Protein-based Emulsions Research Articles

Rheology and 3D printing characteristics of heat-inducible pea protein-carrageenan-glycyrrhizic acid emulsions as edible inks

Protein-based emulsion gels, especially those induced by heat, have been widely used in food 3D printing. However, the rheology and texture of protein-based gels are important factors restricting 3D printing. In this study, glycyrrhizic acid (GA) was used to improve the rheology properties of pea protein (PP)-Kappa carrageenan (κCA) composite emulsion inks, and the suitability of these inks for extrusion 3D food printing was investigated. The results showed that all emulsion inks have shear thinning behavior and could be smoothly extruded during 3D printing. Herschel-Bulkley model fitting results proved that with the increase of PP concentration (from 5% to 10%), the yield stress (σ0) increased from 15.4 to 28.19 Pa, and the consistency coefficient (k) increased from 1.09 to 2.66 Pa.sn. The objects printed with 10% PP-GA0.3 inks showed excellent self-supporting capability, a smooth surface texture, and high printing accuracy. Emulsion inks had good temperature stability and could form emulsion gels following heat induction. The results of small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS) tests confirmed that the addition of GA improved the strength of the gels. This research provides valuable insights for the advancement of food 3D printing inks.

Comparative effects of micro vs. submicron emulsions on textural properties of myofibrillar protein composite gels

This study aimed to investigate the impact of emulsion particle size (micro vs. submicron) on the physicochemical and rheological properties of myofibrillar protein (MP) gels. MP-based oil-in-water micro-emulsions (∼2,091 nm) and submicron-emulsions (∼522 nm) were compared with each other and with lecithin-stabilized micro-emulsions (∼1,330 nm) and submicron-emulsions (∼543 nm). Emulsion particle size, ζ-potential, and morphological properties using transmission and confocal microscopies) were measured. Additionally, dynamic rheological behavior, mechanical strength, water-holding capacity (WHC), water mobility, and protein secondary structures of the emulsion gels containing 2.5% protein and 5% oil) were analyzed. The results showed that emulsion droplet size had no significant effect on gel strength and storage modulus, regardless of the surfactants used. However, the MP-coated submicron-emulsion exhibited a greater improvement in gel WHC (p < 0.05) compared to its micro-emulsion counterpart. Overall, emulsion gels displayed greater strength than oil-free control gels. MP-based emulsions proved more effective than lecithin-stabilized emulsions in modifying the gelling properties, primarily due to the formation of a visible interfacial protein film that prevented oil droplet aggregation. Based on these findings, protein-based emulsions were preferred over lecithin-based emulsions, with MP submicron-emulsions offering the advantage of enhanced moisture retention in cooked MP gels.

Lentil protein stabilized emulsion - Impact of lecithin addition on emulsions properties

Plant-based proteins are currently the focus of a lot of product development research, as they have proved to be a potential replacement of animal-based ingredients and safeguard environmental and human health. However, most of the studies focus on soy and pea based food whereas lentil proteins have received only little attention. The aim of this work is to elucidate the behavior of different lentil protein sources (isolate, concentrate and flour) in stabilizing emulsions and to study their interaction with food emulsifiers such as lecithin. We study the adsorption kinetics at the oil water interface of both, the different protein sources as well as their combination with lecithin. Lentil protein-based emulsions (with 1%wt protein content) reveal bimodal particle size distribution and the emulsion shows various dispersion states (aggregated or well dispersed) depending on the protein sources and processing conditions. The addition of lecithin (with 0.25%wt) reduces aggregation phenomenon and reduce the average droplet size for lentil flour based emulsion. The adsorption kinetic at the oil water interface, suggest the formation of a surface active protein-lecithin complex and a mixed interfaces. Moreover, the mixture of lentil proteins and lecithin can reduce the interfacial tension by up to 12 mN/m compared to lentil protein alone. This demonstrates the presence of synergistic effects at interfaces and potential interactions between lecithin and proteins.

