A usual perception that we live with is that raw food is healthy food.
Nutritional content of fruits and vegetables is mainly assessed once they are harvested and those figures typically depict the item to be nutrient dense.
The myth that cooking, mainly heating, destroys the nutrients in the food is still rampant.
Part of this myth is in fact true cooking does affect nutritional content of every food item.
Vitamins and minerals are the main components that are lost during cooking.
Water soluble and heat sensitive vitamins are affected mainly.
Average cooking techniques utilised at home lead to a loss of 15-55% of Vitamin C. Around 30-40% minerals are lost during cooking.
Highest losses occur by squeezing after boiling and by soaking in water followed by parching, stewing and frying.
Deep frying and barbecuing not only cause vitamin loss but also lead to formation of cancer causing agents.
Yet cooking is a highly necessary technique when it comes to improving palatability of the food.
Eating cooked veggies is better than eating no veggies! Cooking leads to a limited loss of some nutrients and increases the bioavailability of other nutrients.
Some cooking methods such as microwave cooking have minimal effects on nutritional quality.
Are turmeric and black pepper’s benefits lost while cooking?
Now why am I suddenly concerned about nutritional losses occurring during cooking?
An avid reader that I am I keep stumbling across various pieces of information regarding turmeric and boy, they are confusing at times!!
Now this my latest find: A research study was conducted to evaluate the loss of bioactive ingredients of turmeric, red pepper and black pepper namely curcumin, capsaicin and piperine.
They were subjected to heat similar to those occurring in domestic cooking processes.
They were either boiled for 10 or 20 minutes or pressure cooked for 10 minutes.
Around 27-53% of curcumin was lost by heat processing of turmeric and major loss was observed by pressure cooking. Loss of piperine was around 16-34%.
This study demonstrated a loss of 85% of curcumin within 15-30 minutes of cooking.
Also the loss of piperine was around 50-60% when black pepper was used as an ingredient of curry powder and this loss was reduced when only black pepper was used individually.
Now this amazed me. Till date we have been suggesting various recipes to incorporate turmeric and they involve cooking…so do these studies negate our beliefs that cooking turmeric increases its absorption?
Now there are a few things we don’t know about the studies like how was the turmeric cooked, whether turmeric powder was used or roots, were other ingredients included etc.
So we cant completely accept or deny the results. But this gives us a basic idea that certain quantity of curcumin and piperine, active ingredients of turmeric and black pepper are lost on cooking.
What do other researchers have to say about this?
So, what’s next? Well we decided to put on our investigating feelers and detect what other studies say about the heat stability of curcumin and turmeric.
Curcumin in turmeric is sensitive to heat
Research proves that when using curcumin as a food coloring agent, the food processing temperature should not go above 190°C.
An experimental study was conducted wherein the thermal stability of different natural yellow colorants used in food was studied.
Temperature range was from 30-90°C and time for heat exposure was 6 hours! The color degraded with increase in temperature and curcumin was found to have intermediate thermal stability.
So does loss of curcumin from turmeric mean loss of medicinal properties?
So curcumin is not stable at high temperatures, but does that mean its pharmacological properties are lost?
In fact research proves that antioxidant power of turmeric increases with boiling and roasting in comparison to raw turmeric.
In a study, curcumin was roasted at 180°C up to 70 minutes. Its degradation products included vanillin, ferulic acid, and 4-vinyl guaiacol.
When tested for its biological activity, 4-vinyl guaiacol increased antioxidant defences by inducing activity of antioxidant enzymes and it also lowered the production of pro-inflammatory agents in immune cells.
This shows that heat may breakdown curcumin but its anti-inflammatory and antioxidant properties are unaffected.
When heated at high temperatures curcumin-alcohol mixture loses 47% of curcumin by weight and curcumin oil mixture loses 38.9%.
Vanillin and ferullic acid are produced at around 50-60°C. Both these products show significant anti-cancer activity.
