2.5. Malondialdehyde (MDA) content and lipoxygenase (LOX) activity
determination
MDA content was determined according to the method
described by Li et al. (2006) with some modification. Fruit tissues
(1 g) were extracted with 5 mL of 200 mmol L1 sodium phosphate
buffer (pH 6.8). Three milliliters of 0.5% thiobarbituric acid (TBA)
were added to 1 mL of the extract. The solution was heated in a
boiling water bath for 20 min, then immediately cooled, and finally
centrifuged at 10,000 g for 10 min to clarify the solution.
Absorbance was measured at 450, 532 and 600 nm. MDA content
was expressed as mmol kg1 of fresh weight by the method of Li
et al. (2006).
LOX activity was assayed by the method described as Tao et al.
(2008). One unit of LOX activity was defined as 0.1 change of
absorbance at 234 nm per min. Specific LOX activity was expressed
as units per kilogram of fruit fresh weight.