Phase inversion of bigels tuned by the concentration of soy protein isolate in the binary hydrogel matrix

Abstract

Phase inversion of bigels is typically achieved by controlling the oleogel/hydrogel (OG/HG) ratio in previous studies. In this study, a binary hydrogel consisting of different concentrations of soy protein isolate (SPI) to konjac glucomannan (KGM) was designed to fabricate bigels with ethyl cellulose (EC) oleogel at a fixed mass ratio of oleogel to hydrogel (OG:HG), and the phase inversion was subsequently achieved by increasing the concentration of SPI in the binary hydrogel, resulting in a transition from W/O to O/W bigels and then back to W/O bigels. Specifically, when the binary hydrogel contained 1 wt% SPI and 0.5 wt% KGM, the bigel type was O/W. A KGM network existed between the oil droplets of O/W bigels and within the internal phase of W/O bigels, with SPI being adsorbed at the oil-water interfaces of the bigels. As the concentration of SPI increased, the oil-water interfaces became progressively populated with proteins, leading to an increment in droplet diameter and a reduction in hardness, as well as an elevation of free water content within the bigels. This study proposes a novel operational strategy for controlling the phase inversion of bigels and developing encapsulation delivery systems by adjusting the concentration of SPI in binary hydrogels.