Quantification of phenolic compounds in different types of crafts beers, worts, starting and spent ingredients by liquid chromatography-tandem mass spectrometry

Abstract

An accurate quantification of phenolic compounds present in several kind of craft beers, corresponding worts, ingredients and spent products was performed by LC-MS/MS in this study. The dilution 1:2 of the sample with the mobile phase gave the best results, offering a very fast and simple method to reduce the matrix effect. A validated method was applied to six different types of craft beers, their worts, starting and spent products, such as barley malts and barley husks, starting hops and spent hops, and finally, starting yeast and spent yeasts to quantify the selected phenolic compounds. The Total Phenol Content (TPC) of barley malts is not negligible and it results almost prevalently due to trans-p-coumaric acid, which ranges from 76.4 μg/Kg for Mais to 672.6 μg/Kg for Munich. The trans-p-coumaric acid is transferred to the worts during the must preparation and is responsible for the not negligible TPC of worts, that was between 131.1 μg/Kg for Ego to 2041.6 μg/Kg for Alter beer. Bitter acids and prenylflavonoids are mainly present in the starting hops (TPC 323.8 μg/Kg and TPC 500.3 for Saaz and Perle hops, respectively). Their concentration strongly decreases in the spent hops where the TPC ranges between 8.0 μg/Kg for Triplo Malto to 24.4 μg/Kg for Alter, suggesting that they are transferred to the intermediate of production. Phenolic compounds, originally present in the starting barley malts and hops, are limitedly present into the final beers, and their TPC ranges approximately from 65.6 μg/Kg for Fiat lux to 105.3 μg/Kg for Alter. Actually, most phenolic compounds are absorbed into the yeast added for the fermentation, as it is clearly evident from the observation that spent yeasts contain a higher phenolic compounds amount with the respect to the starting yeast, and several phenolic compounds, in particular those coming from hops, are originally absent into the yeast and are only present in the spent ones.

Keywords: Beer by-products; Craft beers; HPLC-ESI-MS/MS; Matrix effect; Method validation; Phenolic compounds.