Scottish Highers Chemistry Chemistry of Cooking: Cheese is a complex substance co

Question

Cheese is a complex substance containing a wide variety of chemicals.

(a)  The structure of a fat found in cheese is shown below.

![structure]

The alcohol needed to form fat molecules is glycerol.

State the systematic name for glycerol.

(b)  Name the type of reaction used to form fat molecules from fatty acids and glycerol.

Fatty acid W reacts as shown.

![Fatty acid structure]

(A): Identify the functional group circled in molecule X.

(B): Name molecule Y.

(C): Identify the type of reaction used to convert molecule Y into molecule Z.

(D): State which of the reactions, A, B, C, or D, results in an increase in the oxygen to hydrogen ratio.

(iii)  Fatty acids can be converted into hydroxycarboxylic acids. An example of a hydroxycarboxylic acid is shown.

![hydroxycarboxylic acid]

The two functional groups in a hydroxycarboxylic acid react together to form a cyclic ester. An example of a cyclic ester is shown.

![cyclic ester]

Draw a structural formula for the hydroxycarboxylic acid that can be used to produce this cyclic ester.

(iv)  The flavour of cheese changes over time as the concentrations of flavour molecules change.

Chromatograms for two samples of cheese are shown below.

![chromatogram X]

![chromatogram Y]

Determine the retention time, in minutes, of the peak in Chromatogram X that is missing in Chromatogram Y.

(B)  The following chromatogram was obtained from another sample of cheese. The concentration of flavour molecule 3 cannot be determined from this chromatogram. Suggest what would need to be done to the sample to allow the concentration of flavour molecule 3 to be determined.

(b)  The main protein in cheese is called casein. The diagram shows part of the structure of a casein molecule.

![casein structure]

The table shows the relative proportions of the amino acids found in this section of protein.

| Amino acid          | Relative proportion |
|---------------------|-------------------|
| Aspartic acid       | 1                 |
| Glutamic acid       | 2                 |
| Isoleucine          | 2                 |
| Leucine             | 2                 |
| Valine              | 1                 |

(i)  Leucine and valine are amino acids that must be obtained through the diet. State the term for this type of amino acid.

(ii)  Using information from the diagram and the table, draw a structural formula for glutamic acid.

(iii)  When cheese is heated, the proteins change shape. State the term used to describe this process.

(c)  Processed cheese is made from cheese, soluble milk proteins, water and an emulsifier. State the function of an emulsifier.

(d)  A compound added to cheese as a mould inhibitor has the formula Ca(C3H5O2)2. Name this compound.

Cheese is a complex substance containing a wide variety of chemicals - Scottish Highers Chemistry - Question 3 - 2023

Worked Solution & Example Answer:Cheese is a complex substance containing a wide variety of chemicals - Scottish Highers Chemistry - Question 3 - 2023

State the systematic name for glycerol.

Name the type of reaction used to form fat molecules from fatty acids and glycerol.

Identify the functional group circled in molecule X.

Name molecule Y.

Identify the type of reaction used to convert molecule Y into molecule Z.

State which of the reactions, A, B, C, or D, results in an increase in the oxygen to hydrogen ratio.

Draw a structural formula for the hydroxycarboxylic acid that can be used to produce this cyclic ester.

Determine the retention time, in minutes, of the peak in Chromatogram X that is missing in Chromatogram Y.

Suggest what would need to be done to the sample to allow the concentration of flavour molecule 3 to be determined.

State the term for this type of amino acid.

Draw a structural formula for glutamic acid.

State the term used to describe this process.

State the function of an emulsifier.

Name this compound.

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