Prepared by:

Dr. Ezzat Mohamad Azman

Department of Food Technology

Faculty of Food Science and Technology

Universiti Putra Malaysia

Ultrasonication is a widely applied technology in scientific and industrial processes, particularly for extraction, emulsification, dispersion, and cell disruption. It relies on high-frequency sound waves (typically 20–40 kHz) that induce acoustic cavitation, the formation and collapse of microscopic bubbles that generate intense localized pressure and temperature gradients. These conditions enhance mass transfer, break cellular structures, and facilitate the release of intracellular compounds such as phenolics and anthocyanins (Chemat et al., 2017). Two major types of ultrasonication equipment are commonly used: probe (horn-type) and batch (ultrasonic bath) systems. Although both operate on the same physical principle, their energy delivery, efficiency, control, and scalability differ markedly, affecting extraction yield, reproducibility, and applicability across sample types.

1. Principle of Operation and Energy Delivery

In probe ultrasonication, a metallic horn (usually titanium) is immersed directly into the sample (Fig. 1). The horn tip converts electrical energy into mechanical vibrations, transmitting ultrasound waves directly into the liquid medium. This setup creates a localized and intense cavitation zone near the probe tip, where energy densities can reach up to 20,000 W/L (Hielscher, 2023). Conversely, batch ultrasonication (also known as ultrasonic bath) operates indirectly. The sample is placed in a container immersed within a water bath, and ultrasonic transducers fixed to the bath walls transmit sound waves through the water into the sample. Because energy must travel through an intermediate medium, cavitation intensity in a bath is significantly lower, typically between 20 – 40 W/L (Hielscher, 2023).

This difference in energy transmission has profound implications. Probe systems deliver focused and controlled cavitation, leading to rapid and efficient processing. Bath systems, in contrast, generate diffuse cavitation throughout the tank, producing non-uniform energy distribution with areas of high and low intensity (Güney & Elik, 2017). As a result, probe ultrasonication achieves faster extraction and better reproducibility, while batch systems often require longer exposure times to achieve similar effects.

Fig. 1. Schematic illustration of probe and bath ultrasonication systems with the cavitation mechanism.

2. Efficiency and Process Control

The higher power intensity of probe sonicators provides superior efficiency in disrupting plant tissues, emulsifying mixtures, and extracting bioactive compounds. For instance, Güney and Elik (2017) compared both systems in a heavy-metal leaching study and found that probe ultrasonication achieved comparable recovery within 15 minutes, whereas batch ultrasonication required 30 minutes. Similar findings have been reported in food matrices, where probe sonication markedly improved polyphenol and anthocyanin recovery compared with bath treatment due to enhanced cell-wall disruption and solvent penetration (Soria & Villamiel, 2010).

Process control is another major advantage of probe systems. Users can regulate amplitude, pulse mode, duration, and probe immersion depth, enabling precise control of cavitation intensity. Temperature rise can also be minimized through pulsed operation or external cooling (Chemat et al., 2017). In contrast, batch systems offer limited control over these parameters. Variations in sample position within the bath can significantly alter cavitation exposure, leading to inconsistent results between replicates (Mikheev et al., 2021).

3. Sample Volume, Throughput, and Scalability

Probe and batch sonicators differ considerably in sample handling capacity. Probe systems are ideal for small to medium volumes (e.g., 5–500 mL) since the energy is localized near the tip, producing highly efficient cavitation within a defined zone. However, scaling up requires careful design, either by increasing probe size or integrating multiple horns or flow-cell reactors to ensure homogeneous treatment (Adamou et al., 2024). Industrial-scale probe reactors with continuous flow have been developed for applications such as emulsification, nanoencapsulation, and juice processing, where reproducibility and high intensity are crucial.

Batch ultrasonication, on the other hand, is more suitable for multiple small samples processed simultaneously. This feature makes it convenient for laboratory screening, sample cleaning, or low-intensity extraction. However, as sample volume increases, energy dissipation becomes inefficient and cavitation uniformity decreases (Hielscher, 2023). Consequently, batch systems are seldom used for large-scale production or high-viscosity materials.

