Compositional Changes of Oca Tubers Following Postharvest Exposure to Sunlight

Oca is an edible starchy tuber grown in the Andes. To improve its culinary quality, harvested oca is typically exposed to direct sunlight (sunned) for several days prior to consumption. Five native cultivars were examined to determine the changes in nutritional composition of oca as a result of sunning. This practice increased the proportions of dry matter, soluble solids, and sugars (mainly sucrose) and decreased total acids, due mainly to a large reduction in malate and glutarate. High levels of oxalate, an anti-nutritional factor, were found, ranging from 306 to 539 and 251 to 451 mg/100 g in edible matter of freshly harvested and sunned tubers, respectively. Sunning reduced oxalate levels in dry matter by an average of 26%. Further study will be necessary to fully assess the food safety of oca and to provide recommen-dations for maximum daily intake. Oca (Oxalis tuberosa Molina) is an edible starchy tuber grown in the high Andes. Native Amerindian communities of Bolivia and southern Peru regard oca as a valuable source of food, second in importance to the potato among root and tuber crops. Oca tubers are usually baked or cooked in stews, although rural children sometimes eat them raw. Cooked oca has a mushy or floury texture depending on the starch content, and a sweet, slightly acid taste. Raw oca is tart and pleasantly crunchy. After harvesting, oca tubers destined for direct consumption are traditionally exposed to direct sunlight for a week or two. This treatment is referred to as sunning, or soleado, and is known to enhance sweetness and improve culinary quality. The chemical composition of oca has not been studied in detail, although we d