Hey guys! This week I’m going to be writing about enzymatic activity and other factors that affect the process of denaturation and coagulation. I made a chicken stir-fry with marinate and without marinate to examine the process of enzymes and how they affect the process of coagulation and denaturation. Also in class, we all did an experiment on how different additives affect the aeration of egg whites.
I observed the differences between the chicken with marinate and without marinate and recorded them in the table below.
|Physical changes||Chemical changes|
|Browner in colour||Intense flavour
|Soft/tender||Denaturation – from the addition of the pineapple juice in the marinade
|Normal cooked colour
|Could taste individual components of dish||Chewy||Denaturation- from the heat applied when cooking chicken.
I think that the better method was the marinated chicken. It had a more intensified flavour and was easier to chew as it was more tender.
The reason that I marinated the chicken was so that the acid from the pineapple juice in the marinade can cause the protein to denature and therefore the chicken becomes more tender. It also adds a really nice flavour, instead of just having plain chicken! Denaturation occurs in this recipe when adding the marinade to the chicken and letting it soak to absorb the flavours and undergo the chemical processes. It also occurs when the chicken is being cooked because the heat causes the protein structure to unravel.
Chicken with no marinate
Enzymes that are present in the marinade are responsible for helping with the denaturation of the chicken.
Enzymes are biological molecules (proteins) that are also known as catalysts (this means they assist in the chemical change without becoming involved in the reaction). They speed up the chemical process by breaking down the peptide bonds in proteins into individual amino acids. The enzymes that break down proteins are referred to as protease. “Proteases refers to a group of enzymes whose catalytic function is to hydrolyse (breakdown) proteins. They are also called proteolytic enzymes or systemic enzymes.” (Enzymeesttentials.com n.d) The image below shows how the proteases break the peptide bond between the protein molecules and causes them to become individual amino acid molecules.
(picture from : bbc.com, 2014)
The enzyme that is responsible for the breakdown of proteins in this experiment is bromelin. The pineapple juice in the chicken marinade is responsible for providing the enzyme in this experiment as it contains bromelin which is responsible for breaking down proteins such as myosin, elastin and collagen, which are the muscle fibre and connective tissue in the meat so when these proteins are broken down it causes the meat to soften and become tender. (Corriher, n.d.)
In class we did an experiment that looked at denaturation and coagulation of the aeration of egg whites and factors that affect it. We tested some of these factors and recorded this results table.
|Start||Soft Peaks||Stiff Peaks||Colour||Texture||Volume||Smoothness of Surface|
|Salt||0||1:29||6:00||White||Foamy, rough, separated||Normal||Flat, not smooth
|Cream of Tartar||0||0:48||1:58||White||Thick, foamy, smooth||Increased & dense||Soft/smooth & dense|
|Lemon Juice||0||0.42||1:52||White||Dense, foamy||Normal||smooth
|Oil||0||0.52||1:25||White||Greasy||Flat||smooth & shiny
|Water||0||0.50||1:15||White||Thick, smooth, shiny||Doubled in volume||Smooth & fluffy
|Sugar||0||0.37||1:02||White||Silky||Greater volume||Smooth & soft
|Room temperature||0||0.41||1:17||White||Fine,stiff, foamy||Glossy & smooth|
|Refrigerated||0||0.43||1:22||Bright white||Smaller bubbled||Dense||Less glossy
Each of the additives had an increased time needed to get to the stiff peak stage. However, salt had the most increased time compared to the other additives. The eggwhites with the water, sugar and cream of tartar all had an increased volume. The eggwhite that was refrigerated altered the colour of the eggwhite.
Egg white with sugar Egg white with 2 tbsp water
Egg white with lemon juice Egg white with oil
I did some research and found this video that explains denaturation and coagulation of proteins, using egg whites as an example. https://www.youtube.com/watch?v=KV5i0VkHtR8
As you can see from the marinated stir-fry I made and the aeration of eggwhite experiment, there are many factors that can affect denaturation and coagulation. These factors include:
Temperature: The temperature affects the denaturation and coagulation of different foods and this affects the final appearance of the food. We found that the eggwhite beaten from the refrigerated egg was less glossy and had smaller bubbles than the room temperature egg. You can also see in the table that the room temperature egg formed into soft and stiff peaks quicker than the refrigerated egg. This is because the warmer temperature causes the proteins to denature quicker. Other examples of temperature that we use in food processing would be scrambling eggs or cooking a steak.
Acids: When denaturation occurs from acids, the food has a pH of less than 7. Acids attack and break the bonds between amino acid strands. Acids are added into meat marinades and used in dairy products (lactic acid) such yoghurt and sour cream to cause denaturation and coagulation to occur.
Agitation: When you are mixing, whipping, beating or kneading, the agitation causes protein strands to stretch. Over mixing can cause the protein to denature and this affects the final result and function of the food. Agitation is used in the making of meringues when egg whites are beaten or when making pastry or bread when you knead the dough.
Enzymes: As I explained earlier, enzymes help break the peptide bonds between amino acids and cause denaturation.Pineapple juice is commonly used in marinades to denature and soften meats as it contains the enzyme bromelin.
Addition of other ingredients: Adding other ingredients such sugar and salt affects denaturation and coagulation. Sugar protects the protein sugar, so in its presence proteins can tolerate higher temperatures before it reaches the stage of denaturation or coagulation. An example of this is when making custard. The temperature needs to be higher so the proteins will coagulate. Salt is added to water when boiling eggs in case there is a crack in the shell. The salt increases the rate of coagulation and limits the loss of egg white from the shell.
I hope this has informed you on enzymatic activity and factors that affect denaturation and coagulation! This is my last blog post so I hope that I have helped you learn about the different functional properties of food and how they’re use in the food industry! I also hope that my post have inspired you to try this recipes and experiments out too so you can see for yourself!
BBC (2014) KS3 Bitesize science – diet, drugs and health: Revision, page 5. Available at: http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/diet_drugs/revision/5/ (Accessed: 21 March 2016).