Combined treatment of pulsed light and nisin-organic acid based antimicrobial wash for inactivation of Escherichia coli O157:H7 in Romaine lettuce, reduction of microbial loads, and retention of quality.

Microbial safety of fresh produce continues to be a major concern. Novel antimicrobial methods are needed to minimize the risk of contamination. This study investigated the antimicrobial efficacy of pulsed light (PL), a novel nisin-organic acid based antimicrobial wash (AW) and the synergy thereof in inactivating E. coli O157:H7 on Romaine lettuce. Treatment effects on background microbiota and produce quality during storage at 4 °C for 7 days was also investigated. A bacterial cocktail containing three outbreak strains of E. coli O157:H7 was used as inoculum. Lettuce leaves were spot inoculated on the surface before treating with PL (1-60 s), AW (2 min) or combinations of PL with AW. PL treatment for 10 s, equivalent to fluence dose of 10.5 J/cm2, was optimal and resulted in 2.3 log CFU/g reduction of E. coli O157:H7, while a 2 min AW treatment, provided a comparable pathogen reduction of 2.2 log CFU/g. Two possible treatment sequences of PL and AW combinations were investigated. For PL-AW combination, inoculated lettuce leaves were initially exposed to optimum PL dose followed by 2 min AW treatment, whereas for AW-PL combination, inoculated lettuce were subjected to 2 min AW treatment prior to 10 s PL treatment. Both combination treatments (PL-AW and AW-PL) resulted in synergistic inactivation as E. coli cells were not detectable after treatment, indicating >5 log pathogen reductions. Combination treatments significantly (P < 0.05) reduced spoilage microbial populations on Romaine lettuce and also hindered their growth in storage for 7 days. The firmness and visual quality appearance of lettuce were not significantly (P > 0.05) influenced due to combination treatments. Overall, the results reveal that PL and AW combination treatments can be implemented as a novel approach to enhance microbial safety, quality and shelf life of Romaine lettuce.

Antimicrobial coating with organic acids and essential oil for the enhancement of safety and shelf life of grape tomatoes.

This study investigated the antimicrobial efficacy of two coatings against populations of nalidixic acid-resistant Salmonella, Listeria monocytogenes and native microorganisms on whole grape tomatoes. Tomatoes were surface-coated in two chitosan-acid coating solutions. Solution 1 (Chitosan) consisted of 1 % chitosan and 2 % acetic, lactic and levulinic acids. Solution 2 (Chitosan+AIT) consisted of Solution 1 plus 2 % allyl isothiocyanate (AIT). After the treatments, tomatoes were placed in PET containers and stored at 10 °C for 21 days. Chitosan and Chitosan+AIT treatments reduced Salmonella populations from 3.65 to 1.28 and <0.70 log CFU/tomato on day 1, respectively. Both treatments reduced Salmonella populations to undetectable levels (<0.70 log CFU/tomato) from Day 2 through Day 21. Similarly, Chitosan+AIT treatments caused a greater reduction in Listeria populations than Chitosan treatment on day 1, but there were no significant differences between the two treatments after day 2. Chitosan and Chitosan+AIT reduced native bacteria populations to an undetectable level after 2 days and reduced the population of native yeasts & molds to an undetectable level after 1 day. The presence of mold was only observed on control sample after 21 days. Quality analyses showed that samples which were subject to coating treatment maintained their texture and color for 21 days at 10 °C with less water loss compared to the controls. This study suggests that chitosan-acid coating is applicable for extending the shelf-life and enhancing the safety of grape tomatoes.

The effect of lauric arginate on the thermal inactivation of starved Listeria monocytogenes in sous-vide cooked ground beef.

The aim of this study was to examine the efficacy of lauric arginate (LAE, 1000 ppm - 3000 ppm) as an assisting tool to reduce starved Listeria monocytogenes population in ground beef following sous-vide processing at different temperatures (55-62.5 °C). Ground beef mixed with LAE was vacuum sealed and a laboratory water bath was used for sous-vide cooking. Loglinear and Weibull models were fit to the survival microbial population and the D and Z-values were determined at 55-62.5 °C. Calculated D-values ranged from 33.62 to 3.22 min at temperature 55-62.5 °C. LAE at higher concentration is an effective antimicrobial to increase the inactivation of the pathogen in sous-vide cooking. With the addition of LAE, D-values at 55 and 62.5 °C determined by the Loglinear model decreased from 31.86 to 2.28 min (LAE 1000 ppm) and 16.71 to 0.56 min (LAE 3000 ppm), respectively; whereas the D-values at 55 to 62.5 °C determined by the Weibull model were 44.26 and 2.09 min (LAE 1000 ppm) and 22.71 and 1.60 min (LAE 3000 ppm), respectively. This study shows that sous-vide processing of ground beef supplemented with higher concentration of LAE effectively inactivates L. monocytogenes and thus, helps increase the microbiological safety and product quality.

