Moisture sorption characteristics and dynamic mechanical thermal analysis of dried petiole and rhizome of red water lily (Nymphaea x rubra)

This research aimed to experimentally determine moisture sorption characteristics and mechanical thermal properties of different parts of red water lily (Nymphaea x rubra). The data obtained from dynamic vapor sorption (DVS) were modeled with six sorption isotherm models. The shape of sorption isotherms of dried petiole and rhizome was classified as Type III and II, respectively. Peleg model was the best fit with the experimental data. GAB and BET models were used to estimate monolayer moisture content (M-0) of the samples and M-0 of petiole ranged between 7.17 to 8.291% d.b. and 10.455 to 10.588% d.b. for GAB and BET models, respectively and M-0 of rhizome ranged between 6.208 to 7.741% d.b. and 3.566 to 3.669% d.b. for GAB and BET models, respectively. Blahovec-Yanniotis model was used to describe the amount of bounded water and solution water in material and the contribution of solution water played an important role in both adsorption and desorption processes of dried petiole and rhizome. Dried red water lilies were equilibrated at different relative humidity levels. Dynamic mechanical thermal analysis (DMTA) was used to estimate the glass transition of the samples at different water activities. Increasing the solicitation frequency shifted the temperature of the relaxation to a higher temperature and Arrhenius equation described well the frequency dependency of the transition temperature. The apparent activation energies (E-a) of dried petiole and rhizome were in the range from 217.98 to 248.49 kJ/mol and 187.34 to 230.30 kJ/mol, respectively.

Automated summary

This research aimed to determine the moisture sorption characteristics and mechanical thermal properties of different parts of the red water lily. Experimental data showed that the sorption isotherms of the dried petiole and rhizome were classified as Type III and II, respectively. The contribution of solution water played an important role in the adsorption and desorption processes of the dried petiole and rhizome.