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Stewart Postharvest Review
An international journal for reviews in postharvest biology and technology
© 2007 Stewart Postharvest Solutions (UK) Ltd.
Online ISSN:1945-9656
www.stewartpostharvest.com
Importance of the phytochemical content of fruits and vegetables to
human health
Limei Chen1, Clément Vigneault1,2*, GS Vijaya Raghavan1, Stan Kubow3
1Department of Bioresource Engineering, Macdonald Campus, McGill University, 21111 Lakeshore Road, Sainte-Anne-de-
Bellevue, Quebec, Canada
2Agriculture and Agri-Food Canada, Gouin Boulevard, Saint-Jean-sur-Richelieu, Quebec, Canada
3School of Dietetics and Human Nutrition, McGill University, 21111 Lakeshore Road, Sainte-Anne-de-Bellevue, Quebec, Canada
Abstract
Purpose of review: Numerous studies have identified a significant inverse association between fruit and vegetable consumption and
the incidence of many diseases, including cardiovascular diseases, cancer, diabetes, osteoporosis and vision diseases. Phytochemicals
contained in plant foods play important roles in disease prevention. This article reviews the importance of certain major phytochemi-
cals, their possible mechanisms of action and the effects of certain physical treatments on the phytochemical content of fruits and vege-
tables.
Recent findings: Every year, numerous scientific publications, science books and even articles and advertisements for the general pub-
lic appear on the positive effects of a specific phytochemical or combination of phytochemicals. However, published books, articles,
sayings and rumours about undemonstrated effects of fruits and vegetables are still widely available. It is important to distinguish be-
tween these kinds of information and to continue to dismiss or demonstrate these effects. The present article is based only on scientific
demonstrations of the effects of phytochemicals on human or animal health.
Directions for future research: An increasing number of convincing studies show the benefits of the phytochemicals in fruits and
vegetables. It is very important to understand their functions and to promote increased fruit and vegetable intake. Since a wide variety
of horticultural produce contains high concentrations of several specific classes of phytochemicals, maintaining a diet that contains a
variety of fruits and vegetables will help the world’s population achieve the combined benefits of the phytochemicals. There is still a
significant need for further investigation into their potential benefits and mechanisms of action, as well as for development of the best
commercial-scale treatments for postharvest produce to improve phytochemical content.
Keywords: phytochemical; fruit; vegetable; physical treatment
Abbreviations
CA Controlled Atmosphere
MAP Modified Atmosphere Packaging
UV Ultraviolet
CVD Cardiovascular Disease
LDL Low-density Lipoprotein
UTI Urinary Tract Infection
*Correspondence to: Clément Vigneault, Agriculture and Agri-
Food Canada 430 Gouin Boulevard, Saint-Jean-sur-Richelieu,
Quebec, Canada J3B 3E6. email: vigneaultc@agr.gc.ca
Stewart Postharvest Review 2007, 3: 2
Published online 01 June 2007
doi: 10.2212/spr.2007.3.2
Introduction
Phytochemicals, also known as phytonutrients, are non-
nutritive plant chemicals that have protective or disease-
preventive properties. These complex molecules are found
in most foods, especially in fruits and vegetables. Numerous
epidemiological studies have shown that there is a consider-
able association between fruit and vegetable consumption
and low risk of many diseases. It was once assumed that
vitamins and minerals played a significant role in disease
prevention; however, recent studies indicate that phyto-
chemicals can make a much greater contribution than vita-
mins or other nutrients. Phytochemicals are associated with
the prevention of certain chronic diseases, including cardio-
vascular diseases (CVDs), cancer, diabetes, osteoporosis
and vision diseases, which are especially severe in Western
Chen et al. / Stewart Postharvest Review 2007, 3:2
2
countries. These diseases are mainly attributed to a high-fat
and high-sugar diet, lack of exercise, smoking and other un-
healthy lifestyles.
Fruit and vegetable consumption is inversely associated with
the incidence of many types of cancer [1, 2], including stom-
ach, colon, breast, lung and prostate cancers. Phytochemicals
in fruits and vegetables are mostly responsible for a protective
effect against these diseases. It appears that there are many
possible ways to affect cancer development. Most cancers re-
sult from the interaction of carcinogens or oxidants with DNA.
The strong antioxidant ability of phytochemicals appears to
reduce this damage [3]. Furthermore, phytochemicals inhibit
phase I enzymes, which initiate carcinogenesis, thus reducing
the risk of carcinogenesis, and they also induce phase II en-
zymes, which detoxify and excrete carcinogens, resulting in
less DNA damage and preventing carcinogenesis initiation [4,
5]. Also, phytochemicals can reduce the rate of cancer spread
by slowing the proliferation of cancer cells [6, 7].
