Shell egg pasteurization using radio frequency in combination with hot air or hot water.

This study investigated the effectiveness of three thermal treatments; hot air (HA), hot water immersion (HWI), and hot water spraying (HWS); alone and in combination with radio frequency (RF) on the inactivation of Salmonella Typhimurium in shell eggs. In addition, the physical quality of the treated eggs and their functional capability to produce angel food cakes were determined. The results showed that HWI and HWS were significantly (P < 0.05) more effective at pasteurizing shell eggs than HA, and the pasteurization time was significantly reduced when eggs were first processed with RF. The times needed for RF/HWI and RF/HWS to achieve 5-log reductions of S. Typhimurium were 19.5 and 24.5 min, respectively. Yolk index was unaffected by heating, but Haugh unit and albumen turbidity were increased dependent on the length of treatment. Eggs after HWI, combined RF/HWI, and RF/HWS treatments were able to make good angel food cakes if whipping times were extended. The results of this study demonstrated that combined RF/HWS treatment was comparable to RF/HWI treatment in terms of shell egg pasteurization without damaging egg quality. Therefore, both HWS and HWI may be used as the second step of radio frequency pasteurization.

Can acceptable quality angel food cakes be made using pasteurized shell eggs? The effects of mixing factors on functional properties of angel food cakes.

Due to recent Salmonella outbreaks, the pasteurized shell egg market is rapidly growing. One objection to using pasteurized eggs is the belief that they will produce unacceptable angel food cakes. Eggs were pasteurized using a hot water immersion process (56.7°C for 60 min) similar to that used by industry. Angel food cakes were made from the pasteurized egg white (PEW) as well as from raw egg white (REW) for comparison. Meringues were made using three mixer speed settings (low, medium, and high) and three durations for each speed. Functional qualities such as egg foaming were evaluated. Angel food cakes were compared in terms of cake volume, texture profile, and color values. When the optimal processing factors used for REW were applied to PEW, an inferior meringue was formed. However, by increasing the mixing time for PEW by 200% at the highest speed, an acceptable meringue was formed. The best angel food cake prepared from PEW had a volume only 6.8% less than that of the best cake prepared from REW. Texture profile analyses showed that the best angel food cake made from PEW was 13% firmer, 7.4% less springy, and 62% chewier than that from REW. Color analyses showed that PEW made a slightly darker colored cake crust than REW, although there were no significant differences in the crumb color. Modifying the mixing conditions for PEW resulted in angel food cakes with quality similar to that of cakes made with REW, thus overcoming an objection to using safer pasteurized shell eggs.

Microbial safety and overall quality of cantaloupe fresh-cut pieces prepared from whole fruit after wet steam treatment.

Fresh-cut cantaloupes have been associated with outbreaks of Salmonellosis. Minimally processed fresh-cut fruits have a limited shelf life because of deterioration caused by spoilage microflora and physiological processes. The objectives of this study were to use a wet steam process to 1) reduce indigenous spoilage microflora and inoculated populations of Salmonella, Escherichia coli O157:H7 and Listeria monocytogenes on the surface of cantaloupes, and 2) reduce the populations counts in cantaloupe fresh-cut pieces after rind removal and cutting. The average inocula of Salmonella, E. coli O157:H7 and Listeria monocytogenes was 10(7)CFU/ml and the populations recovered on the cantaloupe rind surfaces after inoculation averaged 4.5, 4.8 and 4.1logCFU/cm(2), respectively. Whole cantaloupes were treated with a wet steam processing unit for 180s, and the treated melons were stored at 5°C for 29days. Bacterial populations in fresh-cut pieces prepared from treated and control samples stored at 5 and 10°C for up to 12days were determined and changes in color (CIE L*, a*, and b*) due to treatments were measured during storage. Presence and growth of aerobic mesophilic bacteria and Salmonella, E. coli O157:H7 and L. monocytogenes were determined in fresh-cut cantaloupe samples. There were no visual signs of physical damage on all treated cantaloupe surfaces immediately after treatments and during storage. All fresh-cut pieces from treated cantaloupes rind surfaces were negative for bacterial pathogens even after an enrichment process. Steam treatment significantly (p<0.05) changed the color of the fresh-cut pieces. Minimal wet steam treatment of cantaloupes rind surfaces designated for fresh-cut preparation will enhance the microbial safety of fresh-cut pieces, by reducing total bacterial populations. This process holds the potential to significantly reduce the incidence of foodborne illness associated with fresh-cut fruits.

