Studies on chemical composition, rheological and antioxidant properties of pectin isolated from Riang (Parkia timoriana (DC.) Merr.) pod.

Although synthetic antioxidant food additives are widely used in a variety of food products, some of them are suspected of having a noxious effect on human health. As a consequence, much research attention has been focused on developing natural antioxidant compounds from plants. Riang (Parkia timoriana (DC.) Merr.) is known as a traditional medicinal plant in which its various parts have been reported to exhibit antioxidant and numerous biological activities. In this study, pectins from Riang pod husk and pod powder were extracted, and their physico-chemical, rheological, and antioxidant properties were characterized. The extracted pectins showed high uronic acid content (> 65%) and high molecular weight (200-250 kDa) and the yields were approximately 15 and 36%w/w (dry basis), for Riang husk pectin (RHP) and Riang pod powder pectin (RPP), respectively. Furthermore, both pectins were classified as a high methoxyl with their DE of ~66%. Rheological measurements revealed a pseudoplastic behavior above 2% w/v. RHP contained higher content of total phenolics, flavonoids and tannin, compared with RPP. Antioxidant activities of RHP were consequently higher than RPP in all studied assays. The highest antioxidant activities of RHP and RPP, obtained from ABTS assay, were 0.95 and 0.24 mmol Trolox equivalents/g, respectively.

Influence of carrageenan molecular structures on electromechanical behaviours of poly(3-hexylthiophene)/carrageenan conductive hydrogels.

The κ, ι, and λ carrageenans were fabricated by solution casting as soft and electrically responsive actuators. The poly(3-hexylthiophene) (P3HT) was added as a dispersed phase to improve the electrical and electromechanical properties of the pristine carrageenan hydrogels. The electromechanical properties of the carrageenan hydrogels were investigated under the effects of electric field strength, carrageenan type namely κ, ι, and λ, operating temperature, and P3HT concentration. The electromechanical responses of the pristine carrageenans increased with increasing sulfated groups present; the λ-carragenan hydrogel provided the highest storage modulus sensitivity of 4.0 under applied electric field strength of 800 V/mm. With increasing temperature, the double-helical structure of the κ-carrageenan hydrogel changed into a random coil leading to the increase in the storage modulus response. On the other hand, the P3HT/κ-carrageenan hydrogel blend at 0.10%v/v P3HT provided the high storage modulus sensitivity of 2.20 at the electric field strength of 800 V/mm. The higher dielectrophoretic forces were due to the additional P3HT electronic polarization, but lower deflections relative to those of the pristine κ-carrageenan hydrogel. Both κ- and λ-carrageenans with the double helical structures are shown here as possible candidates to be fabricated as electroactive hydrogels for actuator or biomedical applications.

Soft poly(2-chloroaniline)/pectin hydrogel and its electromechanical properties.

Pectin hydrogels were successfully fabricated with various physical crosslinkers and concentrations for soft actuator applications. A small amount of synthesized P2ClAn was added as a dispersed phase into the pectin matrix. The electromechanical properties of the pectin hydrogels and blends were investigated under the effects of electric field strength, ionic crosslinker type and concentration, and P2ClAn concentration. The electromechanical properties of the pectin hydrogel as crosslinked by Fe2+ were superior to other pectin hydrogels. The pristine pectin hydrogel and the P2ClAn/Pectin hydrogel blended with 0.10%v/v P2ClAn provided the high storage modulus sensitivity values of 8.61 and 14.01, respectively, under the electric field strength of 800 V/mm. The P2ClAn/Pectin hydrogel blend responded to the electric field with higher dielectrophoretic forces, but lower deflections relative to the pristine pectin hydrogel due to the additional P2ClAn polarization and the latter lower rigidity.

Electrically responsive materials based on polycarbazole/sodium alginate hydrogel blend for soft and flexible actuator application.

The electromechanical properties, namely the storage modulus sensitivity and bending, of sodium alginate (SA) hydrogels and polycarbazole/sodium alginate (PCB/SA) hydrogel blends under applied electric field was investigated. The electromechanical properties of the pristine SA were studied under effects of crosslinking types and SA molecular weights, whereas the PCB/SA hydrogel blends were studied under the effect of PCB concentrations. The storage modulus sensitivity and bending of the pristine SA as crosslinked by the ionic crosslinking agent were found to be higher than those of the covalent crosslinking. The storage modulus sensitivity and deflection of the SA increased monotonically with increasing molecular weight. The highest electromechanical response of the PCB/SA hydrogel blends was obtained from the blend with 0.10% v/v PCB as it provided surprisingly the highest ever storage modulus sensitivity, (G'-G'0)/G'0 where G'0 and G' are the storage modulus without and with applied electric field, respectively, at 18.5 under applied electric field strength of 800V/mm.