Flocculation, cell surface hydrophobicity and 3-OH oxylipins in the SMA strain of Saccharomyces pastorianus

Abstract

Three-hydroxy-oxylipins (3-OH oxylipins) have been previously detected in brewing yeast production strains at flocculation onset. In this work, the SMA strain of Saccharomyces pastorianus was characterized during growth in a miniature fermentation assay by measuring flocculation and cell surface hydrophobicity (CSH). Proportions of 3-OH oxylipin were also measured concurrently during growth in the miniature fermentation assay and a defined 3-OH oxylipin extraction protocol using ethyl acetate is presented along with a novel derivatization and gas chromatography-mass spectrometry (GC-MS) detection approach. When the SMA strain was grown in the assay, near maximal CSH and flocculation levels were achieved by a 36h fermentation time. Under the same culture conditions, the oxylipin 3-OH decanoic acid (3-OH 10:0) was identified. This oxylipin could not be detected early in the fermentation, but elevated relative levels of 3-OH 10:0 were reached by 36h, coinciding with increased CSH levels. It was previously presumed that the formation of 3-OH oxylipins at flocculation onset might increase the CSH. However, results from this study suggest that 3-OH 10:0 may not contribute to cell wall hydrophobicity. The flocculation behaviour of the SMA strain was also monitored in the presence of 3-OH 10:0, but exposure to this oxylipin did not impact the sedimentation of this yeast, suggesting that 3-OH oxylipins may not act as mediators of quorum sensing in this strain.