A radial mode ultrasonic horn for the inactivation of Escherichia coli K12

Analysis on electric impedance-controlled active ultrasonic horn in radial vibration

As a key component of high-powered ultrasonic vibration systems, ultrasonic horns play an important role in various practical application scenarios. Recent advances in longitudinal ultrasonic horns have enabled them to magnify the Langevin transducer's mechanical vibration and efficiently transmit the mechanical vibration to the mechanical load. However, limited research has been devoted to active radial ultrasonic horns in radial vibration. Here we propose an electric impedance-controlled active radial ultrasonic horn (ARUH) capable of tuning both resonance frequency and displacement magnification in radial vibration. The resulting device consists of a radially polarized piezoelectric ring connected with adjustable electric impedance and two metal rings with variable sections. The underlying mechanism is that the change of the converted mechanical impedance of the piezoelectric material by the external electric impedance connected to the piezoelectric material modulates the resonance frequency and displacement magnification of the ARUH. It can be found that the resonant frequency shifts to higher frequencies as the resistance increases and the resonant frequency shifts to lower frequencies as the inductance and capacitance increase, while the displacement magnification has the opposite trend to the resonance frequency. For example, the resonance frequency of the constant-section radial horn is 41130.2 Hz. When the inductance increases from -0.007 to 0.007H, the resonance frequency shifts from 41171.3 to 34606.2 Hz and the displacement magnification moves from 1.189 to 3.5. The experiments are conducted to verify the effectiveness of the resulting device, which is in good agreement with the simulated results and theoretical predictions. Our design with functionality and flexibility opens up possibilities for the design of ARUHs and may find important application prospects in diverse fields such as cold-drawn steel tubes and ultrasonic plastic welding.

Effects of cavitation on different microorganisms: The current understanding of the mechanisms taking place behind the phenomenon. A review and proposals for further research

A sudden decrease in pressure triggers the formation of vapour and gas bubbles inside a liquid medium (also called cavitation). This leads to many (key) engineering problems: material loss, noise, and vibration of hydraulic machinery. On the other hand, cavitation is a potentially useful phenomenon: the extreme conditions are increasingly used for a wide variety of applications such as surface cleaning, enhanced chemistry, and wastewater treatment (bacteria eradication and virus inactivation). Despite this significant progress, a large gap persists between the understanding of the mechanisms that contribute to the effects of cavitation and its application. Although engineers are already commercializing devices that employ cavitation, we are still not able to answer the fundamental question: What precisely are the mechanisms how bubbles can clean, disinfect, kill bacteria and enhance chemical activity? The present paper is a thorough review of the recent (from 2005 onward) work done in the fields of cavitation-assisted microorganism's destruction and aims to serve as a foundation to build on in the next years.

Recent advances in ultrasound application as a novel technique in analysis, processing and quality control of fruits, juices and dairy products industries: A review

Recently, ultrasound has been widely used in the researches in the food science and technology. Among the food materials, fruits, juices and dairy products are strongly sensitive to ultrasound-based techniques. In this review paper, applications of ultrasound in terms of high and low-power modes in processing, instrumentation and control of the industrial operations are studied in the fruit, juice and dairy sectors of the food science and technology by emphasizing the principles of these techniques and their physicochemical effects on the products. Also, a comprehensive analysis of these methods and important factors influencing their performance are presented, along with the advantages and the drawbacks of each ultrasound-assisted techniques. The solutions for better productivity of this technique would be presented and future trend of this technology would be outlined. By studying the latest researches and advances in the field of ultrasound applications, it has been confirmed that this technique can be helpful in accelerating processes, reducing energy requirements, increasing productivity, and producing better quality food materials in the fields of fruits, juices and dairy products. Notwithstanding, in order to solve the challenges ahead, and for potential applications of ultrasound technology, further researches need to be expanded in the areas mentioned. Also, with the advancement of technology, more advanced equipment, ultrasound transducers and instrumentations would be introduced that needs to be applied in this regard, to solve the current challenges.

