Rheological characterization of in situ yeast biofilms

LOZANO, JORGE E.; TARIFA, MARÍA CLARA; GENOVESE DIEGO B.; BRUGNONI, LORENA INÉS

Valencia

Congreso; 7th Congress of European Microbiologists FEMS 2017; 2017

BACKGROUNDIn industrial processes biofilms are grown under a wide distribution of local hydrodynamic strengths; consequently biofilms are characterized by their thickness, architecture, and rheological properties.OBJECTIVESStudy the response in the mechanical properties of yeast biofilms, found in juice industries, to variations in flow conditions and food matrix.METHODSA suspension of Candida tropicalis, C.krusei, C.kefyr and Rhodotorula mucilaginosa isolated from juice ultrafiltration membranes, was done in apple and pear juice (≈106 cells/ml of each strain). Biofilms were done on stainless steel surfaces for a period of one month under static and turbulent flow, and two juice concentrations (6 and 12 °Brix). Samples were taken off the system for rheological measurements, counts and SEM processing. Viscoelastic properties were determined by small deformation dynamic oscillatory measurements in a Paar Physica rheometer MCR301, using parallel plates, whereas CHROM agar Candida was used for counting.CONCLUSIONSThe results showed that yeast biofilms had a predominately solid-like behaviour indicating gel-type structures, being G? higher than G? at all frequencies studied. Average loss tangent values were low (< 0.25) and approximately independent of frequency. Under turbulent flow biofilms were structurally stronger than under static conditions and presented higher counts (at least 0.5 Log units). The only specie not recovered was R.mucilaginosa; the biofilms formed presented tighter structures when subjected to a flow. Rheology determines the mechanical stability of biofilms, its knowledge is crucial to fully interpret their behavior. From our results the type of flow was de parameter that most influenced the development and strength of the biofilms.