Combining ultraviolet light and mild temperatures for the inactivation of Escherichia coli in orange juice

It is difficult to guarantee the effectiveness of UV technology to reach 5 Log₁₀ cycles of inactivation of Escherichia coli in a large amount of fruit juices with high absorption coefficients and turbidities, such as orange juice. The aim of this work was to overcome this limitation by combining UV light and mild temperatures. UV treatments were carried out in an equipment with eight individual annular thin film flow-through reactors connected sequentially and submerged in a thermostatic water bath. A treatment of 13.55 J/mL reached 0.25 ± 0.04, 0.41 ± 0.13, 0.84 ± 0.32, 0.96 ± 0.12, 2.57 ± 0.05, 5.41 ± 0.23, and more than 6 Log₁₀ cycles of inactivation of E. coli STCC 4201 suspended in commercial sterilized orange juice at 25.0, 40.0, 50.0, 52.5, 55.0, 57.5, and 60.0 °C, respectively. The comparison of UV resistance at 25 °C with heat resistance at mild temperatures demonstrated a synergistic effect of both technologies applied simultaneously. The maximum synergistic lethal effect was reached at 55 °C (68.03%).     

UV-C treatment of juices to inactivate microorganisms using Dean vortex technology

A laboratory-scale UV-C treatment device based on Dean vortex technology was tested for its potential to inactivate spoilage microorganisms in cloudy fruit juices. A log 5 and log 6 reduction could be achieved by inactivating Lactobacillus plantarum BFE 5092 and Escherichia coli DH5α in naturally cloudy apple juice at 1.9 and 7.7 kJ/L, respectively. A treatment with 9.6 kJ/L led to an approximately log 4 inactivation of Saccharomyces cerevisiae DSM 70478 and Alicyclobacillus acidoterrestris DSM 2498. The effects of possible influencing parameters such as optical density, turbidity and viscosity were analyzed with regard to the efficiency of the UV-C treatment. The optical density based on dissolved compounds appeared to be the most important factor which influenced the bacterial inactivation efficiency. Cell counts of L. plantarum BFE 5092 could be reduced in quarter-strength Ringer’s solution adjusted with dye from an initial level of approximately 1 × 10⁸-1 × 10¹ cfu/mL at an optical density (254 nm) of 20 at 9.6 kJ/L. Only a log 1.5 reduction, however, could be achieved at an optical density (254 nm) of 140 using the same UV-C treatment. Furthermore, no noticeable effect on inactivation could be determined by varying the turbidity or the viscosity of the juices investigated. An increasing flow rate and the consequently higher Dean number clearly improved the efficacy of the UV-C treatment. Thus, the inactivation of L. plantarum BFE 5092 in blood orange juice could be enhanced by an approximately 2.5-log reduction by increasing the Dean number from 32 to 256 at 7.7 kJ/L. The UV-C treatment using Dean vortex technology was shown in this study to effectively inactivate microorganisms even in cloudy juices. The optical density value seemed to be the exclusive determining factor on the efficiency of the UV-C inactivation of microorganisms based on Dean vortex technology, while the effect of suspended solids was negligible as a result of the efficient mixing by Dean vortices.     

High-throughput method for a kinetics analysis of the high-pressure inactivation of microorganisms using microplates

Using microplates as pressure and cultivation vessels, a high-throughput method was developed for analyzing the high-pressure inactivation kinetics of microorganisms. The loss of viability from a high-pressure treatment, measured based on the growth delay during microplate cultivation, showed reproducibility with the conventional agar plate method and was applicable for the kinetics analysis.     

