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Research background. Drying represents a viable unit operation for the preservation of food. Convective drying is the most used method for plant materials. However, it can result in negative changes in food nutrient composition, and other quality parameters, besides having high energy consumption. Pretreatments can represent an alternative to minimize these negative aspects of dried materials. This work aimed to evaluate the use of ethanol and ultrasound before pineapple convective drying and its effect on the product´s color, water activity, ascorbic acid, and total carotenoid contents. Experimental approach. For the pretreatment step, fruit samples were immersed in different ethanol concentration solutions, and experiments were carried out for 10 min with and without using ultrasound (25 kHz). Fruit samples were dried at 60 ºC. A control group (without the pretreatment step) was also dried in the same condition. Semi-theoretical models were used for drying data fitting, and the diffusional model was used to describe the moisture transfer and calculate the effective diffusivities. Water activity, ascorbic acid, total carotenoids, and color analyses were performed. Results and conclusions. The association between ethanol and ultrasound as a pretreatment reduced the drying time of pineapple. Higher effective moisture diffusivities were obtained when ethanol and ultrasound were performed before drying. The Two Term Exponential model presented the best fit for drying experimental data. In comparison to the fresh sample, the dried samples showed a darker color. The pretreatment with ethanol resulted in increased retention of the studied bioactive components. This study represents an improvement for the drying process, providing satisfactory results. Novelty and scientific contribution. Ultrasound and ethanol as a pretreatment to convective drying are promising. However, each food matrix has a typical structure and composition. Therefore, the application of the pretreatment in other products or using other conditions is still necessary to deeply understand and explain their effect on the process and the quality of dried products.

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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.

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