Turgor pressure component of calcium-induced firming of tomato (Lycopersicon esculentum Mill, cv Hypeel 45) pericarp tissue

Firmness is the main factor that determines canned tomato quality. It has been known since the 1940's that the addition of calcium salts provides firming on canned tomato products and has remained a common industry practice. This textural improvement is thought to be due to the formation of calcium pectate complexes, acting as a cementing agent in the cell walls of plant cells. However, evidence of the physical interaction of calcium ions with membrane phospholipids suggests a stabilization effect that potentially leads to the improved maintenance of turgor pressure, which is known to be an important component of tissue textural properties.; The objectives of this study were: (1) to determine the effect of calcium chloride treatments on the turgor pressure of tomato parenchyma cells measured directly with a pressure probe and to determine the contribution of turgor to calcium-induced firming; (2) to quantify calcium uptake into tomato discs exposed to calcium chloride solutions of different concentrations for various times and to study physical changes on the tissue associated with the exposure of these treatment solutions; and (3) to evaluate the potential of a micropuncture probe to quantify cell wall strength of calcified tomato tissue concentrations of mannitol resulted in lower turgor pressures. However, inclusion of 0.43% calcium chloride reversed the reduction of turgor pressure induced by mannitol. Firmness values of tomato pericarp discs treated with mannitol and/or calcium chloride solutions followed a parallel pattern to that observed on turgor values. Calcium uptake rates were influenced by the calcium concentration of the solution rather than exposure time, and were more significant in the early portion of the treatments. Tomato discs showed swelling, edge-curving and ultimate collapse during incubation in water. However, this was not observed in tomato discs treated with calcium chloride. Micropuncture force readings in the mN range were successfully obtained in control and calcium treated tomato discs, but displayed a high variability.