Inactivation of Salmonella in Shell Eggs by Hot Water Immersion and Its Effect on Quality.

Thermal inactivation kinetics of heat resistant strains of Salmonella Enteritidis in shell eggs processed by hot water immersion were determined and the effects of the processing on egg quality were evaluated. Shell eggs were inoculated with a composite of heat resistant Salmonella Enteritidis (SE) strains PT8 C405, 2 (FSIS #OB030832), and 6 (FSIS #OB040159). Eggs were immersed in a circulating hot water bath for various times and temperatures. Come-up time of the coldest location within the egg was 21 min. SE was reduced by 4.5 log at both hot water immersion treatments of 56.7 C for 60 min and 55.6 °C for 100 min. Decimal reduction times (D-values) at 54.4, 55.6, and 56.7 °C were 51.8, 14.6, and 9.33 min, respectively. The z-value was 3.07 °C. Following treatments that resulted in a 4.5 log reduction (56.7 °C/60 min and 55.6 °C/100 min), the surviving population of SE remained static during 4 wk of refrigerated storage. After processing under conditions resulting in 4.5 log reductions, the Haugh unit and albumen height significantly increased (P < 0.01) and yolk index significantly decreased (P < 0.05). The shell dynamic stiffness significantly increased (P < 0.05), while static compression shell strength showed no significant difference (P < 0.05). Vitelline membrane strength significantly increased (P < 0.05); although, no significant difference (P < 0.05) was observed in vitelline membrane elasticity. In summary, the hot water immersion process inactivated heat resistant SE in shell eggs by 4.5 log, but also significantly affected several egg quality characteristics.

Liquid egg white pasteurization using a centrifugal UV irradiator.

Studies are limited on UV nonthermal pasteurization of liquid egg white (LEW). The objective of this study was to inactivate Escherichia coli using a UV irradiator that centrifugally formed a thin film of LEW on the inside of a rotating cylinder. The LEW was inoculated with E. coli K12 to approximately 8 log cfu/ml and was processed at the following conditions: UV intensity 1.5 to 9.0 mW/cm²; cylinder rotational speed 450 to 750 RPM, cylinder inclination angle 15° to 45°, and flow rate 300 to 900 ml/min, and treatment time 1.1 to 3.2s. Appropriate dilutions of the samples were pourplated with tryptic soy agar (TSA). Sublethal injury was determined using TSA+4% NaCl. The regrowth of surviving E. coli during refrigerated storage for 28 days was investigated. The electrical energy of the UV process was also determined. The results demonstrated that UV processing of LEW at a dose of 29 mJ/cm² at 10°C reduced E. coli by 5 log cfu/ml. Inactivation significantly increased with increasing UV dose and decreasing flow rate. The results at cylinder inclination angles of 30° and 45° were similar and were significantly better than those at 15°. The cylinder rotational speed had no significant effect on inactivation. The occurrence of sublethal injury was detected. Storage of UV processed LEW at 4° and 10°C for 21 days further reduced the population of E. coli to approximately 1 log cfu/ml where it remained for an additional 7 days. The UV energy applied to the LEW to obtain a 5 log reduction of E. coli was 3.9 J/ml. These results suggest that LEW may be efficiently pasteurized, albeit at low flow rates, using a nonthermal UV device that centrifugally forms a thin film.

Effect of native microflora, waiting period, and storage temperature on Listeria monocytogenes serovars transferred from cantaloupe rind to fresh-cut pieces during preparation.