Inactivation of Escherichia coli by Ultrasound Combined with Nisin

The aim of this study was to investigate the inactivation of nonpathogenic Escherichia coli in nutrient broth and milk through the use of either ultrasound (US) alone or US combined with nisin (US + nisin) treatments. The E. coli cells were treated at 0 to 55°C, 242.04 to 968.16 W/cm² for 0 to 15 min. The results showed that the inactivation of E. coli by US and US + nisin increased when the temperature, US power density, and treatment time were increased. The inactivation kinetics of E. coli in nutrient broth by US and US + nisin both conformed to linear models. The largest reductions of 2.89 and 2.93 log cycles by US and US + nisin, respectively, were achieved at 968.16 W/cm² and at 25°C for 15 min. The suspension media of the E. coli cells influenced the inactivation effect of US, while the growth phases of E. coli cells did not affect their resistance to US. Under all experiment conditions of this study, the differences between US and US + nisin in their respective inactivation effects on E. coli were not obvious. The results suggested that nisin had either no effect at all or a weak synergistic effect with US and that the E. coli cells were inactivated mainly by US, thus indicating that the inactivation of E. coli by US is an "all or nothing" event.

The effect of ultrasound treatment on microbial and physicochemical properties of Iranian ultrafiltered feta-type cheese

Pasteurization failures in the dairy industry have been reported in many previous studies. Hence, ultrasound, as a nonthermal alternative to pasteurization, has been studied in recent years. In this research, retentate of ultrafiltered milk was pasteurized, inoculated with Escherichia coli O157:H7, Staphylococcus aureus, Penicillium chrysogenum, or Clostridium sporogenes, and then treated with ultrasound for 20 min at frequencies of 20, 40, and 60 kHz and intensity of 80%. Microbial and physicochemical properties of the subsequently produced ultrafiltered white cheeses were investigated throughout 60 d of ripening. Sonication at 20, 40, and 60 kHz reduced counts of E. coli O157:H7, S. aureus, P. chrysogenum, and Cl. sporogenes by 4.08, 4.17, and 4.28 log; 1.10, 1.03, and 1.95 log; 1.11, 1.07, and 1.11 log; and 2.11, 2.03, and 2.17 log, respectively. Sonication improved the acidity of ripened cheese, and sonicated samples had lower pH values than control samples at the end of storage. Sonication did not affect fat in dry matter or the protein content of cheese during ripening, but it did accelerate lipolysis and proteolysis; the highest rates of lipolysis index (free fatty acid content) and proteolysis index (water-soluble nitrogen) were observed on d 60 of ripening for samples sonicated at 60 kHz. Sonication did not affect cohesiveness or springiness of cheese samples, but hardness and gumminess increased in the first 30 d and then decreased until 60 d of storage. Furthermore, ultrasound treatment improved organoleptic properties of the cheese. In terms of overall acceptance, samples sonicated at 60 kHz received the highest sensorial scores. Results showed that sonication can improve microbial, physicochemical, and sensorial properties of ultrafiltered white cheese.

Effect of sonication on bioaccessibility and cellular uptake of carotenoids from preparations of photoautotrophic Phaeodactylum tricornutum

With regard to its cost-effective cultivation and the composition of high-value nutrients, the diatom Phaeodactylum tricornutum (P. tricornutum) attracts interest for the use in human nutrition. Besides a number of important nutrients, it is rich in carotenoids. Therefore, this study aimed to investigate the potential of P. tricornutum as a carotenoid source for human nutrition. In photoautotrophically produced P. tricornutum biomass the carotenoid constitution, bioaccessibility (in vitro digestion model) and cellular uptake in differentiated Caco-2 cells (Transwell model system) was determined. Furthermore, the influence of sonication on these parameters was investigated. The results indicate that β-carotene, zeaxanthin and fucoxanthin were the main carotenoids found in P. tricornutum. Moreover, these carotenoids showed a good bioaccessibility (β-carotene: 25%, zeaxanthin: 27%, fucoxanthin: 57%), which is further improved by sonication for β-carotene and fucoxanthin. In line with the good bioaccessibility, fucoxanthin was the most abundant carotenoid in Caco-2 cells followed by zeaxanthin. In contrast, β-carotene could not be detected in the cells. The present study demonstrated that P. tricornutum represents a good source of carotenoids, particularly fucoxanthin. Thus, this diatom can contribute to the intake of bioaccessible carotenoids, even without processing. In addition, sonication might be a useful tool to improve the carotenoid bioaccessibility.