Nisin-Based Organic Acid Inactivation of Salmonella on Grape Tomatoes: Efficacy of Treatment with Bioluminescence ATP Assay.

The antimicrobial activity of a new nisin-based organic acid sanitizer (NOAS), developed in our laboratory, was tested against viable aerobic mesophilic bacteria and Salmonella populations inoculated on produce surfaces. The activity of NOAS was compared with 200 ppm of chlorinated wash water and a bioluminescence ATP technique to determine the efficacy of treatments compared with plate count methods. The activity of the 10% final concentration of NOAS against viable populations of 109 CFU/mL Salmonella in phosphate-buffered saline (PBS), sterile deionized distilled water, and buffered peptone water was tested in vitro and on grape tomatoes inoculated with Salmonella at 2.5 log CFU/g. A similar batch of inoculated tomatoes were treated with 200 ppm of total available chlorinated water. All treatments for inactivation of viable Salmonella in vitro was tested up to 30 min and 5 min for the attached populations on tomatoes. Inactivation of viable Salmonella at 109 log CFU/mL by 10% the NOAS solution averaged >107 log CFU/mL in PBS, sterile deionized distilled water, and buffered peptone water. Similarly, Salmonella bacteria inactivated on tomato surfaces by the NOAS solution was significantly (P < 0.05) greater than numbers on chlorinated washed tomatoes, and surviving bacterial populations on NOAS and chlorine-treated tomatoes were <1 and 4 CFU/g, respectively. A significant linear correlation coefficient (r2 = 0.99) between the bioluminescence ATP assay and aerobic plate counts of inoculated and untreated grape tomatoes were recorded but not with NOAS and chlorine-treated tomatoes, as bacterial populations were less than the minimum baseline for determination. Also, the results indicated that the NOAS solution is a better alternative antimicrobial wash solution than 200 ppm of chlorinated water.

Effect of grape seed extract on heat resistance of Clostridium perfringens vegetative cells in sous vide processed ground beef.

The heat resistance (57.5-65 °C) of a three-strain cocktail of Clostridium perfringens vegetative cells in sous vide processed ground beef supplemented with 0-3% grape seed extract (GSE) was quantified. The surviving cell population was enumerated on tryptose-sulfite-cycloserine agar. The decimal reduction (D)-values in beef that included no GSE were 67.11, 17.15, 4.02, and 1.62 min at 57.5, 60, 62.5, and 65 °C, respectively. Addition of 1.0% GSE resulted in concomitant decrease in heat resistance as evidenced by reduced bacterial D-values. The D-values in beef with added 1.0% GSE were 62.89, 13.70, 3.47 and 1.46 min at 57.5, 60, 62.5, and 65 °C, respectively. The heat resistance was further decreased when the GSE concentration in beef was increased to 2 or 3%. The z-values in beef with or without GSE were similar, ranging from 4.41 to 4.56 °C. The results of this study would be beneficial to the retail and institutional food service establishments in estimating re-heating time and temperature for sous vide processed ground beef to ensure safety against C. perfringens.

Effects of pulsed light and sanitizer wash combination on inactivation of Escherichia coli O157:H7, microbial loads and apparent quality of spinach leaves.

