Seasonal variation of volatile compounds in ewe raw milk La Serena cheese

La Serena cheese is a soft to semi-soft variety made in Extremadura ( western Spain) from Merino ewe rawmilk using an extract of Cynara cardunculus as milk coagulant. A purge and trap apparatus coupled to a GC-MS was used to study the seasonal variation of the volatile fraction of La Serena cheeses made at four artisan dairies. Alcohols and esters were the main chemical families found in La Serena cheese. Most volatile compounds were detected in cheeses made during the whole year, although at different concentrations. Abundances of hydrocarbons, primary alcohols, secondary alcohols of an uneven number of carbon atoms, terpenes, 2,3-butanedione, free fatty acids, nitrogen compounds and aromatic compounds were generally higher in cheeses made during spring. Aldehydes reached the highest levels in spring and summer cheeses. Ethanol and ethyl esters were more abundant in spring and autumn cheeses, while branched chain alcohols and branched chain alkyl esters were more abundant in summer cheeses. Cheeses made in winter showed a lower abundance of most volatile compounds, except dimethyl sulphide and dimethyl disulphide. Cheeses made in spring received the highest scores for odour and aroma quality, and cheeses made in winter received the lowest scores. High amounts of 2,3-butanedione, medium concentrations of most terpenes and alcohols, low levels of methyl ketones, especially of 2-butanone, and very low concentrations of 2-butanol were generally recorded for cheeses with the highest quality scores in sensory evaluation. Concentrations of most ethyl esters and branched chain alkyl esters in the highest scored cheeses were above the mean values in cheeses made during the whole year. However, levels of propyl esters and ethyl esters of branched chain acids were lower in the highest scored cheeses.