Abstract
Relationship between maceration and pectic-substance release of vegetable tissues when they were boiled in different pH solutions was studied. The results obtained were as follows :
1. Vegetable tissues were kept firm when cooked at pH 4. They were rapidly softened by cooking either above pH 5 or below pH 3. By prolonged cooking carrot, potato and Japanese radish were considerably macerated even at pH 4. Maceration of lotus and burdock, however, was very slow under the same conditions.
2. Pectic substances released from vegetables during cooking were the least at pH 4 and they increased above pH 5 and below pH 3.
3. Pectic substances released from vegetables during cooking above pH 6 gave positive results by the thiobarbituric acid tests.
These results suggest that the enhanced softening at neutral and alkaline pH is ascribed to the degradation of pectin by a transelimination mechanism but at low pH it is caused by hydrolytic cleavage of pectin and removal of divalent cation from the cell walls of vegetables.
4. The rate of softening of vegetables by cooking depends on their kinds. It is likely that the obstruction to softening of vegetables such as lotus and burdock is caused by heat-resistant and insoluble substances other than pectin of middle lamella, covalent connections between pectin and other insoluble cell wall materials, or rigid structures of the tissues.
