Factors that affect Denaturation and Coagualtion

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
  Appearance Taste Texture  
Method 1

(marinate)

Browner in colour Intense flavour

 

Soft/tender Denaturation – from the addition of the pineapple juice in the marinade

 

 

Method 2

(no marinate)

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.

Marinated Chicken

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.

12476711_979735718773647_1845118549_o 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.

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                                                          (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.

Additive Record Time Observations
  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!

Claudia xxx

 

Bibliography:

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).

Corriher, S. (1900) Marinades add flavor but don’t always Tenderize. Available at: http://www.finecooking.com/articles/marinades-flavor-tenderize.aspx  (Accessed: 21 March 2016).
Protease digestive enzyme to help digest proteins. Digestive enzyme supplements (no date) Available at: http://www.enzymeessentials.com/HTML/protease.html (Accessed: 21 March 2016).

 

 

 

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Chemistry of Lipids

This weeks post is about the chemistry of lipids (also known as fats). In class we looked at distinguishing between saturated and unsaturated fats and identifying properties of fats and lipids.

In class we looked at the differences in colour when bromine solution was added to saturated and unsaturated fats. The fats we looked at were olive oil, animal dripping, butter and vegetable oil and vegetable shortening (copha). These were the results we recorded.

Olive Oil Animal Dripping Butter Vegetable oil Vegetable shortening (copha)
Colour after adding Bromine colourless Orange/ brown Orange/ brown colourless Orange/ brown
Saturated or unsaturated fat unsaturated saturated unsaturated unsaturated saturated
saturated

When the bromine solution was added to the olive oil, it became colourless but when added to the animal fat the bromine turned it a orange/brown colour.  The reason the colours are different depends on whether the fat is unsaturated or saturated, which determines if the fat contains a double carbon-carbon bond or not. Unsaturated fats contain one or more carbon-carbon double bond, which means that they are easier to break down due to the kink that is caused in the chain (cis configuration) from the carbon-carbon double bond. The carbon-carbon double bond that is present also makes it able for the bromine to attack. When bromine is added to the olive oil (unsaturated fat) , it attacks the carbon-carbon double bond, which produces a dibromo compound. This compound is colourless, which is what caused the olive oil to go colourless.

food chem

This chemical structure shows how the carbon-carbon double bond in a monounsaturated fats reacts with bromine.

The bromine stayed an orange/brown colour when added to the animal fat because it is a saturated fat and the hydrogen atoms are saturated, meaning it is not susceptible to being attacked and the dibromo compound that causes that causes the bromine to go colourless is not created.  (BBC, 2013)

When the bromine solution was added to the vegetable oil and the vegetable shortening (copha), the vegetable oil became colourless whilst the bromine in the vegetable shortening was a brown/orange colour. This again, is because the vegetable oil is an unsaturated fat but the vegetable shortening is a saturated fat.

A polyunsaturated fat delcolourises more bromine than a monounsaturated fat because a monounsaturated fat contains only one C=C bond but a polyunaturated fat contains 2 or more C=C bonds. Since polyunsaturated fats contain at least 2 double bonds it is easier for it to be attacked by the bromine solution.

To explore the properties of fats and lipids, I made sausage rolls with homemade pastry and sweet chili ailoli. The sausage rolls tasted great! The cumin, salt and pepper and moroccan spices that was added into the mixture really enhanced the flavour. When we had removed the sausage rolls from the oven, they were a nice golden brown colour and the pastry had become crunchy and flaky and the meat mixture on the inside was soft. In my opinion, the sausage rolls that I made tasted better than the ones you would buy from the shop. I believe this is because they were homemade, using real, fresh ingredients and didn’t contain over processed ingredients. Also when you purchase sausage rolls from the shop they have usually been frozen and reheated but I had eaten mine fresh from the oven. They were also slightly denser than the one you buy from the shops.

Before and after sausage rolls had been cooked.

When it came to adding the butter, I had accidentally added too much butter into the pastry mixture which caused it to become softer then it should be. So when it came to rolling in the butter between each layer of pastry, less butter was added and it ended up turning out fine.

