Process intensification in the food industry: hydrodynamic and acoustic cavitation in fresh milk treatment
Cavitation phenomena, which are commonly connected to erosion effects in fluid-flow systems, can be valid non-conventional mild disinfection processes for the treatment of fresh milk, clear juices and aqueous beverages. In this work, two flow-through reactors for hydrodynamic and ultrasonic cavitation have been tested in an attempt to achieve the simultaneous pasteurization and homogenization of fresh cow milk at low temperature and in a modified atmosphere. In this work, hydrodynamic cavitation in a loop reactor gives up to 88% microorganism inactivation when working at 6 bar pressure in a CO2 atmosphere for 30 min. Acoustic cavitation in a ultrasonic flow reactor (Sonotube®, power 370 W) gave microorganism abatement percentages of 95% in 10 min. Fast and efficient homogenization occurred in both loop reactors. An additional, and important, advantage of these techniques is the fact that they can easily be scaled-up for industrial applications.
Fresh milk is a perishable foodstuff that requires rapid industrial treatment to make it shelf stable. The classic dairy industry processes used to produce milk at an affordable price are homogenisation and pasteurization. Standard homogenisation is used to reduce the size of fat globules and consists of forcing the liquid through a narrow gap (100–300 mm) in a homogenisation valve at an up-stream pressure of about 20–60 MPa. Thermal treatment, which is used to reduce microbial spoilage, presents several drawbacks (protein denaturation, decrease in nutritional values etc.). These facts have prompted the development of non-thermal procedures which aim to combine both homogenisation and pasteurization steps in a single run. Hydrodynamic and acoustic cavitation can potentially address this need (1). Ultrasound and hydrodynamic cavitation technologies have increasingly been adopted in industrial beverage and food processing. Cavitation is the mechanism by which the desired effects occur in liquid foods. Microorganism killing, enzyme activity inhibition, wine maturation, emulsification and crystallization all rely on the mechanism of cavitati ...