Composition of oxalates in baked taro (Colocasia esculenta var. Schott) leaves cooked alone or with additions of cows milk or coconut milk

Taro (Colocasia esculenta var. Schott) is a major staple food crop in parts of Asia and the Pacific Islands and two different cultivars of taro plants Taro Tonga (C. esculenta) and Taro Futuna (Xanthosoma sagittifolium), known respectively as Maori and Japanese, are grown as a minor crop in New Zealand. The leaves are either boiled or baked before they are consumed. In this experiment the leaves were baked at 150 °C for 1.5 h either alone or with additions of cows milk and coconut milk prior to baking. Oxalate contents of both cultivars of leaves were determined following extraction by either hot distilled water (80 °C) to give soluble oxalates or hot (80 °C) acid (0.2 mol/l HCl) to give total oxalates. The extracted oxalates were then determined by HPLC chromatography. Baked Maori-type taro leaves contained 719.3 ± 12.0 mg total oxalates/100 g fresh weight (FW) and 365.9 ± 11.4 soluble oxalates/100 g FW while baked Japanese-type leaves contained 533.9 ± 14.9 mg total oxalates/100 g FW and 352.6 ± 8.4 mg soluble oxalates/100 g FW. The total and soluble oxalate content of the baked leaves was considerably reduced when the leaves were baked with cows milk, coconut milk or mixtures of these two (mean % reduction of total oxalates was 43.2 ± 3.8% while the mean % reduction of soluble oxalates was 58.7 ± 1.8%).