Characterization of selected species of Pichia and Candida for their growth capacity in apple and grape must and their biofilm parameters.

Pichia and Candida species include biofilm-forming yeasts able to spoil foods and beverages. Strains belonging to 10 Pichia and Candida species isolated from apples, grape musts, and wines were analysed. They were subjected to molecular typing and characterized for their ability to grow and ferment must for cider and wine production, and for their biofilm properties. All strains grew similarly in apple and grape must. Glucose-fermenting strains displayed differentiated fermentation performances. Great variation in SO2 and ethanol sensitivity was observed among the strains. Pichia manshurica strains showed high tolerance to both molecules. Eleven and five surface-spreading biofilm (MAT) phenotypes were identified in solid and liquid media, respectively. Strains produced biofilms with variable thicknesses and widths in culture tubes. Cell adherence and aqueous-hydrocarbon biphasic hydrophobicity assays were carried out. Some Pichia manshurica and P. membranifaciens strains exhibited a high capacity to form a thick biofilm and had high cell adherence and hydrophobicity values. These strains could be more likely to colonize the internal surfaces of tanks. This study evidenced that some Pichia and Candida strains can proliferate during apple and grape must fermentation and may be detrimental the beverage quality, due to their specific biofilm properties.