Studies on the Development of Swelling of Rehydrated Kori-tofu

Abstract

The development of swelling of rehydrated Kori-tofu was studied. The results obtained were as follows.
(1) The development of swelling of rehydrated Kori-tofu occurred with the removal of ammonia held in Kori-tofu into rehydration solution.
(2) Ammonia fixed in Kori-tofu treated with ammonia gas and stored for a long time, became non-soluble, and couldn't take part in the swelling of Kori-tofu as rehydrated.
(3) When Kori-tofu was rehydrated with several kinds of alkali solution (NH4 OH, NaOH, Ca(OH)₂), it swelled with the increase of the concentration of the solution (beyond 0.1M), and beyond pH 9.
(4) Kori-tofu swelled in the alkaline solution showed shrinkage with the addition of acid to it, but its volume was ever larger than that of rehydrated Kori-tofu as control. This will be the reason why it doesn't shrink when treated with water in cooking.
(5) Ammonia treated Kori-tofu, from which most of ammonia liberated with its long storage, swelled similarly by repeated treatment with ammonia gas.
(6) No significant differences were recognized between proteins in ammonia treated Kori-tofu and the control, as observed from the result of SH group and the digestibility with pepsin.