Effects of extraction conditions on oxalate oxidase activity of germinated paddy rice (Oryza sativa L.)

Oxalic acid and its salts, oxalates, are end products of metabolism found widely in plant kingdom. Once consumed, these compounds can bind with calcium, to form calcium oxalate stones, the most common types of kidney stone. Oxalate oxidase (OxO), an oxalate-degrading enzyme, is produced by the metabolic activities of microorganisms or plants, especially during the germination of cereal grains. The purpose of this study was to investigate impacts of extraction conditions on the OxO activity of germinated paddy rice (Oryza sativa L.) using Ultra-high performance liquid chromatography. The effects of three factors namely pH (2–7), solvent-to-sample ratios (3:1–8:1 v/w), and extraction time (15–75 min) were investigated. The results showed that the activity was higher at more acidic pH, ranging from 2 to 4. In addition, the OxO activity rose as the solvent-to-sample ratios increased and reached a peak at the ratio of 5:1 before dropping rapidly. Prolonging extraction times, from 15 to 60 min, resulted in increases in the OxO activity.