Effect of Freeze Drying, Hot Air Drying, and Hot Air Drying Preceded by Freezing on Phytochemical Composition, Antioxidant Capacity, and Technological Properties of Mango Peels

Mango peels have great potential for upcycling in the food industry. This study addressed important knowledge gaps regarding mango peel drying, namely, the effect of drying on mango peels' bound phenolics, and the impact of prior freezing on the composition of hot air-dried mango peels. Hence, the effect of freeze drying (FD) (0.10 mbar; -63 °C (condenser temperature); 25 °C (shelf temperature); 96 h), hot air drying (HAD) (65 °C; 48 h), and HAD preceded by freezing (FZ + HAD) (-20 °C; 30 days) on mango peels' composition, antioxidant capacity, and technological properties was evaluated. Drying did not affect fiber content; however, it caused slight modifications in carbohydrate composition of fiber. Regarding antioxidant compounds, FD, HAD, and FZ + HAD reduced vitamin C by 9%, 53%, and 71%, respectively. FD preserved all free phenolics, while HAD and FZ + HAD decreased most of them, with reductions ranging from 20 to 42% and 17 to 71%, respectively. However, FD, HAD, and FZ + HAD reduced 9, 2, and 6 of the 10 bound phenolics identified, respectively, and decreased their antioxidant capacity. Finally, all identified carotenoids were reduced by FZ + HAD, whereas FD and HAD decreased only violaxanthin. Regarding technological properties, FD showed the highest and lowest oil and water absorption capacities. In conclusion, these findings demonstrated that prior freezing exacerbated the loss of antioxidants during HAD.