Comparison of (+)—Catechin and Ferulic Acid as Natural Antioxidants and Their Impact on Beer Flavor Stability. Part 2: Extended Storage Trials

Abstract

During extended storage at 0, 25, or 40°C, there were measurable changes in the concentration of some carbonyl compounds, UV-active compounds separated by reverse-phase HPLC, and iso-α-acids. The rate of change increased markedly with temperature. The antioxidants (+)– catechin and ferulic acid had no impact on the rate of formation of carbonyl compounds but did change the rate of change of some UV-active compounds and the cis-iso-α-acids. In contrast, (+)–catechin and ferulic acid altered the rate of formation of carbonyl compounds during forced-aging. Beer forced-aged in the absence of air produced a carbonyl pattern similar to that produced during extended storage. Additional carbonyl compounds were formed during exposure to air at high temperatures, and it is the formation of these compounds that was affected by the presence of (+)–catechin or ferulic acid. It appeared that two mechanisms of carbonyl formation were in operation during storage. The first occurred at low levels of oxygen (<0.1 ppm) and involved the formation of trans-2-nonenal. The second occurred on exposure to air, producing additional long-chain carbonyl compounds, including undecanal. The antioxidants (+)–catechin and ferulic acid affected carbonyl formation by the second mechanism but not the first.