Influence of pH-shifting and transglutaminase on the freeze-thaw stability and thermal gel properties of mung bean protein-based liquid egg substitute prepared with two different oil phases

The poor freeze-thaw stability and weak thermal gel properties of plant-based egg substitutes limit their opportunity for application. In the current study, the impact of modification by pH-shifting and transglutaminase (TG) cross-linking on the freeze-thaw stability and thermal gel properties of mung bean protein-based emulsions made by two different oil phases (canola oil and coconut oil) were studied. The pH-shifting induced improved emulsifying activity (up to 77.6% increased) and smaller droplets sizes (from 39.27 to 7.03 μm). After the freeze-thaw process, no matter with TG cross-linking or in different oil phase systems, all emulsion samples prepared with pH-shifting treated mung bean protein (BMBP) exhibited a superior freeze-thaw stability than that with native mung bean protein (NMBP). The apparent viscosity of BMBP emulsion was higher than that of NMBP, and the viscosity of BMBP-based CO-emulsion (222.50 mPa s) before freeze-thaw process was closest to that of real egg liquid (184.86 mPa s). In particular, BMBP was more sensitive to TG, resulting in a superior thermal gel hardness of BMBP-based emulsion. This study could serve as a feasible solution to enhance the freeze-thaw stability and thermal gel properties of plant-based emulsions by pH-shifting and TG cross-linking, providing some novel strategies for their applications as stabilized plant-based egg substitutes.

Protein-Stabilized Emulsion Gels with Improved Emulsifying and Gelling Properties for the Delivery of Bioactive Ingredients: A Review.

In today's food industry, the potential of bioactive compounds in preventing many chronic diseases has garnered significant attention. Many delivery systems have been developed to encapsulate these unstable bioactive compounds. Emulsion gels, as colloidal soft-solid materials, with their unique three-dimensional network structure and strong mechanical properties, are believed to provide excellent protection for bioactive substances. In the context of constructing carriers for bioactive materials, proteins are frequently employed as emulsifiers or gelling agents in emulsions or protein gels. However, in emulsion gels, when protein is used as an emulsifier to stabilize the oil/water interface, the gelling properties of proteins can also have a great influence on the functionality of the emulsion gels. Therefore, this paper aims to focus on the role of proteins' emulsifying and gelling properties in emulsion gels, providing a comprehensive review of the formation and modification of protein-based emulsion gels to build high-quality emulsion gel systems, thereby improving the stability and bioavailability of embedded bioactive substances.

Improving physical stability of pea protein-based emulsions near the isoelectric point via polysaccharide complexation

Development of plant protein-based mildly acidic beverages remains challenging as the pH range falls near the protein isoelectric point, destabilizing emulsions. To overcome this problem, it was hypothesized that complexation between plant proteins and polysaccharides could provide emulsion stability in this critical pH range. Four different polysaccharides (sugar beet pectin, gum Arabic (GA), guar gum, gellan gum) were mixed separately with pea protein isolate (PPI) in 1:1 ratio, and the critical pH values for the formation of soluble complexes were determined. Heating the mixture widened the optimal pH range for soluble complexation for pectin-PPI and GA-PPI below the isoelectric point, which was then used to prepare 5 wt% O/W emulsions with an aqueous phase containing 0.5 wt% biopolymers at pH 8.0 and pH 4.5. Emulsion stability was characterized using droplet size, charge, visual observation, microstructure, and accelerated gravitational separation. PPI-only emulsions were stable at pH 8.0 but extensively destabilized at pH 4.5. The GA-PPI emulsions showed high stability at pH 8.0; however, at pH 4.5, the soluble complexes failed to provide a stable emulsion due to extensive droplet aggregation and phase separation. The emulsion prepared with a co-soluble pectin-PPI mixture at pH 8.0 also showed droplet aggregation and phase separation. The most improved emulsion stability (smallest droplet size, no aggregation) was observed for the pectin-PPI soluble complex at pH 4.5. Findings from this study showed that soluble complexes could be obtained at the desired pH range depending on the polysaccharide sources, which can stabilize O/W emulsions even near the protein's isoelectric point.

