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

International audienceThis 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

New insights into moisture sorption characteristics, nutritional composition, and antioxidant and morphological properties of dried duckweed [ Wolffia arrhiza (L.) Wimm]

International audienceBACKGROUND Duckweed has been considered as an alternative future food material as a result of its high nutritional values, although it also has a high moisture content resulting in a short shelf life. Moisture sorption isotherms are used to design dehydration and storage conditions to prolong the shelf life food products. To date, information regarding the sorption isotherm of duckweed has not been reported. Scanning electron microscopy (SEM) is frequently used to study food microstructure. However, this technique has to be performed under high-vacuum conditions and takes a long time. In the present study, two-photon imaging microscopy was selected to investigate the microstructure of dried duckweed instead of SEM. RESULTS Among five sorption isotherm models, the Peleg model gave the highest goodness of fit. The monolayer moisture content (M-0) of duckweed was in the range 7.43-7.92% dry basis (d.b.) and 8.87-8.86% d.b. for the GAB and BET multilayer kinetic models, respectively. The moisture changing behavior at each relative humidity step could be described by two exponential and reaction order kinetics. A clear cell structure (hexagonal shape) and stomata, as well as structural images (both 2D and 3D), were obtained using the two-photon microscopy technique. CONCLUSION The Peleg model best described the moisture sorption behaviors of dried duckweed and the shape of sorption isotherms were classified as type III isotherm. The M-0 of dried duckweed ranged from 7.43 to 8.86% d.b. Two-photon microscopy was a potent tool for investigating the microstructure and composition of dried duckweed. (c) 2021 Society of Chemical Industry

Evaluation of desorption isotherms, drying characteristics and rehydration properties of crab stick by-product

International audienceCrab stick by-product is the underspecification product from crab stick production. The by-product contains high moisture content inducing a short shelf life. Therefore, drying is considered as a food preservation technique to extend its shelf life. This study is focused on an investigation of desorption isotherms, drying characteristics and rehydration properties of crab stick by-product. Desorption isotherms were determined at three different temperatures (20, 35 and 50 degrees C). The experimental data obtained were modeled by fourteen sorption isotherm models for water activity ranging from 0.36 to 0.99 and Double Log Polynomial model was found to be the best-describing model. The net isosteric heat of desorption increased continuously with decreasing of equilibrium moisture content. The crab stick by-products were dried at 50, 60 and 70 degrees C with a constant air velocity of 1 m/s. The drying data were fitted with five thin layer drying models and Approximation of diffusion model was the best-describing model. Drying curves showed only falling rate period. Moisture diffusivities (D-eff) of the by-product drying were ranging from 8.87 x 10(-10) to 1.47 x 10(-9) m(2)/s and increasing drying air temperature led to an increment of D-eff. Rehydration properties including weight gain (%), rehydration ratio and co-efficient of reconstitution of dried sample at 60 and 70 degrees C were higher than the drying at 50 degrees C. Peleg model was the best fit with rehydration data. The D-eff of moisture absorption was in the range from 6.49 x 10(-9) to 7.31 x 10(-9) m(2)/s