The purpose of this study was to investigate the efficacy of pulsed light (PL), a new formula of sanitizer (HEN) consisting of hydrogen peroxide, EDTA and Nisin, as well as synergy of PL and HEN sanitizer (PL-HEN) wash in inactivating E. coli O157:H7 on spinach. The treatment effect on microbial loads and apparent quality during 13 days storage at 4 °C was also determined. A bacterial cocktail containing three strains of E. coli O157:H7 was used as inoculum based on their association with produce-related outbreaks. Spinach leaves were spot inoculated on surface before treating with PL (1-63J/cm2), HEN sanitizer wash (2 min) or their combinations. PL inactivation was influenced significantly at low doses. Treatment dose of 15.75 J/cm2, equivalent to 15 s intense PL treatment, was found optimal above which adverse quality effect was evident. The optimal PL dose resulted 2.7 log CFU/g reduction of E. coli O157:H7 while a rapid 2 min wash in sanitizer formulation HEN, provided comparatively low, 1.8 log CFU/g, reduction of the pathogen. Two different sequences of PL and HEN treatment combinations were tested. In PL-HEN treatment, inoculated leaves were first treated at optimal PL dose (15.75 J/cm2) followed by 2 min immersion in HEN whereas in HEN-PL treatment, leaves were first washed in HEN before PL exposure. HEN-PL treatment indicated a compound inactivation activity (4.6 logs reduction) while PL-HEN treatment indicated a strong synergistic inactivation as E. coli cells were not detectable after treatment indicating >5 log reduction. The PL-HEN treatment not only significantly reduced spoilage microbial populations on spinach but also slowed their growth during storage. Furthermore, the visual and firmness quality of spinach were not significantly affected by the PL-HEN treatment. Overall, our results demonstrate that integrated PL-HEN technology can be used to enhance microbial safety of spinach.

Inactivation of Salmonella in grape tomato stem scars by organic acid wash and chitosan-allyl isothiocyanate coating.

The objective of this study was to evaluate inactivation of inoculated Salmonella enterica on grape tomato stem scars exploiting integrated treatment of organic acid wash (AW) followed by chitosan-allyl isothiocyanate (CT-AIT) coating. The treatment effect on microbial loads and fruit quality during 21days storage at 10°C was also determined. A bacterial cocktail containing three serotypes of Salmonella enterica was used for this study based on their association with produce-related outbreaks. Tomatoes were spot inoculated on stem scars and then immersed in an organic acid solution (700ml) containing 0.5% (v/v) each of acetic (AA) and formic acid (FA) to wash under mild agitation for 1min at ambient temperature (22°C) followed by 1min dipping in a coating solution containing 6mlAIT/g CT. AW in 0.5% organic acid (AA+FA) for 1min reduced Salmonella population by 2.7logCFU/g from an initial load of 7.8logCFU/g, while additional coating treatment of AW tomatoes reduced the pathogens on stem scars to undetectable levels (<0.7logCFU/g), achieving, in combination, a >7logCFU/g reduction for the pathogen. Although the populations of Salmonella in the controls (approx. 7.8logCFU/g stem scar) did not change significantly during 21days of storage at 10°C, the populations were reduced to undetectable level in the integrated (AW plus CT-AIT) treated stem scars on day 1 and no regrowth was observed during storage. The treatment significantly (p<0.05) reduced background bacterial loads to approx. 1.3logCFU/g and the population remained unchanged through day 21 at 10°C. The treatment also completely inactivated mold and yeast on day 1 with no growth reoccurrence. These results indicate that the integrated treatment can provide a safe and effective intervention strategy for grape tomatoes.

Effect of high hydrostatic pressure processing on the background microbial loads and quality of cantaloupe puree.

The objective of this study was to investigate and evaluate the effects of high hydrostatic pressure (HHP) applied to cantaloupe puree (CP) on microbial loads and product quality during storage for 10days at 4°C. Freshly prepared, double sealed and double bagged CP (ca. 5g) was pressure treated at 300, 400 and 500MPa at 8°C and 15°C for 5min. Microflora populations, soluble solid content, pH, color, antioxidant activity, appearance and aroma were measured at 1, 6, and 10d of storage. Results showed that high pressure treatment of 300MPa (8°C and 15°C) resulted in reduction of total aerobic plate count from 3.3 to 1.8logCFU/g. The treatment reduced the populations of native aerobic plate count to non-detectable levels (detection limit 1logCFU/g) at 400MPa and 500MPa pressures at 15°C. Pressure treatment completely inactivated mold and yeast in puree below the limits of detection at day 1 and no regrowth was observed during 10days of storage at 4°C while mold and yeast in untreated puree survived during the storage. High pressure treatment did not show any adverse impact on physical properties as soluble solid content (SSC, 11.2°Brix) and acidity (pH, 6.9). The instrumental color parameters (L*, a*, b*) were affected due to HHP treatment creating a slightly lighter product, compared to control, as indicated by higher L.* and lower a* values. However the change was not detected by the sensory panel while evaluating appearance scores. Pressure treatment did not affect the antioxidant capacity of puree product compared to control. Visual appearance and sniffing aroma test by panel revealed no adverse changes in the sensory parameters as a result of HHP treatment. HHP method described in this study appears to be a promising way to inactivate spoilage microorganisms in the cantaloupe puree and maintain quality. This study provides a viable option for preservation and marketing this product.

