engleski

Ultrasound-assisted osmotic dehydration of orange peel

The development of new food products that are suited to consumer needs, and processing methods, must be carried out in order to maintain the food nutritional quality, minimising thermal treatments and addition of artificial additives. In this sense, osmotic dehydration (OD) represents a good choice for developing food products of good quality. Orange peel is usually by-product of the fruit juices manufacturing. Taking advantage of its interesting composition, orange peel could be used for a new product production by increasing its sweetness and improving its sensory acceptability. In this work, OD at atmospheric pressure and pulsed vacuum osmotic dehydration (PVOD) assisted by high power ultrasound pre-treatment of orange peel was applied. Orange peel cubes (15x15 mm) were dehydrated by osmosis using commercially produced orange syrup and sucrose-water solution (0.65 w /w). For each treatment, water loss (WL), solid gain (SG) and the dehydration efficiency index (DEI) were calculated. Texture measurements, as well as orange peel total and soluble solids, before and after treatments at 25 °C, were carried out. Colour difference of albedo and flavedo of the fresh orange peel was used to calculate the total colour change (ΔE). PVOD caused fast compositional change in the products. Low values of DEI (-0.13 to 1.26) indicates process aimed at extensive SG with minimal WL. PVOD, assisted by ultrasound pre-treatment (10 min), where 50 mbar were applied for the first 5 min of treatments and afterward 5 min at atmospheric pressure, gave similar results in samples treated in orange syrup, as well as sucrose-water solution (more than 45% of SG). In comparison with OD conducted at atmospheric pressure (2 hours), this kind of treatment implies a sharp reduction in process time because of the impregnation of the porous structure of albedo with the external osmotic solutions. Samples treated by PVOD, assisted by ultrasound, in 65% sucrose solution showed lower force values in texture measurements, indicating greater softening of the structure, which does not occur in samples treated by OD at atmospheric pressure, and in samples treated in 65 % orange syrup. By the calculation, the highest ΔE (23.22 for albedo, 9.35 for flavedo) had samples treated in 65% sucrose solution when PVOD combined with ultrasound pre-treatment applied. In all treatments, albedo layer had higher values of ΔE (8.03-23.22), compared to flavedo layer (1.69-9.35). In order to improve the processing efficiency and the quality of the orange peel product, ultrasound-assisted OD and PVOD treatments are certainly recommendable.

fruit syrup; orange peel; osmotic dehydration; sugar syrup; ultrasound

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