4. Sample Type, Heat Generation, and Maintenance

The choice between probe and batch ultrasonication depends largely on the sample characteristics. Probe ultrasonication is recommended for dense, viscous, or particulate-rich samples such as plant pastes, emulsions, and slurries. Its intense cavitation promotes effective cell-wall rupture and particle dispersion. For heat-sensitive materials, such as anthocyanins, flavonoids, and enzymes, temperature control is crucial since probe systems can rapidly raise the local temperature due to concentrated energy delivery (Chemat et al., 2017). Bath systems produce less heat and are thus gentler, albeit slower and less efficient.

Maintenance and contamination risk also differ. Probe tips require frequent cleaning to avoid cross-contamination, and prolonged use can lead to tip erosion or metal leaching, a concern in food and pharmaceutical applications (Mikheev et al., 2021). Batch systems, by contrast, pose minimal contamination risk since the probe does not contact the sample directly. However, they require consistent monitoring of bath water level, temperature, and sample placement to ensure reproducibility.

5. Reproducibility and Analytical Implications

Reproducibility is a critical factor in analytical and extraction processes. Probe ultrasonication provides consistent cavitation intensity at a fixed amplitude, enabling reproducible results across experiments. Güney and Elik (2017) reported lower relative standard deviations (3.4 – 7.6%) for probe-treated samples compared to bath-treated ones (4.7 – 9.5%), reflecting greater analytical precision. This makes probe systems particularly valuable for quantitative extraction of phenolic compounds and metabolites, where reproducibility directly influences analytical accuracy.

6. Applications and Suitability in Food Science

In food science and technology, probe ultrasonication has demonstrated remarkable efficacy in enhancing bioactive compound recovery and improving emulsion stability. For example, probe treatment of fruit by-products and colored plant tissues significantly increases anthocyanin and total phenolic yields, supporting sustainable valorization of agro-industrial wastes (Chemat et al., 2017). Conversely, batch ultrasonication is commonly used for cleaning glassware, degassing solvents, or mild extraction of thermolabile substances. The selection between these systems should consider energy requirement, sample volume, reproducibility, and compound stability.

7. Summary

In summary, while both probe and batch ultrasonication employ acoustic cavitation, they differ substantially in performance characteristics. Probe ultrasonication offers higher energy intensity, shorter processing times, and greater reproducibility, making it ideal for efficient extraction, cell disruption, and nanoparticle dispersion. However, it requires careful control of temperature and cleaning to prevent sample degradation or contamination. Batch ultrasonication provides convenience, safety, and multi-sample capacity but suffers from lower energy transfer and poor reproducibility. Therefore, the appropriate choice depends on the research objective, probe systems for high-intensity, targeted processes, and batch systems for gentle, simultaneous, or large-scale screening tasks.

References

Adamou, P., Ibarra, D., & Muñoz, R. (2024). Ultrasonic reactor set-ups and applications: A review. Ultrasonics Sonochemistry, 104, 106612.

Chemat, F., Rombaut, N., Sicaire, A.-G., Meullemiestre, A., Fabiano-Tixier, A.-S., & Abert-Vian, M. (2017). Ultrasound-assisted extraction of food and natural products: Mechanisms, techniques, combinations, protocols and applications. A Review. Ultrasonics Sonochemistry, 34, 540–560.

Güney, M. & Elik, A. (2017). Comparison of probe with bath ultrasonic leaching procedures for preparation to heavy-metal analysis of bio-collectors prior to atomic absorption spectrometry. Communications in Soil Science and Plant Analysis, 48(15), 1741–1752.

Hielscher Ultrasonics GmbH (2023). Probe-Type Sonicators vs. Ultrasonic Baths – An Efficiency Comparison. Available at: https://www.hielscher.com/probe-type-sonication-vs-ultrasonic-bath-an-efficiency-comparison.htm (Accessed 26 October 2025).

Mikheev, I. V., Surdukan, Y. A., & Orekhov, V. S. (2021). The pros and cons of an ultrasonic probe. Journal of Analytical Techniques in Chemistry, 2021, 1–8.

Soria, A. C. & Villamiel, M. (2010). Effect of ultrasound on the technological properties and bioactivity of food: A review. Trends in Food Science & Technology, 21(7), 323–331.

Date of Input: 18/12/2025 | Updated: 19/12/2025 | nur_jasni