Abstract
Recent research has demonstrated how ultrasound can benefit the industrial processing of olive paste before oil extraction. However, the absence of a device for controlling pressure inside the sonication cell is a major hindrance to its application. To address this problem, a pneumatic device with a programmable logic controller was implemented to automatically adjust pressure in the sonication cell according to a preset value: its functionality was tested in industrial oil extraction. An experiment was conducted to compare device performance when applied to olive batches with different solid/liquid ratios and differing rheology. The control system adjusted the flow section of the valve at the outlet of the sonication cell and the mass flow rate of the feed pump in order to maintain the pressure preset by the operator. Results indicate that the pressure was 3.0 ± 0.2 bar, 3.5 ± 0.2 bar, and 4.0 ± 0.2 bar when the set point was 3.0 bar, 3.5 bar, and 4.0 bar, respectively: there was thus no significant difference between controlled and set values. This indicates that the device is able to control pressure inside the sonication cell with a maximum deviation of 0.2 bar. In this case, the sonication intensity was stabilized at 135 W/cm2, 150 W/cm2, and 165 W/cm2 at 3.0 bar, 3.5 bar, and 4.0 bar, respectively. This study presents an advancement in ultrasound applications for industrial olive oil extraction: optimal pressure control in the sonication cell.
Highlights
High-intensity ultrasound at a frequency ≥ 20 kHz generates acoustic cavitation
As already predicted by theoretical calculations, experimental results highlighted that using the industrial ultrasound processor with standard equipment (IUP-SE) to process olives with different rheological characteristics leads to significant differences in pressure values; this involves an uncontrolled working of the US machine depending on the rheology of the inlet olive paste
These results highlight that ultrasound treatment of non-Newtonian olive pastes can induce variations in the operating parameters defining the effect of the acoustic wave; maintenance of the pressure value during ultrasonic treatment is essential for the functioning of these systems
Summary
High-intensity ultrasound at a frequency ≥ 20 kHz generates acoustic cavitation. In an acoustic field, microbubbles in solution may grow by rectified diffusion and by Interest in the use of ultrasound (US) to extract various classes of bioactive molecules from agro-industrial products and by-products keeps growing (Kia et al, 2018; Kumari et al, 2018; Osete-Alcaraz et al, 2019).The first study on the application of high-intensity ultrasound in the virgin olive oil extraction process was carried out at laboratory-scale processing plants by Jiménez et al (2007). High-intensity ultrasound at a frequency ≥ 20 kHz generates acoustic cavitation. Microbubbles in solution may grow by rectified diffusion and by Interest in the use of ultrasound (US) to extract various classes of bioactive molecules from agro-industrial products and by-products keeps growing (Kia et al, 2018; Kumari et al, 2018; Osete-Alcaraz et al, 2019). The first study on the application of high-intensity ultrasound in the virgin olive oil extraction process was carried out at laboratory-scale processing plants by Jiménez et al (2007). Ultrasound pre-treatment of the olive paste improved oil extractability. Bejaoui et al (2016a, b) conducted a laboratory study to determine the effects of high-intensity ultrasound pretreatment of olive paste on the quality of the oil. A number of others studies have investigated the effects of ultrasonic treatment on
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