Physical Properties, Carotenoids and Antioxidant Capacity of Carrot (Daucus carota L.) Peel as Influenced by Different Drying Treatments

Carrot peel generated from the juice factories is considered as waste and it can be potential for further recovery of carotenoids. Drying treatment is essential to minimise degradation of carotenoids and ease transportation as well as storage of the peel for further processing. This study aimed to determine the impact of different drying conditions on its physicochemical and antioxidant properties to propose the most suitable conditions for drying carrot peel for further recovery of carotenoids. Drying conditions were found to significantly affect retention of total carotenoids, beta-carotene, lutein and lycopene as well as antioxidant capacity in carrot peel. Optimal conditions for hot-air drying were at 40 degrees C for 3.5 h; vacuum drying were at 60 degrees C, -60 kPa for 4 h; dehumidification drying was at 50 degrees C for 2.5 h with relative humidity (RH) of 16-21 %; and microwave drying was at 600 W for 7 min. In comparison with freeze drying (control) and other three different drying methods at each optimal conditions, dehumidification drying at 50 degrees C with RH of 16-21 % was the most effective method as it retained high levels of total carotenoids (2.75 mg/g DW), beta-carotene (1.57 mg/g DW), lutein (0.17 mg/g DW) and lycopene (0.78 mg/g DW). Dried carrot peel also had potent antioxidant properties (ABTS: 4.71 and CUPRAC: 19 mM TE/g DW). Therefore, these conditions are recommended for drying carrot peel for further recovery of carotenoids.