Thermal dehydration of some forage grasses for livestock feeding: Effect of different methods on moisture diffusivity and the quality of dried leaves

Abstract

• Presentation of optimum drying parameters for efficient dryer design at optimal nutrient retention • Evaluation of shrinkage based effective moisture diffusivity, diffusivity co-efficient and, activation energy • Effect of storage on the quality and colour of thermal dehydrated leaves were presented • Rehydration ability of thermal dehydrated grasses for palatability and its storability is presented after 60 days of storage. The study investigates the influence of drying methods on the quality of Andropogon tectorum (Gamba grass) and Pennisetum puerperium (Elephant grass) forage grasses used for hay making in Africa. The aim is to establish the best drying conditions for the grasses for forage conservation in Africa and the possible scaling up of the drying process for large-scale bale drying applications. Traditional sun drying, hot air oven and microwave drying methods were used. The average moisture diffusivity considering shrinkage for the two grasses varied from 5.71 × 10 −09 to 2.67 × 10 −08 m 2 /s at 40 -70 °C while for microwave drying varied from 9.06 × 10 −6 to 1.08 × 10 −05 W/g at 180 - 720 W. The activation energy ranged from 31.068 to 44.06 kJ/mol. Drying methods adopted significantly affected the nutrient content, colour, and rehydration ratio of the leaves. The optimization of crude fibre (%) yielded, a dry matter of 92.4 %, drying temperature of 70 °C and crude fibre of 51.7 %. In contrast optimization of drying in microwave gave drying power level of 360 W, 47.6 % of crude fibre and 93.13 % dry matter. Optimization of crude protein yielded a drying temperature, of 28.5 °C, dry matter of 39.8 %, and crude protein of 10.8 %. Similarly, crude protein of 11.03 % was obtained at a drying power level of 59.5 W, with the dry matter of 49.50 % value. All the optimization constraints set for maximizing nutrient content showed that crude fibre has the highest value.