Biopolymer Ratio Research Articles

Biocompatibility Studies of Functionalized CoFe2O4 Magnetic Nanoparticles

CoFe2O4 nanoparticles of different sizes were synthesised by controlling the digestion time using precipitation method and were characterised by X-ray diffraction, transmission electron microscopy, dynamic light scattering, and vibrating sample magnetometer. The average crystalline size increases from 13.9 to 19 nm as the digestion time is increased from 1.3 to 120 minutes. The CoFe2O4 nanoparticles were coated with two biological polymers, namely polyvinyl alcohol (PVA) and polyethylene glycol (PEG) at various ratios to enhance their biocompatibility. Coated nanoparticles were analysed for their cytotoxicity by MTT assay against 3T3-L1 adipocytes. Coated nanoparticles were found to be less cytotoxic when compared to uncoated one. The cell viability decreased as the concentration of the polymer (either PVA or PEG) coating increased. Cell viability decreases as the concentration of nanoparticle increases. At 5 μg/ml the cell viability with PEG coated nanoparticles (1:4) was 92.5%, with PVA coated nanoparticles (1:4) was 82.7% and with uncoated nanoparticles it was 46.4%. As the ratio of biopolymers (PVA and PEG) to nanoparticle increases, the viability of the cell increases. The difference between the effect of these two polymers increases as the concentration of the nanoparticle decreases. The antiinflammatory properties of these nanoparticles were determined by RTPCR by measuring the two pro-inflammatory cytokines (namely tumor necrosis factor α and IL6). TNF-α and IL6 were upregulated by 3.57- & 2.86 folds their base level with uncoated nanoparticles. Whereas it was upregulated by 1.54- & 1.68-folds with PEG coated and 1.9- & 2.18-folds with PVA coated nanoparticles. Thus the coated nanoparticles can be used for further biological experiments including magnetic resonance imaging, and in targeted drug delivery systems for various diseases.

Complex coacervation in pea protein isolate–chitosan mixtures

Protein–polysaccharide interactions play an essential structure-controlling role in foods and biomaterials. Turbidity and electrophoretic mobility measurements were used to investigate the formation of soluble and insoluble complexes between pea protein isolate (PPI) and the cationic polysaccharide, chitosan (Ch) as a function of pH and biopolymer mixing ratio (1:1–20:1 PPI–Ch). In addition, pH-induced conformational changes of PPI upon complexation with Ch were studied by fluorometry. As the PPI–Ch mixing ratio increased from 1:1 to 12.5:1, critical structure forming events (i.e., those associated with the formation of soluble and insoluble complexes) shifted to higher pHs, and progressively behaved similar to those for PPI alone. At biopolymer ratios >15:1, mixed systems resembled that of PPI alone. Changes to the tertiary conformation of PPI upon complexation with Ch at a 7.5:1 biopolymer ratio were found to occur at pH 6.2, corresponding to the presence of insoluble complexes.

Effect of pH, salt, and biopolymer ratio on the formation of pea protein isolate-gum arabic complexes.

Turbidity measurements were used to study the formation of soluble and insoluble complexes between pea protein isolate (PPI) and gum arabic (GA) mixtures as a function of pH (6.0-1.5), salt concentration (NaCl, 0-50 mM), and protein-polysaccharide weight mixing ratio (1:4 to 10:1 w/w). For mixtures in the absence of salt and at a 1:1 mixing ratio, two structure-forming transitions were observed as a function of pH. The first event occurred at a pH of 4.2, with the second at pH 3.7, indicating the formation of soluble and insoluble complexes, respectively. Sodium chloride (<or=7.5 mM) was found to have no effect on biopolymer interactions, but interfered with interactions at higher levels (>7.5 mM) due to substantial PPI aggregation. The pH at which maximum PPI-GA interactions occurred was 3.5 and was independent of NaCl levels. As PPI-GA ratios increased, structure-forming transitions shifted to higher pH.

Gum Arabic−Chitosan Complex Coacervation

The formation of electrostatic complexes of gum Arabic (GA) with chitosan (Ch), two oppositely charged polysaccharides, as a function of the biopolymers ratio (RGA/Ch), total biopolymers concentration (TBconc), pH, and ionic strength, was investigated. The conditions under which inter-biopolymer complexes form were determined by using turbidimetric and electrophoretic mobility measurements in the equilibrium phase and by quantifying mass in the precipitated phase. Results indicated that optimum coacervate yield was achieved at RGA/Ch = 5, independently of TBconc at the resulting pH of solutions under mixing conditions. High coacervate yields occurred in a pH range from 3.5 to 5.0 for RGA/Ch = 5. Coacervate yield was drastically diminished at pH values below 3.5 due to a low degree of ionization of GA molecules, and at pH values above 5 due to a low solubility of chitosan. Increasing ionic strength decreased coacervate yield due to shielding of ionized groups.