Characterization, Formation Mechanism, and Curcumin Delivery of Buckwheat Peptide-Based Emulsion Gels.

This study aimed to construct a natural peptide-based emulsion gel (PG) using small peptides (∼2.2 kDa) by mild enzymatic hydrolysis of buckwheat proteins. The obtained PG presented a porous and tight texture and solid-gel viscoelasticity compared with its parent protein-based emulsion gel. Meanwhile, it exhibited good resistance against heating and freeze-thawing. Furthermore, peptide-oil interaction analysis revealed that the gel matrix was enhanced by the hydrophobic aggregation between peptides and oil molecules, H-bonding interaction of peptide molecules, and peptide-oil aggregate repulsion force. Finally, in vitro intestinal digestion experiments demonstrated that PG could embed and pH-responsively release curcumin in the gastrointestinal tract at a release rate of 53.9%. The findings unfold promising opportunities for using natural PG in a range of applications relying on large proteins or other synthesized molecules.

Application of Whey Protein-Based Emulsion Coating Treatment in Fresh-Cut Apple Preservation

Fresh-cut fruit requires an edible and water-resistant coating to remain fresh. This article investigated the effects of transglutaminase (TGase) and sunflower oil on the water-resistant characteristics, mechanical properties, and microstructure of a whey protein-based film. The whey protein-based emulsion coating's preservation effect on fresh-cut apples was confirmed. According to the findings, sunflower oil (added at 1.5% w/w) could interact with β-lactoglobulin, α-lactoglobulin dimer, and β-lactoglobulin dimer to form emulsion droplets that are evenly dispersed throughout the protein film. This effect, combined with the covalent cross-linking of TGase, significantly improves the films' microstructure, mechanical properties, and water resistance. However, too much and unevenly distributed sunflower oil (add 3% w/w) partially prevented the covalent cross-linking of TGase, reducing the elongation at the break of the composite film. In the fresh-cut apple storage experiment, the whey protein-based emulsion coating treatment significantly reduced the weight loss rate and browning index of fresh-cut apples by 26.55% and 46.39%, respectively. This was accomplished by the coating treatment significantly inhibiting the respiration rate increase, PPO and CAT activity enhancement, H2O2 production, and MDA accumulation. This research provides practical, technical, and theoretical guidance for the preservation of fresh-cut fruit.

Influence of the Protein-Based Emulsions on the Rheological, Thermo-Mechanical and Baking Performance of Muffin Formulations

The impact of replacing the sunflower oil in a typical muffin formulation with different protein-based emulsions was investigated. Fundamental rheological measurements indicated significant differences between emulsions prepared with soy, lupin, and yeast proteins. The highest viscosity of 2.04 Pa·s was registered for the lupin protein-based emulsion, whereas the yeast protein-based emulsion exhibited the narrowest linear viscoelastic region. The influence of the protein-based emulsions on the thermo-mechanical properties of wheat flour dough was further investigated using the Mixolab device and Chopin+ protocol. Oil substitution with emulsion resulted in better starch gelatinization with the C3 torque of 0.46 Nm being registered for doughs with soy and lupin protein emulsions. Significant differences in terms of moisture, color, porosity, and texture were observed between muffins prepared with protein-based emulsions and control. The lower fat baked products retained higher amounts of water (25.05–26.00%) and exhibited slightly more vivid color (color intensity of 46.34–46.81) and harder texture (firmness of 5.64–5.86 N). The sensory analysis confirmed that soy, lupin, and yeast protein emulsions can be used for obtaining muffin samples with acceptable taste and flavor, and overall quality comparable to the control. These results indicate that the protein based-emulsions are promising oil replacers in muffin formulations.

