Characterization of cold-set gels produced from heated emulsions stabilized by whey protein

The internal aqueous phase gelation improves the viability of probiotic cells in a double water/oil/water emulsion system

This research studied the viability of probiotic bacterium Lactobacillus plantarum (L. plantarum) encapsulated in the internal aqueous phase (W 1) of a water-in-oil-in-water (W 1/O/W 2) emulsion system, with the help of gelation and different gelling agents. Additionally, the physicochemical, rheological, and microstructural properties of the fabricated emulsion systems were assessed over time under the effect of W 1 gelation. The average droplet size and zeta potential of the control system and the systems fabricated using gelatin, alginate, tragacanth gum, and carrageenan were 14.7, 12.0, 5.1, 6.4, and 7.3 μm and - 21.1, -34.1, -46.2, -38.3, and -34.7 mV, respectively. The results showed a significant increase in the physical stability of the system and encapsulation efficiency of L. plantarum after the W 1 gelation. The internal phase gelation significantly increased the viability of bacteria against heat and acidic pH, with tragacanth gum being the best gelling agent for increasing the viability of L. plantarum (28.05% and 16.74%, respectively). Apparent viscosity and rheological properties of emulsions were significantly increased after the W 1 gelation, particularly in those jellified with alginate. Overall, L. plantarum encapsulation in W 1/O/W 2 emulsion, followed by the W 1 gelation using tragacanth gum as the gelling agent, could increase both stability and viability of this probiotic bacteria.

Application of Emulsion Gels as Fat Substitutes in Meat Products

Although traditional meat products are highly popular with consumers, the high levels of unsaturated fatty acids and cholesterol present significant health concerns. However, simply using plant oil rich in unsaturated fatty acids to replace animal fat in meat products causes a decline in product quality, such as lower levels of juiciness and hardness. Therefore, it is necessary to develop a fat substitute that can ensure the sensory quality of the product while reducing its fat content. Consequently, using emulsion gels to produce structured oils or introducing functional ingredients has attracted substantial attention for replacing the fat in meat products. This paper delineated emulsion gels into protein, polysaccharide, and protein–polysaccharide compound according to the matrix. The preparation methods and the application of the three emulsion gels as fat substitutes in meat products were reviewed. Since it displayed a unique separation structure, the double emulsion was highly suitable for encapsulating bioactive substances, such as functional oils, flavor components, and functional factors, while it also exhibited significant potential for developing low-fat or functional healthy meat products. This paper summarized the studies involving the utilization of double emulsion and gelled double emulsion as fat replacement agents to provide a theoretical basis for related research and new insight into the development of low-fat meat products.

Structuring functional mayonnaise incorporated with Himalayan walnut oil Pickering emulsions by ultrasound assisted emulsification

Nowadays Pickering emulsions have attracted immense attention due to their enhanced stability and numerous food applications. In this context, the present study was aimed to introduce Pickering emulsions stabilized by soy protein isolate (SPI)-maltodextrin (MD)-pectin complex incorporated with Himalayan walnut oil (HWO) for development of novel mayonnaise by ultrasound assisted emulsification. The functional mayonnaise was characterised for its stability, structural, textural, rheological and morphological properties. The rheological and microstructure measurements indicated that use of SPI-pectin HWO emulsions had a viscoelastic solid behaviour (G' > G″) with highly interconnected gel-like network structure leading to diffused oil droplet distribution. An increase in particle size diameter (1.86-5.09 µm) and hardness values (43.16-69.08 N) was seen with increase in the SPI-pectin wall material concentration. A significant reduction in whiteness (L* value) from 91.12 to 53.52 was noted during storage for encapsulated samples. Mayonnaise formulations containing encapsulated HWO depicted significantly lower peroxide value (2.65 meqO₂/kg) after extended storage period in comparison to free oil (8.33 meqO₂/kg). FTIR analysis of mayonnaise formulations depicted successful complexation of HWO with SPI-MD-pectin matrix. These findings would be of immense importance in designing of Pickering emulsions stabilized by protein-polysaccharide particles with aim of delivering nutraceuticals associated with myriad health benefits.

Influence of calcium chloride and pH on soluble complex of whey protein-basil seed gum and xanthan gum

Interaction between biopolymers generates different rheological behaviors, which can be effective on the structure of food products. One way to control the polysaccharide-protein interaction is the variation of acidic and ionic strength. In this research, the different amounts of pHs (3-7) and calcium chloride (5-20 mM) were investigated on a soluble complex of whey protein concentrate (WPC) with xanthan gum (XG) and basil seed gum (BSG). The complex characteristic was investigated according to turbidity, viscosity behavior, and electrostatic interactions. The turbidity test showed that WPC:BSG and WPC:XG absorbance increased at pH 3.5 and 4.5, respectively, due to the formation of insoluble complex. pH 6 was the start point of the turbidity increment, which showed the formation of soluble complexes between WPC and polysaccharides. The FTIR analysis confirmed creation of soluble complex at pH 6. The absorbance raised with increasing the molar of CaCl2 to 10 mM, but no significant difference was observed by turbidity test in the range of CaCl2<10 mM. Also, the highest viscosity value was obtained by 10 mM CaCl2.

