Efeito da aplicação de cobertura comestível de pectina na secagem de fatias de abacaxi

Abstract

Pineapple is a fruit known for its juicy, aromatic, edible pulp, rich in sugars and organic acids. To reduce deterioration and post-harvest losses, and also to extend the shelf life of pineapple, drying is an effective option. The technique with heated air, although widely used, results in sensory and nutritional changes due to the high temperatures employed. The application of an edible coating prior to drying fruits, such as pineapple, has the potential to reduce these changes, due to the barrier effect, which regulates gas exchange and moisture loss during drying. The objective of this study was to evaluate the effect of applying an edible pectin coating on the convective drying kinetics of pineapple slices. For this purpose, pineapples cut into 1 cm thick slices were sliced into 2.76 x 1.77 cm pieces and coated or not with an edible low-methoxylated pectin coating. Fresh and coated slices were dried in a convective dryer at 50 and 70 °C. Drying was monitored by successive weighings at regular intervals. The experimental data were adjusted to Fick's law to calculate the effective water diffusion coefficient, and to empirical and semi-empirical models. The following were determined for the samples: moisture content, water activity, and color. It was found that the Fick model moderately represented the experimental data of fruit drying. On the other hand, the experimental data were adjusted to the Modified Henderson and Pabis empirical model with R² > 0.98, root mean square error values lower than 0.03, and the lowest percentages of relative mean error, close to 10%. It was found that temperature had a significant influence on the drying operation, since its increase resulted in higher drying rates. he instrumental color analysis showed that most of the samples presented negative values of a* (tendency towards green) and positive values of b* (tendency towards yellow), indicating a predominance of yellowish-green tones. Drying at 70 °C significantly affected the color parameters, especially when the operation was carried out without the application of the edible coating. Despite the visual changes in appearance and structure, the slices with pectin were visually lighter and less damaged than those dried without coating. The results indicate that the application of the edible coating prior to drying exerted a protective effect against the degradation of carotenoids in the samples and that this effect occurred mainly when the operation was carried out at a higher temperature.