Nutrient composition and effect of processing on antinutritional factors and mineral bioavailability of cultivated amochi in Ethiopia

Abstract

Amochi (Arisaema schimperianum Schott) is an important off-season tuber crop in Southern Ethiopia. Uncooked amochi is irritating in contact with the skin. Proximate contents, antinutritional factors (oxalate and phytate) and effects of processing (cooking and fermentation) on antinutritional factors and mineral availability were determined for amochi cultivars using established methods of the AOAC. The ranges of proximate contents from five cultivars were: moisture 65.25–85.37%, fat 0.10–0.15%, protein 0.56– 1.13%, crude fibre 0.59–0.70%, ash 0.88–1.03%, carbohydrate 12.60–33.16% and caloric value 52.70–133.56 kcal/100 g dry matter per wet tuber mass. The differences between cultivars were significant (p<0.05), although the overall levels of fat and protein were low. The carbohydrate and caloric values indicated that amochi could be a valuable food crop if supplemented with animal or plant protein. For antinutrient determination, four cultivars were analysed as raw, cooked and cooked after five days’ fermentation. Amochi tubers had high oxalate levels and low phytate levels. Cooking resulted in reduction of oxalate and phytate levels. Further significant reduction occurred when the tubers were cooked after fermentation. These reductions were coupled with an increase in the levels of Fe, Zn and Ca. Cultivars differed significantly in their levels of phytate but not of oxalate. High levels of oxalate might have been the cause of skin irritation. Amochi meal preparation should follow extended fermentation and cooking. Effects of different heat and fermentation processes, and environmental factors such as season, soil and water conditions on amochi oxalate levels should be determined.