Cold plasma-activated hydrogen peroxide aerosol inactivates Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria innocua and maintains quality of grape tomato, spinach and cantaloupe.

The purpose of this study was to investigate the efficacy of aerosolized hydrogen peroxide in inactivating bacteria and maintaining quality of grape tomatoes, baby spinach leaves and cantaloupes. Stem scars and smooth surfaces of tomatoes, spinach leaves, and cantaloupe rinds, inoculated with Escherichia coli O157:H7, Salmonella Typhimurium and Listeria innocua, were treated for 45s followed by additional 30min dwell time with hydrogen peroxide (7.8%) aerosols activated by atmospheric cold plasma. Non-inoculated samples were used to study the effects on quality and native microflora populations. Results showed that two ranges of hydrogen peroxide droplets with mean diameters of 40nm and 3.0µm were introduced into the treatment chamber. The aerosolized hydrogen peroxide treatment reduced S. Typhimurium populations by 5.0logCFU/piece, and E. coli O157:H7 and L. innocua populations from initial levels of 2.9 and 6.3logCFU/piece, respectively, to non-detectable levels (detection limit 0.6logCFU/piece) on the smooth surface of tomatoes. However, on the stem scar area of tomatoes, the reductions of E. coli O157:H7, S. Typhimurium, and L. innocua were only 1.0, 1.3, and 1.3 log, respectively. On the cantaloupe rind, the treatment reduced populations of E. coli O157:H7, S. Typhimurium and L. innocua by 4.9, 1.3, and 3.0logCFU/piece, respectively. Under the same conditions, reductions achieved on spinach leaves were 1.5, 4.2 and 4.0 log for E. coli O157:H7, S. Typhimurium and L. innocua, respectively. The treatments also significantly reduced native aerobic plate count, and yeasts and mold count of tomato fruits and spinach leaves. Furthermore, firmness and color of the samples were not significantly affected by the aerosolized hydrogen peroxide. Overall, our results showed that the efficacy of aerosolized hydrogen peroxide depended on type of inoculated bacteria, location of bacteria and type of produce items, and aerosolized hydrogen peroxide could potentially be used to sanitize fresh fruits and vegetables.

Effect of Hydrogen Peroxide in Combination with Minimal Thermal Treatment for Reducing Bacterial Populations on Cantaloupe Rind Surfaces and Transfer to Fresh-Cut Pieces.

Surface structure and biochemical characteristics of bacteria and produce play a major role in how and where bacteria attach, complicating decontamination treatments. Whole cantaloupe rind surfaces were inoculated with Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes at 10(7) CFU/ml. Average population size of Salmonella, Escherichia coli O157:H7, and L. monocytogenes recovered after surface inoculation was 4.8 ± 0.12, 5.1 ± 0.14, and 3.6 ± 0.13 log CFU/cm(2), respectively. Inoculated melons were stored at 5 and 22°C for 7 days before washing treatment interventions. Intervention treatments used were (i) water (H2O) at 22°C, (ii) H2O at 80°C, (iii) 3% hydrogen peroxide (H2O2) at 22°C, and (iv) a combination of 3% H2O2 and H2O at 80°C for 300 s. The strength of pathogen attachment (SR value) at days 0, 3, and 7 of storage was determined, and then the efficacy of the intervention treatments to detach, kill, and reduce transfer of bacteria to fresh-cut pieces during fresh-cut preparation was investigated. Populations of E. coli O157:H7 attached to the rind surface at significantly higher levels (P < 0.05) than Salmonella and L. monocytogenes, but Salmonella exhibited the strongest attachment (SR value) at all days tested. Washing with 3% H2O2 alone led to significant reduction (P < 0.05) of bacteria and caused some changes in bacterial cell morphology. A combination treatment with H2O and 3% H2O2 at 8°C led to an average 4-log reduction of bacterial pathogens, and no bacterial pathogens were detected in fresh-cut pieces prepared from this combination treatment, including enriched fresh-cut samples. The results of this study indicate that the microbial safety of fresh-cut pieces from treated cantaloupes was improved at day 6 of storage at 5°C and day 3 of storage at 10°C.

