Oxalate Content of Raw and Cooked Oca (Oxalis tuberosa)

Oca (Oxalis tuberosa Mol.) or New Zealand yam, in common with other members of this genus, contains oxalate, an antinutritive factor. Twelve South American and two New Zealand cultivars of oca were analysed for the total oxalate contents of tubers. Total oxalate levels ranged from 80 to 194 mg/100 g wet matter (WM). As these tubers are normally cooked before consumption, the oxalate levels were measured after they had been cooked by three conventional cooking methods. Oxalate levels ranged from 77 to 220 mg/100 g WM for boiled and steamed tubers, while the levels of oxalate found in baked tubers were significantly increased when compared to the raw tubers. The oxalate content of the baked tubers ranged from 164 to 335 mg/100 g WM. Total calcium content of the raw tubers ranged from 7.5 to 15.5 mg/100 g WM; cooking had little effect on the calcium content. Among cultivars mean oxalate/calcium ratio of the raw, boiled and steamed tubers ranged from 2.5 to 9.9. Baked tubers had a significantly increased oxalate/calcium ratio (mean for all cultivars 9.5).