Raw fruits can be used to tenderise meat before cooking because they contain enzymes that break down proteins.
Marinades are usually added to meats such as beef, chicken or pork before cooking. Marinades have two main roles – they add flavour, and they may also tenderise the meat, making it softer and less chewy.
Marinades are a mixture of ingredients that can include acids (typically vinegar, lemon juice or wine), oils, herbs, spices, dairy products, fruits and vegetables.
Natural meat tenderisers
Meat consists of muscle and connective tissues that are made up of proteins. Proteins contain lots of amino acids linked together in chains to make large molecules. Meat tenderisers act by breaking apart the amino acids. Marinades designed to tenderise meat usually contain acids or enzymes.
Acidic ingredients in marinades
Acidic ingredients in marinades like vinegar, wine and lemon juice will tenderise meat by denaturing or unwinding the long protein in the muscle. In fact, if you leave an acidic marinade on a piece of meat for a long time, it will eventually break down all the proteins – leaving behind a mushy mess.
Enzymes in marinades
Enzymes can speed up or catalyse the breakdown of proteins into amino acids. For example, fruits like papaya, kiwifruit, pineapple, fig and mango are a good source of enzymes that can break down meat proteins. These fruits all contain a type of enzyme called a protease.
Fruit enzymes work at higher temperatures
Enzymes in our bodies tend to work best around 37 °C. However, enzymes from fruits, such as papaya or pineapple work best between 50–70 °C. If left too long on the meat, they can completely digest it.
Fruit enzymes can be inactivated by high heat. This is the reason that fruits or vegetables are often blanched (dipped briefly in boiling water) before being frozen, because this inactivates the proteases and stops them from discolouring in the freezer.
Tenderising without enzymes
There are other ways to tenderise meat including chopping, mincing or even pounding the meat with a mallet. These methods also break up the muscle and connective tissue, making the meat more tender. Alternatively, cooking the meat slowly for a long time will also make it softer.
Classroom experiment
You can try a simple experiment to look at the action of marinades as an introduction to experiments with enzymatic digestion of proteins. This could be used as the basis for further experimentation.
Learn more about the function of enzymes in digestion then try this activity with your class, Enzyme action.
The article Catalysing chemical reactions with enzymes includes an animated video outlining in detail how enzymes work.
