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

Identification of water transitions using a combination of moisture sorption characteristics and dielectric properties of different parts of jasmine rice (Oryza sativa)

BACKGROUND

In this work, water transition points (first transition: monolayer-multilayer water; and second transition: multilayer-free and solvent water) of different parts of jasmine rice including white rice, brown rice and bran were identified through the integration of sorption isotherm and dielectric properties data. Desorption isotherm data were fitted to four established models to select the optimal model for describing the sorption behaviors. Then, dielectric properties such as dielectric constant (ε') and dielectric loss factor (ε″) were measured across various moisture content levels within the frequency range of 200-20 000 MHz.

RESULTS

A type III isotherm was observed for all samples and the Peleg model was the best fit with the experimental data. Monolayer moisture content of the samples, estimated using the GAB model, ranged from 3.25% to 4.17% dry basis. For dielectric properties, frequency and moisture dependencies were evident for all sample types. Moreover, the sorption isotherm models effectively described the relationship between water activity (aw) and dielectric properties as reflected by their goodness of fit, and their strong correlation through principal component analysis and Pearson's correlation results.

CONCLUSION

The first water transition occurs at aw values of 0.11, 0.12, and 0.22, while the second transition appears at aw values of 0.9, 0.9 and 0.75-0.85 for white rice, brown rice and bran, respectively. This knowledge will be useful for food processors, providing insights into the optimization of food processing and storage conditions to extend food products' shelf life. © 2024 Society of Chemical Industry.

Structural change kinetics, drying characteristics, antioxidant properties, and the correlation between quality parameters of dried duckweed (Wolffia arrhiza (L.) Wimm) affected by different levels of microwave power

BACKGROUND

Duckweed is considered as a future food material due to its fast growth, high yield, high nutritional value, and low impact on land use. However, in its fresh form, it has high moisture content (95% wet basis), resulting in a short shelf life. In this study, microwave drying (MWD) was conducted to produce a shelf-stable duckweed with minimal loss of quality. Drying characteristics and quality aspects of dried duckweed were assessed. Reaction order kinetics, including zero and first order, was applied to describe structural changes during drying process. Hierarchical cluster analysis (HCA) was used to select the appropriate drying conditions.

RESULTS

Of five drying models, the Midilli-Kucuk model was the one that best described the drying process. Drying at high microwave power could reduce energy consumption and increase energy efficiency. Increasing both microwave power and drying time increased the structural shrinkage rate as described by first-order reaction kinetics. High correlations among quality parameters were observed using Pearson's correlation. Drying treatments were differentiated into two main clusters by HCA and the results showed that MWD at 720 and 900 W provided samples that were closer in terms of quality to a freeze dried sample (the positive control) than samples that had been subjected to MWD at 450 W.

CONCLUSION

Drying behaviors of duckweed were well-described by the Midilli-Kucuk model. Microwave drying at 900 W gave the lowest energy consumption and displayed the most efficient use of energy. The first-order equation could be used effectively to describe the structural changes in the duckweed. Microwave drying at 720 and 900 W was the appropriate drying condition according to the HCA classification. © 2023 Society of Chemical Industry.