Comparative analysis of drying methods and optimization of Teff Injera drying parameters using RSM and SLP approach

The drying process of Teff Injera, a staple and highly favored traditional Ethiopian food made from Teff, was investigated to optimize moisture removal and determine the ideal drying time under controlled conditions. The study focused on the effects of drying temperature and airflow speed on the drying rate. Experiments were conducted using both open sun drying and oven drying methods. The sun drying trials were carried out between January 26th and 29th, 2023, in Bahir Dar, Ethiopia, within the sunlight window of 10:30 AM to 3:30 PM, utilizing a K-type thermocouple connected to a data logger and computer equipped with SquirrelView software. Oven drying experiments explored the combined effects of drying parameters, considering both free and forced convection methods at temperatures ranging from 40 °C to 90 °C and airflow speeds of 0, 0.5, and 1 m/s. Analysis of variance (ANOVA) was used to statistically analyze the data, while Response Surface Methodology (RSM) and Sequential Linear Programming (SLP) were employed to optimize the Injera drying process by minimizing drying time through two key process parameters, drying temperature and airflow speed. Results indicated that four days were required to achieve optimal drying using the sun drying method. In contrast, forced convection at 90 °C and 1 m/s airflow speed reduced the drying time to just 140 min. A third-order polynomial regression with a coefficient of determination (R² = 0.993) was applied to the forced convection data to identify the optimal drying conditions. The optimum parameters, with a 99% confidence level, were determined to be a drying temperature of 84 °C, an airflow speed of 0.8 m/s, and a drying time of 146 min.