Liofilização e secagem convectiva de quiabo.

Abstract

The okra is a vegetable that stands out agronomically because it presents fast vegetative cycle of high return, besides considerable food and nutritive value. Due to its composition and to being consumed still green and tender, its shelf life is quite short. Therefore, the objective of this work was to dehydrate the okra with and without peel, using the freeze drying and convective drying processes, evaluate the obtained powder product and the in natura in relation to its physical, chemical and physicochemical characteristics, verify the stability of the powder during the accelerated shelf-life test under controlled conditions of temperature and relative humidity in addition to determining the water adsorption isotherms. For freeze-drying the shelled and unshelled okra were cut into slices of approximately 2 mm, frozen at -18 °C for 48 h and freeze-dried for a period of 72 h. For convective drying, oak and peeled oats with the same thickness (2 mm) were submitted to oven drying with forced air circulation at temperatures of 50, 60, 70 and 80 °C, and fitted the mathematical models of Approximation Diffusion, Henderson and Pabis, Logarithmic, Midilli, Newton, Page and Thompson. The shelled and unshelled okra showed high moisture content and moisture activity and low acidity, with emphasis on okra with peel in relation to the content of lipids, chlorophylls and total carotenoids and the shelled in relation to the pectin content. As for the kinetics of convective drying, it was observed that the drying time was reduced with the elevation of the temperature and the Midilli model was the one that provided the best adjustments to the experimental data of both materials. In the powders obtained in the two drying processes, the concentration of ascorbic acid, sugars, pectin, proteins, chlorophylls, and carotenoids was observed, highlighting the freeze-dried powder, also presenting high hygroscopicity and low solubility. The moisture adsorption isotherms of the powders were classified as Type II and III. During storage of the powder it was observed that the packaging was not efficient to maintain its stability since, during the packaging, there was a gradual increase in moisture content and water activity, degradation of ascorbic acid, chlorophylls and carotenoids and degradation of the proteins in freeze-dried powder, where they remained stable in the stored powder obtained by convective drying.