Basal catalase activity and high glutathione levels influence the performance of non-Saccharomyces active dry wine yeasts

Highlights

• Production of active dry wine yeast is not optimized for non-Saccharomyces yeasts.

• High lipid peroxidation in dry crabtree negative yeast cells does not cause low viability.

• Total fatty acids composition can be correlated to active dry yeast performance.

• Antioxidant protection is relevant for non-Saccharomyces active dry yeast performance.

Abstract

Non-Saccharomyces wine yeasts are useful tools for producing wines with complex aromas or low ethanol content. Their use in wine would benefit from their production as active dry yeast (ADY) starters to be used as co-inocula alongside S. cerevisiae. Oxidative stress during biomass propagation and dehydration is a key factor in determining ADY performance, as it affects yeast vitality and viability. Several studies have analysed the response of S. cerevisiae to oxidative stress under dehydration conditions, but not so many deal with non-conventional yeasts. In this work, we analysed eight non-Saccharomyces wine yeasts under biomass production conditions and studied oxidative stress parameters and lipid composition. The results revealed wide variability among species in their technological performance during ADY production. Also, for Metschnikowia pulcherrima and Starmerella bacillaris, better performance correlates with high catalase activity and glutathione levels. Our data suggest that non-Saccharomyces wine yeasts with an enhanced oxidative stress response are better suited to grow under ADY production conditions.

Introduction

The use of commercial starter cultures for grape must fermentations is a well-established practice in modern wineries as they provide a dominant yeast from the beginning of fermentation, produce wines with a fixed and reproducible quality, and avoid sluggish or stuck fermentations. In recent years, interest in producing wines with enhanced and complex aromas and flavour profiles, or with reduced ethanol content, has grown. This can be achieved by using non-Saccharomyces wine yeasts, which have positive impact on wine character (reviewed by Jolly et al., 2014), when present in early fermentation stages.

There are examples of using non-Saccharomyces wine yeasts, belonging to different genera, in mixed and sequential fermentations to improve organoleptic properties (Belda et al., 2015; Benito et al., 2015; Englezos et al., 2016; Garavaglia et al., 2015; Lleixà et al., 2016; Renault et al., 2015), diminish ethanol content (Ciani et al., 2016; Contreras et al., 2014a, 2014b; Tronchoni et al., 2018) and as biocontrol agents (Comitini et al., 2004; Freimoser et al., 2019; Oro et al., 2014). Several yeasts are commercially available, such as Torulaspora delbrueckii, Lachancea thermotolerans or Metschnikowia pulcherrima and Metschnikowia fructicola, from Lallemand Inc and Laffort, and Pichia kluyveri, from Hansen. However, the ADY production process has been optimized for the baker's yeast Saccharomyces cerevisiae (Reed and Nagodawithana, 1991) and non-Saccharomyces yeasts are not always well adapted (Jolly et al., 2014; Varela and Borneman, 2017).

Oxidative stress plays a key role during the industrial biomass propagation and dehydration processes as it affects biomass yield and technological ADY performance (reviewed by Matallana and Aranda, 2017). In the fed-batch phase of industrial growth (Gómez-Pastor et al., 2010a; Pérez-Torrado et al., 2005) and during dehydration (Garre et al., 2010), many oxidative stress-related genes are induced. The main defense mechanisms that help to maintain redox balance or to scavenge reactive oxygen species (ROS) (Herrero et al., 2008) include enzymatic activities (catalase, superoxide dismutase, glutathione reductase) and protective molecules (trehalose, glutathione). Recently we described a set of biochemical markers for prediction of better S. cerevisiae ADY performance, which include catalase and glutathione reductase activities, trehalose and glutathione (Gamero-Sandemetrio et al., 2014). The still scarce literature on non-Saccharomyces wine yeasts under biomass production conditions shows a correlation between a better oxidative stress response and improved tolerance to dehydration, and focus on the importance of trehalose and glutathione (Câmara et al., 2019a; Gamero-Sandemetrio et al., 2018; Kim et al., 2019). However, there is still much to uncover, especially in the characterisation of different wine species and strains under ADY production conditions.

Oxidative stress causes direct damage to membrane lipids and severe membrane damage is associated with loss of viability (Avery, 2011). The main fatty acids (FA) in yeasts are oleic, palmitoleic, stearic and palmitic acid (Daum et al., 1998). The degree of FA unsaturation influences membrane fluidity insofar as the more unsaturated the membrane is, the more fluid it will become, and it will be able to adapt to unfavourable changes in the environment, such as the conditions that yeasts face during dehydration. Sterols also play an important role in tolerance against oxidative stress. The presence of ergosterol, the main sterol in yeasts, is necessary for the survival under oxidative stress conditions, as mutants unable of synthetizing it are hypersensitive to oxidative stress (Higgins et al., 2003). Studies in S. cerevisiae have revealed a correlation between greater membrane fluidity and better tolerance to different stresses (Beltran et al., 2008; Casey and Ingledew, 1986; Sakamoto and Murata, 2002). Recently, the importance of membrane unsaturation when facing oxidative stress has been underlined in two non-Saccharomyces yeasts (Vázquez et al., 2019).

Understanding how non-Saccharomyces yeasts behave under ADY production conditions will be useful to develop suitable inocula. The aim of this work was to characterize a set of non-Saccharomyces wine yeasts under laboratory scale simulations of ADY production, to understand the role of the oxidative stress response in the process. We simulated industrial growth and desiccation following the conditions that had been deemed as optimal for S. cerevisiae propagation, in order to understand how well these species could adapt to an already established process. We analysed the viability and fermentative capacity of the ADY produced that way, as for S. cerevisiae they define the technological performance of the commercial product. Then, we tested the aforementioned set of oxidative stress biomarkers and we extended the analysis to the total lipid composition of two selected non-Saccharomyces species.