UV Inactivation of E. coli in Liquid Egg White

Liquid egg white is currently pasteurized using heat; however, this treatment damages the functional properties of the egg. In this study, a nonthermal ultraviolet light (UV) system was developed to pasteurize liquid egg white. The system consisted of low-pressure mercury bulbs surrounded by UV transparent tubing. Egg white was inoculated with Escherichia coli K12 and pumped through the UV system at a flow rate of 330 ml/min. The effects of treatment time (0 to 160 s), temperature (30 to 50 °C), and egg white pH (7 to 9) on the inactivation of E. coli were investigated. The population of E. coli in egg white was reduced by 4.3 log after being exposed to UV at 50 °C for 160 s. Inactivation was linearly dependent on treatment time and was adequately described using first-order kinetics (r ² of 0.94). The electrical energy of the process was calculated to be 44 J/ml. Inactivation was directly dependent on temperature and inversely dependent on pH. Nonthermal UV processing has the potential to improve the safety and functional properties of liquid egg white. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.     

Inactivation of Escherichia coli by ozone treatment of apple juice at different pH levels

This research investigated the efficacy of gaseous ozone on the inactivation of Escherichia coli ATCC 25922 and NCTC 12900 strains in apple juice of a range of pH levels, using an ozone bubble column. The pH levels investigated were 3.0, 3.5, 4.0, 4.5 and 5.0. Apple juice inoculated with E. coli strains (10⁶ CFU/mL) was treated with ozone gas at a flow rate of 0.12 L/min and ozone concentration of 0.048 mg/min/mL for up to 18 min. Results show that inactivation kinetics of E. coli by ozone were affected by pH of the juice. The ozone treatment duration required for achieving a 5-log reduction was faster (4 min) at the lowest pH than at the highest pH (18 min) studied. The relationship between time required to achieve 5 log reduction (t_5d) and pH for both strains was described mathematically by two exponential equations. Ozone treatment appears to be an effective process for reducing bacteria in apple juice and the required applied treatment for producing a safe apple juice is dependant on its acidity level.     

Short-wave ultraviolet-C light effect on pitaya (Stenocereus griseus) juice inoculated with Zygosaccharomyces bailii

Fresh pitaya (Stenocereus griseus) juice was inoculated with Zygosaccharomyces bailii to be processed using a continuous ultraviolet-C light (UV-C) (57 μW/cm²) system. Inoculated and uninoculated juices were processed at selected flow rates (16.49, 23.78, and 30.33 mL/s) and treatment times (5, 10, 15, 20, 25, and 30 min). Untreated, inoculated, and uninoculated pitaya juices were stored at 4 °C during 25 days. Microbiological (yeasts plus molds and total counts) and physicochemical (pH, total soluble solids, color, phenolic compounds, betalains, and antioxidant activity) characteristics were evaluated in fresh and processed juices. The net change in color increased as treatment time increased, reaching a maximum value of 3.9. A substantial reduction of phenolic compounds (11.6%), betalains (14.6%), and antioxidant activity (37.0%) were observed in juice treated at 30.33 mL/s during 30 min. A reduction of 1.8 log cycles of Z. bailii was observed at the highest UV-C light treatment.     

The effect of high hydrostatic pressure on the microbiological quality and safety of carrot juice during refrigerated storage

The microbial quality of untreated and pressure-treated carrot juice was compared during storage at 4, 8 and 12 °C. High pressure treatment at 500 MPa and 600 MPa (1 min/20 °C) reduced the total counts by approximately 4 log CFU ml⁻¹ and there was very little growth of the survivors during storage at 4 °C for up to 22 days. Total counts increased during storage of pressure-treated juice at 8 °C and 12 °C but took significantly longer to reach maximum levels compared to the untreated juice. The microflora in the untreated juice consisted predominantly of Gram-negative bacteria, identified as mostly Pantoea spp., Erwinia spp. and Pseudomonas spp. Initially the pressure-treated juice contained low numbers of spore-forming bacteria (Bacillus spp. and Paenibacillus spp.) and Gram-positive cocci; the spore-formers continued to dominate during storage.     

