Raw fruits can be used to tenderise meat before cooking because they contain enzymes1 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 acids2 (typically vinegar, lemon juice or wine), oils, herbs, spices, dairy products, fruits and vegetables.
Natural meat tenderisers
Meat consists of muscle3 and connective tissues that are made up of proteins. Proteins contain lots of amino acids4 linked together in chains to make large molecules5. 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
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 heat6. 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 enzymatic7 digestion8 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.
- enzyme: A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.
- acid: A hydrogen-containing substance that is capable of donating a hydrogen ion to another substance.
- muscle: The tissue that makes it possible for an animal to move and to maintain its posture. Muscles also make the heart beat, force blood to circulate and move food along the digestive system. The human body has more than 600 muscles.
- amino acid: The basic building block of proteins. A short chain of amino acids is called a peptide, and a long chain of amino acids (normally more than 50) is called a protein.
- molecule: Two or more atoms bonded together. The molecule of an element has all its atoms the same. The molecule of a compound has two or more different atoms.
- heat energy (heat): Heat energy: the transfer of energy in materials from the random movement of the particles in that material. The greater the random movement of particles the more heat energy the material has. Temperature is a measure of the heat energy of a material.
Heat: the flow of energy from a warm object to a cooler object. - enzyme: A complex protein that acts as a catalyst (speeds up chemical reactions) in specific biochemical reactions. For example, saliva contains an enzyme called amylase that can break down starch into simple sugars.
- digestion: The mechanical and chemical breaking down of food into smaller components that can be absorbed into a bloodstream.
