Food science

Role of gluten in bread making

• proteins gliadin and glutenin found in wheat flour

  • form gluten when mixed with water and kneaded

• bread (strong) flour contains a large amount of these

  • glutenin gives dough strength and elasticity

  • gliadin binds the dough together into a sticky mass

Conduction

• when heat travels through solid materials through a heat source (direct contact)

• e.g. stir fry, frying eggs

Convection

• When heat travels through air or water in a convection current

• e.g. boiling water for pasta, baking a cake in the oven

Radiation

• When heat rays directly warm and cook food

• e.g. microwaves, grills

Functions of eggs

• coagulation: when the protein in eggs sets through heating e.g. boiled eggs

• thickening: sauce thickened by adding egg and heat

• binding: holds ingredients together (coagulates) e.g. fish cakes

• coating: enables coating to stick- protective barrier e.g. breaded fish

• glazing: brushed over surface, glossy golden finish e.g. sausage rolls

• emulsification: egg yolk prevents oil and water separating e.g. mayo

• foaming: whisking incorporates air- produces foam e.g. meringue

Why is food cooked?

• To make it safe to eat- destroy harmful bacteria

• To improve shelf life

• To improve texture

• To improve flavour

Stages of gelatinisation

1. Starch granules placed in a liquid and heated

2. At 60C bonds between the starch molecules break and they start to swell

3. At 80C the granules burst, releasing starch and causing the liquid to thicken

4. At 100C gelatinisation is complete

What is dextrinization?

When a dry heat turns a starch brown e.g. bread, toast

Caramelisation and dextrinisaiton = malliard process

What is caramelisation?

When heat is applied to a sugar, causing it to brown 180C

Science behind bread

• Yeast is biological raising agent- type of fungus

• Produces carbon dioxide by fermentation

• Needs warmth, food, liquid, time

• Fresh yeast- firm, moist block

• Dried yeast- very small granules

• Oil- increases shelf life, strong-flour- high in gluten, elastic texture, warm water- 25-29C

Moist methods of coooking

• Heat applied through liquid

• Uses low temperature over a long period

• Causes water soluble vitamins to leach into cooking liquid- lose flavour, colour

• E.g. simmering, boiling, steaming

Dry methods of cooking

• Heat applied directly onto food e.g. roasting, grilling, heat turns starch golden brown (dextrinisation), or caramelisation, frying (destroying nutrients)

• Water soluble vitamins lost to heat, improves colour and texture

Microwave cooking

• Electromagnetic rays from magnetron valve

• Microwaves reflected off metal walls and absorbed by foods- vibrate causing friction

• Very quick- less nutrients lost

Cooking method depends on:

• Time for cooking and preparation

• Facilities available

• Nutrient loss and healthy eating

• Needs of individual, individual preference

What is coagulation?

• When heat applied to a protein, it goes from a liquid to a solid e.g. cooking eggs

• If we overcoagulate, a protein can become hard, tough and difficult to digest

Protein denaturation

• Change in the structure of protein (long chain of amino acids) which unfold from their original state

Protein denaturation by heat

• Proteins can be denatured by acid, heat or mechanical action

  • Eggs- white coagulates at 60C, yolk coagulates at 70C

  • Meat, fish proteins shrink, overheating can make chewy and change protein collagen to gelatine

  • Cheese- melts, over time will form skin (like milk), overheat will become rubbery

Protein denaturation by acid

• Marinating- using acid to soften fibres

• Curdling- when the protein in milk clumps together from adding an acid or heat

  • In cheese, ‘curds’ taken away from the liquid ‘whey’ part of milk- then pressed together

Protein denaturation by mechanical action

• Denaturing protein- unraveling protein strands through whisking

  • This allows tiny air bubbles to incorporate into the egg white, making a foam until stands in soft peaks

  • When foam heated, air bubbles expand and protein coagulates around them- gives firmness

• Kneading bread- stretching the protein (gluten)- permanent change in structure of dough

• Pounding, mincing meat- break up muscle fibres- alters physical structure and tenderises

Plasticity definition

• Ability of a solid fat to soften over a range of temperatures

• Plasticity of fat linked to melting point

• Affects the creaming and shortening ability of fat

Emulsification definition

Emulsification- when two immscible liquids are forced together- tiny droplets spread- emulsion e.g. mayonaise, egg-yolk is the emulsifier

Aeration definition

Trapping air into a mixture e.g. creaming butter and sugar to trap air bubbles to create a springy texture

Shortening definition

The ability for fat to give biscuits and pastries a crumbly texture e.g. the rubbing in method- fat coats flour particles, prevents absorption of water, prevents development of gluten- crumbly texture

Raising agents

An ingredient or process that introduces a gas into a mixture so it rises when cooked e.g. air, steam, CO2

Mechanical raising agent

• Air- sieving, whisking, creaming fat and sugar, rubbing in fat to flour

• Steam- used as a raising agent in mixtures that have a high volume of water and are cooked at a high temperature- create open texture

Chemical and biological raising agents

• Introduce carbon dioxide

• Bicarbonate of soda- alkali- soapy taste- therefore must be used with strong tasting ingredients

• Baking powder- mixture of bicarbonate and an acid- acid neutralises reaction- added to plain flour to give self raising

• Biological- yeast