Guo-Qing Huang

Complex coacervation of soybean protein isolate and chitosan

The formation of coacervates between soybean protein isolate (SPI) and chitosan was investigated by turbidimetric analysis and coacervate yield determination as a function of pH, temperature, time, ionic strength, total biopolymer concentration (TB(conc)) and protein to polysaccharide ratio (R(SPI/Chitosan)). The interaction between SPI and chitosan yielded a sponge-like coacervate phase and the optimum conditions for their coacervation were pH 6.0-6.5, a temperature of 25 °C, and a R(SPI/Chitosan) ratio of four independently of TB(conc). NaCl inhibited the complexation between the two biopolymers. Fourier transform infrared spectroscopy (FTIR) revealed that the coacervates were formed through the electrostatic interaction between the carboxyl groups of SPI (-COO(-)) and the amine groups of chitosan (-NH(3)(+)), however hydrogen bonding was also involved in the coacervation. Differential scanning calorimetry (DSC) thermograms indicated raised denaturation temperature and network thermal stability of SPI in the coacervates due to SPI-chitosan interactions. Scanning electron microscopy (SEM) micrographs revealed that the coacervates had a porous network structure interspaced by heterogeneously sized vacuoles.

Complex Coacervation of O-Carboxymethylated Chitosan and Gum Arabic

The effects of O-carboxymethylation modification on the coacervation of chitosan with gum arabic (GA) were investigated. O-carboxymethylated chitosan (O-CMC) carried less net positive charge in acidic solutions and its optimum pH and biopolymer ratio for coacervation with GA were lower than those of native chitosan. O-carboxymethylation modification decreased the optimum coacervation temperature from 45 to 25°C and greatly increased the sensitivity to ionic strength. Meanwhile, insoluble O-CMC–GA coacervates were formed in relative lower critical total biopolymer concentration than chitosan–GA coacervates. It was concluded that the O-carboxymethylation modification markedly influenced the electrostatic interaction of chitosan with GA. GRAPHICAL ABSTRACT

Characterization of O-Carboxymethyl Chitosan – Gum Arabic Coacervates as a Function of Degree of Substitution

Three O-carboxymethylated chitosans (O-CMCs) with degrees of substitution (DS) 0.41, 0.51, and 0.83 were synthesized and the effects of the DS of O-CMC on its coacervation with gum Arabic (GA) and partial characteristics of resultant coacervates were investigated. All the O-CMCs exhibited the same optimum pH of 3.0 for coacervation with GA and the O-CMC–GA coacervates displayed similar differential scanning calorimetry (DSC) patterns, thermogravity (TG) profiles, and porous microstructures, but differed markedly in their rheological properties. As the O-CMC DS increased, the elasticity of the coacervates raised accordingly. It was concluded that O-CMC–GA coacervates with desired viscoelasticity can be obtained by varying the DS of O-CMC. GRAPHICAL ABSTRACT

Cross-linking of soybean protein isolate–chitosan coacervate with transglutaminase utilizing capsanthin as the model core

Abstract Transglutaminase (TG) is an alternative coacervate cross-linking agent to aldehydes due to its safety. In this work, the cross-linking conditions of soybean protein isolate (SPI)–chitosan coacervates with TG-utilizing capsanthin as the model core were optimized and its cross-linking effectiveness was compared with that of glutaraldehyde. Results indicated that the optimum capsanthin microcapsule cross-linking conditions were as follows: a suspension pH of 6.0, an incubation duration of 3 h, a TG concentration of 18.75 U/g SPI and a reaction temperature of 45 °C. Under these conditions, TG provided a cross-linking effectiveness comparable with that of glutaraldehyde in regards to microcapsule stability against swelling in 80 °C water and heating at 150 °C. Differential scanning calorimetry analysis revealed that TG cross-linking increased the integrity of the microcapsule walls. It was concluded that the SPI–chitosan coacervation pair has potential applications in the food industry in terms of cross-linker safety and effectiveness.

Effect of coacervation conditions on the viscoelastic properties of N,O-carboxymethyl chitosan – gum Arabic coacervates

The effects of coacervation acidity, phase separation temperature, ionic strength, and biopolymer ratio on the viscoelasticity of the N,O-carboxymethyl chitosan (NOCC) - gum Arabic (GA) coacervate were investigated by using coacervate yield as the indicator of electrostatic interaction strength. The strongest interaction between NOCC and GA occurred at pH 3.0, whereas the highest modulus values were found in the coacervate separated at pH 6.0. The coacervate yield did not vary with phase separation temperature in the range 4-55°C, but the coacervate viscoelasticity declined as the temperature increased from 25°C to 45°C and then peaked at 55°C. The presence of NaCl weakened the electrostatic interaction between the two polyelectrolytes, but no dose-dependent reduction in viscoelasticity was observed for their coacervates. Besides, the highest electrostatic interaction strength and coacervate viscoelasticity were recorded at different GA to NOCC ratios. It is proposed that the strength of electrostatic interaction is not the only parameter that determines the viscoelasticity of the NOCC - GA coacervate.

