Pasteurization of grapefruit juice using a centrifugal ultraviolet light irradiator

• Published in: Journal of food engineering 2012-07, Vol.111 (2), p.241-246
• Main Authors: Geveke, David J., Torres, Daniel
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Cylinders; Escherichia coli; Food engineering; Food industries; Food microbiology; Foods; Fundamental and applied biological sciences. Psychology; General aspects; Grapefruit; Grapefruit juice; Inactivation; Juices; Nonthermal; Pasteurization; Saccharomyces cerevisiae; Thin films; Ultraviolet; Ultraviolet light
• ISSN: 0260-8774; 1873-5770
• DOI: 10.1016/j.jfoodeng.2012.02.026

► A centrifugal UV irradiator nonthermally inactivated microorganisms in grapefruit juice. ► The centrifugal irradiator formed a very thin film of juice which is conducive to UV treatment. ► Escherichia coli and Saccharomyces cerevisiae in grapefruit juice were reduced by 5 and 6log, respectively. ► Treatment took 3.2s and used a fraction of the energy of traditional thermal pasteurization. ► Grapefruit juice may be pasteurized using a nonthermal UV irradiator that centrifugally forms a thin film. Studies are lacking on the nonthermal pasteurization of liquid foods using UV irradiators that centrifugally form very thin films to overcome the problem of limited penetration depth of UV. Grapefruit juice inoculated with Escherichia coli or Saccharomyces cerevisiae was processed at the following conditions: UV dose 4.8–24mJ/cm2; treatment time 3.2s, cylinder rotational speed 450–750rpm, cylinder inclination angle 15–45°, outlet temperature 11°C, and flow rate 300ml/min, and was stored for 35days. Appropriate dilutions of the samples were pour plated with TSA and TSA+3% NaCl for E. coli and Sabouraud dextrose agar (SDA) and SDA+5% NaCl for S. cerevisiae. Nonthermal UV processing at 19mJ/cm2, 450rpm and 15° reduced E. coli in grapefruit juice by 5.1log10. A dose of 14mJ/cm2 reduced S. cerevisiae by 6.0log10. Inactivation increased linearly with increasing UV dose. The inactivations at 600 and 750rpm were similar, and were better than at 450rpm. The results at 30° and 45° were similar, and were better than at 15°. The occurrence of sublethal injury in either microorganism was not detected. Storing UV processed grapefruit juice at 4 and 10°C reduced the surviving E. coli to below 1log10cfu/ml in 14days. Processing UV juice reduced the population of S. cerevisiae to less than 1log10cfu/ml where it remained for 35days during refrigerated storage. These results suggest that grapefruit juice may be pasteurized using a nonthermal UV irradiator that centrifugally forms a thin film.