Lots of food gets heat-treated during processing, but what happens if you apply pressure instead, asks Dick Ahlstrom
People complain about pressure at work but few experience the kind of pressure dealt with by Kaushal Kothari. It equates to the weight of two adult elephants standing together on the head of a pin.
Kothari is a PhD student based at Teagasc's Moorepark Research Centre in Fermoy, Co Cork. Earlier this month he won the RDS Teagasc Walsh Fellowship Seminar silver medal for the best presentation at the event.
His talk, selected from among 13 doctoral research projects, was all about high-pressure processing of foods and ingredients.
When he describes pressure, he means pressure. Foods are put under pressures in the 200 to 800 megapascal range, or 29,000 to 116,000lbs per square inch or 2,000 to 8,000 bar.
While high-pressure treatment of this kind can be used as an alternative to heat treatment to kill bacteria, he is more interested in what it does to the consistency of the food.
"Our main interest is how does it change the texture of the products," says Kothari. "We are looking at the effect on proteins and fats. You get a lot of changes in the food or ingredient depending on the pressure and the time at high pressure."
The changes can be quite dramatic, he says. "When you high-pressure treat skimmed milk, when it comes out it changes to become translucent like whey."
Pressure treatment may have specific advantages over heat-based treatments. "There are two main advantages. Heat treatment damages a lot of the nutrients in milk and other foods," says Kothari. Less damage is done with pressure treatment.The second is alteration to the consistency of an ingredient or finished product.
Changing food consistency may help later with less subsequent processing depending on the product, he says. Milk for yoghurt production is often heated to between 90 and 95 degrees for a short time to kill bacteria. Unfortunately the resultant yoghurt is more likely to separate or form small pools of water on its surface, something consumers find off-putting, he says.
This change does not seem to occur with pressure treatment, and in fact the treatment improves texture.
"What we found is when we made yoghurt from milk, because the proteins changed in size the yoghurt was more viscous and thicker than when using heat-treated milk."
Heat treatment requires the addition of extra ingredients such as modified starch to prevent water separation, but there was no need for these additives when using pressure treatments, he adds. "We tried to avoid the addition of anything else."
Kothari is in the final year of his PhD programme at Moorepark, run in conjunction with University College Cork. His Moorepark supervisors are Dr Tom Beresford and Dr Tim Guinee and the UCC supervisor is Dr Alan Kelly.
Kothari and the 13 other Walsh Fellowship students he competed against are judged on the quality of their presentations to three scientist adjudicators. The winner receives the RDS Teagasc Silver Medal.
The fellowship programme, which has led to 800 PhD graduates, is named after Dr Tom Walsh, the first director of the then Agricultural Institute, which was the forerunner to Teagasc. Fellows receive about €17,500 a year for the three years of their PhD programme.