Formation, Stability, and Antioxidative Properties of 2-Methylthioproline and 2-Methylthioprolineglycine in Grape Wines

Thioprolines formed by reacting cysteine with reactive carbonyls have been demonstrated to possess antitumor, antioxidative, and hepatoprotective properties. Using our developed QuEChERS sample preparation in combination with a liquid chromatography-tandem mass spectrometry coupled with stable isotope-dilution method, we identified and quantitated 2-methylthioproline (1) and 2-methylthioprolinylglycine (2) in grape wines. In particular, 2 was identified for the first time in wines. We further tested the hypothesis that these adducts, despite originating from carcinogenic acetaldehyde condensing with aminothiols, could serve as antioxidants protecting cells from oxidative insults. Results showed that human liver cells pretreated with 1 or 2 were more tolerant to oxidative stress, as indicated by a concentration-dependent increase in cell viability under an H₂O₂-oxidative environment. It is believed that these compounds may contribute to the antioxidative properties of grape wines.