Investigation of Bioactive Complexes of Chitosan and Green Coffee Bean or Artichoke Extracts

The formation of water-insoluble complexes between chitosan (ChS) and caffeoylquinic acid (CQ) derivatives present in artichoke (AE) and green coffee bean (GCBE) extracts was investigated by the equilibrium adsorption method. The UPLC/HPLC analysis revealed that the phenolic compounds accounted for 8.1% and 74.6% of AE and GCBE respectively, and CQ derivatives were the predominant compounds. According to the applied Langmuir adsorption model, anionic compounds present in natural extracts were adsorbed onto the active centers of ChS, i.e., primary amino groups. The driving forces of adsorption were electrostatic interactions between cationic groups of ChS and anionic compounds of natural extracts. Chromatographic analysis revealed that not only CQ derivatives, but also other phenolic compounds of natural extracts were attached to ChS. The release of adsorbed compounds into different media as well as the bioactive properties of complexes were also studied. With the immobilization of bioactives onto ChS, increased and prolonged ABTS^•+ radical scavenging activity and decreased antifungal activity against Fusarium graminearum and Botrytis cinerea were observed compared to those of ChS. The findings of the current study highlight that the adsorption approach could be used to successfully prepare water-insoluble complexes of ChS and components of natural extracts with prolonged antioxidant activity.

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 (E_a) 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 E_a 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 E_a 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.