Effect of drying methods on physicochemical properties and antioxidant activities of okra pods

Abstract

The effects of hot air drying (HD), freeze-drying (FD), microwave drying (MWD), natural convective drying (NCD), and vacuum drying (VD) on the physicochemical, nutritional, and antioxidant properties of okra pods were investigated. Changes in the surface morphology, color, rehydration ratio, protein, pectin, ascorbic acid, and phenolics, as well as antioxidant activities of okra pods measured by 2,2′-azinobis (3-ethylbenzo thiazoline-6-sulphonic acid) diammonium salt (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and Ferric Ion Reducing Antioxidant Power (FRAP) assays were evaluated. In general, FD products exhibited a better retention of the texture characteristics, nutritional, and antioxidant activities, and was suitable for okra pods drying, although FD was the longer time-consuming method among the five drying methods. Furthermore, NCD products were poorer in color, texture, and nutrition. Future studies should continuously focus on various combinations of different types of drying methods to supply okra pods products with the most affordable cost and the highest quality. Practical applications Physicochemical properties and antioxidant capacities of okra pods are affected by the drying process. The drying process with nonthermal, low temperature, and low content of oxygen is beneficial to the retention of nutrients and functional components. In general, freeze-drying exhibited a better texture characteristics and good antioxidant activities, although higher energy and longer time consumption was the current challenge. How to combine the different types of drying methods has become an inevitable trend and research focus.