Source: MICHIGAN STATE UNIV submitted to NRP
MICROBIAL SAFETY, QUALITY AND SHELF-LIFE OF FRESH PRODUCE AND OTHER READY-TO-EAT FOODS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
HATCH
Reporting Frequency
Annual
Accession No.
1002973
Grant No.
(N/A)
Cumulative Award Amt.
(N/A)
Proposal No.
(N/A)
Multistate No.
(N/A)
Project Start Date
Jul 1, 2014
Project End Date
Jun 30, 2019
Grant Year
(N/A)
Program Code
[(N/A)]- (N/A)
Recipient Organization
MICHIGAN STATE UNIV
(N/A)
EAST LANSING,MI 48824
Performing Department
Food Science
Non Technical Summary
The overall goal of this five year project is to enhance the microbial safety and quality of ready-to-eat, fresh-cut produce with three segments in the fresh produce chain being specifically targeted, namely processing, packaging, and retail distribution. In the first of these objectives, a series of laboratory as well as pilot-plant based studies will be conducted to quantify the extent of cross-contamination that occurs during simulated commercial and retail slicing/dicing of fresh fruits and vegetables as related to the various parameters of both the process (e.g., cutting force, friction, knife blade design/material) and the product (e.g., texture, bulk density, water, cellulose, lignin). Dr. Bradley Marks will then use these findings to develop and test a generalized mathematical model for pathogen attachment/transfer/internalization during slicing/dicing of fresh produce which we will then validate in a series of independent experiments using other types of fresh produce and slicing/dicing conditions. Since commercially diced produce is normally conveyed and washed before packaging, the impact of various single and/or combined treatments (e.g., chlorine, peroxyacetic acid, electrolyzed water, ozone sonication) on pathogen reduction during washing and conveying will also be assessed by several collaborators from other universities using our unique pilot-scale processing line for fresh-cut fruits and vegetables (e.g., lettuce, tomatoes, onions). Thereafter, optimal packaging systems will be developed to enhance microbial safety and quality of the types of fresh-cut produce being investigated with assistance from Dr. Eva Almenar from the School of Packaging. Based on a wealth of both in-transit and in-store time/temperature data that was previously collected across the country in conjunction with several other USDA grants led by Dr. Keith Vorst at Cal Poly, we will also will assess the growth of E. coli O157, Salmonella, L. monocytogenes, background bacteria, and yeasts/molds in the same packaged products from the previous objective under real-world conditions encountered during commercial transport, retail storage and display using a programmable incubator to mimic these same time/temperature fluctuations during periods of temperature abuse. Overall, these efforts will lead to the development of 1) improved practices for handling fresh-cut produce at both the processing and retail levels, and 2) improved risk assessments for fresh-cut produce that will help in guiding future government decisions in relation to the Food Safety Modernization Act.
Animal Health Component
80%
Research Effort Categories
Basic
20%
Applied
80%
Developmental
0%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
71224101100100%
Knowledge Area
712 - Protect Food from Contamination by Pathogenic Microorganisms, Parasites, and Naturally Occurring Toxins;

Subject Of Investigation
2410 - Cross-commodity research--multiple crops;

Field Of Science
1100 - Bacteriology;
Goals / Objectives
The overall goal of this five-year project is to continue to enhance the microbial safety and quality of ready-to-eat, fresh-cut fruits and vegetables via integrated multi-disciplinary research that specifically targets the processing, packaging, and distribution sectors of the farm-to-fork continuum. A series lab- and pilot-scale slicing/dicing/washing experiments will be conducted that capitalize on the unique capabilities of our fresh-cut produce processing line which has continued to receive national attention. This proposal which is structured around three well-defined links in the food chain consists of the following objectives:Objective 1. Quantify the impact of different product, process and equipment parameters on the transfer of various foodborne pathogens during pilot plant-scale production of fresh-cut fruits and vegetables.Objective 2. Evaluate a range of chemical and physical strategies for reducing pathogenic and spoilage organisms on fresh-cut fruits and vegetables during simulated commercial production in a pilot-scale processing line.Objective 3. Evaluate a Portable Multi-use Automated Concentration System (PMACS) for concentrating pathogens from centrifugation water using a pilot-scale leafy green and tomato/citrus processing line containing wash water of various organic loadsObjective 4. Assess the impact of the physiological state of pathogens on their survival on fresh-cut produce during processing and subsequent storage under simulated time/temperature profiles encountered during transport and retail storage/display.Objective 5. Develop optimal packaging systems for enhanced microbiological safety and quality of fresh-cut produce.Objective 6. Assess and model the growth of pathogens, mesophilic aerobic bacteria, and yeasts/molds in packaged fresh-cut produce during transport, retail storage and display using previous collected time/temperature histories.
