Study of adsorption isotherms and physicochemical characterization of natural food colourants

Abstract

Synthetic colourants are widely used for colouring foods. However, their safety has been questioned. Due to this limitation and the global trend of consuming healthy foods, the industry is faced with the need to replace artificial colourings, which has given rise to a growing interest in colourants from natural sources. Thus, this work obtained the moisture adsorption isotherms of the natural food dyes of anthocyanins, betalains and curcumin and evaluated the humidity, water activity (a w), hygroscopicity, colour and antioxidant capacity in vitro. Osotherms were determined by the static gravimetric method with saturated salt solutions (LiCl. H 2 D, MgCl 2 .6H 2 D, Mg(ND 3) 2 .6H 2 D, NaCl, KCl and K 2 SD 4) at 25 °C. Experimental data were adjusted by GAB, BET, Halsey, Dswin and Henderson models. All models, except Henderson's for Curcumin, fitted the data and BET was used to represent the moisture adsorption isotherm. All the isotherms were type sigmoidal, characteristic of most foods. The observed water content (<0.3%) and a w (<0.03) can be considered favourable to stability. Colour analysis indicated a high colouring strength and the antioxidant capacity suggested that, in addition to representing a source of colour in food products, natural dyes may have an additional function, with possible health benefits.

Co‐encapsulation of anthocyanins extracted from grape skins ( Vitis vinifera var. Syrah) and α‐tocopherol via spray drying

“…Hygroscopicity was determined according to the method described by Viana et al (2019), using the static gravimetric technique. Briefly, 0.6 g of powder from each treatment was placed in a desiccator containing saturated NaCl solution.…”

“…The hygroscopicity of powdered food products is one of the most important properties in determining the shelf life and stability of these materials. Lower hygroscopicity results in lower susceptibility to product deterioration (Vergara et al, 2014;Viana et al, 2019).…”