Selective 1D TOCSY NMR method for the determination of glutathione in white wine†
Abstract
Glutathione, a naturally occurring tripeptide, is the main thiol in must and wine which inhibits must oxidative browning and prevents the loss of wine aroma. In the present work a direct quantification of glutathione in fresh white wine with the use of selective 1D TOCSY NMR experiments is demonstrated. The method is based on the selective excitation of the βCH2SH protons of the Cys residue resulting in the magnetization transfer to the αCH proton followed by its quantification with the use of the standard addition method. The method: (i) does not involve any derivatization and/or extensive sample preparation procedures; (ii) it allows the spin-coupling network of the L-cysteine residue to be elucidated even in the presence of strongly overlapped abundant analytes; (iii) has good NMR analytical performance characteristics and (iv) allows the simultaneous identification and quantification of both reduced and oxidized glutathione.