New prospects for high quality ingredients obtained from citrus fruit peel

Vacuum infusion is used to facilitate the peeling of citrus fruit for the fresh-cut market, giving, as a by-product, a peel soaked with water but quite undamaged. Osmotic dehydration, commonly used to remove part of the water content of fruit before further drying, could increase the stability of the colour pigment and minimize the shrinkage phenomenon. The aim of this research is to apply to orange peels the osmodehydration followed by air-drying in order to obtain a high quality food ingredient both from a nutritional and sensorial aspect. Peels from vacuum infused organic oranges, cv Tarocco and cv Navel, were cut into slices (1x2 cm) and then osmodehydrated at 20 °C in sucrose solution (60% w/w) for different times (1-2-3-4-5-6-24 h), followed by air drying at 80 °C up to a constant weight. Solid gain and water loss of the osmotic process were assessed. Changes of colour and shape, due to processing, were evaluated by image analysis technique. The bitterness sensorial characteristic of powders, obtained from grinding the dried peel, was judged by a panel test. The high solid gain of peels, due to the osmotic step, was attributed to the particular structure of pith, which was able to absorb an elevated amount of sugar solution thanks to its wide intercellular spaces and not turgid cells. The solid gain allowed colour attributes of slices after air dehydration to be maintained. The air drying without pre-treatment, caused a structural collapse of peels which looked wrinkled. This effect was noticeably reduced in pre-osmodehydrated slices with a positive progressive trend in function of osmosis time. Furthermore the solid-liquid exchanges and the consequent sucrose intake had a positive effect on sensorial quality of the dried product, decreasing the characteristic bitter perception.