Inactivation of Salmonella enterica and Listeria monocytogenes in cantaloupe puree by high hydrostatic pressure with/without added ascorbic acid.

The objective of this research was to evaluate and develop a method for inactivation of Salmonella enterica and Listeria monocytogenes in cantaloupe puree (CP) by high hydrostatic pressure (HHP). Cantaloupe being the most netted varieties of melons presents a greater risk of pathogen transmission. Freshly prepared CP with or without 0.1% ascorbic acid (AA) was inoculated with a bacterial cocktail composed of a three serotype mixture of S. enterica (S. Poona, S. Newport H1275 and S. Stanley H0558) and a mixture of three strains of L. monocytogenes (Scott A, 43256 and 51742) to a population of ca. 10(8)CFU/g. Double sealed and double bagged inoculated CP (ca. 5g) were pressure treated at 300, 400 and 500MPa at 8°C and 15°C for 5min. Data indicated increased inactivation of both Salmonella and Listeria spp. with higher pressure. Log reduction for CP at 300MPa, 8°C for 5min was 2.4±0.2 and 1.6±0.5logCFU/g for Salmonella and Listeria, respectively. Survivability of the pathogens was significantly compromised at 400MPa and 8°C, inactivating 4.5±0.3logCFU/g of Salmonella and 3.0±0.4logCFU/g of Listeria spp. Complete inactivation of the pathogens in the puree (log reduction >6.7logCFU/g), with or without AA, was achieved when the pressure was further increased to 500MPa, except that for Listeria containing no AA at 8°C. Listeria presented higher resistance to pressure treatment compared to Salmonella spp. Initial temperatures (8 and 15°C) had no significant influence on Salmonella log reductions. Log reduction of pathogens increased but not significantly with increase of temperature. AA did not show any significant antimicrobial activity. Viable counts were about 0.2-0.4logCFU/g less in presence of 0.1% AA. These data validate that HHP can be used as an effective method for decontamination of cantaloupe puree.

Physical and chemical changes in whey protein concentrate stored at elevated temperature and humidity.

In a case study, we monitored the physical properties of 2 batches of whey protein concentrate (WPC) under adverse storage conditions to provide information on shelf life in hot, humid areas. Whey protein concentrates with 34.9 g of protein/100g (WPC34) and 76.8 g of protein/100g (WPC80) were stored for up to 18 mo under ambient conditions and at elevated temperature and relative humidity. The samples became yellower with storage; those stored at 35 °C were removed from the study by 12 mo because of their unsatisfactory appearance. Decreases in lysine and increases in water activity, volatile compound formation, and powder caking values were observed in many specimens. Levels of aerobic mesophilic bacteria, coliforms, yeast, and mold were <3.85 log10 cfu/g in all samples. Relative humidity was not a factor in most samples. When stored in sealed bags, these samples of WPC34 and WPC80 had a shelf life of 9 mo at 35 °C but at least 18 mo at lower temperatures, which should extend the market for these products.

Interactive effects of temperature, pH, and water activity on the growth kinetics of Shiga toxin-producing Escherichia coli O104:H4 3.

The risk of non-O157 Shiga toxin-producing Escherichia coli strains has become a growing public health concern. Several studies characterized the behavior of E. coli O157:H7; however, no reports on the influence of multiple factors on E. coli O104:H4 are available. This study examined the effects and interactions of temperature (7 to 46°C), pH (4.5 to 8.5), and water activity (aw ; 0.95 to 0.99) on the growth kinetics of E. coli O104:H4 and developed predictive models to estimate its growth potential in foods. Growth kinetics studies for each of the 23 variable combinations from a central composite design were performed. Growth data were used to obtain the lag phase duration (LPD), exponential growth rate, generation time, and maximum population density (MPD). These growth parameters as a function of temperature, pH, and aw as controlling factors were analyzed to generate second-order response surface models. The results indicate that the observed MPD was dependent on the pH, aw, and temperature of the growth medium. Increasing temperature resulted in a concomitant decrease in LPD. Regression analysis suggests that temperature, pH, and aw significantly affect the LPD, exponential growth rate, generation time, and MPD of E. coli O104:H4. A comparison between the observed values and those of E. coli O157:H7 predictions obtained by using the U. S. Department of Agriculture Pathogen Modeling Program indicated that E. coli O104:H4 grows faster than E. coli O157:H7. The developed models were validated with alfalfa and broccoli sprouts. These models will provide risk assessors and food safety managers a rapid means of estimating the likelihood that the pathogen, if present, would grow in response to the interaction of the three variables assessed.

