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.