Solid-phase microextraction in combination with GC/MS for quantification of the major volatile free fatty acids in ewe cheese

• Type: Article in International Scientific Journal
• Date: 2002

Authors

Pinho, O (Author) FCNAUP; Ferreira, IMPLVO (Author) FFUP; Ferreira, MA (Author) Other

Journal

Title: Analytical Chemistry

Vol. 74 No. 20

Pages: 5199-5204

ISSN: 0003-2700

Publisher: American Chemical Society

Indexing

ISI Web of Knowledge - 89 Citations

Scopus - 100 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

CORDIS: Health sciences

Other information

Authenticus ID: P-000-MP2

DOI: 10.1021/ac020296m

Abstract (EN): This work describes a method for quantification of the major free fatty acids of ewe cheese that contribute to its distinct and strongly marked flavor. A headspace SPME method in combination with GC/MS was used for the extraction, identification, and quantification of butanoic, hexanoic, octanoic and decanoic acids in ewe cheeses. The method used for sample preparation was simple. A fiber coated with 85-mum polyacrylate film was chosen to extract the free fatty acids. To perform a reliable quantification, several factors were taken into consideration for reliable quantification, namely, (i) the influence of addition of water, of an electrolyte or of a hygroscopic salt, on the release of free fatty acids from the matrix, (ii) the linear relationship between the amount of analyte adsorbed by the SPME polymer film and the initial concentration of the analyte in the cheese sample; and (iii) the competition for adsorption by fiber. Water removal with sodium sulfate promoted a more efficient extraction of volatile free fatty acids; biases due to competition or linear range excesses were controlled by choosing the appropriate amount of sample for each ewe cheese. The method of standard additions was used with success for the quantification of free fatty acids. Calibration curves that were constructed for the major short-chain free fatty acids (butanoic, hexanoic, octanoic, and decanoic acids) spiked into cheese followed linear relationships with highly significant (p < 0.001) correlation coefficients (r > 0.999). Coefficients of variation of <7.9% indicated that the technique was reproducible. A marked increase in concentration of short-chain free fatty acids was observed during cheese ripening, ranging from 0.35 to 9.33 mg/100 g for butanoic acid, 0.363 to 4.34 mg/100 g for hexanoic acid, 0.343 to 2.0 mg/100 g for octanoic acid, and 1.291 to 3.85 mg/100 g for decanoic acid. The limits of quantification were registered at levels of parts per million. The absolute quantification of butanoic acid was also carried out by using isotope dilution assays (IDA). The levels of acid obtained with this method were similar to those obtained by the standard additions method.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 6