Inactivation of trypsin inhibitors in sweet potato and taro tubers during processing

In order to understand the extent of elimination of trypsin inhibitors during processing of sweet potato (Ipomoea batatas) and taro (Colocasia esculenta) tubers, a detailed study was conducted using tubers processed by oven drying, cooking, and microwave baking. Between 80 and 90% trypsin inhibitor (TI) activity was retained in sweet potato chips up to 2h at 70 °C. Among the four cultivars of sweet potatoes, RS-III-2 trypsin inhibitors were more heat labile. Heating at 100 °C led to rapid inactivation of TI of sweet potatoes. Varietal differences in thermal stability were more pronounced for the trypsin inhibitors of taro than sweet potatoes. Taro inhibitors were also more rapidly inactivated than sweet potato TI. Between 17 and 31% TI activity was retained in cooked tuber pieces of sweet potatoes, while only 3-10% were retained in taro cultivars. Very effective inactivation of trypsin inhibitors of sweet potatoes and taro could be obtained through microwave baking. Flour prepared from taro was devoid of TI activity, while 5-12% TI activity was retained in the flour prepared from sweet potatoes. The study clearly established that among the four techniques used, microwave baking and flour preparation were the best methods to eliminate TI from sweet potatoes and taro.