Combinations of High Intensity Light Pulses and Thermosonication for the inactivation of Escherichia coli in orange juice

The non-thermal technologies High Intensity Light Pulses (HILP) and Thermosonication (TS) were applied alone and in combination to study their effect on Escherichia coli inactivation in orange juice. Two different energy settings were chosen in the current study, ‘Low’ (L) and ‘High’ (H), being the combinations applied: HILP(L) (4.03 J/cm²), HILP(H) (5.1 J/cm²), TS(L) (2.8 min residence time at 40 °C) and TS(H) (5 min residence time at 50 °C). Both the individual technologies and their combinations (HILP&TS and TS&HILP) were studied. Results showed inactivation ranging from 1.10 (TS(H)) to 2.42 (HILP(H)) log cfu/ml for the hurdles when applied individually and from 2.5 (HILP(L)&TS(H)) to 3.93 (HILP(H)&TS(L)) log cfu/ml for the combined treatments. Similar reductions in E. coli populations were achieved in orange juice by all treatment combinations irrespective of the sequence in which they were applied.     

Effectiveness of High Intensity Light Pulses (HILP) treatments for the control of Escherichia coli and Listeria innocua in apple juice, orange juice and milk

High Intensity Light Pulses (HILP) represent an emerging processing technology which uses short (100-400 μs) light pulses (200-1100 nm) for product decontamination. In this study, model and real foods of differing transparencies (maximum recovery diluent (MRD), apple and orange juices and milk) were exposed to HILP in a batch system for 0, 2, 4 or 8 s at a frequency of 3 Hz. After treatment, inactivation of Escherichia coli or Listeria innocua was evaluated in pre-inoculated samples. Sensory and other quality attributes (colour, pH, Brix, titratable acidity, non-enzymatic browning, total phenols and antioxidant capacity (TEAC)) were assessed in apple juice. Microbial kill decreased with decreasing transparency of the medium. In apple juice (the most transparent beverage) E. coli decreased by 2.65 and 4.5 after exposure times of 2 or 4 s, respectively. No cell recovery was observed after 48 h storage at 4 °C. No significant differences were observed in quality parameters, excepting TEAC and flavour score, where 8 s exposure caused a significant decrease (p < 0.05). Based on these results, HILP with short exposure times could represent a potential alternative to thermal processing to eliminate undesirable microorganisms, while maintaining product quality, in transparent fruit juices.     

Inactivation of Escherichia coli in orange juice using ozone

This research investigated the efficacy of gaseous ozone for the inactivation of Escherichia coli ATCC 25922 and NCTC 12900 strains in orange juice. Orange juice inoculated with E. coli (10⁶ CFU mL^− 1) as a challenge microorganism was treated with ozone at 75–78 µg mL^− 1 for different time periods (0–18 min). The efficacy of ozone for inactivation of both strains of E. coli was evaluated as a function of different juice types: model orange juice, fresh unfiltered juice, juice without pulp, and juice filtered through 500 µm or 1 mm sieves. Fast inactivation rates for total reduction of E. coli were achieved in model orange juice (60 s) and in juice with low pulp content (6 min). However, in unfiltered juice inactivation was achieved after 15–18 min. This indicated that juice organic matter interferes with antibacterial activity of gaseous ozone. The effect of prior acid (pH 5.0) exposure of E. coli strains on the inactivation efficacy of ozone treatment was also investigated. There was a strain effect observed, where prior acid exposure resulted in higher inactivation times in some cases by comparison with the control cells. However, the overarching influence on inactivation efficacy of ozone was related to the pulp content. Generally, the applied gaseous ozone treatment of orange juice resulted in a population reduction of 5 log cycles.

Industrial relevance

To facilitate the preservation of unstable nutrients many juice processors have investigated alternatives to thermal pasteurisation, including un-pasteurised short shelf life juices with high retail value. This trend has continued within the European Union. However within the US recent regulations by the FDA have required processors to achieve a 5-log reduction in the numbers of the most resistant pathogens in their finished products. Pathogenic E. coli may survive in acid environments such as fruit juices for long periods. This study demonstrates that the use of ozone as a non-thermal technology is effective for inactivation of E. coli and acid exposed E. coli in orange juice. Information on the design of the ozone treatment for inactivation of E. coli which results into safe juice products is also among the main outputs of this work. Ozone auto-decomposition makes this technology safe for fruit juice processing.     