Project Methods
Objective 1. Quantify the impact of different product, process and equipment parameters on the transfer of various foodborne pathogens during pilot plant-scale production of fresh-cut fruits and vegetables.Experimental design: A range of fruits and vegetables of varying composition and structure (density, cellulose and lignin content, surface texture), including those previously associated with foodborne outbreaks and/or recalls (e.g. leafy greens, tomatoes, onions, celery, cantaloupe among others) will be surface-inoculated with multi-strain cocktails of E. coli O157:H7, Salmonella or L. monocytogenes and then processed to mimic foodservice or large-scale commercial practices. Manual countertop slicers and dicers will be used to duplicate foodservice practices; whereas the MSU pilot-scale commercial processing line which includes an Urschel shredder and dicer, step conveyor, various types of roller conveyors, a 3.3-m long recirculating flume tank for washing, mechanical shaker table and centrifugal dryer will be used to duplicate large-scale commercial practices.Objective 2. Evaluate a range of chemical and physical strategies for reducing pathogenic and spoilage organisms on fresh-cut fruits and vegetables during simulated commercial production in a pilot-scale processing line.Experimental design. Various fruits and vegetables will again be surface-inoculated with different pathogens and subjected to pilot-plant-scale processing as described in Objective 1. While Objective 1 focused on quantifying the extent of bacterial transfer in the absence of chemical sanitizers, Objective 2 will assess the efficacy of a range of commonly used chemical sanitizers (e.g., chlorine, peroxyacetic acid, ozone, chlorine dioxide, electrolyzed oxidizing water) in combination with different physical treatments (e.g., sonication, pulsed UV light, and light activated photocatalytic nanocoatings) for inactivation of various foodborne pathogens (e.g., E. coli O157:H7, Salmonella, L. monocytogenes, Clostridium difficile, viruses) on fresh-cut fruits and vegetables during simulated commercial production using the MSU pilot-scale processing line.Objective 3. Evaluate a Portable Multi-use Automated Concentration System (PMACS) for concentrating pathogens from centrifugation water using a pilot-scale leafy green and tomato/citrus processing line containing wash water of various organic loads.Experimental design. Recovery of E. coli O157:H7, L. monocytogenes and Salmonella Typhimurium from flume tank and centrifugation water containing 0, 2.5, 5, 7.5 and 10% (w/v) homogenized lettuce solids will be assessed with the Portable Multi-use Automated Concentration System (PMACS) after processing 50 lbs. (22.7 kg) batches of iceberg lettuce simultaneously inoculated with all three pathogens at 104,102 and 100 CFU/g, using a chlorine-based sanitizer with sanitizer-free water serving as the control (n = 90).Objective 4. Assess the impact of the physiological state of pathogens on their survival on fresh-cut produce during processing and subsequent storage under simulated time/temperature profiles encountered during transport and retail storage/displayExperimental design. The physiological state of a bacterium (e.g., healthy, sublethally injured, viable-but-non-culturable, dead) influences its ability to adapt and survive new stresses and persist in foods. The goal of this project is to use gene expression data to identify the physiological state of EHEC and L. monocytogenes on pre-inoculated lettuce plants during harvest, processing, transport, and retail storage/display (Figure 1). Lettuce plants grown at North Dakota State University (NDSU) in a growth chamber under the same temperature and light conditions as those found in Salinas Valley will be inoculated with EHEC or L. monocytogenes. After 5 days of assimilation under these same conditions, the lettuce will be harvested, sent to MSU and subjected to flume washing, shaker table dewatering and centrifugal drying using the pilot-scale leafy green processing line. Four different wash water conditions will be used: water alone, 50 ppm chlorine, 50 ppm peroxyacetic acid, and 50 ppm with T-128.Objective 5. Develop optimal packaging systems for enhanced microbiological safety and quality of fresh-cut