Quantitative analysis and interfacial properties of mixed pea protein isolate-phospholipid adsorption layer

Proteins and low-molecular-weight (LMW) surfactants are widely used for the physical stabilization of many emulsion-based food products. This study investigated the oil-water interfacial behavior between pea protein isolate (PPI) and phospholipid (PL). The emulsions prepared with different concentrations of PPI and PL were stabilized by their synergetic or competitive adsorption at the oil-water interface. In addition, the quantitative proteomics results could illustrate the displacements of proteins by PL. The result showed that the vicilin (7S) could be preferentially displaced by PL. Meanwhile, the results of quartz crystal microbalance with dissipation (QCM-D) indicated the high affinity of legumin (11S) with PL, suggesting that the legumin possessed higher interfacial affinity to prevent interfacial displacement. This research could help us to understand the interaction and competitive adsorption between plant proteins and LMW surfactants profoundly, which could promote the development of plant protein-based emulsion beverage with improved stability.

Improvement of stability and in vitro bioaccessibility of nervonic acid by nonionic surfactant in protein-based nanoemulsions

Nervonic acid (NA, ω-9) is beneficial for brain health, but its poor water solubility limits its bioaccessibility. The protein-based emulsions were unstable under environmental stress. In this study, the effects of a nonionic surfactant (Tween 20, T20) on the characteristics, stability, and in vitro digestion properties of NA-loaded nanoemulsions prepared with proteins (whey or soybean protein isolate) were evaluated. The emulsions stabilized by protein-T20 mixtures had smaller droplets with more even distributions, more negative charges, and higher encapsulation efficiencies for NA. The addition of T20 improved the interfacial properties of the systems, as confirmed by spectral and rheological analyses. Emulsion stability under various conditions was enhanced by the improved interfacial composition and emulsifying ability. In particular, the effective interfacial layers produced by the protein-T20 mixture decreased lipid digestion but increased NA bioaccessibility. Therefore, the co-adsorption of proteins with suitable nonionic surfactants at oil-water interfaces is a promising approach for designing functional food delivery systems with improved stability and NA bioaccessibility.

Improving emulsifying properties using mixed natural emulsifiers: Tea saponin and golden pompano protein

Emulsion stability could be improved by combining two natural emulsifiers. In this research, we studied the potential of combining golden pompano protein (GPP) and tea saponin (TS) on the O/W emulsion properties. At first, we investigated the influence of TS addition on the fourier transform infrared spectroscopy, free sulfhydryl content and fluorescence spectrum of the GPP. With the increase of TS addition, the content of α-helix decreased and the content of β-sheet increased, the free sulfhydryl content was also increased. We also determined the interfacial tension of GPP, TS and GPP-TS mixture. TS had stronger ability to reduce the oil-water interfacial tension. And the viscoelasticity of GPP-TS emulsion increased with the addition of TS, which might be due to the thickening effect of emulsifiers. These results indicated that the interaction between GPP and TS molecules was enhanced, which further increased the adsorption rate of GPP at the oil/water interface, reduced the interfacial tension, and improved the emulsification properties of the GPP-TS mixture. Compared with GPP emulsion, the mixed interfacial layer of GPP-TS emulsions got thicker and the steric repulsion become stronger. In addition, emulsion morphology was also affected by pH condition. GPP-TS emulsion droplets carried a great amount of net surface charge at alkaline condition, resulting in stronger electrostatic repulsion force and the emulsion distributed more uniformly. Rheological properties measurement indicated that the increase of TS addition increased the emulsion viscosity, thereby improving the emulsion stability. Our research demonstrated that the addition of TS could improve the GPP functional properties, and the GPP-TS mixture could form a more stable emulsion. This study showed that food-grade binary surfactant mixtures can be used to form stable emulsions with properties being tunable by altering the mixing ratios between surfactants. This mixed system demonstrated great potential as functional protein ingredient to control emulsion-type meat products or design of protein-based emulsion delivery systems in the food industry.

