Effect of pH on the functional behaviour of pea protein isolate–gum Arabic complexes

Improving functional properties of pea protein isolate for microencapsulation of flaxseed oil

Unhydrolysed pea protein (UN) forms very viscous emulsions when used at higher concentrations. To overcome this, UN was hydrolysed using enzymes alcalase, flavourzyme, neutrase, alcalase-flavourzyme, and neutrase-flavourzyme at 50 °C for 0 min, 30 min, 60 min, and 120 min to form hydrolysed proteins A, F, N, AF, and NF, respectively. All hydrolysed proteins had lower apparent viscosity and higher solubility than UN. Foaming capacity of A was the highest, followed by NF, N, and AF. Hydrolysed proteins N60, A60, NF60, and AF60 were prepared by hydrolysing UN for 60 min and used further for microencapsulation. At 20% oil loading (on a total solid basis), the encapsulated powder N60 had the highest microencapsulation efficiency (ME = 56.2). A decrease in ME occurred as oil loading increased to 40%. To improve the ME of N60, >90%, UN and maltodextrin were added. Flowability and particle size distribution of microencapsulated powders with >90% microencapsulation efficiency and morphology of all powders were investigated. This study identified a new way to improve pea protein functionality in emulsions, as well as a new application of hydrolysed pea protein as wall material for microencapsulation.

Characteristics of soy protein isolate/gum arabic-stabilized oil-in-water emulsions: influence of different preparation routes and pH

pH adjustment before or after homogenization with oil greatly influenced the droplet size and emulsifying stability of emulsions.

Effect of genotype on the physicochemical and functional attributes of faba bean (Vicia faba L.) protein isolates

The functionality and surface characteristics of protein isolates prepared from seven genotypes of faba bean were investigated. All factors studied were independent of genotype. The average protein and isolate (~94% protein) yields were ~77% and ~25%, respectively, using an alkaline extraction process followed by isoelectric precipitation. The overall averages were: surface charge +22.1 mV, surface hydrophobicity 47.2 arbitrary units, and surface and interfacial tensions of 65.0 mN/m and 10.7 mN/m, respectively. The ratio of the major globulin fractions (legumin:vicilin) shifted from 3.8 for the flours to 4.5 in the isolates. Average values for foaming capacity and stability, emulsion capacity, creaming stability, oil holding capacity, emulsifying activity and stability indices, and solubility were 162.0%, 65.0%, 184.0 g/g, 94.0%, 5.7 g/g, 13.0 m²/g, 10.7 min, and 81.0%, respectively. The lack of significant varietal effects would be advantageous to food processors as the source of the feedstock would not affect ingredient functionality.

Interaction and formation mechanism of binary complex between zein and propylene glycol alginate

The anti-solvent co-precipitation method was used to fabricate the zein-propylene glycol alginate (PGA) binary complex with different mass ratios of zein to PGA (20:1, 10:1, 5:1, 2:1 and 1:1) at pH 4.0. Results showed that attractive electrostatic interaction between zein and PGA occurred and negatively charged binary complex with large size and high turbidity was formed due to the charge neutralization. Hydrogen bonding and hydrophobic effects were involved in the interactions between zein and PGA, leading to the changed secondary structure and improved thermal stability of zein. Aggregates in the irregular shape with large size were obviously observed in the AFM images. PGA alone exhibited a fine filamentous network structure, while zein-PGA binary complex showed a rough branch-like pattern and the surface of "branch" was closely adsorbed by lots of spherical zein particles. Q in zein-PGA binary complex dispersions presented the improved photochemical and thermal stability. The potential mechanism of a two-step process was proposed to explain the formation of zein-PGA binary complexes.

Influence of pea protein aggregates on the structure and stability of pea protein/soybean polysaccharide complex emulsions

The applications of plant proteins in the food and beverage industry have been hampered by their precipitation in acidic solution. In this study, pea protein isolate (PPI) with poor dispersibility in acidic solution was used to form complexes with soybean soluble polysaccharide (SSPS), and the effects of PPI aggregates on the structure and stability of PPI/SSPS complex emulsions were investigated. Under acidic conditions, high pressure homogenization disrupts the PPI aggregates and the electrostatic attraction between PPI and SSPS facilitates the formation of dispersible PPI/SSPS complexes. The PPI/SSPS complex emulsions prepared from the PPI containing aggregates prove to possess similar droplet structure and similar stability compared with the PPI/SSPS emulsions produced from the PPI in which the aggregates have been previously removed by centrifugation. The oil droplets are protected by PPI/SSPS complex interfacial films and SSPS surfaces. The emulsions show long-term stability against pH and NaCl concentration changes. This study demonstrates that PPI aggregates can also be used to produce stable complex emulsions, which may promote the applications of plant proteins in the food and beverage industry.

