Postharvest Biology and Technology 173 (2021) 111415 0925-5214/© 2020 Elsevier B.V. All rights reserved. Ethanol vapor treatment inhibits apple ripening at room temperature even with the presence of ethylene Fabio Rodrigo Thewes a, b, *, Basem Mahmoud Balkees b, c , Felix Büchele b, c , Jens Norbert Wünsche c , Daniel Alexandre Neuwald b , Auri Brackmann a a Department of Plant Science, Postharvest Research Center, Federal University of Santa Maria, Roraima Avenue 1000, Camobi, Santa Maria 97105-900, RS, Brazil b Competence Centre for Fruit Growing at Lake Constance (KOB), Schuhmacherhof 6, Ravensburg, Germany c University of Hohenheim, Institute of Crop Science, Crop Physiology of Specialty Crops, Stuttgart, Germany A R T I C L E INFO Keywords: Malus domestica ‘Elstar’ ‘Nicoter’ Anaerobic metabolism Membrane permeability Ethylene Flesh firmness ABSTRACT The present study aimed to evaluate the effect of two ethanol vapor doses (250 and 500 ppm), 1-methylcyclo- propene (1-MCP) (0.650 ppm) with or without ethylene application (150 ppm) on the aerobic and anaerobic metabolism and quality of ‘Elstar’, a fast ripening apple cultivar, and ‘Nicoter’, a slowly ripening apple cultivar, over 14 d of holding at room temperature (20 ± 2 ◦ C). Fruit were subjected to treatments for 24 h and analyses performed after 0, 7 and 14 d holding at room temperature (20 ± 2 ◦ C). For both cultivars studied, ethanol vapor treatments, especially 500 ppm, inhibited the ripening of apples even when combined with 150 ppm of ethylene, but not as much as 1-MCP treatment in ‘Nicoter’ apples. Fruit treated with ethanol vapor maintained lower electrolyte leakage, higher flesh firmness, greener color and had more healthy fruit. However, its application increased the pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) activity, acetaldehyde and ethyl acetate accumulation, but in concentrations below the odor threshold reported in the literature. The 1-MCP treatment increased decay incidence, reducing the healthy fruit amount in ‘Nicoter’ apples after 14 d, but maintained a very low ethylene production and respiration rate, which allowed higher acidity maintenance after 14 d holding at room temperature. There was no incidence of external and internal physiological disorders in both cultivars. 1. Introduction Apples are climacteric fruit, which allows the fruit to ripen after harvest as a response to ethylene exposure. Nevertheless, the sensitivity to ethylene is different among cultivars produced worldwide (Kitte- mann, 2012; Gwanpua et al., 2016). Apples of the cultivar Elstar are very sensitive to ethylene, with a fast softening over the ripening period (Kittemann, 2012; K¨ opcke, 2015). On the other hand, ‘Nicoter’ apples produce low ethylene amounts and ripen slowly over the storage in room temperature (Gwanpua et al., 2016; Weber et al., 2019). After harvest or storage, fruit is subjected to selection and transportation processes before they are marketed. This process generally takes one or two weeks, during which fruit are subjected to room temperatures and the ripening process is enhanced. Several technologies can be used to suppress fruit ripening at room temperatures such as absorbing ethylene from storage rooms (Brackmann et al., 2014, 2010; Corrˆea et al., 2011), modified atmo- sphere packaging (Putnik et al., 2017; Rocha et al., 2004) and 1-methyl- cyclopropene application (1-MCP), which blocks ethylene action (Blankenship and Dole, 2003; Sisler and Serek, 1997; Watkins, 2006). Among these technologies, the most widely used is 1-MCP application which reduces ethylene production, respiration rate, and the loss of flesh firmness (McCormick et al., 2012; Nock and Watkins, 2013; Thewes et al., 2017a). However, 1-MCP application also reduces the volatile compounds emission (Kondo et al., 2005; Thewes et al., 2019; Yang et al., 2016), increases susceptibility to decay (Janisiewicz et al., 2003) and flesh breakdown (Jung and Watkins, 2011; Koushesh Saba and Watkins, 2020). Furthermore, its use is not permitted for organic apples in Europe (Gabioud Rebeaud and Gasser, 2015). Thus, the study of other strategies to block apple ripening is necessary as an alternative to 1-MCP treatment. One possible method to delay fruit ripening is the ethanol vapor * Corresponding author at: Department of Plant Science, Postharvest Research Center, Federal University of Santa Maria, Roraima Avenue 1000, Camobi, Santa Maria 97105-900, RS, Brazil. E-mail addresses: fthewes@yahoo.com.br, fthewes@pq.cnpq.br (F.R. Thewes). Contents lists available at ScienceDirect Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio https://doi.org/10.1016/j.postharvbio.2020.111415 Received 30 June 2020; Received in revised form 5 October 2020; Accepted 16 November 2020