Food+Quality

= = = = toc = Food Quality =

**Functional Properties of Food**

Proteins
Functional properties of food are the properties which affect the appearance, quality and behaviour of many food products. Watch the video "Functional Properties of food" through clickview and answer the questions on the pdf below. The role of proteins in
 * coagulation
 * denaturing
 * gelation
 * foaming
 * browning

Each protein is made up of its own combination of amino acids and are therefore slightly different from each other with varying functions and reactions. However coagulation adn denaturation are common to all proteins. These changes occur when the structure of protein is altered by:
 * heat
 * mechanical action (agitation)
 * the presence of acids or salt
 * enzymatic action

Denaturation occurs when the bonds holding the helix shape are broken and the strands of helix separate and unravel. The change is not always visible and depends on the protein type. **Globular** proteins denature more easily and visibly. e.g. adding lemon juice to milk, the foam created when beating eggwhites. Denaturation of **fibrous** proteins is less visible as the protein structure is stronger, however given time it can be identified. e.g. marinating tough cuts of meat overnight in acid ingredients to tenderise. The acid denatures the collagen, reducing the strength and the pressure required to break it apart.
 * Denaturation**

Coagulation is a more visible process than denaturation. It occurs when denatured proteins separate from other nutrients and solidify. These coagulated protein strands can bind liquids to form a soft elastic solid (gels). However is over coagulated they shrink and toughen, forcing liquid out. Coagulation is the reaction in which a protein changes from a liquid state to a semi-solid or solid state in the presence of heat, pressure or chemicals.
 * Coagulation**


 * media type="youtube" key="y77dNgSbrQI" height="349" width="560" || media type="youtube" key="Rtst1iRXI1g" height="345" width="560" ||

1. Define the term coagulation. What is required for this process to occur? 2. List 3 examples of foods/recipes where coagualtion is used to a) thicken a food b) set a food
 * TASK**

Carry out the experiment on page 85, "Does low temperature affect the functional properties of proteins?" Write out the aim, method, prediction, results and conclusion. media type="youtube" key="SEfO4cL-yqM" height="345" width="420"
 * Factors contributing to denaturation and coagulation**
 * 1. Temperature**
 * Heat causes protein to denature, the higher the temperature the faster proteins denature and then coagulate.
 * Temperatures during preparation can also affect the functional properties of food, e.g. eggs beaten at room temperature will give a different outcome to those beaten straight from the fridge.
 * Meat that is well done is fully coagulated, medium-rare is partially denatured and coagulated. As the internal temperature of the meat increases so does the degree of coagulation
 * TASK**
 * 2. Acidity**
 * When the pH is less than 7 (acidic) proteins will denature. The acid attacks and breaks the salt bridges between amino acid strands. This is an advantage for marinating meats or thickening dairy products (lactic acid producing bacteria is added to thicken sour cream and yoghurt).
 * Acids have a sour taste
 * Common acids found naturally in food include citric acid (from citrus fruits) and acetic acid (vinegar)
 * Alkali's have a bitter taste and will also denature proteins, however they are not commonly found in foods except for sodium bicarbonate.

The chart below shows the pH scale of common foods and liquids.
 * || **pH Level 0-14** || **Foods** ||
 * Alkaline || 9 || Soda Bread ||
 * Alkaline || 8 || egg white ||
 * Neutral || 7 || water ||
 * Acidic || 6 || eggs, milk, potato, meat, chicken, fish ||
 * Acidic || 5 || bread ||
 * Acidic || 4 || tomatoes, pineapple, fruit cake ||
 * Acidic || 3-3.5 || red & white wine ||
 * Acidic || 3 || apples, mineral water ||
 * Acidic || 2 || lemon, lime, vinegar ||


 * 3. Agitation**
 * Kneading, mixing, whipping and beating are all mechanical actions that can all cause denaturation. Proteins are stretched which is desirable for making ice cream, bread and most cakes, however too much mixing or beating can break the strands. e.g. overbeating egg whites causes clotting not the desired fluffy foam.


 * 4. Enzymes**
 * Are chemical substances that act as catalysts in chemical reactions. e.g. enzymes used to tenderise meat can denature the tough protein elastin. Pineapple juice contains the enzyme bromelin. The process is quicker when marinating at room temperature (however the risk of bacterial growth increases at room temperature too).
 * The enzyme rennin is sometimes used to coagulate milk for cheesemaking.

- cooked eggs - speeds up the setting of egg - making cheese - helps firm the curd
 * media type="youtube" key="Mnt071tC8EI" height="345" width="420" || media type="youtube" key="jBPYopcoeqs" height="345" width="420" ||
 * 5. Salt**
 * Salt can denature and coagulate proteins, e.g. salt added to:


 * 6. Sugar**
 * Sugar added to a protein increases the tolerance of higher temperatures, before coagulation or denaturation occurs. E.g. honey glaze on ham prevents the outer layer from toughening, custard with sugar requires longer heating time before coagulation occurs.

Gelation is the formation of a gel. It occurs wen a protein (or carbohydrate) reacts under certain conditions. E.g. In proteins when tiny droplets of liquids are trapped within coagulated proteins, forming soft, elastic products, such as cheese, junket, custard. The presence of HEAT, ENZYMES or ACIDS are required for gels to form.
 * Formation of Protein Gels**

Lipids
Click here to download the worksheet for the content below.
 * The role of fats in emulsifying and aerating**

**__Emulsification__**

Lipids do not naturally mix with water. They can be shaken to form a temporary mixture for example vinaigrette. After a time the mixture will separate. Watch the youtube clip on how to make a vinaigrette. [] media type="youtube" key="xGUKPxtS4ow" height="345" width="420"

An emulsion is a stable combination of oil and water. Emulsification is the process that produces an emulsion. To form a permanent emulsion the following techniques are used;
 * Fat globules are reduced in size to a uniform diameter and evenly distributed throughout the water. This method is used in the production of **homogenisation** and is used in the production or regular and low fat milk.


