Sensory Quality and Physiological Responses in Two Mandarin Varieties Differing in Ethanol Accumulation after Waxing and Storage

‘Gold Nugget’ (GN) and ‘Pixie’ (P) mandarins had been previously found to greatly differ in the amount of ethanol accumulated in the fruit after waxing and storage.  Since ethanol is linked to off-flavor in waxed citrus it was of interest to investigate the potential physiological mechanisms that cause the dissimilarity in ethanol accumulation between the two varieties and also determine whether flavor is influenced by this difference.   Harvests were conducted at four times during the season, three in the San Joaquin Valley (SJV) and one in the coastal area of California.  As had been previously observed, P accumulated more ethanol than did GN following waxing and storage.  However, there was no clear association of higher ethanol and greater ethyl ester concentration which could show a direct effect on flavor quality.  In general, P had lower levels of internal O₂ and higher CO₂ following waxing that increased the potential for more intensive fermentative metabolism in P than in GN.  This was associated with a greater peel thickness and the possibility of lower gas exchange in fruit from the SJV location.  Analysis of some of the components of the fermentation pathway indicated that pyruvate levels and alcohol dehydrogenase activity was higher in P than in GN, while pyruvate decarboxylase activities were not consistently different.  Exposure of fruit to nitrogen induced the production of ethanol in P and GN to the same degree, indicating that the major difference may be in what determines the internal oxygen concentration in the fruit following waxing.  Sensory evaluations indicated a higher potential for P to have off-flavor development and a decrease in acceptability following storage than GN.  Potential reasons for the differences in sensory response to waxing and storage of the two varieties will be discussed.