Denaturation and Coagulation

In class today we made a baked custard tart. The two functional properties of protein we looked at during this practical was denaturation and coagulation.

Custard Tart

Blind baked pastry

DENATURATION: occurs when the bonds holding the helix shape are broken and the strands of the helix separate and unravel. It is a permanent change in the structure of proteins. The functional property of protein, denaturation is useful in food preparation for example whisking eggs which is a component of many food products, the marinating a piece of meat where the acid tenderises the meat before cooking, making sour cream and yoghurt.

COAGULATION: Is more visible then denaturation, this process occurs when denatured proteins separate from other nutrients and solidify or semi soldify. Applying heat for a long period of time will cause the protein structure to create a network and trap liquid which will form a gel. Coagulation is used in food preparation  most commonly for cooking eggs, some examples include; raw eggs being cooked eg boiled or scrambled as part of a dish, making a quiche with coagulated eggs, meringue (denaturation for beating the eggs, coagulation for cooking the egg product), pretty much any egg product being cooked. Also cooking meats like chicken, and the process of making cheese.

Difference between denaturation and coagulation:

• Denaturation happens before coagulation
• coagulation is more visible then denaturation
• coagulation uses denatured proteins
• you can over coagulate, but cant over denature

The physical changes that occurred throughout the making of the custard tart is the mixing ingredients together for both the pastry and the custard. The rolling out of the dough to make a smooth thin pastry and pricking the bottom of the pastry to allow steam to escape

Custard before heated

The main sources of protein found in the custard was the egg and the milk. Both the egg and the milk are globular proteins. Globular proteins are strands of proteins that are twisted into a rounded, compact shape. The type of globular found in the eggs, or more specifically the egg whites is albumin. The main type of globular protein found in the milk is alpha lacto globulin and beta lacto globulin.

In the making of the custard, then process of denaturation and coagulation occurred. When denaturation is occurring the bonds holding the helix shape are broken and unravel. When coagulation is occurring the unravelled protein strands begin to re-join with other strands forming a solid mass. Egg was the food mainly responsible for this. For this change to occur several factors were present for this to occur. Some factors include temperature, acidity, agitation and sugar. Heat causes proteins to denature or unravel. Proteins will denature and coagulate quicker in higher temperatures, but different temperatures will affect the processes properties of different foods. Acid will help proteins denature. Denaturation occurs when the acid begins to break the bonds between strands of amino acids. Acid is used for thickening of dairy products. Agitation causes the protein strands to stretch, if there is too much mixing the strands are stretched too much to the point the protein is denatured which affects the function of the food. Finally sugar, in this case caster sugar, with proteins will mean the product will need a higher temperature before denaturation or coagulation occurs. The custard requires a higher temperature to coagulate the protein in the milk and thicken eggs due to the sugar. Other factors that affect denaturation and coagulation include enzymes and salt.

At 63 degrees Celsius egg whites begin to thicken, at 65 degree Celsius egg whites become a tender solid since coagulation has occurred. Eggs will continue to over coagulate as water is pushed out from between protein molecules. Between 63 degrees Celsius and 65 degrees Celsius is the optimum temperature for coagulation of eggs whites, the egg yolks require a slightly higher temperature to coagulate up to 70 degrees celsius.

Before coagulation of eggs

Coagulated eggs

Overall the custards tasted great, but its a relief its the last blog! 🙂

Chemistry of Lipids

This week we started looking at chemistry of fat. At the start we spoke about distinguishing between saturated and unsaturated fatty acids and what colour bromine goes when mixed with. After this we went into the kitchen and made sausage rolls with home made puff pastry, and a sweet chilli aioli.

Even though we didn’t actually do the prac for this, first thing in class we talked through the difference between saturated and unsaturated fat when adding a bromine water solution to it. If you added the bromine solution to olive oil you will get a clear colour as it is an unsaturated fat. If you do the same thing to animal fat you will get an orangey brown colour as animal fat is a saturated fat.  This also works for testing both vegetable oil and vegetable shortening. as vegetable oil is unsaturated, the colour will go clear with the addition of bromine. Even though vegetable shortening is of plant origin (normally unsaturated), it has gone through a process of hydrogenation making it a saturated fat. this means when bromine is added to the vegetable shortening it will go a brown/ orange colour.

