process for the preparation of a material comprising conjugated isomers of a polyunsaturated fatty acid comprises: treating a first fatty acid mixture comprising saturated fatty acids, monounsaturated fatty acids and polyunsaturated fatty acids in the presence of ethanol to form (i) a solid fraction and (ii) a liquid fraction comprising a second fatty acid mixture, wherein the second fatty acid mixture has a higher molar ratio of total polyunsaturated fatty acids to total saturated and monounsaturated fatty acids than the first fatty acid mixture; separating the solid fraction and the liquid fraction; and subjecting the second fatty acid mixture or a derivative or reaction product thereof to treatment with a base in the presence of a solvent, to form conjugated isomers of at least some of the polyunsaturated fatty acids.