Food Science Reactions

Question 1

Define gelatinisation

Answer 1

When starch is heated in the presence of water, the starch granules absorb water & swell. They eventually rupture upon further heating, resulting in a thick consistency.
Gelatinisation softens the hard texture of starchy food (Eg, rice)

Question 2

Define caramelisation

Answer 2

Involves simple sugars
When sugar becomes brown after it is heated to high temperatures (160<)
Contributes to the caramel flavour that is sweet, bitter and nutty

Question 3

Define dextrinization

Answer 3

When dry heat Is applied to starch at high temperatures, the long chain starch molecules are broken down into shorter chain dextrins, resulting in toasty and nutty flavours

Question 4

Define shortening

Answer 4

Fat’s ability to shorten glucose strands formed when water is added to wheat flour.
When butter is added to wheat flour, the fat molecules coat the flour proteins (gliadin & glutenin).
This reduces the contact between the water & flour when water is added.
As a result, fewer gluten networks are formed. This gives a crumbly texture that is desired in some baked products (Eg. scones)

Question 5

Define emulsion

Answer 5

A mixture formed by combining 2 liquids that do not normally mix with an emusifier. (Can but it’s temporary and unstable)
An emulsifier is a substance that consists of a fat-loving part & a water-loving part.
When added to water & oil mixtures, emulsifiers can bring the water & oil phases together without separation. (Eg. Lecithin in egg yolk)
2 types of emulsions:
- oil in water and emulsions (Eg. Mayonnaise/cream) in which oil droplets are dispersed throughout a water phase
- water in oil emulsions (Eg. Butter/margarine) in which tiny water droplets are dispersed throughout an oil phase

Question 6

Define foaming

Answer 6

When denatured protein molecules trap air in a liquid/solid by wrapping around the air bubbles, producing foam.
Sugar is often used to stabilise egg white foam

Question 7

Define coagulation

Answer 7

Te solidifying/curdling of protein rich food brought about by heat/acids.
Causes change in physical appearance of food
Normally happens after denaturation
Upon heating, uncoiled protein strands come together to form a network which changed liquid egg white to solid, egg yolk becomes hard and powdery

Question 8

Define gluten development

Answer 8

A protein network developed when wheat flour is mixed with water and subsequently kneaded.
When wheat flour is mixed with water, the wheat proteins (gliadin & glutenin) join together to form gluten. Kneading or further mixing rearranges the gluten to form a network of dough.
This network can trap gases produced by yeast & baking powder, increasing the size of the dough during fermentation & baking. The gluten network coagulates upon heating, giving structure & volume to baked products, (Eg.bread)

Question 9

Define Millard browning

Answer 9

Occurs as a result of reactions between sugars and proteins at high temperatures (140<)
Contribute to the desirable brown colour of roasted meat & distinctive roasted flavour

Question 10

Define denaturation

Answer 10

When proteins are subjected to heat, agitation or extreme pH changes, it uncoils and loses its original structure - normally changes the physical appearance & texture of food

Question 11

Define melting point (of a fat)

Answer 11

The temperature at which the fat turns from a solid to a liquid state.
Plant oils tend to have lower melting points - liquiid @ rtp
Animal fats usually solid @ rtp - higher melting point
Some fats have a range of melting points
Affects mouthfeel of some high-fat food

Question 12

Define smoke point ( of a fat )

Answer 12

The temperature at which it begins to decompose & discolour, producing toxic smoke that has an unpleasant smell.
Under high heat, fats are broken down into glycerol & free fatty acids, producing smoke.
Heating hot oil further above smoke point may cause it to catch fire
Oils with lower smoke points (olive/canola) for salad making
Oils with higher smoke points (corn/soya bean) for deep frying

Question 13

Define Enzymatic browning

Answer 13

A reaction observed on surface of certain fruit & vegetables when they are cut or bruised.
When the flesh of these fruit & vegetables are exposed to oxygen in the air for a period of time, a brown discolouration is formed because of an enzyme found in the plant tissues.
Although the brown discolouration is not toxic, it causes an unappealing appearance.

Question 14

5 Measures that can be taken to reduce enzymatic browning

Answer 14

• immerse cut fruit pieces in lemon juice to reduce its pH, which inactivates the enzyme
• keep cut fruit in the chiller, in cling wrap. Low temperature reduces enzyme activity. Cling wrap reduces contact between cut surface & the oxygen in the air
• pack cut fruit in vacuum packs to reduce its contact with air, so oxygen is less available for enzymatic browning
• coat cut fruit with sugar syrup & salt water. They have the ability to reduces enzyme activity
• cut fruit & vegetables just before use / consumption

Question 15

Flour in cake making

Answer 15

• 2 main components - protein & starch
• wheat flour with a low protein content (Eg, cake flour) is commonly used for making cakes as it forms less gluten.
• This gives cakes a soft & more tender texture, which is a desirable sensory quality
• protein & starch in the flour undergoes coagulation & gelatinisation respectively, & add structure to the cake.
• the golden crust of cakes is contributed by the dextrinisation of starch & Millard browning between the sugar & flour proteins

Question 16

Raising agents in cake making

Answer 16

Used to increase the volume of cakes
chemical raising agents:
- when baking powder (a mixture of baking soda & acid) is mixed in a moist environment, the chemical reaction between the baking soda & acid produces carbon dioxide.
- the gas expands when heated & adds volume to the baked cake
- baking soda may also be used as a raising agent, but acidic ingredients (Eg. Lemon juice/cream of tartar) need to be added for the chemical reaction to take place
physical raising agents:
- in cream cakes, air is normally incorporated by creaming sugar & fats (Eg. Butter). Butter is able to trap air to form air bubbles, which expand during baking.
- in sponge cakes, air is normally incorporated by whisking eggs & sugar until a foam is formed. The air bubbles in the foam expand when heated, giving volume to sponge cakes. Steam converted from water at high temperatures also helps to increase the height of cakes during baking

