2.1. Fruit materials
Fresh fruit banana (Musa spp., AAA group, cv. ‘Brazil’) were harvested at 70–80% maturity from a commercial orchard in Guangzhou. Fruit were immediately sent back to laboratory, and dipped in water to clean the surfaces. They were then air-dried till the solution dropping from the fruit surface disappeared completely. The fruit were selected carefully by visual defects and uniformity of weight or shape. Bananas were then soaked into each treatment for 10 min. The treatments were: A, control, water only; B, 8 mM oxalic acid; C, 20 mM oxalic acid. After treatments, they were air-dried, packed into plastic polyethylene bags (0.03 mm), and stored at about 23 ± 2 °C and 75–90% relative humidity (RH). Eight fingers from each treatment were randomly taken out for measurement of hue value, chlorophyll fluorescence and browning index. The peel tissue from another eight fingers were sliced, mixed, frozen in liquid N2 and stored at −20 °C prior to enzyme and total phenol analysis.