Food-grade bigels: Evaluation of hydrogel:oleogel ratio and gelator concentration on their physicochemical properties

Abstract

Soft-matter formulations like bigels (i.e., hybrid systems) usually exhibit superior properties than single-structured emulsion gels. In this study, a bigel system was developed using a carrageenan/locust bean gum-based hydrogel (1:1 ratio with concentrations of 0.52.5 wt%) and a glyceryl monostearate-based oleogel (5, 10 and 20 wt%), obtaining self-standing semi-solid structures. Solvent holding capabilities, micro-structural, rheological and textural properties, a X-ray diffraction and infrared spectroscopy (FTIR) were accessed. Furthermore, bigel formulations starting at 70 wt% of hydrogel fraction showed elevated structural matrix continuity, linked to self-standing ability. The most balanced properties, concerning microstructural stability were exhibited by the formulations containing 2 wt% of biopolymers. These formulations also demonstrate an increased capacity to arrest the oil phase even compared to formulations with high biopolymer concentrations. Rheology studies showed a certain level of destabilization among the sol-gel transition at higher temperatures for high polymer concentrations. The higher storage and loss modulus values were recorded at the end of the non-isothermal sweeps and positively correlated with the glyceryl monostearate (GM) concentration. Despite that, texture analysis did not evidence any increase of bigel hardness when concentrations of GM surpassed 5% (w/w), probably due to a lack of interfacial stabilization. Major differences in bigel hardness due to increased oleogel content were only seen for higher biopolymer concentrations. Also, the non-chemical arrangement was confirmed through FTIR. These results guide the development of bigel systems towards their use in novel food products.