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Quantification of Short-Chain Free Fatty Acids in "Terrincho" Ewe Cheese: Intravarietal Comparison

O. Pinho^,, I. M. P. L. V. O. Ferreira and M. A. Ferreira

REQUIMTE/Serviço de Bromatologia, Faculdade de Farmácia, Universidade do Porto, Rua Aníbal Cunha, 4050-047 Porto, Portugal
Faculdade de Ciências da Nutrição e Alimentação da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal

Corresponding author: I. M. P. L. V. O. Ferreira; e-mail: isabel.ferreira{at}ff.up.pt.

Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry was employed for the quantification of volatile free fatty acids (FFA) in "Terrincho" ewe cheese. Solid-phase microextraction quantitative analysis was feasible under equilibrium situations as long as the conditions of agitation and the adsorption time were held constant. An excellent linear relationship between the amount of the adsorbed analyte and its initial concentration in the sample matrix was obtained when an adequate amount of sample was chosen. Thus, quantification was possible if biases due to competition or linear range excesses were controlled. Solid-phase microextraction sampling was carried out at 65°C, and a fiber coated with an 85-µm polyacrylate film was chosen. After equilibration at 65°C for 40 min, the fiber was exposed to the headspace above the sample for 20 min and then inserted into the gas chromatograph. The evolution of the volatile FFA during Terrincho ewe cheese ripening was analyzed for a 60-d period. An overall increase in FFA contents was verified up to 30 d of ripening. Between 30 and 45 d most FFA did not suffer significant changes. All FFA increased significantly by the 60-d ripening period. The excessive lipolysis observed at 60 d of ripening may result in the presence of off-flavors.

Principal component analysis performed for intravarietal comparison of volatile FFA composition of 19 Terrincho cheeses, analyzed at 30 ripening days, enabled discrimination between cheeses produced at five different dairy plants.

Key Words: volatile free fatty acid • ewe cheese • ripening

Abbreviation key: GC/MS = gas chromatography/mass spectrometry, HS = headspace, i-C₄ = isobutanoic acid, i-C₅ = isopentanoic acid, PCA = principal components analysis, PDO = Protected Denomination of Origin, SPME = solid-phase microextraction

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