, 2012 and Luthria, 2008). In addition, the oxidation of phenolic compounds should be avoided, since they are involved in the enzymatic browning reaction and consequently lose their phenol function and antioxidant capacity (Nicolas, Richard-Forget, Goupy, Amiot, & Aubert, 1994). It is advisable to use dry, frozen or lyophilised samples to avoid enzyme action (Escribano-Bailón & Santos-Buelga, 2004). The optimisation of the extraction of phenolic compounds is essential to reach an accurate analysis. Response surface methodology (RSM) is an effective tool for optimising this process. Moreover, it is a method

for developing, improving and optimising processes, and it can evaluate the effect of the variables and their interactions

(Farris and selleck Piergiovanni, 2009 and Wettasinghe and Shahidi, 1999). Thus, this study aimed to evaluate the effect of concentrations of the solvents, methanol and selleck screening library acetone, time and temperature on the extraction of apple phenolic compounds and their antioxidant capacity using RSM as the optimisation technique. Gala apples (10 kg) used in the experiments were obtained in the city of Ponta Grossa (25° 05′ 42′′ S 50° 09′ 43′′ O), Paraná, Brazil. The reagents Folin–Ciocalteau, Trolox (6-hydroxy-2,5,7,8-tetremethychroman-2-carboxylic acid), TPTZ (2,4,6-Tri (2-pyridyl)-s-triazine), DPPH (2,2-diphenyl-2-picrylhydrazyl), chlorogenic acid, p-coumaric acid, phloridzin, phloretin, (+)-catechin, (-)-epicatechin, procyanidin B1, procyanidin B2, quercetin, quercetin-3-D-galactoside, quercetin-3-β-D-glucoside, quercetin-3-O-rhamnoside, quercetin-3-rutinoside, aminophylline caffeic acid and gallic acid were purchased from Sigma–Aldrich (St. Louis, MO, USA). Methanol, acetone, acetic acid and acetonitrile were purchased from J. T. Baker (Phillipsburg, NJ, USA) and sodium nitrite and aluminium chloride from Vetec (Rio de Janeiro, RJ, Brazil) and Fluka (St. Louis, MO, USA), respectively. The liquid nitrogen (99%)

used was produced with StirLIN-1 (Stirling Cryogenics, Dwarka, New Delhi, India). The aqueous solutions were prepared using ultra-pure water (Milli-Q, Millipore, São Paulo, SP, Brazil). The apples were fragmented in a microprocessor (Metvisa, Brusque, SC, Brazil), immediately frozen with liquid nitrogen (1:2, w/v) to avoid the oxidation of the phenolic compounds (Guyot, Marnet, Sanoner, & Drilleau, 2001), and lyophilised (LD 1500, Terroni, São Paulo, SP, Brazil). The freeze-dried material (without seeds) was homogenised by crushing in a mortar. 1 g of the crushed apple was extracted with 60 mL of methanol or acetone in different concentrations, followed by incubation at different temperatures and times (Table 1).