This doctoral thesis, directed by Emilia Matallana and Agustín Aranda, compares various strains of non-Saccharomyces yeast and analyses their potential to constitute useful inoculums for the industry. Part of the results of the thesis have been published in the journal Food Microbiology. The thesis was defended on October 2, 2020.
The main objective of the thesis, entitled "Biochemical characterisation of non-Saccharomyces wine yeasts and technological adaptation of their industrial production as active dry yeast" was to characterise the behaviour of non-conventional wine yeasts and the optimisation of their preparation as active dry yeast (ADY), the way they are used as inoculums in industry. To this end, eight yeast strains from the non-commercial collection of Lallemand Inc. and not belonging to the Saccharomyces genus were analysed. These non-conventional yeasts are appreciated because they allow wines with complex aromatic profiles and lower alcoholic content to be obtained. Under the conditions of obtaining ADY, these strains showed very different biochemical profiles and response capacity to oxidative stress. The use of antioxidant agents of natural origin, as well as the technological adaptation of the biomass production process to the requirements of each species, has allowed for the improvement of ADY production. The ADY obtained in this research was used in mixed fermentations with natural grape must and in biomass production optimisation trials on a bioreactor scale. The wines obtained were analysed to determine the effect of the presence of these yeasts on conventional chemical parameters and the production of volatile compounds. Non-Saccharomyces yeasts have a clear effect on the organoleptic profile of the wines, without this being negatively affected by the different treatments applied during the propagation of the biomass.
Max Torrellas' doctoral thesis was developed in the Industrial Yeast Biotechnology group at I2SysBio under the supervision of Emilia Matallana (Professor of Biochemistry and Molecular Biology at the University of Valencia) and Agustín Aranda (Senior Scientist at the CSIC). During the development of his thesis Max Torrellas has been the beneficiary of a contract from the FPI program and did a research stay at Università degli Studi della Basilicata (Potenza). The panel was made up of Roberto Pérez Torrado (Institute of Agrochemistry and Food Technology IATA, CSIC), Mª Jesús Torija Martínez (Rovira i Virgili University) and Jordi Tronchoni (International University of Valencia), who rated the thesis as outstanding.
