Development of Moisture Sorption Isotherm and Mathematical Modeling of Finger Millet (Eleusine coracana)

Abstract

In the literature, only a limited number of studies have explored the sorption characteristics of finger millet-based products.Moisture sorption isotherms provide information on the interaction between food and the storage environment. The sorption isotherms of finger millet based food product were studied with dynamic vapor sorption method, isopiestic Method and static gravimetric methods at different temperatures ranging from 25–70◦C with humidity ranges from 5-100%. Additionally, no research has been conducted on whole grains concerning their storage for further processing. This study deals with the sorption properties of whole finger millet grains. Methodically, the equilibrium moisture content of whole finger millet grains was determined by the dynamic humidity chamber method. The Guggenheim–Andersen–de Boer (GAB), Brunauer–Emmett–Teller (BET), Henderson, and Halsey sorption models were applied to describe the relationship between detected water activity and equilibrium moisture content. The study was conducted at three different temperature levels of 25◦C, 30◦C, and 35◦C. The relative humidity ranged from 10% to 90%, with an increment of 10%. The value of average R2 for each model is 0.9103, 0.7226, 0.9123 and 0.8853, respectively. Furthermore, a new mathematical model incorporating exponential and power-law (nonlinear) relationships was developed, achieving an average R2 value of 0.9720. Furthermore, this study validates the developed mathematical model for fitting sorption isotherms across different millet varieties and temperature levels. Experimental data from EX-BORNO millet were utilized for model validation. The results demonstrate high accuracy, with the coefficient of determination R2 values for adsorption at 30°C, 40°C, 50°C, 60°C, and 70°C recorded as 0.976, 0.968, 0.963, 0.951, and 0.977, respectively. Similarly, the R2 values for desorption at these temperatures were 0.978, 0.970, 0.963, 0.954, and 0.963. These findings confirm the robustness of the developed model in capturing moisture sorption behavior, providing a reliable tool for optimizing storage and processing conditions for millet. The developed mathematical model enhances the accuracy of moisture equilibrium predictions, facilitating the development of improved storage systems and drying strategies. These findings contribute to extending the shelf life and optimizing the processing efficiency of finger millet grains in the food industry. Additionally, this study offers a comprehensive analysis of the moisture sorption behavior of whole finger millet grains.