The rate of electrolyte leakage was determined according to the
method described by Wang and Luo et al. (2013). Twenty discs of
banana fruit peel were excised randomly with a 1 cm diameter
stainless steel borer. The discs were rinsed with distilled water
three times before transferred into a beaker with 20 mL distilled
water and incubated at 25 C for 30 min in water bath shaker. Then
the discs were boiled for 30 min, cooled down to room temperature
and measured for electrolyte conductivity (L1). The electrolyte
conductivity of leach liquor (L0) was measured using a conductivity
meter. The rate of electrolyte leakage was also calculated.
The MDA concentration was measured according to the method
described by Chen, He, Jiang, Wang, Joyce, Ji, and Lu (2008) with
minor modifications. Two grams of frozen banana fruit samples
were homogenized in 7 mL of 50 mM PBS buffer (pH 7.8) in
ice-bath and centrifuged at 4 C for 20 min at 12,000 g. 1 mL
supernatant liquor was added in 3 mL of 35 mM thiobarbituric
acid. The mixture was heated to boiling in water bath for 15 min
and centrifuged for 10 min at 12,000 g after cooling down
quickly. The absorbance of supernatant was measured at 532 nm,
600 nm and 450 nm. The MDA concentration was calculated.