Milk Processors Work on Making Pasteurization Cool
Nonthermal pulsed electric field technology gets a boost from Arla Foods, European 'Smartmilk' researchers.
By Bob Sperber, Plant Operations Editor | 05/11/2011
Milk processors for decades have relied on heat pasteurization to kill pathogens and prevent foodborne illness. But increasing numbers of people seem to be saying they don't want to settle for the product degradation of high-temperature conventional pasteurization.
"Probably for its superior taste, raw milk has continued to be consumed by significant numbers of people in rural areas across Europe and Eastern Europe," notes literature from a Spanish advanced engineering and research provider, Iris (www.iris.cat). The company is coordinating a "Smartmilk" (www.smartmilk.eu) consortium backed by the European Commission and joined by engineering, consulting and dairy firms. In addition to small and mid-sized companies, multinational Arla Foods (www.arla.com) has joined the effort.
The two-year Smartmilk project, officially launched in October 2010, seeks to better preserve the taste and nutrition of milk while retaining the safety and shelf-life of pasteurized milk.
The effort follows in the footsteps of prior, successful research into nonthermal pulsed electric field (PEF) technology. The technology has already proven it can process milk at a significantly lower temperature while delivering a safe product that preserves the integrity of milk fat and proteins, enzymatic activity and other desirable attributes. In addition, the Smartmilk project seeks to deliver those results along with evidence that shelf life can match that of conventionally pasteurized milk.
Diversified Technologies' units start with a 25 kW, $250,000 lab-scale system with 300 l/hr. capacity (shown), but are said to be scalable to thousands of gallons of milk per hour.
PEF has been researched and applied on both sides of the Atlantic. "It's a proven technology," says Iris' Edurne Gaston, Smartmilk project coordinator. "It has already been used for fruit juices in processing, also for waste management and water purification." Since 2005 the method has had clearance from the U.S. FDA, and research continues to move forward.
A PEF processing system has three basic components: a high-voltage power supply, a pulse modulator to switch the voltage on and off very – very, very – rapidly, and a treatment chamber where pulses are applied to the product flowing through pipes and the electrodes.
In a PEF milk pasteurization processing system, milk flows through narrowly spaced electrodes and is subjected to quick pulses to break open the cell walls of vegetative bacteria, mold and yeast. Process parameters such as electrode spacing, voltage and pulse modulation vary with the application.
"To size a system, you start with desired flow rate, size your treatment chamber accordingly and then develop the electrical specifications," says Mike Kempkes, an electrical engineer turned vice president of marketing for Diversified Technologies Inc. (www.divtecs.com), Bedford. Mass., a manufacturer of PEF systems.
A large, commercial fluid milk application, for instance, might require a treatment chamber diameter (and electrode spacing) of a centimeter and a half. The larger the span, the higher the voltage required to maintain the desired electric field, measured in volts per meter. Most food applications, Kempkes says, are in the 30-35 kV/cm range.
And those quick pulses? They're measured and controlled down to a few microseconds, and applied at high frequency to ensure treatment of the entire volume of product flowing through the treatment chamber. This can translate to anywhere from hundreds of pulses to several thousand per second.
PEF can be used alone or in conjunction with other technologies. For example, one application has treated milk for three seconds at roughly 50 degrees Celsius (122 degrees Fahrenheit) to control quality while avoiding the alleged heat degradation of conventional pasteurization. Citing PEF's track record and potential in dairy foods, Carmen Moraru, associate professor at Cornell University, noted that in milk processing, thermally assisted PEF can improve safety, freshness, nutritional value and retention of proteins such as the lactoferrin and lactoglobulin.
Similarly, the Smartmilk project is taking a cue from prior research at University College Dublin, where researchers combined PEF and manothermosonication (MTS), which combines ultrasound, pressure and heat, but less of the latter than conventional pasteurization requires. That research reduced inactivation of L. innocua on a par with conventional pasteurization.
Gaston says the MTS "assist" will provide "synergistic effects, so we expect to have a situation where one plus one equals three."
Milk processing presents a special challenge owing, for example, to its higher initial microbial load compared to high-acid juice. "While PEF kills yeasts and molds in their vegetative state, it does not kill spores because they do not have an active cell wall PEF can work on," says Kempkes.
While "cranking-up the power" can affect enzymes, it's the high energy and not the PEF specifically that can break them down.
That said, combination of PEF and MTS may be an effective treatment for spores, and something the Smartmilk project will test, according to Gaston.