2.4. Preparation of samples
A 5.0 g of ground food samples was transferred into a 100 ml beaker and 0.05 M NaOH solution was added to give a final volume of 50 ml. After it was mixed by a homogenizer for 2 min, the sample was shaken mechanically for 10 min with a shaking rate of 300 min1. The extract was centrifuged for 5 min at 5000 rpm.The 10 ml supernatant was then filtered with 0.45 lm membrane filter for injection into HPLC.