Emulsion gel-based inks for 3D printing of foods for dysphagia patients: High internal type emulsion gel-biopolymer systems

High internal type emulsion gels (HIPE gels) are usually a soft semi-solid material consisting of tightly packed oil droplets stabilized by a layer of emulsifier. The semi-solid nature of HIPE gels means they can be used as edible inks in 3D food printing applications. However, the rheological properties of HIPE gels are typically unable to satisfy the demands of 3D printing applications, resulting in unsatisfactory printing performance. In this study, HIPE gel-based inks (85% by volume of oil) with improved 3D printing performance were prepared by using pea protein-inulin complexes as emulsifiers. In addition, the effects of oil type type (corn, sunflower, flaxseed, or olive oil) on the 3D printing property, rheological properties, and microstructure of the HIPE gels was analyzed since different oils have different nutritional and physicochemical properties. Moreover, International Dysphagia Diet Standardization Initiative (IDDSI) foods created by 3D printing with these edible inks were evaluated in a population of the elderly suffering from dysphagia. It was found that HIPE-based edible inks containing an optimized inulin level (0.75% w/v) had the best 3D printing properties. In terms of oil type, the edible inks formulated from corn oil and from flaxseed oil had the best 3D printing property. As analyzed in the Lissajous plot, the addition of inulin remarkably improved the viscoelasticity of the inks, which improved their 3D printing property. These inks also exhibited high thixotropic recovery and good thermal stability. Moreover, cryo-SEM analysis showed that the PPI-inulin complex formed a barrier on the oil droplets' surface and a dense cross-linked structure between the particles. The IDDSI evaluation found that the HIPE gel inks were able to satisfy the requirements of Class IV and V foods in the IDDSI framework and could be classified as transitional foods, which would satisfy the food needs of patients with dysphagia.