Effect of Gel Structure on the In Vitro Gastrointestinal Digestion Behaviour of Whey Protein Emulsion Gels and the Bioaccessibility of Capsaicinoids

This study investigated the effect of gel structure on the digestion of heat-set whey protein emulsion gels containing capsaicinoids (CAP), including the bioaccessibility of CAP. Upon heat treatment at 90 °C, whey protein emulsion gels containing CAP (10 wt% whey protein isolate, 20 wt% soybean oil, 0.02 wt% CAP) with different structures and gel mechanical strengths were formed by varying ionic strength. The hard gel (i.e., oil droplet size d_4,3 ~ 0.5 μm, 200 mM NaCl), with compact particulate gel structure, led to slower disintegration of the gel particles and slower hydrolysis of the whey proteins during gastric digestion compared with the soft gel (i.e., d_4,3 ~ 0.5 μm, 10 mM NaCl). The oil droplets started to coalesce after 60 min of gastric digestion in the soft gel, whereas minor oil droplet coalescence was observed for the hard gel at the end of the gastric digestion. In general, during intestinal digestion, the gastric digesta from the hard gel was disintegrated more slowly than that from the soft gel. A power-law fit between the bioaccessibility of CAP (Y) and the extent of lipid digestion (X) was established: Y = 49.2 × (X - 305.3)^0.104, with R² = 0.84. A greater extent of lipid digestion would lead to greater release of CAP from the food matrix; also, more lipolytic products would be produced and would participate in micelle formation, which would help to solubilize the released CAP and therefore result in their higher bioaccessibility.

Effect of soybean oil content on textural, rheological, and microstructural properties of WBAXs-SPI emulsion-filled gels

This study aimed to prepare wheat bran arabinoxylans-soy protein isolate (WBAXs-SPI) emulsion-filled gels with different oil contents and investigate their rheological, textural, water-holding capacity (WHC), and microstructural properties. The rheological analysis results showed that the maximum correlation interaction occurs when the soybean oil concentration was 10%, and the elastic modulus (G') reaches the highest value of 13,562 Pa. Interestingly, the WHC and texture change trend of WBAXs-SPI emulsion-filled gel were consistent with rheology. Meanwhile, confocal laser scanning microscopy (CLSM) observation indicated that the emulsion-filled gels formed an interpenetrating polysaccharide-protein complex network system. Therefore, the filling emulsion performance could be adjusted by changing the concentration of oil droplets as the active filler. This provides the possibility of developing new food materials encapsulating fat-soluble substances with a low oil rate and more stable structure.

Salt and pH-Induced Attractive Interactions on the Rheology of Food Protein-Stabilized Nanoemulsions

This research aimed to investigate the possibility of forming gelled nanoemulsions (NEs) by inducing attractive interactions among the nanodroplets. The effect of salt concentration and changes in pH on the stability and gelation behavior of 2, 4, and 5% sodium caseinate (SC) and whey protein isolate (WPI)-stabilized 40% canola oil-in-water NEs were investigated. For the effect of salt, sodium chloride was added in a concentration of 0.1, 0.5, and 1 M in the continuous phase of the NEs at neutral pH, whereas to study the effect of acidification, the pH of the NEs was adjusted to the isoelectric point (pI) of the proteins. The addition of salt led to attractive gelation in WPI NEs because of a screening of charge. In contrast, the gel strength of SC-stabilized NEs was reduced with salt, which was attributed to the loss of close packing of droplets and their surrounding repulsive barriers because of charge screening and to the steric barrier of interfacial SC preventing droplet aggregation. All the NEs with pH at the pI of proteins transformed into strong attractive gels made of droplet aggregates irrespective of the type or concentration of protein because of the complete charge neutralization. The strength of the acidified NE gels increased with a decrease in droplet size and the type of protein used. Overall, research on the effect of different environmental factors on the stability and gelation behavior of protein-stabilized NEs could be useful for possible applications of these nanoscale materials in various food systems.

