Polymer or microgel particle: Differences in emulsifying properties of pectin as microgel or as individual polymer chains

Texturing of Soy Yoghurt Alternatives: Pectin Microgel Particles Serve as Inactive Fillers and Weaken the Soy Protein Gel Structure

Soy-based yoghurt alternatives were highly requested by consumers over the last few years. However, their texture does not always fulfil consumers' demands as such yoghurt alternatives are often perceived as too firm or too soft, sandy, or fibrous. In order to improve the texture, fibres, for example, in the form of microgel particles (MGP), can be added to the soy matrix. MGP are expected to interact with soy proteins, creating different microstructures and, thus, different gel properties after fermentation. In this study, pectin-based MGP were added in different sizes and concentrations, and the soy gel properties after fermentation were characterised. It was found that the addition of 1 wt.% MGP influenced neither the flow behaviour nor the tribological/lubrication properties of the soy matrix, regardless of the MGP size. However, at higher MGP concentrations (3 and 5 wt.%), the viscosity and yield stress were reduced, the gel strength and cross-linking density decreased, and the water-holding capacity was reduced. At 5 wt.%, strong and visible phase separation occurred. Thus, it can be concluded that apple pectin-based MGP serve as inactive fillers in fermented soy protein matrices. They can, therefore, be used to weaken the gel matrix purposely to create novel microstructures.

Effect of a Change in the CaCl2/Pectin Mass Ratio on the Particle Size, Rheology and Physical Stability of Lemon Essential Oil/W Emulgels

A three-step (rotor-stator-microfluidization-rotor stator) protocol was used to prepare 15% lemon essential oil in water emulgels using a mixture of Tween 80 and Span 20 surfactants as low molecular mass emulsifiers and 0.4% low-methoxyl citrus peel pectin as a gelling agent. Ca2+ was used as a gel-promoting agent. Different CaCl2/pectin mass ratio values from 0.3 to 0.7 were used. Emulgels showed a microstructure consisting of oil droplets embedded in a sheared gel matrix, as demonstrated by bright field optical microscopy. Laser diffraction tests showed multimodal particle size distributions due to the coexistence of oil droplets and gel-like particles. Multiple light scattering tests revealed that the physical stability of emulgels was longer as the CaCl2/pectin mass ratio decreased and that different destabilization mechanisms took place. Thus, incipient syneresis became more important with increasing CaCl2 concentration, but a parallel creaming mechanism was detected for CaCl2/pectin mass ratio values above 0.5. Dynamic viscoelastic and steady shear flow properties of the emulgels with the lowest and highest CaCl2/pectin mass ratio values were compared as a function of aging time. The lowest ratio yielded an emulgel with enhanced connectivity among fluid units as indicated by its wider linear viscoelastic region, higher storage modulus, loss modulus and viscosity values, and more shear thinning properties than those of the emulgel formulated with the highest CaCl2/pectin mass ratio. The evolution of the dynamic viscoelastic properties with aging time was consistent with the information provided by monitoring scans of backscattering as a function of sample height.

Can Enzymatic Treatment of Sugar Beet Pectins Reduce Coalescence Effects in High-Pressure Processes?

While sugar beet pectins (SBPs) are well known for effectively stabilizing fine oil droplets in low-fat food and beverages, e.g., low-fat dressings and soft drinks, it often fails in products of higher oil contents. The aim of this study was to improve the emulsifying properties of SBPs and, consequently, their ability to reduce coalescence during high pressure homogenization of products with increased oil content. Therefore, the molecular size of SBPs was reduced by partial cleavage of the homogalacturonan backbone using the enzymes exo- and endo-polygalacturonanase and varying incubation times. The sizes of SBPs were compared based on the molecular size distribution and hydrodynamic diameter. In addition, to obtain information on the interfacial activity and adsorption rate of SBPs, the dynamic interfacial tension was measured by drop profile analysis tensiometry. The (non)modified SBPs were used as emulsifying agents in 30 wt% mct oil–water emulsions stabilized with 0.5 wt% SBP at pH 3, prepared by high-pressure homogenization (400–1000 bar). By analyzing the droplet size distributions, conclusions could be drawn about the coalescence that occurred after droplet breakup. It could be shown that SBPs modified by exo-polygalacturonanase stabilized the oil–water interface more rapidly, resulting in less coalescence and the smallest oil droplets. In contrast, SBPs modified with endo-polygalacturonanase resulted in poorer emulsification properties, and thus larger oil droplets with increasing incubation time. The differences could be attributed to the different cleavage pattern of the enzymes used. The results suggest that a minimum molecular size is required for the stabilization of fine oil droplets with SBPs as emulsifiers.

