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.