The carbon-carbon double bonds, found in unsaturated fats, react with the element bromine. The more double bonds there are in the fat, the more the bromine will react and decolourise. the term ‘polyunsaturated fats’ means the fat has many carbon-carbon double bonds. This means the bromine will react with the polyunsaturated fat and decolourise more compared to the reaction with a monounsaturated fat which only has one carbon-carbon double bond.

bromine solution with monounsaturated fat

Saturated fats are said to be ‘saturated’ with hydrogen atoms as every carbon bond has the maximum amount of hydrogen atoms connected. These fatty acids have no carbon-carbon double bonds. Unsaturated fatty acids have hydrogen atoms missing leaving the carbon atoms joined with a double bond instead of a single bond. Monounsaturated fatty acids have one f these carbon to carbon double bonds, where as polyunsaturated have 2 or more of these bonds.

(pictures from: http://dontwastethecrumbs.com/2013/02/the-truth-about-fats-fat-is-essential-and-the-type-of-fat-matters/)

The sausage rolls we made today in class were delicious. They didn’t taste like regular sausage rolls you buy from a bakery or frozen ones from a grocery store. The ones we made had more of a taste to them and they tasted fresher. The herbs and spices in the meat mixture worked really well and gave it a great taste. When they came out of the oven, they had a nice golden brown colour to them and smelt amazing. the puff pastry was flaky when you bit into it with the meat part being soft. The ones we made in class were different from the ones we buy at the shop as ours had more of a taste compared to the more bland ones we buy which have been frozen then reheated. I found that the puff pastry was pretty similar except ours tasted less sweet due to  us not having time to roll all the butter in, and since ours were fresh they ended up more flaky then some of the ones I’ve tasted from shops. Some reasons ours tasted different from shop brought sausage rolls could be, we used some different ingredients which is a given from using different recipes, ours were fresh out of the oven and we made our own puff pastry which takes more time but gets a slightly different texture to the puff pastry you can buy from grocery shops. Our puff pastry didnt puff as much as we didnt have time to roll in all the butter to make more layers.

Only picture we got of the final sausage rolls.

The purpose of rolling the butter into the pastry several times is too create the light flaky layers of pastry. This happens as the butter in between the layers, when heated, will create steam forming the puff between the pastries

The purpose of refrigerating pastry each time after you have rolled the butter in is too keep the butter cool, if we left it out the whole time while rolling the layers in, the butter would start melting into the pastry making it soggy. The quick melting of the butter makes the pastry have a more flakier consistency. It is also easier to mold when cold, as butter is hard to handle in room temperature. It also gives the gluten time to rest so your pastry wont shrink when cooking it.

Pastry dough just out of the fridge

In the recipe for the sausage rolls, puff pastry and the sweet chilli aioli the following ingredients had a source of fat:

• Sausage mince: contains both unsaturated and saturated fats
• Egg: Contains all three, monounsaturated, polyunsaturated and saturated fats
• Butter: both unsaturated and saturated fats
• Olive oil: mostly unsaturated fats
• Dijon mustard: Dijon mustard only has roughly 0.19g of fat per teaspoon, but contains all three types of fats.

One functional property in this recipe is ‘shortening’. We used shortening when we rubbed the butter into the flour to incoorporate air. The fat also surrounds the gluten to prevent it from being tough as the gluten is unable to react with the liquid. Shortening is used in food industry for mostly used in baked goods like pastries, cookies and cakes. The other functional property we used was emulsifying when making the sweet chilli aioli when adding the oil. We used an egg to hold the oil in with the other ingrediants that dont normally mix. This functional property is used to make most salad dressings and mayonnaise.

Overall it was a fun and tasty lesson 🙂

Cooking with chemistry: gelatinisation

In class today we studied the shape and structure of three different starch granules, corn flour, wheat flour and potato starch. In addition we looked at the usefulness of gelatinization in cooking by making a risotto, and a white sauce.

STRUCTURE OF STARCH GRANULES

Gelatinization is the process in which starch thickens by absorbing liquid in the presence of heat. The heat breaks down the starch molecules allowing it to absorb the liquid. When the starch is heated to roughly 60 degrees, it starts to absorb liquid. At around 80 degrees the molecules burst releasing amylose and amylopectin allowing even more liquid to be absorbed, then around boiling point (100 degrees) the process of gelatinisation is completed.  The process breaks down starch molecules with the presence of heat and moisture. With the application of heat, the starch lose their structure until they burst and absorb the surrounding moisture.

