Composition and availability of soluble and insoluble oxalates in raw and cooked taro ( Colocasia esculenta var. Schott) leaves

Abstract

Taro ( Colocasia esculenta var. Schott) is a major staple food crop in parts of Asia and the Pacific Islands and is grown as a minor crop in New Zealand. Soluble, insoluble and total oxalate content of young and older leaves were determined by HPLC following hot water (80 °C) and hot (80 °C) acid (0.2 mol/L HCL) extractions. Young taro leaves contained 589 ± 35.8 mg total oxalates/100 g fresh weight (FW) while older taro leaves contained (443 ± 15.0 mg total oxalates/100 g FW). Soluble oxalates were 74% of the total oxalate content of the young and old leaves. Oxalate analysis was also carried out on leaves baked at 150°C for 1.5 h either alone or with 50 ml cows milk. The soluble oxalate content of the fresh baked tissue fell to a mean of 59% for both samples of leaves. Baking the young and old leaves with milk led to a further reduction of the soluble oxalate content in the cooked leaves (mean 21.4% of the total oxalates). The results from this study suggest that baked taro leaves should be regarded as a high oxalate food but baking with milk significantly reduces the amount of soluble oxalate that could be absorbed from the cooked leaves.