Mathematical modeling and thermodynamic properties in the drying of citron watermelon seeds/Modelagem matemática e propriedades termodinâmicas na secagem de sementes de melancia africana

Citron watermelon is an agricultural product of excellent economic potential. Its seeds are widely used for oil extraction, serving as an energy source, showing nutritional characteristics that make them a suitable product to be studied. Thus, the objective was to characterize citron watermelon seeds regarding their physicochemical composition, in addition to determining drying kinetics, fitting mathematical models to the data, and determining the effective diffusivity coefficients and thermodynamic properties. The seeds were dried in a convective dryer, varying the drying temperature, with air velocity of 1.0 m [s.sup.-1]. With the increase in drying temperature, there were reductions in moisture content, water activity ([a.sub.w]), ash concentration, total titratable acidity, lipids and reducing sugar. Citron watermelon seeds are rich in lipids and ash, have low sugar concentration and low acidity; their drying kinetics was very well described by the Two Terms and Approximation of Diffusion models, followed by the models of Midilli and Page, which resulted in acceptable fits. Effective diffusivity accompanied the increase in drying temperature, and this behavior was well fitted by an Arrhenius-type equation. Enthalpy and entropy variations were reduced with drying temperature, with increments in Gibbs free energy. Key words: Citrullus lanatus var. citroides, agricultural residues, sustainability, unconventional food, effective diffusivity A melancia africana é um produto agrícola de excelente potencial econômico. Suas sementes são muito utilizadas para extração de óleo, servindo como fonte energética, demonstrando características nutricionais que a habilitam como produto a ser estudado. Assim, objetivou-se caracterizar quanto à composição físico-química, as sementes de melancia africana, além de determinar a cinética de secagem, ajustar modelos matemáticos aos dados, determinar os coeficientes de difusividade efetiva e propriedades termodinâmicas. As sementes foram submetidas à secagem em secador convectivo, variando-se a temperatura de secagem, com velocidade do ar de 1,0 m [s.sup.-1]. Com o aumento da temperatura de secagem diminuiu o teor de água, atividade de água, teor de cinzas, acidez total titulável, lipídios e açúcar redutor. As sementes de melancia africana são ricas em lipídios e cinzas, tem baixos teores de açúcares e baixa acidez; as cinéticas de secagem foram muito bem descritas pelos modelos Dois Termos e Aproximação da Difusão, seguidos p