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."strong>Pulsed-milk challenges
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.
Milk is, however, well suited to PEF in other ways. It is a continuously pump-able fluid with low electrical conductivity and low or no solids, which affect power levels and electrode spacing. PEF, like conventional pasteurization (barring ultrapasteurization), does not kill spores or enzymes. With refrigeration, growth of spores can be inhibited for a conventional shelf life, and the presence of enzymes in milk can be seen as a benefit.
The Smartmilk project follows a long line of PEF developments in the food industry that extends as far back as a 1920 "Electro-Pure" process.
The heart of the pulsed electric field system at the Ohio State University pilot plant.
Kraft, General Mills and other processors and technology companies joined forces in 2000 with The Ohio State University and the U.S. Army's Natick Laboratory to create a PEF pilot system that continues to inform ongoing research. DTI provided the project with a solid-state PEF pulse modulator. OSU developed the PEF treatment chamber and pulse generator, which DTI has since licensed for sale to its customers. The system successfully demonstrated pasteurization of juices, milk, yogurt, soups and liquid eggs.
The project was over by mid-decade; the equipment now resides at the Eastern Regional Research Center of the USDA Agricultural Research Service in Wyndmoor, Pa.
The Smartmilk project started with a laboratory-scale system. A larger scale prototype will be ready in spring, 2012, Gaston says. This pre-industrial-scale processing system is as far as the two-year project expects to take the technology before, researchers hope, a suitor comes calling for a full-scale system.
Earlier in the decade, OSU reported that across food applications, PEF would add "only $0.03-$0.07/L to final food costs," and that the technology is scalable and capable of processing between 1,000 and 5,000 liters of liquid foods per hour.
And, says Kempkes: "The largest system we have is sized at 10,000 liters per hour for activated sludge in a wastewater application." He says that system could be applied to "about 6,000 liters an hour of orange juice… with or without the pulp."
The cost of that system would be roughly $800,000, not including fluid handling and packaging before and after the process. Larger systems are possible, but the economics of operating larger systems versus multiple smaller systems remains to be determined.
Followers of nonthermal processing already know the process works. What remains is to prove its mainstream commercial viability, especially following the short-lived PEF success of Genesis Juice Cooperative.
Genesis sold unpasteurized juices, and was shuttered in 2004 following FDA's warnings of "serious deviations" in Juice Hazard Analysis Critical Control Point regulations. The company was missing HACCP plans and had no sanitation control records. Genesis successfully introduced a PEF treated line of FDA-compliant juices in 2005, but was unable to overcome the financial impact of the shutdown, and was subsequently sold to another company, without the PEF process.
On the upside, researchers continue to show PEF is a promising method for juice, milk and other applications across the food industry. There remains significant potential for this and other nonthermal alternatives for producing safe, practical alternatives that improve upon the current compromises of high-heat processing.