Crispy air-dried pineapple rings: optimization of processing parameters

Great changes in the structure of vegetal tissue could be produced by both osmotic dehydration and air drying. Texture of material moves from elastic-visco-plastic to rigid, becoming fragile and brittle. These changes are welcomed when the final product is a crispy and crunchy snack food. The aim of this work is to define the combined process, involving the osmodehydration and air-drying techniques, in order to obtain dried and crispy pineapple rings, having high qualitative characteristics. Six mm thick pineapple rings were osmodehydrated for 30 minutes in pineapple juice and sucrose solution, both at 50 degrees Bx. Not pre-treated and pre-osmodehydrated rings were air dried at 70-75-80 degrees C till constant weight. Dry matter, soluble refractometric residue, pH and titratable acidity of raw and osmodehydrated samples were measured. Solid gain and water loss of the osmotic process were assessed. Dry matter and water activity of dried product were also measured. Changes of colour and surface area due to processing were evaluated by image analysis technique. Final product crispness was determined by bending snapping test. The sensorial characteristics were judged by a panel test. From both instrumental and sensorial aspects air-dehydrated samples resulted crispier than the respective osmo-airdehydrated ones regardless of solution type and temperature. This behaviour could be linked to the higher residual water content of the osmo-airdehydrated pineapple rings. The higher the drying temperature the better the results for instrumental and sensorial crispness. As expected the colour was negatively influenced with the increase in drying temperature. The osmotic pre-treatment in sucrose solution protected the colour during drying but the osmo-dehydration with pineapple juice hadn't the same positive influence. The best result was obtained with not pre-treated pineapple rings dried at 75 degrees C: the product was slightly amber-coloured, crispy and not hard and consequently appreciated by the tasters. (c) 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of 11th International Congress on Engineering and Food (ICEF 11) Executive Committee.