Validation and biochemical characterisation of beneficial argan oil treatment in biomass propagation for industrial active dry yeast production
Introduction
Propagation and dehydration of yeast biomass is an economically relevant industrial process where cellular oxidative stress plays a detrimental role by decreasing the biomass yield and fermentative efficiency of the final product (Pérez-Torrado, Bruno-Barcena, & Matallana, 2005; Pérez-Torrado, Gómez-Pastor, Larsson, & Matallana, 2009). These two negative physiological effects are the result of multiple damages in molecular components, e.g., lipids and proteins, and of alterations in redox metabolites, e.g., glutathione, and enzymatic activities, e.g., catalase (Gómez-Pastor, Pérez-Torrado, Cabiscol, Ros and Matallana, 2010, Gómez-Pastor, Pérez-Torrado, Cabiscol, Ros and Matallana, 2012; Pérez-Torrado, Gómez-Pastor, Larsson, & Matallana, 2009). The adaptation and resistance of the most abundantly produced yeast species, the baker's yeast Saccharomyces cerevisiae, during that process include protection against oxidative stress through ROS (Reactive Oxygen Species) scavenging enzymes, such as catalase and glutathione reductase, and protective metabolites, such as trehalose and reduced glutathione (GSH). In fact we previously identified a set of biochemical parameters (levels of oxidised glutathione and trehalose, and catalase and of glutathione reductase activities) after dehydration to predict physiologically relevant phenotypes for wine yeasts of potential interest for ADY production (Gamero-Sandemetrio, Gómez-Pastor, & Matallana, 2014), and showed that a low level of oxidative defense characterises the worse performing strains. Moreover, by measuring these biochemical parameters, we recently demonstrated that supplementating molasses with natural food-grade antioxidant ingredients, such as argan oil, diminishes ADY production-related oxidative damage. Thus, we proposed its use in industrial processes that involve high cellular oxidative stress, such as the biotechnological production of ADY starters (Gamero-Sandemetrio et al., 2015).
Based on its composition and especially on its antiproliferative, antidiabetic and cardiovascular risk prevention effects, argan oil is considered a functional food (Cabrera-Vique, Marfil, Giménez, & Martínez-Augustin, 2012) but it is still considered a novel food in the European Union. It contains high levels of linoleic (35%) and oleic (45%) acids, and other minor components with antioxidant properties such as tocopherols 62 mg/100 g (mainly γ-tocopherol 89%), pigments 300 mg/100 g (carotenoids and xanthophylls), phenols 5.6 mg/100 g (caffeic and ferulic acids, etc.), (Cabrera-Vique, Marfil, Giménez, & Martínez-Augustin, 2012; El Abbassi, Khalid, Zbakh, & Ahmad, 2014), and melatonin among others (Venegas et al., 2011). These molecules can detoxify free radicals, reducing agents and potential complexes of pro-oxidant metals. Methods based on using electron transfer compounds, such as ABTS, have determined that the antioxidant capacity of virgin argan oil is due mainly to tocopherols (Sanchez, Gonzalez, Gracía-Parrilla, et al., 2007; Valavanidis et al., 2004). Previous work in our lab showed that argan oil improved fermentative capacity and biomass yield during the ADY production process. The beneficial effect of argan oil can be mediated by preventing cellular damage as it significantly reduced lipid peroxidation in S. cerevisiae strains (Gamero-Sandemetrio et al., 2015). This effect that can be attributed to some components (fatty acids, such as linoleic acid, palmitic acid, stearic acid; other lipids, as tocopherols; tpolyphenols, as ferulic acid) which act as neutralisers of lipid peroxyl radicals (Sies & Stahl, 1995). However, we observed no the parallel predictable reduction in bulk protein oxidative damage by carbonylation. So, the first specific objective of this study was to investigate specific protein carbonylation which could allow the selective protection of enzymes and pathways, thus explaining the effects of argan oil on the fermentative capacity of ADY. Our second objective was to assess the effect of argan oil supplementation of molasses for ADY production under bench-top trials of large-scale yeast propagation and microvinifications on natural must, as affordable approximations to industrial performance.
Section snippets
Strains and cultivation conditions
Three Saccharomyces cerevisiae wine yeast strains were used in this study: the well-known commercial T73 wine yeast (Querol, Barrio, Huerta, & Ramón, 1992), and previously described strains D170 and D301 from Lallemand Inc. (Montreal, Quebec, Canada) (Gamero-Sandemetrio, Gomez-Pastor, & Matallana, 2013).
Precultures for the biomass propagation experiments were prepared in YPD liquid medium (1% yeast extract, 2% peptone, 2% glucose) and were incubated overnight at 30 °C with shaking (250 rpm).
Argan oil supplementation protects from specific protein oxidation during simulations of ADY production
We have recently described the effect of the argan oil supplementation of molasses on ADY production for S. cerevisiae wine strains at the laboratory scale (Gamero-Sandemetrio et al., 2015). Supplementation of molasses increased biomass yield and fermentative capacity. Moreover, lipid peroxidation diminished by argan oil, in agreement with its beneficial effects. However, bulk protein carbonylation was not affected (Gamero-Sandemetrio et al., 2015). As the carbonylation of specific glycolytic
Discussion
The industrial process of wine yeast biomass propagation and dehydration affects the viability and vitality of yeast cells (Matthews & Webb, 1991). This is largely due to oxidative damage of cellular components caused by ROS production (França, Panek, & Eleutherio, 2007; Gómez-Pastor, Pérez-Torrado, Cabiscol, Ros and Matallana, 2010, Gómez-Pastor, Pérez-Torrado, Cabiscol, Ros and Matallana, 2012; Pérez-Torrado, Gómez-Pastor, Larsson, & Matallana, 2009). We recently described the beneficial
Conclusion
We conclude that argan oil supplementation in molasses medium for yeasts propagation generally improves the biomass yield and fermentative capacity of ADY, regardless of the employed wine strain yeast. This technological improvement is due to the enhanced oxidative stress response and to the derived specific metabolic effects. The potential use of argan oil treatment in ADY production industry is general for any application that requires high biomass yield and fermentative capacity, such as
Competing interests
The authors declare that they have no competing interests.
Acknowledgements
We are grateful to Lallemand Inc. for providing the non-commercial strains from their collection. This work has been supported by grants AGL2011-24353 and AGL2014- AGL2014-52984-R from the Spanish Ministry of Economy and Competitiveness (MINECO) to E.M, and has been performed as part of the Programme VLC/Campus, Microcluster IViSoCa (Innovation for a Sustainable Viticulture and Quality), and Microcluster BBLM (Model Yeasts in Biomedicine & Biotechnology). E.G-S. was a predoctoral fellow of the
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Present address: Department of Neuroscience, Medical School, University of Minnesota, Minneapolis, Minnesota, USA.