Comparison of Volatile Profiles From Frozen and Refrigerated Southern Highbush Blueberry Fruit

The University of Florida blueberry breeding program has been developing southern highbush blueberry cultivars adapted to the sub-tropical Florida climate for over 50 years.  During this process, many Florida native, uncultivated Vaccinium species were used as sources of adaptive traits.  Unfortunately, reliance on wild germplasm resulted in many generations of selection before an adequate commercial phenotype was recovered, and selection for Florida low-chill cultivars has focused on yield and climate adaptability, not flavor.  Currently, selection for flavor in the breeding program is based on subjective breeder ratings and calculation of a sugar/acid ratio (total soluble solids / titratable acidity).  However, the flavor we experience from eating a blueberry also consists of sensory perception of volatile compounds, or secondary metabolites, produced in plants.  A greater focus on flavor would add value to Florida blueberry cultivars by increasing consumer demand. After comparing volatile profiles of various released cultivars and unreleased selections using gas chromatography-mass spectrometry (GC-MS), it will be possible to correlate the preferences of consumer flavor panels with the presence or absence of specific volatile compounds. Due to the short marketing season in Florida, fruit samples must be stored prior to GC-MS evaluation.  Therefore, we compared data collected from berries of multiple cultivars frozen at -80°C with those refrigerated at 4°C.  Results indicated that frozen fruit contain similar, if not higher, concentrations of volatile compounds, potentially due to dehydration during freezing. Certain volatiles, such as peaks at GC retention times 13.021 and 13.002, which likely correspond to 1-hexanol and trans-2-hexenol, are substantially higher in refrigerated berries, but these compounds are generally associated with green, leafy flavors and result from wound response pathways that are halted upon freezing. Potentially more critical to flavor is the absence of peak 18.397, likely hexyl acetate, and a significantly lower concentration of peak 9.706, likely methyl isovalerate, in frozen fruit. Both of these compounds are associated with sweet, fruity flavors. The development of a robust volatile collection protocol will be critical for evaluation of flavor profiles of southern highbush blueberries.