title: Physicochemical surface properties of brewing yeast influencing their immobilization onto spent grains in a continuous reactor.
abstract: Immobilization of brewing yeast onto a cellulose-based carrier obtained from spent grains, a brewing byproduct, by acid/base treatment has been studied in a continuously operating bubble-column reactor. The aim of this work was to study the mechanisms of brewing yeast immobilization onto spent grain particles through the information on physicochemical surface properties of brewing yeast and spent grain particles. Three mechanisms of brewing yeast immobilization onto spent grains carrier were proposed: cell-carrier adhesion, cell-cell attachment, and cell adsorption (accumulation) inside natural shelters (carrier's surface roughness). The possibility of stable cell-carrier adhesion regarding the free energy of interaction was proved and the relative importance of long-range forces (Derjaguin-Landau-Verwey-Overbeek theory) and interfacial free energies was discussed. As for the cell-cell attachment leading to a multilayer yeast immobilization, a physicochemical interaction through localized hydrophobic regions on cell surface was hypothesized. However, neither flocculation nor chain formation mechanism can be excluded so far. The adsorption of brewing yeast inside sufficiently large crevices (pores) was documented with photomicrographs. A positive effect of higher dilution rate and increased hydrophobicity of base-treated spent grains on the yeast immobilization rate has also been found.
authors.affiliation: Centro de Engenharia Biológica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal.
authors.forename: Tomás
authors.initials: T
authors.lastname: Brányik
authors.forename: António
authors.initials: A
authors.lastname: Vicente
authors.forename: Rosário
authors.initials: R
authors.lastname: Oliveira
authors.forename: José
authors.initials: J
authors.lastname: Teixeira
mesh_terms: D002448:Cell Adhesion; D002462:Cell Membrane / Q000187:drug effects; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002523:Edible Grain; D005427:Flocculation; D057927:Hydrophobic and Hydrophilic Interactions; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D013499:Surface Properties
chemical_list: D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins