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The effects of lecithin addition at different concentrations (0-2.0%) on the physicochemical and emulsifying properties of mussel water-soluble proteins (MWP) were investigated. In solution system, low lecithin concentration (0.5%-1.0%) induced the aggregation and increased turbidity of composite particles. Lecithin addition caused changes in secondary structure and induced partial unfolding of MWP. Hydrophobic interactions between MWP and lecithin may contribute to the exposure of chromophores and hydrophobic groups of MWP. The interfacial tension decreased with lecithin addition. However, at a high lecithin concentration (1.5%-2.0%), the degree of aggregation and state of unfolding alleviated due to competitive adsorption. In emulsion system, with the low concentration of lecithin addition (0.5%-1.0%), droplet size and surface charge of emulsion decreased. The emulsion activity index, emulsion stability index, percentage of adsorbed protein increased. Both creaming stability and viscoelastic properties improved. At an intermediate lecithin concentration (1.0%), the emulsion showed the highest physical stability, while further addition of lecithin caused a slight deterioration in emulsifying properties. Overall, these results indicated the possibility that the lecithin-MWP mixed emulsifiers can be used to obtain emulsions with desirable properties.

In order to expand the utilization of shellfish proteins in various products, the physicochemical, rheological and emulsifying properties of oyster myofibrillar protein (OMP) affected by high-pressure homogenization (HPH) were evaluated. HPH (0, 40, 80 and 120 MPa) was applied to treat OMP dispersion. The results showed that HPH at varying pressures (0, 40, 80 and 120 MPa) led to changes in physicochemical, rheological and emulsifying properties of OMP. The shear stress, apparent viscosity and the viscosity coefficients (k) decreased, but flow index (n) increased. EAI, ESI, AP% and creaming stability increased but droplet size distribution of emulsions became narrower. Absolute zeta potential and protein solubility increased but particle size and turbidity of OMP reduced after HPH treatment. HPH changed the OMP secondary structure and caused tertiary and quaternary structural changes. The HPH treatment contribute to improvement in OMP rheological and emulsifying properties, and 80 MPa was the optimum pressure for modification. The improvements in functional properties of OMP could be attributed to its unfolded conformation structure with reduced particle size and higher surface net charges produced by HPH. The findings of improved functional properties demonstrated the potential use of OMP as protein supplement in formulated foods.

Emulsifiers are usually incorporated in emulsion preparation to make kinetically stable emulsions. HPH is often used to prepare food emulsions, producing stable emulsion with fine texture. The purpose of this study is to investigate the effect of high-pressure homogenization (HPH) at 40, 80 and 120 MPa on oil-in-water (O/W) emulsion stabilized with mussel myofibrillar proteins (MMP) and lecithin. Emulsifying properties, creaming index, microstructure, particle size and zeta-potential, apparent viscosity of HPH treated emulsions, together with protein solubility and surface hydrophobicity were analyzed. HPH treatment resulted in increase in emulsifying activity index (from 56.93 to 87.68 m2/g), emulsifying stability index (from 59.33 to 154.62 min), apparent viscosity and absolute zeta-potential (from 10.67 to 37.03 mV) of MMP and lecithin stabilized O/W emulsion. Droplets size (from 3.95 to 0.46 μm) and creaming index of high-pressure homogenized emulsion reduced. These changes may resulte from the improved solubility (from 16.5% to 75.1%) and exposed hydrophobic groups (from 196.37 to 258.50) of MMP. The most suitable processing pressure to produce fine and stable emulsions was 80 MPa. These results will contribute for improving the formulation of emulsions and their properties and provide new understanding into MMP as a natural emulsifier in the food production.

The present work investigated effects of high-pressure homogenization (HPH) pressure (0, 40, 80 and 120 MPa) on physicochemical, functional and rheological properties of clam myofibrillar protein (CMP). Results showed that HPH changed the CMP secondary and tertiary structures. Absolute zeta potential and protein solubility increased but particle size and turbidity of CMP decreased after HPH treatment. Both of emulsifying properties and foaming properties were significantly improved. The shear stress, apparent viscosity and the viscosity coefficients reduced, but flow index increased. Application of HPH improved the physicochemical, functional and rheological properties of CMP, and 120 MPa was the optimal pressure for modification.

