It is commonly thought that heat destroys vitamins. But;

  • what temperatures are we talking?
  • what vitamins?
  • What about vitamins in vegetables? 

Lets explore these questions.

Vitamin C and heat

The International Journal of Scientific and Technology Research study looked at the effect of heat on different vegetables and measured the percentage of vitamin C lost at 5, 15 and 30 minutes while exposed to constant heat of 60°C / 140°F.

The impact is material (Table I). As the authors state: “Vitamin C is water-soluble and, as such, is easily leached into the water and then degraded by heat.”

The negative effects of heat increase significantly at 60°C / 140°F, and even more at 77°C / 170 °F.

Boiling has been shown to reduces vitamin C content more than any other cooking method. Broccoli, spinach, and lettuce may lose up to 50% or more of their vitamin C when boiled.

Vitamin C is water-soluble and sensitive to heat, it can leach out of vegetables when they’re immersed in hot water.

Probiotics and heat

Probiotic cultures are even more delicate and cannot live above 48°C / 120 °F, as with virtually all bacteria and yeast.

Vitamin B Groups and heat

For some water soluble vitamins such as the B group vitamins, lab tests showed that when they are placed in hot water 60°C / 140°F, the nutrient content of the vitamin is extracted. 

It's been shown that heat harms the potency and effectiveness of a variety of vitamins and other nutrients. Degradation generally starts to occur in foods or beverages exposed to temperatures of greater than 48°C / 120 °F.  

Up to 60% of thiamine, niacin, and other B vitamins may be lost when meat is simmered and its juices run off. However, when the liquid containing these juices is consumed, 100% of the minerals and 70–90% of B vitamins are retained.

Amino Acids and heat

If in a dry, powder form supplements containing whey protein and branched-chain amino acids (BCAAs); won't break down within the range of temperatures normally experienced during shipping or in the home. Although higher temperatures may change their shapes (called protein denaturation), they will continue to provide the same nutritional benefits. 

How does this work? Cooking involves dividing the amino acids / proteins into smaller amino acid chains and therefore technically more digestible.

Does cooking alter the properties of protein powders?

however there is some research outlining that cooking above 200° C may cause the production of polycyclic aromatic hydrocarbons, which are toxic to our health. 

How does heating affect antioxidant levels in food?

Antioxidants are sensitive to heat, and freezing seems to preserve antioxidant activity. However, different antioxidants are heat sensitive at different temperatures.

For example, in tomatoes, 30 minutes of heating at 87° C / 190° F causes a loss of 29% of vitamin C, but total antioxidant activity increases by 62%. 

Short cooking times and reduced exposure to heat preserve the nutrients in microwaved food. In fact, studies have found that microwaving is the best method for retaining the antioxidant activity of garlic and mushrooms.

Meanwhile, about 20–30% of the vitamin C in green vegetables is lost during microwaving, but this is less than most cooking methods.

So surprisingly cooking via microwaving is one of the best cooking methods for nutrient retention on average. 

Key Takeaways

  1. D3B should only be put in warm water below 46° Celsius.
  2. Cooking either on grill or microwave instead of water is a better option all round noting different vegetables react slightly differently.
  3. Cook vegetables for shorter periods of time and ideally still partly raw (that extra crunch).

    References

    1. Degradation of vitamins, probiotics and other active ingredients caused by exposure to heat, water and sunlight. https://www.nutraceuticalbusinessreview.com/news/article_page/Degradation_of_vitamins_probiotics_and_other_active_ingredients_caused_by_exposure_to_heat_water_and_sunlight/145924#:~:text=Nevertheless%2C%20heat%20remains%20extremely%20common,greater%20than%20120%20%C2%B0F
    2. Effect of different cooking methods on the content of vitamins and true retention in selected vegetables https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6049644/
    3. https://www.nutritionletter.tufts.edu/healthy-eating/antioxidants/q-how-do-heating-and-freezing-affect-antioxidant-levels-in-food/
    4. For “naturally occurring” vitamins, such as vitamin C in orange juice, FDA allows meaningful variance; but, for “fortified vitamins” added into products, the level of vitamins contained in the product on the shelf must exceed label claims.
    5. www.ijstr.org/final-print/nov2013/Effect-Of-Heating-On-Vitamin-C-Content-Of-Some-Selected-Vegetables.pdf.
    6. www.bevnet.com/news/2017/kevita-targeted-class-action-suit-authenticity.
    7. www.ganedenprobiotics.com/images/uploads/white_paper_pdfs/beyond_the_dairy_case.pdf.
    8. https://scialert.net/fulltext/?doi=tasr.2009.79.84.
    9. www.ncbi.nlm.nih.gov/pubmed/15055922.
    July 05, 2023 — stephanie dowling

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