Timothy J. Mason

The uses of ultrasound in food technology

Abstract The same physical and mechanical effects which have been utilised in sonochemistry, i.e. strong shear forces, particle fragmentation, increased mass and heat transfer, nucleation of seedling, have been applied to food processing. Examples are quoted from various applications where power ultrasound has been used to influence the development of living cells, improve sterilisation and effect enzyme activity. Typically ultrasound can be used as a processing aid in extraction, crystallisation, freezing, emulsification, filtration and drying.

Ultrasound in synthetic organic chemistry

High-power ultrasound can generate cavitation within a liquid and through cavitation provide a source of energy which can be used to enhance a wide range of chemical processes. Such uses of ultrasound have been grouped under the general name sonochemistry. This review will concentrate on applications in organic synthesis where ultrasound seems to provide a distinct alternative to other, more traditional, techniques of improving reaction rates and product yields. In some cases it has also provided new synthesic pathways.

Quantifying sonochemistry : casting some light on a 'black art'

Despite the ever increasing usage of power ultrasound to enhance reactivity in synthetic chemistry, many experimentalists experience difficulty in reproducing the work of other groups. Although such problems are most commonly encountered with chemical reactions which have been performed in ultrasonic baths, even reactions involving probe systems have sometimes proved difficult to reproduce. The origin of many of tehse problems can be traced to a failure of the original report to specify the exact sonication conditions, e.g. the frequency of ultrasonic irradiation, the precise power entering the reaction system, the geometry of the reaction vessel, the presence of a bubbled gas or even the temperature of the reaction∗. In this article we report the results of some model reactions performed using the newly developed Undatim Sonoreactor probe system. This particular instrument is equipped with an automatic transducer resonance frequency search device, enabling the power input to a system to be maintained accurately throughout a reaction, thereby offering considerable advantages over the normal commercially available equipment in terms of both the monitoring and control of irradiation parameters. Using this facility we are able to report how ultrasonic energy input to a chemical reaction is affected by the following important reaction parameters: ultrasonic power used, the presence of bubbled gas, temperature, solvent composition and reaction volume. In addition, a comparison is made of the ultrasonic power available from three different laboratory sonicators operating at a nominal frequency of 20 kHz.

Investigation of the effects of ultrasound on vegetal tissues during solvent extraction.

The paper presents an insight into the mechanism of the ultrasonic enhancement of solvent extraction through the effect of ultrasound on the vegetal material involved. Thus, a series of experiments has been developed to investigate the effect of ultrasonic energy on the vegetal material and the solvent used. Several results concerning the ultrasonic extractive value, ultrasonic swelling index and the effects of frequency on vegetal material are presented.

Dosimetry in sonochemistry : The use of aqueous terephthalate ion as a fluorescence monitor

The generation of HO radicals by acoustic cavitation in water was monitored by their reaction with terephthalic acid (TA) anion to produce fluorescent hydroxyterephthalate ions using a cleaning bath (38kHz) and a probe system (20, 40 and 60 kHz) as different sources of ultrasound. When using the ultrasonic bath as a source of energy for sonochemical studies, the shape of the reaction vessel is important. In the case of HO production from water (50 cm3), reaction in a conical flask (100 cm3) produces 2.75 times more radicals than a round-bottomed flask of the same capacity. The fluorescence yield (fluorescence intensity/ultrasound dosage) obtained using the conical flask and ultrasonic bath was similar to that for a probe operating at 40 kHz on the same volume of solution. For a probe system operating at 20, 40 and 60 kHz the greatest sonochemical efficiency was attained at the highest of these frequencies (60 kHz). For the probe system the fluorescence yield is directly proportional to power input and the concentration of TA. The fluorescence yield decreases as the temperature is increased.

The development and evaluation of ultrasound for the treatment of bacterial suspensions. A study of frequency, power and sonication time on cultured Bacillus species☆

Some species of bacteria produce colonies and spores which agglomerate in spherical clusters (Bacillus subtilis) and this serves as a protection for the organisms inside against biocidal attack. Flocs of fine particles e.g. clay can entrap bacteria which can also protect them against the biocides. It is because of problems such as these that alternative methods of disinfecting water are under active investigation. One such method is the use of power ultrasound, either alone or in combination with other methods. Ultrasound is able to inactivate bacteria and deagglomerate bacterial clusters or flocs through a number of physical, mechanical and chemical effects arising from acoustic cavitation. The aim of this study was to investigate the effect of power ultrasound at different powers and frequencies on Bacillus subtilis. Viable plate count techniques were used as a measure of microbial activity. Results showed a significant increase in percent kill for Bacillus species with increasing duration of exposure and intensity of ultrasound in the low-kilohertz range (20 and 38 kHz). Results obtained at two higher frequencies (512 and 850 kHz) indicated a significant increase in bacteria count suggesting declumping. In assessing the bacterial kill with time under different sonication regimes three types of behaviour were characterized: High power ultrasound (lower frequencies) in low volumes of bacterial suspension results in a continuous reduction in bacterial cell numbers i.e. the kill rate predominates. High power ultrasound (lower frequencies) in larger volumes results in an initial rise in cell numbers suggesting declumping of the bacteria but this initial rise then falls as the declumping finishes and the kill rate becomes more important. Low intensity ultrasound (higher frequencies) gives an initial rise in cell numbers as a result of declumping. The kill rate is low and so there is no significant subsequent decrease in bacterial cell numbers.

The use of ultrasound for the extraction of bioactive principles from plant materials

The paper presents our results concerning the ultrasonically assisted extraction of bioactive principles from plant material. A comparison with classical methodologies is presented and technological aspects of ultrasonically assisted extraction are discussed.

A review of research into the uses of low level ultrasound in cancer therapy

The use of low power ultrasound in therapeutic medicine is a developing field and this review will concentrate on the applications of this technology in cancer therapy. The effects of low power ultrasound have been evaluated in terms of the biological changes induced in the structure and function of tissue. The main fields of study have been in sonodynamic therapy, improving chemotherapy, gene therapy and apoptosis therapy. The range of ultrasonic power levels that can be effectively employed in therapy appears to be narrow and this may have hindered past research in the applications in cancer treatment.

The extraction of rutin from flower buds of Sophora japonica

The efficiency of extraction of rutin from Sophora japonica is improved by ultrasound but is dependent on the solvent employed. Rutin is a compound with antioxidant activity and aqueous solvents appear to be unsuitable for ultrasonic extractions due to the formation of free radicals from the insonation of the solvent. The application of ultrasound to methanolic extraction gave a significant reduction in extraction time and an increase in maximum yield.

Enhancement of ultrasonic cavitation yield by multi-frequency sonication

The paper reports the enhanced effect of multi-frequency ultrasonic irradiation on cavitation yield. The cavitation yield is characterized by electrical conductivity determination, fluorescence intensity determination and iodine release method. Two-frequency (28 kHz/0.87 MHz) orthogonal continuous ultrasound, two-frequency (28 kHz/0.87 MHz) orthogonal pulse ultrasound and three-frequency (28 kHz/1.0 MHz/1.87 MHz) orthogonal continuous ultrasound have been used. It has been found that the combined irradiation of two or more frequencies of ultrasound can produce a significant increase in cavitation yield compared with single frequency irradiation. The possible mechanisms of the enhanced effect are briefly discussed.