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A. J. MORENO¹, A. Chiralt², I. Escriche², and J. A. Serra². (1) Departament of Agroindustries, Universidad del Bio-Bio, Casilla 447, Chillan, Chile, (2) Departament of Food Technology, Universidad Politecnica de Valencia, Camino de Vera, 14, Valencia, 46022, Spain

Strawberry is one of the fruits more used in the industry as ingredient of dairy products, drinks, yoghurt, ice, etc. Traditional processing methods used for it conservation seriously affect sensorial and nutritive values of fresh fruit. Osmotic dehydration of fruits allows a reduction of the water activity, providing high moisture products (a_w=0.92-0.97) with sensorial characteristics very similar to those of the fresh fruit, maintaining color, texture and aroma.

Our objective is to analyze the combined effect of two kinds of blanching (steam (S) and microwave (MW)) and osmotic (atmospheric pressure (OD) and pulsed vacuum (PVOD)) treatments on some physiochemical parameters (a_w, pH, color and firmness) and microstructure of strawberry.

In steam treatment, the fruit were exposed for 0.5 min at atmospheric pressure and microwave treatment, loads of 400 g of fruit were exposed to 400 W for 2.5 min. Osmotic treatments were carried out at OD or by applying a PVOD, at 30ºC during 4 hours. The two osmotic and blanching treatments were combined in different order to obtain 8 different combined treatments.

The pulsed vacuum osmotic dehydration with 65 ºBrix sucrose solution of strawberry, carried out after steam blanching treatment was the most effective in a_w (0.961) depression due to the highest sucrose (22 ºBrix) gain during osmotic treatment. This implies the highest loss of firmness and color changes. Cryo-SEM observations shows that, steam treated samples suffer a great degree of cell decompartmentation near the fruit skin, as compared with the well 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.

These results show greater efficiency in the a_w reduction of the samples when blanching treatment was applied before of the osmotic process, the bets results being obtained for the S-PVOD treatment. Although the S-PVOD treatment induce some alterations in firmness and color of the strawberries, these changes are maintained reasonable values.