Research Progress of Food-Grade High Internal Phase Pickering Emulsions and Their Application in 3D Printing

In situ transglutaminase cross-linking mediated protein-stabilized high internal phase emulsion gels to emulate dorsal adipose tissue: The role of continuous phase networks

High internal phase emulsions (HIPEs) are potential fat substitutes. However, the insufficient mechanical strength of current HIPEs restricts their capacity to emulate the organization of adipose tissue in meat products. We developed an "one-pot" strategy termed in-situ transglutaminase cross-linking (ITC), to enhance the mechanical strength of protein-stabilized HIPEs. Through systematic evaluation of five commercial proteins-stabilized HIPEs, we found that only gelatin and whey protein isolation capability to form continuous phase networks (CPNs), which synergized with enzymatic cross-linking significantly enhancing HIPEs' mechanical properties. Further studies reveal that transglutaminase acts as a spatial enhancer rather than a chain extender. Nevertheless, the formed isopeptide linkages provide sufficient strength to confer anti-fusible properties and environmental resilience to gelatin-stabilized ITC-HIPEs. This strategy facilitates such ITC-HIPEs to functionally emulate dorsal adipose tissue in coarse-ground sausages applications. Collectively, this study establishes a framework for developing robust HIPEs and offers new insights into adipose tissue-mimetic material design.

Research on the preparation of soy protein isolate and whey protein isolate composite nanoparticles and their characteristics in high internal phase Pickering emulsions

This study investigated the role of thermal drive in the formation of soy protein isolate and whey protein isolate (SPI-WPI) complexes, as well as the stability effect of SPI-WPI complexes on high internal phase Pickering emulsions (HIPPEs). The shift in the peaks in the infrared spectrum and the change in fluorescence intensity indicated the interaction between these two proteins, which implies that SPI-WPI is not two dispersed groups of particles. Maximum emulsification activity (10.65 m2/g) and the absolute value of potential (37.87 mV) were achieved at an SPI to WPI mass ratio of 7:3. As the concentration and pH of the SPI-WPI complex increased, the droplets become evenly uniform and compact. It is predicted that the high concentration conditions are more favorable for the formation of a gel network structure. This research provides an effective strategy for HIPPEs stabilization using complex proteins.

Rheology of high internal phase ratio emulsions and foams

A comprehensive review of the rheology and related phenomena of high internal phase ratio emulsions (referred to as HIPREs) and foams is presented. Emulsions and foams with Brownian and non-Brownian inclusions (droplets/bubbles) are considered. The topics covered are osmotic pressure, modelling and experiments of the rheology of HIPREs/foams, time-dependent rheology (thixotropy/rheopexy), normal stresses, shear banding and slip effects in flow of HIPREs/foams, influence of solid particle stabilizers (Pickering emulsion/foam), and finally pipe rheology and flow of HIPREs/foams. This is the first review article that covers all aspects of the rheology of HIPREs/foams. The theoretical and empirical models describing the osmotic pressure and rheology (yield stress, storage modulus, viscosity, etc.) of HIPREs/foams are presented and their limitations pointed out. The contributions of entropic effects in the rheology of HIPREs/foams consisting of Brownian inclusions (droplets/bubbles) are given special consideration. The key experimental studies available in the literature are reviewed including measurements of yield stress, storage modulus, and viscosity of HIPREs/foams. Comparisons of experimental data with the theoretical and semi-theoretical models are made and the limitations of the models are identified. Experimental studies elaborating special effects in HIPREs/foams rheology such as thixotropy, rheopexy, normal stresses in fixed shear strain and steady shear, shear banding in thixotropic HIPREs/foams, and slip effects are also reviewed. The effects of average size and size distribution of inclusions (droplets/bubbles) on the rheology of HIPREs/foams are evaluated. The rheology of Pickering HIPREs/foams stabilized with solid nanoparticles at the interface is reviewed and compared with the rheology of surfactant-stabilized systems. Finally, the experimental work published on the pipe flow of HIPREs/foams and its connection to rheology is presented and discussed. The gaps in the existing knowledge of the rheology of HIPREs/foams are identified and future research directions in the area are given.

