Hygroscopic behavior and morphological characteristics of okra powder obtained by convective drying

Okra is a vegetable that has a fast vegetative cycle of high yield, in addition to considerable nutritional and commercial value, thereat stands out agronomically. Its composition allows it to be consumed while it is still green, but its shelf life in natural form is short. Therefore, the objective of this work was to evaluate the hygroscopic behavior and morphological characteristics of okra powders obtained by convective drying. The okra was cut into slices of approximately 2 mm and dried in an oven with forced air circulation at temperatures of 50, 60, 70 and 80 °C until the hygroscopic balance was reached and ground in a knife mill to obtain the powders. Then, the hygroscopic behavior of the powders was evaluated through water adsorption isotherms at a temperature of 25 °C and mathematical models of GAB, Peleg, Oswin, Halsey and Henderson were adjusted to the experimental data of water contents and activity of water. The powders were also submitted to morphological analysis by scanning electron microscopy (SEM) and X-ray diffraction analysis. The results showed that all the models were well adjusted to the isotherms of the okra powders, with emphasis on the GAB model, with determination coefficients (R2) greater than 0.99 and average percentage deviations (P) less than 5%; isotherms were classified as type II, typical of products with a large amount of sugar and solutes and with low adsorption. The powders presented morphologically irregular, asymmetrical structures with amorphous characteristics.