Effect of pH on the Efficiency of Pyrogallol, Gallic Acid, and Alkyl Gallates in Trapping Methylglyoxal.

Methylglyoxal (MGO) is a highly reactive -dicarbonyl compound produced in foods and endogenously in humans and constitutes a predominant precursor of advanced glycation end products that contribute to the pathology of several diseases, including diabetes and neurodegenerative diseases. In this study, the efficiency of pyrogallol, gallic acid, ethyl, and propyl gallate in trapping MGO was investigated at pH 6.5 to 8.0. Pyrogallol was the most efficient MGO-trapping agent, followed by gallic acid, whereas the alkyl gallates were notably less efficient, particularly at slightly acidic and neutral pH. The increase of pH from slightly acidic to alkaline enhanced the MGO-trapping efficiency of all compounds, albeit to a different extent that correlated inversely to the p of the most acidic -OH phenolic group, demonstrating the contribution of the deprotonated forms of the phenolic compounds in the enhanced reactivity towards MGO. The reaction products of pyrogallol, identified as the most efficient compound in MGO-trapping, were analyzed and characterized by liquid chromatography-mass spectrometry (LC-MS). Both mono-MGO and di-MGO conjugated adducts of pyrogallol were detected, with the mono-MGO adduct being dominant solely at acidic pH and the di-MGO pyrogallol adducts becoming prevalent at neutral and alkaline pH. Therefore, the pH was determined as a main factor that controls the reaction pathways of the phenolic compounds with MGO.