Impact of Phenolic Acid Derivatives on β-Lactoglobulin Stabilized Oil-Water-Interfaces

The physical stability of protein-based emulsions depends on intra- and intermolecular interactions of the interfacial protein-film. As studied in aqueous systems before, phenolic acid derivatives (PADs) non-covalently or covalently crosslink proteins depending on pH-value and thus, may impact interfacial protein-films. Whether these interactions occur in the same manner at the interface as in water and how they vary the properties of the interfacial protein-film has not been clarified. The present study aimed to investigate the interfacial protein-film viscoelasticity and physical emulsion-stability after non-covalently (pH 6.0) and covalently (pH 9.0) crosslinking depending on PAD-structure. For this purpose, we studied an interfacial β-lactoglobulin film with dilatational rheology after crosslinking with PADs, varying in number of π-electrons and polar substituents. Then, we analyzed the physical emulsion-stability by visual evaluation and particle size distribution. The results indicate that PADs with a high number of π-electrons (rosmarinic acid and chicoric acid) weaken the protein-film due to competing of phenol-protein interactions with protein-protein interactions. This is reflected in a decrease in interfacial elasticity. PADs with an additional polar substituent (verbascoside and cynarine) seem to further weaken the protein film, since the affinity of the PADs to the interface increases, PADs preferentially adsorb and sterically hinder protein-protein interactions. In emulsions at pH 6.0 and thus low electrostatic repulsion, PADs promote bridging-flocculation. Due to higher electrostatic repulsion at pH 9.0, the PADs are sterically hindered to form bridges, even though they are polymeric. Hence, our research enables the control of protein-film viscoelasticity and emulsion-stability depending on the PAD-structure.Graphical abstract

Molecular modeling of the interface of an egg yolk protein-based emulsion

Many food emulsions are stabilized by functional egg yolk biomolecules, which act as surfactants at the oil/water interface. Detailed experimental studies on egg yolk emulsifying properties have been largely hindered due to the difficulty in isolating individual chemical species. Therefore, this work presents a molecular model of an oil/water interfacial system where the emulsifier is one of the most surface-active proteins from the egg yolk low-density lipoproteins (LDL), the so-called Apovitellenin I. Dissipative particle dynamics (DPD) was here adopted in order to simulate large systems over long time scales, when compared with full-atom molecular dynamics (MD). Instead of a manual assignment of the DPD simulation parameters, a fully automated coarse-graining procedure was employed. The molecular interactions used in the DPD system were determined by means of a parameter calibration based on matching structural data from atomistic MD simulations. Despite the little availability of experimental data, the model was designed to test the most relevant physical properties of the protein investigated. Protein structural and dynamics properties obtained via MD and DPD were compared highlighting advantages and limits of each molecular technique. Promising results were achieved from DPD simulations of the oil/water interface. The proposed model was able to properly describe the protein surfactant behavior in terms of interfacial tension decrease at increasing protein surface concentration. Moreover, the adsorption time of a free protein molecule was estimated and, finally, an LDL-like particle adsorption mechanism was qualitatively reproduced.

Physical Properties of Peanut and Soy Protein-Based Emulsion Gels Induced by Various Coagulants.

Emulsions of peanut and soy proteins, including their major components (arachin, conarachin, glycinin and β−conglycinin), were prepared by ultrasonication (300 W, 20 min) at a constant protein concentration (4%, w/v) and oil fraction (30%, v/v). These emulsions were then induced by CaCl2, transglutaminase (TGase) and glucono-δ-lactone (GDL) to form emulsion gels. The optimum coagulant concentrations were obtained for peanut and soy protein-stabilized emulsion gels, such as CaCl2 (0.15 and 0.25 g/dL, respectively), TGase (25 U/mL) and GDL (0.3% and 0.5%, w/v, respectively). For the CaCl2-induced emulsion gels, the hardness of the β−conglycinin gel was the highest, whereas that of the conarachin gel was the lowest. However, when TGase and GDL were used as coagulants, the strength of the conarachin emulsion gel was the best. For the GDL-induced emulsion gels, microstructural analysis indicated that the conarachin gel showed more homogeneous and compact structures. The gelation kinetics showed that the storage modulus (G′) of all the GDL-induced emulsions increased sharply except for the arachin-stabilized emulsion. The interactive force nature varied between conarachin and arachin emulsion gels. This work reveals that peanut conarachin could be used as a good protein source to produce emulsion gels when suitable coagulants are selected.

Effects of mono- and di-glycerides/phospholipids (MDG/PL) on the bioaccessibility of lipophilic nutrients in a protein-based emulsion system.

