Zongcai Tu

Relationship between functional properties and aggregation changes of whey protein induced by high pressure microfluidization.

Aggregation changes of whey protein induced by high-pressure microfluidization (HPM) treatment have been investigated in relation with their functional properties. Whey protein was treated with HPM under pressure from 40 to 160 MPa. Functional properties (solubility, foaming, and emulsifying properties) of whey protein concentrate (WPC) ultrafiltered from fluid whey were evaluated. The results showed significant modifications in the solubility (30% to 59%) and foaming properties (20% to 65%) of WPC with increasing pressure. However, emulsifying property of WPC treated at different pressures was significantly worse than untreated sample. To better understand the mechanism of the modification by HPM, the HPM-induced aggregation changes were examined using particle size distribution, scanning electron microscopy, and hydrophobicity. It was indicated that HPM induced 2 kinds of aggregation changes on WPC: deaggregation and reaggregation of WPC, which resulted in the changes of functional properties of WPC modified by HPM.

Aggregation and conformational changes of bovine β-lactoglobulin subjected to dynamic high-pressure microfluidization in relation to antigenicity.

Our previous research indicated that dynamic high-pressure microfluidization (DHPM) had a significant effect on the antigenicity of β-lactoglobulin (β-LG). In this study, aggregation and conformational changes subjected to DHPM (0.1-160 MPa) were investigated in relation to antigenicity. When DHPM pressure increased from 0.1 to 80 MPa, disaggregation of β-LG samples and partial unfolding of the molecule were accompanied by an increase in β-LG antigenicity, which was reflected in the decrease of particle size, increase of free sulfhydryl (SH) contents and β-strands contents, and slight exposure of aromatic amino acid residues. At pressures above 80 MPa, the reaggregation of β-LG may contribute to the decrease in antigenicity, which was reflected by an increase in particle size, the formation of aggregates, a decrease of in SH and β-strands contents, and slight changes in aromatic amino acid residues. Aggregation and conformational changes of β-LG under DHPM was related to its antigenicity.

Pectin and enzyme complex modified fish scales gelatin: Rheological behavior, gel properties and nanostructure

The rheological behavior, gel properties and nanostructure of complex modified fish scales gelatin (FSG) by pectin and microbial transglutaminase (MTGase) were investigated. The findings suggested that MTGase and pectin have positive effect on the gelation point, melting point, apparent viscosity and gel properties of FSG. The highest values of gel strength and melting temperature could be observed at 0.8% (w/v) pectin. Nevertheless, at highest pectin concentration (1.6% w/v), the gel strength and melting temperature of complex modified gelatin gels decreased. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis revealed that MTGase catalyzed cross-links among soluble fish scales gelatin - pectin complexes, which could be responsible for the observed increase in rheological behavior, gel strength and melting temperature of modified complex gels.

Antigenicity and functional properties of β-lactoglobulin conjugated with fructo-oligosaccharides in relation to conformational changes

Bovine β-lactoglobulin (β-LG) was conjugated with fructo-oligosaccharides (FOS) by Maillard reaction to investigate the relationship among antigenicity, functional properties, and conformational changes of β-LG. When comparing the antigenicity of β-LG conjugated with FOS at different ratios, the lowest antigenicity of β-LG was observed at a ratio of 1:4, which was about 7 times lower than that of the control β-LG. Thus, the ratio of 1:4 was chosen to conjugate β-LG with FOS, and the functional properties and conformational changes of β-LG-FOS conjugates were investigated. The functional properties (solubility, emulsifying ability, and emulsion stability) of β-LG were enhanced after conjugation with FOS. Furthermore, the molecular weight of β-LG increased from 18.4 to 19.9 kDa after conjugation with FOS, as evaluated by sodium dodecyl sulfate-PAGE and mass spectrometry. Partial unfolding of β-LG occurred after conjugation with FOS, as reflected by the quenching of fluorescence, the red-shift of fluorescence spectra, and the increase of β-strands, which may contribute to the decrease in antigenicity and the improvement of functional properties.

Rheological behavior, emulsifying properties and structural characterization of phosphorylated fish gelatin

Rheological, microstructural and emulsifying properties of fish gelatin phosphorylated using sodium trimetaphosphate (STMP) were studied. Phosphorylation was carried out at 50 °C for 0, 0.5, 1 or 2 h. Rheological behaviors indicated that phosphorylation decreased gelation rate constant (kgel) and apparent viscosity of gelatin solutions. Phosphorylation time was inversely proportional to tan δ; gelling and melting points of fish gelatin gels; however gel properties could be improved by short time of phosphorylation. Scanning electron microscopy and atomic force microscopy revealed that longer time of phosphorylation resulted in looser gel network with more aggregation. Longer phosphorylation time could stabilize fish gelatin emulsions, and endowed emulsions with smaller particle size and lower coefficient viscosity, but higher ζ-potential values. These results suggested that phosphorylation could be applied to obtain fish gelatin with varying functional properties suitable for numerous industrial applications.

Microgel-in-Microgel Biopolymer Delivery Systems: Controlled Digestion of Encapsulated Lipid Droplets under Simulated Gastrointestinal Conditions

Structural design principles are increasingly being used to develop colloidal delivery systems for bioactive agents. In this study, oil droplets were encapsulated within microgel-in-microgel systems. Initially, a nanoemulsion was formed that contained small whey protein-coated oil droplets ( d43 = 211 nm). These oil droplets were then loaded into either carrageenan-in-alginate (O/MC/MA) or alginate-in-carrageenan (O/MA/MC) microgels. A vibrating nozzle encapsulation unit was used to form the smaller inner microgels ( d43 = 170-324 μm), while a hand-held syringe was used to form the larger outer microgels ( d43 = 2200-3400 μm). Calcium alginate microgels (O/MA) were more stable to simulated gastrointestinal tract (GIT) conditions than potassium carrageenan microgels (O/MC), which was attributed to the stronger cross-links formed by divalent calcium ions than the monovalent potassium ions. As a result, the microgel-in-microgel systems had different gastrointestinal fates depending upon the nature of the external microgel phase; i.e., the O/MC/MA system was more resistant to rupture than the O/MA/MC system. The rate of lipid digestion under simulated small intestine conditions decreased in the following order: free oil droplets > O/MC > O/MA > O/MA/MC > O/MC/MA. This effect was attributed to differences in the integrity and dimensions of the microgels in the small intestine, because a hydrogel network surrounding the oil droplets inhibits lipid hydrolysis by lipase. The structured microgels developed in this study may have interesting applications for the protection or controlled release of bioactive agents.