Ferulic acid and p-coumaric acid solubilization by alkaline hydrolysis of the solid residue obtained after acid prehydrolysis of vine shoot prunings: Effect of the hydroxide and pH

Laboratory-scale experiments were conducted with the goal of releasing ferulic acid (FA) and p-coumaric acids (p-CA) from the solid residue obtained after prehydrolysis of prunings of vine shoots. Firstly, an alkaline hydrolysis with different hydroxides at mild conditions of temperature (35 °C) was performed, followed by acidification of liquors, and liquid–liquid extraction with ethyl acetate. The influence of two operational variables was tested on three levels in a 9 factorial design. The independent variables were the type of hydroxide (3N NH4OH, KOH or NaOH) and pH in the range 1.5–7.5. Under the optima conditions (3N KOH, pH 2.88), 228.6 mg FA/L, 0.41 mg FA/g vine shoots, 102.6 mg p-CA/L, and 0.147 mg p-CA/g vine shoots, were achieved.