Stability Evaluation of Bambara Groundnut (Vigna subterranea L. Verdc.) Powder Using Adsorption Isotherm Analysis and GAB Modeling

The transformation of foods into powder form, for improved preservation, ensures their availability throughout the year despite their seasonal nature. Moisture adsorption isotherms therefore constitute an essential source of information for assessing food stability and defining optimal drying and storage conditions. The storage of Bambara groundnut (Vigna subterranea) powder requires prior hygroscopic characterization to ensure better preservation. The adsorption isotherm of Bambara groundnut powder was experimentally determined using the gravimetric method with different saturated salt solutions. The water activity range studied extended from 0.07 to 0.95 at an ambient temperature of 28 ± 2 °C. Desiccators were used to contain the prepared salt solutions at various relative humidities, above which the samples were placed. Hygroscopic equilibrium was reached after 27 to 31 days. The results revealed that the adsorption isotherm obtained was classified as type II, characterized by a sigmoid shape typical of carbohydrate-rich food products. Experimental data were fitted using the Guggenheim–Anderson–de Boer (GAB) mathematical model. The modeling showed excellent agreement with the experimental data (R² = 0.982), indicating that this model effectively predicts the hygroscopic behavior of the product. Furthermore, the moisture content of Bambara groundnut powder should be maintained below the monolayer moisture content (X₀), estimated at 0.0517 (5.17%), to ensure extended shelf life during storage.