Texturing Fermented Emulsion Gels from Soy Protein: Influence of the Emulsifying Agent—Soy Protein vs. Pectin Microgels—On Gel Microstructure, Rheology and Tribology

Soy-based yoghurt alternatives are nowadays preferred by consumers. However, they are often perceived as too firm or too soft, sandy, or fibrous. In order to improve this, fibres, especially as in form of microgel particles (MGP), and fats are added to the soy matrix to create a creamy mouthfeel. Both fat and pectin-based MGP can interact with each other and with the protein matrix, creating different microstructures. This can influence the rheological and tribological properties of plant-based protein gels. This works focuses on the effect droplet stabilisation (coconut oil) on the rheological and tribological behaviour of the fermented stirred soy protein gels. For this, fat droplets were stabilised with MGP, SPI, or a mixture of both. Whilst the rheological behaviour remained unchanged for all investigated samples, the tribology of the samples depended on the emulsifier used. The addition of fat decreased the traction coefficient compared to the reference samples without fat. Even though all samples had the same fat content and identical droplet sizes, differences were observed in their lubricating properties. Droplets stabilised solely with SPI presented the best lubricating properties, as indicated by the lowest traction coefficient. Samples stabilised with MGP (or in mixture with SPI) caused higher friction.

Emulsions stabilised with pectin-based microgels: investigations into the effect of pH and ionic strength on emulsion stability

Pectin-based microgel particles (MGPs) are encouraging sustainable emulsifying agents for food-applications. Based on polyelectrolytes, pectin-based MGPs are assumed to be pH and ionic strength sensitive, in a similar manner to MGPs of synthetic polymers. Besides building a barrier around oil droplets, charged MGPs repulse each other. Thus the stabilisation mechanisms of pectin-based MGPs should be both steric and electrostatic. To investigate this, emulsions were homogenised with MGP concentrations ranging from 0.5 to 2 wt% MGPs. After emulsification, the pH of the emulsions was adjusted to 4, 3, or 2; and the resulting droplet sizes were measured. We found out that the droplet size and the appearance of agglomerates increased with decreasing pH values. This was caused by the loss of the MGP surface charge, as stated by their ζ-potential, showing an increase from -33.71 ± 4.1 mV for samples with pH 4 to -17 ± 0.6 mV, and -3.4 ± 0.6 mV for pH 3 and 2, respectively. However, the degree of coalescence was dependent on the MGP concentration, as samples with 0.5 wt% coalesced more readily than samples with 2 wt% MGP. These results help understand the emulsion stabilisation mechanisms of pectin-based MGPs and what effect formulation parameters have on the long-term stability of MGP-stabilised emulsions.

Modified Rhamnogalacturonan-Rich Apple Pectin-Derived Structures: The Relation between Their Structural Characteristics and Emulsifying and Emulsion-Stabilizing Properties

In the context of the increasing interest in natural food ingredients, the emulsifying and emulsion-stabilizing properties of three rhamnogalacturonan-rich apple pectin-derived samples were assessed by evaluating a range of physicochemical properties. An apple pectin (AP74) was structurally modified by a β-eliminative reaction to obtain a RG-I-rich pectin sample (AP-RG). Subsequent acid hydrolysis of AP-RG led to the generation of pectin material with partially removed side chains (in particular arabinose depleted) (AP-RG-hydrolyzed), thus exhibiting differences in rhamnose, arabinose, and galactose in comparison to AP-RG. All samples exhibited surface activity to some extent, especially under acidic conditions (pH 2.5). Furthermore, the viscosity of the samples was assessed in relation to their emulsion-stabilizing properties. In a stability study, it was observed that the non-degraded AP74 sample at pH 2.5 exhibited the best performance among all the apple pectin-derived samples evaluated. This emulsion presented relatively small oil droplets upon emulsion production and was less prone to creaming than the emulsions stabilized by the (lower molecular weight) RG-I-rich materials. The AP-RG and AP-RG-hydrolyzed samples presented a slightly better emulsion stability at pH 6.0 than at pH 2.5. Yet, neither pectin sample was considered having good emulsifying and emulsion-stabilizing properties, indicated by the presence of coalesced and flocculated oil droplets.