With the warmer weather, the grills are being dusted off and fired up. What is a better way to celebrate the arrival of summer than that evening with friends around the grill? For food chemists, it also means having to explain if and why grilled food, meat especially, are carcinogenic. It has already began, Dr Free-ride lit her grill a few weeks ago, but not after checking if there was any truth to the scare stories about grilling.
The main carcinogens produced by food processing/cooking require temperatures in excess of 120 oC. There are two major types of potential carcinogens formed by the Maillard reaction. This reaction, between amino acids and reducing sugars, is essential to food quality as it one of the major reaction responsible for color and flavor formation. I’ll be writing more about the Maillard reaction in the future, as it is the reaction I primarily study. It is known as a non-enzymatic browning reaction, as that is the final result of the reaction.
The first class of potential carcinogens identified were heterocyclic amines (HAs) (Skog, 1993). The other is acrylamide. Acrylamide is formed during the frying of potatoes, baking of bread, and other plant-based high temperature processed food products. Acrylamide formation appears to require a reducing sugar and the amino acid, asparagine. Interestingly, asparagine is used by plants, such as the potato, as the storage amino acid and therefore it is present in high concentrations. Unsurprisingly, asparagus – namesake of asparagine – when fried produces large amounts of acrylamide. Since acrylamide was only identified in foods in 2002, the research on reducing it is still on going. Current research suggests that limiting reducing sugar levels (storage temp of potato changes this) and cooking temperature reduces acrylamide formation.
For HAs to form, in addition to amino acid and sugar, creatinine is required. Creatinine is formed from creatine as a byproduct when muscle is broken down, so HAs only form in meat products. We can’t prevent meat animals from producing creatinine, so that isn’t an option in stopping HA formation. Using a marinade will reduce HAs. Any kind of marinade seems to work, it isn’t clear how this works. Perhaps one or more of the reactants moves into the marinade or perhaps the coating of marinade prevents to outside of the meat from over heating.
The toxicological evidence is still out for both acrylamide and heterocyclic amines. But if we want to be cautious, how can we prevent or reduce their formation? Easily, if we boiled most of our food products, we could avoid HAs and acrylamide, but how would that influence the gastronomic experience? You could eat casseroles and hot dish as long as you didn’t fry or brown the meat first. No more meaty aromas, which come from the Maillard reaction of sulphur-containing amino acids, methionine and cysteine. No roasted flavors or colors. No toast! Cooking food quickly for a short time also reduces HA formation. But be careful – it is important to make sure that the inside of your meat reaches that crucial 72 oC to kill off most of the bacteria.
Also not all bacteria or micro-organisms, especially viruses are destroyed by boiling, especially as the internal temperature is important. So higher temperatures external temperatures are required. Complete sterilization of milk, for example, is typically carried out at 120 oC for 3 sec. One of the reasons sterilized milk tastes different from pasteurized milk is because the Maillard reaction has caused the formation of flavors that don’t occur at the lower temperatures of pasteurization.
Sometimes, we joke that the choice can be the difference between a quick (food poisoning) or a slow (cancer) death.