The purpose of rolling butter into the pastry after each layer is because the heat causes the butter in between each layer begins to steam, causing the puffiness between each of the layers. You can see the separate layers that formed in the pastry in the photo of the sausage rolls. The reason we refrigerate the pastry each time we have rolled a layer of butter in, is so that the butter doesn’t melt into the pastry causing it to go soggy and would prevent the pastry from puffing. The butter being cooked when it’s cold also affects the end result of the pastry’s texture.”When very cold butter melts in the oven, leaving air pockets between the thin pastry layers after they have firmed, resulting in loads of crisp, flaky layers.” ( Matt Preston. NewsLifeMedia, 2016)  It also gives time for the gluten in the pastry to rest which will prevent the pastry from shrinking when the heat is applied.

The sources of fat that are present in this recipe include:

  • Sausage mince – contain saturated and unsaturated fats
  • Butter – saturated and unsaturated fats
  • Olive oil – unsaturated fats
  • Eggs – contain saturated fats, monounsaturated and polyunsaturated fats
  • Dijon mustard – dijon mustard contains saturated, monounsaturated and polyunsaturated fats. There is 0.19 grams of fat in one teaspoon (Fat Secret Australia).      

One of the functional properties of fat that are present in this recipe is shortening. When making the pastry, rubbing the butter into the flour and pastry encourages the flour particles to separate and incorporate air.  The fat also surrounds the strands of gluten and prevents the gluten from reacting in the liquid and stopping it from being tough. This can also be known as tenderising. Shortening is commonly used in the food industry for the production of pastries and cakes. Vegetable shortening is also widely used in the food industry by takeaway franchises for deep frying due to the high smoke point (allows it to cook quickly without burning oil) and low moisture level (reduces splatter, delays rancidity).

When making the sweet chili aioli, we needed to add an emulsifying agent to help the oil and water to mix together. The emulsifying agent we used was egg yolk. The reason we used egg yolk was because they contain a protein called lecithin. Lecithin’s ability to interact with both oil and water makes it a successful and stable emulsifier. Emulsifying is also used for the creation of mayonnaise and salad dressings.

Trans fatty acids are an unsaturated fatty acid and can occur naturally in foods or be formed and added into foods when being manufactured. When hydrogen atoms are on the opposite side of the C=C double bond then the molecule is linear and referred to as a Trans fatty acid. Trans fatty acids are commonly found in animal products such a margarine, cheese and meat. When margarine is manufactured, the oils present undergo the process of hydrogenation, which causes the hardening of the spread. (Food Standards Australia and New Zealand,2015). 

Hope you learnt from this blog post and I definitely encourage you to try making the sausage rolls because they are super tasty!

Talk to you in my next post!

Claudia xx

 

 

 

 

 

Gelatinisation

Hey there! Welcome back to my blog! This week I have made a risotto and white sauce to examine the process and usefulness of gelatinisation in cooking.

So I bet you’re wondering what I’m talking about when I say gelatinisation? Gelatinisation is the process in which starch thickens mixtures by absorbing liquid in the presence of heat.The gelatinisation process breaks down the starch molecules with the help of the heat and moisture. The starch molecules then loose their structure due to the heat and begin to absorb the surrounding moisture/liquid. This process will take place no matter what the type of starch is. Starch molecules are made from two substances, amylose and amylopectin. Majority of starches contain roughly 25%  amylose and 75% amylopectin but the amount of these substances can vary. Differences in the levels of amylose and amylopectin in different starches can lead to the use of one starch creating a thicker mixture than another.

The starches we looked at in class were corn flour and wheat flour. We watched video clips of what happened to the starches when they are heated in a microscopic view.

