The liquid remaining at the bottom of each jar was also sampled. For the extraction of the total oxalic acid, 0.2 g of ground oven-dried sample was weighed accurately into a 100 mL flask and 40 mL of 0.2 M HCl was added and the mixture was then incubated with shaking for 20 min at 80 °C. After cooling, each mixture was transferred to a 100 mL volumetric flask and made up to volume with 0.2 M HCl.