produce.Experimental design: Prototype packages will be developed for different types of fresh-cut produce based on modified atmosphere composition, package dimensions and material permeability. After inoculation with E. coli O157:H7, Salmonella, L. monocytogenes or C. difficile, the products will be packaged and analyzed for levels of pathogenic and spoilage bacteria, respiration rate, color, firmness, weight loss, and off-flavors at 3 to 5 day intervals during 3 weeks of storage at 4 and 10 °C The equilibrium gas concentration (steady-state condition) of the different packages will be determined by headspace analysis using gas chromatography. Up to three sensory analyses (uninoculated products) using consumer panels (n = 75) will be conducted in the MSU Sensory Evaluation Laboratory using uninoculated, pathogen-free control samplesObjective 6. Assess and model the growth of pathogens, mesophilic aerobic bacteria, and yeasts/molds in packaged fresh-cut produce during transport, retail storage and display using previous collected time/temperature histories. Experimental design. Different time/temperature histories collected from previous work which represents varying degrees of abuse during product transport, retail storage and display will be uploaded to a Blue M Environmental Chamber (FRS-13B; All-Temp Engineering, San Jose, CA) at MSU for product incubation. In triplicate experiments, inoculated and uninoculated packages of fresh-cut produce from the prior objectives will be evaluated at pre-determined intervals for growth of the target pathogen with mesophilic aerobic bacteria, psychrotrophic bacteria, lactic acid bacteria, yeast, and mold quantified according to standard methods while the environmental chamber cycles through temperature profiles matching the actual profiles collected from the retail study.

Progress 07/01/14 to 06/30/19

Outputs
Target Audience:This project addresses the fresh produce and low moisture food industries with the results disseminated to industry, government and academia through various meetings sponsored by the International Association for Food Protection and other professional organizations. The impact of this work will result in altered behaviors among processors, distributors and retailers of fresh produce and low moisture foods such as almonds, flour, peanut butter and dates with the end-result being enhanced safety and shelf-life. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project is providing training for 5 graduate and 3 undergraduate students at Michigan State University as well as 1 graduate student and 1 postdoctoral researcher at North Carolina State University. How have the results been disseminated to communities of interest?Our results were presented at various national/international annual meetings including The Center for Produce Safety (apple growers, apple packers and others in the fresh produce industry), The International Association for Food Protection (academia, government, industry) American Chemical Society (academia, government, industry) and The International Symposium on Problems of Listeriosis (academicians with a strong interest in Listeria monocytogenes (molecular pathogenesis, foodborne listeriosis, epidemiology). Thus, our findings reached widely different audiences. What do you plan to do during the next reporting period to accomplish the goals?Our new project contains the following two primary objectives - 1) assess the survival of eight Lm strains grown planktonically or as a biofilm on three unwaxed apple varieties (Gala, Granny Smith, Honeycrisp) from two different harvest seasons and three different growing regions (Michigan, Washington, Pennsylvania) during air (21% O2) or controlled atmosphere (1.5% O2, 0 - 3% CO2) (CA) storage, and 2) assess Lm survival on these same apples after waxing. These two objectives are based on the following underlying hypotheses: 1) Lm will not grow on the apples but may persist on surface-inoculated apples for several months during storage, 2) The extent of Lm survival on apples will vary based on strain of Lm, physiological state (i.e. derived from planktonic cells vs. biofilm) of Lm, apple variety, growing region, growing season and type of storage (air, controlled atmosphere), and 3) Waxing of apples may enhance the survival of Lm.

