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Abstract In the present work, we studied the influence of particle size and charge density on the structure formation and rheological property of high internal phase emulsion gels (HIPE-gels) stabilized with zein/tannic acid complex particles (ZTPs). The size (68 and 108 nm) and charge density (+38, +20, and +1 mV) of ZTPs were controlled by adjusting the pH during the preparation of the particles and in the respective particle suspensions. Extensive centrifugation of the emulsions stabilized by those ZTPs resulted in stable HIPE-gels with an oil content ranging between 72 and 87% (w/w) and a particle concentration of 0.7–1.4% (w/w) only. Microscopy showed that even at these high oil volume fractions, limited coalescence between the oil droplets occurred. A decrease in the particle size resulted in a decrease in the oil content in the HIPE-gels, due to a more efficient particle network in the continuous phase. This increased the storage modulus of the HIPE gels, indicating that this particle network plays an important role for the gel strength. When increasing the interactions between the particles (by lowering the charge density), the gel strength increased even further. It was noted that the gel strength was independent of the oil content, suggesting that the oil droplets do not contribute a lot to the gel strength. These HIPE-gels with tunable rheological property may have various applications in industry. Graphical abstract The structure formation and rheological behavior of the high internal phase emulsion gels stabilized with zein/tannic acid complex particles (ZTPs) can be tuned by changing the particle size and charge density. Image 1 Highlights • Zein particles were used to stabilize high internal phase emulsions (HIPEs). • The HIPEs had an oil volume fraction of 72–87% and a protein content of 0.7–1.4%. • The storage moduli of these HIPEs were between 13000 and 27000 Pa. • The rheological behavior of HIPEs can be tuned by changing the particle properties. [ABSTRACT FROM AUTHOR]

In this paper, we report the structure formation and rheological properties of Pickering emulsions stabilized with zein/tannic acid complex particles (ZTPs) over a wide range of particle concentration (1–5%, w/v) and oil content (5–60%, v/v). Microscopy shows that the ZTPs provide stabilization at the droplet interfaces, and that excess ZTPs provide a particle network in the continuous phase to give a solid-like structure to the ZTPs-stabilized emulsions (ZTPEs). The low frequency dependency of G′ and low values for tan δ imply that ZTPEs have very elastic networks. The storage modulus (G′) of ZTPEs increases in a power-law manner with increasing particle concentration ( c p ) and oil content ( φ ), which can be scaled as G’ ∼  c p n and G’ ∼  φ m , respectively. The exponent n decreases with an increase of oil content, and m decreases with increase of particle concentration. This indicates that the structure of the network depends on both the particle concentration and the oil content. The difference in the network structure is also seen in the critical strain γ co , since three regimes are observed: for φ  ≤ 20%, γ co decreases with an increase in particle concentration; for 30% ≤ φ  ≤ 50%, γ co increases with increasing particle concentration; and for φ  = 60%, γ co is almost independent on the particle concentration. The results show that the microstructure and rheological properties of ZTPEs can be tuned by changing both the particle concentration and oil content, which may provide interesting features for various applications in industry. [ABSTRACT FROM AUTHOR]

The present work was aimed to evaluate the potential of the gel-like Pickering emulsions (50%, v/v, oil) stabilised by zein/tannic acid (TA) complex colloidal particles (ZTPE) as a new encapsulation system of lipophilic ingredients. Compared with sodium caseinate-stabilised emulsions (SCE) and bulk oil, the better protective effects of ZTPE on the chemical stability of curcumin were observed when they suffered from UV light, and the lipid oxidation rate remarkably reduced in ZTPE. Also, the zein particle layers loaded with TA around the oil droplets can provide protection against harsh gastric environment, facilitating to slow down the release of free fatty acids (FFA) and curcumin during in vitro simulated digestion. These findings show that ZTPE have a good potential to act as an efficient encapsulating agent to protect functional ingredients from degradation and control their release during digestion, which can further improve the bioavailability of bioactive ingredients. [ABSTRACT FROM AUTHOR]

In the present work, the influence of hydrophobicity of zein/tannic acid complex particles (ZTPs) on the rheological behavior of ZTP-stabilized emulsion gels is described. The hydrophobicity of the particles was controlled by the incorporation of different amounts of hydrophilic tannic acid, while retaining a similar particle size. The resulting ZTPs with varying hydrophobicity were successfully used to form emulsion gels with similar oil droplet size. With a decrease in the hydrophobicity of ZTPs, the storage modulus (G′) of emulsion gels increased, while tan δ and the frequency dependence decreased, indicating the formation of a stronger gel network. The crossover strain, γ co , increased with a decrease in the hydrophobicity of ZTPs, indicating the gel network becomes more resistance against breakdown. In all cases, G′ increased in a power-law manner with an increase in protein concentration (G' ∼  c p n ) and oil content (G' ∼  φ m ). The exponent n and m decreased with decreasing particle hydrophobicity, indicating that hydrophobic interactions between particles within the particle network in the continuous phase and the oil droplets provide a relatively larger contribution to the gel strength for emulsion gels stabilized by ZTPs with higher hydrophobicity. Increasing the oil polarity provided a lower gel strength for emulsions stabilized by particles with high hydrophobicity, while it increased the gel strength for particles with low hydrophobicity. The results show that the rheological behavior of ZTP-stabilized emulsion gels can be tuned by changing the particle hydrophobicity and oil polarity, which provide interesting features for various applications in the food industry. [ABSTRACT FROM AUTHOR]

Interparticle forces that govern the assembly of particles adsorbed at fluid interfaces determine the rheology and microstructure of particle laden interface. In this study, natural small molecule, tannic acid (TA), was used to modify particle-particle interactions and assembly behaviors of food grade hydrophobic protein particle (zein nanoparticle) at air-water interface. For bare zein particle (ZP), the rapid adsorption and high interparticle forces led to the low coverage and formation of large ZP aggregates at the interface. The hydrogen-bonding of TA weakened the particle hydrophobicity and thus interparticle forces at fluid interfaces. Therefore, the adsorption process and assembly rate of ZTP at the interface obviously reduced, which also provided enough time for ZTP to rearrange into orderly interfacial networks. Furthermore, the Lissajous plots of surface pressure versus deformation are used to understand the surface rheological response to large mechanical deformation in terms of interfacial microstructure. The rheological response of interface stabilized by ZTP showed strain hardening during extension and strain softening during compression. These findings indicate that the interfacial rheology and microstructure of zein particle-laden interface can be tuned by changing the TA content. [ABSTRACT FROM AUTHOR]

[Display omitted] • Complex gum arabic (GA) and tannic acid (TA) was confirmed by ITC. • GA inhibit the interaction of mucoadhesive TA with mucins. • TA modulate the retention of emulsions and aroma release. Flavour is a crucial sensory element that determines the consumers' preference for food and beverages. In this study, we determined the effects of complex gum arabic (GA) and tannic acid (TA) on the aroma release of flavour oil emulsions in vitro by simulating oral processing conditions. GA and TA were used to stabilize flavour oil emulsions. Visualization of in vitro retention using ex vivo porcine tongue, detection of aroma release in the model mouth, and sensory evaluation of flavour emulsions were performed to determine the effect of TA and GA. The results indicated that the retention of emulsions and the release of aroma compounds were modulated by TA and GA, which could be because of interactions that occurred between GA and TA in emulsions and mucins on the tongue. GA enhanced aroma release, whereas TA contributed to the retention or slow release of target aroma compounds. [ABSTRACT FROM AUTHOR]