Oxalate content of cormels of Japanese taro (Colocasia esculenta (L.) Schott) and the effect of cooking

Taro (Colocasia esculenta L. Schott) is a major starchy 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 the cormels of Japanese taro cultivars, Akame, Ishikawa-wase, Yamato-wase and an unnamed cultivar were determined by HPLC following hot water (80 °C) or hot acid (0.2 mol/L HCL) extractions. Oxalate analysis was carried out on the peeled raw, boiled (40 min) and baked corms (180 °C for 40 min). Akame contained the highest level of total oxalate (171.4±11.4 mg/100 g fresh weight (FW)) in the raw tissue and was significantly higher than the other three cultivars (P<0.001). The raw tissue of the four cultivars contained a mean of 60.6% soluble oxalates; boiling reduced the level of soluble oxalate in the cooked tissue to below detectable levels as soluble oxalates leached into the cooking water. Baking led to a significant reduction in the moisture content of the taro concentrating oxalates in the cooked tissue (overall mean, 229.0±34.4 mg/100 g FW). The results from this study suggest that baked taro corms contain moderate amounts of oxalates.