Research background. Drying is one of the most traditional processes for food preservation. Optimizing the process can result in a competitive product on price and quality to the market. One technology in use as a pretreatment to drying is ultrasound. This work had as the goal to analyze different drying systems with and without applying ultrasound (US) pretreatment, on heat and mass transfer, simulating numerically the temperature profile by computational fluid dynamics (CFD).
Experimental approach. The melon slices were pretreated with ultrasound for 10 (US10), 20 (US20), and 30 (US30) min at 25 kHz, and the water loss and solids gain were evaluated. Drying was performed at different temperatures (50, 60, and 70 °C). The effective diffusivity was estimated, and experimental data were modeled using empirical models. The airflow in the dryer and the temperature profile in the melon slice were simulated via computational fluid dynamics (CFD).
Results and conclusions. Drying time had a 25 % (US20 and US30 at 50 °C) to 40 % (US20 and US30 at 70 °C) reduction. The Two terms model presented the best fit to the experimental data, and the diffusivity coefficients showed a tendency to increase as the time of exposure of the melon to ultrasonic waves increased. Pretreatment water loss and solid gain behavior and drying kinetic and diffusion data were used to choose the best experimental condition to be simulated with CFD. The heat transfer modelling through CFD showed that the temperature distribution along the melon slice was representative. Therefore, the profile obtained via CFD satisfactorily describes the drying process.
Novelty and scientific contribution. The use of simulation tools in real processes allows the monitoring and improvement of existing technologies, such as food drying processes, that involve complex mechanisms, making it difficult to obtain some data. Application of CFD in the drying processes of fruits and vegetables is still very recent, being a field little explored. There is no record in the literature that uses CFD in the drying of melon.
This study aimed to evaluate the effectiveness of pretreatments on papaya drying behavior and quality parameters. The pretreatment consisted of submerging the samples in ethanol or distilled water for 20 min. The ultrasonic step was conducted in an ultrasonic bath (25 kHz). Samples were dried in an infrared dryer and a convective oven at 60 C. The material pretreated with ultrasound and ethanol and submitted to infrared drying presented the shortest drying time (84 min). The two-term exponential model was the most predictive for the drying data fitting. All dried samples showed water activity values below 0.60. Among the pretreatments performed, the use of ultrasound associated with ethanol was more effective in reducing losses of total phenolics, ascorbic acid, and antioxidant activity of dried papaya when compared to the use of water. Infrared drying of the fruit pretreated with the combination of ultrasound and ethanol resulted in no significant difference from the untreated papaya concerning the evaluated quality parameters.
Practical applicationsThe consumption of tropical fruits and their derived products has increased in national and international markets, due to the growing recognition of their nutritional properties and subsequent use in the food industry. The presence of nutrients such as bioactive compounds, demonstrates their potential for use in different sectors, increasing the added value of the cultivar. Thus, this study represents a contribution to society, recognizing and valuing the consumption of fruit, contributing to the nutritional conditions of the population, favoring food and nutritional security, and conservation of the species. It also allows, with the use of pretreatments and different types
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