P-15
New insights into the role of polyphenols in aged beer astringency
Presenter: Sonia Collin, Universite Catholique de Louvain, Louvain-la-Neuve, Belgium
Co-Authors: D. Callemien and M. Bennani, Universite Catholique de Louvain, Louvain-la-Neuve, Belgium

Various factors affect beer quality through storage, such as beer composition and aging conditions. For a long time, we have investigated in our laboratory the evolution of stale flavors such as trans-2-nonenal, dimethyltrisulfide, or beta-damascenone. The present work tries to quantify the impact of aging on other beer active compounds, most probably involved in beer astringency and bitterness. We have optimized an extraction procedure for recovering beer proanthocyanidins. The resulting extracts were then concentrated and analyzed by HPLC-UV and tandem mass spectrometry with electrospray ionization (ESI). The antioxidant efficiency AAPH method has been measured on various fresh and aged beers. A specific sensory analysis method, Time Intensity, has been used to "quantify" the astringency perception in the mouth. Based on our sensory data, we can assume that monomers of proanthocyanidins are more bitter than astringent, whereas polymer fractions are more astringent than bitter. In other words, as the degree of polymerization increases, bitterness decreases, while astringency and reduction power significantly increase. Therefore, surprisingly, bottled oxygen can in some cases increase the reduction power of beer. Polyphenol oligomers will be followed by HPLC-MS for various bottling conditions, including the use of oxygen scavengers. We will also show that pH strongly modifies beer astringency: the lower the pH, the higher this trigeminal perception.

Sonia Collin received a PhD. in chemical sciences from the University of Namur, Belgium (1988). Professor of malting and brewing sciences at the Université Catholique de Louvain, Louvain-la-Neuve, Belgium, since 1993, she is currently head of the Department of Brewery and Food Industries (INBR). She is a member of the ASBC, the Institute of Brewing, and the EBC Brewing Science Group. She has published around 100 papers, mainly on flavor stability, sulfur aroma, pyrazines, and hops.