The physicochemical properties of legume protein isolates and their ability to stabilize oil-in-water emulsions with and without genipin

The physicochemical and emulsifying properties of legume protein isolates prepared from chickpea (CPI), faba bean (FPI), lentil (LPI) and soy (SPI) were investigated in the presence and absence of genipin. Solubility was highest for CPI (~94 %), followed by LPI (~90 %), FPI (~85 %) and SPI (~50 %). Surface characteristics revealed similar zeta potentials (~ - 47 mV) for CPI, LPI and FPI, but lower for SPI (~ - 44 mV). Contrastingly, surface hydrophobicity was greatest for CPI (~137 arbitrary units, AU), followed by SPI/LPI (~70 AU) and FPI (~24 AU). A significant (from 16.73 to ~8.42 mN/m) reduction in interfacial tension was observed in canola oil-water mixtures in the presence of non-crosslinked legume protein isolates. The extent of legume protein isolate-genipin crosslinking was found to be similar for all isolates. Overall, creaming stability increased in the presence of genipin, with maximum stability observed for SPI (65 %), followed by FPI (61 %), LPI (56 %) and finally CPI (50 %).

A review of the preparation and application of flavour and essential oils microcapsules based on complex coacervation technology

This paper briefly introduces the preparation and application of flavour and essential oils microcapsules based on complex coacervation technology. The conventional encapsulating agents of oppositely charged proteins and polysaccharides that are used for microencapsulation of flavours and essential oils are reviewed along with the recent advances in complex coacervation methods. Proteins extracted from animal-derived products (gelatin, whey proteins, silk fibroin) and from vegetables (soy proteins, pea proteins), and polysaccharides such as gum Arabic, pectin, chitosan, agar, alginate, carrageenan and sodium carboxymethyl cellulose are described in depth. In recent decades, flavour and essential oils microcapsules have found numerous potential practical applications in food, textiles, agriculturals and pharmaceuticals. In this paper, the different coating materials and their application are discussed in detail. Consequently, the information obtained allows criteria to be established for selecting a method for the preparation of microcapsules according to their advantages, limitations and behaviours as carriers of flavours and essential oils.

Complexation of sodium caseinate with gum tragacanth: Effect of various species and rheology of coacervates

We investigated complex coacervation of sodium caseinate/Astragalus rahensis (A.r) as a function of pH with light scattering, spectrophotometry, and viscosity measurements. Interestingly, sodium caseinate/A.r displayed five structural transitions; pH 7.00 to pH ∼5.40: no interaction occurred, pH ∼5.40 to pH ∼4.80: initiation of the formation of primary soluble complexes, pH ∼4.80 to ∼4.30: formation of interpolymer complexes, pH ∼4.30 to ∼4.02: optimum coacervation and pH ∼4.02 to ∼2.50: suppression of coacervation. In addition, rheological properties of sodium caseinate/A.r coacervates were studied at various pH values. A much higher storage modulus (G') than loss modulus (G″) for all sodium caseinate/A.r coacervates suggests the formation of highly interconnected gel-like network structures with mainly elastic behaviour. Moreover, sodium caseinate/A.r coacervates at all pH values exhibited a shear thinning behaviour across the entire shear rate range investigated. Effects of different species of gum tragacanth on the interactions with sodium caseinate have been scarcely studied. Our study showed that systems containing various species (A.r, soluble fraction of A.r and Astragalus gossypinus (A.g)) had different critical pH values and particle sizes during complex coacervation, which could be due to different ratio of soluble to insoluble fractions and uronic acid content of various species.

