Short communication Advances in the control of the spoilage caused by Zygosaccharomyces species on sweet wines and concentrated grape musts Alejandro Alonso, Ignacio Belda, Antonio Santos, Eva Navascu  es, Domingo Marquina * Department of Microbiology, Biology Faculty, Complutense University of Madrid, Madrid 28040, Spain article info Article history: Received 17 September 2014 Received in revised form 6 November 2014 Accepted 11 November 2014 Available online 20 November 2014 Keywords: Biocontrol Zygosaccharomyces Killer toxin Re-fermentation Sweet wines Concentrated grape must abstract Zygosaccharomyces is one of the most damaging foodborne spoilage yeast, and tools for controlling its growth are limited due to its reported resistance to preservatives and osmotic stress. Zygosaccharomyces contamination may result in spoilage of grape juice concentrates or in re-fermentation and CO 2 pro- duction in sweet wines so, biological control of these yeasts could be important. In this study, thirty-four strains belonging to Zygosaccharomyces have been identified and tested against a panel of eighteen killer yeasts. Here, for the first time, PMKT is proven to be effective against different strains of Zygosacchar- omyces. Cultures in media composed by sweet wine and concentrated grape juice showed that PMKT has the ability to inhibit Zygosaccharomyces, while Saccharomyces cerevisiae was fully resistant in such conditions indicating that PMKT could be used to avoid the Zygosaccharomyces spoilage. Additionally, PMKT activity was determined in the presence of potassium sorbate and potassium metabisulphite showing unexpected synergistic effects with the latter, and making possible the promising application of reducing preservative concentrations in beverages. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Yeasts play a central role in the spoilage of foods and beverages, mainly those with high acidity and reduced water activity (Deak & Beuchat, 1996; Loureiro & Malfeito-Ferreira, 2003) where other microorganisms such as bacteria are not competitive (Boekhout et al., 2002; Tudor & Board, 1993). In order to meet the emerging consumer trend for more natural products, nowadays food manufacturers are forced to limit the use of chemical preservatives. Adverse effects of some common pre- servatives on humans have been discussed; for instance, sodium benzoate was recently linked to the hyperactivity in children (Kemp, 2008; McCann et al., 2007). Biological control agents are potential alternatives for the chemical fungicides presently used in agriculture to fight plant diseases, avoid the spoilage of industrial fermentations and prevent the deterioration of foods and bever- ages (Liu, Sui, Wisniewski, Droby, & Liu, 2013; Santos & Marquina, 2011). Yeasts are interesting microorganisms for use in biological control and, in particular, they are relatively easy to handle and show economy of manipulation and cultivation (Pimenta et al., 2009). In this context, killer yeasts and their toxins have been proposed to combat contamination by wild yeasts in the food and beverage industries (Ciani & Fatichenti, 2001; Goretti et al., 2009; Jacobs & Van Vuuren, 1991; Kimura, Kitamoto, Imura, & Kito, 1995; Liu & Tsao, 2009; Lowes et al., 2000; Palpacelli, Ciani, & Rosini, 1991). In recent years our research group has focused its attention on killer toxins produced by Pichia membranifaciens (Santos, Alonso, Belda, & Marquina, 2013; Santos,  Alvarez, Mauro, Abrusci, & Marquina, 2005; Santos & Marquina, 2004a, 2004b, 2011; Santos, Marquina, Leal, & Peinado, 2000; Santos, San Mauro, Abrusci, & Marquina, 2007; Santos, San Mauro, Bravo, & Marquina, 2009;). P. membranifaciens CYC 1106 and CYC 1086 secrete particularly strong, broad-spectrum killer toxins (called PMKT and PMKT2, respectively). It was found that the toxins pro- duced by these yeasts are versatile anti-spoilage agents in foods and beverages, with the limitations imposed by their stability to physical-chemical factors (Santos et al., 2009; Santos & Marquina, 2004b). Killer toxins have been proposed to control the proliferation of undesirable yeasts in winemaking, showing that they are a valuable asset for biocontrolling wine spoilage yeasts such as Brettanomyces * Corresponding author. Department of Microbiology III, Faculty of Biology, Complutense University of Madrid, C./ Jos e Antonio Novais, 12, 28040 Madrid, Spain. Tel./fax: þ34 91 3944964. E-mail address: dommarq@bio.ucm.es (D. Marquina). Contents lists available at ScienceDirect Food Control journal homepage: www.elsevier.com/locate/foodcont http://dx.doi.org/10.1016/j.foodcont.2014.11.019 0956-7135/© 2014 Elsevier Ltd. All rights reserved. Food Control 51 (2015) 129e134