engleski

INFLUENCE OF ULTRASONIC PRE-TREATMENT ON THE ENERGY CONSUMPTION OF PUMPKIN (Cucurbita moschata) DRYING

Energy consumption during drying operations has great potential to be improved using novel non- thermal processing technologies. Technologies such as high-intensity ultrasonics can be used as pre- treatment to drying operations, which due to mechanical and thermal effects of cavitation can improve mass diffusion and consequently shorten drying times. Shortening the drying time could potentially lead to a decrease in energy consumption and waste production, which improves the ecological and economic aspects, increasing the sustainability of the whole process. This study investigates the effect of pre-treatment of pumpkin in an ultrasonic bath on the drying time and total energy consumption for the drying process. Square pumpkin pieces were processed using 30 %, 60 %, and 90 % of maximal ultrasonic power (380 W at 37 kHz) for 30 min, 45 min, and 60 min. Drying is conducted under atmospheric (1 bar) and low (0.1 bar) pressure at 60 oC. Obtained results show a significant difference in total used energy during conventional and vacuum drying (2, 04 ± 0, 17 kWh kg-1 compared to 3, 92 ± 0, 11 kWh kg-1). An increase of ultrasonic power leads to a significant shortening of the drying time from 365 min to 320 min for conventional and from 265 to 190 min for vacuum drying. Pre-treatment using 90 % of maximal power combined with drying at 1 bar uses 2, 75 ± 0, 21 kWh kg-1, while the same treatment at 0.1 bar uses 4, 88 kWh for drying 1 kg of fresh pumpkin material. An increase in ultrasonic processing time exhibits the same behavior, as there is a significant increase in total energy consumption (3, 75 kWh kg-1 for conventional and 5, 41 kWh kg-1 for vacuum) while there is still a significantly shorter drying time. However, vacuum-dried pretreated samples had much better sensory properties such as texture and color. In conclusion, while pre-treatment using an ultrasonic bath did not have any influence on the decreasing of total energy consumption, it contributes to significantly shorter drying times. The combination of pre-treatment with vacuum drying has the potential to contribute to the sustainability of the drying process, as total energy consumption can be further improved using larger batches of material or possibly using much shorter processing times. Such processes would be much more beneficial using high powered ultrasound with an immersion probe, as it can process the surface of the material with the same amount of mechanical energy in a much shorter amount of time. Acknowledgment: This work was supported by means of the Croatian Science Foundation project IP-2019-04-9750.

energy, ultrasonic pre-treatment, vacuum drying

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