Associative interactions between chitosan and soy protein fractions: Effects of pH,mixing ratio,heat treatment and ionic strength

The objective of this paper is to explore the complexation between the soy protein fractions (glycinin and β-conglycinin) and chitosan (CS) and to investigate the influence of pH, mixing ratio, heat treatment and ionic strength. Phase behavior and microstructure showed that soluble complex and coacervate were obtained in glycinin/CS and β-conglycinin/CS mixtures at specific pHs, following a nucleation and growth mechanism. Moreover, the coacervates showed higher thermal stability than protein alone. Specially, the glycinin/CS mixture displayed a gel-like network structure at pH 5.5 and 6.0, and this structure kept the mixture soluble at a long pH region. The turbidity versus ζ-potential pattern showed that, independent of protein, the self aggregation of soy protein fractions and the coacervation of glycinin/CS and β-conglycinin/CS mixtures were all obtained at charge neutralization pH, indicating that the ζ-potential is the most critical parameter to understand the stability of soy protein/chitosan mixture. This predictive parameter was less affected by mixing ratio and heating but was significantly affected by ionic strength because mixing ratio and heating only changed the equilibrium between repulsive and attractive forces in colloid system while sodium chloride destroyed the predictability of colloidal stability via shielding charged reactive sites on both biopolymers to disrupt electrostatic interactions.     

Antibacterial activity of N-alkylated disaccharide chitosan derivatives

Antibacterial activity of the water-soluble N-alkylated disaccharide chitosan derivatives against Escherichia coli and Staphylococcus aureus was investigated. It was found that the antibacterial activity of chitosan derivatives was affected by the degree of substitution (DS) with disaccharide and the kind of disaccharide present in the molecule. Regardless the kind of disaccharide linked to the chitosan molecule, a DS of 30-40%, in general, exhibited the most pronounced antibacterial activity against both test organisms. E. coli and S. aureus were most susceptible to cellobiose chitosan derivative DS 30-40% and maltose chitosan derivative DS 30-40%, respectively, among the various chitosan derivatives examined. Although the disaccharide chitosan derivatives showed less antibacterial activity than the native chitosan at pH 6.0, the derivatives exhibited a higher activity than native chitosan at pH 7.0. Antibacterial activity of the chitosan derivatives (DS 30-40%) against E. coli increased as the pH increased from 5.0 and reached a maximum around the pH of 7.0-7.5. The effect of pH on the antibacterial activity of chitosan derivatives against S. aureus was not as pronounced as that observed with E. coli. Population reduction of E. coli or S. aureus in nutrient broth increased markedly upon increasing the concentration of chitosan derivatives from 0 to 500 ppm. No marked increase in population reduction was noted with further increase in the concentration of chitosan derivatives even up to 2000 ppm.     

Factors affecting the susceptibility of Staphylococcus aureus CCRC 12657 to water soluble lactose chitosan derivative

In this study, the susceptibility of Staphylococcus aureus CCRC 12657 to water-soluble lactose chitosan derivative as influenced by pH, temperature and cell age were investigated. Besides, the effect of this chitosan derivative on enterotoxin production and cell leakage of S. aureus CCRC 12657 was also examined.It was found that the susceptibility of S. aureus CCRC 12657 to lactose chitosan derivative varied with incubation temperature, pH and cell age. The lactose chitosan derivative exerted a higher antibacterial activity against S. aureus CCRC 12657 at 37°C than at 22 and 5°C. At pH 6.5–7.0, S. aureus CCRC 12657 was more susceptible to the chitosan derivative than at pH 6.0 or 7.5. Besides, cells of S. aureus CCRC 12657 in the late-exponential phase (12 h) were most susceptible to the chitosan derivative followed by cells in the stationary phase (24 h) and mid-exponential phase (6 h). Supernatant of cell suspension showed a marked increase in absorbance at 280 nm after the cells of the test organism were exposed to deionized water-containing lactose chitosan derivative. Furthermore, it was also noted that the lactose chitosan derivative not only caused the death of S. aureus CCRC 12657 but also inhibited enterotoxin production in Brain–Heart infusion broth.     

