Influence of hot-air drying and freeze-drying on functional, rheological, structural and dielectric properties of green banana flour and dispersions

The green banana flour (GBF) is a rich source of resistant starch, minerals, and phytochemicals and can be used as a functional ingredient for food product development. Two types of drying, namely, freeze-drying (FD) and hot-air tray drying (TD) were employed for the production of GBF, and thereafter, the resultant flour quality was compared by measuring physicochemical, functional, structural, dielectric and rheological properties. The structural and rheological properties of flour samples were examined by using scanning electron microscopy, X-Ray Diffractometer, rheometer, and visco-amylograph. Both the TD and the FD affect the particle size, color, starch, resistant starch, and water hydration properties of GBF significantly. During thermal scanning, the peak gelatinization temperature (T-p) (82.5-83.4 degrees C) and the starch-lipid melting transitions (102.4-109.2 degrees C) were detected in both samples. The flour in dispersion (F/W=1:3) showed the solid-like behavior (G'>G '') and the mechanical rigidity influenced by the drying methods (P < 0.05). The dielectric properties of the two types of dried flour dispersions varied with the process temperature, in particular, above the gelatinization temperature. The drying methods did not influence the crystallinity of the starch. The information obtained in this study would help processors to consider the GBF as an important ingredient in food product development by selecting a suitable drying method.