Ultraviolet Treatment of Orange Juice to Inactivate E. coli O157:H7 as Affected by Native Microflora

Abstract

The effect of yeast concentration on ultraviolet (UV) inactivation of five strains of Escherichia coli O157: H7 from different sources, inoculated both individually and simultaneously in orange juice, was analyzed and mathematically modeled. The presence of yeast cells in orange juice decreases the performance of UV radiation on E. coli inactivation. UV absorption coefficients in the juice increased with increasing yeast concentration, and higher UV doses were necessary to inactivate bacterial strains. UV intensities of I=3.00±0.3 mW/cm 2 and exposure times (t) between 0 and 10 min were applied; radiation doses (energy, E=I×t) ranging between 0 and 2 J/cm 2 were measured using a UV digital radiometer. All the tested individual strains showed higher resistance to the treatment when UV radiation was applied at 4°C in comparison to 20°C. UV inactivation of E. coli O157:H7 individual strain was satisfactory fitted with a first order kinetic model. A linear relationship was found between UV absorptivities and D values (radiation doses required to decrease microbial population by 90%) for each strain. The dose required to reach 5-log reduction for the most unfavorable conditions that is the most UV resistant strain, and maximum background yeast concentration was 2.19 J/cm 2 at 4°C (corresponding to 11 min of UV treatment) and 2.09 J/cm 2 at 20°C (corresponding to 10.55 min of UV treatment). When a cocktail of strains was inoculated in orange juice, the logistic equation was the best model that fits the experimental results due to the deviation from the log-linear kinetics. The UV resistance between strain cocktail and single strain were mathematically compared. Slopes of the decline curves for strain cocktail at high UV doses were lower than the slopes of the log-linear equation calculated for the individual strains, even for the most resistant one. Therefore, microbial inactivation tests using a cocktail of strains are particularly important to determine the performance of the UV inactivation treatment.

Inactivation of Escherichia coli O157:H7 and spoilage yeasts in germicidal UV-C-irradiated and heat-treated clear apple juice

“…However, instead of characteristic lags or shoulders, the investigators observed marked tailings or upward concavities in the inactivation curves, which were hypothesized to be due to a number of factors such as the mechanisms of UV-C hits, experimental bias, cellular aggregation and the presence of resistant subpopulation (Koutchma, 2009;Yousef and Marth, 1998). In orange juice, loglinear UV-C inactivation patterns were similarly reported by Oteiza, Giannuzzi, and Zaritzkym (2009) for five individual E. coli O157:H7 strains, but tailing was observed in the inactivation curve of the composited inoculum. Interestingly in this study, nonlinear patterns were not observed in inactivation studies that involved composites of inoculum which, clearly had component strains having variable sensitivities to the inactivating agents tested.…”

Use of High-Intensity Ultrasound and UV-C Light to Inactivate Some Microorganisms in Fruit Juices

“…Numerous studies have examined its effect in the disinfection of water (Litved and Cripps 1999;Sutton et al 2000). Since FDA has approved the use of UV-C light as a novel technology for pasteurization of fruit juices (US FDA 2000, 2004, in recent years this technology has been focused to the treatment of liquid foods and beverages (Unluturk et al 2008;Koutchma 2009;Oteiza et al 2009). …”

Inactivation of Salmonella enterica by UV-C Light Alone and in Combination with Mild Temperatures

“…The use of UV radiation has been suggested for disinfection of the surfaces of fresh products (50) and for pasteurization of liquids such as juices (12,35), milk (10), liquid egg (9), soft drinks (19), beer (26), sugar syrup (45), and wines (13).…”