CONICET | Buscador de Institutos y Recursos Humanos

Agroindustrial by-products and residues can be transformed into valuable compounds in biorefineries. Here we present a new concept: production of fuel ethanol and viable yeast from cheese whey. For this purpose, a microorganism must be employed that is capable of converting lactose into ethanol with a good compromise among yield, rate and titer. Besides, it should also maintain high viability after this conversion, in order to be used for downstream applications. Kluyveromyces marxianus, a respiro-fermentative and generally regarded as safe yeast species, has been explored separately as an ethanol producer and as viable bioactive microorganism. We started our study with a selection involving thirty K. marxianus strains, which were screened on plates for the capacity to grow on cheese whey (7.5 g lactose/L) under aerobic and anaerobic conditions, at 5% ethanol concentration and also at pH 2.5 (achieved by H2SO4 addition). K. marxianus strains Km9 (an isolate from a fermented milk in Argentina) and NCYC1429 displayed good growth properties compared to the other strains and were further evaluated in a miniaturized first generation fuel ethanol process that had been previously benchmarked with Saccharomyces cerevisiae on sugarcane molasses. The system included five consecutive fermentation rounds with cell recycling and acid treatment between two consecutive fermentations. Both K. marxianus strains produced ethanol with high yields (≈40 g of ethanol produced on 100 g of lactose) and rates, and maintained cell viability higher than 90%, even after the five fermentation cycles. We are currently investigating the bioactive properties of these two strains, aiming at evaluating the possibility of using them as an ingredient in functional foods.