Relationship between drying and grinding parameters and physicochemical properties of Hibiscus sabdariffa calyx powders

Abstract

To set up a stabilization process preserving the beneficial properties of Hibiscus sabdariffa calyxes, known as coupled drying and grinding, an option for powdering is proposed. The impacts of these unitary operations on powder physicochemical properties and flowability were studied. Calyxes were sun-dried and/or oven-dried for 1 or 2 h then ground at 10,000, 12,000, or 14,000 rpm. Upon increase in drying duration and/or grinding frequency, more heterogeneous and irregularly shaped particles of smaller-sized, low fiber powder was obtained which in turn affected the flow properties. Powders are less cohesive, therefore, they are less sensitive to compression and shear. This results in a good flowability. The red color intensity of powder solutions related to the anthocyanin content was raised when decreasing the drying duration and increasing the grinding frequency. However, to improve the solubility of these powder solutions, high drying duration and grinding frequency was required. High drying duration and grinding frequency may be ideal to achieve an easy-flowing powder, a long shelf life, and an appealing red-colored product for consumers.