The most recent outbreak of listeriosis linked to consumption of fresh-cut cantaloupes indicates the need to investigate the behavior of Listeria monocytogenes in the presence of native microflora of cantaloupe pieces during storage. Whole cantaloupes were inoculated with L. monocytogenes (10(8)-CFU/ml suspension) for 10 min and air dried in a biosafety cabinet for 1 h and then treated (unwashed, water washed, and 2.5% hydrogen peroxide washed). Fresh-cut pieces (∼3 cm) prepared from these melons were left at 5 and 10°C for 72 h and room temperature (20°C) for 48 h. Some fresh-cut pieces were left at 20°C for 2 and 4 h and then refrigerated at 5°C. Microbial populations of fresh-cut pieces were determined by the plate count method or enrichment method immediately after preparation. Aerobic mesophilic bacteria, yeast and mold of whole melon, and inoculated populations of L. monocytogenes on cantaloupe rind surfaces averaged 6.4, 3.3, and 4.6 log CFU/cm(2), respectively. Only H(2)O(2) (2.5%) treatment reduced the aerobic mesophilic bacteria, yeast and mold, and L. monocytogenes populations to 3.8, 0.9, and 1.8 log CFU/cm(2), respectively. The populations of L. monocytogenes transferred from melon rinds to fresh-cut pieces were below detection but were present by enrichment. Increased storage temperatures enhanced the lag phases and growth of L. monocytogenes. The results of this study confirmed the need to store fresh-cut cantaloupes at 5°C immediately after preparation to enhance the microbial safety of the fruit.

Inactivation of Salmonella enterica on tomato stem scars by antimicrobial solutions and vacuum perfusion.

A study was conducted to identify sanitizing solutions effective at inactivating ca. 5logCFU of Salmonella enterica inoculated onto the stem scar of red round tomatoes during two-minute immersion treatments. Sixty-three antimicrobial combinations were tested. Vacuum perfusion was applied to tomatoes during selected treatments to promote infiltration of sanitizer into porous tomato stem scar tissue. Red round tomatoes were inoculated to ca. 6.9logCFU/stem scar with a four-serovar composite of Salmonella enterica, air dried, and tomatoes were immersed in circulating sanitizing solutions for 120s at ca. 22°C. Stem scars were aseptically excised, macerated in DE neutralizing broth, and the homogenate was spiral plated. Twenty-four washes inactivated ≥3.0logCFU/stem scar. Seven treatments reduced ≥4.8 log (viz., 40% EtOH, sulfuric acid, and organic acid combinations). LogCFU/stem scar reductions for various sanitizers are listed in parenthesis, as follows: 90ppm peroxyacetic acid (1.31), 200ppm chlorine (1.53), 190ppm chlorine+15″ Hg vacuum perfusion (2.23), 0.2N sodium hydroxide (NaOH) (3.78), 2% total of lactic+acetic acid (4.35), 3% total of phosphoric+lactic acids (4.51), and 40% ethanol (4.81). Solutions that achieved ≥4.95 log reductions were 5.1% total of lactic+acetic+levulinic acids, 49% ethanol, 6% total of lactic+acetic acids, and a 0.2M H(2)SO(4) (sulfuric acid) solution. The use of vacuum perfusion with 200ppm chlorine increased inactivation by 0.7logCFU over chlorine alone, however, P>0.05. Results from this study provide tomato processers with some sanitization options effective at inactivating Salmonella from the stem scars of tomatoes. These results may also help processors and scientists design future decontamination studies by incorporating combinations of these chemical treatments.

Inactivation of Salmonella on whole cantaloupe by application of an antimicrobial coating containing chitosan and allyl isothiocyanate.

This study investigated the antimicrobial effect of a chitosan coating+allyl isothiocyanate (AIT) and nisin against Salmonella on whole fresh cantaloupes. Cantaloupes were inoculated with a cocktail of three Salmonella strains and treated with chitosan, chitosan+AIT, chitosan+nisin, and chitosan+AIT+nisin coatings. With AIT concentrations increasing from 10 to 60 µl/ml, the antibacterial effects of coating treatments against Salmonella increased. Chitosan coatings with 60 µl/ml AIT (chitosan+60AIT) reduced more than 5 log10 CFU/cm² of Salmonella. The addition of nisin to the chitosan-AIT coating synergistically increased the antibacterial effect; coatings with nisin (25 mg/ml or 25,000 IU/ml)+30 µl/ml AIT resulted in a 4.8 log10 reduction of Salmonella. The chitosan+60AIT coating significantly (p<0.05) reduced populations of native bacteria on cantaloupes to ca. 2 log10 CFU/cm² during the first 6 days and populations remained unchanged through day 14 at 10 °C. The same coating treatment completely inactivated mold and yeast on cantaloupe at day 1 and no regrowth occurred even up to 14 days of storage. Scanning electron microscopy revealed that cell membrane damage and leakage of intercellular components occurred as a result of the chitosan-AIT coating treatments. No visual changes in overall appearance and color of cantaloupe rind and flesh due to coating treatments were observed. These results indicate that the application of an antimicrobial coating may be an effective method for decontamination of cantaloupes.