Impacts
What was accomplished under these goals? In the first of three studies, the efficacy of a new sulfuric acid/surfactant sanitizer was assessed against Salmonella during simulated commercial washing of diced tomatoes. Triplicate 9.1 kg batches of Roma tomatoes were dip-inoculated in a 2- strain avirulent Salmonella cocktail, air- dried, mechanically diced and the subjected to 60 sec of washing in a pilot-scale flume system with tap water, 80 ppm peroxyacetic acid (PAA), sulfuric acid/surfactant sanitizer (SS) at pH 1.8 and 2.0, 80 ppm PAA/SS at pH 1.8, or chlorine (5 and 10 ppm free chlorine. Treating with SS/PAA provided greater reductions in both Salmonella and lactobacilli at short treatment times compared to PAA (P<0.05) and chlorine. Immediately after dicing, Salmonella was present at 3.50±0.40 log CFU/g, with populations decreasing an average of 1.95±0.93, 1.70±1.22, 0.75±0.52, 0.61±0.21, 0.52±0.11, 0.48±0.07, and 0.47±0.07 logs after 60 sec of washing in 80 ppm PAA, SS/PAA, tap water, 10 ppm chlorine, 5 ppm chlorine, SS at pH 2.0, and SS at pH 1.8, respectively. After 14 days of storage at 7°C, Salmonella decreased 3.62±0.23, 3.25±0.07, 1.53±0.38, 1.35±0.85, 1.28±0.15, 1.22±0.13, and 0.94±0.47 in tomatoes previously processed using SS/PAA, PAA, 10 ppm chlorine, SS at pH 1.8, SS at pH 2.0, 5 ppm free chlorine, and tap water, respectively. Based on these findings, the safety of commercially washed diced tomatoes can be enhanced using SS/PAA. In the second study, the behavior of silver nanoparticles was evaluated under different wash water conditions for leafy greens. Aggregation and dissolution kinetics of silver nanoparticles (AgNPs) were systematically investigated in wash water with or without dissolved lettuce extract (DLE) or chlorine as a sanitizer. For the 50 and 100 mg/L chlorine treatments, the dissolved Ag concentration was lower (P<0.05) compared to the control. At 12 h, dissolved Ag concentrations were 0.005 and 0.026 mg/L for 50 and 100 mg/L chlorine, respectively, compared to 0.468 mg/L for the control (P<0.05). While less aggregation occurred during the first 12 h, AgNPs increasingly aggregated in the presence of 50 and 100 ppm chlorine after 4 days (168.1 and 180.0 nm) compared to the control (89.7 nm) (P<0.05), with the zeta-potential values more negative compared to the control. AgNP treatments with DLE yielded similar findings. Since the fate of AgNPs in fresh produce washing systems is affected by both chlorine and organic matter in wash water, these interactions are important in evaluating the sorption of AgNPs to leafy greens. The last study compared the thermal resistance of Enterococcus faecium and a Salmonella cocktail (Agona, Reading, Tennessee, Montevideo, Mbandaka) in skim milk powder (SMP), lactose-free skim milk powder (LFSMP), lactose powder (LP), and milk protein isolate (MPI) at 0.25 water activity (aw) at 65 - 90°C. E. faecium and Salmonella demonstrated similar (P>0.05) thermal resistance in LFSMP (D70°C-Ef 14.5±0.4 min; D70°C-Sal 15.6±0.4 min). Based on a DT-80°C, E. faecium was more resistant (P<0.05) in LP (33.1±4.8 min) than in LFSMP (2.6±0.1 min), however no difference in z-values (zT-LP = 15.3±1.4°C; zT-LFSMP = 13.7±0.3°C) was observed. This study demonstrates that E. faecium can be used as a Salmonella surrogate for validating thermal treatment of dairy powders, considering that thermal resistance of both microorganisms can be affected by lactose and milk protein levels.

