To determine pH, 10 g of the sample was homogenised with 50 mL of chilled distilled water. The pH values were measured with a portable digital pH metre attached with a probe (Model pH 510, Eutech Instrument, Ayer Rajah Crescent, Singapore). Three readings were taken by dipping the pH metre probe in the homogenate and mixing the homogenate on a magnet stirrer until the reading was stable. The pH metre was calibrated after every three readings using two buffers of pH 4.0 and 7.0.