Formation and characteristics of alginate and anthocyanin complexes.

Sodium alginates with different mannuronate to guluronate units ratio ALG1 and ALG2 were employed in the formation of insoluble complexes with anthocyanins (ATC) extracted from Vaccinium myrtilus by exploiting the electrostatic interaction between carboxylate groups of sodium alginate (ALG) and flavylium cations of ATC. Monomer composition of ALG1 and ALG2 was determined from the 13C CP-MAS NMR spectra. The amount of ATC incorporated into the complex depended on the type of ALG used, the ALG to ATC weight ratio and the total concentration of the components in the solution. ALG1 having higher amount of G-blocks was favourable in the complex formation with ATC. At ALG to ATC weight ratio being 0.4 to 1 and total concentration of 0.66 g/L, about 1.54 g of ATC per gram of ALG1 and about 1.24 g of ATC per gram of ALG2 was incorporated into the complex. Thermogravimetric analysis showed that the rate of ALG and ATC complex decomposition also depended on the type of ALG used and was 2.5 times higher for ALG2 and ATC complex compared to ALG1 and ATC complex. Furthermore, ALG/ATC complexes showed prolonged antioxidant activity when compared to ATC.

Thermogravimetric analysis of caffeic and rosmarinic acid containing chitosan complexes.

Thermal behaviour and stability of chitosan (CH) and phenolic acids complexes could be of high importance in regard both the practical applications and understanding the complex formation. Thermal degradation of insoluble complexes of CH and caffeic (CACH) or rosmarinic acid (RACH) was investigated in air and nitrogen atmosphere. Thermal decomposition of CACH proceeded in two stages, first of which was attributed to decarboxylation of adsorbed CA in the temperature interval from 150 °C to 200 °C, and second one was related to decomposition of CH backbone at temperatures higher than 200 °C. Thermal degradation of RACH proceeded in one stage at temperatures higher than 200 °C, in the broad temperature range and was related to decomposition of formed complex. Values of apparent activation energy (Ea) related to the second stage of thermal decomposition of CACH and decomposition of RACH at conversion values (α) from 0.1 to 0.8 were determined by using Flynn-Wall-Ozawa method. For CACH the dependence between Ea and α was very similar to that of CH and showed that products of CA thermal degradation formed in the first stage didn't influence the thermal degradation of CACH in the second stage. Meanwhile, for RACH, initially, values of Ea increased with an increase of conversion degree, at certain value of α reached the maximum which depended on the RA to CH molar ratio, and then decreased.

Adsorption of rosmarinic acid from aqueous solution on chitosan powder.

In present study the adsorption of rosmarinic acid (RA) on chitosan (CH) powder from aqueous solution have been investigated in order to obtain insoluble RA-CH complexes with high amount of RA. The pseudo-second kinetic model and the Langmuir adsorption model described the kinetic and equilibrium adsorption of RA on CH with high correlation coefficients. With the increase of adsorption temperature the rate of adsorption decreased but amount of adsorbed RA increased. It was established that adsorption of RA on CH occurred in two steps, and relevant adsorption mechanism was proposed. The formation of RA-CH with the molar ratio of RA to CH equal to 0.11, 0.22. 0.39, 0.6 and 0.8 was investigated by FT-IR and steady-state fluorescence spectroscopic techniques. By the increase of RA amount in RA-CH complexes the character of both FT-IR and fluorescence spectra changed. The antioxidant activity of RA-CH was investigated by ABTS method and showed that RA-CH having higher amount of adsorbed RA has prolonged antioxidant activity.

Equilibrium adsorption of caffeic, chlorogenic and rosmarinic acids on cationic cross-linked starch with quaternary ammonium groups.

In the present study, the equilibrium adsorption of caffeic acid (CA) and its derivatives, namely, chlorogenic (CGA) and rosmarinic (RA) acids on cationic cross-linked starch (CCS) with degree of substitution of quaternary ammonium groups of 0.42 have been investigated in relation to the structure and acidity of phenolic acids. The Langmuir, Freundlich and Dubinin-Radushkevich adsorption models have been used to describe the equilibrium adsorption of CA, CGA and RA from their initial solutions and solutions having the equimolar amount of NaOH at different temperatures. In the case of adsorption from the initial solutions of acids the values of adsorption parameters were closely related to the dissociation constants of investigated acids. According to the increasing effectiveness of adsorption, phenolic acids could be arranged in the following order: CA

Interaction between κ- and ι-carrageenan and anthocyanins from Vaccinium myrtillus.