The benefits of phytochemicals in terms of CVDs such as
coronary heart disease and stroke have been identified by
many studies [8, 9]. The mechanism of action may be the
ability of some phytochemicals to inhibit the synthesis of
low-density lipoproteins (LDLs), components that are be-
lieved to contain “bad” cholesterol. When cholesterol is at a
high level, it becomes a key factor in the development of
most CVDs. Some phytochemicals have been shown to have
an anti-inflammatory function. Inflammation involves the
secretion of oxidants and aggregation of platelets, which ini-
tiate blood clotting [10, 11] and thereby induce stroke. As a
result, certain phytochemicals prevent strokes from occurring
by reducing inflammation or inhibiting clot formation.
Thousands of phytochemicals have been identified in fruits
and vegetables, and they are grouped into several classes
according to their chemical structure and biological activity
(Table 1). The classification, however, is still quite contro-
versial. Although the importance of the individual phyto-
chemical classes will be discussed in the following section,
the benefits of phytochemicals to human health are the result
of synergistic effects.
Some major phytochemicals
Carotenoids
Carotenoids are widespread plant pigments that contribute to
the yellow, orange and red colours of fruits and vegetables.
Over 600 different carotenoids have been identified to date.
Of those, about 50 can be converted to Vitamin A. It is esti-
mated that approximately 60% of dietary vitamin A comes
from plant food sources [12], and the interest in obtaining
vitamin A from fruits and vegetables keeps growing. Vitamin
A hypervitaminosis cannot be caused by excessive intake of
carotenoids, since they convert to vitamin A only when it is
needed in the body. Additionally, carotenoids are well known
for their antioxidant property, which is associated with a re-
duction in the risk of several cancers, CVDs, macular degen-
eration and cataracts, as well as enhancement of the immune
system [13, 14].
Beta-carotene, which has the highest provitamin A activity, is
found mainly in orange-coloured fruits and vegetables and
dark green leafy vegetables, including carrots, pumpkin,
sweet potato, apricot, spinach and kale [15]. In addition, beta-
carotene may protect the skin from ultraviolet (UV) irradia-
tion [16]. Hundreds of studies have shown that people who
eat more beta-carotene-rich fruits and vegetables have lower
risks of cancer or heart disease [17].
Lycopene is a red carotenoid found in tomato, watermelon,
pink grapefruit and other red fruits, and it has been recog-
nised as the most effective antioxidant in the family of caro-
tenoids. Many animal and human studies have shown that
lycopene has a protective effect against carcinogens in the
liver, brain, colon, breast, cervix and prostate, therefore pre-
venting or delaying certain types of cancer [18–21]. In addi-
tion, lycopene has a preventive effect against coronary heart
disease [22].
Some specific carotenoids such as lutein and zeaxanthin that
are contained in green and yellow leafy vegetables can play
an important role in reducing the risk of age-related macular
degeneration and cataracts, the most common causes of vis-
ual impairment in North America [23]. Lutein and zeaxanthin
are the only carotenoids that accumulate in the macula of the
human retina, which may contribute to their association with
prevention of eye diseases.
Flavonoids
Flavonoids are a group of phenolic compounds that includes
anthocyanins, catechins, flavanones, flavones, isoflavones
and flavonols. More than 4,000 flavonoids have been identi-
fied, and they are widely found in fruits and vegetables,
mostly concentrated in berries, citrus fruit, broccoli, cabbage,
cucumber, green pepper, etc. Flavonoids have been shown to
have a wide range of benefits to human health, such as the
ability to prevent cancers, cardiovascular disorders, urinary
tract infections (UTIs) and other degenerative diseases [24–
26]. These protective effects of flavonoids against diseases
Phytochemical class Major phytochemicals
Terpenoids Carotenoids, saponins, limonoids
Phenolics Flavonoids, phenolic acids, tannins, lignans
Organosulphur compounds Glucosinolates, isothiocyanates, indoles
Alkaloids and nitrogen-
containing compounds
Piperidine, pyrrolidine, quinoline
Table 1. Classification of phytochemicals.
Chen et al. / Stewart Postharvest Review 2007, 3:2
3
may be associated mainly with their strong antioxidant prop-
erty [27, 28], as well as with other biological properties, in-
cluding action against allergies, inflammation, free radicals,
hepatotoxins, platelet aggregation, bacteria, viruses, ulcers
and tumours [29].
Anthocyanins are red pigments in cherry and strawberry, as
well as blue pigments in blueberry. The antioxidant property
of anthocyanins is mainly due to free-radical scavenging in
biological systems. This ability might be beneficial to ath-
letes because heavy exercise can increase oxygen utilisation,
resulting in a significant increase in free radical generation
[30]. It is well known that free radicals are responsible for
damaging important cellular components such as DNA and
the cell membrane; however, studies are still controversial
regarding whether antioxidant supplementation can lessen
exercise-induced oxidative stress [31]. In addition, antho-
cyanins are involved in the treatment of capillary fragility
[32].