Publications

  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Steinbrunner, P. Limcharoenchat, Q. Suehr, E.T. Ryser, and B.P. Marks, and S. Jeong. 2019. Effect of food structure, water activity, and long-term storage on X-ray irradiation for inactivating Salmonella Enteritidis PT 30 in low-moisture foods. J Food Prot. 82:1405-1411
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Ahmad, N., C. �ztabak, B.P. Marks, and E.T. Ryser. 2019. Effect of talc as a dry-inoculation carrier on thermal resistance of Enterococcus faecium NRRL B-2354 in almond meal. J. Food Prot. 82:1110-1115.
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Garces-Vega, F., E.T. Ryser, and B.P. Marks. 2019. Relationships of water activity and moisture content to the thermal inactivation kinetics of Salmonella in low-moisture foods. J. Food Prot. 82:963-970.
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Oladimeji, V., S. Jeong, E. Almenar, B. P. Marks, K. L. Vorst, W. Brown, and E. T. Ryser. 2019. Predicting the growth of Listeria monocytogenes and Salmonella Typhimurium growth in diced celery, onions, and tomatoes during simulated commercial transport, retail storage, and display. J. Food Prot. 82:287-300
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Parsons, C., E.T. Ryser, R. Raftopoulou, and S. Kathariou. 2019. Sequence tagging of Listeria monocytogenes strains for monitoring relative fitness on fresh apples. Abst. International Symposium on Problems of Listeriosis, Toronto, Canada, September 24  27.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Gunathilaka, G., J. He, H. Li, W. Zhang, and E.T. Ryser. 2019. Fate of silver nanoparticles in lettuce wash water as impacted by chlorine and organic matter. Abst. Annual Meeting of the American Chemical Society. San Diego, CA August 25  29.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Sloniker, N., C. Kang, and E.T. Ryser. 2019. Inactivation of Salmonella Typhimurium during flume washing of diced tomatoes with a sulfuric acid/surfactant-based sanitizer. Abst. Ann. Mtg. Int. Assoc. Food Prot., Louisville, KY, July 21  24
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Hildebrandt, I., N. Hall, M. James, E.T. Ryser, and B.P. Marks. 2019. Humidity affects Salmonella lethality and USDA FSIS Appendix A compliance for impingement-cooked meat and poultry products. Abst. Ann. Mtg. Int. Assoc. Food Prot., Louisville, KY, July 21  24.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Steinbrunner, P.J., E.T. Ryser, K. Dolan, B.P. Marks, and S. Jeong. 2019. Quantifying the inactivation of Enterococcus faecium during spray drying. Abst. Ann. Mtg. Int. Assoc. Food Prot., Louisville, KY, July 21  24.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Gomez, C., B.P. Marks, S. Ilic, E.T. Ryser, and J. Mitchell. 2019. Creating a risk model for nosocomial listeriosis in cancer patients who consume ready-to-eat salads. Abst. Ann. Mtg. Int. Assoc. Food Prot., Louisville, KY, July 21  24.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Ahmad, N.H., B.P. Marks, and E.T. Ryser. 2019. Enterococcus faecium NRRL B-2354 as a Salmonella surrogate for validating thermal treatment of dairy powders with different lactose and milk compositions. Abst. Ann. Mtg. Int. Assoc. Food Prot., Louisville, KY, July 21  24
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Gunathilaka, G., J. He, H. Li, W. Zhang, and E.T. Ryser. 2019. Behavior of silver nanoparticles under wash water conditions for leafy green processing. Abst. Ann. Mtg. Int. Assoc. Food Prot., Louisville, KY, July 21  24
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Ryser, E.T., S. Kathariou, R. Beaudry, C. Parsons, D. Matthews, and R. Raftopoulou. 2019. Fate of different Listeria monocytogenes strains on different whole apple varieties during long-term simulated commercial storage. Abst. Ann. Mtg. Center for Produce Safety. Austin, TX June 18-19.
  • Type: Conference Papers and Presentations Status: Published Year Published: 20109 Citation: Zhang, W., J. He, L. Zhang, S.Y. He, E.T. Ryser, and H. Li. 2019. Stomata facilitated sorption of silver nanooparticles by Arabidopsis thaliana. Abst. European Geoscience Union General Assembly, Vienna, Austria, April 7  12.
