Antioxidants in Food

By Dr Ananya Mandal, MD

Antioxidants are present in large amounts in several foods. However, actual amount of antioxidants in several plant products may differ due to several factors. These include:

  • soil type and chemistry
  • available nitrogen and levels of other plant nutrients
  • moisture levels
  • temperature
  • pests

It has been seen that plants which are exposed to stress are driven to synthesize antioxidants and are richer in these polyphenols and flavonoids.

Phenolic antioxidants are present in plants at concentrations up to several grams per kilogram. In general, levels are higher in the rinds and skins of the fruits rather than within them. A number of chemical assays have been developed to measure different antioxidants. In vitro assays are designed to test antioxidant levels in foods, while other assays measure levels in blood, urine or blood cells.

Antioxidant food sources

Some food sources of antioxidants include:

Food

Antioxidant Nutrients

Acorn squash, pumpkin, winter squash

Beta carotene

Apples

Catechins

Apricots, cantaloupe, peaches

Beta carotene

Beans

Catechins, vitamin E

Beets

Anthocyanins

Bell peppers

Beta carotene, vitamin C

Berries

Anthocyanins, catechins, ellagic acid (in raspberries and strawberries), resveratrol (in blueberries),vitamin C

Broccoli, greens, spinach

Beta carotene, lutein, vitamin C

Brown rice

Selenium

Carrots

Beta carotene

Chicken

Selenium

Citrus fruits

Vitamin C

Corn

Lutein

Egg

Lutein (in yolks); selenium, vitamin A

Eggplant

Anthocyanins

Garlic and onions

Selenium

Grapefruit, pink

Lycopene, vitamin C

Grapes, red wine

Anthocyanins (in red and purple grapes), resveratrol

Mango and papaya

Beta carotene, vitamin C

Milk

Vitamin A

Nuts, nut butters, oils, seeds

Vitamin E

Oatmeal

Selenium

Peanuts

Resveratrol

Prunes

Anthocyanins

Salmon, tuna, seafood

Selenium

Sweet potatoes

Beta carotene, vitamin C

Tea, black or green

Catechins

Tomatoes (canned)

Lycopene, vitamin C

Watermelon

Lycopene, vitamin C

Wheat germ, whole grains

Selenium, vitamin E

In addition to the above:

  • Linseed is the major source of lignans in the diet. Lignans are also found in other cereals, legumes and vegetables
  • Stilbenes are found in only low quantities in the human diet. Resveratrol is the most widely studied stilbene and is found in grape seeds, peanuts or knotweed roots. These stilbenes have cancer protective effects.
  • Flavonoids are divided into six classes including flavonols, flavones, isoflavones, Flavonols (catechins and proanthocyanidins), Flavanones and Anthocyanidins. Of these Flavonols are the most common flavonoids in foods.

Flavanols

The richest sources of flavonols are onions, kale, leeks, broccoli, and blueberries. Flavonol concentrations are highest in or near the peel or rinds of fruits since their biosynthesis is stimulated by light.

In green leafy vegetables, the outer leaves often contain flavonol concentrations more than 10 times the concentrations found in inner leaves. Also smaller fruits of the same species, compared to larger fruits, tend to have higher concentrations of flavonols due to the relationship between surface area and fresh weight.

Flavonols exist in both the monomer form (catechins) and polymer form (proanthocyanidins). Catechins are present in green tea and chocolate and in apricots. Red wine is another major source.

Flavones, isoflavanones and flavanones

Parsley and celery are important sources of flavones.

Isoflavones are found almost exclusively in legumes and soybeans.

Flavanones are found mostly in citrus fruits, tomatoes, mint etc.

Anthocyanins

Anthocyanins are pigments that give fruits and vegetables their color. Levels increase as fruits ripen and are highest in the skins and peels of fruits.

Reviewed by April Cashin-Garbutt, BA Hons (Cantab)

References

  1. http://www.nutritionj.com/content/supplementary/1475-2891-9-3-s1.pdf
  2. http://www.organic-center.org/reportfiles/Antioxidant_SSR.pdf
  3. http://voh.chem.ucla.edu/vohtar/fall06/classes/153C/pdf/Best%20antioxidant%20foods.pdf
  4. http://acudoc.com/Antioxidants.PDF
  5. http://ocw.jhsph.edu/courses/humannutrition/PDFs/Lecture8.pdf
  6. http://www.womenfirst.net/pdf/ADA/ADA_Antioxidants.pdf
  7. http://class.fst.ohio-state.edu/fst821/Lect/AA.pdf
  8. http://www.medlabs.com/Downloads/Antiox_acti_.pdf

Further Reading

Read in | English | Español | Français | Deutsch | Português | Italiano | 日本語 | 한국어 | 简体中文 | 繁體中文 | Nederlands | Русский | Svenska | Polski
Comments
The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News-Medical.Net.
Post a new comment
Post