Comparison of purge and trap and solid phase microextraction techniques for studying the volatile aroma compounds of three European PDO hard cheeses

Solid phase microextraction (SPME) and purge and trap (P&T) methods were compared to establish their effectiveness for the extraction of cheese aroma compounds from selected raw milk protected designation of origin (PDO) cheeses. The profiles of the volatile fraction from each cheese variety obtained by using the two extraction methods were significantly different. SPME fibres were more effective for extracting medium and high boiling compounds, P&T was better for extracting the highly volatile compounds. Gruyère Switzerland cheeses showed high concentrations of alkenes, aldehydes, methyl ketones, butane-2,3-dione, unsaturated alcohols, branched chain acids and 2,6-dimethyl pyrazine. Manchego cheeses contained high concentrations of alkanes, alkanols, prop-2-en-1-ol, propan-2-one and butan-2-one and their corresponding reduction products propan-2-ol and butan-2-ol, propyl esters and aromatic compounds. Ragusano cheeses contained high concentrations of fatty acids and ethyl and butyl esters. Discriminant analyses, performed separately for each extraction method, correctly classified all the samples by their PDO origin.