Chiral amino acid analysis of vinegars using gas chromatography – selected ion monitoring mass spectrometry

Abstract

 Twenty-five vinegars were examined quantitatively for their content of free amino acid (AA) enantiomers using chiral gas chromatography/mass spectrometry. Vinegars manufactured from grape must contained l-proline (l-Pro) as the major AA. Balsamic vinegars (aceto balsamico di Modena), with one exception, contained the highest amounts of l-AAs (861–2000 mg l^–1) as well as d-AAs (46–361 mg l^–1). The amounts of d-Pro and d-alanine (d-Ala) increased in the course of maturation. Sherry vinegars had a AA pattern similar to that of balsamic vinegars but with much lower amounts: concentrations of l-AAs were 244 mg l^–1 and 456 mg l^–1 and of d-AAs were 18 mg l^–1 and 19 mg l^–1. The l-AA content of cider vinegars was very low (34 mg l^–1 and 44 mg l^–1) and only traces of d-AAs (<2 mg l^–1) were found. In spirit vinegars few d-AAs and low amounts of most l-AAs were detected, with the exception of l-glutamic acid (l-Glu) (210–847 mg l^–1), probably added as a flavour enhancer. The AA content of spirit vinegars blended with wine vinegar was influenced by the portion of wine vinegar added. Rice vinegars had concentrations of l-AAs from as low as 36 mg l^–1 to as high as 6860 mg l^–1, and the concentrations of d-AAs ranged from 6 mg l^–1 to 531 mg l^–1. All vinegars declared as "produced by microbial fermentation" contained d-Ala, d-aspartic acid, and d-Glu as typical bacterial markers. From the data it is concluded that chiral AA analysis can be used to distinguish among fermented and synthetic vinegars and to identify raw materials used for their production. In particular, the amount of d-Pro can be used as proof of the maturation process of balsamic vinegar.