Abstract
A novel method of yeast immobilization, called biocapsules, has been developed in which cells of the yeast Saccharomyces cerevisiae become attached to the hyphae of the fungus, Penicillium chrysogenum, remaining adhered following loss of viability of the fungus. Yeast immobilization facilitates higher cell densities than traditional fermentation methods, improves yield and allows the reutilization of the biocatalyst. Yeast cells may be adherent to each other via specific cell surface molecular interactions (flocculation) or attach to surfaces (biofilm formation), and the role of these two distinct mechanisms of attachment in biocapsule formation is unknown. To elucidate the influence of biofilm formation versus flocculation on the yeast-fungus co-immobilization, a screening of selected strains from the Viticulture and Enology Department collection at University of California, Davis was carried out and their ability to flocculate and form biofilm was quantified. Eighteen yeast strains capable of flocculation and biofilm formation were concluded from this screening. Strains displaying differential capabilities in flocculation or biofilm formation plus two control strains were further evaluated for their ability to specifically immobilize with P. chrysogenum. Seven strains were found to show different patterns of flocculation and biofilm formation. Yeast strains able to form biofilm displayed higher rates of immobilization with P. chrysogenum and formed more consistent biocapsules. In contrast, strains able to flocculate developed smaller, inconsistent biocapsules. Although the size and number of biocapsules formed varied by yeast strain, the total mass of biocapsules generated was similar for all strains. These results shed light on parameters that influence yeast-fungus co-immobilization, which may lead to an improvement of biocapsule consistency and further the field of application for this new immobilization system.
- Received August 2017.
- Revision received January 2018.
- Accepted March 2018.
- Published online April 2018
- ©2018 by the American Society for Enology and Viticulture