Food Tech: Chapter 5 Flashcards
What has a pH of 2?
- lemon juice
- lime juice
- vinegar
What are the natural components of food?
- starch
- enzymes
- acids
- sugar
- fats and oils
- protein
- alkalis
What has a pH of 3?
- apples
- mineral water
What has a pH of 4?
- honey
- buttermilk
- soda water
What has a pH of 5?
- pumpkin
- carrot
- maple syrup
What has a pH of 6?
- milk
- potatoes
- flour
What has a pH of 7?
- water
- chocolate
What has a pH of 8
- egg whites
- bicarbonate of soda
Effect of acid on milk and creams
- causes the protein,casein, to coagulate and become lumpy (curdle)
- makes the milk/cream become sour
Effect of acid on meat and poultry
The acidic ingredient in the marinade acts as a tenderising agent by breaking down the connective tissue and converting the collagen to gelatin.
Effect of acid on fish
- Fish has very little connective tissue and is tenderised or softened easily by acid.
- marinating a fish for longer than 5-10minutes turns raw flesh white and the texture becomes firm. The sensory properties are much like those in cooked fish
Effect of acid on eggs
- addition of acid stabilises the egg whites
- vinegar added to poached egg water speeds up coagulation and lowers the temperature for which coagulation occurs
Effect of acids on starches
- Acids decrease the ability of starches to thicken liquids, particularly when they are heated together.
- The process of gelatinisation is disrupted
- The acid breaks down the starch grains into smaller particles
Effect of acids on sugar
- Acid slows down or prevents the crystallisation process in a sugar mixture
- to make a jam, the right proportion of sugar, acid and pectin is needed to form a gel.
Effect of acids on fruit and vegetables
- Acid slows down the process of enzymatic browning.
- fruits don’t go brown
- acid can be used to preserve vegetables and fruits (pickling)
What level of pH can bacteria not survive
Anything below 4.5
Acids as raising agents
-acids react with bicarbonate soda to produce carbon dioxide gas, which leaven the mixture of a cake
Acidic ingredients used in baked products
- sour cream, yoghurt and buttermilk
- fruit and fruit juice
- vinegar
- honey and golden syrup
- brown sugar
- unsweetened cocoa powder
How is bicarbonate soda act as a raising agent?
When combined with moisture and heated, steam and carbon dioxide is produced. The carbon dioxide leavens the mixture causing it to froth and expand up and out.
What are enzymes?
Enzymes are chemical substances that as a a biological catalyst in plants, animals and micro-organisms.
They bring about and speed up chemical reaction in foods without becoming involved in the reaction.
Enzymes in bread making
- flour contains an enzyme amylase which changes some of the starch in flour to a sugar, maltose.
- yeast contain 3 enzymes: Maltase, sucrase, zymase. There simple sugars are important in the process of fermentation and the production of carbon dioxide which causes bread to rise
Yeast: What is Maltase?
Maltase changes maltose to glucose
Yeast: What is sucrase?
Also known as invertase. It changes sucrose to invert sugar (a mixture if glucose and fructose)
Yeast: What is zymase?
Zymase splits up both glucose and invert sugar into carbon dioxide and alcohol
Enzymes found in fruits and vegetables
- In the presence of oxygen from the air, these enzymes catalyse to form brown pigments called ‘melanins’. This process is called ‘enzymatic browning’.
- enzymes in fruits are responsible for the ripening of fruits as they convert starch to sugar.
Properties of sugar
- sugars are carbohydrates
- contain elements of carbon, hydrogen and oxygen
- two types of sugars (monosaccharide and disaccharide-> formed when two monosaccharides join together)
What are monosaccharides?
- glucose (carbohydrate the body uses for energy)
e. g. Onions - fructose (fruit sugar)
e. g. Fruits, honey - galactose (found in milk)
e. g. Milk sugar, lactose
What are disaccharides?
- sucrose
e. g. Fruits, vegetables, sugar cane - lactose
e. g. Milk - maltose
e. g. Flour ?
Functions of sugar
- sweetening
- preserving
- reducing curling
- activator (yeast dough)
- crisp crust
- colour
- moisture retention (softness in cakes)
- aeration
- tenderising
Define caramelisation
Caramelisation is the process that sugars undergo when heated to high temperatures to develop a golden brown colour.
Define physical properties
Physical properties are a particular trait such as size, viscosity or shape
Define functional properties
Functional properties are the physical and chemical properties of ingredients that impact on food preparation and processing
Properties of starches
- cannot dissolve in water
- do not have a sweet taste
- can be broken down into smaller saccharine units by enzymes or acids
- when starch and water is heated, the water penetrates the starch grains, the granules become bigger and the liquid becomes thicker (Gelantinisation)
Why is corn flour often added to dry products?
It absorbs the moisture
Define gelatinisation
Gelantinisation is the process that occurs where starch granules absorb liquid in the presence of heat and thicken the liquid, forming a gel
What is a roux?
A roux is a mixture of butter or fat and a starch. It is used to thicken a liquid.
What is syneresis?
After a gelatinised mixture is allowed to cool and stand for a long period of time, the starch cools and the molecules pull close together, tightening the ‘gel’ structure and squeezing out liquid.
Define dextrinisation
Dextrinisation is the process that occurs when a starch is exposed to dry heat; the starch is broke down to dextrin, result in a change in colour to golden brown.
E.g. Toasted bread
Define the Maillard reaction
The Maillard reaction occurs when sugar or starch, and a protein such as egg or milk, are present in the same mixture and dry heat is applied during baking. This reaction produces a golden brown colour.
Properties of proteins
Proteins undergo denaturation and coagulation when cooked
Define the Maillard reaction
The Maillard reaction occurs when sugar or starch, and a protein such as egg or milk, are present in the same mixture and dry heat is applied during baking. This reaction produces a golden brown colour.
Function of milk
- Adds moisture
- colour development
- richness
- soft crusts
What is the function of gluten?
Gluten gives dough the ability to stretch and change shape as it captures the bubbles or carbon dioxide which are formed during fermentation.
What is a saturated fat?
Saturated fat us the fat found in foods such as milk, butter and fats in meats. They are solid at room temperature and are the ‘unhealthy fats’
What is a unsaturated fat?
Fats that are present in plant and vegetable oils such as peanut, olive, maize and canola oils
Function of fats and oils: improving keeping qualities
Fate delay the process of staling
Functions of fats and oils: sensory properties
- moist often oily texture and smooth mouth feel
- makes cakes moist
- enhance the flavour of foods
- pleasant aroma of fried food comes from the breakdown of fats and oils
- causes food to form a golden brown appearance
Function of fats and oils: aeration
Fats trap tiny air cells during the beating or creaming process. This trapped air gives a light, airy texture to baked products
Function of fats and oils: transferring heat-cooking foods
Fats and oils are good conductors of heat. Foods also absorb some fats or oils giving it a distinctive flavour and brown crisp texture.
Function of fats and oils: shortening effect
The fat coats the starch grain and separate the grains and separates the gluten strands, prevents strong cohesion and providing a crisp shortening effect which is described as ‘short’.
Function of fats and oils: emulsification
Emulsification is the ability of a fat or oil to be equally dispersed or suspended throughout a liquid.
Emulsifiers allow fats and oils to mix with water to form low-fat spread and salad dressings