Anthocyanins (ATCs) from the Vaccinium myrtillus water extract have been incorporated into the κ-carrageenan (κ-CARG) or ι-carrageenan (ι-CARG) during complexation in dilute solutions or adsorption onto the microgranules of κ-CARG or ι-CARG cross-linked with epichlorohydrin. At the optimal weight ratio of CARG to ATC at 0.4:1 and the total ATCs and CARG concentration≤0.07g/L, stable dispersions of the κ-CARG/ATCs or ι-CARG/ATCs complex nanosize particles were obtained. The Langmuir, Freundlich and Dubinin-Radushkevich adsorption models have been used to describe the equilibrium adsorption of ATCs on cross-linked CARG. The introduction of ATCs into CARG and cross-linked CARG was confirmed by FT-IR spectroscopy. The data of the HPLC analysis showed that during adsorption on cross-linked ι-CARG microgranules ATCs are isolated from the crude water extract of wild bilberries, whereas other phenolics remain in the adsorption solution. After desorption from cross-linked CARG/ATC into different media the sufficiently pure and stable solutions of ATCs were obtained.

Complexes of dextran sulfate and anthocyanins from Vaccinium myrtillus: Formation and stability.

To improve the stability and antioxidant activity of anthocyanins (ATC), complexes of dextran sulfate (DESU) and ATC extracted from Vaccinium myrtillus were formed during electrostatic interaction between sulfo groups of DESU and cationic moieties of ATC. At the optimal weight ratio DESU/ATC=0.4 g/g, the amount of ATC introduced into a complex depended on the total concentration of the reagents. About 1.7 g of ATC per g of DESU could be incorporated into a complex. The formation of DESU/ATC complexes was confirmed by HPLC and FT-IR spectroscopy. According to HPLC analysis, the amount of individual ATC incorporated into a complex varied from 73.7% in the case of malvidin-3-O-glucoside to 90.8% in the case of delphinidin-3-arabinoside.

Preparation, stability and antimicrobial activity of cationic cross-linked starch-iodine complexes.

Cationic cross-linked starch (CCS)-iodine complexes containing different amounts of quaternary ammonium groups (different degrees of substitution (DS)) and iodine have been obtained by iodine adsorption on CCS from aqueous iodine potassium iodide solution. Equilibrium adsorption studies showed that with an increase of DS the amount of iodine adsorbed on CCS and the affinity of iodine to CCS increased linearly. The influences of the DS of CCS and the amount of adsorbed iodine on the stability of CCS-iodine complexes in a solution of 0.02M sodium acetate and reactivity toward l-tyrosine have been investigated. At the same DS, the stability of CCS-iodine complexes decreased with an increase of the amount of adsorbed iodine. With increasing the DS, the stability of CCS-iodine complexes increased. The iodine consumption in the reaction with l-tyrosine increased significantly with an increase of the amount of adsorbed iodine. The influence of DS on iodine consumption was lower and depended on the amount of adsorbed iodine. The antibacterial activity of CCS-iodine complexes against Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli was determined by the broth-dilution and spread-plate methods. The obtained results have demonstrated that an appropriate selection of the CCS-iodine complex composition (the DS of CCS and the amount of adsorbed iodine) could ensure good antimicrobial properties by keeping a low concentration of free iodine in the system. The main advantage of using CCS-iodine complexes as antimicrobial agents is the biodegradability of the polymeric matrix.

Cationic starch nanoparticles based on polyelectrolyte complexes.

Cationic starch nanoparticles were obtained by aqueous polyelectrolyte complex formation between cationic quaternary ammonium substituted starches and anionic sodium tripolyphosphate. The formation of nanosized starch particles of spherical shape was verified by dynamic light scattering and scanning electron microscopy measurements. The cationic starch nanoparticles of different constitution and containing various contents of free quaternary ammonium groups were produced and their zeta potential was modulated between +4 mV and +34 mV by varying polycation/polyanion ratio. Furthermore, the polyelectrolyte complex formation was confirmed by differential scanning calorimetry and FTIR analyses. The thermal stability of cationic starch nanoparticles increased with the introduction of polysalt into polyelectrolyte complex. The solubilization capacity of nanoparticles was varying with the concentration and composition as revealed by fluorescence probe experiments. The capability to accommodate hydrophobic pyrene quest molecule was decreasing with the increasing number of cationic groups in cationic starches and little depended on polyanion/polycation ratio in starch nanoparticles.

Adsorption of hexavalent chromium on cationic cross-linked starches of different botanic origins.

The influence of origin of native starch used to obtain cationic cross-linked starch (CCS) on the adsorption of Cr(VI) onto CCS has been investigated. CCS granule size is influenced by the botanic source of native starch. The equilibrium adsorption of Cr(VI) onto CCS was described by the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. The more equal the adsorption energy of the quaternary ammonium groups in CCS granule as indicated by low value of change of Temkin adsorption energy DeltaE(T) the greater amount of Cr(VI) was adsorbed onto CCS. The value of DeltaE(T) decreased and sorption capacity of CCS increased with the decrease of CCS granule size and with the increase of number of amorphous regions in CCS granules. The affinity of dichromate anions increases and adsorption proceeds more spontaneously when Cr(VI) is adsorbed onto more amorphous CCS. Adsorption process of Cr(VI) onto such CCS is more exothermic and order of system undergoes major changes during adsorption. After the adsorption on CCS Cr(VI) could be regenerated by incineration at temperature of 800 degrees C.