Soy protein/soy polysaccharide complex nanogels: folic acid loading, protection, and controlled delivery

In this study, we developed a facile approach to produce nanogels via self-assembly of folic acid, soy protein, and soy polysaccharide. High-pressure homogenization was introduced to break down the original aggregates of soy protein, which benefits the binding of soy protein with soy polysaccharide and folic acid at pH 4.0. After a heat treatment that causes the soy protein denaturation and gelation, folic acid-loaded soy protein/soy polysaccharide complex nanogels were fabricated. The nanogels have a polysaccharide surface that makes the nanogels dispersible in acidic conditions where folic acid is insoluble and soy protein forms precipitates after heating. More importantly, the protein and polysaccharide can inhibit the reactions between dissolved oxygen and folic acid during UV irradiation. After the preparation and storage of the nanogels in the presence of heat, oxygen, and light in acidic conditions, most of the folic acid molecules in the nanogels remain in their natural structure and can be released rapidly at neutral pH, that is, in the intestine. Because most food and beverages are acidic, the nanogels are a suitable delivery system of folic acid in food and beverages.

Food proteins: a review on their emulsifying properties using a structure-function approach

Proteins are of great interest due to their amphiphilic nature, which allows them to reduce the interfacial tension at the oil-water interface. The incorporation of proteins at the oil-water interface has allowed scientists to utilise them to form emulsions (O/W or W/O), which may be used in food formulations, drug and nutrient delivery. The systematic study of the proteins at the interface and the factors that affect their stability (i.e., conformation, pH, solvent conditions, and thermal treatment) has allowed for a broader use of these emulsions tailored for various applications. In this review, the factors affecting the stability of emulsions using food proteins will be discussed. The use of polysaccharides to complex with proteins will also be explored in relation to enhancing emulsion stability.

Stable nano-sized emulsions produced from soy protein and soy polysaccharide complexes

In this research, a simple, green and effective strategy was developed to produce long-term stable oil in water emulsion from soy protein and soy polysaccharide. Soy protein and soy polysaccharide formed dispersible complexes at pH around 3.25 aqueous solution through electrostatic and hydrophobic interactions. A high pressure homogenization produced the protein/polysaccharide complex emulsion having a droplet size about 250 nm. A heat treatment of the emulsion resulted in the protein denaturation, forming irreversible oil-water interfacial films composed of soy protein/soy polysaccharide complexes. The droplets of the emulsion were characterized by dynamic light scattering, ζ-potential, transmission electron microscopy, polysaccharide digestion via pectinase, and confocal laser scanning microscopy observation via dual fluorescence probes. As a result of the polysaccharide being fixed on the droplet surface, the emulsions exhibited long-term stability in the media containing pH values of 2-8 and 0.2 mol/L NaCl. The stable soy protein/soy polysaccharide complex emulsion is a suitable food-grade delivery system in which lipophilic bioactive compounds can be encapsulated.

Investigation into the physicochemical stability and rheological properties of beta-carotene emulsion stabilized by soybean soluble polysaccharides and chitosan

In this study, the possibility of producing stable O/W emulsions incorporating beta-carotene in oil droplets surrounded by multiple-layer interfacial membranes has been demonstrated. Emulsions were prepared using a two-stage process by homogenization, which relied on the adsorption of chitosan to anionic droplets coated with soybean soluble polysaccharides (SSPS). Results showed that the zeta-potential, particle size, and rheological properties of emulsions were greatly dependent on the chitosan concentration. The electrical charge on the droplets increased from -34 to 58.2 mV as the chitosan concentration was increased from 0 to 2 wt %, which indicated that chitosan adsorbed to the droplet surfaces. The mean particle diameter of the emulsions increased dramatically with the rise of chitosan concentration from 0 to 0.33 wt %, indicating the formation of large aggregated structures. At chitosan concentrations above 0.33 wt %, the mean particle diameter of emulsions decreased and reached a minimum value of 0.79 mum at a chitosan concentration of 0.5 wt %. Dynamic oscillatory shear tests indicated that the viscoelastic behavior could be enhanced by the adsorption of chitosan onto the SSPS-coated droplet surfaces. Chitosan concentration had a significant (p < 0.05) impact on the stability of beta-carotene. The least degradation occurred in the emulsion with chitosan concentration of 0.5%. These results implied that the physicochemical stability of beta-carotene emulsions has been improved by the adsorption of chitosan.