Fig. 2a clearly shows both turbidity and soluble oxalate content of the extract were sensitive to pH of the extract. The starting extract contained considerable amounts of oxalate ions (249.1 μg mL−1), confirming the acidic extraction of oxalates from the material. Turbidity of the extract increased as pH increased from 1.5 to 4.0, thereafter, it tended to be constant. In contrast, the soluble oxalate level decreased as pH increased from 1.5 to 4.5, and it leveled off despite further increased the pH. Moreover, the lowest oxalate level was obtained at pH 4.5, which corresponded to the highest turbidity. These results suggested the increase in turbidity of the extract was related to the amount of insoluble oxalate salts formed with increasing pH. It was observed that both the turbidity and oxalate level (72.9 μg mL−1) remained constant when pH was greater than 4.0, an indicative of the maximum formation of insoluble oxalates. The residue oxalates of the pH-adjusted extract suggested that the pH-adjustment was unable to completely eliminate the presented oxalates.