved in final
correction and editing of the manuscript.