When the critical balance between generation of free radicals and the antioxidant defenses is unfavorable, oxidative damage can accumulate. Oxidative stress is defined as “a condition that is characterized by accumulation of non-enzymatic oxidative damage to molecules that threaten the normal function of the cell or the organism” (Blomhoff, 2005). Compelling evidence has emerged that oxidative stress makes a significant contribution to a lot of diseases.
An antioxidant enzyme is “a
protein that limits oxidative stress“ (Blomhoff,
2005).
A plant-based diet protects
against chronic oxidative stress-related diseases. Dietary plants contain
variable chemical families and amounts of antioxidants. This is a comprehensive
food database consisting of the total antioxidant content of typical foods as
well as other dietary items such as traditional medicine plants, herbs and
spices and dietary supplements.
The results demonstrate that
there are several thousand-fold differences in antioxidant content of foods.
Spices, herbs and supplements include the most antioxidant rich products, shown
in a lot of studies, some exceptionally high.
It shows that plant-based foods
introduce significantly more antioxidants into human diet than non-plant
foods.
It is widely accepted that a
plant-based diet with high intake of fruits, vegetables, and other
nutrient-rich plant foods may reduce the risk of oxidative stress-related
diseases [1-6].
Antioxidants can eliminate free
radicals and other reactive oxygen and nitrogen species, and these reactive
species contribute to most chronic diseases. It is hypothesized that
antioxidants originating from foods may work as antioxidants in their own right
in vivo, as well as bring about beneficial health effects through other mechanisms,
including acting as inducers of mechanisms related to antioxidant defense [7,8], longevity [9,10], cell maintenance and DNA repair [11].
Several assays have been used
to assess the total antioxidant content of foods,
A complex endogenous
antioxidant defense system has been developed to counteract oxidative damage
and oxidative stress. Such an antioxidant defense is essential for all aerobic
cells. The endogenous antioxidant defense has both enzymatic and non-enzymatic
components that prevent radical formation, remove radicals before damage can
occur, repair oxidative damage, and eliminate damaged molecules (Halliwell, 1996; Gutteridge & Halliwell, 2000;
Lindsay & Astley, 2002).
In addition to the
endogenous antioxidant defense, it has been hypothesized that dietary
components also may contribute to the antioxidant defense either by providing
redox active compounds that can directly scavenge or neutralize free radicals
or other ROS and RNS, or by providing compounds that can induce gene expression
of the endogenous antioxidants (Blomhoff, 2005).
DIETARY COMPOUNDS WITH THE
ABILITY TO INDUCE
PRODUCTION OF ENDOGENOUS
ANTIOXIDANTS
An important antioxidant
defense mechanism involves detoxification enzymes.
Dietary plants rich in
compounds that induce detoxification enzymes include the vegetables broccoli,
Brussels sprouts, cabbage, kale, cauliflower, carrots, onions, tomatoes,
spinach and garlic. The evidence for phase 2 enzyme inductions at ordinary
intake levels of plant foods in humans is, however, limited, and the importance
of this defense mechanism in the overall protection against oxidative damage is
still uncertain.
DIETARY COMPOUNDS WITH THE
ABILITY TO DIRECTLY
SCAVENGE OR NEUTRALIZE
REACTIVE OXIDANTS
In addition to the
well-known antioxidants, vitamin C, vitamin E, and selenium, there are numerous
other antioxidants in dietary plants. Carotenoids are ubiquitous in the plant
kingdom, and as many as 1000 naturally occurring variants have been identified.
At least 60 carotenoids occur in fruit and vegetables commonly consumed by
humans (Lindsay & Astley,
2002).
2002).
Phenolic compounds are
also ubiquitous in dietary plants (Lindsay &
Astley, 2002).. Over 8000 plant phenols have been isolated. Plant
phenols are antioxidants.
MEASUREMENTS OF TOTAL
ANTIOXIDANT CONTENTS IN FOODS e
METHODOLOGICAL
CONSIDERATIONS
Several assays have been
used to assess the total antioxidant content of foods.
TOTAL AMOUNTS OF
ANTIOXIDANTS IN FOODS
We have recently performed
a systematic measurement of the total antioxidant content of more than 3100
foods. This novel antioxidant food table enables us to calculate the total
antioxidant content of complex diets, to identify and rank potentially good
sources of anti- oxidants, and to provide the research community with
comparable data on the relative anti- oxidant capacity of a wide range of
foods.
There is not necessarily a
direct relationship between the antioxidant content of a food sample consumed
and the subsequent antioxidant activity in the target cell. Factors influencing
the bioavailability of phytochemical antioxidants include the food matrix,
absorption, and metabolism. Also, the methods measuring total antioxidant
capacity do not identify single antioxidant compounds, and they are therefore
of limited use when investigating the mech- anisms involved. This is, however,
not the scope of this initial study. With the present study, food samples with
high antioxidant content are identified, but further investigation into each
individual food and phytochemical antioxidant compound is needed to identify
those which may have biological relevance, and the mechanisms involved.
The aim of the present
study was to screen foods to identify the total antioxidant capacity of fruits,
vegetables, beverages, spices, and herbs, in addition to common everyday foods.
In nutritional epidemiologic and intervention studies, the antioxidant food
database may be utilized to identify and rank diets and subjects with regard to
antioxidant intake, and as a tool in planning dietary antioxidant
interventions.
The results show large
variations both between as well as within each food category; all of the food
categories contain products almost devoid of antioxidants (Table 6.1).
