2.3.8. Phenolic compounds and hydroxycinnamic acid-derivatives
Frozen fruit pulp was ground in a mill with liquid N2 (Multi-mill attached to a Kenwood Major Titanium KM023, Germany) and 2 g of the resulting powder were poured in 5 mL of cool ethanol. Samples were then centrifuged at 9000 × g for 15 min at 4 °C. The supernatant was collected and the pellet was re-extracted with 5 mL ethanol and centrifuged as described above. The supernatants were combined to make a final volume of 10 mL. The determination of phenolic compounds was performed according to Obied, Allen, Bedgood, Prenzler, and Robards (2005). Briefly, 1 mL of each fruit extract was mixed with 1 mL of an ethanolic solution containing 27 mmol/L HCl. Subsequently 8 mL an ethanolic solution containing 0.55 mol/L HCl were added to each test tube and the absorbance of the solutions was measured at 280 nm and 320 nm to evaluate total phenolics and hydroxycinnamic acid derivatives respectively. Corresponding standard curves were prepared using ethanolic solutions of gallic acid, and caffeic acid respectively. Results were expressed in mg per kilogram of fresh fruit.