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Wang, H., and E.T. Ryser. 2019. Quantitative transfer and sanitizer inactivation of Salmonella during simulated commercial dicing and conveying of tomatoes. Food Control https://doi.org/10.1016/j.foodcont.2019.106762.


Progress 10/01/17 to 09/30/18

Outputs
Target Audience:This project addresses the fresh-cut produce and low moisture food industries with the results disseminated to industry, government and academia through various meetings sponsored by the International Association for Food Protection and other professional organizations. The impact of this work will result in altered behaviors among processors, distributors and retailers of fresh-cut produce and low moisture foods such as almonds, flour, peanut butter and dates with the end-result being enhanced safety and shelf-life. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has provided training for two doctoral students with both students presenting their findings at the Annual Meeting of the International Association for Food Protection in Salt Lake City, Utah. Both students were finalists in the graduate student poster competition with Nurul Ahmad awarded 1st place. How have the results been disseminated to communities of interest?In addition to formal presentations at the International Association for Food Protection, Nurul Ahmad's low misture food findings have been incorporated into various workshops for industry stakeholders. What do you plan to do during the next reporting period to accomplish the goals?Three manuscripts from the three studies described will be submitted to the Journal of Food Protection for publication. This year's goal is to investigate effect of protein and lactose composition on thermal resistance of E. faecium and Salmonella in milk-based powders at 0.25 aw and with this aim achieved through the following sub-objectives: 1) Quantify the effect of milk protein and lactose content on thermal resistance of Salmonella and E. faecium in milk protein concentrate (MPC40), milk protein isolate (MPI) and lactose powder (Lac); 2) Determine the influence of milk protein type on thermal resistance of Salmonella and E. faecium using milk protein isolate (MPI) and milk protein hydrolysates (MPH); and 3) Determine the influence of lactose on thermal resistance of Salmonella and E. faecium using skim milk powder (SMP) and hydrolyzed lactose-skim milk powders (HLSMP). In addition, two projects assessing the fate of Listeria monocytogenes on apples during storage and the transfer of nanoparticles during simulated commercial processing of leafy greens will be initiated.

Impacts
What was accomplished under these goals? The first study aimed to quantify the impact of intrinsic produce characteristics (water content, pH, cutting force, soluble solids content and surface hydrophobicity) on Listeria monocytogenes transfer during mechanical slicing. Locally purchased whole onions, radishes, tomatoes, potatoes, gray zucchini, sweet potato zucchini, cantaloupe, apples, pear, and cucumbers were dip-inoculated with a 3-strain avirulent cocktail of L. monocytogenes (M3, J22F and J29H) to contain ~7 log, CFU/cm2 and airdried for 1 h. Thereafter, one intact sample was sliced to contaminate a NEMCO vertical slicer(modified for constant cutting speed) followed by 15 uninoculated samples of the same product type. Three slices per sample were homogenized by stomaching, appropriately diluted and surface-plated on Modified Oxford Agar. For each of the different products assessed, a two-parameter exponential decay model was fitted to Listeria populations obtained during slicing. Moreover, the intrinsic produce data including water content, pH, cutting force, soluble solids content and surface hydrophobicity were determined and fitted to a linear model to assess their effect on Listeria transfer. All experiments were conducted in triplicate. A multiple comparison of all product transfer data yielded significantly different (P < 0.05) Listeria decay rates, ranging from 0.008 ± 0.002 to 0.09 ± 0.01 for cucumbers and radish, respectively. After fitting a linear model to describe the effects of these inherent produce