Before the three different starches; corn flour, wheat flour and potato starch were heated, all their shapes were different. The corn flour had few small sized molecules, the wheat flour had larger molecules and more of them, and the potato starch had a small amount of molecules with a large size.

After gelatinization the molecules change in size and consistency, but the difference between them were still the same. The corn flour breaks down and grows with the absorption of a liquid. The wheat flour would do the same but due to overcrowding the molecules will group together. The potato starch grows even larger but takes a longer time for movement to occur.

Most starches contain around 25% amylose. The proportions of amylase and amylopectin differed from each flour, the corn flour had 28% amylose, the wheat flour had 26% amylose, and the potato starch had the smallest amount being 20% amylose. The lower levels of amylose in the potato starch, and higher levels of amylopectin, means that out of the three the potato starch will become the thickest after gelatinization, it will also be clearer then the other starches. Oppositely, the corn flour will be the least thick starch type out of the three.

RISOTTO& WHITE SAUCE

We were able to tell that gelatinization had occurred in both the white sauce and the risotto, as they became thicker and more gel like. The white sauce went from being a runny liquid, to a thicker liquid after the heat had been applied. In the risotto the rice went from being hard, to breaking down, absorbing the liquid and becoming a thick gel that stuck together. These observations showed us that gelatinization had occurred.

White sauce with wheat flour

The following table helps explain the similarities and differences of the rice before and after cooking

Rice before	Rice after
Hard and grainy   White   Did not stick together   Thin oval shape	Soft and smoother Semi transparent Stuck together Slightly fatter oval shape

rice before gelatinisation

Rice after gelatinisation

Temperature, agitation and other ingredients contributed to the gelatinization of the rice and the white sauce. In order for the gelatinization to occur in these two products heat was necessary. The heat softens the starch (rice and flour) allowing them to swell with the liquid, eventually the starch granule bursts releasing the amylose and amylopectin which absorbs the liquid leaving us with a thicker product. Agitation is important during the gelatinization process to ensure that the product is smooth and all lumps don’t form. The third factor that affects gelatinization is other ingredients, the ingredients that affected gelatinization in the white sauce and the risotto is the addition of fat. Fat helps during the process to minimize the formation of lumps. The addition of butter in the white sauce, and the addition of oil, bacon and cheese to the risotto would have helped this process. Not a concern in these products but the addition of either acid or sugar can also alter the gelatinisation process. For example acids will affect the final thickness of  the starch and adding sugar will raise the temperature of gelatinisation. The amount of moisture also contribute to gelatinization, as a liquid has to be present for the starch to absorb.  Not enough moisture will result in a hard product where the maximum amount of gelatinization has not occurred.

Starch is a polysaccharide, which means it is able to break down. This allows the molecule to undergo processes like dextrinisation and gelatinisation. Gelatinisation is used in food preparation as an adhesive and a thickening agent for foods. Gelatinisation of starch is used for meals like risotto, and for sauces like gravy my favourite to use with any type of roast! and white sauces used as a part of a dish like lasagne. In the kitchen we can use, most commonly, plain flour and corn starch to help thicken liquids. A lot of food industries, and fast food restaurants (e.g. KFC) use potato starch for soups, and mashed potato. The process of gelatinisation is also used when making edible lolly wrappers.

If long grain rice or brown rice is used for making risotto, it won’t be the sticky creamy texture you get with Arborio rice. In this way long grain rice is not suitable for making risotto. Both brown rice and long grain rice has lower levels of starchiness compared to Arborio rice. As the levels of starch are different, the rice won’t thicken as much. Long grain and brown rice have lower levels of amylopectin and higher levels of amylose compared to the short grain rice, this is why the long grain/ brown rice won’t be as sticky and thick as it doesn’t absorb as much liquid.

Cooking with Chemistry

Today in class we made toffee, honeycomb, and cookies. In my blog today I will talk about caramelisation, crystallisation and dextrinisation processes and how they related to our products.

