Differentiation between Ripening Stages of Iberian Dry-Cured Ham According to the Free Amino Acids Content

Abstract

In this paper, the differentiation of three ripening stages, postsalting, drying, and cellar, of Iberian dry-cured ham has been carried out according to their free amino acids contents. Eighteen L-amino acids, alanine, 2-aminobutanoic acid, aspartic acid, cysteine, glutamine, glycine, histidine, hydroxyproline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tyrosine, and valine have been determined by gas chromatography with derivatization with N,O-bis(trimethylsilyl)-trifluoroacetamide. Gas chromatography-mass spectrometry was used to confirm the presence of the eighteen amino acids in the ham samples, and gas chromatography using a DB-17HT column and flame ionization detector was used for quantitative determination. Extraction with a mixture methanol-acetonitrile has been carried out, achieving recoveries in the range 52-164%. Methimazole was used as internal standard. Limits of detection ranged between 7.0 and 611.7 mg·kg^-1. Free amino acids have been used as chemical descriptors to differentiate between the ripening stages. Principal component analysis and linear discriminant analysis have been used as chemometric techniques, achieving complete differentiation between the ripening stages. Alanine, tyrosine, glutamine, proline, 2-aminobutanoic acid, cysteine, and valine were the most differentiating amino acids.

Keywords: Iberian dry-cured ham; chemometrics; food authentication; free amino acids; gas chromatography; mass spectrometry; pattern recognition.

Figure 1

Chromatogram of amino acid standards obtained by GC–FID. Chromatographic conditions are included in paragraph 2.3. Peak numbers corresponding to amino acids appear in Table 1.

Figure 2

Chromatogram of amino acids in Iberian dry-cured ham obtained by GC–MS. Chromatographic conditions are included in paragraph 2.3. Peak numbers corresponding to amino acids appear in Table 2.

Figure 3

Chromatogram of amino acids in Iberian dry-cured ham obtained by GC–FID. Chromatographic conditions are included in Setcion 2.3. Peak numbers corresponding to amino acids appear in Table 2.

Figure 4

Variation of percentages of different amino acids (from 1 to 6) in Iberian dry-cured ham according to the ripening time.

Figure 5

(A) Scores plot of Iberian dry-cured ham samples for the first PCs; blue, red, and green dots correspond to postsalting, drying, and cellar samples, respectively; (B) Scatter plot of the Iberian dry-cured ham samples in the plane of the two first DFs (discriminant functions).