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