In the US, an Agricultural Research Service scientist has devised a means of using radio waves to make fruit juice safer.
The radio frequency electric fields (RFEF) technique is said to inactivate bacteria inapple juice without heating it. Although RFEF has been studied for more than 50 years as a pasteurisation method, this is the first confirmed instance ofa successful inactivation of bacteria using this technique in fruit juice.
Conventional pasteurisation using heat can affect the nutrient compositionand flavour of fruit and vegetable juices. The RFEF technique itself is non-thermal because the inactivation is not produced by heat. However, when moderate heat is applied, the combined effect is much greater than theeffect of either process used alone.
David Geveke, a chemical engineer in the ARS Food Safety Intervention Technologies Research Unit at the agency's Eastern Regional Research Center in Pennsylvania, built a specially designed treatment chamber to applyhigh-intensity RFEF to apple juice. Researchers conducted experiments usingEscherichia coli K12, a harmless form of bacteria used by researchers tostudy similarly behaving pathogenic strains, such as E. coli O157:H7.
Apple juice was exposed to electrical field strengths of up to 20 kilovoltsper centimetre and frequencies in the range of 15 to 70 kilohertz, using a4-kilowatt power supply. For some perspective, lightning occurs at fieldstrengths of 30 to 40 kilovolts per centimetre, and 20 kilohertz isconsidered to be in the upper range of human hearing. Increasing the fieldstrength and temperature, as well as decreasing the frequency, enhancedinactivation, according to Geveke. E. coli in juice at 50 degrees Celsius was reduced by 99.9 per cent.
RFEF could provide an alternative to pasteurisation by heat. According to Geveke, the RFEF process could be used to treat heat-sensitive products such as fruit juices, vegetable juices and liquid egg products.
ARS is the US Department of Agriculture's chief scientific research agency.