Four-dimensional food printing: A revolutionary approach to next-generation foods

Four-dimensional (4D) food printing is a cutting-edge technology that allows the creation of shape-shifting transformative food structures. This innovative approach to food design enables food scientists to craft edible creations that change form and texture over time, thereby providing a unique and dynamic dining experience. Beyond its novelty and aesthetic appeal, 4D food printing has practical applications that address pressing issues in the food industry. In this review, we explore the technology behind 4D food printing, food ink types, and other natural ingredients that can be programed to change shape with stimuli, and the possibilities and potential applications of 4D food printing, from tantalizing taste sensations to revolutionary solutions for food sustainability, and explore the latest research and innovations in this field. Ultimately, 4D food printing represents a new frontier in food processing and culinary arts, offering fresh canvas for creative expression, a means to address pressing food-related challenges, and a way to rethink our relationship with the food we eat.

Rheology and printability of biopolymeric oil-in-water high internal phase Pickering emulsions: a review

Biopolymeric oil-in-water (O/W) high internal phase Pickering emulsions (HIPPEs) due to their unique rheological behaviors of HIPPEs such as shear-thinning property, viscoelasticity, and thixotropic recovery have emerged as highly promising printing inks in the 3D printing process. O/W biopolymer-based HIPPEs are categorized as complex fluids, where rheological parameters are crucial for optimizing printability. However, existing reviews have not fully elucidated the interrelationship between rheology and printability for HIPPEs in enhancing the quality and performance of printed parts. This review delved into the influence factors of the continuous phase (e.g., biopolymer type, concentration, pH, and ionic strength) and the oil phase (e.g., oil type, volume fraction, and encapsulated components) on their rheology, to adjust their rheological behaviors in order to prepare more eligible HIPPEs as printing inks. Moreover, a spectrum of rheology-printability relationships, derived from empirical trends and rigorous analytical models, is examined to provide generalized rheological guidelines for achieving successful printability in O/W biopolymer-based HIPPEs. Furthermore, unique challenges and future perspectives on preparing their complex rheological behaviors suitable for additive manufacturing in O/W biopolymer-based HIPPEs were presented. Leveraging these insights significantly reduces reliance on trial-and-error methods in printing, thereby fostering the robust development of novel O/W biopolymer-based HIPPEs and enhancing the overall quality of printed products.

3D printing of Pickering emulsions, Pickering foams and capillary suspensions - A review of stabilization, rheology and applications

Pickering emulsions and foams as well as capillary suspensions are becoming increasingly more popular as inks for 3D printing. However, a lack of understanding of the bulk rheological properties needed for their application in 3D printing is potentially stifling growth in the area, hence the timeliness of this review. Herein, we review the stability and bulk rheology of these materials as well as the applications of their 3D-printed products. By highlighting how the bulk rheology is tuned, and specifically the inks storage modulus, yield stress and critical balance between the two, we present a rheological performance map showing regions where good prints and slumps are observed thus providing clear guidance for future ink formulations. To further advance this field, we also suggest standard experimental protocols for characterizing the bulk rheology of the three types of ink: capillary suspension, Pickering emulsion and Pickering foam for 3D printing by direct ink writing.

Characteristics of Pickering emulsions stabilized by microgel particles of five different plant proteins and their application

Pickering emulsions stabilized by protein particles are of great interest for use in real food systems. This study was to investigate the properties of microgel particles prepared from different plant proteins, i.e., soybean protein isolate (SPI), pea protein isolate (PPI), mung bean protein isolate (MPI), chia seed protein isolate (CSPI), and chickpea protein isolate (CPI). MPI protein particles had most desirable Pickering emulsion forming ability. The particles of SPI and PPI had similar particle size (316.23 nm and 294.80 nm) and surface hydrophobicity (2238.40 and 2001.13) and emulsion forming ability, while the CSPI and CPI particle stabilized emulsions had the least desirable properties. The MPI and PPI particle stabilized Pickering emulsions produced better quality ice cream than the one produced by SPI particle-stabilized emulsions. These findings provide insight into the properties of Pickering emulsions stabilized by different plant protein particles and help expand their application in emulsions and ice cream.

Protein and protein-polysaccharide composites-based 3D printing: The properties, roles and opportunities in future functional foods

The food industry is undergoing a significant transformation with the advancement of 3D technology. Researchers in the field are increasingly interested in using protein and protein-polysaccharide composite materials for 3D printing applications. However, maintaining nutritional and sensory properties while guaranteeing printability of these materials is challenging. This review examines the commonly used protein and composite materials in food 3D printing and their roles in printing inks. This review also outlines the essential properties required for 3D printing, including extrudability, appropriate viscoelasticity, thixotropic properties, and gelation properties. Furthermore, it explores the wide range of potential applications for 3D printing technology in novel functional foods such as space food, dysphagia food, kid's food, meat analogue, and other specialized food products.