Inactivation of Saccharomyces cerevisiae in pineapple, grape and cranberry juices under pulsed and continuous thermo-sonication treatments

Pineapple, grape and cranberry juice were thermo-sonicated (24 kHz, 400 W, 120 μm) at 40 °C, 50 °C and 60 °C during 10 min at continuous and pulsed mode. Inactivation of Saccharomyces cerevisiae was tested from 0 to 10 min; color and pH were measured. Survivor’s curves were fitted with Weibull distribution, four parameter model and modified Gompertz equation. The acoustic energy (AE) was also calculated. S. cerevisiae was inactivated in the treatments at 60 °C, with the continuous mode being more effective. Grape juice showed total inactivation (7-log) after 10 min. Results showed that pH and color changed significantly (p < 0.05); ultrasound may promote chemical reactions and extract some components. The modified Gompertz equation showed the best fit. Energy analysis showed that pineapple juice (4287.02 mW/ml) required a higher amount of energy; grape juice showed the lowest value (3112.13 mW/ml). Ultrasound represents a viable option for juice pasteurization.     

Bacterial inactivation in fruit juices using a continuous flow Pulsed Light (PL) system

In this work, the susceptibility to pulsed light (PL) treatments of both a Gram-positive (L. innocua 11288) and a Gram-negative (E. coli DH5-??) bacteria inoculated in apple (pH = 3.49, absorption coefficient 13.9 cm^− 1) and orange juices (pH = 3.78, absorption coefficient 52.4 cm^− 1) was investigated in a range of energy dosages from 1.8 to 5.5 J/cm². A laboratory scale continuous flow PL system was set up for the experiments, using a xenon flash-lamp emitting high intensity light in the range of 100-1100 nm. The flashes lasted 360 ??s at a constant frequency of 3 Hz.The results highlighted how the lethal effect of pulsed light depended on the energy dose supplied, the absorption properties of liquid food as well as the bacterial strain examined. The higher the quantity of the energy delivered to the juice stream, the greater the inactivation level. However, the absorbance of the inoculated juice strongly influenced the dose deliver and, therefore, the efficiency of the PL treatment. Among the bacteria tested, E. coli cells showed a greater susceptibility to the PL treatment than L. innocua cells in both apple and orange juices. Following treatment at 4 J/cm², microbial reductions in apple and orange juices were, respectively, 4.00 and 2.90 Log-cycles for E. coli and 2.98 and 0.93 Log-cycles for L. innocua.Sublethally injured cells were also detected for both bacterial strains, thus confirming that membrane damage is an important event in bacterial inactivation by PL.     

Effect of crust freezing applied alone and in combination with ultraviolet light on the survival of Campylobacter on raw chicken

The application of crust freezing (CF) applied as a stand-alone treatment or in combination with ultraviolet (UV) light for reducing the level of artificially inoculated Campylobacter jejuni on raw chicken was investigated. CF air temperatures of −5, −15 and −27 °C (±3 °C) with freezing times of 70, 15 and 6 min, respectively, were used. The level of C. jejuni on chicken was also examined following subsequent refrigerated (0–4 °C) storage at 3 and 7 days. All CF treatments resulted in significant reductions compared to untreated controls (P < 0.05). Although combining CF with UV also resulted in significant reductions for C. jejuni, the combined treatments were generally no more effective than treatment by CF alone. Overall, the color of chicken drumsticks was not affected by CF treatments (P ≥ 0.05). In general, CF resulted in increased drip loss (P < 0.05), which increased over storage time and was greater at higher CF temperatures. The current study indicates that CF has potential for reducing the levels of C. jejuni by between 0.5 and 1.5 log₁₀ CFU/g and impacts minimally on the color of treated skin.     

