Detection of Thiol Groups in Beer and Their Correlation with Oxidative Stability

摘要

A method for quantification of thiol groups directly in beer was established based on fluorescent detection using the maleimide-derived probe ThioGlo 1. Interference from sulfite during thiol determination was overcome by subtracting the contributions from sulfite-ThioGlo adducts, which could be calculated based on separate sulfite determinations. The method was improved further using a standard addition protocol instead of the conventional protocol with external standards due to an observed inner filter effect of colored beers compared with uncolored standards. Thiol concentrations varied between 13.6 and 46 iM glutathione equivalents in 12 different beers. Principal component analysis showed the level of thiol groups in beer was highly correlated to sulfite content and oxidative stability, which was determined by electron spin resonance lag-phase measurements, suggesting that thiol groups are important for the oxidative stability of beer. SDS-PAGE of proteins showed that protein content did not correlate with thiol concentration, proving that the quantified thiols were not only protein bound but also derived from peptides and possibly smaller compounds.