2.6.1. Lipoxygenase (LOX) activity
The LOX extraction was performed following the method described by Van der Ven, Matser, and Van den Berg (2005) with some modifications. Soymilk (30 mL) was placed in polypropylene tubs and centrifuged for 60 min at 12,000g at 4 C. Supernatants were used for enzyme activity test. The assay to determine LOX activity was performed following
method described by Axelrod, Cheesbrough, and Laasko (1981). The reaction was carried out at 25 C in quartz cuvettes in a spectrophotometer (Cecil 9000, Cambridge, England) at 234 nm. The assay mixture contained (2.975 e x) mL of borato buffer, pH 9.0, 0.025 mL of sodium linoleate substrate, and x mL of LOX extract (enzyme). After each addition the mixture was stirred. The blank cuvette contained no enzyme. The activity was expressed as absorbance per minute (abs/min) read in the spectrophotometer and transformed to units of lipoxygenase activity (ULA). One unit of enzyme was defined as absorbance increase of 0.1/min.