We find that plant-based
foods are generally higher in antioxidant content than animal-based and mixed
food products
The antioxidant food table
is a valuable research contribution, expanding the research evidence base for
plant-based nutritional research, and may be utilized in epidemiological
studies where reported food intakes can be assigned antioxidant values. It can
also be used to test antioxidant effects and synergy in experimental animal and
cell studies, or in human clinical trials. The ultimate goal of this research
is to combine these strategies in order to understand the role of dietary
phytochemical antioxidants in the prevention of cancer, cardiovascular diseases,
diabetes, and other chronic diseases related to oxidative stress.
The total content of
antioxidants has been assessed in more than 3100 foods.
l The
results show large variations both between as well as within each food
category.
l Nuts and seeds are among the food categories that include the most
antioxidant-rich food
items.
l Walnuts
contain massive amounts of antioxidants.
l Pecans, chestnuts,
peanuts, pistachios, and sunflower seeds are very rich in total
antioxidants.
l Hazelnuts,
almonds, Brazil nuts, macadamias, pine kernels, cashew nuts, flax seeds, poppy
seeds, and sesame seeds
contain significant amounts of total antioxidants. l A
significant portion of nut antioxidants is located in the pellicle.
Antioxidants may occur
naturally in different source materials or may be synthe- sized by different
means. Higher plants and their constituents provide a rich source of natural
antioxidants, such as tocopherols and phenols/polyphenols, which are found
abundantly in spices, herbs, fruits, vegetables, cereals, grains, seeds, teas,
and oils. Antioxidants from marine origin such as algae, sh/shell sh, and
marine bacteria have also been considered (Amarowicz,
Karamac, & Shahidi, 1999; Athukorala et al., 2003; Shahidi &
Amarowicz, 1996).
The effectiveness of
antioxidants is generally influenced by their structural features,
concentration, temperature, type of oxidation substrate, and physical state of
the system, as well as presence of prooxidants and synergists (Yanishlieva-Malslarova, 2001). The chemical
structure of an antioxidant determines its intrinsic reactivity toward free
radicals and other ROS and, hence, the antioxidant activity. Efficiency of
antioxidants also depends on their concentration and location in the system
(e.g., distribution at interface) (Shahidi &
Zhong, 2011; Zhong & Shahidi, 2012a). The reaction kinetics plays an
important role in their short-term or long-term protection against oxidation,
and it involves the rate at which an antioxidant reacts with a speci c oxidant,
the thermodynamics of the reaction, and the extent to which the antioxidant
reacts (Antolovich, Prenzler, Patsalides, McDonald,
& Robards, 2002).
Our results show large
variations both between as well as within each food category; all of the food
categories contain products almost devoid of antioxidants. Please refer to Additional file 1, the Antioxidant Food Table, for the FRAP
results on all 3139 products analyzed. The categories "Spices and
herbs", "Herbal/traditional plant medicine" and "Vitamin
and dietary supplements" include the most antioxidant rich products
analyzed in the study. The categories "Berries and berry products",
"Fruit and fruit juices", "Nuts and seeds", "Breakfast
Cereals", "Chocolate and sweets", "Beverages" and
"Vegetables and vegetable products" include most of the common foods
and beverages which have medium to high antioxidant values. We find that plant-based foods are generally
higher in antioxidant content than animal-based and mixed food products, with
median antioxidant values of 0.88, 0.10 and 0.31 mmol/100 g, respectively. Furthermore, the 75th percentile of plant-based foods is 4.11 mmol/100 g compared
to 0.21 and 0.68 mmol/100 g for animal-based and mixed foods, respectively. The
high mean value of plant-based foods is due to a minority of products with very
high antioxidant values, found among the plant medicines, spices and herbs. In
the following, summarized results from the 24 categories are presented.
Most of the spices and herbs
analyzed have particularly high antioxidant contents. Although spices and herbs
contribute little weight on the dinner plate, they may still be important
contributors to our antioxidant intake, especially in dietary cultures where
spices and herbs are used regularly. We interpret the elevated concentration of
antioxidants observed in several dried herbs compared to fresh samples, as a
normal consequence of the drying process leaving most of the antioxidants
intact in the dried end product. This tendency is also seen in some fruits and
their dried counterparts. Thus, dried herbs and fruit are potentially excellent
sources of antioxidants.
Nuts are a rich source of many
important nutrients and some are also antioxidant-rich. The observed increase
in antioxidant content in nuts with pellicle compared to nuts without pellicle
is in good agreement with earlier studies showing the flavonoids of many nuts
are found in the nut pellicle.
Chocolate have for several
years been studied for its possible beneficial health effects. Our results show a high correlation between
the cocoa content and the antioxidant content, which is in agreement with
earlier studies.
As
demonstrated in the present study, the variation in the antioxidant values of
otherwise comparable products is large. Like the content of any food component,
antioxidant values will differ for a wide array of reasons, such as growing
conditions, seasonal changes and genetically different cultivars [46,58], storage conditions [59-61] and differences in manufacturing
procedures and processing [62-64]. Differences in unprocessed and processed
plant food samples are also seen in our study where processed berry products
like jam and syrup have approximately half the antioxidant capacity of fresh
berries. On the other hand, processing may also enhance a foods potential as a
good antioxidant source by increasing the amount of antioxidants released from
the food matrix which otherwise would be less or not at all available for
absorption [65]
