EFFECT OF CALCIUM PRETREATMENTS ON THE TEXTURE OF FROZEN CHERRIES - ROLE OF PECTINESTERASE IN THE CHANGES IN THE PECTIC MATERIALS

Pretreatments by immersion in 10 and 100 mM CaCl2 prevent the loss in firmness of sweet frozen cherries. This effect can even be detected in fruits preserved for 6 months in a frozen state. The increase in firm ness, through the treatments, is mostly apparent after freezing and is attributed to the formation of calcium bridges in the pectic material , caused by a decrease in the degree of, esterification of pectins and an increase in the pectic fraction soluble in EDTA and the Ca2+ catio n content in the cell wall. These changes in the pectic materials are of an enzymatic origin, since we observed an increase in the pectinest erase activity of the fruits after treatments with increasing calcium concentrations.