The pericarp pH was determined according to the method of Underhill & Critchley.4 Pericarp tissue (4.0 g) was washed in distilled water to remove adhesive aril juice. The pericarp tissue was finely chopped and homogenized in 40 ml of distilled water for 1 min. The pH was measured while stirring the homogenate. The pH of each acid solution was also measured.