High internal phase emulsions stabilized by pea protein isolate-inulin conjugates: Application as edible inks for 3D printing

High internal phase emulsions (HIPEs) are soft materials that can be designed to contain nutrients and active agents. As a result, they are being explored for their potential application as edible inks in 3D food printing applications. However, the rheological characteristics of HIPEs are often unsuitable for this purpose, resulting in unsatisfactory precision and resolution performance during 3D printing. This study aims to overcome these problems by creating HIPEs with improved rheological properties by using pea protein-inulin glycosylation products as plant-based emulsifiers. These conjugates were prepared from pea protein isolate (PPI) and inulin by glycosylation using a combined ultrasound/pH-shift method. The oil phase of these emulsions consists of omega-3 rich algal oil and lemon oil. We showed that stable HIPEs could be formed at an oil phase content of 80%. At this oil content, the oil droplets were uniform and stable, and the emulsions exhibited higher storage modulus. Compared to PPI alone or physical mixture of PPI and inulin, PPI-inulin conjugates formed oil droplets with smaller diameters and better uniformity, as well as thicker and denser biopolymer coatings. Compared with protein alone, the rheological analysis demonstrated that the HIPEs formulated with PPI-inulin conjugates had a higher viscosity, higher elasticity, higher recovery rate, and better thixotropy, indicating that they had physiochemical characteristics suitable for edible inks applications. This was confirmed by using the HIPEs as edible inks to 3D print model food objects. In conclusion, the pea protein-inulin conjugates fabricated in this study can be used as plant-based emulsifiers to form edible inks based on HIPEs. In principle, a range of nutrients and other bioactive agents could be incorporated into these inks for personalized nutrition applications.