Heat stability of trypsin inhibitors in tropical root crops and rice and its significance for nutrition

Abstract

AbstractThe heat stability of trypsin inhibitors from rice (Oryza sativa L), sweet potato (Ipomoea batatas (L) Lam), taro (Colocasia esculenta var esculenta (L) Schott), giant taro (Alocasia macrorrhiza (L) G Don) and giant swamp taro (Cyrtosperma chamissonis (Schott) Merr) was studied. Rice trypsin inhibitor (TI) occurred only in the germ, so it is absent from white rice. Taro, giant taro and giant swamp taro (but not rice or sweet potato) showed an initial large increase (one‐ to tenfold) in the amount of TI present on heating at about 80°C. The heat release mechanism, which was accompanied by a change to a rubbery texture in the food, amounted to a breakdown of the cellular structure making TI available for extraction. Such heat release of TI would cause partially cooked food to be deleterious for human consumption. Brown rice, sweet potato, taro and giant swamp taro contained moderate amounts of TI, which was fully inactivated when the boiled or baked food was soft enough to eat. Giant taro, however, contained 10–100 times as much TI (which in this case also inhibited chymotrypsin) as the other foods, and a boiling time of at least 30 min was needed for its inactivation.