heat Capsaicinoid Stability During Cooking

I think we’ve all noticed the dramatic difference between eating a fresh pepper and eating a meal cooked with that same pepper: the meal is much milder and less physically irritating, even when large numbers of pods are used compared to eating just one raw pod. This effect seems larger than simple dilution would explain, so I looked deeper and found a study which partially answers the question.

Stability of Capsaicinoid Content at Raised Temperatures


All three tested capsaicinoids:
  • Higher temperatures resulted in more reduction than lower temperatures
  • Longer cooking results in more reduction than shorter, with most change happening within the first 15 minutes
  • Both low and high pH result in more reduction than neutral pH

Capsaicin and dihydrocapsaicin:
  • After 15 minutes, reduced by between ~60-75%

  • After 15 minutes, reduced by between ~95-100%

To remind ourselves of the burn profiles of these capsaicinoids:

The investigations of Krajewska and Powers (1988) revealed that nordihydrocapsaicin was the “least irritating,” and the burning was located in the front of the mouth and palate. It caused a “mellow warming effect.” The heat sensation developed immediately after swallowing and receded rapidly. In comparison, capsaicin and dihydrocapsaicin were more “irritating,” and were described as having a “typical” heat sensation. Both compounds produced the heat in the mid-mouth and mid-palate as well as the throat and the back of the tongue. In contrast, homodihydrocapsaicin was very “irritating, harsh and very sharp.” The heat did not develop immediately and it affected the throat, back of the tongue, and the palate for a prolonged period.

Immediately, this makes me wonder how homodihydrocapsaicin is effected by cooking. A hypothesis could be that it is heavily reduced, like nordihydrocapsaicin is, and that this could explain the gulf in irritation between raw and cooked peppers: not just an overall reduction in capsaicinoids, but possibly a disproportionate reduction of the most irritating capsaicinoids. That said, of the three capsaicinoids studied above, the least irritating was the most reduced.
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The reason you cough when cooking with peppers is capsaicin in the air from evaporation. The longer you cook the higher the loss.
Actually capsaicin is an alkaloid which is highly thermostable, but, is steam-volatile which explains it entering the air through evaporation since peppers are filled with the water that creates the steam that passes through the steam-volatile cap releasing it.
I think you should read the study. In this case, the effect cannot be due to evaporation because the study used sealed containers…
I don't seal my pots when I cook. 🤣
I didn't say the effect wasn't those conditions, I am saying evaporation also occurs. Cap is thermostable to about 410°F so any higher heat cooking will release more. That's one effect. The other is evaporation since cap is steam-volatile which means when steam passes directly through it, it releases it into the air (perhaps through binding particles not sure, they could be separate). Steam is produced at temperatures before the degradation process occurs so you will be coughing when cooking anything that is steaming in the pot/pan which includes just putting a pepper in a pan since the cell walls are water.
Right, and not "steaming" the peppers, the pepper is creating its own steam since it's mostly water. So any type of cooking is going to produce this effect since the water inside turns to steam at 212°F. Combined with the losses in the study, it's compounded. Which means, yeah, when we cook, we lose heat. In more ways than we think which explains a lot. Pretty sure the coughing/burning eyes is more of the evaporation than the loss in the study though, or what do you think there? I'm coming at this from a cooking perspective, and you are coming at if from a scientific one.
The peppers do contain water and thus produce their own steam. However, in the study all of that steam would have been captured in the sealed containers and measured along with everything else once cool. No capsaicinoids were lost by escaping; it’s a closed system.

Your observation is also correct, and no doubt there would be further loss of capsaicinoids if steam were allowed to escape, as you say. This would likely be a minor effect compared to the large reduction measured from degradation… but it would take another study to know for sure!
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Interesting notes.
An easy test...but it costs a few dollars....is to make hot sauce recipe, take a sample before cooking. Then cook for 15+ minutes, take another sample. Send both to a lab for HPLC testing.
Not sure, but evaporation occurs before the boiling point of water. Water off the sidewalk evaporates, and when you dehydrate it evaporates. So surely you have effects from it at low temps, compounded with what @thoroughburro posted. I think heat just intensifies both. Evaporation and degradation.
I don’t know for sure, but my guess is that the fermentation wouldn’t reduce capsaicinoids to an appreciable degree. The time spent at room temperature or above, the decreasing pH, etc probably do decrease it a bit, but unlikely to be as dramatic as cooking.
Increase/decrease of capsaicinoid content during fermentation depends on the members of the fermentation consortium. There are bacteria that can break down capsaicin very efficiently. Here is a reference that describes the spontaneous fermentation of pepper mash (full text available by following the link):

Dynamics of Bioactive Compounds during Spontaneous Fermentation of Paste Obtained from Capsicum ssp.-Stage towards a Product with Technological Application

Abstract: Six cultivars of chili (Cherry, Bulgarian Chilli, Cayenne, Fatalii, Habanero, and Carolina Reaper) from two species (Capsicum annuum and Capsicum chinense) have been studied. Anaerobic, spontaneous fermentation of pure chili paste was conducted for 21 days at 20 °C. The unfermented (UCP) and fermented chili pastes (FCP) were both subjected to physicochemical and microbiological characterization consisting of capsaicinoid, ascorbic acid, short-chain organic acids, phenolic compounds, and simple sugars analysis. Cell viability for Lactic Acid Bacteria (LAB) and Leuconostoc was determined before and after fermentation. Results indicate that capsaicinoids are very stable compounds, as notable differences between unfermented and fermented samples could not be seen. Carolina Reaper and Fatalii cultivars were amongst the most pungent, whereas Cherry, Cayenne, and Bulgarian types were low to moderate in pungency. Average loss of total ascorbic acid was 19.01%. Total phenolic compounds ranged between 36.89-195.43 mg/100 g for the fresh fruits and 35.60-180.40 mg/100 g for the fermented product. Losses through fermentation were not significant (p < 0.05). Plate counts indicated low initial numbers for LAB in the fresh samples, values ranging between 50-3700 CFU/g (colony-forming units). After fermentation, day 21, concentration of LAB (3.8 × 106-6.2 × 108 CFU/g) was high in all samples. Fermented chilies paste with enhanced biochemical and bacterial properties might further be used in the technology of vegetable (brining) or meat (curing) products, processes that generally involve the fermenting activity of different microorganisms, especially (LAB). Thus, the purpose of this research was the investigation of biochemical and microbial transformations that naturally occur in fermented chilies with a future perspective towards technological applications in cured meat products.