Lipophilic nutrients are known to have relatively poor absorption, thus limiting their bioaccessibility. Consequently, researchers in food and pharmaceutical areas are exploring different techniques to promote the efficient delivery of lipophilic nutrients. The effects of two polar lipids, namely mono-, di-glycerides (MDG) and lecithin (PL), on the bioaccessibility of lipophilic nutrients were investigated in this study with a protein-based emulsion model system. During the emulsion preparation and formation, the incorporation of MDG/PL was found to benefit the dissolution and stabilization of lipophilic nutrients, such as lutein, and could also modify the construction of the emulsion surface. An in vitro digestion study showed that the use of MDG/PL could significantly increase the bioaccessibility of lipophilic nutrients [lutein, vitamin E, and docosahexaenoic acid (DHA)] by 13.52%, 186.90%, and 36.17% in a protein-based emulsion system. The use of MDG and PL decreased the interfacial tension in all the samples: protein only 20.65 mN m-1, protein-PL 6.47 mN m-1, and protein-MDG/PL 4.23 mN m-1, as well as 12.11 mN m-1, 1.26 mN m-1 and 1.16 mN m-1 with the presence of bile salts. Caco-2 cell culture results showed that, with the application of MDG/PL, the absorption rate of micelles was higher than that in the other groups and this resulted in a 70% absorption increase for lutein. Therefore, MDG/PL can improve the lipophilic nutrient absorption via promoting the affinity of formed micelles to the enterocytes of the small intestine. This study exhibited the effectiveness of MDG/PL on improving the bioaccessibility of lipophilic nutrients in a protein-based emulsion system mimicking the digestion and absorption fate of breast milk in an infant's gastric intestinal tract, thus suggesting that MDG/PL can be used as a technical pathway to improve the absorption of lipophilic nutrients.

Impact of Saturation of Fatty Acids of Phosphatidylcholine and Oil Phase on Properties of β-Lactoglobulin at the Oil/Water Interface

Oil in water emulsions are commonly stabilized by emulsifying constituents like proteins and/or low molecular weight emulsifiers. The emulsifying constituents can compete or coexist at the interface. Interfacial properties thus depend on molecular structure of the emulsifying constituents and the oil phase and the resulting molecular interactions. The present study systematically analyzed the impact of fatty acid saturation of triacylglycerides and phosphatidylcholine on the interfacial properties of a β-lactoglobulin-stabilized interface. The long-term adsorption behaviour and the viscoelasticity of β-lactoglobulin-films were analyzed with or without addition of phosphatidylcholine via drop tensiometry and dilatational rheology. Results from the present study showed that increasing similarity in fatty acid saturation and thus interaction of phosphatidylcholine and oil phase increased the interfacial tension for the phosphatidylcholine alone or in combination with β-lactoglobulin. The characteristics and stability of interfacial films with β-lactoglobulin-phosphatidylcholine are further affected by interfacial adsorption during changes in interfacial area and crystallization events of low molecular weight emulsifiers. This knowledge gives guidance for improving physical stability of protein-based emulsions in foods and related areas.Graphic abstract

Interfacial rheology of alkali pH-shifted myofibrillar protein at O/W interface and impact of Tween 20 displacement

In the current study, the interfacial rheological properties of alkali pH-shifted MP under pH 11.0 → 7.0, pH 11.5 → 7.0 and pH 12.0 → 7.0 have been firstly investigated. The molecular weight and microstructure of myofibrillar protein (MP) treated by alkali pH-shifting were investigated by gel-permeation chromatography (GPC) and transmission electron microscopy (TEM). Results indicated a swollen, organized and aggregated structure of refolded MP. Overall, the molecular change in refolded MP led to faster protein adsorption towards the O/W interface, enhanced intermolecular interaction between adsorbed proteins and improved elasticity of interfacial film compared to native MP. After β-mercaptoethanol (β-ME) was added, the advantage of refolded MP in diffusion phase no more existed due to the disruption of aggregation and decreased molecular size, besides the penetration and rearrangement were interfered because the disruption of disulfide bond inhibited the formation of interfacial protein layers. With the protein concentration increasing, MP molecules crowding at O/W (oil in water) surface limited the development of a highly elastic network. As revealed by Tween 20 displacement, MP layers with higher interfacial elasticity were more resistant to displacement. Moreover, after displacement the coalescence stability of emulsion droplet was enhanced but the mechanical strength of interfacial MP layer was reduced. Altogether MP (0.04 or 0.2 mg/mL) treated by pH 11.0 → 7.0 exhibited the best adsorption performance and interfacial properties, which were important in stablizing emulsions. Thus, interfacial behavior regulation by alkali pH-shifting may be a applicable process for developing meat protein-based emulsions in food industry.

