Effect of pre-treatment conditions on content and activity of water and colour of freeze-dried pumpkin

This work shows the effect of blanching, osmotic dehydration duration, freezing method and duration of frozen storage on the colour, water activity and water content of osmotically dehydrated and freeze-dried pumpkin. Pumpkin was or was not subjected to blanching process in distilled water at a temperature of 100 °C for 1 min and osmotically dehydrated in starch syrup solution (0, 3 and 20 h) and frozen at −18° (24 h) or −70 °C (2 h). Then, after short (72 h) or long duration (60 days) the pumpkin in frozen storage was freeze-dried on heating shelves at a temperature of 10 °C. Different pre-treatment methods were not found to have clear effect on values of colour coefficient of freeze-dried pumpkin. Osmotic dehydration caused changes in water content and activity of samples. Elongation of osmotic dehydration duration influenced the decrease of water content and activity of freeze-dried pumpkin and had also slight effect on colour changes. Blanching decreased water content and activity, but no significantly. Similar results were obtained also for changes at a temperature of freezing and duration of frozen storage.