Investigation of the composite system of β-lactoglobulin and pectin in aqueous solutions

The compatibility in aqueous systems of β-lactoglobulin (β-lg) with low and high esterified-sodium polypectates (LMP and HMP) was investigated. The mixture did not separate into two co-existing liquid phases in any case studied. At pH above the isoelectric point (IP) of β-lg, the behavior of LMP and HMP was similar when mixing with β-lg. Pectins and β-lg were co-soluble was around a particular ionic strength (μ) (0.07 M for HMP and 0.3 M for LMP). In these circumstances, the flow behavior of pectin was hardly affected by the addition of β-1g . At all other μ, the mixture formed a liquid phase containing both β-lg and pectin and a small amount of β-lg precipitates. Here, the viscosity of the liquid phase was slightly higher than the viscosity of a solution containing the same concentration of pectin. At pH 3.5, i.e. pH⩽IP of β-lg, the behavior of LMP and HMP was different when mixing with β-lg. LMP formed insoluble complexes with β-lg at low μ (⩽0.25 M), but precipitation was suppressed at high μ (0.5 M). The composite system of β-lg/HMP formed a white, homogeneous and stable dispersion at low μ (0.07 M). The viscosity of this dispersion was much higher than the additive viscosity of individual solutions would be. Probably, the oppositely charged β-lg and HMP formed soluble complexes, which further associated into large aggregates. This complexation was also suppressed at high μ (0.5 M).     

Rheological properties of the hot-water extracted polysaccharides in Ling-Zhi (Ganoderma lucidum)

The intrinsic viscosity, coil overlap and Mark–Houwink parameters of the hot water extracted polysaccharides from the fruit body and mycelia of Ganoderma lucidum were measured as a function of solvents and dehydration methods. Effects of ionic strength on the intrinsic viscosity, salt tolerance and chain stiffness parameters of G. lucidum polysaccharides were also characterized. It was found that when water was used as the solvent for the polysaccharides extracted from the fruit body (GLFP) and mycelium (GLMP) of G. lucidum, molecular aggregations were likely occurred to some extent. However, as DMSO was used, a less compact, more extended conformation was obtained, as indicated by the higher Mark–Houwink exponents (1.32–1.66) and lower power dependence of viscosity on concentration. Intrinsic viscosity of both GLFP and GLMP decreased with increasing ionic strength, possibly due to the presence of uronic acid groups in the polysaccharide structure. GLMP generally showed higher viscosity than GLFP, possibly due to larger molecular size. Drying method, including hot-air, vacuum, and freeze drying, did not show a significant influence on the rheological properties of GLFP and GLMP in the dilute domain. Such information would be relevant during the development of functional foods containing G. lucidum polysaccharide.     

离子强度对壳聚糖分子链构象的影响

通过特性黏度法和光散射法研究离子强度对高（712.6 kD）、中（205.8 kD）、低（76.4 kD）3 种分子质量壳聚糖分子链构象的影响。结果表明：随着离子强度的增加,3 种壳聚糖的特性黏度均降低,分子链均方旋转半径也表现出下降趋势。壳聚糖分子质量越高,分子链刚性度越低。溶液中离子强度升高时,质子化氨基逐渐被反离子屏蔽,这可能是壳聚糖特性黏度和分子链均方旋转半径下降的原因。因此,壳聚糖的增稠效果可通过控制环境条件改变壳聚糖的分子链构象进行调节。     

Rheology of Dead Sea shampoo containing the antidandruff climbazole

In this study, the effect of the antidandruff climbazole on the rheology of hair shampoo containing Dead Sea (DS) salt was investigated. The presence of either DS salt or the climbazole led to increase in the shampoo viscosity. An optimum concentration was found where the viscosity of shampoo was maximum. In the absence of DS salt, the viscosity of hair shampoo increased with increasing the climbazole concentration to reach a maximum value at 1.0 wt%. Further addition of climbazole decreased the viscosity of shampoo. Adjusting the pH of the shampoo at 5.5 and 5.0 shifted the optimum climbazole concentration (corresponds to maximum viscosity) to 0.8 wt% and led to increase in the viscosity of shampoo. On the other hand, the addition of climbazole to the shampoo containing DS salt resulted in a decrease in shampoo viscosity. This decrease of shampoo viscosity became more pronounced with increasing the climbazole and/or DS salt concentrations. By controlling the pH of shampoo, an optimum formula of shampoo comprising both climbazole and DS salt and having maximum viscosity was obtained.     

