Antioxidant effect of melatonin on Saccharomyces and non-Saccharomyces wine yeasts
- Autores: Jennifer Vázquez González
- Directores de la Tesis: María Jesús Torija Martínez (dir. tes.), Gemma Beltran Casellas (codir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Emilia Matallana Redondo (presid.), Nicolas Rozès (secret.), Bruno Blondin (voc.)
- Programa de doctorado: Programa de Doctorado en Nutrición y Metabolismo por la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: hdl.handle.net TDX
- Resumen
The present work entitled “Antioxidant effect of melatonin on Saccharomyces and non-Saccharomyces wine yeasts” aimed to obtain a PhD degree has as the main goal to evaluate the possible antioxidant properties of melatonin and its mechanisms of actions in different wine yeasts. Melatonin modulates circadian rhythms and exerts multiple pleiotropic functions in humans. One of them is its powerful antioxidant activity by which melatonin protects against oxidative stress acting as a direct scavenger to detoxify free radicals, or indirectly, by increasing the activities of endogenous cellular antioxidant defenses.
Melatonin has been recently detected in wine, and, as other indolic compounds, it seems to come mostly from tryptophan metabolism of yeasts involved in the alcoholic fermentation. However, the knowledge about its physiological effects or metabolic reason of its synthesis by yeast is completely unknown. Winemaking process is a hostile medium for yeasts which are exposed to several environmental changes. One of them is the oxidative stress which can cause early mortality of yeasts in fermentation. S. cerevisiae is the yeast preferred to be used commercially as starter culture, however, nowadays non-Saccharomyces yeasts are being used with the desire to produce consumer-directed wines with differentiated styles. These non-conventional yeasts are considered less resistant to ethanol stress. Although ethanol also produces free radicals, little information is available about non-Saccharomyces and oxidative stress. Thus, the knowledge of physiological roles of melatonin in yeast will be able to give added value to the production of fermented foods.
Therefore, we hypothesized: Melatonin acts as antioxidant compound in both Saccharomyces and non-Saccharomyces yeasts, reducing the oxidative stress damage directly or indirectly interacting with yeast endogenous defense mechanisms.
To test the hypothesis three specific objectives were developed as follows:
Objective 1: Analysis of the tolerance against oxidative stress of Saccharomyces and non-Saccharomyces yeasts.
To reach this objective, yeast response to oxidative stress was evaluated in S. cerevisiae, Torulaspora delbrueckii, Merschnikowia pulcherrima, Starmerella bacillaris and Hanseniaspora uvarum. We focused mainly on changes in lipid composition evaluating by standard chromatographic methods the composition of fatty acids, sterols and phospholipids. Additionally, lipid peroxidation, catalase acitivity and peroxisome proliferation were analyzed. Results showed that non-conventional yeasts containing higher unsaturation, mainly polyunsaturated fatty acids, in their lipid composition are more tolerant to oxidative stress. This result could indicate that these yeasts have been evolutionarily adapted to better a better resistance against the oxidative stress. Furthermore, under oxidative stress, non-Saccharomyces yeasts were more able to adapt their lipid composition as a defense mechanism, decreasing their percentage of polyunsaturated fatty acids and squalene and increasing monounsaturated fatty acids Objective 2 and 3: Evaluation of the antioxidant role of melatonin on Saccharomyces cerevisiae and non-Saccharomyces yeasts.
To reach these objectives, melatonin effect was first evaluated on a wine S. cerevisiae strain (QA23) in presence and absence of oxidative stress with H2O2. Reactive oxygen species production, defenses systems, such as glutathione and catalase activity, lipid peroxidation and gene expression related with antioxidant defenses, were evaluated by flow cytometry, qPCR and transcriptomics among other methodologies. When S. cerevisiae incorporates exogenous melatonin, this bioactive compound was able to act at transcriptional level, regulating a more efficient oxidative stress response. In unstressed cells, melatonin prepares cells to better endure further stresses. Under stress conditions melatonin exerted its antioxidant properties, decreasing ROS production, lipid peroxidation and oxidized glutathione, and increasing reduced glutathione. Catalase activity also was modulated by melatonin.
Seven strains of Saccharomyces and eight strains of non-Saccharomyces species were further compared with QA23, based on catalase activity and lipid peroxidation. Results showed that melatonin also exerts antioxidant properties in other S. cerevisiae and non-Saccharomyces strains.
The main conclusions obtained from this thesis were as follows:
-Metschnikowia pulcherrima, Torulaspora delbrueckii and Starmellera bacillaris wine yeasts resist better an oxidative stress induced by hydrogen peroxide.
-High proportion of unsaturated fatty acids, particularly linolenic and linoleic acids, are associated with higher stress tolerance in non-conventional yeast.
-S. cerevisiae is able to incorporate exogenous melatonin at nanomolar concentrations, which act on genome-wide gene expression, interfering on regulation of specific and general stress response.
-In absence of oxidative stress, melatonin prepares cells to better endure further stresses, by activating cellular antioxidant defenses systems in both S. cerevisiae and non-Saccharomyces species.
-Under oxidative stress, melatonin exerts antioxidant properties in yeast, partially mitigating the damage produced by oxidative stress, by decreasing intracellular ROS and lipid peroxidation, what enhance yeast viability
