Adsorption Isotherms of Extruded Bambara Groundnut (Vigna subterranea) Based Ready-to-eat Breakfast Meal

Abstract

The growing demand for nutrient-rich ready-to-eat foods has increased the need to understand moisture sorption characteristics and packaging stability of extruded Bambara groundnut-based breakfast meals to enhance their quality, safety, and shelf life. The objective of this study was to evaluate the adsorption isotherms of extruded Bambara groundnut-based ready-to-eat breakfast meal. Banana, pearl millets, sorghum and Bambara groundnut flours were blended in the ratio of 10:20:20:50, respectively. Response surface methodology was utilised for experimental design. The blend was hot extruded at 180-220 oC (barrel temperature), 300-350 rpm (screw speed) and 12-16% (feed moisture) to produce unsweetened, sweetened and sweetened-flavoured extruded samples. The adsorption isotherm was determined by gravimetric static methods using salt slurries at 25 oC and 30 oC. The experimental data were analysed using eight model equations, including Chun-Pfost, BET, Bradley, Smith, BET, modified Henderson, Halsey, Oswin and GAB. The extruded samples all exhibited a type II sigmoidal pattern and showed better stability at 30 oC. Equilibrium moisture content and water activity of the samples increased rapidly until water activity of 0.8. The GAB and Oswin sorption models fitted most with experimental results. The GAB model estimated the monolayer moisture content to be 13.25, 13.23, and 10.41 g water/g dry solids (d.s.) at 30°C and 11.41, 14.87, and 14.77 g water/g d.s. at 25 °C for unsweetened, sweetened, and sweetened-flavoured extrudates, respectively. The GAB model also showed the least number of points with deviation greater than 5% at 38.5% for both sweetened and sweetened-flavoured extrudates. An adsorption isotherm study was helpful in establishing the necessary parameters for the packaging and storage of extruded Bambara groundnut-based ready-to-eat breakfast meal.