RESUMO
Jambolan (Syzygium cumini) is a native fruit from Asia that has adapted well to the tropical climate of the Amazonian region. However, due to its limited annual availability and high perishability, the jambolan fruit is still underexploited. Thus, this study aimed to preserve the jambolan through a combined process of pulsed vacuum osmotic dehydration (PVOD) and convective air-drying and to monitor the total phenolic contents (TPCs) and total monomeric anthocyanins (TMAs) during these processes. To this end, jambolan fruits were pretreated with increasing PVOD times. After monitoring of moisture loss, solid gain, weight reduction, water activity, TPC, and TMA, pretreated (PT) and non-pretreated (NPT) fruits underwent convective air-drying (50-70 °C). The PVOD reduced half of the water present in the fruits; nonetheless, PVOD decreased the TPC and TMA over time. The increase in air-drying temperature shortened the drying time for both NPT and PT jambolan, and PVOD reduced even further the drying time of the fruits. Moreover, the fruits pretreated and dried at 60 °C showed promising results, potentially being a good alternative to extend the fruit's shelf life and make it available throughout the year.
RESUMO
The study objectives were to establish isotherms and thermodynamic properties for the moisture desorption process of jambolan pulp (JP) and jambolan seed (JS), harvested in the city of Belém (Brazil). These characteristics can contribute for the proper selection of the operating drying conditions. Thus, the following essays were made for both JP and JS. Firstly, proximate composition was performed, followed by moisture desorption essays at 25, 35, 45 and 55 °C. In addition, six mathematical models were fitted to the experimental data to simulate the desorption behavior; and based on the chosen models, the thermodynamic properties were calculated. The results have shown that JP isotherms followed the typical behavior of products rich soluble solids, and JS isotherms were more influenced by protein components. The influence of temperature was evidenced throughout the entire range of water activity (aw) studied. The GAB and Oswin models represented the best fitted equations for the JP and JS, respectively. In general, the energies involved in the desorption process of jambolan showed a greater dependence of JP with the equilibrium moisture content (EMC), in comparison with JS. Still, there was an increasing tendency of the thermodynamic properties with EMC decreasing. Besides of being non-spontaneous processes, desorption phenomena of JP and JS were enthalpy-driven mechanisms.
RESUMO
This study evaluated the effect of convective drying on the degradation of color and phenolic compounds of purple basil (Ocimum basilicum L.) leaves, and the hygroscopic behavior of dried leaves. The fresh leaves underwent drying at 40 °C, 50 °C, 60 °C, and 70 °C. Degradation of chlorophyll, flavonoids, and phenolic compounds were evaluated during drying and the hygroscopicity was evaluated through the moisture sorption isotherms. The drying mathematical modeling and the moisture sorption data were performed. The effective diffusivity for the drying increased from 4.93 × 10−10 m2/s at 40 °C to 18.96 × 10−10 m2/s at 70 °C, and the activation energy value (39.30 kJ/mol) showed that the leaves present temperature sensibility. The leaves dried at 40 °C had less degradation of phenolic compounds and color variation, but the drying process was too slow for practical purposes. Modified Page, Diffusion Approximation, and Verna models had excellent accuracy in drying kinetics. The isotherms showed that, in environments with relative humidity above 50%, the purple basil leaves are more susceptible to water gain, and at 8.83 g H2O/100 g db moisture, it guarantees the microbiological stability of the dried leaves. The Oswin model was the most suitable for estimating the moisture sorption isotherms of the dried leaves.