2.6. Cell viability of free and immobilized cells
Cell viability quantifies the overall number of live cells, based on a complete sample of cells. Live cells refer to all living cells susceptible or not to reproduce (Hinshelwood, 1944). Methylene blue stains dead cells cytoplasm, living cells are not colored by the dye (Bonora and Mares, 1982). Methylene blue staining over hydrogel discs was used to determine cell viability immobilized and free yeast. Microbial counts were performed on 50 μm × 50 μm fields and analyzed by optical microscope binocular Arcane X57 107E with a 40X objective. The cell counting was carried out using the software Motic Image Plus 2.0. L.M®. Immobilized pAAm-Sc yeasts were previously hydrated in phosphate buffer for 24 h. Statistical cell count was performed using a population of 10 arbitrarily selected disks. Cell viability percentage was calculated as the ratio between living cells population and the total population of cells. For comparison, free yeast viability was quantified by the same method with a Neubauer chamber with 1:100 dilutions (Mills, 1941). Each experiment was made in triplicate.