Yanxiang Gao

Investigation into the physicochemical stability and rheological properties of β-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.

Effects of Homogenization Models and Emulsifiers on the Physicochemical Properties of β-Carotene Nanoemulsions

Microfluidization and high pressure valve homogenization were applied to prepare β-carotene nanoemulsions, and the mathematical relationship between homogenization pressures and emulsion temperatures, homogenization pressures/cycles, and droplet sizes, were established. Emulsions through Microfluidizer had lower temperature and much smaller droplet sizes, compared with those through high pressure valve homogenizer. Four emulsifiers were compared for their capacities to stabilize nanoemulsions. The two large molecule emulsifiers, octenyl succinate starch (OSA) and whey protein isolate (WPI), were less effective for the formation of nanoemulsions with smaller droplets than the two small molecule emulsifiers, polyoxyethylene sorbitan monolaurate (Tween 20, TW) and decaglycerol monolaurate (DML). The nanoemulsion containing WPI was the most stable, while the one containing DML was the least stable. During storage, significant degradation of β-carotene occurred in all nanoemulsions, especially in the DML stabilized one, while WPI showed the greatest capacity to protect β-carotene from degradation.

Utilization of interfacial engineering to improve physicochemical stability of β-carotene emulsions: Multilayer coatings formed using protein and protein–polyphenol conjugates

The impact of lactoferrin (LF)-chlorogenic acid (CA) and (-)-Epigallocatechin-3-gallate (EGCG) conjugates on the physicochemical properties of β-carotene emulsions was investigated. Formation of lactoferrin-polyphenol conjugates, which was confirmed by SDS-PAGE, caused changes in the structure and nature of lactoferrin. Based on layer-by-layer electrostatic deposition, β-carotene bilayer emulsions were prepared by lactoferrin and lactoferrin-polyphenol conjugates at pH 7.0. The physicochemical properties of primary and secondary emulsions were evaluated and the results suggested that LF-polyphenol conjugates-stabilized primary and secondary emulsions exhibited better emulsifying properties and improved physical stability of β-carotene bilayer emulsions under freeze-thaw, ionic strength and thermal treatments. In addition, the lactoferrin-polyphenol conjugates could effectively enhance chemical stability of β-carotene in oil-in-water emulsions against heat treatment and ultraviolet light exposure, and the least degradation of β-carotene occurred in LF-EGCG conjugate-stabilized primary emulsion. The interfacial engineering technology utilized in this study may lead to the formation of emulsions with improved physicochemical and functional performance.

Structure and antimicrobial mechanism of ɛ-polylysine–chitosan conjugates through Maillard reaction

The aim of the study was to testify the formation and antimicrobial activity of ɛ-polylysine-chitosan conjugate through Maillard reaction. The results of UV absorbance, browning index and fluorescence changes of Maillard reaction products (MRPs) between ɛ-polylysine and chitosan indicated there existed Maillard reaction between ɛ-polylysine and chitosan and the formation of their conjugate. The conjugate showed strong antibacterial activity against Escherichia coli, Staphylococcus aureus, Bacillus subtilis and beer yeast. Morphologies of E. coli and S. aureus treated with the conjugate were observed by transmission electron microscopy (TEM). The results revealed that the conjugate of ɛ-polylysine and chitosan increased the permeability of the outer membrane (OM) and inner membrane (IM) and ultimately disrupted bacterial cell membranes, with the release of cellular cytoplasm.

Structural characterization and functional evaluation of lactoferrin–polyphenol conjugates formed by free-radical graft copolymerization

Covalent modifications of lactoferrin (LF) with epigallocatechin gallate (EGCG), chlorogenic acid (CA) and gallic acid (GA) were performed by adopting a free-radical grafting procedure in aqueous media. The resulting LF–polyphenol conjugates were characterized in terms of structural and functional properties. Results showed that the covalent binding amount into the LF molecule of EGCG, CA and GA was 68, 58 and 17 nmol mg−1, respectively. Covalent insertion of polyphenols into the LF molecule was verified by SDS-PAGE and MALDI-TOF-MS analysis, and in particular the molecular weight was increased from 84 011 Da (LF) to 85 906 Da (LF–CA conjugate). The circular dichroism and Fourier transform infrared spectroscopy analyses revealed that the content of α-helix increased and the contents of the remaining structures decreased, while the differential scanning calorimetry data indicated that the thermal stability of LF–polyphenol conjugates was enhanced after the modification. In addition, the antioxidant activity of LF–polyphenol conjugates was 0.23- to 2.10-fold (ABTS˙+ scavenging assay), and 0.04- to 2.19-fold (reducing power assay) higher than that of the control LF. Moreover, the covalent modification obviously changed the solubility and emulsifying properties of LF. The emulsifying properties of the LF–CA conjugate were better than those of the LF–EGCG and LF–GA conjugates.

