Resumen de Saccharomyces & non-saccharomyces yeasts with probiotic potential
Pilar Fernández Pacheco Rodríguez
The intestinal microbiota is the most populated community of the human body in which trillions of microorganisms live in symbiosis, contributing to the normal functioning of the organism through its interactions with the host. However, a dysbiosis can cause multiple alterations. One of the most widely used current approaches in the modulation of intestinal microbiota balance is based on the administration of probiotics.
The work carried out in this Doctoral Thesis has consisted of the selection of yeasts with great probiotic potential through a "step by step approach", which has allowed the choice of the most suitable strain for use in the area of functional foods.
The study was carried out with 357 yeasts (142 Saccharomyces and 215 non-Saccharomyces) from food environments (wines, cheeses, oils, pickles and distillates among others).
As a first step, isolates of non-Saccharomyces were identified at strain level, since all of the starting Saccharomyces had already been identified. Next, a protocol was prepared to select those capable of resisting gastric and intestinal conditions.
With the 69 strains that overcame this screening, auto-aggregation and hydrophobicity tests were carried out as the beginning of the study of adhesion properties, which allowed selecting the best 20 (10 Saccharomyces and 10 non-Saccharomyces). To enhance this study, the capacity of biofilm formation and adhesion of yeasts to Caco-2/TC7 cells was evaluated in vitro.
Following this, several biotechnological tests were carried out to study possible beneficial effects through the production of metabolites and extracellular enzymes, the assimilation of cholesterol and properties and resistance to antimicrobial compounds, as well as preliminary tests of attenuation, as a possible method to incorporate yeasts in a hydrated food without these modifying their organoleptic properties.
All parameters analysed allowed the selection of five strains: two Saccharomyces cerevisiae, two Hanseniaspora osmophila and one Kluyveromyces thermotolerans (recently renamed Lachancea thermotolerans). Their gastrointestinal resistance properties were reassessed through a complex machine (simgi®), which allows the dynamic and fully monitored emulation of the different physiological variables (peristaltic movements, gastrointestinal fluids, pH regulation, etc.). This trial allowed the selection of strains with greater resistance to these conditions; S. cerevisiae 3 and H. osmophila 1056. With these strains an experiment was carried out in vivo with mice to study the repopulation of the intestinal microbiota after a disturbance in the homeostasis caused by the use of antibiotics. For this purpose, the presence of lactobacilli and enterococci in the faeces was evaluated, and the type of colonisation of the yeast strains was also tested.
As a last step, a functional probiotic food was designed. Without losing sight of the importance of technological tests in this type of process, the selected strains were lyophilised before their incorporation into the chosen food matrix. The lyophilisation conditions were optimised and the individual with the lowest loss of cell viability, Saccharomyces cerevisiae 3, was introduced into a food whose acceptability by the consumer was determined through a sensory analysis and its viability was studied throughout the shelf life of the food product.
In addition, the kinetic parameters of the yeast in the matrix were evaluated and compared with those of the microbiota found in other foods and commercial probiotic supplements. The results obtained were satisfactory.