Nonthermal inactivation and sublethal injury of Lactobacillus plantarum in apple cider by a pilot plant scale continuous supercritical carbon dioxide system.

The objective of this study was to evaluate the efficacy of supercritical carbon dioxide (SCCO(2)) for inactivating Lactobacillus plantarum in apple cider using a continuous system with a gas-liquid metal contactor. Pasteurized apple cider without preservatives was inoculated with L. plantarum and processed using a SCCO(2) system at a CO(2) concentration range of 0-12% (g CO(2)/100g product), outlet temperatures of 34, 38, and 42 °C, a system pressure of 7.6 MPa, and a flow rate of 1 L/min. Processing with SCCO(2) significantly (P<0.05) enhanced inactivation of L. plantarum in apple cider, resulting in a 5 log reduction with 8% CO(2) at 42 °C. The response surface model indicated that both CO(2) concentration and temperature contributed to the microbial inactivation. The extent of sublethal injury in surviving cells in processed apple cider increased as CO(2) concentration and processing temperature increased, however the percent injury dramatically decreased during SCCO(2) processing at 42 °C. Structural damage in cell membranes after SCCO(2) processing was observed by SEM. Refrigeration (4 °C) after SCCO(2) processing effectively inhibited the re-growth of surviving L. plantarum during storage for 28 days. Thus this study suggests that SCCO(2) processing is effective in eliminating L. plantarum and could be applicable for nonthermal pasteurization of apple cider.

Selection of surrogate bacteria in place of E. coli O157:H7 and Salmonella Typhimurium for pulsed electric field treatment of orange juice.

Pulsed electric field (PEF) technology has been used for the inactivation of microorganisms and to prevent flavor loss in liquid foods and beverages in place of thermal pasteurization. When used to pasteurize orange juice, PEF may prevent loss of volatile sensory attributes. Enterohemorrhagic E. coli O157:H7 (EHEC), two strains of Salmonella Typhimurium, and twenty strains of non-pathogenic bacteria were screened for inactivation in orange juice by PEF at 22 and 20kV/cm at 45 and 55 degrees C, respectively. Higher populations of both salmonellae were inactivated (2.81 and 3.54 log CFU/ml) at 55 degrees C, in comparison with the reduction of EHEC (2.22 log). When tested under the same conditions, inactivation of EHEC was slightly greater than that of a non-pathogenic E. coli (NPEC) ATCC 35218 (2.02 log). NPEC was further tested as a surrogate for EHEC by comparing inactivation kinetics at 45, 50 and 55 degrees C at field strengths of between 7.86 and 32.55kV/cm. Statistical comparison of revealed that EHEC and NPEC inactivation curves were homogeneous at outlet temperatures of 45 and 50 degrees C; however, EHEC was slightly more sensitive to PEF than the surrogate NPEC at 55 degrees C. The higher PEF resistance of non-pathogenic E. coli 35218 at 55 degrees C may provide a desirable margin of safety when used in pilot plant challenge studies in place of E. coli O157:H7.

A combined treatment of UV-light and radio frequency electric field for the inactivation of Escherichia coli K-12 in apple juice.

Radio frequency electric fields (RFEF) and UV-light treatments have been reported to inactivate bacteria in liquid foods. However, information on the efficacy of bacterial inactivation by combined treatments of RFEF and UV-light technologies is limited. In this study, we investigated the relationship between cell injury and inactivation of Escherichia coli K-12 in apple juice treated with a combination of RFEF and UV-light. Apple juice purchased from a wholesale distributor was inoculated with E. coli K-12 at 7.8 log CFU/ml, processed with a laboratory scale RFEF unit at 20 kHz, 15 kV/cm for 170 micros at a flow rate of 540 ml/min followed by UV-light treatment (254 nm) for 12s at 25, 30 and 40 degrees C. Treated samples were analyzed for leakage of UV-substances as a function of membrane damage and were plated (0.1 ml) on Sorbitol MacConkey Agar (SMAC) and Trypticase Soy Agar (TSA) plates to determine the viability loss and percent injury. At 40 degrees C, UV-light treatment alone caused 5.8 log reduction of E. coli in apple juice while RFEF caused only 2.8 log reduction. A combination of the two processing treatments did not increase cell injury or leakage of intracellular bacterial UV-substances more than that from the UV-light treatment. Similarly, the viability loss determined was not significantly (P<0.05) different than UV-light treatment alone. However, the UV-substances determined in apple juice treated with RFEF was significantly (P>0.05) different than UV-light treated samples. The results of this study suggest that RFEF treatment causes more injury to the bacterial cells leading to more leakage of intracellular UV-substances than cells treated with UV-light alone. Also, the effect of the two processing treatment combination on bacterial inactivation was not additive.

