Effects of Different Foaming Agent Types and Ratios on Physicochemical Properties of Foam Mat Freeze Dried Roselle Powder

Hibiscus sabdariffa L. has been utilised in traditional medicine and its roselle calyx extract offers potential as a natural colourant alternative to synthetic red colourant in food products. Fresh roselle calyxes have a limited shelf life thus, drying and processing into powder can improve its shelf stability and preserve the quality and nutritional content. The objective of this study is to study the effect of different foaming agent ratios on the physicochemical properties of foam mat freeze dried (FMFD) roselle powder. The roselle powder was produced by mixing 5% (w/v) maltodextrin with foaming agents, whey protein isolate (WPI) and egg albumen (EA) at concentrations of 5%, 15%, and 30% (w/v), followed by freeze-drying for 24 hours. The FMFD roselle powder produced was further analysed for its total soluble solids, moisture content, water activity, bulk density, tapped density, flowability, solubility, colour and vitamin C. From this study, the total soluble solids, bulk density, tapped density, flowability and solubility of the FMFD roselle powder increase significantly as the foaming agent concentration increases. However, the moisture content, water activity, colour, and vitamin C content of FMFD roselle powder decrease significantly as the concentration decreases. In comparison to EA, whey protein isolate exhibits better moisture removal, reduced water activity, increased solubility, and a higher vitamin C concentration when used as a foaming agent. Meanwhile, EA, as a foaming agent, retained the colour of FMFD roselle powder the most, compared to the control sample. As a recommendation, FMFD roselle powder can be used in the food industry as a natural food colourant in various food products.