Metabolomic Variation In North Carolina Red Raspberry

Raspberries and other berry polyphenols contain powerful antioxidants, and regular consumption of these compounds may help prevent and/or moderate chronic diseases. Metabolomic methods for compositional analysis of fruit samples have applications for human health and breeding programs. In this study, metabolomic variation was determined among three fall-fruiting red raspberry cultivars (‘Autumn Britten’, ‘Caroline’, and ‘Nantahala’) grown at three locations in North Carolina with varying day/night temperatures (harvest season max/min averages of 32°/21°, 28°/16°, 24°/14° C) and elevation (214, 630, 917 m above sea level).  A metabolite profile quantifying 10 flavonoid compounds in 27 freeze-dried fruit samples from the 2010 growing season was assembled using liquid-chromatography-time-of-flight-mass-spectrometry (LC-TOF-MS) technology.  Additionally, assays analyzing total anthocyanins, total phenolics, and Ferric Reducing Antioxidant Power (FRAP) of samples were used to determine cultivar, location, harvest date, and temperature effects. Differences in metabolite composition were seen among cultivars and locations, with cyanidins varying most and pelargonidin least among cultivar and location.  The highest levels of cyanidin-3-glucoside, cyanidin-3-galactoside, cyanidin-3-sophoroside, and quercetin-3-galactoside were found in ‘Caroline’, and were highest when grown at lowest elevation and highest day/night temperature.  ‘Autumn Britten’ had the highest levels of quercetin-3-glucoside, cyanidin-3-rutinoside, and kaempferol-3-glucoside, with location effects varying by metabolite. The ‘Royalty’ purple raspberry background of ‘Nantahala’ was exhibited through much higher levels of cyanidin-3-sambubioside (2.53 mg/g DW) in comparison with levels in ‘Caroline’ (0.159 mg/g DW) and ‘Autumn Britten’ (0.719 mg/g DW).  Consistent with individual metabolite measurement, ‘Caroline’ averaged the highest in total phenolics (2498.44 mg GAE/kg) and FRAP antioxidant capacity (13.76 µmoles Trolox eq./g FW) across the three locations, followed by ‘Autumn Britten’ (2338.88 mg GAE/kg, 12.76 µmoles Trolox eq./g FW) and ‘Nantahala’ (2169.24 mg/kg, and 11.97 µmoles Trolox eq./g FW, respectively). For total anthocyanins, ‘Caroline’ (690.49 mg/L) and ‘Autumn Britten’ (690.82 mg/L) were significantly higher than ‘Nantahala’ (470.71 mg/L).  Among production environments and averaged across cultivars, fruit grown at medial elevation and temperature was highest in total anthocyanin levels (695.17 mg/L), and fruit grown at the two lowest elevations and two highest temperatures was  highest in total antioxidants (13.12 µmoles Trolox eq./g FW) and total phenolics (2381.12 mg/kg). Specific metabolite quantification versus total anthocyanin and total phenolic trends indicate that genetic and environmental effects vary by individual metabolite and composition.  These methods and results can be utilized in breeding programs to identify key metabolites contributing to antioxidant properties and health benefits for humans, and further tailoring for functional foods.