Enhanced quantitative extraction and HPLC determination of hop and beer bitter acids

A pleasant and consistent bitterness is an essential flavour attribute of beer. Hop-derived iso-alpha-acids are largely responsible for beer bitterness and accurate determination of these primary flavour compounds is very important in relation to quality control. The most widely used way to determine beer bitterness is based on spectrophotometry, measuring the absorbance of an iso-octane extract of acidified beer. However, this approach is far from specific as it measures all of the extracted compounds, including non-bittering principles. For that particular reason, High Performance Liquid Chromatography (HPLC) is increasingly applied for the quantitative determination of hop-derived iso-a-acids and, if present, reduced iso-a-acids. However, to obtain accurate data on beer bitterness profiles, both quantitative sample preparation and state-of-the-art HPLC are essential. In this paper, several extraction procedures based on solid phase extraction (SPE) and liquid-liquid extraction (LLE), respectively, were evaluated and an optimised extraction methodology using H3PO4 for sample acidification prior to extraction is presented. The proposed extraction/HPLC methodology allows for the quantitative recovery and analysis of hop-derived beer bitterness.