Chemistry Of Cooking

Question 1

What holds polypeptide chains together

Answer 1

Intermolecular bonding between the side chains of amino acids and hydrogen bonding between.

Question 2

Why does the texture of protein change when it is cooked

Answer 2

The heat involved in cooking breaks intermolecular bonds within proteins and consequently changes the shapes and structure. This is called denaturing and is irreversible

Question 3

Cooking proteins changes the texture of the food

Answer 3

.

Question 4

3 types of alcohols

Answer 4

Primary secondary and tertiary

Question 5

Which alcohols can be oxidised

Answer 5

Primary and secondary

Question 6

What occurs when primary alcohol oxidised

Answer 6

An aldehyde

Carboxylic acid

Question 7

What happens when secondary alcohol oxidised

Answer 7

Ketone

Question 8

What is definition of oxidation

Answer 8

Increase in oxygen to hydrogen ratio

Question 9

Name two oxidising agents that can be used to oxidised primary and secondary alcohols

Answer 9

Hot copper(II) oxide
Acidified potassium dichromate solution

Question 10

Why does dichromate oxidising agent need to be acidified

Answer 10

To provide hydrogen ions for the reaction

Question 11

Why are aldehydes an important group of food chemicals

Answer 11

Many flavour and aroma molecules are aldehydes

Question 12

Functional group in aldehydes and ketones

Answer 12

Carbonyl

Question 13

Aldehyde is on the … of molecule and ketone is on the …. of molecule

Answer 13

Aldehyde end

Ketone middle

Question 14

Ending of aldehyde

Ending of ketone

Answer 14

Al

One

Question 15

Name the 3 oxidising agents that can oxidised alcohols into ketones and there colour change

Answer 15

• tollens colourless to silver mirror
• fehlings/benedicts blue to brick red
• acidified potassium dichromate orange to green

Question 16

Describe an experiment which could be used to distinguish between an aldehyde and a ketone

Answer 16

Place substances in test tube with suitable oxidising agent.

Warm water bath and observe colour change

Question 17

Why does an apple go brown when the skin is removed

Answer 17

Substances in the apple are reacting with oxygen in the air causing oxidation

Question 18

How can manufacturing prevent oxidation

Answer 18

Packed in vacuum

Question 19

What are antioxidants

Answer 19

Molecules that are added to foodstuffs to prevent them from undergoing reactions

(Reducing agents or free radical scavengers)

Question 20

Edible oils react with oxygen to form compounds that give food a rancid flavour

Answer 20

.

Question 21

What reaction does vitamin c undergo when it acts as an antioxidant in food

Answer 21

Oxidation

Question 22

What is votality

Answer 22

How easily a substance vaporises

Question 23

What do volatile molecules contained within food we eat do

Answer 23

Give the food flavour

Question 24

Why do some food taste better when cooked in oil rather than water

Answer 24

Some of the flavour molecules are soluble in oil than water

Question 25

How does size of flavour molecule affect …

• boiling point
• volatility

Answer 25

The larger the molecule the higher the boiling point

The larger the molecule the less volatile the molecule is

Question 26

Explain why size affects boiling point volatility

Answer 26

Increased van der waals (intermolecular)

Question 27

How does the functional group present in flavour molecules affect….

• boiling point
• volatility

Answer 27

In general the more polar the functional group present ….

The higher the boiling point

The less volatile the molecule

Question 28

Explain why the functional groups affect boiling point and volatility

Answer 28

Increased van der waals forces. The more polar the functional group in the molecule the stronger the intermolecular bonding