Effect of cooking on oxalate content of pulses using an enzymatic procedure

An enzymatic method proposed for the determination of oxalate in urine is adapted for the estimation of soluble oxalate content in beans, chickpeas and lentils. Oxalates were extracted in water by refluxing for 2 h. The method is based on the oxidation of oxalate by the oxidase and the determination of the resulting hydrogen peroxide, which in presence of peroxidase, 3-methyl-2 benzotiazinolone and 3-dimethylamino benzoic, gives an indamine compound with an absorption maximum at 590 nm. The linearity (from 0.015 to 0.6 mM) of the method is adequate to the analysis of oxalate contents in pulses, and the inter-day precision of the method expressed as relative standard deviation was good (3.01%), with an accuracy of (98.7+/-2.5%) estimated by recovery assays. This method is applied to estimate the losses of soluble oxalate as a consequence of cooking. All the cooking procedures reduce the soluble oxalate content, but microwave and industrial procedures are more effective than traditional domestic cooking.