FCT (Fundação para a Ciência e Tecnologia) e o FEDER através do programa COMPETE através dos projetos projects FCOMP-
01-0124-FEDER-008703 (FCT/PTDC/AGR-AAM/102447/2008),
PEst-C/EQB/LA0006/2011, e PEst-OE/AGR/UI0690/2011
The main objective of the present work was to optimize the extraction conditions for simultaneous maximization of total reducing (TRC) and antioxidant (AC) capacities for lettuce (Lactuca sativa L.) by-products
extracts, using response surface methodology. For this, a design of experiments (DOE) with different
combinations of solvents (water, methanol and acetone) extraction temperatures (30–60
◦C) and time (10–60 min) on the TRC and AC was applied. Higher and consistent fittings using second order polynomial models of the experimental data with regard to TRC (R2 = 0.529, p lack of fit > 0.05) and AC (R2 = 0.900, p lack of fit > 0.05) were obtained with methanol. The optimum extraction conditions based on combination responses for TRC and AC were: 30% methanol (v/v), 60
◦C and 60 min. A close agreement between
experimental and predicted values was found when applying these conditions. Furthermore, when aqueous extracts were prepared (e.g. 45
◦ C, 10 min), these presented similar TRC and AC properties to those obtained by the above optimum extraction conditions, having the advantage of applying mild extraction
conditions and avoiding the use of organic solvents in their preparation.
