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Stage of lactation, use of bulk milk or milk from individual flocks, and cheese-making in farmhouse or industrial factory are important factors affecting the production and quality of Idiazabal cheese. The volatile composition of cheese samples made from raw ewe's milk in farmhouses or industrial plants at two different times of the year and aged for 90 and 180 days was analysed by dynamic headspace coupled to GC-MS. Short-chain fatty acids, primary and secondary alcohols, methyl ketones and ethyl esters were the most abundant compounds in the aroma of Idiazabal cheese samples. Differences in the volatile composition were found between farmhouse and industrial cheeses made at different times of the year and ripened for 90 or 180 days. Likewise, the sensory profiles of the farmhouse and industrial cheeses were significantly different, regardless of the time of the year and ripening time. The results for the principal component analysis (PCA) performed on the sensory attributes of the cheese samples showed two PCs defined as 'farmhouse flavour factor' and 'industrial flavour factor'.Farmhouse cheeses showed high scores for buttery, milky and toasty odours, and buttery and nutty flavours, whereas industrial cheeses showed high scores for sharp, rennet and brine odours, and rennet and rancid flavours. The percentages of methyl ketones such as 3-hydroxy-2-butanone, 2-butanone, 2-pentanone and 2-heptanone, and acids such as n-propanoic, 2-methylpropanoic and 3-methylbutanoic acids were higher in farmhouse cheeses than in industrial cheeses. On the other hand, the percentages of esters such as ethyl butanoate and ethyl hexanoate, and alcohols such as 3-methyl-1-butanol, and acids like n-hexanoic acid were higher in industrial cheeses than in farmhouse cheeses. Relationships between sensory attributes and volatile compounds were studied on the basis of the differences found in sensory profile and volatile composition between farmhouse and industrial cheeses.

-Different dynamic headspace (DHS) methods used for determination of volatile compounds in cheeses were compared. Three different laboratories using gas chromatography coupled to mass spectrometry carried out the analyses of volatile compounds of Spanish Protected Designation of Origin ewe's raw milk cheeses. One laboratory used "purge and trap" (P&T) with thermal desorption of the trap by ultrafast microwave heating (MWH) and the other two laboratories used P&T with thermal desorption of the trap by resistive heating (RH). Each method detected around 78-85 different individual compounds which belonged to different chemical groups, namely, acids, alcohols, ketones, esters, aldehydes, sulphur compounds, hydrocarbons and terpenes. Using the P&T-MHW method, larger percentages of acids and aldehydes in the cheeses were found compared with the P&T-RH methods, whereas the contrary occurred for the percentages of alcohols and ketones. Differences in the percentages of some volatile compounds such as ketones, alcohols and acids between the laboratories using P&T-RH under different analytical conditions were also recorded. The results pointed out differences in the selectivity for the extraction of various volatile compounds from cheese samples according to the DHS methods used, particularly when using tenax or graphitised carbon as trap absorbents. In spite of these differences, both P&T-MWH and P&T-RH methods were equally satisfactory for the comparison of the different cheese varieties. However, each of the DHS methods was more suitable for the characterisation of the volatile compounds of a particular cheese type. De plus, des différences dans les pourcentages de certains composés volatils, tels que cétones, alcools et acides ont également été observées entre les laboratoires utilisant le système de P&T-CR dans des conditions différentes. Les résultats soulignent des différences en termes de sélectivité d'extraction des volatils à partir des échantillons de fromage selon la technique d'extraction employée, et en particulier selon la nature de l'absorbant du piège (tenax ou charbon). Malgré ces différences, les deux méthodes P&T-CMO et P&T-CR se sont révélées également satisfaisantes pour comparer différentes variétés de fromages. Cependant, chacune des méthodes d'extraction était plus appropriée pour caractériser les composés volatils pour un type de fromage en particulier.fromage / composé volatil / espace de tête dynamique / étude inter-laboratoire