Effect of storage temperature on survival and recovery of thermal and extrusion injured Escherichia coli K-12 in whey protein concentrate and corn meal.

Previously, we reported inactivation of Escherichia coli populations in corn product (CP) and whey protein product (WPP) extruded at different temperatures. However, information on the effect of storage temperatures on injured bacterial populations was not addressed. In this study, the effect of storage temperatures on the survival and recovery of thermal death time (TDT) disks and extrusion injured E. coli populations in CP and WPP was investigated. CP and WPP inoculated with E. coli bacteria at 7.8 log(10) CFU/g were conveyed separately into the extruder with a series 6300 digital type T-35 twin screw volumetric feeder set at a speed of 600 rpm and extruded at 35°C, 55°C, 75°C, and 95°C, or thermally treated with TDT disks submerged into water bath set at 35°C, 55°C, 75°C, and 95°C for 120 s. Populations of surviving bacteria including injured cells in all treated samples were determined immediately and every day for 5 days, and up to 10 days for untreated samples during storage at 5°C, 10°C, and 23°C. TDT disks treatment at 35°C and 55°C did not cause significant changes in the population of the surviving bacteria including injured populations. Extrusion treatment at 35°C and 55°C led to significant (p<0.05) reduction of E. coli populations in WPP as opposed to CP. The injured populations among the surviving E. coli cells in CP and WPP extruded at all temperatures tested were inactivated during storage. Population of E. coli inactivated in samples extruded at 75°C was significantly (p<0.05) different than 55°C during storage. Percent injured population could not be determined in samples extruded at 95°C due to absence of colony forming units on the agar plates. The results of this study showed that further inactivation of the injured populations occurred during storage at 5°C for 5 days suggesting the need for immediate storage of 75°C extruded CP and WPP at 5°C for at least 24 h to enhance their microbial safety.

Survival and growth of Salmonella enterica serovar enteritidis in membrane-processed liquid egg white with pH, temperature, and storage conditions as controlling factors.

Processing temperature and pH are known to influence the lethality and cell injury in many microbial interventions. A study was undertaken to determine the effects of variations in solution pH and process temperature on the removal and growth of Salmonella enterica serovar Enteritidis in liquid egg white (LEW) by microfiltration (MF) membrane process. The effects of various storage conditions on the growth of Salmonella in membrane-separated LEW were evaluated. Pretreated and pH-adjusted (pH 6 to pH 9) LEW was inoculated with a five-strain composite of S. enterica serovar Enteritidis at ca. 7 log CFU/ml, microfiltered at 25 or 40°C, and stored at 4 or 10°C. Temperature had a greater influence on Salmonella reduction than did pH. The maximum reduction of Salmonella and background microflora in LEW by MF was observed at 40°C and pH 8 and 9. However, the influence of temperature on permeate flow was less than that of pH. The mean permeate flow increased by 180% at 25°C as the pH decreased from 9 to 6, while flow increased merely by 18% at pH 6 as temperature increased from 25 to 40°C. Salmonella populations in processed LEW at 4°C storage remained quite stable (0.01 to 0.55 log CFU/ml), irrespective of MF experimental conditions. At 10°C the population was greater, but no major outgrowth was observed. Findings from this study would be advantageous to liquid egg processing industries.

Kinetics of thermal destruction of Salmonella in ground chicken containing trans-cinnamaldehyde and carvacrol.

