Characterization of Hop Acids in Spent Brewer's Yeast from Craft and Multinational Sources

Spent brewer's yeast, a significant byproduct of brewing, presents a disposal issue for craft breweries. To understand value-added opportunities for its use, we measured hop acid profiles of spent yeast from three beer styles produced by a craft brewery and spent yeast from three multinational breweries using high-performance liquid chromatography with photodiode array detection/mass spectrometry. The average a-acid content of craft yeast (2,074 +/- 531 mu g/g) was 12-fold higher than multinational brewery samples (167 89 mu g/g), and the average total hop acid content of craft yeast samples (2,557 +/- 622 mu g/g) was fivefold higher than the multinational brewery yeast samples (487 +/- 136 mu g/g). Centrifuged craft yeast slurry from both light and dark ales had 7- to 10-fold, 150- to 158-fold, and >200-fold higher content of iso-alpha-, alpha-, and beta-acids, respectively, than that in the corresponding beer, demonstrating a high affinity of brewer's yeast for hop acids. Ongoing research has shown that hop acids have antioxidant, anti-inflammatory, anticancer, and antibacterial activities. The elevated content found in spent craft brewer's yeast suggests consideration for use as a high-value functional food ingredient.