Toxicogenomics using yeast DNA microarrays

Development of genomics and bioinformatics enable us to analyze the global gene expression profiles of cells by DNA microarray. Changes in gene expression patterns indicate changes in its physiological conditions. Following the exposure of an organism or cell to toxic chemicals or other environmental stresses, the global genetic responses can be expeditiously and easily analyzed. Baker's yeast, Saccharomyces cerevisiae, is one of the most studied and useful model eukaryotes. The biggest advantage of yeast genomics is the available functional information for each gene and a considerable number of data are accumulating in the field of toxicity assessment using yeast DNA microarray. In this review, we discuss the toxicogenomics of metal ions, alcohols and aldehydes, and other chemicals.     

Inactivation of Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes in apple juice with gaseous ozone

This research was initiated to assess the efficacy of gaseous ozone for inactivation Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes in apple juice. Juice samples with solids content of 18, 36, and 72 °Brix inoculated with a culture cocktail of three foodborne pathogens were treated with gaseous ozone at a flow rate of 3.0 L/min and an ozone generation rate of 0.10, 0.90, 3.51, and 5.57 g/h for 0.5, 1, 5, and 10 min, respectively. The inactivation kinetics of gaseous ozone on foodborne pathogens conformed to the Weibull model. The time required to achieve a 5 log reduction (t_5d) was estimated using the parameters of the Weibull model. The t_5d increased with increasing solids content of apple juice. The ozone generation rate did not impart a significant effect (p > 0.05) on t_5d. Gaseous ozone is effective at inactivating foodborne pathogens in apple juice but the efficacy is dependent on the solids content of the juice sample.     

Membrane permeabilization and cellular death of Escherichia coli, Listeria monocytogenes and Saccharomyces cerevisiae as induced by high pressure carbon dioxide treatment

In this study, the relationship between (irreversible) membrane permeabilization and loss of viability in Escherichia coli, Listeria monocytogenes and Saccharomyces cerevisiae cells subjected to high pressure carbon dioxide (HPCD) treatment at different process conditions including temperature (35–45 °C), pressure (10.5–21.0 MPa) and treatment time (0–60 min) was examined. Loss of membrane integrity was measured as increased uptake of the fluorescent dye propidium iodide (PI) with spectrofluorometry, while cell inactivation was determined by viable cell count. Uptake of PI by all three strains indicated that membrane damage is involved in the mechanism of HPCD inactivation of vegetative cells. The extent of membrane permeabilization and cellular death increased with the severity of the HPCD treatment. The resistance of the three tested organisms to HPCD treatment changed as a function of treatment time, leading to significant tailing in the survival curves, and was dependent on pressure and temperature. The results in this study also indicated a HPCD-induced damage on nucleic acids during cell inactivation. Transmission electron microscopy showed that HPCD treatment had a profound effect on the intracellular organization of the micro-organisms and influenced the permeability of the bacterial cells by introducing pores in the cell wall.     