壳聚糖溶液的流变学性质及应用研究

对壳聚糖稀溶液的流变学性质进行了研究,探讨了分子量和脱乙酰度结构参数以及温度、浓度、剪切速率、pH、离子强度等环境因素对壳聚糖稀溶液流变性质的影响。结果表明:壳聚糖溶液的黏度随分子量的增大而增大;随着脱乙酰度的增大和pH的增大,壳聚糖溶液的黏度先减小后增大,分别在脱乙酰度70.8%和pH4.9时黏度达到最小;离子强度的增大导致壳聚糖溶液的黏度降低。壳聚糖溶液是剪切变稀的假塑性流体,其黏度随浓度的增加逐渐增加,随温度的升高而减小,在0~80℃范围内,温度对壳聚糖溶液的黏度的影响符合Arrhenius模型,活化能为32.60kJ/mol。因此当作为食品增稠剂时,应该选用高分子量、高脱乙酰度的壳聚糖,添加到酸性低盐食品体系中。     

The effect of chitosan on the properties of emulsions stabilized by whey proteins

The influence of the cationic amino polysaccharide chitosan content (0–0.5%) on particle size distribution, creaming stability, apparent viscosity, and microstructure of oil-in-water emulsions (40% of rapeseed oil) containing whey protein isolate (WPI) (4%) at pH 3 was investigated. The emulsifying properties, apparent viscosity and phase separation behaviour of aqueous WPI/chitosan mixture at pH 3 were also studied. The interface tension data showed that WPI/chitosan mixture had a slightly higher emulsifying activity than had whey protein alone. An increase in chitosan content resulted in a decreased average particle size, higher viscosity and increased creaming stability of emulsions. The microstructure analysis indicated that increasing concentration of chitosan resulted in the formation of a flocculated droplet network. This behaviour of acidic model emulsions containing WPI and chitosan was explained by a flocculation phenomenon.     

离子强度对煮制前后猪肉胶原蛋白乳化特性的影响

为研究离子强度对煮制前后猪肉胶原蛋白乳化特性的影响,测定煮制前后不同NaCl浓度（0.0、0.2、0.4、0.6 mol/L）猪肉可溶性胶原蛋白和不溶性胶原蛋白的乳化特性,包括乳化活性指数（emulsification activity index,EAI）、乳化稳定性指数（emulsion stability index,ESI）、黏度及乳化液微观结构,同时测定猪肉胶原蛋白溶解度。结果表明：随着介质离子强度的提高,猪肉可溶性胶原蛋白溶解度降低,黏度增大,EAI先升高后降低,ESI先降低后升高;猪肉不溶性胶原蛋白溶解度升高,黏度增大,EAI、ESI均呈先升高后降低趋势。改变胶原蛋白的离子强度或对胶原蛋白进行热处理,均能使猪肉可溶性胶原蛋白和不溶性胶原蛋白的乳化特性发生显著变化。     

PSEUDOPLASTIC AND RHEOPECTIC PROPERTIES OF A GLOBULAR PROTEIN (β-LACTOGLOBULIN) SOLUTION1

The apparent viscosity of β-lactoglobulin solutions was studied as a function of shear rate using a cone and plate uiscometer (Ferranti-Shirley Viscometer System). Aqueous buffered solutions (pH 7, ionic strength 0.04) containing up to 40% protein were subjected to a rate of shear between 800 and 17,000 sec ^-1. At protein concentrations of 5% and lower, the viscosity was independent of the shear rate or the time of shearing. At protein concentrations of 10% or higher, the viscosity decreased asymptotically with an increasing shear rate. At a constant shear rate, the viscosity of 10-30%β-lactoglobulin solutions increased with shearing time. However, this rheopectic property was not consistently observed but, rather, was dependent on the rate of shear at concentrations lower than 20%. A rheopectic hysteresis effect was observed for 10-30% protein solutions whereas thixotropy was observed for 40% solutions. The rheopectic nature appeared to be the result of the permanent denaturation of protein characterized by UV absorption and gel filtration.     

