The light-struck flavor is a beer off-flavor that arises from a riboflavin photooxidation-induced sequential chemical reaction. We measured riboflavin concentration sequentially under light exposure and evaluated the ease of photooxidation in various beer types from a decreasing riboflavin rate. We observed that beer-like beverage, low-malt beer, schwarzbier, amber ale, and barley wine were hard to photooxidize. The initial riboflavin concentration was particularly low in beer-like beverage and low-malt beer, which was suggested to be the main reason for their characteristic of being hard to photooxidize. To evaluate other characteristics, such as antioxidant activity and chromaticity, riboflavin was added to various beer types, and their degree of photooxidation was investigated. Schwarzbier, IPA, barley wine, and stout were hard to photooxidaze upon riboflavin supplementation. We also measured antioxidant activity and chromaticity of various beer types and established a photooxidation correlation coefficient for the antioxidant activity and chromaticity at R＝－0.423 (p＜0.01) and R＝－0.363 (p＜0.01), respectively. These results suggest that riboflavin concentration, antioxidant activity, and chromaticity affect the ease of photooxidation in beers.
