Effect of Growth Conditions on Flocculation and Cell Surface Hydrophobicity of Brewing Yeast

Abstract

Flocculation and cell surface hydrophobicity (CSH) were determined in anaerobic, static, and aerobic shaken stationary (72- and 96-h growth) cultures of two lager and two ale brewing yeast strains in YPD medium and in 12 and 18°P all-malt worts at 30°C. Ale and lager strains showed no substantial differences in the number and distribution of their FLO genes. In cultures grown anaerobically under CO2, both flocculation and CSH were high and very similar (81.26 ± 4.61% flocculation and 82.07 ± 4.09% CSH) regardless of culture medium and yeast strain. Strain- and medium-specific differences appeared only when the cultures were supplied with oxygen. In static cultures, flocculation was somewhat higher in lager strains (87.76 ± 3.07%) than in ale strains (81.26 ± 5.09%); in aerobic cultures, the difference was even higher (lager 58.69 ± 7.96%; ale 39.90 ± 9.24%). Flocculation in static YPD- and wort-grown lager cultures was similar, while in ale strains it was always higher in wort-grown cultures depending on the wort gravity. In aerobic cultures, flocculation was, in general, lower than in static cultures, and it was strongly reduced in wort-grown cultures. Similar to flocculation, CSH in both static and aerobic cultures was strain-dependent, always being higher in lager strains. Furthermore, in static YPD-grown cells, CSH was lower than in wort-grown cultures, while in aerobic cultures, it was higher. Correlation between flocculation and CSH, which was missing in anaerobic cultures, was strong in lager yeast strains in both static and aerobic shaken ones. Strong correlation was found between lager and ale yeast strains in both 12 and 18°P worts, while a relationship was missing after growth in YPD.