Synthesis of chitosan-caffeic acid derivatives and evaluation of their antioxidant activities

In this study, the antioxidant activities of different molecular weights (M_w) and grafting ratios of chitosan–caffeic acid derivatives were investigated. The grafting process was achieved using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC) as covalent connector under different conditions such as molecular-weight of chitosan, molar ratio of chitosan and caffeic acid, reaction temperature, pH, and reaction time. The half-inhibition concentrations (IC₅₀) of products were calculated by reduction of the 1,1-diphenyl picryl hydrazyl in the radical-scavenging assay and reduction of the Fe³⁺/ferricyanide complex to the ferrous form in reducing power assay. The EDAC showed maximum activity at 3-h, pH 5.0 and room temperature conditions, except high-molecular-weight chitosan in pH 2.0. The products were water-soluble in all pH and showed lower viscosity than native chitosan. The highest grafting ratio of caffeic acid was observed at 15% in low-molecular-weight chitosan. After 5% grafting of caffeic acid into chitosan, the grafting efficiency was increased by decreasing molecular-weight of chitosan at the same conditions. Caffeic acid has main role in the antioxidant activity of products. The maximum IC₅₀ of radical-scavenging activity (0.064 mg/ml) was observed at the highest caffeic acid containing derivative. Water-soluble chitosan and caffeic acid derivatives were obtained by this study without activity loss.     

Characterisation of sodium caseinate as a function of ionic strength, pH and temperature using static and dynamic light scattering

Extensive static and dynamic light scattering (DLS) measurements were done on sodium caseinate solutions as a function of the ionic strength (3–500 mM NaCl), pH (5–8) and temperature (10–70 °C). DLS results were analysed in terms of two populations: the caseinate and a small weight fraction of large particles with a hydrodynamic radius (R_h) of about 65 nm that was independent of the ionic strength, pH and temperature. Caseinate was present as individual molecules at low ionic strength (3 mM), but formed small aggregates (R_h=11 nm) at high ionic strength (>100 mM). The aggregation number (N_agg) increased weakly with decreasing pH between pH 8 and 6, but extensive acid-induced aggregation occurred below pH 5.4 at 250 mM and below pH 6.0 at 3 mM. N_agg increased reversibly with increasing temperature.     

Isolation,Chemical Modification and Rheological Characterization of Leucaena Gum. Part I: Carboxymethylation

Leucaena gum was isolated from leucaena seeds and subjected to chemical modification via carboxymethylation under a variety of conditions. Variables studied include concentration of the etherifying agents and the preparation medium. It was found that the extent of carboxymethylation expressed as DS increases by increasing the concentration of the etherifying agents. Higher DS values were obtained in non-aqueous medium. The carboxymethylated leucaena derivatives are cold water soluble and can be precipitated by ethanol. Their pastes are characterized by non-Newtonian pseudoplastic behaviour regardless of the method of preparation or DS of the products. The apparent viscosity at various rates was thouroughly investigated. The effect of storing of these pastes on the rheological properties was also studied.     

Performance of β-galactosidase pretreated with lactose to prevent activity loss during the enzyme immobilisation process

In this study, Kluyveromyces lactis β-galactosidase was pretreated with lactose to prevent loss of activity during the immobilisation process, and glutaraldehyde was used as a linker to immobilise β-galactosidase on the surface of a silica gel. The pretreatment of β-galactosidase strongly improved its activity after immobilisation. Specifically, the activity of pretreated immobilised β-galactosidase was 2.6 times greater than that of non-pretreated immobilised β-galactosidase. The optimal temperature, pH and ionic strength of buffer for pretreated immobilised β-galactosidase were 37 °C, pH 7.5 and 20 mM potassium phosphate buffer, respectively. These values were shifted by 5 °C and pH by 0.5 when compared to the soluble β-galactosidase. Moreover, the pretreated immobilised β-galactosidase showed a better reusability than did non-pretreated immobilised β-galactosidase, with 63.9% of its original activity being retained after 10 reuses.     

Synthesis and Characterization of low DS Succinate Derivatives of Cassava (Manihot esculenta Crantz) Starch

Succinylation of cassava starch was carried out in aqueous medium to prepare derivatives with low degree of substitution (DS) and the physicochemical properties of the products were determined. A response surface design was used for the experiment with three levels of each of the three variables viz., concentration of succinic anhydride, reaction time and pH of the reaction medium. The reaction was followed in terms of the DS of the products and reaction efficiency (RE). The degree of substitution of the derivatives varied from 0.001 to 0.022 and reaction efficiency from 2.2 to 46.8%. The DS and RE showed an adequate fit to a second order polynomial model of the variables used. Succinylation brought about increase in the swelling volume, peak viscosity and paste clarity of the starch. However, the pasting temperature and solubility did not show any significant change. The in‐vitro α‐amylase digestibility of the succinylated derivatives decreased in comparison to that of native starch and this decrease correlated with a corresponding increase in DS.     

