Explain, giving their names, the two types of reaction by which foods may become rancid.

Reaction 1:

Reaction 2:

Reaction 1: hydrolytic (rancidity)/hydrolysis and

OR

hydrolytic (rancidity) and hydrolysis of ester links/breaking down of lipid/fat to glycerol/propane-1,2,3-triol and fatty/carboxylic acids;

Reaction 2: oxidative (rancidity)/oxidation and addition of O2 across C=C/carbon−carbon double bonds / oxidation of C=C/carbon−carbon double bonds;

Do not penalize omission of “carbon−carbon” if already penalized in F.17(b)(i).

Award [1 max] for “hydrolytic (rancidity)/hydrolysis” and “oxidative (rancidity)/oxidation” only.

Some candidates gained a mark for naming both processes by which food becomes rancid. However, candidates rarely explained the reactions correctly.