Modeling of water absorption of Botswana bambara varieties using Peleg’s equation

Abstract

Hydration kinetics of five bambara seed varieties from Botswana was studied by soaking in water at temperatures 25–100 °C in constant-temperature water bath for 0.5–24 h using Peleg equation. Peleg’s equation adequately described the hydration characteristics of bambara seeds under the experimental condition with the mean relative percentage deviation modulus (E) of less than 10% for each variety. For each variety, Peleg’s rate constant K1 decreased significantly as the hydration temperature was increased from 25 to 100 °C suggesting a corresponding increase in the initial water absorption rate. Peleg capacity constant K2 increased with increase in temperature (25–75 °C) and dropped at 100 °C in all varieties, demonstrating that the water absorption rate increased and water absorption capacity decreased with increase in temperature. While an Ea of 37.83, 39.60, 33.02, and 33.33 kJ/mol was calculated for NTSR, BotR, DipC1, DipC2 bambara seeds, respectively, a lower value of 16.46 kJ/mol was obtained for AS17. The negative values of enthalpy (ΔH∗) for all the variety indicate that changes during the hydration of bambara seeds are associated with exothermic and energetically favorable transformation. The higher values of Ea and free energy of activation (ΔG∗) for NTSR, BotR, DipC1, and DipC2 indicate that the seeds experience a large change and hydration was more influenced by temperature. However, the lower value of Ea and the negative values of entropy of activation (ΔS∗) for AS17 indicate that the seeds were more thermally stable and hydration changes was less influenced by temperature. The optimum soaking time for bambara seeds for all the varieties appear to be 6 h at temperature ⩽75 °C.