 To whom correspondence and reprint requests should be addressed. Tel. 64 3 3252 803. Fax: 64 3 3253 851. E-mail: Savage@Lincoln.ac.nz JOURNAL OF FOOD COMPOSITION AND ANALYSIS (2000) 13, 201 } 206 doi:10.1006/jfca.2000.0879 Available online at http://www.idealibrary.com on ORIGINAL ARTICLE Effect of Cooking on the Soluble and Insoluble Oxalate Content of Some New Zealand Foods G. P. Savage, L. Vanhanen, S. M. Mason, and A. B. Ross Food Group, Animal and Food Sciences Division, Lincoln University, Canterbury, New Zealand Received January 7, 1999, and in revised form January 5, 2000 Oxalates occur as end products of metabolism in a number of plant tissues; some leafy plants and some root crops contain markedly high levels of soluble and insoluble oxalates. When consumed these oxalates can bind calcium and other minerals. Measurement of oxalate content in vege- tables commonly consumed in New Zealand shows that cooking reduces the oxalate content of the food by leaching losses into the cooking water. Roots and brassicas grown in New Zealand appear to contain relatively low levels of oxalates. Leafy vegetables such as silverbeet and NZ spinach appear to approach and exceed levels found in rhubarb stalks, although New Zealand silverbeet stems contain lower levels.  2000 Academic Press Key = ords: Oxalic acid; soluble oxalates; insoluble oxalates; vegetables; raw; boiled. INTRODUCTION Oxalic acid forms water-soluble salts with Na,K and NH  ions, it also binds with Ca, Fe and Mg rendering these minerals unavailable. Oxalates can be found in relatively small amounts in many plants. Oxalate-rich foods are usually minor components in human diets but are sometimes important in seasonal diets in certain areas of the world. Plants such as spinach and beetroot are well known for containing higher concentrations of oxalates than other plants but until recently no attempt has been made to summarize the world literature. The review published by Noonan and Savage (1999) highlighted the lack of data available on the oxalate content of common foods. It also showed that little data are available on the e!ect of cooking on oxalate content. Almost all high oxalate containing foods are cooked before consumption and much of the available data have been determined on raw foods. In addition, some of the data that are often quoted in the literature have been derived from older analytical techniques. The gas chromatographic technique (Oh- kawa, 1985) and HPLC methods (Holloway et al., 1989) have made accurate and reliable determinations of oxalic acid in plant materials possible. The oxalic acid content is variable within some species; some cultivars of spinach (Universal, Winter Giant) contain 400 } 600 mg/100 g fresh weight, FW while others range from 700 to 900 mg/100 g FW (Gontzea and Sutzescu, 1968). Oxalic acid 0889}1575/00/030201#06 $35.00/0  2000 Academic Press