Effect of the Solid Fat Content on Properties of Emulsion Gels and Stability of β-Carotene

Whey-protein-isolate-based emulsion gels were prepared through a cold-set gelation process, and the effect of the solid fat (coconut oil) content in the oil phase on gel properties and β-carotene stability was investigated. An increase in solid fat content (0, 20, 50, 80, and 100% of the oil phase) resulted in a smaller droplet size, higher viscosity, and improved creaming stability of the emulsions. When glucono-δ-lactone was added to initiate gelation, a higher solid fat content contributed to an earlier onset of gelation and a higher storage modulus of the gels. Textural analysis indicated that the increase in the solid fat content allowed for an increase in fracture stress and Young's modulus of the emulsion gels. Microscopic observation revealed that emulsions containing a higher solid fat content formed gels with a denser and more uniform particulate network structure. The stability of β-carotene against thermal treatment (55 °C for 12 days) and ultraviolet light exposure (8 h) was determined. The results suggested that the solidification of the oil phase can improve the stability of β-carotene, and gels with higher hardness were capable of retaining more β-carotene after the treatments. These findings indicated that emulsion gels with a solidified oil phase could be potential delivery systems for lipophilic bioactive compounds.

Rheological, structural, and microstructural properties of ethanol induced cold-set whey protein emulsion gels: Effect of oil content

The aim of this research was to prepare ethanol-induced cold-set emulsion gels contain different content of oil and to investigate the effect on the rheological, textural, and microstructural properties. The results showed that the gelation rate, gel strength, water-holding capacity (WHC), and hardness of the ethanol-set emulsion gels improved as the content of oil increased. Rheological analysis showed that the emulsion gels changed from combined polymer/particle gel behavior at low oil contents to particle gel behavior at high oil contents. The emulsion gels contained a three-dimensional network of aggregated oil droplets at high oil contents, while they contained an even distribution of isolated droplets at lower oil contents. The results showed that the properties of the ethanol-set emulsion gels could be modulated by altering the oil content because the oil droplets acted as active fillers. Ethanol-induced gelation presents an intriguing possibility for encapsulation of alcohol-soluble, lipid-soluble and heat-labile bioactive compounds.

Rheology and microstructure of myofibrillar protein-olive oil composite gels: effect of different non-meat protein as emulsifier

BACKGROUND

Heat-induced composite gels were prepared with 20 g kg^-1 (2%) myofibrillar protein (MP) sol and 100 g kg^-1 (10%) olive oil pre-emulsified by MP or non-meat protein in 0.6 mol L^-1 NaCl, at pH 6.2. The effect of different non-meat protein (soy protein isolate, egg-white protein isolate and sodium caseinate) pre-emulsions on the rheological properties and microstructure of MP gel was evaluated.

RESULTS

Adding emulsion enhanced the gel strength of MP gel except for the soy protein isolate (SPI) as emulsifier group, but all emulsion group markedly improved (P < 0.05) the water-holding capacity and the storage modulus (G') of MP gels. SDS-PAGE show that some non-meat protein bands partially participated in the formation of MP composite gels with different kinds of emulsion added. Micrographs revealed that these emulsions made the gels become denser and more compact with subtle diverse effects.

CONCLUSION

Different meat or non-meat proteins as emulsifier have varied impacts on the rheology and microstructure of MP gels, indicating the potential and feasibility of these non-meat proteins as emulsifiers to modify the textural properties in comminuted meat products. © 2017 Society of Chemical Industry.

Responsive Emulsion Gels with Tunable Properties Formed by Self-Assembled Nanofibrils of Natural Saponin Glycyrrhizic Acid for Oil Structuring

Saponin nanofibrils assembled from natural glycyrrhizic acid (GA) have been recently shown to be an effective structurant for edible oil structuring. This work showed that the microstructure and mechanical properties of the novel emulsion gels formed by GA fibrils could be well tuned by oil phase polarity. For more polar oils (algal oil), the GA fibrils had a higher affinity to the oil-water interface, showing a faster adsorption kinetics, thus leading to the formation of fine multilayer emulsion droplets with smaller droplet size. Accordingly, the emulsion gels had a denser network microstructure and higher mechanical strength, which should be attributed to the fact that the smaller emulsion droplets could be packed more tightly within the continuous network, providing stronger interdroplet interactions, and thereby contribute to reinforcing the gel matrix. In addition, all emulsion gels had interesting thermoresponsive behavior, independent of oil phase, which is probably due to the thermoreversibility of the hydrogen-bond fibrillar network in the continuous phase.

Oral processing of emulsion systems from a colloidal perspective

This review discusses recent understanding of the oral destabilization of food emulsions from a colloidal perspective.

