Role of riboflavin in beer flavor instability: Determination of levels of riboflavin and its origin in beer by fluorometric apoprotein titration

A method for the quantitative determination of riboflavin levels in beer was developed. The method is based on the quenching of riboflavin fluorescence, which occurs when riboflavin binds to the aporiboflavin-binding protein from egg white. The method does not require any pretreatment of the beer before analysis, other than dilution, and proved to be simple, reliable, and sensitive. The lowest concentration that could be detected was similar to10 nM riboflavin. The possible interference of flavin mononucleotide (FMN) and flavin adenine dinucleoticle (FAD) with the determination of the riboflavin content of beer was excluded, because beer contains only a very small amount of FAD (0.03muM) and no FMN. The riboflavin levels of the types and brands of beer investigated were in the range of 0.5-1.0 muM. The origin of the riboflavin in beer proved to be the malt. Hop and yeast hardly contributed to the riboflavin content of beer. Besides its use in the determination of riboflavin levels, the aporiboflavin-binding protein also provides a way to remove riboflavin from beer, which reduces the light sensitivity and the related lightstruck off-flavor formation in beer.