Efficacy of supercritical carbon dioxide for nonthermal inactivation of Escherichia coli K12 in apple cider.

This study evaluated the efficacy of a supercritical carbon dioxide (SCCO(2)) system with a gas-liquid porous metal contactor for eliminating Escherichia coli K12 in apple cider. Pasteurized, preservative-free apple cider was inoculated with E. coli K12 and processed using the SCCO(2) system at CO(2) concentrations of 0-10% (wt.%, g CO(2)/100g product), outlet temperatures of 34, 38, and 42 degrees C, a system pressure of 7.6 MPa, and a flow rate of 1L/min. Increased CO(2) concentrations and temperatures significantly (P<0.05) enhanced the bactericidal effect, resulting in a maximum reduction of 7.31 log CFU/mL at 8% CO(2) and 42 degrees C. A response surface model indicated that minimum CO(2) concentrations of 9.9% at 34 degrees C, 7.4% at 38 degrees C, and 5.4% at 42 degrees C are needed to achieve a 5-log reduction of E. coli K12 in apple cider. SEM observations showed morphological changes in the cell envelope after SCCO(2) processing. At a processing condition of 8% and 38 degrees C, the reduction of E. coli was 6.03 log and the sublethal injury of the survivors was 84%. The regrowth or survival of E. coli in SCCO(2) processed apple cider was not observed during storage for 28 days at 4, 8, and 20 degrees C. Thus this study showed the potential of SCCO(2) processing with a gas-liquid porous metal contactor for the nonthermal pasteurization of apple cider.

Inactivation of Lactobacillus plantarum in apple cider, using radio frequency electric fields.

Radio frequency electric fields (RFEF) nonthermal processing effectively inactivates gram-negative bacteria in juices, but has yet to be shown effective at reducing gram-positive bacteria. Apple cider containing Lactobacillus plantarum ATCC 49445, a gram-positive bacterium, was RFEF processed under the following conditions: field strength of 0.15 to 15 kV/cm, temperature of 45 to 55 degrees C, frequency of 5 to 65 kHz, treatment time of 170 micros, and holding time of 5 to 50 s. The effect of refrigerating the inoculated cider prior to processing, the extent of sublethal injury, and the effect of storing the treated cider for 35 days were investigated. The population of L. plantarum was reduced by 1.0 log at 15 kV/cm, 20 kHz, and 50 degrees C, with a 5-s hold time. There is a synergistic effect between RFEF and heat above 50 degrees C. Inactivation significantly (P < 0.05) increased as frequency was decreased from 65 to 5 kHz. Inactivation increased linearly with field above 8 kV/cm. Holding cider at 55 degrees C after RFEF treatment for 5 and 50 s resulted in 2.5- and 3.1-log reductions, respectively. The surviving population was composed of 1.4-log sublethally injured cells. Storing processed cider at 4 degrees C for 35 days steadily and significantly (P < 0.05) reduced L. plantarum from 4.5 to 0.9 log CFU/ml. The electrical energy density was 51 J/ml. This provides the first evidence that nonthermal RFEF processing inactivates gram-positive bacteria, and that surviving cells may die off during refrigerated storage.

Membrane damage and viability loss of Escherichia coli K-12 in apple juice treated with radio frequency electric field.

