14A-9 |
Effect of blanching/osmotic dehydration combined treatments on the physicochemical and microstructural properties on minimally processed strawberries |
J. MORENO, SR.1, A. Chiralt, Sr.2, I. Escriche, Sr.2, and J. Serra, Sr.2. (1) Departamento de Agroindustrias, Universidad del Bío-Bío, Avda. Andrés Bello s/n, Casilla 447, Chillán, Chile, (2) Department of Food Technology, Universidad Politécnica de Valencia, Camino de Vera, 14, Valencia, 46022, Spain Strawberry products are in great demand by the food industry as ingredients for dairy and confectionery products, among others. Traditional processing methods for strawberries seriously affect sensory and nutritional attributes of the fresh fruit. Osmotic dehydration allows a reduction of the water activity, providing high-moisture products (aw=0.92 to 0.97) with sensory characteristics similar to those of the fresh fruit, maintaining color, texture, and aroma. Blanching treatments at controlled conditions are advisable in minimally processing the strawberry in order to preserve its color altered by enzyme activity. The aim of this work was to analyze the combined effect of two kinds of blanching (steam (S) and microwave (MW)) and osmotic treatments (at atmospheric pressure (OD) and with a vacuum pulse (PVOD)) on some physicochemical parameters (aw, pH, color, and firmness) and microstructure of strawberry. Steam blanching was carried out at atmospheric pressure for 0.5 min. Microwave treatment was performed on 400 g of fruit at 400 W for 2.5 min. Osmotic treatments were carried out at 30 °C with 65 °Brix sucrose solution for 4 h. In PVOD 50 mbar pressure was applied at the beginning of the process, followed by an atmospheric pressure treatment. The greatest aw reduction was observed when blanching treatment was applied before of the osmotic process, the best results being obtained for the S-PVOD treatment (aw=0.961) due to the highest sucrose gain during osmotic treatment. This also implied one of the highest losses on firmness and color changes, but these parameters maintained reasonable values. Cryo-SEM observations show that steam-treated samples suffer a great degree of cell disruption near the fruit skin, as compared with the better preserved cells in MW-treated samples. Differences in microstructural features observed between OD and PVOD treated samples were not reflected on the measured mechanical parameters.
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