Flocculation in Saccharomyces cerevisiae: a review

Abstract

Summary The present work reviews and critically discusses the aspects that influence yeast flocculation, namely the chemical characteristics of the medium (pH and the presence of bivalent ions), fermentation conditions (oxygen, sugars, growth temperature and ethanol concentration) and the expression of specific genes such as FLO1, Lg‐FLO1, FLO5, FLO8, FLO9 and FLO10. In addition, the metabolic control of loss and onset of flocculation is reviewed and updated. Flocculation has been traditionally used in brewing production as an easy and off‐cost cell‐broth separation process. The advantages of using flocculent yeast strains in the production of other alcoholic beverages (wine, cachaça and sparkling wine), in the production of renewal fuels (bio‐ethanol), in modern biotechnology (production of heterologous proteins) and in environmental applications (bioremediation of heavy metals) are highlighted. Finally, the possibility of aggregation of yeast cells in flocs, as an example of social behaviour (a communitarian strategy for long‐time survival or a means of protection against negative environmental conditions), is discussed.

125th Anniversary Review: Yeast Flocculation and Sedimentation in Brewing

“…The present review targets practical aspects of yeast flocculation that are relevant to brewer's yeast strains under industrial brewery conditions. Earlier reviews include Verstrepen et al, 2003 103 , Verstrepen and Klis, 2006 106 and Soares, 2010 73 and a recent symposium contains relevant articles 76 .…”

A role for histone acetylation in regulating transcription elongation

“…FLO1 encodes a lectin-like cell wall protein which mediates a cell aggregation stress-response known as flocculation, whereby yeast cells within the ‘floc’ are protected against the outside environment [10]. This phenotype, although attenuated in laboratory strains, is important for industries such as brewing, and is of relevance to biofilm formation.…”

Cleanup of industrial effluents containing heavy metals: a new opportunity of valorising the biomass produced by brewing industry

“…These yeast cells aggregate in multicellular masses, called flocs, in a spontaneous and reversible way, which rapidly settle in the medium where they are suspended. According to current knowledge, the flocculation of brewing yeasts occurs due to the interaction of a specific lectin-like protein (only present on flocculent cells) with the surface carbohydrate residues of the α-mannan (receptors) of neighbouring cells (Soares 2011). It was described that Ca ions are directly involved in the binding of the flocculation lectin to the α-mannan receptors (Veelders et al 2010).…”

“…It was described that Ca ions are directly involved in the binding of the flocculation lectin to the α-mannan receptors (Veelders et al 2010). Yeast flocculation is influenced by characteristics of the medium and the presence of specific FLO genes (such as FLO1, FLO5,FLO8,FLO9,and FLO10) (Soares 2011). For a review of brewing yeast flocculation phenomena, the reader can consult the recent reviews (Soares 2011;Vidgren and Londesborough 2011;Panteloglou et al 2012).…”

“…The yeast strains used in brewing industry belongs to S. cerevisiae sensu stricto complex (Vaughan-Martini and Martini 1998) being traditionally divided in two main groups: (a) ale brewing strains (S. cerevisiae), which classi-cally rise to the top of fermenter at the end of the primary fermentation most likely due to the affinity for the CO2 bubbles (top fermentation) where they are skimmed off; and (b) lager strains (Saccharomyces pastorianus, also re-ferred as Saccharomyces carlsbergensis for historical rea-sons), which settle in the bottom of the fermenter (bottom fermentation) (Stewart 2009;Soares 2011).…”