Determination of oxalate in foods by enzymatic analysis

An enzymatic analysis was developed in order to determine oxalate in many kinds of foods. Oxalate was converted into formate by oxalate decarboxylase, then formate dehydrogenase was added in the presence of nicotinamide-adenine dinucleotide. Contents of oxalate were calculated from the increase in absorbance at 340nm due to reduced nucleotide-adenine dinucleotide produced. Oxalate concentrations were determined in various kinds of foods (61 vegetable and 30 animal). High concentrations of oxalate were found in several vegetables, e. g., spinach (1760mg/100g), New Zealand spinach (894mg/100g) and green tea (426mg/100g). In the case of spinach, the oxalate content tended to increase with the extent of growth of the plants. Algae such as green layer (193mg/100g) and Tengusa (165mg/100g) had fairly high oxalate contents. Animal foods contained lower levels of oxalate. The content of oxalate in fish muscle was 0.3 to 3.7mg/100g and that of beef was 8.0mg/100g.