Development of an Antioxidative Pickering Emulsion Gel through Polyphenol-Inspired Free-Radical Grafting of Microcrystalline Cellulose for 3D Food Printing.

The manufacture of next-generation 3D-printed foods with personalized requirements can be accelerated by in-depth knowledge of the development of a multifunctional biopolymeric-based ink. As a fat replacer in the food industry, microcrystalline cellulose (MCC) has the potential to address the growing need for sustainable healthy reduced-fat 3D printed foods. The modification of MCC structure by polyphenols gives the way to produce a multifunctional antioxidative Pickering emulsion with improved emulsifying properties. In this study, different types of polyphenols, including gallic acid (GA), tannic acid (TA), and cyanidin-3-O-glucoside (C3G), were individually used to synthesize the grafted MCC-g-polyphenol conjugates by the free-radical grafting method. Then, the antioxidative grafted microconjugates were added to a soy protein-based emulsion gel to partially substitute its oil, and each Pickering emulsion gel variant was printed through an extrusion-based 3D printing system. Emulsifying properties and antioxidant character of MCC were proven to be enhanced after the fabrication of grafted microconjugates. Compared to MCC-g-TA, MCC-g-GA and MCC-g-C3G could efficiently improve the stability of a reduced-fat soy-based emulsion gel upon storage. Moreover, the reduced-fat soy-based emulsion gel containing grafted microconjugates endowed a characteristic shear-thinning behavior with a gel-like structure and superlative thixotropic properties. Following the printing, the antioxidative Pickering emulsion gels containing grafted microconjugates produced well-defined 3D structures with superior lubrication properties. This study demonstrated that the grafting of polyphenols onto MCC could enhance bioactive properties and improve emulsifying performance of MCC, making it a useful component in the development of personalized functional foods.

Construction of 3D printed reduced-fat meat analogue by emulsion gels. Part I: Flow behavior, thixotropic feature, and network structure of soy protein-based inks

The fabrication of high-quality low-fat 3D printed foods is strongly dependent on the development of shear-thinning, viscoelastic, and thixotropic ink with a monomodal particle size distribution. In this study, oil was partially or totally replaced with hydrophobically modified biosurfactants (acetylated starch, octenyl succinic anhydride starch, ethyl (hydroxyethyl) cellulose, and dodecenyl succinylated inulin) in a soy protein-based emulsion to produce the desired reduced-fat emulsion gels for potential applications in the 3D printing process. These reduced-fat emulsion gels exhibited pseudoplastic behavior with viscoelastic properties, where viscosity recovery, frequency crossover point, and storage modulus were found to increase with increasing biosurfactants ratio. Higher levels of surface-active biopolymers also yielded inks with lower creep compliance, a smaller droplet size having a more uniform distribution, and possessing improved structural strength and storage stability. Spherical droplets of inks with higher ratios of biosurfactants remained well dispersed. The differences in molecular weight and radius of gyration of biosurfactants accounted for the observed differences in flow behavior and emulsion stability, where inks including dodecenyl succinylated inulin and ethyl (hydroxyethyl) cellulose offered stable structures with strong gel-like properties compared to acetylated and octenyl succinic anhydride starches. All ink networks were also dynamic and recoverable, thus demonstrating the potential of these reduced-fat inks in 3D printing processes.