Nanostructural characterization and sorption isotherm analysis of spray-dried date powder

Abstract

ABSTRACTDates are naturally rich in antioxidants and other bioactive molecules. To enhance the shelf life and market value of these bioactive molecules, free flow spray-dried date powder was produced in a pilot scale spray drier. To better understand the rheological properties of the spray-dried date powder produced by different carrier materials (maltodextrin (MD) and gum Arabic (GA)), different drying temperatures (150 and 170°C) and different flow rates of the atomizer (25 and 40 mL/min), a microstructural characterization of the scanning electron microscopy images of the date powder was performed using the graphical user interface design environment and image analysis toolbox in MATLAB. Also, the fundamental rheological characteristics of deformation and flow of particulate solids (i.e., packing, permeability, and strength) were obtained using an advanced rheometer and helium pycnometer. The microstructural and rheological properties of the date powders were significantly affected by the processing conditions used in this study. The date powder produced with MD had smooth, regular-shaped spherical particles along with good agglomeration and packing characteristics. Date powder with GA had irregular-shaped relatively smaller particles with dented surfaces with poor agglomeration and packing properties. Moreover, the rheological quality of the date powders was inversely proportional to the temperature and flow rate. The Guggenheim–Anderson–de Boer model for sorption isotherms was a suitable fit for the date powder. The monolayer moisture content for gum Arabic was twice that of the maltodextrin carrier material, whereas the monolayer heat of sorption was higher for maltodextrins. Using maltodextrin as the carrier material and drying at 150°C with a flow rate of 25 mL/min produced a free flowing less caking product as depicted by the sorption isotherms.