They also suppress the activity of nuclear factor-kappa B and COX enzymes which are key players in inflammatory process.
Despite of turmeric’s low bioavailability, Asian countries have a lower incidence of cancer.
Could this be linked to inclusion of turmeric in diet and if yes does cooking modify turmeric’s anti-cancer activity.
A study demonstrated that curcumin is broken down at high temperatures and one of its decomposition products are deketene curcumin.
This compound is far more toxic to cancerous cells than curcumin itself. So cooking actually increases curcumin’s anti-cancer activity!
Most studies investigate the effect of curcumin by exposing the cells to it but dietary turmeric can also reduce risk of cancer.
Hot water extract of turmeric is stronger than vitamin C when it comes to antioxidant activity.
What happened to the ‘Heating increases turmeric’s bioavailability’ notion?
Including turmeric in food and cooking it increases its bioavailability.
A study evaluating this point, demonstrated the difference in curcumin’s properties when exposed to oil in water preparations.
Temperatures selected were 30 °C and 100 °C to create conditions similar to that of salad dressings and cooking sauces.
Interestingly, curcumin was found to be more soluble and stable in the preparations at 100°C rather than 30°C.
Total curcumin available in the gastrointestinal tract increased as the oil in water emulsions protected it from degradation.
This study depicts the idea that at higher temperatures curcumin is made more bioavailable.
The solubility of curcumin in water is proven to increase by 12 folds and turmeric by 3 folds when it is heated.
A study shows that heat solubilised curcumin can prevent antibody-antigen binding a hallmark of autoimmune conditions and in this study curcumin was boiled in water for 10 minutes but it still showed pharmacological action.
So these studies do depict that curcumin’s bioavailability increases with heating.
What about piperine in black pepper?
Not much data is accessible when it comes to thermal stability of piperine, but here are some points that we would like to mention:
- Flavour of black pepper, that is mainly loss of piperine, is lost due to heating and cooking within a range of 50-120°C.
- Hot water extract of black pepper prepared by boiling black pepper in water demonstrates antispasmodic effect.
- In a study among the various spices tested, black pepper was the only one that showed increase in antioxidant activity on thermal treatment.
- Various cooking methods such as pan-frying, deep-frying, roasting of meat can lead to formation of carcinogenic compounds and research suggests that application of black pepper during processing can reduce production of such compounds.
- Drying black pepper corns at 70°C for 30 minutes or sun drying can lead to degradation of carcinogenic compounds like safrole.
The purpose behind presenting these points is that heating may lead to loss of piperine but it also destroys harmful content of spices.
Also pepper still retains its biological properties despite of heat treatment.
Few tips on how you can reduce cooking losses in case of turmeric
Here are a few tips that could minimize cooking losses of curcumin:
- When cooking sprinkle turmeric in the end to avoid loss of curcumin.
- Reduce the cooking time when you use turmeric.
- Cooking turmeric with oil can help protect it from degradation and increase its bioavailability.
- Use turmeric in gentle cooking methods for example while making a soup and steaming vegetables. Also make sure you consume the liquid resulting from steaming as it would contain the curcumin that is lost while cooking.
- Add turmeric to food items that do not require to be heated. For example buttermilk increases stability and solubility of curcuminoids.
- Marinate your meat prior with turmeric if you plan to barbecue it to avoid formation of carcinogenic compounds.
- Make use of the ‘Golden Paste’ as it cooked on low heat with turmeric and pepper.
- Use fresh black pepper corns while cooking.
So it is true that curcumin and piperine, active ingredients of turmeric and black pepper are lost when heated. But the good news is that the pharmacological properties are not lost.
Spices are heat resistant. Back in India spices are dry roasted before using them in food and sometimes they are even sun-dried to get rid of toxins and bacteria.
In case of turmeric, the degradation products show equivalent or better action than curcumin.
And pepper can lose its flavour by storage and grinding just as it would occur during cooking.
So you don’t need to worry about whether you will lose all the healthy stuff from spices when you cook it.