Effect of high-pressure treatment on the texture of cherry tomato

The effect of high-pressure treatment (200-600 MPa for 20 min) on the textu re of cherry tomatoes and on the key softening enzymes (pectinmethylesteras e and polygalacturonase) was investigated. When subjected to high-pressure treatment whole cherry tomatoes showed increasing textural damage with incr easing pressures up to 400 MPa. However, treatment at pressures above 400 M Pa (500-600 MPa) led to less apparent damage than treatment at 300 and 400 MPa; the tomatoes appearing more like the untreated samples. These visual c hanges were reflected in the texture (firmness) and amount of cell rupture in the tomatoes, with the least firmness and the most cell rupture being se en after treatment at 400 MPa. Light and scanning electron microscopy suppo rted these observations. Although a sample of purified commercial pectinmet hylesterase was partially inactivated at pressures above 200 MPa, irrespect ive of pH (4-9), in the whole cherry tomatoes no significant inactivation w as seen even after treatment at 600 MPa, presumably because other component s in the tomato offered protection or the isoenzymes were different. Polyga lacturonase was more susceptible to pressure, being almost totally inactiva ted after treatment at 500 MPa. It is concluded that the textural changes i n tomato induced by pressure involve at least two related phenomena. Initia lly, damage is caused by the greater compressibilty of the gaseous phase (a ir) compared to liquid-solid components, giving rise to a compact structure which, on pressure release, is damaged as the air rapidly expands, leading to increases in membrane permeability. This permits egress of water, and t he damage also enables enzymatic action to increase, causing further cell d amage and softening. The major enzyme involved in the further softening is polygalacturonase, which is inactivated at 500 MPa and above, and not pecti nmethylesterase, which in the whole fruit, is barotolerant.