3.3. Lipase Activity Assay

Enzyme activity was measured by monitoring spectrophotometrically the increase in absorbance at 410 nm, produced by the release of p-nitrophenol (pNP) in the hydrolysis of p-nitrophenylpalmitate (pNPP). For the hydrolytic assay, the substrate solution was prepared by mixing 1 mL of solution A (90 mg of pNPP dissolved in 30 mL 2-propanol) and 9 mL of solution B (90 mM Tris-HCl buffer (pH 8.0); 2.0% Triton X-100; and 0.2% gum arabic) [37]. All analyses were performed in triplicate. One unit of lipase (U) was defined as the amount of soluble enzyme (mL) or prepared biocatalyst (g) that releases 1 µmol p-nitrophenol (pNP) per min in the assay conditions (pH 8.0, 37 °C). The lipolytic activity of each derivative corresponded to the measurement of the derivative enzyme activity per gram of support (U/g).