A review of high internal phase Pickering emulsions: Stabilization, rheology, and 3D printing application

High internal phase Pickering emulsion (HIPPE) is renowned for its exceptionally high-volume fraction of internal phase, leading to flocculated yet deformed emulsion droplets and unique rheological behaviors such as shear-thinning property, viscoelasticity, and thixotropic recovery. Alongside the inherent features of regular emulsion systems, such as large interfacial area and well-mixture of two immiscible liquids, the HIPPEs have been emerging as building blocks to construct three-dimensional (3D) scaffolds with customized structures and programmable functions using an extrusion-based 3D printing technique, making 3D-printed HIPPE-based scaffolds attract widespread interest from various fields such as food science, biotechnology, environmental science, and energy transfer. Herein, the recent advances in preparing suitable HIPPEs as 3D printing inks for various applied fields are reviewed. This work begins with the stabilization mechanism of HIPPEs, followed by introducing the origin of their distinctive rheological behaviors and strategies to adjust the rheological behaviors to prepare more eligible HIPPEs as printing inks. Then, the compatibility between extrusion-based 3D printing and HIPPEs as building blocks was discussed, followed by a summary of the potential applications using 3D-printed HIPPE-based scaffolds. Finally, limitations and future perspectives on preparing HIPPE-based materials using extrusion-based 3D printing were presented.

Modulating the properties of myofibrillar proteins-stabilized high internal phase emulsions using chitosan for enhanced 3D-printed foods

The 3D printability of myofibrillar proteins (MP)-based high internal phase emulsions (HIPEs) is a concern. This study investigated the influence of chitosan (CS) concentrations (0-1.5 wt%) on the physicochemical properties, microstructure, rheological properties, and stability of MP-based HIPEs. Results showed that the interaction between MP and CS efficiently modulated the formation of HIPEs by modifying interfacial tension and network structure. The addition of CS (≤ 0.9 wt%, especially at 0.6 wt%) acted as a spatial barrier, filling the network between droplets, which triggered electrostatic repulsion between CS and MP particles, enhancing MP's interfacial adsorption capacity. Consequently, droplet sizes decreased, emulsion stability increased, and HIPEs became more stable during freeze-thaw cycles, centrifugation, and heat treatment. The rheological analysis further demonstrated that the low energy storage modulus (G', 330.7 Pa) of MP-based HIPEs exhibited sagging and deformation during the self-supporting phase. However, adding CS (0.6 wt%) significantly increased the G' (1034 Pa) of MP-based HIPEs. Conversely, increasing viscosity and spatial resistance attributed to CS (> 0.9 wt%) noticeably caused larger droplet sizes, thereby diminishing the printability of MP-based HIPEs. These findings provide a promising strategy for developing high-performance and consumer-satisfaction 3D printing inks using MP-stabilized HIPEs.

Tunable rheological properties of high internal phase emulsions stabilized by phosphorylated walnut protein/pectin complexes: The effects of pH conditions, mass ratios, and concentrations

The current study reported high internal phase emulsions (HIPEs) stabilized by phosphorylated walnut protein/pectin complexes (PWPI/Pec) and elucidated how their rheological properties were modulated by pH conditions, mass ratios, and concentrations of the complexes. At pH 3.0, the HIPEs stabilized by PWPI/Pec exhibited smaller oil droplet sizes, as well as higher storage modulus (G') and flow stress, in comparison to those stabilized by the complexes formed at pH 4.0-6.0. These observations can be directly linked to pH-dependent changes in particle size, surface hydrophobicity, and wettability of the PWPI/Pec complexes. Rheological analysis revealed that all generated HIPEs displayed weak strain overshoot behavior, irrespective of pH conditions. Notably, HIPEs stabilized by PWPI/Pec at mass ratios of 2:1 and 4:1 showed enlarged oil droplet sizes, lower G' and flow stress but higher flow strain with unaffected loss factor compared to those stabilized by PWPI/Pec 1:1. However, reducing the concentration of PWPI/Pec led to a simultaneous decrease in G', flow stress, and flow strain, along with a significant increase in the loss factor of the HIPEs. Furthermore, the HIPEs formed with 1% PWPI/Pec 1:1 at pH 3.0 demonstrated excellent stability against heat treatment and long-term storage. These results provide valuable insights into the modulation of rheological characteristics of HIPEs and offer guidance for the application of walnut protein-based stabilizers in HIPE systems.