Design parameters for the separation of fat from natural whole milk in an ultrasonic litre-scale vessel

Abstract

The separation of milk fat from natural whole milk has been achieved by applying ultrasonic standing waves (1 MHz and/or 2 MHz) in a litre-scale (5L capacity) batch system. Various design parameters were tested such as power input level, process time, specific energy, transducer-reflector distance and the use of single and dual transducer set-ups. It was found that the efficacy of the treatment depended on the specific energy density input into the system. In this case, a plateau in fat concentration of ∼20% w/v was achieved in the creamed top layer after applying a minimum specific energy of 200 kJ/kg. In addition, the fat separation was enhanced by reducing the transducer reflector distance in the vessel, operating two transducers in a parallel set-up, or by increasing the duration of insonation, resulting in skimmed milk with a fat concentration as low as 1.7% (w/v) using raw milk after 20 min insonation. Dual mode operation with both transducers in parallel as close as 30 mm apart resulted in the fastest creaming and skimming in this study at ∼1.6 g fat/min.

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

“…During high frequency separation, the physical effects of unstable cavitation are negligible [10] and therefore will not affect the integrity of milk fat globules. Application of ultrasound using 1 MHz at similar power levels considered in this study has shown no evidence of damage to the structural integrity of the fat globules previously by zeta potential and visual inspection [4]. Even though the cavitational yield due to transient collapse peaks between 600 kHz and 1 MHz, decreasing at higher frequencies [11,12], free radicals formed are unlikely to affect the structural integrity of such globules, although modification of other components in the bulk medium may occur [13][14][15].…”

“…A similar protocol as reported by Leong et al [4] using raw whole bovine milk sourced from the farm (Department of Primary Industries Ellinbank, Australia) has been employed.…”

“…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.…”

Ultrasonic Processing for Dairy Applications: Recent Advances

“…Typically performed in large-scale manufacture by centrifugation, high-frequency ultrasound ([400 kHz) has recently been reported as an alternative separation technology that can enhance the rate of milk creaming by 'natural' gravitational sedimentation [69,70].…”

“…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). Further studies by the same group have demonstrated that operation at moderate temperatures between 25 and 40°C are more optimal to the fat separation process due to the influence of temperature on the physical properties of the fat globules such as density, viscosity and liquid/solid ratio [70].…”