Effect of harvest date on off-flavor development in mandarins following postharvest wax application

Abstract

Mandarins (Citrus reticulata Blanco) are very prone to off-flavor formation following the postharvest application of wax and it had been previously observed that off-flavor also increases with advanced fruit maturity. To more fully evaluate the maturity effect on off-flavor and to determine potential causal mechanisms for it, ‘Owari’ and ‘China S-9’, two Satsuma varieties, were harvested at three to four dates within the harvest season, waxed and placed into storage for either 2 weeks at 5 °C or 1 week at 5 °C + 1 week 20 °C, the latter treatment being expected to develop off-flavor. The testing was conducted over three seasons with ‘W. Murcott’, a non-Satsuma variety, being included in the third season. In all three seasons analyses were conducted for various parameters related to fruit internal atmosphere composition. At the end of the storage period, in the first two seasons, the fruit were evaluated for flavor using a semi-expert sensory panel. Consistently, in seasons 1 and 2 where flavor was evaluated, both Satsuma varieties did not develop off-flavor or a loss in acceptability in the initial harvest. In subsequent harvests, however, off-flavor became increasingly noticeable and was correlated with the decline in flavor acceptability. There were occasional impacts on other flavor attributes, but the results were inconsistent. Advancing maturity in all three seasons was associated with a decrease in internal oxygen and an increase in internal carbon dioxide, except in the case of ‘W. Murcott’ where there was little or no change in internal oxygen and an increase in carbon dioxide. Enhanced fermentative metabolism was indicated in the later harvests in the form of higher ethanol in the Satsuma varieties. Peel gas permeance measurements performed in season 3 showed no meaningful relationship with the internal gas concentrations measured during the season. Respiration rate, however, strongly increased during the season in the Satsuma varieties and decreased in ‘W. Murcott, both changes being associated with the internal gas composition. It is concluded that maturity influences the propensity for off-flavor development in mandarins, but it does not occur in every instance and is influenced by year, storage and temperature. The potential mechanism modulating the change in the three varieties examined in this study appeared to be changes in the rate of respiration, since when respiration is sufficiently high, oxygen levels decline to a level where fermentation occurs, and off-flavor becomes apparent.