Submitted to: Postharvest Biology and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/2/2009
Publication Date: 5/1/2009
Citation: Obenland, D.M., Collin, S., Mackey, B.E., Sievert, J., Field, K., Arpaia, M. 2009. Determinants of flavor acceptability during the maturation of navel oranges. Postharvest Biology and Technology. 55(2):2009:156-163. Interpretive Summary: Navel oranges must have a soluble solids (sweetness) to acidity ratio (SSC/TA) of 8:1 before the fruit can be legally harvested in California. However, the relationship of this maturity standard with taste is not well defined and its ability to keep poor-tasting fruit out of the market is in doubt. A variety of different quality measurements, including the abundance of volatile flavor compounds, were taken over the course of three seasons in addition to taste evaluations. It was found that BrimA, a measurement calculated by subtracting acidity from soluble solids, is more closely related to taste than SSC/TA. Volatile components were identified that likely play a role in the development of taste and have the potential of serving as maturity markers. Sensory panelists disliked fruit at a SSC/TA ratio of 8:1, indicating that the current standard is set too low. The findings of this study offer a number of means by which the citrus industry can immediately use to raise the taste quality of early season navel oranges.
Technical Abstract: Navel oranges of differing maturities were harvested at regular intervals for three successive seasons and evaluated for external color, percent juice, soluble solid content (SSC) and titratable acidity (TA). Fruit from each harvest date were rated by a sensory panel for flavor likeability (hedonic score), sweetness, tartness and richness. Gas chromatograpy/olfactometry was used to identify odor-active volatiles present at each harvest date in the final season. Peel color and BrimA, a parameter calculated by subtracting TA times a constant from SSC, were the most closely related quality parameters to the hedonic score and ratings of sweetness, richness and tartness. A predictive equation for hedonic score was developed using stepwise regression that combined color, percent juice and BrimA and accounted for 63% of the variation in the data. Year, location and navel strain had only minor effects on the relationship between the quality parameters and the sensory ratings. Nineteen different odor-active compounds were identified, of which six were significantly correlated with changes that occurred in the sensory attributes during navel orange maturation. The SSC/TA ratio, the basis for the current maturity standard in California, was not as closely related to likeability as BrimA. At the maturity standard (SSC/TA) of 8:1, the hedonic score calculated from the overall regression equation was 4.4, a value well into the “dislike” range, indicating that the current standard is likely set at too low of a value.