Sandra E. Kentish

Minimising oil droplet size using ultrasonic emulsification

The efficient production of nanoemulsions, with oil droplet sizes of less than 100nm would facilitate the inclusion of oil soluble bio-active agents into a range of water based foods. Small droplet sizes lead to transparent emulsions so that product appearance is not altered by the addition of an oil phase. In this paper, we demonstrate that it is possible to create remarkably small transparent O/W nanoemulsions with average diameters as low as 40nm from sunflower oil. This is achieved using ultrasound or high shear homogenization and a surfactant/co-surfactant/oil system that is well optimised. The minimum droplet size of 40nm, was only obtained when both droplet deformability (surfactant design) and the applied shear (equipment geometry) were optimal. The time required to achieve the minimum droplet size was also clearly affected by the equipment configuration. Results at atmospheric pressure fitted an expected exponential relationship with the total energy density. However, we found that this relationship changes when an overpressure of up to 400kPa is applied to the sonication vessel, leading to more efficient emulsion production. Oil stability is unaffected by the sonication process.

Effects of ultrasound on the thermal and structural characteristics of proteins in reconstituted whey protein concentrate.

The sonication-induced changes in the structural and thermal properties of proteins in reconstituted whey protein concentrate (WPC) solutions were examined. Differential scanning calorimetry, UV-vis, fluorescence and circular dichroism spectroscopic techniques were used to determine the thermal properties of proteins, measure thiol groups and monitor changes to protein hydrophobicity and secondary structure, respectively. The enthalpy of denaturation decreased when WPC solutions were sonicated for up to 5 min. Prolonged sonication increased the enthalpy of denaturation due to protein aggregation. Sonication did not alter the thiol content but resulted in minor changes to the secondary structure and hydrophobicity of the protein. Overall, the sonication process had little effect on the structure of proteins in WPC solutions which is critical to preserving functional properties during the ultrasonic processing of whey protein based dairy products.

Innovations in separations technology for the recycling and re-use of liquid waste streams

As the costs of wastewater disposal increase more emphasis is being placed upon the recovery and recycling of valuable chemicals contained within these streams. In this article, we review three separations technologies that facilitate such recycling. Solvent extraction is an established technique for recovery of heavy metals and other pollutants and is most useful in large and medium scale operations when solute concentrations are high. Membrane technology is a more recent development that can be used in conjunction with extraction solvents to extend the range of conditions under which such processes are viable. Finally, adsorption and ion-exchange processes provide the means for extracting valuable contaminants when the concentrations of such so lutes are low.

Carbon Dioxide Separation through Polymeric Membrane Systems for Flue Gas Applications

The capture and storage of carbon dioxide has been identified as one potential solution to greenhouse gas driven climate change. Efficient separation technologies are required for removal of carbon dioxide from flue gas streams to allow this solution to be widely implemented. A developing technology is membrane gas separation, which is more compact, energy efficient and possibly more economical than mature technologies, such as solvent absorption. This review examines the recent patented developments in polymeric based membranes designed for carbon dioxide separation from mixed-gas systems. Initially, the background to polymeric membrane separation is provided, with an overview of past polymeric designs. This is followed by a discussion on the current state of the art; in particular developments in mixed matrix polymeric membranes and facilitated transport polymeric membranes for improved carbon dioxide permeation and selectivity. Recent developments in other membrane types, carbon and inorganic, are reviewed for comparison purposes with polymeric developments. Finally, a brief comment on the future directions of polymeric membrane gas separation technologies is provided.

Effects of Minor Components in Carbon Dioxide Capture Using Polymeric Gas Separation Membranes

Abstract: The capture of carbon dioxide by membrane gas separation has been identified as one potential solution to reduce greenhouse gas emissions. In particular, the application of membranes to CO2 capture from both pre‐ and post‐combustion strategies is of interest. For membrane technology to become commercially viable in CO2 capture, a number of factors need to be overcome, one being the role of minor components in the process on membrane performance. This review considers the effects of minor components in both pre‐ and post‐combustion use of polymeric membranes for CO2 capture. In particular, gases such as SOx, NOx, CO, H2S, NH3, as well as condensable water and hydrocarbons are reviewed in terms of their permeability through polymeric membranes relative to CO2, as well as their plasticization and aging effects on membrane separation performance. A major conclusion of the review is that while many minor components can affect performance both through competitive sorption and plasticization, much remains unknown. This limits the selection process for membranes in this application.

