Analysis of Gruyere-type cheeses by purge and trap GC-MS and solvent assisted flavour evaporation GCO/MS

Abstract

The aim of this study was to characterise the volatile flavour compounds in a Gruyere-type cheese manufactured from pasteurised milk using different strains of Lactobacillus casei. These strains were used as non-starter cultures to manufacture the different cheeses. A dynamic headspace extraction technique, purge and trap, coupled to gas chromatography-mass spectrometry (GC-MS), and solvent assisted flavour evaporation (SAFE) in combination with GC-MS and GC-olfactometry (GCO) were used to determine the volatile aroma compounds formed after 180 days of ripening. The purge and trap method revealed aldehydes and ketones, such as 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, and 2,3-butanedione, as well as dimethyl disulfide and dimethyl trisulfide among other compounds, which have been described earlier as key aroma compounds of Gruyere and Cheddar cheeses. Free fatty acids were not detected by the purge and trap extraction method. On the other hand, the analysis of the SAFE extract revealed intense signals for propanoic, butanoic, 2- and 3-methylbutanoic acid as well as pentanoic acid and hexanoic acid. Less volatile, more polar odorants, such as the caramel-like 2,5-dimethyl-4-hydroxy-3(2H)-furanone and 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone, but also the mushroom-like smelling 1-octen-3-one were detected in the SAFE extract by GCO, however, not using purge and trap GC-MS.