Secagem de polpa de goiaba pelo método de camada de espuma

Abstract

Brazil is the third biggest fruit producer in the world. In this scenario, guava has a prominent role in the national economy, since its pleasant flavor and aroma are widely accepted by Brazilians, as well as for its nutritional value, especially for the high vitamin C content. However, the fresh fruit consumption is limited by high perishability, whose senescence process begins as soon as it is harvested, which is aggravated by inadequate practices in harvest, transportation and storage. Therefore, processing guava is necessary to increase its shelf life and commercial applications. Foam-mat drying is a low-cost process in which liquids and semi-liquids are whipped with emulsifying agents to obtain a stable foam, which is exposed to hot air, and results in a good quality powder with water reconstitution properties. For guava pulp drying, egg albumin was used as emulsifying agent, at 5% of concentration. To set a standard whipping time for the drying process, a preliminary study was carried, resulting in a whipping time of 9 minutes and 619,2% of foam expansion. The drying kinetics studies were performed at three temperatures: 60°C, 70°C e 80°C, and the page Model was fitted to the experimental data. The correlation factor for the Page model was R² > 0,99 for all three temperatures and drying rate ranged from 2,6 x 10-2 to 5,7 x 10-2 min-1. The effective diffusivity ranged between 6,8 x 10-7 and 1,33 x 10-6 m²/s, and the activation energy was of 3,410 kJ/mol. The powders went through physical-chemical analysis and the results were compared using the Tukey test with 95% of confidence coefficient and it was attested that, except for humidity and water activity – which were smaller for the powder obtained at 80°C, there were no significant differences in the characteristics analyzed in the three temperatures. However, the powder obtained at 80°C presented the best analysis results of humidity (5,01%), water activity (0,30), reconstitution time (120 seconds) and higher vitamin C content (19,31 g/100g), as well as reasonably good results for solubility (64,58%) and good powder flow. Therefore is reasonable to state that 80°C is the best process condition for foam-mat drying of guava pulp.