TOFFEE AND HONEYCOMB: CARAMELISATION AND CRYSTALLISATION

The change that is taking place during the melting of sugar is caramelisation. Caramelisation is the application of heat on monosaccharaides and disaccharides which turns them brown. In the experiment we conducted, we can see that caramelisation occurred with the sugar being heated at a high temperature and turning into a liquid.

caramelised sugar (http://www.polyvore.com/diy_sugar_waxing/set?id=59541635)

Sucrose + heat -> glucose + fructose + water

SAMPLE	OBSERVATION
Sugar with no added bicarbonate soda	Darkest colour, lustrous surface
Sugar with added bicarbonate soda	Greatest volume, lightest texture

toffee

honeycomb (bicarbonate sugar added)

 

The process off caramelisation can add flavour, texture, and a better appearance to a dish. Uses for caramelisation in food production include: toffee and honeycomb which we would fine at grocery stores in confectionary aisles, crème caramel made generally at restaurants or at home, caramelized onions used as part of a dish to add flavour, we would find this served at a form of restaurant and more. When we added the bicarbonate to the caramelized sugar we got a honeycomb product which was lighter in colour and a greater volume. This is because the soda reacts with the acid in the caramelized sugar forming bubbles. When the syrup is then poured out to set the bubbles are unable to escape leaving us with this honeycomb product that is greater in volume and easier to bite. This honeycomb can be used as confectionary like chocolate bars and ice creams to give it flavour etc.

“Temperature, acidity, and agitation are all factors which affect the crystallization of disaccharides.” The temperature of the water dictates how much sugar is dissolved, the higher the temperature the greater the amount of sugar that is able to be dissolved. If you wanted to make a softer solution like fudge, you would use a lower temperature, and if you wanted to make a harder temperature like brittle you would use a higher temperature. Adding acids to the sugar and water stops the development of large crystals, giving the product a smoother texture. Some commonly used acids include vinegar and cream of tartar. Depending on the product, different products require agitation at different points. Crystal development is encouraged by the movement of sugar solutions. If solutions is stirred while hot, the product will have a grainy texture. Sugar must be dissolved before boiling starts.

COOKIES: DEXTRINISATION

Dextrinisation is the process of browning of food made by the dry heat on starch breaking down into dextrin’s. For example toasting bread and baking cookies and cakes.

In our practical assessment, the process of dextrinisation was seen in our choc chip cookies from the starch in the flour. Before we baked the cookies, the dough was a pale golden colour, after the cookies came out of the oven they were a golden, brown colour.

cookie mixture before oven

cookie mixture after oven

By using the oven as the method of cooking, we were baking and therefor using a dry heat method of cooking.

If the mixture was cooked for another 30 minutes the end product would come out burnt and a black colour. When the mixture is being burnt it goes from the starch molecule being broken down into dextrin’s, and as it burns it breaks down further into a maltose molecule which then will break down into two glucose molecules leaving us with lots of glucose.

Starch >                    Dextrin >                    Maltose >                   Glucose (polysaccharide)                                            (disaccharide)             (monosaccharide)

If we were to substitute honey and golden syrup in place for the brown sugar and castor sugar we would find the cookies would change in flavour, consistency and texture. The golden syrup would make the cookie chewy as fructose being the sugar in golden syrup does not solidify. This is the same for the honey as it is made up of glucose molecules. We would also find the mixture will be close to a liquid rather than a dough as both honey and golden syrup are runny. Substituting honey in for the brown and castor sugar wouldn’t really change the sweetness, on the other hand if golden syrup was added in replacement, the mixture would be a lot sweeter as the main sugar in golden syrup is fructose which is the sweetest type of sugar.

Both dextrinisation and caramelisation has been spoken about earlier, but what is crystallization? Crystallization is when sugar dissolved in water is heated to form a syrup then allowed to cool. Now its time to compare the three processes! the most obvious differences is that dextrinisation involves starches (polysaccharides), where as caramelisation and crystallisation both involve sugars most commonly being sucrose or fructose. Both caramelisation and dextrinisation involve the process of  ‘browning’, but crystallisation doesn’t. All three process have differences in their usefulness in food preparation. Dextrinisation is used in a large of variety of products like, browning of toast, cakes, cookies etc. Dextrinisation is used to change the colour of food like browning of toast, but also a flavour change like the crust of bread. Caramelisation is also used for many things from basic as toffee to caramelized onion, potato and carrot which can then be added to meals. Likewise to dextrinisation, caramelisation is also involved in the making of cakes and baked products. With the addition of other products like bicarbonate soda, caramelized sugar will produce another product like honeycomb. Caramelization is used for both confectionary and as a part of a meal served at restaurants. It can be also used for many sweet sauces. Finally, Crystallisation is mostly used for confectionary like fudge, caramel, toffee etc. The way crystallisation is done changes the textures of food. In this way crystallisation can be used in food preparation in different ways determined on the form of texture you would like.

I hope you learnt a lot from my blog post today…. Love Ellie!