To what extent does heating (boiling, baking, frying) foods like vegetables destroy vitamins?
It’s true that cooking methods alter the nutritional composition of fruits and vegetables, but that’s not always a bad thing.
Several studies have shown that while cooking can degrade some nutrients, it can enhance the availability of others. As a result, no single cooking or preparation method is best, and that includes eating vegetables raw. Many people believe that raw vegetables are packed with more nutrition than cooked vegetables, but, again, it depends on the type of nutrient.
One study of 200 people in Germany who ate a raw food diet found that they had higher levels of beta carotene, but their plasma lycopene levels were well below average. That’s likely because fresh, uncooked tomatoes actually have lower lycopene content than cooked or processed tomatoes. Cooking breaks down the thick cell walls of many plants, releasing the nutrients stored in them.
Water-soluble nutrients like vitamin C and vitamin B and a group of nutrients called polyphenolics seem to be the most vulnerable to degradation in processing and conventional cooking. Canned peas and carrots lose 85 to 95 percent of their natural Vitamin C. After six months, another study showed that frozen cherries lost as much as 50 percent of anthocyanins, the nutrients found in the dark pigments of fruits and vegetables. Cooking removes about two-thirds of the vitamin C in fresh spinach.
Depending on the method used, loss of vitamin C during home cooking typically can range from 15 percent to 55 percent, according to a review by researchers at the University of California, Davis. Interestingly, vitamin C levels often are higher in frozen produce compared with fresh produce, likely because vitamin C levels can degrade during the storage and transport of fresh produce.
Fat-soluble compounds like vitamins A, D, E and K and the antioxidant compounds called carotenoids fare better during cooking and processing.
A report in The Journal of Agriculture and Food Chemistry concluded that over all, boiling was better for carrots, zucchini and broccoli than steaming, frying or serving them raw. Frying vegetables was by far the worst method for preserving nutrients. But when it comes to cooking vegetables, there are always tradeoffs. A method may enhance the availability of one nutrient while degrading another.
Boiling carrots, for instance, significantly increases measurable carotenoid levels compared with raw carrots. However, raw carrots have far more polyphenols, which disappear once you start cooking them. And while many people think microwaving is bad for food, vegetables cooked in a microwave may have a higher concentration of certain vitamins.
A March 2007 study looked at the effects of boiling, steaming, microwaving and pressure cooking on the nutrients in broccoli. Steaming and boiling caused up to 34 percent loss of vitamins. Vacuum cooked vegetables retained over 95 percent of their vitamin C and nutrients.
When cooking in a vacuum vapor the temperature does not accede 73 degrees Celsius or 165 Fahrenheit. But because the vegetables are cooked just enough, it will fully break down in the digestive process, and also the cell walls of the vegetable break down, all while not disturbing any of the nutritional value. So your body will assimilate the most possible amount of vitamins, enzymes, minerals and nutrients when cooked in a vacuum vapor. Even more than eating them raw.
However, to be able to cook in a vacuum vapor, your pan needs certain features, just like a pressure cooker needs safety features and good seals. Without the vapor seal, whistle Vac-control valve and heat conducting inner cores going up the sides of the pan, cooking in a vacuum vapor would not work.
The vacuum vapor method of cooking vegetables has been around for over 50 years. The method has since been perfected a few times.
We used to call it waterless cooking, as an ounce of water, or just the moisture from the washed vegetables, were all that was needed. However, in time we discovered the old waterless way was in fact just steaming the vegetables. Only when the heat was turned off, or the pan removed from the burner did a partial vacuum occur. As the air tries to reenter the pan it can’t due to the sealed lid. This creates a vacuum vapor on the inside. Water boils at a much lower temperature with less pressure. This is the total opposite of pressure cooking.
Because the internal temperature of the pan does not exceed 73 degrees Celsius, or 165 Fahrenheit non of the nutritional value of your vegetables are damaged, but most importantly, if the vegetable and cell wall are softened enough to fully break down in the digestive process you will assimilate more nutrient and vitamins than eating them raw.