How To Cook Antioxidant-Rich Foods Without Destroying Their Antioxidants

Photo by Emile Guillemot on Unsplash

You lose 80% of the nutrient benefits by cooking the wrong way

Polyphenols are micronutrients which are readily available in everyday food. They're packed with antioxidants - as long as you don't destroy these antioxidants by cooking the wrong way.

For example, boiling some polyphenol-rich foods destroys 80% of their polyphenol content. In this article, I'll guide you through how to preserve the most benefit from polyphenol "superfoods" like tomatoes.

TL;DR slip a steam oven under your microwave and enjoy the best of both.

Why you should care

Over the past 10 years, researchers and food manufacturers have become increasingly interested in polyphenols. The chief reason for this interest is the recognition of their antioxidant properties, their abundance in our diet, and their probable role in the prevention of various diseases associated with oxidative stress, such as cancer and cardiovascular and neurodegenerative diseases.

It's also thought that polyphenols can improve or help treat digestion issues, weight management difficulties, and diabetes. Polyphenols furnish the immune system, 

The generally known benefits of foods such as green tea, black tea, coffee, blueberries, aubergines, cherries, broccoli, red wine, miso, tofu, tempeh, apples, chocolate, lemons, grapefruit juice and blackberries - to name just a few - are down in large part to their polyphenol content. 

Polyphenols are also the source of the vital health benefits of Extra Virgin Olive Oil.

Go as sunny, fresh and natural as possible for your source

However, there is a devil in the details. Whether or not we even have a chance of accessing the benefits of polyphenols depends on many factors, most of which are beyond our control. These factors include:

• How the food is grown, e.g. soil type, rainfall, tree density
• The ripeness of the food source
• How long the food is stored and how it is stored
• The industrial preparation of the food source, e.g. green tea versus black tea, or industrial orange juice versus fresh juice.
• The domestic preparation of the food source, e.g. skin on, skin off, boiled, microwaved
• What combination the food is eaten with, and
• How well our body absorbs the specific polyphenol in conjunction with its food carrier.

For example, the grinding of oranges results in oxidative degradation of polyphenols resulting in brown pigments. Manufacturers add clarification steps aimed explicitly at removing certain flavonoids responsible for this discolouration and haze formation.

Hence, manufactured fruit juices have low polyphenol (flavonoid) content. 

It is for related reasons that (cold-pressed) Extra Virgin Olive Oil is the best olive oil source of polyphenols and not the more processed variants.

While we cannot control most of the factors above, we can control the preparation in our kitchen and the cooking.

Preparation has a marked effect on the polyphenol content of foods.

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Leave the skin on, eat the outer leaves

Polyphenols are generally present in higher concentrations in the outer parts of fruit and vegetables than in the inner portions.

The simple act of peeling fruit and vegetables removes a significant portion of the total polyphenol load.

In fruits and vegetables, flavonols are the most common form of polyphenol. These flavonols accumulate in the outer and aerial tissues (skin and leaves) because sunlight stimulates their biosynthesis. Marked differences in concentration exist between pieces of fruit on the same tree and even between different sides of a single piece of fruit, depending on exposure to sunlight.

Similarly, in leafy vegetables such as lettuce and cabbage, glycoside (another polyphenol) concentration is more than ten times as high in the green outer leaves as in the light-coloured inner leaves. This phenomenon also accounts for the higher flavonol content of cherry tomatoes than of standard tomatoes, because they have different proportions of skin to whole fruit.

The skin of citrus fruit contains large quantities of polyphenols.

Also, the solid parts of citrus fruit, particularly the white spongy portion and the membranes separating the segments, have a very high polyphenol content. The whole fruit may contain up to 5 times as much as a glass of orange juice.

Avoid overcooking, try steam cooking

Cooking also has a significant effect on the preservation of the health value of polyphenols

Onions and tomatoes lose between 75% and 80% of their original polyphenol (quercetin) content after boiling for 15 minutes.

They lose 65% after cooking in a microwave oven, and 30% after frying.

Steam cooking of vegetables, which avoids leaching, is preferable. You can do this in a steam oven - I have a Cuisinart domestic combo convection steam oven for this purpose.

Cuisinart Convection Steam Oven | Image: Reviewed.com

Potatoes contain polyphenols (up to 190 mg chlorogenic acid/kg), mainly in the skin. Extensive loss occurs during cooking - so, again, best to steam cook smaller potatoes if you can.

In case you're wondering, no remaining polyphenols were found in French fries or freeze-dried mashed potatoes.

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Stream cook, eat the skin, and enjoy your coffee

In summary, choose fruit and vegetables that have a nice even exposure to sunlight. Eat more of the outer leaves and upper leaves, e.g. in spring onions, and eat the whole citrus fruit including the pith and membranes.

For vegetables, leave the skin on, use more of the outer leaves, e.g. cabbages and lettuce, and steam cook when you can. 

In all cases, avoid industrially processed foods as these have generally had the polyphenols removed - for cosmetic and other processing purposes. Remember, industrial orange juice has only low remaining polyphenols, and French fries and freeze-dried mashed potatoes have none.

Ensuring that you get a healthy dose of polyphenols each day is one of the best dietary choices that you can make. Your mind and body will thank you.

​Good luck.

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PS I have some good news for we coffee-drinkers. Coffee is a good source of polyphenols (as hydroxycinnamic acid). Cultures whose people drink several cups per day e.g. Finland, Germany, may ingest as much as 32-times more polyphenols than those in cultures who do not drink coffee (and who also eat small quantities of fruit and vegetables), e.g. United States

Why I Am Not Cutting My Coffee Back To 2 Cups Daily Despite The Latest Research

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