The interaction between sodium alginate (SA) and turbot myofibrillar proteins (TMP) and the effects of SA concentration (0.1%-0.5%) on the rheological and emulsifying properties of the mixture at neutral pH were investigated. TMP and SA formed complexes through electrostatic repulsion and hydrophobic interaction. The FT-IR analysis indicated that hydrogen bonding was also related to the interaction. With the addition of SA, the electrostatic repulsion between molecules enhanced, which prevented protein aggregation and improved the stability of dispersions. The TMP/SA mixture showed non-Newtonian shear-thinning behavior. The viscosity gradually increased with the increasing SA concentration. TMP and SA formed an interconnected gel-like network structure with a predominant elastic behavior. The strength of network increased due to the strong repulsion between the two biopolymers. Both EAI and ESI of TMP significantly increased after SA addition. The addition of SA reduced droplet size of emulsions. The emulsions also showed pseudoplastic behavior. Addition of SA increased stability of emulsions by increasing viscosity of continuous phase. Complexation with SA effectively improved the rheological and emulsifying properties of fish myofibrillar proteins. These results contributed to the efficient utilization of marine fish proteins as functional ingredients in food products.

Structural and functional changes in ultrasonicated oyster protein isolates (OPI) were investigated. Ultrasound treatments were carried out with probe (20 kHz) at 200, 400 and 600 W for 15 and 30 min. The results showed that functional properties of OPI significantly improved after sonication. Absolute zeta potential and protein solubility increased by 18.40 mV and 82.5 % at 600 W for 15 min. Oil holding capacity, emulsifying activity index, emulsion stability index, foaming ability and foaming stability increased by 300 %, 15.23 m2/g, 9.24 min, 23.9 % and 14.8 % at 600 W for 30 min. However, ultrasound treatment significantly (P< 0.05) decreased particle size and water holding capacity. The conformation of OPI became stretched and unfolded after sonication. Functional improvements resulted from stretched and unfolded conformation and reduction of particle size. Controlled condition of ultrasound can produce OPI with distinct structural and functional properties, which could meet the complex needs of manufactured food products in food industry, but further study is needed to understand the specific mechanism.

The effects of HPH (high-pressure homogenization) pre-treatment on the functional properties of OPIH (oyster protein isolates hydrolysates) were studied. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles, solubility, particle size distribution, zeta potential, surface hydrophobicity, emulsifying activity index and microstructure of emulsions were analyzed. Results indicated that HPH pre-treatment increased the accessibility of OPI to trypsin hydrolysis, resulting in decease in particle size, increase in solubility, absolute zeta potential, surface hydrophobicity and emulsifying activity index. In addition, HPH pre-treated OPIH emulsions became more uniform and the particle size of droplets decreased. These results revealed that HPH pre-treatment has the potential to modify the functional properties of OPIH.

This study investigated the effects of high-intensity ultrasonication (HIUS) treatment (0, 5, 10, 20, 30 min) on the physicochemical and functional properties of mussel sarcoplasmic proteins (MSP). MSP dispersion was treated by HIUS (20 kHz) at 600 W for 5, 10, 20 and 30 min. The results showed that HIUS treatment changed the physicochemical properties of MSP, thereby increasing the stability of the emulsion stabilized by ultrasonicated MSP. HIUS treatment improved the functional properties of MSP, including solubility, foaming ability, foaming stability, emulsifying activity index, emulsifying stability index, percentage of adsorbed proteins. More uniform emulsions with smaller droplets and higher stability were observed. There was a decrease in particle size, zeta-potential and turbidity of ultrasonicated MSP. Proteins partially unfolded as a result of HIUS treatment. Associations between conformation structure, physicochemical properties and functional properties were also found. It can be speculated that improvements in functional properties were caused by the changes in conformation structure and physicochemical properties. The results suggested that HIUS treatment has great potential in modifying the foaming and emulsifying properties of shellfish proteins, and ultrasonication treatment at 20 kHz, 600 W for 20 min was the optimum condition for modification.