Elucidating the biochemical factors governing off-flavor perception in mandarins Livnat Goldenberg a,d , Yossi Yaniv b , Hyun Jin Choi c , Adi Doron-Faigenboim b , Nir Carmi b , Ron Porat a, * a Department of Postharvest Science of Fresh Produce, ARO, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel b Department of Fruit Tree Crops, ARO, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel c Postharvest Research Team, National Institute of Horticultural and Herbal Science, Wanju-gun, Jeollabuk-do, South Korea d Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel A R T I C L E I N F O Article history: Received 10 April 2016 Received in revised form 23 May 2016 Accepted 12 June 2016 Available online 24 June 2016 Keywords: Citrus Ethanol Mandarin Off-flavor Postharvest Storage A B S T R A C T Mandarins tend to develop off-flavors during storage, and this is attributed to induction of ethanol fermentation metabolism and accumulation of ethanol and its by-products. In order to elucidate the biochemical factors contributing to off-flavor formation in mandarins, we conducted sensory and aroma- volatile analyses of 41 different mandarin varieties within the Israeli citrus breeding collection, at harvest and after 6 weeks of cold storage at 6  C followed by 5 days at 20  C. Descriptive sensory analysis with the aid of a trained panel revealed great diversity among mandarin varieties, in perceived off-flavors; and gas chromatography (GC) analysis revealed only a low correlation (R = 0.14) between ethanol levels and perception of off-flavors. Gas-chromatography mass-spectrometry (GC–MS) analysis of levels and compositions of total aroma volatiles during postharvest storage revealed general increases in levels of alcohols and ethyl esters, and consequent decreases in levels of monoterpenes, sesquiterpenes, and aldehydes. Detailed volatile analysis of diverse varieties with strong and weak off-flavors revealed that the aroma volatiles compositions and the ratios between chemical classes of volatiles have completely changed during storage in varieties with strong off-flavors, but were less altered in varieties with weak off-flavors. In addition, we observed a negative correlation (R = 0.58) between monoterpene levels and off-flavor perception, i.e., most varieties with weak off-flavors had relatively high terpene levels, which might mask the perception of off-flavors. Overall, it is suggested that perception of off-flavors in mandarins does not depend solely on accumulation of specific volatile compounds, such as ethanol, but rather evolves during storage because of general changes in juice aroma-volatiles profiles and compositions which create an atypical or spoiled flavor. ã 2016 Elsevier B.V. All rights reserved. 1. Introduction During the last decade, there has been a continuous rise in consumption and global marketing of fresh, easy-to-peel man- darins, with a production forecast of 29 million tons per year (USDA, 2016). However, although they offer an attractive appear- ance and convenience for consumption, mandarins are much more perishable than other citrus varieties and, in particular, undergo deterioration in sensory acceptability and accumulation of off- flavors after harvest (Cohen, 1999; Tietel et al., 2011b). Previous studies attributed development of off-flavors in mandarins mainly to induction of ethanol-fermentation metabolism and accumulation of high levels of ethanol; and this was demonstrated in several mandarin varieties (Cohen et al., 1990; Davis et al., 1967; Marcilla et al., 2009; Obenland et al., 2011; Shi et al., 2007; Tietel et al., 2010). Ethanol fermentation is a two- step process, catalyzed by pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH); it provides a major route for energy production under low-oxygen conditions (Geigenberger, 2003). Furthermore, accumulation of off-flavors is enhanced by applica- tion of wax coatings. These coatings restrict gas exchange through the peel surface, and result in increased CO 2 and reduced O 2 levels in the internal atmosphere of the fruit, leading, in turn, to stimulation of anaerobic respiration (Davis and Hofmann, 1973; Hagenmaier and Baker, 1993; Navarro-Tarazaga et al., 2007; Porat et al., 2005). In addition to the direct effect of ethanol accumulation during storage on fruit-flavor perception, together with other acyl-CoAs * Corresponding author. E-mail address: rporat@volcani.agri.gov.il (R. Porat). http://dx.doi.org/10.1016/j.postharvbio.2016.06.009 0925-5214/ã 2016 Elsevier B.V. All rights reserved. Postharvest Biology and Technology 120 (2016) 167–179 Contents lists available at ScienceDirect Postharvest Biology and Technology journal homepa ge: www.elsev ier.com/locate/postharvbio