ABSTRACT Guava is a fruit that stands out for its aroma, intense flavor, vitamins, and minerals. Its availability as a powdered food enhances its commercial applications. This study aimed to evaluate mathematical models for adsorption isotherms and determine the properties and flowability of guava pulp powder obtained by foam-mat drying. The models of GAB, BET, Henderson and Oswin were fitted to determine the isotherms of powders with 4 and 8% albumin, at temperatures of 35°C and 45°C. The powders were evaluated by wall friction angle, flow index, apparent density, and particle microstructure analysis. The best fit to the isotherms was obtained by the GAB model. Wall friction angle ranged from 15.7 to 21.9° and from 13.6 to 20.4° for samples containing 4 and 8% albumin, respectively. Higher densities were observed in the powder containing 8% albumin. The powders were classified as easy flowing when the flow index was between 8.00 and 8.68. The presence of albumin in powders resulted in particles with less rough surfaces, less hygroscopicity, and improved flowability.

RESUMO Na secagem em camada de espuma o alimento líquido é transformado em espuma, através da adição de um agente espumante, por exemplo, a albumina. Objetivou-se, neste trabalho, avaliar o ajuste de modelos matemáticos das curvas de secagem por camada de espuma de polpa de goiaba. Na avaliação dos ajustes utilizaram-se concentrações de 4 e 8% (m m-1) de albumina e temperaturas de secagem de 75, 80 e 85 °C. As amostras foram colocadas em bandejas de alumínio. A secagem foi realizada em secador de bandejas. Os modelos de Lewis, Page, Midilli e Logarítmico foram ajustados aos dados experimentais e avaliados segundo os coeficientes de determinação (R2), os desvios médios estimados e os testes qui-quadrados. Os modelos propostos se ajustaram bem aos dados experimentais, porém o melhor foi o de Midilli. A concentração de albumina e a temperatura influenciaram na velocidade de secagem, em que os menores tempos de secagem foram para a maior concentração de albumina e a maior temperatura de secagem.

ABSTRACT In foam-mat drying, the liquid food is foamed by the addition of a foaming agent, for example, albumin. The aim of this study was to evaluate the adjustment of mathematical models to foam mat drying curves of guava pulp. The fits were evaluated using samples with 4 and 8% albumin (m m-1) and drying temperatures of 75, 80 and 85 °C. The samples were placed on aluminum trays. Drying was carried out in a tray dryer. The Lewis, Page, Midilli and Logarithmic models were fitted to the experimental data and evaluated based on the coefficient of determination (R2), root-mean-square error (RMSE) and chi-square test. All models fitted well to experimental data and Midilli was the best. Albumin concentration and temperature influenced the drying rate; the lowest drying times occurred for the highest albumin concentration and highest drying temperature.