Ultrasonic processing of dairy systems in large scale reactors

High intensity low frequency ultrasound was used to process dairy ingredients to improve functional properties. Based on a number of lab-scale experiments, several experimental parameters were optimised for processing large volumes of whey and casein-based dairy systems in pilot scale ultrasonic reactors. A continuous sonication process at 20 kHz capable of delivering up to 4 kW of power with a flow-through reactor design was used to treat dairy ingredients at flow rates ranging from 200 to 6000 mL/min. Dairy ingredients treated by ultrasound included reconstituted whey protein concentrate (WPC), whey protein and milk protein retentates and calcium caseinate. The sonication of solutions with a contact time of less than 1 min and up to 2.4 min led to a significant reduction in the viscosity of materials containing 18% to 54% (w/w) solids. The viscosity of aqueous dairy ingredients treated with ultrasound was reduced by between 6% and 50% depending greatly on the composition, processing history, acoustic power and contact time. A notable improvement in the gel strength of sonicated and heat coagulated dairy systems was also observed. When sonication was combined with a pre-heat treatment of 80 degrees C for 1 min or 85 degrees C for 30s, the heat stability of the dairy ingredients containing whey proteins was significantly improved. The effect of sonication was attributed mainly to physical forces generated through acoustic cavitation as supported by particle size reduction in response to sonication. As a result, the gelling properties and heat stability aspects of sonicated dairy ingredients were maintained after spray drying and reconstitution. Overall, the sonication procedure for processing dairy systems may be used to improve process efficiency, improve throughput and develop value added ingredients with the potential to deliver economical benefits to the dairy industry.

Hot topic: sonication increases the heat stability of whey proteins.

The thickening or gelling of protein-based dairy streams and ingredients upon exposure to heat has been an ongoing problem in dairy processing for many decades. This phenomenon can restrict the range of dairy product options and reduce manufacturing efficiencies by limiting the type and extent of heat treatment that can be used. In this report, we outline a novel approach to overcoming this problem. The use of preheating treatments to induce whey protein aggregate formation in whey products is well known in the field. However, we show that the application of ultrasound for a very short duration after such a heating step breaks down these aggregates and prevents their reformation on subsequent heating, thereby reducing the viscosity increase that is usually associated with this process. This novel technique has the potential to provide significant economic benefit to the dairy manufacturing industry.

The Physical and Chemical Effects of Ultrasound

Ultrasound refers to sound waves above the human hearing range. The physical effects of ultrasound include the turbulence associated with cavitational bubble collapse, microjetting, and the streaming movement of cavitational microbubbles to the pressure antinodes of a standing wave field. These physical effects are strongest near to fluid/solid and fluid/fluid boundaries, which mean that ultrasound is extremely effective in enhancing heat and mass transfer within such boundary layers. Chemical effects arise from free radical production during transient cavitational collapse of bubbles.

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.

The pasting properties of sonicated waxy rice starch suspensions

The effect of sonication on the pasting properties of waxy rice starch solutions (5 wt%) was investigated. It has been found that the functionality of starch granules was significantly influenced by the length of sonication and the solution temperature. A comparison of the pasting behaviour showed that the peak and final viscosities of the starch dispersions sonicated at temperatures near the onset temperature of gelatinisation were lower than those of the non-sonicated dispersions. The particle size measurements showed that the size of the heated and sonicated granules were smaller than that of the heated non-sonicated starch granules. Scanning electron microscopy (SEM) observations showed that the starch granule surface was not affected by sonication, and the size exclusion chromatography did not show any reduction in the size of the starch molecules. Based on these observations, the change in the pasting behaviour is explained in terms of the solubilisation of the swollen starch granules and starch aggregates induced by sonication.