Creaming enhancement in a liter scale ultrasonic reactor at selected transducer configurations and frequencies

Abstract

Recent research has shown that high frequency ultrasound (0.4-3 MHz), can enhance milkfat separation in small scale systems able to treat only a few milliliters of sample. In this work, the effect of ultrasonic standing waves on milkfat creaming was studied in a 6L reactor and the influence of different frequencies and transducer configurations in direct contact with the fluid was investigated. A recombined coarse milk emulsion with fat globules stained with oil-red-O dye was selected for the separation trials. Runs were performed with one or two transducers placed in vertical (parallel or perpendicular) and horizontal positions (at the reactor base) at 0.4, 1 and/or 2 MHz (specific energy 8.5 ± 0.6 kJ/kg per transducer). Creaming behavior was assessed by measuring the thickness of the separated cream layer. Other methods supporting this assessment included the measurement of fat content, backscattering, particle size distribution, and microscopy of samples taken at the bottom and top of the reactor. Most efficient creaming was found after treatment at 0.4 MHz in single and double vertical transducer configurations. Among these configurations, a higher separation rate was obtained when sonicating at 0.4 MHz in a vertical perpendicular double transducer setup. The horizontal transducer configuration promoted creaming at 2 MHz only. Fat globule size increase was observed when creaming occurred. This research highlights the potential for enhanced separation of milkfat in larger scale systems from selected transducer configurations in contact with a dairy emulsion, or emulsion splitting in general.

Temperature effects on the ultrasonic separation of fat from natural whole milk

“…The particle size distribution and the associated volume weighted mean diameter, D [4,3], was determined for all samples before and after processing by ultrasound using a Malvern Mastersizer 2000 (Malvern Instruments Ltd., Worcestershire) with deionised water as the dilutant. Further details of the analysis can be found in Leong et al [4].…”

“…Further details of the analysis can be found in Leong et al [4]. The D [4,3] value represents the mean particle size of the samples, weighted by the total volume of the fat droplets. The purpose of this measurement was to provide an indication of the selectivity of ultrasound under different conditions (frequency and temperature) to manipulate different sized fat globules in a sample of natural whole milk to the fat enriched top or fat depleted bottoms.…”

“…The technique using ultrasound waves to initiate separation of fat globules from milk has been recently reported by Juliano et al [2,3] using a recombined emulsion and Leong et al [4] using natural milk. Milk fat separation rates many times faster than natural creaming have been reported using ultrasound.…”

“…It was observed that the input of ultrasound to the milk system resulted in heat generation over time, causing the overall system to increase in temperature. Studies by Juliano et al [2,3] demonstrated the enhanced ultrasonic-assisted fat separation using reconstituted milk fat emulsions at 400 kHz, 1 and 2 MHz ($35 W/L per transducer used). These studies were performed with an initial temperature of 35°C, on the supposition that the higher proportion of liquid milk fat at these temperatures would be more readily separable by ultrasound.…”

Ultrasonic Processing for Dairy Applications: Recent Advances

“…Juliano et al [56] demonstrated the concept of ultrasonic separation for natural whole milk in small test tubes of 7-mL volume and was later successful in scaling this process up to 6 L using a recombined milk emulsion [57]. Leong et al [69] established suitable ultrasonic parameters that enable successful separation of natural whole milk in large scale, demonstrating the importance of energy density and effectiveness of high-frequency ultrasound (1 and 2 MHz) to separate the small fat globules distributed in milk (*4 lm diameter).…”