We investigated the heat resistance of an eight-strain cocktail of Salmonella serovars in chicken supplemented with trans cinnamaldehyde (0 to 1.0%, wt/wt) and carvacrol (0 to 1.0%, wt/wt). Inoculated meat was packaged in bags that were completely immersed in a circulating water bath and held at 55 to 71°C for predetermined lengths of time. The recovery medium was tryptic soy agar supplemented with 0.6% yeast extract and 1% sodium pyruvate. D-values in chicken, determined by linear regression, were 17.45, 2.89, 0.75, and 0.29 min at 55, 60, 65, and 71°C, respectively (z = 9.02°C). Using a survival model for nonlinear survival curves, D-values in chicken ranged from 13.52 min (D(1), major population) and 51.99 min (D(2), heat-resistant subpopulation) at 55°C to 0.15 min (D(1)) and 1.49 min (D(2)) at 71°C. When the Salmonella cocktail was in chicken supplemented with 0.1 to 1.0% trans-cinnamaldehyde or carvacrol, D-values calculated by both approaches were consistently less at all temperatures. This observation suggests that the addition of natural antimicrobials to chicken renders Salmonella serovars more sensitive to the lethal effect of heat. Thermal death times from this study will be beneficial to the food industry in designing hazard analysis and critical control point plans to effectively eliminate Salmonella contamination in chicken products used in this study.

A comparison of analytical and data preprocessing methods for spectral fingerprinting.

Spectral fingerprinting, as a method of discriminating between plant cultivars and growing treatments for a common set of broccoli samples, was compared for six analytical instruments. Spectra were acquired for finely powdered solid samples using Fourier transform infrared (FT-IR) and Fourier transform near-infrared (NIR) spectrometry. Spectra were also acquired for unfractionated aqueous methanol extracts of the powders using molecular absorption in the ultraviolet (UV) and visible (VIS) regions and mass spectrometry with negative (MS-) and positive (MS+) ionization. The spectra were analyzed using nested one-way analysis of variance (ANOVA) and principal component analysis (PCA) to statistically evaluate the quality of discrimination. All six methods showed statistically significant differences between the cultivars and treatments. The significance of the statistical tests was improved by the judicious selection of spectral regions (IR and NIR), masses (MS+ and MS-), and derivatives (IR, NIR, UV, and VIS).

Removal of Salmonella Enteritidis from commercial unpasteurized liquid egg white using pilot scale cross flow tangential microfiltration.

Effectiveness of a cross flow microfiltration (MF) process for removal of a cocktail of Salmonella enterica serovar Enteritidis species from commercial unpasteurized liquid egg white (LEW) from a local egg breaking plant, while maintaining its functional properties was evaluated. To facilitate MF, LEW was wedge screened, homogenized and then diluted (1:2 w/w) with distilled water containing 0.5% sodium chloride. Diluted unpasteurized LEW was inoculated with five strains of S. Enteritidis (ATCC 4931, ATCC BAA-708, ATCC 49215, ATCC 49218, and ATCC BAA-1045) to a level of approximately 10(7)CFU/mL of LEW and microfiltered using a ceramic membrane. Process parameters influencing egg white functional properties and pathogen removal efficiency were evaluated. Average permeates flux increased by almost 126% when pH of LEW was adjusted from pH 8 to pH 7 at 25 degrees C. Microbial removal efficiency was at least, on average, 6.8Log(10)CFU/mL (limit of detection < or =0.5Log(10)CFU/mL). Functional property analysis indicated that the MF process did not alter the foaming power of LEW.

UV spectral fingerprinting and analysis of variance-principal component analysis: a useful tool for characterizing sources of variance in plant materials.

UV spectral fingerprints, in combination with analysis of variance-principal components analysis (ANOVA-PCA), can differentiate between cultivars and growing conditions (or treatments) and can be used to identify sources of variance. Broccoli samples, composed of two cultivars, were grown under seven different conditions or treatments (four levels of Se-enriched irrigation waters, organic farming, and conventional farming with 100 and 80% irrigation based on crop evaporation and transpiration rate). Freeze-dried powdered samples were extracted with methanol-water (60:40, v/v) and analyzed with no prior separation. Spectral fingerprints were acquired for the UV region (220-380 nm) using a 50-fold dilution of the extract. ANOVA-PCA was used to construct subset matrices that permitted easy verification of the hypothesis that cultivar and treatment contributed to a difference in the chemical expression of the broccoli. The sums of the squares of the same matrices were used to show that cultivar, treatment, and analytical repeatability contributed 30.5, 68.3, and 1.2% of the variance, respectively.