The need for a nonthermal intervention technology that can achieve microbial safety without altering nutritional quality of liquid foods led to the development of a radio frequency electric fields (RFEF) process. In order to understand the mechanism of inactivation of bacteria by RFEF, apple juice purchased from a wholesale distributor was inoculated with Escherichia coli K-12 at 7.8 log CFU/ml and then treated with RFEF. The inoculated apple juice was passed through an RFEF chamber operated at 20 kHz, 15 kV/cm for 170 micros at a flow rate of 540 ml/min. Treatment condition was periodically adjusted to achieve outlet temperatures of 40, 45, 50, 55, and 60 degrees C. Samples at each outlet temperature were plated (0.1 ml) and the number of CFU per milliliter determined on nonselective and selective agar media was used to calculate the viability loss. Bacterial inactivation and viability loss occurred at all temperatures tested with 55 degrees C treatment, leading to 4-log reductions. No significant effect was observed on bacterial population in control samples treated at 55 degrees C with a low-RFEF (0.15 kV/cm) field strength. These observations suggest that the 4-log reduction in samples treated at 15 kV/cm was entirely due to nonthermal effect. RFEF treatment resulted in membrane damage of the bacteria, leading to the efflux of intracellular ATP and UV-absorbing materials. Populations of injured bacteria recovered immediately (<30 min) from the treated apple juice averaged 0.43 log and were below detection after 1 h of RFEF treatment and determination using selective plates (tryptic soy agar containing 5% sodium chloride). The results of this study suggest that mechanism of inactivation of RFEF is by disruption of the bacterial surface structure leading to the damage and leakage of intracellular biological active compounds.

Furan formation in sugar solution and apple cider upon ultraviolet treatment.

Furan is a possible human carcinogen induced by thermal processing of food. While ultraviolet C (UVC) is used to decontaminate apple cider and to sterilize sugar solutions, it is unknown whether UVC induces furan formation in cider or solutions of its major components. This study was conducted to investigate the possible formation of furan by UVC in apple cider and in solutions of common constituents of apple cider. Our results showed that UVC treatment induced furan formation in apple cider, and the major source of furan was apparently fructose. UVC treatment (at incident doses up to 9 J/cm (2)) of fructose solutions produced a higher amount of furan, while very low concentrations of furan were induced by UVC in glucose or sucrose solutions, and virtually no furan was induced by UVC from solutions of ascorbic acid or malic acid. When an isotope (d(4)-furan) of furan was treated with UVC, d(4)-furan was destroyed rapidly even at low doses in fructose solution, suggesting that the accumulation of furan is the balance between destruction and formation. The UV sensitivity of E. coli K12 (a surrogate of E. coli O157:H7) in two sources of apple cider was also determined. At UVC doses that could inactivate 5-log of E. coli, very low concentrations (<1 ppb) of furan were induced. Our results suggest that UVC could induce furan formation, but when used for the purpose of juice pasteurization, little furan was induced in apple cider.

UV inactivation of bacteria in apple cider.

Apple cider, inoculated with Escherichia coli and Listeria innocua, was processed using a simple UV apparatus. The apparatus consisted of a low-pressure mercury lamp surrounded by a coil of UV transparent tubing. Cider was pumped through the tubing at flow rates of 27 to 83 ml/min. The population of E. coli K-12 was reduced by 3.4 +/- 0.3 log after being exposed for 19 s at a treatment temperature of 25 degrees C. The population of L. innocua, which was more resistant to UV, was reduced by 2.5 +/- 0.1 log after being exposed for 58 s. The electrical energy for the process was 34 J/ml and is similar to that for conventional thermal processing. UV processing has the potential to improve the safety and extend the shelf life of apple cider.

Inactivation of Saccharomyces cerevisiae with radio frequency electric fields.

The application of radio frequency (RF) electric fields as a nonthermal alternative to thermal inactivation of microorganisms in liquids was investigated. A novel RF system producing frequencies in the range of 20 to 60 kHz was developed. Electric field strengths of 20 and 30 kV/cm were applied to suspensions of Saccharomyces cerevisiae in water over a temperature range of 35 to 55 degrees C. The flow rate was 1.2 liters/min. The S. cerevisiae population was reduced by 2.1 +/- 0.1 log units following exposure to a 30-kV/cm field at 40 degrees C. The results of the present study provide the first evidence that strong RF electric fields inactivate microorganisms at moderately low temperatures. Increasing the field strength, the number of treatments, and the temperature enhanced inactivation. Frequency had no effect on inactivation over the range of frequencies studied.