Influence of pH and biopolymer ratio on whey protein–pectin interactions in aqueous solutions and in O/W emulsions

Combining total carbon (TC) and total nitrogen (TN) measurements, the solubility of both protein and pectin in mixtures of 0.5% whey protein isolate and non-amidated high methoxyl sugar beet pectin was determined at pH 4.0, as well as pH 5.5. The experimental results indicated that insoluble complexes with a protein to pectin ratio of 3.84 ± 0.88 were formed at pH 4.0 at protein to pectin ratios ranging from 5 to 0.5. At pH 5.5, the protein solubility was independent from the amount of pectin added, indicating that at these pH conditions, located above the whey protein's iso-electric point, either soluble complex formation or cosolubility occurred. Light microscopic analysis of the corresponding emulsions revealed that the large droplet sizes at a protein–pectin ratio of 5 at pH 4.0 were due to the low amount of soluble protein left due to complexation with pectin. Comparing the residual dissolved protein and pectin concentrations in the absence and presence of oil droplets indicated that not only the protein, but also the pectin was accumulated at the O/W interface both below and above the protein's iso-electric point. Electrophoretic mobility measurements clearly indicated that pectin adsorption to the whey proteins induced a charge reversal at pH 4.0 at higher pectin concentrations, giving rise to smaller droplet sizes. At pH 5.5, on the other hand, the electrophoretic mobility of the whey protein stabilised emulsion droplets became gradually more negative upon pectin addition, which not only resulted in a smaller droplet size, but also in a significant increase of the creaming stability. From the experimental results, it follows that pectin has an emulsion stabilising effect on protein stabilised emulsions both below and above the protein's iso-electric point, provided that electrostatic protein precipitation is prevented.

Influence of pH and biopolymer ratio on sodium caseinate—guar gum interactions in aqueous solutions and in O/W emulsions

Many colloidal food systems contain both proteins and polysaccharides. In the present study, the phase behaviour of mixed sodium caseinate—guar gum aqueous solutions was investigated: segregative phase separation was observed in solutions containing at least 0.04% of guar gum and 1.6% of sodium caseinate, thus indicating the limited compatibility of the polysaccharide and the protein. In addition, the functionality of guar gum as gravitational stabilizer in sodium caseinate stabilized 25% O/W emulsions was checked. At pH conditions significantly larger than the iso-electric point (IEP) of sodium caseinate, addition of small amounts of guar gum (0.1–0.2%) gave raise to fast serum separation, which was thought to be due to depletion flocculation. Increasing the polysaccharide concentration and/or the oil volume fraction limited the degree of phase separation, since depletion flocculation induced a sufficiently strong three-dimensional network to withstand gravity effects. Considering different guar gum concentrations at pH 5.0, 5.5, 6.0 and 6.5, it became obvious that the phase separation behaviour in the absence of guar gum was largely affected by the pH, whereas in the presence of at least 0.1% of guar gum it became mainly affected by the guar gum concentration. Hereby, higher guar gum concentrations introduced a longer delay time before separation could effectively be detected. As laser diffraction particle size analysis results were not significantly affected by guar gum addition, it was concluded that the guar gum-induced flocculation was weak in nature and largely reversible. Combining all results, it was concluded that guar gum could effectively be used to prevent phase separation problems that could occur due to flocculation around the protein's IEP, provided that at least 1.0% of guar gum is added to ensure depletion stabilization by formation of a sufficiently strong three-dimensional network to overcome separation effects. Increasing the ionic strength through addition of salt further reinforces the network in order to prevent its collapse due to gravity.

Complex coacervation of silk fibroin and hyaluronic acid

This study aimed to investigate the pH-induced complexation of silk fibroin (SF) and hyaluronic acid (HA). SF–HA complex coacervation was investigated by monitoring turbidity of the SF–HA system under slow acidification. Gravimetric analysis was performed to determine the yield of complex coacervation and viscosity of the system was measured to study the formation of the complexes at different pH values. The influences of total biopolymer concentration and biopolymer weight ratio on complex coacervation were examined during the analyses. Formation of the complexes was evidenced by the minimum viscosity and the maximum turbidity observed in the system. SF–HA complexes were formed within the pH–window of 2.5–3.5 regardless of the total biopolymer concentration or biopolymer ratio. Complex coacervation of SF–HA showed a reversible behavior and coacervation could be handled even in excess amounts of the biopolymers, which pointed out a non-stoichiometric complexation.