Analysis of Drying Characteristics of Sorghum Varieties Grown in Kenya a Case Study of Elgeyo-marakwet County

Abstract

Inefficient sorghum drying results in post-harvest losses that contribute to cases of hunger, malnutrition, poverty and food insecurity. One possible solution to reduce these losses is to design an affordable dryer for the sorghum farmers in Kenya. In order to do this, it was necessary to define the drying characteristics of the sorghum varieties grown, and develop thin layer drying equations that would be adopted when determining the design conditions for a sorghum dryer. This research was done to evaluate the drying characteristics of sorghum varieties grown in Kenya. In the evaluation of sorghum varieties that are grown in Kenya- Elgeyo Marakwet County, four common sorghum grain varieties grown were found to be Serena, Seredo, Gadam and KARI/Mtama 1. From this study, it was established that 99% of the farmers in Elgeyo- Marakwet County practise the traditional field-drying/sun drying, whereas 1% dry sorghum in the house in hanging cobs. The farmers were both small scale and large scale farmers. Thin layer drying of these four sorghum varieties were each studied under temperatures of 40°C, 50°C and 60°C in a convective laboratory dryer in order to analyse the drying conditions. The moisture content during the drying process was measured using the oven method and moisture meters until equilibrium moisture content was achieved. The drying rate was then determined by plotting the moisture ratio against time. From the data collected, drying curves of the sample varieties were analysed. The experimental results were fitted into seven preexisting thin layer drying equations, and non-linear regression analysis was performed for each variety. The values of R2, RMSE and χ2 were evaluated and used to predict the most suitable model for each variety i.e. Highest R2, Lowest RMSE and lowest χ2. From the drying curves, a decay pattern was observed for all the sorghum varieties studied. The drying rate was fastest at a temperature of 60°C. Following the non-linear regression analysis of drying data of the four varieties, all the models chosen showed a high R2 value (>90%) and RMSE range of 0.006 to 0.159. The χ2 ranged from 0.0005 to 0.2079. The recurrent and best fit model was found to be the Logarithmic model for Gadam, Kari Mtama 1 variety, Serena and Seredo varieties. The thin layer drying equation for the Logarithmic model will form a basis in the design of an efficient and low-cost drying system for the sorghum farmers in Kenya.