Subjecting food to ultra-high pressures seems a certain recipe for making mush, but scientists who are taking a fresh look at this 100-year-old approach to food processing have been surprised at what the technology offers.
Preliminary results suggest that cheese ripening can be greatly accelerated by subjecting cheeses to these high pressures. Milk and fruit juices could be treated to reduce spoiling and lengthen shelf life. Other studies examine why meat becomes tenderer when subjected to pressure treatment.
The Dairy Products Research Centre at Moorepark and the department of food science at University College Cork are collaborating on an EU-funded study looking at how high-pressure treatment might be used with dairy products. Dr Alan Kelly heads the work at UCC and Dr Tom Beresford and Dr Pat Murphy are involved at Moorepark.
The treatments require the application of remarkable pressures, ranging from 500 to 10,000 atmospheres. The higher figure is close to 150,000 pounds of pressure per square inch, 10 times the pressure encountered at the bottom of the Pacific Ocean, Dr Kelly explained. "It is a technology that has been around for a long time, but is in its infancy in food processing," he says.
Remarkably, the foods do not emerge from the test rig fit for the bin. "The products come out looking about identical as when they went in," Dr Kelly said. "The pressure is isostatic. It is generated uniformly throughout the sample."
A small test rig at Moorepark can take cheese samples of up to 150 grams. The sample is covered and placed in the chamber, which is filled with a water and oil mix, and high-pressure pumps apply the pressure.
Pressure treatment has advantages over heat treatment, Dr Kelly said. Both techniques are effective at destroying microbes. Pressure treatment has much less effect on flavour compared with heating and helps to preserve the nutritional content. It can also deliver interesting and potentially useful changes in the food, by altering the properties of an ingredient without loss of nutritional value or taste, for example. High-pressure treatment therefore represents a potentially valuable new tool for minimal processing of foods, Dr Kelly explained. Pressure-treated foods are already reaching some markets. Treated orange juice, which has a taste identical to fresh juice but a far longer shelf life, is already available in Japan.
The work at UCC and Moorepark focuses on dairy products and the results are particularly promising in cheese production. Cheeses must mature for months, and in some cases for years, before they are ready for sale, and storage and ripening facilities are a significant fraction of the total production cost.
The ripening process is highly complex, Dr Kelly said, involving contributions by both bacterial starter cultures and rennet, the substance which causes the milk to coagulate. An early Japanese study suggested that cheese could be ripened in three days when exposed to 500 atmospheres pressure, and the UCC/Moorepark team is conducting experiments to test this process.
The Japanese results were not duplicated, but pressure treatment does speed ripening, Dr Kelly said. Preliminary results using the Moorepark device showed that the biochemical changes associated with maturing happened more quickly. Even a small improvement in ripening time would be of major benefit to producers, who could reduce costs. The process was also found to kill off bacteria and moulds, which could make a safer cheese that keeps longer.
The team is now examining this process, trying to understand how the pressure influences the rennet and starter bacteria enzymes that contribute to ripening. The object is to try to find the best combination of pressure and variety of starter to deliver good flavour in a quicker-ripening cheese.