Effect of Temperature on the Drying Behavior and Quality of Citrus Peels

The effects of the drying temperature and the residual moisture content on the drying behavior, energy consumption and quality of dried citrus peels (CPs), which are value-added food ingredients, were studied. The CP samples were dried in a laboratory-scale hot-air dryer at air temperatures from 40 to 70 °C under a constant air velocity of 1 m/s until the desired moisture content for safe storage was reached or until the final moisture level was achieved for the specific drying conditions. Cakes prepared from blends containing different proportions (0 %, 10 %, 15 % and 20 %) of dried CPs were also evaluated for chemical composition and sensory attributes. The optimal drying temperatures were 50–60 °C, and the optimal moisture content was 10±0.2 % w.b.; these conditions reduced the drying time and energy consumption and maximized the product quality. In contrast, over-drying CPs with the higher temperatures and to a final moisture level of 5.4±0.2 % sharply increased the loss of vitamin C, carotenoids as antioxidants and essential oils. Incorporation of 15 % dried orange and mandarin peels in cake formulas increased the dietary fiber by 33.5 % and 29.6 %, the crude fat by 2.9 % and 4.6 % and the ash by 30.6 % and 29.0 %, respectively, whereas the protein and total carbohydrate content decreased slightly. Highly acceptable nutritious cakes could be obtained by incorporating 15 % orange or mandarin peel dried to 10 % w.b. moisture content into the formulation.