The adsorption of dragon fruit (Hylocereus polyrhizus) pigments on chitin for food colorants

Abstract

BACKGROUNDGrowing concern over the potential adverse health effects of synthetic colorants has led to a rising utilization of plant‐derived pigments within the food industry. Purple betacyanins from red dragon fruits (Hylocereus polyrhizus) have been subjected to an environmentally sustainable purification process for natural colorants.RESULTSThe violet‐hued pigments were absorbed onto preconditioned chitin material, a biodegraded polymer derived from shrimp shells. Liquid chromatographic–electrospray ionization–tandem mass spectrometric analysis was employed to analyze the betalain pigment composition in the raw fruit extract, making comparisons between the adsorbed supernatant and desorbed solutions. Fourier transform infrared analysis, optical microscopy, and scanning electron microscopy were conducted on the resin pre‐ and post‐adsorption stages, revealing distinctive infrared bands (RNHR, CO, CO, OH) indicative of betacyanin functional groups in the pigmented materials. The uniform adsorption of the colorant onto the adsorbents causes the intense purple color of the resin, with a maximum removal efficiency of 0.29 mg g−1. Adsorption data were subjected to various kinetic models, with the pseudo‐second‐order model demonstrating the optimal fit to the kinetic data (R2 = 0.97), while the Freundlich model proved most suitable for describing the sorption isotherm (R2 = 0.98). The adsorption energy, as determined by the Dubinin–Radushkevich equation, was 0.23 kJ mol−1, implying a physical adsorption mechanism on a heterogeneous surface.CONCLUSIONBetacyanins derived from red dragon fruits could be recovered for food colorants through chitin adsorption. This recovery mechanism is attributed to electrostatic interactions among the functional groups, including hydroxyl and carboxyl groups, and hydrogen bonds. © 2024 Society of Chemical Industry (SCI).