Aptitude of Saccharomyces yeasts to ferment unripe grapes harvested during cluster thinning for reducing alcohol content of wine Barbara Bovo a , Chiara Nadai a , Chiara Vendramini a , Wilson Josè Fernandes Lemos Junior a , Milena Carlot a,b , Andrea Skelin c , Alessio Giacomini a,b, ⁎, Viviana Corich a,b a Department of Agronomy Food Natural resources Animals and Environment (DAFNAE), University of Padova, Legnaro, PD, Italy b Interdepartmental Centre for Research in Viticulture and Enology (CIRVE), University of Padova, Conegliano, TV, Italy c Department of Microbiology, Faculty of Agriculture, University of Zagreb, Zagreb, Croatia abstract article info Article history: Received 26 August 2015 Received in revised form 7 July 2016 Accepted 13 July 2016 Available online 15 July 2016 Among the viticultural techniques developed to obtain wine with reduced alcohol content, the use of unripe grapes with low sugar and high malic acid concentration, harvested at cluster thinning, was recently explored. So far, no studies have evaluated the fermentation performances of Saccharomyces in unripe grape musts, in terms of fermentation ability and reducing malic acid contents, to improve the quality of this low-alcohol bever- age. In this work, we evaluated 24 S. cerevisiae strains isolated from Italian and Croatian vineyards with different fermentation aptitudes. Moreover, four S. paradoxus were considered, as previous works demonstrated that strains belonging to this species were able to degrade high malic acid amounts in standard musts. The industrial strain S. cerevisiae 71B was added as reference. Sugar and malic acid contents were modified in synthetic musts in order to understand the effect of their concentrations on alcoholic fermentation and malic acid degradation. S. cerevisiae fermentation performances improved when glucose concentration decreased and malic acid level in- creased. The conditions that simulate unripe grape must, i.e. low glucose and high malic acid content were found to enhance S. cerevisiae ability to degrade malic acid. On the contrary, S. paradoxus strains were able to degrade high amounts of malic acid only in conditions that resemble ripe grape must, i.e. high glucose and low malic acid concentration. In fermentation trials when low glucose concentrations were used, at high malic acid levels S. cerevisiae strains produced higher glycerol than at low malic acid condition. Malic acid degradation ability, test- ed on the best performing S. cerevisiae strains, was enhanced in fermentation trials when unripe grape must was used. © 2016 Elsevier B.V. All rights reserved. Keywords: Saccharomyces cerevisiae Saccharomyces paradoxus Malic acid Glycerol Unripe grape must 1. Introduction The production of low-alcohol wines is one of the major challenges in winemaking areas worldwide. In the past, ethanol content (up to 14–16% v/v) was considered a fundamental requirement for wine qual- ity since it was linked to high sugar content of grapes that positively af- fect the overall flavor of wines (Meillon et al., 2010). Nowadays consumers pay more attention on negative effects of alcohol on health, leading the World Health Organization to introduce a global strategy for reducing alcohol consumption (Saliba et al., 2013). Moreover, alcohol abuse is associated with economic and social issues, such as concerns on road safety. Reduction of alcoholic content is a complex process that could posi- tively limit the perception of hotness due to ethanol, but can also nega- tively influence the organoleptic properties of wine limiting the solubility of polyphenols and other volatile compounds (Guth and Sies, 2002). Many different techniques have been developed to control or reduce alcohol content with the challenging aim of preserving the physicochemical and sensory characteristics of wine. This goal could be achieved with the coordinated use of agronomic strategies, winemaking practices and microbiological approaches. The most com- mon techniques, dealing with reducing sugar content in the must, rely on the use of membrane and/or thermal distillation and include reverse osmosis, osmotic distillation, pervaporation and spinning cone columns (Pickering, 2000). Recently, microbiological strategies to reduce ethanol content, based on the development of S. cerevisiae wine yeast producing less alcohol during fermentation, have been proposed (Kutyna et al., 2010; Tilloy et al., 2014), including genetically-modified strains designed to de- crease ethanol yield (Cambon et al., 2006). The use of non-Saccharomy- ces yeasts was also evaluated. Bely et al. (2013) found that sequential fermentation of Candida zemplinina followed by S. cerevisiae caused the reduction of up to one alcoholic degree. The third strategy takes into account the reduction of sugar level of grapes directly in the vineyard. In the last decades, viticultural practices but especially the global warming affected the physiology of grapevine. Indeed, if the International Journal of Food Microbiology 236 (2016) 56–64 ⁎ Corresponding author at: Department of Agronomy Food Natural resources Animals and Environment (DAFNAE), University of Padova, Legnaro, PD, Italy. E-mail address: alessio.giacomini@unipd.it (A. Giacomini). http://dx.doi.org/10.1016/j.ijfoodmicro.2016.07.022 0168-1605/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro