Estudo da origem biossintética do ácido acético e determinação da acidez em amostras de vinagres comerciais via RMN de 2H e 1H

Abstract

In this work we describe the use of NMR in the biosynthetic origin study of acetic acid and acidity determination in commercial vinegar samples. The sitespecific natural isotope fractionation of hydrogen and deuterium was investigated by 2H and 1H Nuclear Magnetic Resonance Spectroscopy (SNIF-NMR). This method is based on the ratio of deuterium/hydrogen content at a specific position (methyl site) of acetic acid molecule. The acetic acid, after ethanol fermentation, can be obtained from plants sugars with different biosynthetic mechanisms C3, C4 or CAM and resulting in different isotopic ratios. In this study we measured the isotopic ratio of vinegars obtained from C3 plants 98,6 111,8 ppm, C4 plants about 130 ppm, and CAM plants 106,0 ppm. We also measured contend of agrins, which are vinegars of alcohol and wine, 115,2 129,3 ppm, and for the synthetic acetic acid with higher value, 153,5 ppm. Commercial samples were obtained in the local shopping in São Carlos SP and the standard samples were obtained from reliable origin and provided isotopic ratio values used as reference. Sample acidity was studied through 1H NMR and by titration. These techniques provided acidity between 1 and 7%. Commercial samples showed acidity about 4% that agree with the values in product labels instruction.