Submitted to: Journal of Food Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/5/2012
Publication Date: 2/22/2012
Citation: Geveke, D.J., Torres, D. 2012. Pasteurization of grapefruit juice using a centrifugal ultraviolet light irradiator. Journal of Food Engineering. 111(2):241-246. Interpretive Summary: The pharmaceutical industry uses centrifugal force UV irradiators to inactivate viruses in serum plasma without heat; however, studies are lacking on nonthermal pasteurization of juices using centrifugal force UV irradiators. This study determined the nonthermal inactivation of Escherichia coli and Saccharomyces cerevisiae in grapefruit juice using a centrifugal UV irradiator that formed a very thin film which allowed the UV to penetrate all the way through the juice. E coli was reduced by 99.999% and S. cerevisiae was reduced by 99.9999% within 3.2 seconds using only a fraction of the energy of the traditional thermal pasteurization treatment. These results suggest that grapefruit juice, as well as other liquid foods, may be pasteurized using a UV irradiator that centrifugally forms a thin film. Such rapid UV treatments could ensure food safety while maintaining quality.
Technical Abstract: The pharmaceutical industry uses UV irradiators to inactivate viruses in liquids without heat. The penetration depth of UV in some liquids, such as serum plasma, can be short. To overcome this, very thin films may be produced by centrifugal force, small diameter tubing, or other means. Many liquid foods also have low UV penetration depths. Studies are lacking on nonthermal pasteurization of juices using a UV irradiator that centrifugally forms a thin film. The objective of this study was to determine the nonthermal inactivation of Escherichia coli and Saccharomyces cerevisiae in grapefruit juice using such a device. Grapefruit juice was inoculated with E. coli K12 ATCC 23716 or S. cerevisiae ATCC 4026602 to 7.5 and 7.0 log cfu/ml, respectively. The juice was processed at the following conditions: UV intensity 1.5 to 7.5 mW/cm2; treatment time 3.2 s, cylinder rotational speed 450 to 750 RPM, cylinder inclination angle 15 to 45 degrees, outlet temperature 11 deg C, and flow rate 300 ml/min. The effect of storing the UV treated cider for 35 d was also investigated. Appropriate dilutions of the samples were pour plated with TSA for E. coli and Sabouraud dextrose agar (SDA) for S. cerevisiae. Sublethal injury was determined using TSA + 3% NaCl and SDA + 5% NaCl. Nonthermal UV processing at 19 mJ/cm2, 450 RPM and 15 degrees reduced E coli in grapefruit juice by 5.1 log. A dose of 14 mJ/cm2 reduced S. cerevisiae by 6.0 log. Inactivation increased linearly with increasing UV intensity. The inactivations at 600 and 750 RPM were similar, and were better than at 450 RPM. The results at 30 and 45 degrees were similar, and were better than at 15 degrees. The occurrence of sublethal injury of E. coli and S. cerevisiae was not detected. Storing UV processed grapefruit juice at 4 and 10 deg C reduced the surviving E coli to below 1 log cfu/ml in 14 deg. Processing UV juice reduced the population of S. cerevisiae to less than 1 log cfu/ml where it remained for 35 deg during refrigerated storage. These results suggest that grapefruit juice may be pasteurized using a nonthermal UV irradiator that centrifugally forms a thin film. Such UV devices may be able to pasteurize other liquid foods, and have significance for ensuring food safety while maintaining quality.