The effect of brine composition and pH on the yield and nature of water-soluble proteins extractable from brined muscle of cod (Gadus morhua)

Fillets of Atlantic cod (Gadus morhua) were held for 36 h in brines of pH 6.5 and 8.5, respectively, containing various combinations of NaCl, KCl, MgCl₂ and CaCl₂. Proximate analyses and chloride content were determined. Soluble muscle protein extracted in distilled water and protein released into the brine following salting was determined by SDS–PAGE. The soluble fraction was not affected by the presence of divalent salts or KCl in the brines, but it was affected by the initial pH. Both actin and myosin heavy chain (MHC) were released in pH 6.5 brines after immersion of the fish. On the other hand, an initial pH of 8.5 did not favour the release of these proteins. There was a smaller variety of remaining soluble proteins in salted muscle with an initial pH of 6.5, than with 8.5. However, this effect of the lower pH was offset to the extent that the ionic strength of the brine was higher.     

Chitosan coating minimises eggshell breakage and improves egg quality

The interior quality of eggs, shell impact strength, and consumer perception of eggs coated with chitosan containing an organic acid (acetic, lactic and propionic) were evaluated. Uncoated eggs had the highest albumen pH and lowest albumen viscosity. The viscosity of eggs coated with chitosan and lactic or propionic acids were the highest. Chitosan coating also improved shell strength with chitosan + lactic acid being the best coating in this regard. The colour of shell and yolk as measured by lightness (L*), a*, b*, chroma and hue of coated and uncoated eggs were not significantly different but the difference was detected in the colour of albumen, which is an effective indication of freshness and egg quality. Based on sensory evaluation, consumers could not differentiate coated eggs from uncoated eggs; thus the general acceptability of the coated eggs was the same as uncoated eggs. This study shows a great potential of using chitosan and lactic acid mixture as a coating material for egg coating to extend the shelf life. It has no effect on consumer acceptability of the product. Copyright © 2007 Society of Chemical Industry     

The effect of fermentation on carbohydrate and fatty acid composition of African oil bean seed (Pentaclethra macrophylla)

The effect of fermentation of African oil bean seed (Pentaclethra macrophylla) on chemical composition was studied. The samples were analysed for carbohydrates and fatty acids using gas-liquid chromatography. There was an increase in the pH, titratable acidity, soluble nitrogen and soluble solids during a 4-day fermentation. Trimethylsilyl (TMS) derivatives of carbohydrates extracted from the samples showed good chromatographic separations giving clear and defined peaks for each sugar. Sucrose and the flatus-forming oligosaccharides, stachyose, verbascose and raffinose were the predominant carbohydrates, with lower contents of monosaccharides in the unfermented sample. Fructose, galactose, glucose and some unidentified monosaccharides were predominant in the fermented sample. Fermentation considerably reduced or eliminated the sucrose and the flatus-forming oligosaccharides. Fermentation did not have much effect on the fatty acid composition except for a very slight reduction in the total saturated fatty acids and an increase in the total unsaturated fatty acids.     

Chitosan effects on quality properties of Greek style fresh pork sausages

The effect of chitosan (0.5% and 1%) added individually or in combination with nitrites (150 ppm) on microbiological (Total Viable Counts, Lactic acid bacteria, Pseudomonas spp., Brochothrix thermosphacta, Enterobacteriaceae, yeasts and moulds), physicochemical-chemical (pH, chemical composition, lipid oxidation) and sensory properties of fresh pork sausages stored at 4 °C for 28 days was investigated. Chitosan addition resulted in significant (p < 0.05) inhibition of microbial growth, while nitrites did not seem to protect sausages from microbial spoilage. A gradual reduction of nitrites was observed till the end of storage, when nitrites were almost depleted in all nitrite containing samples. The rate of lipid oxidation in fresh pork sausages was significantly decreased (p < 0.05) by addition of increasing levels of chitosan, while samples containing both chitosan and nitrites showed the lowest malondialdehyde (MDA) values, indicating a synergistic antioxidative effect. Consequently, the samples containing the combination of nitrites and chitosan at any level deteriorated less rapidly and were judged as more acceptable than all the other samples.