 * An **emulsifier** is added to stop the separation of lipid and water. An emulsifier is a substance that has an attraction for both the lipid and the water acting as a bridge.

Emulsions though stable can be destroyed under certain conditions, such as high temperatures, freezing, agitation and the addition of salt.
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 * Identify the three parts of an emulsion
 * 1) Dispersed phase
 * 2) Continuous phase
 * 3) Emulsifier

Butter, margarine, salad dressings, gravies
 * List some examples of emulsions

**//Factors affecting the Emulsification of Lipids//**

**//Temperature//** Lipids become more fluid under high temperatures and water moves more rapidly making it more difficult for the emulsifier to form bridges.
 * How does high temperature affect an emulsion?

<span style="font-family: Arial,Helvetica,sans-serif;">Freezing causes crystallisation which breaks the connections between the emulsifier, oil and water to break.
 * <span style="font-family: Arial,Helvetica,sans-serif;">Why does the oil and emulsifier float to the top after a frozen product is defrosted?

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">**//Agitation//** <span style="font-family: Arial,Helvetica,sans-serif;">So the oil has access to the emulsifier.
 * <span style="font-family: Arial,Helvetica,sans-serif;">Why should a mixture be beaten rapidly?

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">**//Addition of salt//** <span style="font-family: Arial,Helvetica,sans-serif;">The chemical attraction between water and salt is greater than the attraction between water and emulsifier, therefore the emulsion separates.
 * <span style="font-family: Arial,Helvetica,sans-serif;">How does salt affect an emulsion?

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 90%;">**Aeration of Fats**

<span style="font-family: Arial,Helvetica,sans-serif;">Aeration occurs when air is added to a mixture affecting consistency and texture. Fat can be used to aerate products bin a number of ways:


 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Creaming butter and sugar- the mixture becomes light and fluffy


 * <span style="font-family: Arial,Helvetica,sans-serif;">Why does the colour change? Sugar crystals are pressed into fat, trapping air.


 * 1) <span style="font-family: Arial,Helvetica,sans-serif;">Rubbing in this process also introduces air to the mixture.
 * 2) <span style="font-family: Arial,Helvetica,sans-serif;">Layering fat between layers of gluten such as the making of puff pastry.
 * 3) <span style="font-family: Arial,Helvetica,sans-serif;">Whipping cream to form a foam

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">**//Foams//**

<span style="font-family: Arial,Helvetica,sans-serif;">Foams are formed when air is whipped or beaten into a liquid. E.g. Cream
 * <span style="font-family: Arial,Helvetica,sans-serif;">The whipping action partly solidifies the fat and partly denatures the protein. After these two changes occur the liquid becomes fairly stable.
 * <span style="font-family: Arial,Helvetica,sans-serif;">The fat content needs to be 22-35%.
 * <span style="font-family: Arial,Helvetica,sans-serif;">Evaporated milk has a higher concentration of fat and protein, therefore must be chilled first.

<span style="font-family: Arial,Helvetica,sans-serif;">media type="youtube" key="f2fFcjwvTWs" height="345" width="420"

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 110%;">**//Factors that affect the foaming of cream//**
 * <span style="font-family: Arial,Helvetica,sans-serif;">**The age of cream**: cream whips best if it is 2-3 days old.
 * <span style="font-family: Arial,Helvetica,sans-serif;">**Temperature:** cream should be between 1-7° as at this temperature range it is thicker, less runny and whips more easily.
 * <span style="font-family: Arial,Helvetica,sans-serif;">**Amount of beating**: the cream will take on a curdled appearance if over beaten because the fat globules clump on the surface.
 * <span style="font-family: Arial,Helvetica,sans-serif;">**Addition of gelatine**: this makes the cream less runny. Thickened cream contains gelatin so is quicker to foam.
 * <span style="font-family: Arial,Helvetica,sans-serif;">**Addition of sugar** this decreases the foam but if added towards the end of beating will decrease the likelihood of curdling.

**<span style="font-family: Arial,Helvetica,sans-serif;">When oxygen reacts with food **

<span style="font-family: Arial,Helvetica,sans-serif;">//Oxidative reactions affect the quality of the food through:// <span style="font-family: Arial,Helvetica,sans-serif;">The fat being exposed to the air for a long period – usually in high temperatures the oxygen reacts with the double bonds in fatty acid chains making oil more vulnerable. Rancid fats have a bitter flavour and unpleasant odour.
 * <span style="font-family: Arial,Helvetica,sans-serif;">Changing colour in protein foods
 * <span style="font-family: Arial,Helvetica,sans-serif;">Oxidative rancidity - what does this involve?

<span style="font-family: Arial,Helvetica,sans-serif;">Enzymes are exposed and react with the air causing discolouration.
 * <span style="font-family: Arial,Helvetica,sans-serif;">Why are fruits and vegetables susceptible to oxidative reactions?

<span style="font-family: Arial,Helvetica,sans-serif;">Packaging to reduce exposure to air <span style="font-family: Arial,Helvetica,sans-serif;">Coating food with acids <span style="font-family: Arial,Helvetica,sans-serif;">Coating with an antioxidant
 * <span style="font-family: Arial,Helvetica,sans-serif;">How can this be prevented?

<span style="font-family: Arial,Helvetica,sans-serif;">