Osmotic processing: Effects of osmotic medium composition on the kinetics and texture of apple tissue

The effect of modification of osmotic medium composition with salts on the texture changes and process kinetics was evaluated in the present study. Inner and outer apple cortex parenchyma (Kim var.) was subjected to osmotic processing at 20, 40 and 60 °C. The four osmotic media used were of identical osmotic pressure but slightly different compositions. The solution 1, S1, was a 50% w/w sucrose solution. The solution 2, S2, was 49.47% sucrose + 0.25% CaCl2. The solution 3, S3, was 48.27% sucrose + 0.5% CaCl2. The solution 4, S4, was 40.52% w/w sucrose + 0.50% w/w CaCl2 + 2% w/w NaCl. The solid gain and water loss were influenced by the initial structure (inner-outer cortex). The osmotic processing kinetics of the apple tissue revealed that both the water loss and the solid gain were influenced by the osmotic medium used. At each temperature when the S1 medium is used the uptake of the solids is the highest, and when one of the S2 and S3 is used the solid uptake is the lowest. A possible explanation is that apart from affecting cell vitality the addition of the minerals influences the cell wall permeability. Furthermore it was possible to reduce the tissue softening by the use of any of the S2, S3 and S4 solutions as osmotic medium as long as the process temperature was ambient to moderate. Processing at 60 °C caused pronounced tissue softening irrespective of the osmotic medium used for the immersion of the apple tissue.

Research Highlights► Plant tissue structure influences significantly osmotic processing responses. ► Plant cell viability alone cannot explain the effect of mineral additions on solute uptake. ► Effect of mineral additions on cell wall porosity can be a mechanism that explains solute update. ► Tissue softening can be drastically reduced by addition of Ca at low levels in the osmotic medium.