Effect of different drying methods on morphological,thermal, and biofunctional properties of lulo (Solanum quitoense Lam.) fruit powders

Four different powders of dried lulo (Solanum quitoense Lam.) were obtained by hot air drying (HD), ultrasound-assisted hot air-drying (HDUS), freeze-drying (FD), and spray-drying (SD). The morphological (SEM) and thermal (TGA–DSC) characterization were made, and some biofunctional properties such as dietary fiber (DF) content and antioxidant capacity (ABTS and DPPH assays) were evaluated. The homogeneous morphology of SD particles was evident from SEM analysis, in contrast to the irregular morphology of the other dried powders. All of the dried lulo powders were thermally stable until 220°C. Although, the initial composition of the mixtures (fruit pulp/maltodextrin DE-20, 2:1, w/w) was the same, some differences on DF content and antioxidant activity were found, indicating that the drying method influenced significantly the chemical composition of powdered products. A higher insoluble dietary fiber (IDF) percentage was found in FD sample; in contrast, a higher in vitro antioxidant capacity values against ABTS and DPPH free radicals were found for HD and SD powders.