PRESSURE PRETREATMENT OF VEGETABLES FOR CONTROLLING THE HARDNESS BEFORE COOKING

The effects of pressure pretreatment before cooking on the hardness of vegetables were studied. The vegetables used here were Japanese radis h, carrot, burdock and potato. The hardness of the samples which had b een treated at 50-500 MPa for 0-120 min at room temperature before coo king at 99.5 degrees C was evaluated. The ratio of hardness of the pre treated vegetables to that of the untreated ones, called ''relative ha rdness'', increased substantially with the magnitude and the retention time of applied pressure. The relative hardness of vegetables pretrea ted at 400 MPa for 120 min was in the range of 2-3 after 30 min cookin g. The period of optimum cooking time for the desirable hardness of ve getables was prolonged twice by the pressure pretreatment. This phenom enon, the suppression of softening in the cooking process, depended ma inly on the time after reaching the prescribed pressure and little on whether the pressure was retained for a long time or released immediat ely after the short-time application. The replaceability of the standi ng time after release of pressure and the retention time during pressu rization indicates that the loss of intra- and intercellular water mol ecules and ions, induced by the membrane collapse due to pressure, pro ceeds at almost the same rate under atmospheric pressure as at high pr essure. This suggests that the loss of water plays an important role i n determining the pressure-induced hardening. This work also shows tha t pressure pretreatment at room temperature can be used to avoid the o vercooking of vegetables instead of preheating.