Starches before being heated Starches after gelatinisation
Corn Flour:

  •  Few small molecules

Wheat Flour:

  •  Lots of larger molecules
Corn Flour:

  • Molecules break down and grow with absorption
  • Changed in size and consistency

Wheat Flour:

  • Molecules grow from absorption but due to the overcrowding, molecules group together
  •  Changed in size and consistency

Because different starches develop differently after being heated we made two different white sauces to examine the differences. One we made using rice flour and the other we made using wheat flour. The rice flour sauce had a sticker and more gluggy consistency, whilst the wheat flour sauce was creamier and more dense. I liked the taste of the white sauce made from the wheat flour more, I think this was because the consistency of it appealed more to me.

12772942_1102453609817699_1897172648_o           White sauce with rice flour (left)  & White sauce with wheat flour (right).

Risotto & White Sauce

I was able to tell that gelatinisation had occurred in the risotto and the white sauce as they both had become a thicker and gel like consistency. The rice in the risotto had gone from being hard to absorbing all the liquid and forming a thick, gluey like mixture that stuck together. At first the white sauce was a quite runny liquid but once the heat had been applied, it became a lot thicker and creamier. Seeing these changes in the texture of the mixtures shows that gelatinisation had occurred.

White sauce made with wheat flour.

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Factors that affect the gelatinisation of starch include:

  • Temperature: For gelatinisation to take place, warm and moist conditions are required. The starch granule is softened during the heating process, which allows it to absorb the liquid. Once the temperature reaches around 80 to 90 degrees, the starch granule bursts open and release amylose and amylopectin, which allows even more liquid to be absorbed and causes the mixture to thicken into a gel. I saw this take place when making the risotto when almost all of the water had been absorbed by the rice and the mixture was beginning to thicken.
  • Agitation: To ensure that your mixture is smooth and not lumpy, agitation is required. When making the risotto and white sauce we made sure to constantly stir the mixture from start to finish to prevent lumps that form from the starch.
  • Other ingredients: Gelatinisation can be effected by the addition of sugars,acids and fats. Sugar competes with the starch for water consumption, so there is less water that the starch can absorb. Acids can affect the final production of the thickness of the mixture. Sugars weren’t a concern for me when I made the risotto and white sauce but when adding the lemon rind in the risotto, I made sure to add it before serving. Another ingredient I did add was fats. The bacon, cheese and oil in the risotto and the butter in the white sauce helped in stopping the amount of lumps forming in both the mixtures.

I made the following observations of the rice before and after it had undergone the process of gelatinisation.

Rice prior to cooking Rice after cooking
·         Hard/grainy

·         Dry

·         Didn’t stick

·         Thin, beady shape

·         Soft

·         Mushy consistency

·         Glue texture, stuck together

·         Increased in size, slightly flatter

Rice before gelatinisation                      Rice after gelatinisation

It is necessary to heat starch molecules for gelatinisation to occur. If there is no heat applied, the amylose and amylopectin will not be released and the mixture will not thicken.

As starch is a polysaccharide, it is able to break down. This makes starch able to undergo the process of gelatinisation. Gelatinisation is used in food preparation to alter the texture so it thickens and becomes stickier, it’s considered as an adhesive and thickening agent in the food industry. Gelatinisation of starch can be used to make risottos, gravy or deliciously creamy white sauces!

If you’re curious as to why we specifically use arborio rice instead of brown or grain rice, it’s because of the levels of amylopectin and amylose. Other rices have a lower level of  amylopectin and higher levels of amylose compared to arborio rice. If you used brown or grain rice, the incorrect levels of starch would cause it to not have the creamy, sticky texture that is created when arborio rice is used because not as much liquid will be absorbed.

As I explained earlier, the additions of acidic substances can affect the thickness and texture of the mixture. This is why the lemon rind or juice is adding to the risotto right before we serve it. Adding the lemon rind or juice any earlier could result in the gelatinisation process being disturbed and your rice may still be hard.

I hope from reading this post, you’ve learned as much as I have about gelatinisation and the structure of starch granules! Talk to you in my next post!