Rheology of Emulsion-Filled Gels Applied to the Development of Food Materials

Emulsion-filled gels are classified as soft solid materials and are complex colloids formed by matrices of polymeric gels into which emulsion droplets are incorporated. Several structural aspects of these gels have been studied in the past few years, including their applications in food, which is the focus of this review. Knowledge of the rheological behavior of emulsion-filled gels is extremely important because it can measure interferences promoted by droplets or particle inclusion on the textural properties of the gelled systems. Dynamic oscillatory tests, more specifically, small amplitude oscillatory shear, creep-recovery tests, and large deformation experiments, are discussed in this review as techniques present in the literature to characterize rheological behavior of emulsion-filled gels. Moreover, the correlation of mechanical properties with sensory aspects of emulsion-filled gels appearing in recent studies is discussed, demonstrating the applicability of these parameters in understanding mastication processes.

Disintegration kinetics of food gels during gastric digestion and its role on gastric emptying: an in vitro analysis

The understanding of the disintegration and gastric emptying of foods in the stomach is important for designing functional foods.

Study on the rheological properties and volatile release of cold-set emulsion-filled protein gels

Emulsion-filled protein gels (EFP gels) were prepared through a cold-set gelation process, and they were used to deliver volatile compounds. An increase in the whey protein isolate (WPI) content from 4 to 6% w/w did not show significant effect on the gelation time, whereas an increase in the oil content from 5 to 20% w/w resulted in an earlier onset of gelation. Gels with a higher WPI content had a higher storage modulus and water-holding capacity (WHC), and they presented a higher force and strain at breaking, indicating that a more compact gel network was formed. An increase in the oil content contributed to gels with a higher storage modulus and force at breaking; however, this increase did not affect the WHC of the gels, and gels with a higher oil content became more brittle, resulting in a decreased strain at breaking. GC headspace analysis showed that volatiles released at lower rates and had lower air-gel partition coefficients in EFP gels than those in ungelled counterparts. Gels with a higher WPI content had lower release rates and partition coefficients of the volatiles. A change in the oil content significantly modified the partition of volatiles at equilibrium, but it produced a minor effect on the release rate of the volatiles. The findings indicated that EFP gels could be potentially used to modulate volatile release by varying the rheological properties of the gel.

Behaviour of whey protein emulsion gel during oral and gastric digestion: effect of droplet size

A set of whey protein stabilized-emulsion gels with different droplet size distributions (D4,3 = ∼1, 6 and 12 μm) was produced, and the mechanical properties of the gels in the linear viscoelastic region and at large deformation were measured, along with the physicochemical and structural changes of the gels during oral mastication and gastric digestion. The gels containing 1 μm oil droplets had an aggregated particle structure with proteins coating at oil droplets whereas the gels containing 12 μm oil droplets had a particle-filled structure with spatially continuous matrix. During oral processing, the release of oil droplets from the gels increased as the droplet size increased, with coalescence being seen in gels containing oil droplets of 6 and 12 μm diameter. Under gastric digestion, high degrees of coalescence and phase separation of oil droplets occurred in the gels containing 6 and 12 μm oil droplets because of oil droplet release from the gel matrix; this led to slow gastric emptying. The gels were finally broken down into peptide aggregates and oil droplets (or free oil). The gels, containing 1 μm oil droplets disintegrated into various particles of several to several tens of microns with a low degree of oil droplet release and coalescence. Protein breakdown was slower in these gels, suggesting that the protein structures of the gel matrices were affected by the sizes of the incorporated oil droplets.

Effect of gel structure on the gastric digestion of whey protein emulsion gels

This study aimed to characterize and determine the disintegration of emulsion gels in a human gastric simulator (HGS) and the physicochemical characteristics of gastric digesta. Using thermal treatment at 90 °C, whey protein emulsion gels with different structures and gel strengths were formed by varying the ionic strength. Simulated boluses of soft (containing 10 mM NaCl) and hard (200 mM NaCl) gels, which had similar particle sizes to those of human subjects, were created for gastric digestion. Soft gels disintegrated faster than hard gels in the HGS. The boluses of both gels gradually disintegrated into particles of size ∼10 μm. With further digestion, the protein matrix of the soft gel particles dissolved, the proteins were disrupted mainly by proteolysis and large quantities of oil droplets were released. In contrast, for the hard gel particles, although all proteins were hydrolysed after 240 min the breakdown of the particles was slow and no oil droplets were released after 300 min. The differences in the breakdown of soft and hard gels in the HGS were attributed to the structures of the emulsion gel, which may result in different sets of peptides in the digestion. In addition, coalescence of the oil droplets was observed only for the soft gel.

Influence of heat and shear induced protein aggregation on the in vitro digestion rate of whey proteins

Protein intake is essential for growth and repair of body cells, the normal functioning of muscles, and health related immune functions.