Question 17

Sugar in cake making

Answer 17

• provides sweetness to cakes
• contributes to the browning of the cake surface via caramelisation & Millard browning
• improves tenderness of cakes. As sugar has the ability to attract water, it competes with flour proteins & starch for water. This limits gluten formation & delays gelatinisation, making the cake tender.
• traps more air during creaming of fat when making cream cakes
• stabilised egg foam & increases the volume in whisked cakes
• retains moisture in cakes due to its ability to attract water from the surroundings. As a result, cakes can be kept for a longer period without drying out

Question 18

Eggs in cake making

Answer 18

• as eggs are beaten into the cake mixture, air is trapped. This increases volume & contributes to the soft & fluffy texture of some cakes
• provide moisture to the cake & contribute flavour. Along with fats, eggs contribute to the golden brown colour of eggs through Millard browning
• lecithin, found in egg yolk, is a natural emulsifier. It helps to bind water & fats together, resulting in a finer & more even texture

Question 19

Fats in cake making

Answer 19

• coat flour proteins & make cakes softer by shortening the gluten strands
• solid fats, together with sugar, can trap air during creaming, contributing to the fluffiness & volume of cakes.
• contributes to the golden yellow colour & distinctive aroma of cakes

Question 20

Liquids in cake making

Answer 20

• function as an agent to bind the dry ingredients & a solvent to dissolve ingredients
• are essential for starch gelatinisation & the formation of a gluten network because flour must be hydrated before these 2 reactions can take place
• steam converted from the liquids found in the batter during baking also helps the cake to rise, increasing its volume
• used in many baked products (Eg, milk & eggs) if used in significant amts, additional water may not be required

Question 21

Rubbing in method

Answer 21

Fats are rubbed into the flour to delay gluten formation
Use cold, hard fats as solid fats are able to coat flour proteins more thoroughly, thus delaying gluten formation
Chemical raising agents are commonly added to increase the volume of cakes

Question 22

Creaming method

Answer 22

• produces cakes with rich flavour & tender texture
• creaming of fat & sugar introduces air into the creamed mixture. These air bubbles expand during baking, increasing the volume of the cake

Question 23

Whisking method

Answer 23

• produces cakes with a light & airy texture
• produce egg foam by whisking egg & sugar until a soft peak is formed. This incorporates air into the mixture.
• sifted flour is then gently folded to prevent knocking out of air bubbles in the foam.
• during baking, the heat causes the air trapped in the egg foam to expand, giving volume to the cake.
• gelatinisation of wheat flour & coagulation of egg proteins during baking sets the cake, providing structure.

Question 24

Flour in pastry making

Answer 24

All purpose/plain flour is commonly used in pastry making as it is able to form a strong gluten network to support structure yet does not create a tough texture like that of bread.
Dextrinisation of starch molecules contributes to golden brown colour of pastries
Undergo browning due to caramelisation of sugar & Millard browning between sugar and flour proteins

Question 25

Liquids in pastry making

Answer 25

Are essential for gelatinisation & gluten formation
Should be cold to prevent the fat from melting
During baking, steam from the liquids create air pockets & cause the pastry dough to rise. However, excessive rising is not desirable in short crust pastry making

Question 26

Fats in pastry making

Answer 26

Contributes crumbliness, flavour & colour in pastry
Main function - shortening
Normally mixed with flour to inhibit excessive gluten formation in the presence of water. This results in a crumbly pastry

Question 27

Flour in batter making

Answer 27

Gelatinisation of starch & formation of a gluten network provides structure to the batter
Starch contributes to the golden brown colour formed during frying as a result of dextrinisation.
To prevent lump formation, sift flour

Question 28

Raising agents in batter making

Answer 28

Chemical raising agents may be added to thin batter for a fluffy texture
Baking powder is also added to thick batter to achieve a crispy mouthfeel

Question 29

Eggs in batter making

Answer 29

Normally beaten before adding into batter
Contributes colour, flavour & nutrients to batter
Enhances structure of the batter as proteins coagulates upon heating

Question 30

Liquids in batter making

Answer 30

Milk/water is used to bind flour to form a batter
Amount Determines consistency of batter
High proportion of liquid will yield a thin batter

Question 31

Thin batter

Answer 31

Runny consistency
Normally poured onto hot plates to make flat cakes (Eg. Pancakes, crepes)
Air is introduced during mixing to give the final product a fluffy texture
Baking powder/self raising flour may be added/used to create a fluffy texture

Question 32

Thick batter

Answer 32

Thicker consistency - less liquid used
Normally used to coat deep fried food - prevents moisture loss, adds additional flavour & creates a crispy texture
Helps prevent breakage of delicate food (Eg. Fish)

Question 33

Reasons for adding sauce into a dish

Answer 33

• sauces imparts flavour
• helps complement the richness of meat dishes
• adds colour
• contributes to a variety of textures

Answer 34

Prepared by heating equal amounts of flour & butter in a pan with constantly stirring.
During heating, the water in butter evaporates, leaving a flour-flat mixture called roux, which is used for thickening.
The fat is able to coat starch granules individually & prevent them from clumping together when liquid is added.
In the presence of liquid & heat, the individual fat-coated starch granules undergo gelatinisation, resulting in a smooth & thickened sauce

White roux;
Brown roux; white roux is further heated to allow browning

Question 35

Blended sauces

Answer 35

Thickened by a starch-water mixture called slurry
Mix starch with cold water to disperse the starch granules evenly throughout the cold water
This helps to avoid lump formation as starch will not gelatinise in cold water