Proanthocyanidins are found in berries, especially cranberry,
blueberry, blackberry and black raspberry. They have been
shown to have a function of reducing the risk of UTIs, which
develop when bacteria are introduced into the urinary tract
and stick to tissues in the body. Proanthocyanidins and cer-
tain other flavonoids have the ability to bind to cell walls,
thus preventing the adhesion of bacteria to tissues. Some
studies have also indicated that cranberry is effective in de-
creasing the congregation of certain substances that cause
tooth decay, thereby improving dental health [33]. Another
study has shown that consumption of cranberry juice inhibits
excessive platelet aggregation, which leads to blood vessel
blockage [34].
Quercetin is one of the key flavonols, which are the most
widespread flavonoids in foods, and is mainly contained in
apple skin, red onion and red grape. Quercetin is one of the
best antihistamines for relieving allergy symptoms and may
also interact with specific carcinogens in the gastrointestinal
tract [35]. Many studies have found an inverse association
between quercetin intake and coronary heart disease, which
may be attributed to the actions of preventing LDL oxidation,
reducing damage to DNA and inhibiting platelet aggregation
[36–38].
Glucosinolates
Glucosinolates are a group of organosulphur compounds that
can be transformed into isothiocyanates and indoles. Vegeta-
bles such as cabbage, kale, broccoli, cauliflower and Brussels
sprout account for the bulk of glucosinolate consumption.
Indoles, which are found in cabbage, broccoli and other cru-
ciferous vegetables, are known to have anticarcinogenic
properties, as well as a detoxification ability. Indole-3-
carbinol, one of the indole derivatives, is an inhibitor of
chemically-induced cancer [39], mostly because it can boost
carcinogen metabolism capacity [40]. In addition, indole-3-
carbinol can activate cytochrome P450 enzymes, which have
been shown to metabolise oestrogen [41], and can therefore
markedly reduce breast and uterine cancers.
Isothiocyanates are widely distributed in cruciferous vegeta-
bles, such as watercress, broccoli and radish. It has been re-
ported that isothiocyanates can activate phase II detoxifica-
tion enzymes and suppress phase I cancer-promoting en-
zymes, actions that may contribute to the inhibition of tu-
morigenesis [42]. One study has shown that watercress con-
sumption accelerates excretion of a pulmonary carcinogen
that is one of the causes of lung cancer in smokers [43]. In
addition to reducing the risk of lung cancer, isothiocyanates
have also been shown to have a preventive effect against tu-
mours in other organs, including the mammary gland, liver,
bladder, oesophagus, pancreas and colon [42, 44].
Effects of physical treatments on phytochemi-
cals in fruits and vegetables
With the public’s growing awareness of environmental is-
sues, many environmentally friendly technologies aimed at
improving the quality of agricultural produce, including heat
treatment, modified atmosphere packaging (MAP), controlled
atmosphere (CA) storage, UV irradiation and other chemical-
free treatments, have been studied. Many studies have re-
ported that such treatments also positively affect the levels of
phytochemicals in postharvest produce.
Numerous studies have shown that the application of heat
treatment, such as exposure to hot dry air, hot water dipping
or hot water drenching, has a beneficial effect in terms of
reducing decay development, chilling injury and superficial
scald. Certain studies have also reported the effect of heat
treatment on the phytochemical content of produce. In to-
mato, melon and mango, for example, hot water treatment (at
35°C for 12 h, 45°C for 3 h and 55°C for 5 min) has been
reported to delay anthocyanin synthesis and thus protect the
red colour pigment in postharvest produce [45–47].
Low doses of UV irradiation elicit pathogen resistance in
fruits and vegetables and generate clear increases in stress-
response compounds such as phenols, flavonoids and phy-
toalexins [48–50]. For example, it has been suggested that
UV treatment could be used to increase the levels of resvera-
trol in grape [51], flavanones in citrus fruit [48] and antho-
cyanins in peach [52]. Also, research has determined that
anthocyanins and quercetin, found in strawberry and onion,
are enhanced by UV irradiation after harvest [53].
Atmosphere modifications, such as CA storage and MAP,
have been recognised as an effective method for improving
the quality of postharvest produce and have been widely ap-
plied. Furthermore, altered gas composition treatment also
affects the phytochemical content of fruits and vegetables.
For example, CA storage of mature pepino fruit using high
CO2 concentrations (15% for 2 days followed by 5% for 19
Chen et al. / Stewart Postharvest Review 2007, 3:2
4
days) maintained the chlorophyll and beta-carotene contents.
However, continuous high CO2 concentrations (15% for 14
days) resulted in a significant decrease in chlorophyll and
beta-carotene [54]. It has also been shown that the glucosi-
nolate content increased in broccoli stored under CA for 7
days, while the absence of O2 with a 20% CO2 concentration
caused a decrease in this phytochemical [55].
The above findings generally indicate that suitable treatments
applied postharvest could have a positive effect on the phyto-
chemical content of fruits and vegetables. However, inappro-
priate treatments would reduce the health benefit properties
of the produce. Detailed discussions about specific treatment
are presented in the same journal issue in separate review
articles.
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