Tietel, Z., Department of Postharvest Science of Fresh Produce, ARO, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel
Lewinsohn, E., Department of Vegetable Crops, ARO, Newe ya'Ar Research Center, P.O. Box 1021, Ramat Yishay 30095, Israel
Fallik, E., Department of Postharvest Science of Fresh Produce, ARO, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Porat, R., Department of Postharvest Science of Fresh Produce, ARO, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel

To elucidate the roles of ethanol fermentation metabolism in causing off-flavors, 'Mor' mandarins were exposed to anaerobic atmospheres for 0, 2, 4, 7, and 10 days to gradually increase juice ethanol and acetaldehyde levels through enhanced fermentation. Exposure to anaerobic atmosphere caused progressive decline in fruit sensory quality, from nearly "good" to "very bad", because of decreased typical mandarin flavor and increased sensation of 'musty' and 'ethanol' off-flavors. GC-MS analysis revealed significant (p ≥ 0.05) increases in the contents of 12 aroma volatiles, including the ethanol fermentation metabolites ethanol and acetaldehyde, and several fatty acid and amino acid catabolism derivates, 7 of which were ethyl esters, which suggests that they were esterification products of ethanol and acyl-CoA's derived from fatty acid and amino acid catabolism. These de novo synthesized anaerobiosis-regulated ethyl esters impart 'pungent', 'ethereal', 'waxy', 'musty', and 'fruity' notes. Overall, these results suggest that besides the direct effects of ethanol and acetaldehyde, downstream ethanol esterification products may also be involved in causing off-flavor sensation in mandarins. © 2011 American Chemical Society.