Effect of pectinmethylesterase infusion methods and processing techniques on strawberry firmness

Strawberry halves were pretreated with fungal pectinmethylesterase (PME) and calcium chloride using, respectively, passive osmotic infusion, vacuum-assisted infusion, and pressure-assisted infusion with the aim to improve the firmness. The vacuum-assisted procedure was observed to be the only method able to accomplish an uptake of infusion solution and hence capable of improving the firmness of the strawberries. Significantly less firmness increase was realized when tomato PME was vacuum-infused instead of fungal PME. Strawberry halves were pretreated by vacuum-assisted infusion with fungal PME and calcium chloride and were subsequently subjected to thermal treatments at 60 degrees C and 80 degrees C and pressure treatments at about 400 MPa and 550 MPa. For all treatments studied, the pretreated sample was significantly firmer compared with the reference sample. For the thermal processes, the residual firmness relative to the initial value before treatment was depending on the temperature of the treatment and not on the pretreatment. However, vacuum-assisted infusion of PME and calcium could limit the portion of firmness loss due to pressure treatment to 30% compared with 80% for non-pretreated fruits.