Optimization study for refractance window drying process of Langra variety mango.

Refractance window (RW) drying of mango pulp has shown good quality retention compared to conventional drying methods. Different pulp thickness (2, 3 and 4 mm) and drying temperature (85, 90 and 95 °C) were optimized for RW drying of mango pulp for responses as drying time, ascorbic acid, total phenolics content (TPC) and hardness of mango leather. Face-centered central composite design was performed for optimization using Design-Expert software. RW drying of 2 mm thick mango pulp took the shortest drying time, however lower ascorbic acid and TPC were determined as compared to 3 mm and 4 mm thick pulp mango leather. Hardness of RW dried mango leather was determined to be in the chewable range as 3.62-5.33 N. The optimum solution generated for RW drying temperature and pulp thickness was 95 °C and 2.49 mm, respectively. The drying time was 22.5 min with high quality retention in terms of ascorbic acid, TPC and hardness as 62.33 mg/100 g DW, 7.72 mg GAE/g DW and 4.60 N respectively of dried product with desirability function obtained was 0.969. More nutrients were preserved in mango leather as well as microstructure of mango powder was observed as smooth and flaky with uniform thickness of powder particles with RW drying process when compared with tray and oven drying at 95 °C drying temperature and 2.50 mm mango pulp thickness.