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

BACKGROUND
Duckweed has been considered as alternative future food materials due to its high nutritional values but it contains high moisture content resulting in short shelf life. Moisture sorption isotherms are used to design dehydration and storage conditions in order to prolong food products shelf life. Nowadays, the information of sorption isotherm of duckweed has not been reported then it was investigated in this study. Scanning electron microscopy (SEM) is frequently used to study food microstructure. However, this technique has to perform under high-vacuum condition and take long period of time. Two-photon imaging microscopy was then selected to study the microstructure of dried duckweed instead of the SEM.


RESULTS
Among five sorption isotherm models, Peleg model gave the highest goodness of fit. The monolayer moisture content (M0 ) of duckweed was in the range from 7.43 to 7.92 % d.b. and 8.87 to 8.86 % d.b. for GAB and BET models, respectively. The moisture changing behaviors at each relative humidity step could be described by two exponential and reaction order kinetics. A clear cell structure (hexagonal shape's like) and stomata as well as the structural images (both 2D and 3D) were obtained from two-photon microscopy technique.


CONCLUSION
The Peleg model was the best-describing moisture sorption behaviors of dried duckweed and the shape of sorption isotherms were classified as type III isotherm. The M0 of dried duckweed ranged from 7.43 - 8.86% d.b. Two-photon microscopy was a potent tool for studying microstructure and compositing 3D image of dried duckweed. This article is protected by copyright. All rights reserved.