Preparation and physicochemical properties of soluble dietary fiber from orange peel assisted by steam explosion and dilute acid soaking

The coupled pretreatment of orange peel with steam explosion (SE) and sulfuric-acid soaking (SAS) was investigated to enhance the yield and improve the functionality of soluble dietary fiber (SDF). When orange peel was pretreated by SE at 0.8MPa for 7 min, combined with 0.8% SAS, the content of SDF was increased from 8.04% to 33.74% in comparison to the control and SDF prepared with SE-SAS showed the high water solubility, water-holding capacity, oil-holding capacity, swelling capacity, emulsifying activity, emulsion stability and foam stability. SDF from orange peel treated by SE-SAS exhibited significantly (p < 0.05) higher binding capacity for three toxic cations (Pb, As and Cu) and smaller molecular weight (Mw = 174 kDa). Furthermore, differential scanning calorimetry (DSC) measurement showed that SDF from orange peel treated by SE-SAS had a higher peak temperature (170.7 ± 0.4 °C) than that of the untreated sample (163.4 ± 0.3 °C). Scanning electron micrograph (SEM) images demonstrated that the surface of SDF from orange peel treated by SE-SAS was rough and collapsed. It can be concluded that SDF from orange peel treated by SE-SAS has the higher potential to be applied as a functional ingredient in food products.

Molecular interaction between (−)-epigallocatechin-3-gallate and bovine lactoferrin using multi-spectroscopic method and isothermal titration calorimetry

The molecular interaction between bovine lactoferrin (LF) and (-)-epigallocatechin-3-gallate (EGCG) was investigated in an aqueous solution at pH6.0. The presence of EGCG did not change the size and turbidity of LF-EGCG complex in an aqueous solution until the LF/EGCG molar ratio was over a critical value of 1:25. The fluorescence spectra revealed that both tryptophanyl and tyrosyl groups of LF were associated with the interaction with EGCG. The infrared spectra of freeze-dried LF-EGCG complexes showed that they were different from those of LF and EGCG alone, FTIR and far-UV CD results indicated that EGCG induced a progressive increase in the proportion of α-helix structure at the cost of β-sheet structure of LF. The near-UV CD data testified that LF tertiary conformation was altered in the presence of EGCG. Isothermal titration calorimetry (ITC) analysis implied that EGCG was spontaneously bound to LF by a two-stage mechanism, about 31 EGCG molecules were integrated with 1 molecule LF and hydrogen bonds were always involved in the assembly process.

Food‐Grade Covalent Complexes and Their Application as Nutraceutical Delivery Systems: A Review

Food proteins, polysaccharides, and polyphenols are 3 major food constituents with distinctly different functional attributes. Many proteins and polysaccharides are capable of stabilizing emulsions and foams, thickening solutions, and forming gels, although they differ considerably in their abilities to provide these functional attributes. Many plant polyphenols exhibit beneficial physiological functions, such as antitumor, antioxidant, antibacterial, and antiviral properties. Proteins, polysaccharides, and polyphenols can form complexes with each other, which leads to changes in the functional and nutritional properties of the combined systems. Recently, there has been considerable interest in understanding and utilizing covalent interactions between polyphenols and biopolymers (proteins and polysaccharides). The binary or tertiary conjugates formed may be designed to have physicochemical properties and functional attributes that cannot be achieved using the individual components. This article provides a review of the formation, characterization, and utilization of conjugates prepared using proteins, polysaccharides, and polyphenols. It also discusses the relationship between the structural properties and functionality of the conjugates, and it highlights the bioavailability of bioactive compounds loaded in conjugate-based delivery systems. In addition, it highlights the main challenges to be considered when preparing and analyzing conjugates. This article provides an improved understanding of the chemical reactions that occur between major food ingredients and how they can be utilized to develop biopolymer-based delivery systems with enhanced functional attributes.

A novel copigment of quercetagetin for stabilization of grape skin anthocyanins.

The thermal and light stability of grape skin anthocyanins combined with quercetagetin was investigated at designed pH values of 3, 4 and 5. The molar ratios of anthocyanins to quercetagetin were 1:10, 1:20 and 1:40 for thermally treatment at 70 °C, 80 °C and 90 °C, respectively, and the ratios were tested at 5:1, 1:1, 1:5 and 1:10 in the light exposure experiments. The degradation reaction of anthocyanins in the presence of quercetagetin followed the first-order kinetic model. The half-life (t₁/₂) of anthocyanins was extended significantly with the increase of quercetagetin concentration (p<0.05). The total colour difference values (ΔE(∗)) for the anthocyanin solutions with quercetagetin were smaller than those without copigment under the same experimental conditions (pH and light exposure time). Compared with epigallocatechin gallate (EGCG), tea polyphenols (TP), myricitrin and rutin, quercetagetin was the most effective copigment to stabilize grape skin anthocyanins.

Covalent complexation and functional evaluation of (-)-epigallocatechin gallate and α-lactalbumin.

The covalent complexation between (-)-epigallocatechin gallate (EGCG) and α-lactalbumin (α-La), and the effect of EGCG on the antioxidative activity and emulsifying properties of α-La were investigated. The turbidity of a solution of 1% α-La and 0.2% EGCG decreased after 24h reaction at pH 8.0 and 60°C, less than the value of α-La alone. The interaction between α-La and EGCG at pH 8.0 was more pronounced than that at pH 6.0 or 7.0, as evidenced by the reduced amplitude of amide A, and I, and II bands of α-La by FT-IR and the increase in the total phenolic content and denaturation temperature. These results implied that EGCG was covalently linked to α-La at pH 8.0. In addition, compared with the control of α-La, α-La-EGCG complexes had significantly increased antioxidative activity. The emulsions stabilized by α-La-EGCG complexes, compared with that by α-La alone, had much smaller droplet sizes, which indicated the emulsifying property of α-La was improved.