Influence of microwave drying process on microstructure and thermodynamic properties of nopal cladodes

Abstract

Introduction: The drying of nopal offers an alternative for their preservation, storage, handling and consumption. Objective: The effects of microwave drying on the microstructural characteristics of nopal and their thermodynamic properties at the food-water interface were evaluated. Methodology: Nopal cladodes were microwave-dried by applying powers of 75 and 158 kW∙kg-1. Microstructure of the samples was evaluated by Scanning Electron Microscope. Adsorption isotherms were determined at temperatures of 10, 20, 30 and 40 °C. Net isosteric heat (q-st) was calculated using the Clausius-Clapeyron equation and the Peleg model. Results: Samples dehydrated at 75 kW∙kg-1 showed greater preservation of their internal and external structure. When applying a higher power (158 kW∙kg-1), greater damage was observed in the microstructure of the material. Type III adsorption isotherm curves were obtained according to the Brunauer classification. The q-st of the dehydrated nopal was 7.51 kJ∙mol-1 for a moisture content of 0.05 kgH2O∙kg-1. Limitations of the study: The results obtained are valid only for microwave drying by applying powers of 75 and 158 kW∙kg-1. Originality: This work proposes the microwave drying of nopal as an alternative method that reduces drying time and allows the preservation of the material’s structural properties. Conclusions: The power applied in the microwave drying of nopal had a direct impact on the microstructure of the samples. The use of a power of 75 kW∙kg-1 was the best drying condition to preserve the structures constituting the cladodes.