Bioaccessibility of carotenoids from Chlorella vulgaris and Chlamydomonas reinhardtii

Microalgae can contribute to a balanced diet because of their composition. Beside numerous essential nutrients, carotenoids are in the focus for food applications. The bioavailability of carotenoids from photoautotrophic-cultivated Chlorella vulgaris (C. vulgaris) and Chlamydomonas reinhardtii (C. reinhardtii) was compared. An in vitro digestion model was used to investigate carotenoid bioaccessibility. Furthermore, the effect of sonication on bioaccessibility was assessed. Lutein was the main carotenoid in both species. C. reinhardtii showed higher amounts of lutein and β-carotene than C. vulgaris. In contrast to C. reinhardtii, no β-carotene and only 7% of lutein were bioaccessible in nonsonicated C. vulgaris. Sonication increased the bioaccessibility of carotenoids from C. vulgaris to a level comparable with C. reinhardtii (β-carotene: ≥ 10%; lutein: ≥ 15%). Thus, C. reinhardtii represents a good carotenoid source for potential use in foods without processing, while the application of processing methods, like sonication, is necessary for C. vulgaris.

Inactivation of Enterobacter aerogenes in reconstituted skim milk by high- and low-frequency ultrasound

The inactivation of Enterobacter aerogenes in skim milk using low-frequency (20kHz) and high-frequency (850kHz) ultrasonication was investigated. It was found that low-frequency acoustic cavitation resulted in lethal damage to E. aerogenes. The bacteria were more sensitive to ultrasound in water than in reconstituted skim milk having different protein concentrations. However, high-frequency ultrasound was not able to inactivate E. aerogenes in milk even when powers as high as 50W for 60min were used. This study also showed that high-frequency ultrasonication had no influence on the viscosity and particle size of skim milk, whereas low-frequency ultrasonication resulted in the decrease in viscosity and particle size of milk. The decrease in particle size is believed to be due to the breakup of the fat globules, and possibly to the cleavage of the κ-casein present at the surface of the casein micelles. Whey proteins were also found to be slightly affected by low-frequency ultrasound, with the amounts of α-lactalbumin and β-lactoglobulin slightly decreasing.

Applications of power ultrasound in food processing

Acoustic energy as a form of physical energy has drawn the interests of both industry and scientific communities for its potential use as a food processing and preservation tool. Currently, most such applications deal with ultrasonic waves with relatively high intensities and acoustic power densities and are performed mostly in liquids. In this review, we briefly discuss the fundamentals of power ultrasound. We then summarize the physical and chemical effects of power ultrasound treatments based on the actions of acoustic cavitation and by looking into several ultrasound-assisted unit operations. Finally, we examine the biological effects of ultrasonication by focusing on its interactions with the miniature biological systems present in foods, i.e., microorganisms and food enzymes, as well as with selected macrobiological components.

On the physical origin of conical bubble structure under an ultrasonic horn

The cavitation field generated by an ultrasonic horn at low frequency and high power is known to self-organize into a conical bubble structure. The physical mechanism at the origin of this bubble structure is investigated using numerical simulations and acoustic pressure measurements. The thin bubbly layer lying at horn surface is shown to act as a nonlinear thickness resonator that amplifies acoustic pressure and distorts acoustic waveform. This mechanism explains the self-stabilization of the conical bubble structure as well as the generation of shock wave and the focusing at very short distance.

Effect of dissolved gas on efficacy of sonochemical reactors for microbial cell disruption: Experimental and numerical analysis

In the present work the effect of dissolved gases on the extent of ultrasonically induced microbial cell disruption has been explored using a mathematical model and it has been validated by experimental data from literature. Degassing experiments are carried out and a degassing kinetics model for horn type ultrasonic device is presented. An overall model combining hydrodynamic and kinetics of cell disruption for horn type reactor is then proposed. The model includes several important operational parameters such as stress generated by the cavity, cell wall strength, dissolved gas concentration, degassing due to sonication, acoustic streaming generated due to sonication and attenuation of ultrasound in water. Model basically realizes in categorizing the volume of sonochemical reactor as active cavitation zone (ACZ) and inactive cavitation zone (ICZ). All the transformations are seen to occur only in ACZ. The two regions, i.e. ACZ and ICZ are assumed to behave as two mixed flow reactor arranged in closed loop. Suggestions have been also made for efficient design and scale up of ultrasonic devices for microbial cell disruption. The same model can be extended for other applications like particle size reduction, nano particle synthesis, leaching, emulsification with the knowledge of critical rate controlling parameter.