Claudia xx

Caramelisation, Crystallisation and Dextrinisation

Hey guys, welcome to my first blog post! Today I made a toffee/almond brittle and chocolate chip cookies to explore the chemical process of caramelisation, crystalisation and dextrinisation

Toffee/Almond Brittle

For my first experiment, I made a toffee to help us learn more about caramelisation and crystalisation. To begin the chemical process, I melted the sugar with the butter and water. As the temperature of the mixture increases and the sugar begins to melt, it starts to turn a light brown/caramel colour. This reaction is because of the heat that is applied to the monosaccharides and disaccharides causes them to change colour.

 

I made two separate batches of toffee, one which we mixed in with bicarbonate soda.

I compared the physical results of the toffee with bicarbonate soda to the toffee with no bicarbonate soda and observed the outcome of volume, texture, colour and which had a more shiny/lustrous surface. I found that the toffee with bicarbonate soda had a greater volume and lighter texture, whilst the toffee without bicarbonate soda had a darker colour and shinier surface.

Uses of caramelisation in food preparation include things such as change of colour and to enhance flavour. Caramelisation is a commonly used technique in the food industry and is used to make foods such as toffees, honeycomb caramel sauces, caramelised onions and carrots etc.  When I added the bicarbonate soda to the toffee, it started to foam and form bubbles. Whilst the syrup is hardening, the bubbles get trapped and don’t have enough time to escape, which makes it turn into a honeycomb. The reason that this happens is because the heat from the toffee causes the bicarbonate soda to release carbon dioxide and this creates the air.

You may be wondering why you don’t stir the toffee mixture whilst it’s on the heat and if you have done this before when you’ve made toffee, I’m sure you will know that it ends up being a disaster! The process that takes place if you continuously stir the toffee while you wait for it to change colour is called crystallisation.  This process is triggered when you stir the sugar  because it creates air, when then promotes the formation of sugar crystals because of the rapid movement of the molecules. The sugar then crystalisies and will cause your toffee to have a very grainy like texture.

Temperature and acidity are also factors that effect the crystallisation process. The higher your temperature is, the more amount of sugar is able to dissolve so that’s why we used a higher temperature when we made the toffee. When acids are added to the sugar and water, it stops the development of large sugar crystals which will prevent a grainy texture.

 

Chocolate Chip Cookies

To explore the process of dextrinisation, I made classic chocolate chip cookies and they were absolutely delicious!

So what exactly is dextrinisation? It’s the chemical process in which starch breaks down into dextrins.Dextrins are the halfway point in the complete breakdown of a starch molecule into the monsaccharide glucose.

Before I placed the cookies in the oven, the mixture had a doughy, dense and sticky like texture and they were flat with a light yellow colour. After the cookies had been removed from the oven, the cookies had risen and become harder and the colour had turned into a nice golden brown.

By cooking the cookies in the oven, I’m using the dry heat method which transfers heat via air. If I had left the cookies in the oven for another 30 minutes they would be overcooked and become burnt and black in colour. The reason for this is because the longer the heat is applied, it causes further breakdown of the dextrins into maltose which then breaks into two glucose molecules and we are left with an excess amount of glucose.

Starch -> dextrins   -> maltose   -> glucose

Now to compare the difference between caramelisation, crystallisation and dextrinisation. The most obvious difference would be that carmaelisation and crystallisation typically involve sugars, sucrose and fructose but dextrinisation involves starches. Dextrinisation and caramelisation both involve the browning process but crystallisation doesn’t. All of these processes can be useful in different aspects of food preperation.

Caramelisation can be used to make cakes, baked products, icecream, honeycomb and you will find that many products in the confectionary aisle of the supermarket use the carmelisation process.

Crystallisation is used to create toffees, brittle, fudge and caramel. Dextrinisation is responsible for bread turning brown during toasting and the formation of brown crust on baked bread and pastries. Dextrins can also be used as colouring and sweetening agents.

So, I’ve pretty much covered everything I observed whilst doing these experiments and I hope that the information I have provided has helped you gain some knowledge on the chemical processes of caramelisation, crystallisation and dextrinistion in cooking.

Talk to you in my next post! Claudia xxx