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Stability of some Vitamins and other nutrients in different cooking and environmental conditions

Vitamins are good for health in moderate doses. Right. And we get lots of information  on which food item contains what vitamins and innumerable advises to eat them. But do we get all the required vitamins even if we eat all those foods? No! Why?

Because nutrients are chemicals and they need stable conditions to sustain and favourable ones to get absorbed into our body. What are these conditions? Let us examine now some of them...

 

Vitamin D: Some of the vitamin D compounds found in foods are damaged by cooking. For example cooking eggs in an oven at normal temperatures destroy 60% of the vitamin D, after 40 minutes exposure to the heat. Frying however, which is hotter than baking, but done for a shorter period of time, only destroy about 20% of the vitamin D, while boiling destroy only about 15%. (Technical University of Denmark)  http://www.foodconsumer.org/newsite/Nutrition/Vitamins/cooking_and
Raw fish contains more vitamin D than when it is cooked, and fatty ones will contain more than lean cuts. As well, fish canned in oil will have more vitamin D than those canned in water.
Cooking eggs does reduce the amount of vitamin D.  Shorter cooking times and lower temperatures preserve the amount of vitamin D.
Vitamin  C: Vitamin C, also known as ascorbic acid, is a water-soluble vitamin found in fruits and vegetables, including oranges, strawberries, broccoli, tomatoes and green peppers.Vitamin C is easily destroyed by excessive heat and water, as well as exposure to air.
Just ten minutes of boiling reduce the vitamin C level by about 25 percent. The vitamin can also leach out into the water when vegetabless are cooked. Heat and other chemical processes also can break it down.
We might get more vitamin C from some cooked vegetables than raw.
Most people probably don’t blend their vegetables before they eat them. But we do chew and digest them. That’s how the body is able to crack into the hard cell walls of plants to access their vitamins.
How? Cooking or blending can soften and break up plant cell walls. This can make it easier for the body to use the vitamins inside. Some of those vitamins can stay locked within raw vegetables if chewing and digesting doesn’t break up enough cell walls. But it depends on what the vegetable is, how it’s cooked and how much is eaten. In other words, it is difficult to know exactly how much will be taken up from different foods unless blood vitamin-C levels are tested.
 
Vitamin A: Is vitamin A heat sensitive? That depends on the pH of the  food.
The effect of pH on heat sensitivity: 
Below are the amounts of vitamin A (IU) from tomato products listed on the USDA nutrient database. 

Tomato, pH 4-5
Red, ripe, raw average 833 IU Vitamin A
Red, ripe, cooked 489 IU Vitamin A

Carrot, pH 6
Carrot, frozen, cooked- 16928 IU Vitamin A
Carrot, Raw - 16706 IU Vitamin A
Vitamin A is best absorbed when cooked due to the beta carotene content which increases when cooked but can also be lost into water so these types of food are best baked and roasted as they will only lose 5% of beta carotene compared to boiling and stir frying which could lose up to 10%. This includes foods such as; carrots, spinach, green leafy vegetables, watercress, red and yellow peppers, and tomatoes. 
Also Vitamin A occurs in different forms and depending on its initial configuration can, or can not, be broken down by heat.
The main enemies of Vitamin A are air and light in which it becomes unstable. That means that retinol heated while exposed to air and light will break down faster than retinol in a dark, anaerobe, environment. In any situation, temperatures above 40°C will begin to slowly degrade and break down retinol. For shorter term exposure above 70°C (such as cooking), Vitamin A is quite stable against heat but will oxidize rapidly in acidic environments. In alkaline setups, however, stability is rather high.
Vitamins B complex: The Vitamin B group including thiamin, niacin, biotin, folic acid, vitamin B6 and B12 are all water soluble and so are better steamed or eaten raw and include green leafy vegetables, bean sprouts, avocados, nuts, and mushrooms. When heated in water, they are lost as they are water soluble and get evaporated with steam. 

 

Factors that effect Vitamins:

FACTORS THAT CAN INDUCE
VITAMIN LOSS


Nutritional Element

Is substance susceptible to losses
under given condition?

Soluble
in Water

Exposure
to Air

Exposure
to Light

Exposure
to Heat

Vitamin A

no

partially

partially

relatively stable

Vitamin D

no

no

no

no

Vitamin E

no

yes

yes

no

Vitamin K

no

no

yes

no

Thiamine

highly

no

?

> 100°C

Riboflavin

slightly

no

in solution

no

Niacin

yes

no

no

no

Biotin

somewhat

?

?

no

Pantothenic Acid

quite stable

?

?

yes

Folate

yes

?

when dry

at high temp

Vitamin B-6

yes

?

yes

?

Vitamin B-12

yes

?

yes

no

Vitamin C

very unstable

yes

yes

yes

(table, continued)

Nutritional Element

Is substance susceptible to losses
under given condition?

