Total and soluble oxalates were extracted from the samples using the method of Ohkawa (Ohkawa, 1985) with
some modifications. 0.15 g of the herb or 1.0 g of the fruit was weighed into a 15-ml centrifuge tube and 5 ml of
2 N HCl (for total oxalate extraction) or 5 ml of distilled deionized water (for soluble oxalate extraction) were
added to the sample. The tube was tightly capped and vortexed for 5 min and then centrifuged at 4200 rpm for 10
min. The supernatant was transferred to a 25-ml volumetric flask and the remaining oxalate in the pellet was
extracted two additional times. The final volume of the collected supernatant from the 3 successive extractions
was diluted to 25 ml with distilled deionized water. The extracts were kept frozen until the time of oxalate
analysis. Each sample was extracted in duplicate.