Effect of Temperatures on the Drying Behaviors and Quality of Citrus Peels

Abstract

The changes in citrus peels (CP) moisture content, drying rate, moisture ratio, drying time and energy consumption at various drying air temperatures was studied. The effect of drying temperatures and residual moisture contents on the quality of CP after drying was also evaluated. The test samples were dried in a laboratory scale hot air dryer at air temperature in the range of 40-70 o C and a constant air velocity of 1m/s to desired moisture for save storage and final moisture level of drying conditions. Cakes prepared from blendes containing different proportion (0, 10, 15 and 20%) of dried orange and mandarin peels were also evaluated for chemical composition and sensory attributes. The results indicated that, the drying temperature was very effective in removing moisture from citrus peels. The drying time was decreased by 50% and specific energy consumption decreased by about 28.5% with increasing drying temperature from 40 to70 o C for drying citrus peels. The simple exponential equation satisfactorily described the drying behavior of CP as indicated by the higher coefficient of determination. The optimal drying temperature was 60°C to reach 10±0.2%, w.b, moisture level, which reduced drying time and saved energy consumption and product quality. Meanwhile, overdrying to reach final moisture levels of citrus peels (5.4±0.2%)with higher drying air temperature sharply increased the losses of vitamin C, carotenoids and essential oils. Incorporation 15% of dried orange and mandarin peels in cakes formula increased dietary fiber by 33.5 and 29.6%, ether extract by 2.9 and 4.6% and ash by 30.6 and 29.0%, respectively, while protein and total carbohydrates contents were slightly decreased. Highly acceptable cakes could be obtained by incorporating 15% of orange and mandarin peels dried to 10%, w.b., moisture content in the cakes formulation and it can be used as value-added food ingredients.