Genipin-crosslinked O-carboxymethyl chitosan–gum Arabic coacervate as a pH-sensitive delivery system and microstructure characterization

The possibility of genipin-crosslinked O-carboxymethyl chitosan–gum Arabic coacervate as a pH-sensitive delivery vehicle was investigated. O-carboxymethyl chitosan–gum Arabic coacervates separated in pH 3.0, 4.5, and 6.0 were crosslinked by genipin for different durations and the crosslinked products were subjected to crosslinking degree, swelling behavior, bovine serum albumin release profile, and microstructure characterization. Genipin-crosslinking greatly improved the stability of the coacervates against the simulated gastric solution and created certain pH-sensitivity. The coacervates displayed higher swelling ratios in the simulated gastric solution than in the simulated intestine and colon solutions; meanwhile, the coacervates prepared in pH 4.5 and 6.0 swelled more severely than the complex separated in pH 3.0. Nevertheless, the bovine serum albumin release in the simulated gastric solution from the microcapsules prepared in pH 6.0 was much lower than those prepared in pH 4.5 and 3.0, whose cumulative release percentages in the three simulated solutions were 17.14%, 55.23%, and 79.79%, respectively, in crosslinking duration 2 h. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analysis revealed that genipin-crosslinking improved the regularity and compactness of coacervate structure, whereas confocal laser scanning microscopy observation indicated that O-carboxymethyl chitosan content was possibly the major reason for the different swelling and bovine serum albumin release behavior of the coacervates. It was concluded that the genipin-crosslinked O-carboxymethyl chitosan–gum Arabic coacervate was a potential intestine-targeted delivery system and its delivery performance could be tailored by varying the crosslinking degree and coacervation acidity.

Effects of coacervation acidity on the genipin crosslinking action and intestine-targeted delivery potency of the O-carboxymethyl chitosan–gum arabic coacervates

ABSTRACT O-carboxymethyl chitosan (O-CMC)–gum arabic (GA) coacervates separated in different acidities were crosslinked by genipin and subjected to FTIR analysis, viscoelasticity measurement, DSC characterization, pH response evaluation, and in vitro BSA release profiling to explore the influence of coacervation acidity on genipin crosslinking and intestine-targeted delivery potency of the coacervates. Genipin crosslinking greatly improved the stability of the coacervates against various simulated gastrointestinal fluids and the coacervation acidity exerted different effects on the pH response of coacervates and BSA-loaded microcapsules. It was concluded that genipin-crosslinked O-CMC–GA coacervates could be used to deliver hydrophobic compounds to the intestine. GRAPHICAL ABSTRACT

Intestine-targeted delivery potency of the O-carboxymethyl chitosan–gum Arabic coacervate: Effects of coacervation acidity and possible mechanism

The potential of the glutaraldehyde-crosslinked O-carboxymethyl chitosan (O-CMC)-gum Arabic (GA) coacervate as an intestine-targeted delivery system for hydrophobic compounds was concerned. OCMC-GA coacervates and emulsified bovine serum albumin (BSA)-loaded microcapsules were prepared in pH3.0, 4.5, and 6.0 and their swelling behaviors as well as BSA release profiles in simulated gastrointestinal fluids were measured. All the coacervates showed higher swelling ratios in the simulated gastric solution than in the simulated intestine and colon solutions and the values increased as the coacervation pH increased from 3.0 to 6.0, but a reversed trend was observed for the BSA release profile. SEM, TEM, and CLSM analysis revealed that the coacervation acidity influenced the swelling and BSA release behavior by changing the matrix density and O-CMC content of the coacervates. It was concluded that the O-CMC-GA coacervate could be used to deliver hydrophobic compounds to the intestine and its delivery performance could be tailored by selecting appropriate coacervation acidity and crosslinking degree.

Glutaraldehyde-crosslinked O-carboxymethyl chitosan–gum Arabic coacervates: Characteristics versus complexation acidity

ABSTRACT Glutaraldehyde-crosslinked O-carboxymethyl chitosan (O-CMC)–gum Arabic (GA) coacervates were characterized against coacervation acidity. As the coacervation pH increased from 3.0 to 6.0, the crosslinking degree of the coacervates and its sensitivity to glutaraldehyde concentration variation declined gradually, but the elasticity increased markedly. Crosslinking improved the structure compactness and thermal stability of the coacervates and high coacervation pH favored the increase of the two parameters, but a reverse trend was observed regarding swelling ratio in the simulated gastric fluid. It was concluded that glutaraldehyde-crosslinked O-CMC–GA coacervates with required properties could be tailored by selecting an appropriate complexation acidity. GRAPHICAL ABSTRACT

pH-Dependent intestine-targeted delivery potency of the O-carboxymethyl chitosan – gum Arabic coacervates

Bovine serum albumin (BSA)-loaded microcapsules were prepared at pH 3.0, 4.5, and 6.0 through O-carboxymethyl (O-CMC) - gum Arabic (GA) coacervation followed by genipin crosslinking to explore the effects of coacervation acidity on the intestine-targeted delivery potency of resultant microcapsules. Confocal laser scanning microscope observation revealed that microcapsules with the multilayer structure were successfully prepared. As the coacervation pH rose from 3.0 to 6.0, the amount of O-CMC deposited on the microcapsule surface and the particle size increased accordingly. Swelling and BSA release results indicated that coacervation at higher pH conferred greater stability against simulated gastric fluid and better intestine-targeted delivery potency to the microcapsules. Circular dichroism analysis demonstrated that the structural integrity of entrapped BSA was well maintained during microencapsulation and incubation in simulated gastrointestinal fluids. Hence, genipin-crosslinked O-CMC - GA coacervates could be used to deliver nutraceuticals to the intestine and its delivery performance could be tailored by varying the coacervation pH.