Almost everyone has accidentally burnt food before, and many of them still eat the burnt areas either because they especially enjoy the crispy parts or because it is just unavoidable. However, people are often warned against doing so and are told that burnt food is carcinogenic. What’s the truth behind this? Does burnt food actually increase cancer risk? In order to have a better understanding, we need to consider the chemistry in burnt food.
One solid reason to not eat burnt food is that it contains polycyclic aromatic hydrocarbons (PAHs), which are a class of air pollutants. Some of these chemicals have been proven to be carcinogenic, and some are even found in coal tar and cigarette smoke. The toxicity of PAHs depends heavily on its structure; while many PAHs may have the same chemical formula and same number of rings, different isomers can vary from being nontoxic to being extremely toxic.
The most well-known of PAHs is benzo(a)pyrene (shown below in Figure 1), which damages DNA, which in turn can possibly cause cancer. Cooked meat products contain up to 4 ng/g of benzo(a)pyrenes and up to 5.5 ng/g in fried chicken. However, in overcooked beef, the amount of benzo(a)pyrene can reach over 60 ng/g.
The mechanism of action of DNA damage from benzo(a)pyrenes is relatively simple. The benzo(a)pyrene molecules (shown in Figure 1) intercalate themselves into DNA strands. This means that they fit between base pairs, as shown in the Figure 2, thereby interfering with transcription and possibly causing mutations.
The smell of smoke from burning food is not only acrid, but also contains these benzo(a)pyrenes. Therefore, in addition to avoiding eating burnt food, we should avoid burning food in the first place. While accidentally leaving the bread in the toaster for too long is sometimes hard to avoid during the morning rush, at least we now have a good reason to not eat burnt food.
Author: Jonathan Yu