Production of wara, a West African soft cheese using lemon juice as a coagulant

As an important protein source for West African consumers, wara cheese made from the leave extract of Calotropis procera has extremely short shelf life of only 2-3 days [Adegoke, G. O., Nse, E. N., & Akanni, A. O. (1992). Effects of heat, processing time, and pH on the microflora, aflatoxin content, and storability of wara, a soft white cheese. Die Nahrung, 36(3), 259-264; Umoh, V. J., & Solomon, O. (2001). Safety assessment and critical control point of milk product and some cereal beverages in Northern Nigeria. In: Proceedings of USDA/USAID/NIGERIA international conference on food safety and security, August 1-3 (pp. 122-127). Ibadan, Nigeria: IITA; Belewu, M. A., Belewu, K. Y., & Nkwunonwo, C.C. (2005). Effect of biological and chemical preservatives on the shelflife of West African soft cheese. African Journal of Biotechnology, 4, 1076-1079; Adetunji, A. O., Alonge, D. O., & Chen, J. (Unpublished). Microbial quality of wara, a southwestern Nigerian soft cheese]. Lemon juice was used in this study as a substitute coagulant during wara manufacture in order to improve the microbial quality of wara. The cheese was manufactured from pasteurized milk inoculated with 10¹ or 10² CFU ml⁻¹ of Listeria monocytogenes. Samples of the milk or cheese were taken along the manufacturing steps and during a 5 d storage period at 15 and 28 °C in order to determine the populations of L. monocytogenes, total aerobes, Enterobacteriaceae, and psychrotrophs, as well as mold and yeast. On the 4th day of storage, portions of the un-inoculated control cheese from 28 °C were deep fried in vegetable oil, mimicking the practice of West African local cheese processors. The results showed that L. monocytogenes, at both inoculation levels, did not survive the manufacture of wara. In samples initially inoculated with 10¹ CFU ml⁻¹ of L. monocytogenes, the Enterobacteriaceae counts decreased from the initial 1.78 to 1.00 Log₁₀ CFU g⁻¹ with the addition of lemon juice, and became undetectable (<1.00 Log₁₀ CFU g⁻¹) at the curdling point as well as during the 5 d storage period at both temperatures. The total aerobic counts increased from the undetectable level on the 1st day of storage to 7.65 and 3.39 Log₁₀ CFU g⁻¹, respectively at 28 or 15 °C on the 5th day of storage. The psychrotrophic, as well as the yeast and mold counts increased from the undetectable levels on the 1st day of storage to 7.11 and 5.03 Log₁₀ CFU g⁻¹, respectively at 28 °C. At 15 °C however, the population of pyschrotrophs remained undetectable throughout the 5 d storage period whereas, the yeast and molds count increased to 3.08 Log₁₀ CFU g⁻¹ on day 3 before quickly decreasing to the undetectable levels on the 5th day of storage. A similar trend was observed in cheese made from the milk with an initial Listeria inoculation level of 10² CFU ml⁻¹. The results of this study showed that lemon juice significantly reduced the populations of the sampled microorganisms, especially the populations of Enterobacteriaceae.     

Determination of the antigenotoxic potencies of some luteolin derivatives by using a eukaryotic cell system, Saccharomyces cerevisiae

In this study, we aimed to examine the mutagenic and antimutagenic potencies of three luteolin derivatives (luteolin-7-O-glucoside, luteolin-7-O-rutinoside and luteolin-7-O-glucuronide) by using a eukaryotic cell system, Saccharomyces cerevisiae (RS112).     

Simple procedure for fatty acid analysis of glycerophospholipids in Escherichia coli and Saccharomyces cerevisiae

Rapid, convenient methods have been developed for fatty acid analysis of membrane glycerophospholipids in microorganisms. Fatty acid methyl esters derived from glycerophospholipids have been prepared directly from wet pellets of Escherichia coli cells or Saccharomyces cerevisiae spheroplasts without lipid extraction and fractionation in high yields under mild temperature conditions for analysis by gas chromatography.     

Inactivation of Escherichia coli, Listeria innocua and Saccharomyces cerevisiae by UV-C light: Study of cell injury by flow cytometry

Flow cytometry (FCM) is a powerful tool for analyzing physiological characteristics of microorganisms on a single-cell basis and identifying heterogeneities within population. This work analyzed the UV-C induced damage on Escherichia coli ATCC 11229; Listeria innocua ATCC 33090 and Saccharomyces cerevisiae KE162 cells by applying flow cytometry technique. The UV-C doses, obtained by altering the exposure time and measured by the iodide-iodate chemical actinometer, ranged between 0 and 5 kJ/m². E. coli; L. innocua and S. cerevisiae populations were quantified by plate count technique. For flow cytometry studies, cells were labeled with fluorescein diacetate (FDA) for detecting membrane integrity and esterase activity, and with propidium iodide (PI) for monitoring membrane integrity. The results showed that mechanisms of cellular damage differed according to time of exposure to ultraviolet radiation and the organism tested. E. coli and S. cerevisiae sub-populations with PI increased within the first minutes of UV-C treatment, without much change afterwards. On the contrary, FCM was used to detect the inactivation of those L. innocua sub-populations of viable microorganisms (maintaining metabolic activity) which were non-culturable due to membrane rupture and thus not detectable by viable plate count technique.