Acid
Solution

Alkali
Solution

Other

Vitamin A

?

?

--

Vitamin D

?

?

--

Vitamin E

?

?

contact with iron or copper

Vitamin K

strong acids

yes

--

Thiamine

no

yes

--

Riboflavin

no

yes

long cooking in large volume of water

Niacin

no

no

--

Biotin

strong acids

yes

oxidizing substances

Pantothenic Acid

yes

yes

--

Folate

heat-labile

?

storage

Vitamin B-6

no

yes

--

Vitamin B-12

strong acids

yes

contact with iron or copper

Vitamin C

?

yes

Tables Source: beyondveg.com
Some recommendations to get max vitamins from foods: use of utilizing foods when fresh; using steaming in preference to boiling; and avoiding overly long cooking times.

People think raw foods are good than cooked ones. This is only partially true. Some foods are less nutritious raw because they contain substances that destroy or disarm other nutrients. For example, raw dried beans contain enzyme inhibitors that interfere with the work of enzymes that enable your body to digest protein. Heating disarms the enzyme inhibitor. Some, foods (such as meat, poultry, and eggs) are positively dangerous when consumed raw (or undercooked) because they harbour micro-organisms.

Virtually all minerals are unaffected by heat. Cooked or raw, food has the same amount of calcium, phosphorus, magnesium, iron, zinc, iodine, selenium, copper, manganese, chromium, and sodium. The single exception to this rule is potassium, which — although not affected by heat or air — escapes from foods into the cooking liquid.

With the exception of vitamin K and the B vitamin niacin, which are very stable in food, many vitamins are sensitive and are easily destroyed when exposed to heat, air, water, or fats (cooking oils).

The following table shows which nutrients are sensitive to these influences.

What Takes Nutrients Out of Food?
Nutrient Heat Air Water Fat
Vitamin A X X
Vitamin D X
Vitamin E X X X
Vitamin C X X X
Thiamin X X
Riboflavin X
Vitamin B6 X X X
Folate X X
Vitamin B12 X X
Biotin X
Pantothenic acid X
Potassium X

It is important to note that most vitamins are sensitive to heat and water. Water-soluble vitamins, especially most of the B vitamins and vitamin C, leach into cooking water. Vitamins A, D and E are fat-soluble and leach into cooking oils. Vitamin C is the most likely to get lost in cooking. It's susceptible to heat, air and water. Other vitamins that cooking may degrade include B-6, which is susceptible to heat, air and water; and E, which is sensitive to heat, air and fat. Only two vitamins, K and B-3, or niacin, are stable enough to hold up well during cooking.

So to avoid specific types of vitamin loss, keep the following tips in mind:

  • Vitamins A, E, and D: To reduce the loss of fat-soluble vitamins A and E, cook with very little oil. For example, bake or broil vitamin A–rich liver oil-free instead of frying. Ditto for vitamin D–rich fish.

  • B vitamins: Strategies that conserve protein in meat and poultry during cooking also work to conserve the B vitamins that leak out into cooking liquid or drippings: Use the cooking liquid in soup or sauce.

    Do not shorten cooking times or use lower temperatures to lessen the loss of heat-sensitive vitamin B12 from meat, fish, or poultry. These foods and their drippings must be thoroughly cooked to ensure that they’re safe to eat.

    Do not rinse grains (rice) before cooking unless the package advises you to do so (some rice does need to be rinsed). Washing rice once may take away as much as 25 percent of the thiamin (vitamin B1). Toast or bake cakes and breads only until the crust is light brown to preserve heat-sensitive Bs.

  • Vitamin C: To reduce the loss of water-soluble, oxygen-sensitive vitamin C, cook fruits and vegetables in the least possible amount of water. For example, when you cook 1 cup of cabbage in 4 cups of water, the leaves lose as much as 90 percent of their vitamin C. Reverse the ratio — one cup water to 4 cups cabbage — and you hold on to more than 50 percent of the vitamin C.

    Serve cooked vegetables quickly: After 24 hours in the fridge, vegetables lose one-fourth of their vitamin C; after two days, nearly half.

    Root vegetables (carrots, potatoes, sweet potatoes) baked or boiled whole, in their skins, retain about 65 percent of their vitamin C.

  • Another important point to note is that cooked vegetables lose a quarter of their vitamin C after 24 hours in the fridge and after two days nearly half – so try to eat up when they’re fresh out the steamer. This is why orange juice is really not a good source of vitamin C and unfortunately many people have been to led to believe otherwise.

    Vitamins A, E, and D are fat soluble so to preserve them cook them with very little oil. For example if you are cooking salmon which is rich in vitamin E and D it would be better to bake it rather than fry it.

Read here more on vitamins:  the-other-side-of-vitamins-and-other-micro-nutrients

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