characteristics on the Listeria decay rate, Water content, surface hydrophobicity, and surface roughness had more effect of decay rates with parameter estimate of 0.001, 0.0003, and 0.00006, respectively. The second study compared E. faecium as a surrogate for thermal inactivation of Salmonella in date paste and assessed reproducibility of the results across two laboratories- Michigan State University (MSU) and University of Georgia(UGA). A 600-g sample of pitted date pieces (~1 x 1 cm) was surface- inoculated with either E. faecium NRRLB-2354 or a 5-strain Salmonella cocktail (Agona, Enteritidis PT30,Tennessee, Montevideo, Mbandaka) on the outer skin, pre-conditioned to 0.65 ± 0.025aw, and then ground into a paste by three passages through a meat grinder. Individual 1-g sub-samples were conditioned for 2 - 3 days and tested to ensure a homogeneous inoculum before use. Isothermal treatments were performed at 65, 70, 75, and 80°C by heating 1-g samples (in triplicate, at two laboratories, with ≥ 6 durations per temperature) in aluminum test cells. Survivors were enumerated on designated non-selective/differential media after incubation. E. faecium exhibited higher thermal resistance (P < 0.05) (D70C-Ef of 7.5 ± 0.3 min) than the Salmonella cocktail (D70C-Sal of 4.6 ± 0.5 min) at both MSU and UGA. Both laboratories also demonstrated a significant (P < 0.05) impact of temperature on thermal inactivation of E. faecium, (MSU: D70C = 8.8 ± 0.2 min; D75C = 4.4 ± 0.1min; D80C = 1.8 ± 0.1 min) and (UGA: D70C = 4.5 ± 0.2 min; D75C = 2.5 ± 0.1 min; D80C = 1.0 ± 0.1 min) with repeatability observed at 75C. Based on this cross-laboratory study, E. faecium NRRLB-2354 appears to be a valid surrogate for thermal inactivation of Salmonella in date paste. The last study aimed to determine: (1) the effect of wet- and dry-inoculation on thermal resistance of E. faecium (Salmonella surrogate) in almond meal at 80°C, and (2) the influence of talc powder as a carrier. Whole almonds were either immersed in an E. faecium suspension for wet inoculation (WI) or added to inoculated talc powder for dry inoculation (DI). After sieving the DI almonds to remove excess talc, almonds were pre-conditioned to 0.45 aw, ground into a meal and re-conditioned to 0.45 aw. Thermal resistance of E. faecium in talc alone (T) and WI almond meal with added talc (WT) was also determined. Isothermal treatments were performed by heating ~1 g of almond meal in aluminum test cells at 80°C (in triplicate, > 5 time points analyzed), and then immediately cooling, diluting, and plating samples on esculin-TSAYE (48 h at 35°C). WI yielded a higher initial population (7.6±0.2 log CFU/g) than DI (5.5±0.3 log CFU/g). E. faecium was more thermally resistant in DI (D80?C: 63.5±1.9 min) compared to WI almond meal (D80?C: 40.5±1.0 min) (P < 0.05), but E. faecium resistance in WT almond meal(46.9±0.9 min) was between and different (P < 0.05) from both DI and WI. While E. faecium is a well-documented surrogate for Salmonella in almonds, the efficacy of talc as an inoculum carrier for dry inoculation of low-moisture foods is complicated and needs further study.

Publications

  • Type: Journal Articles Status: Accepted Year Published: 2018 Citation: Bhalsod, G.D., Y.-H. Chung, S. Jeon, W. Gui, H. Li, E.T. Ryser, A.K. Gruber, and W. Zhang. 2018. Uptake and accumulation of pharmaceuticals in overhead- and surface-irrigated greenhouse lettuce. J. Agr. Food Chem. (accepted).
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Smolinski, H.S., S. Wang, L. Ren, Y. Chen, B. Kowalcyk, E. Thomas, and E.T. Ryser. 2018. Transfer and redistribution of Salmonella Typhimurium LT2 and E. coli O157:H7 during pilot-scale processing of baby spinach, cilantro, and romaine lettuce. J. Food Prot. 81:953-962.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Casulli, K.E., F.J Garces-Vega, K.D. Dolan, E.T. Ryser, L.J. Harris, and B.P. Marks. 2018. Impact of process temperature, humidity, and initial product moisture on thermal inactivation of Salmonella Enteritidis PT30 on pistachios during hot-air heating. J. Food Prot. 81:1351-1356.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Limcharoenchat, P., S.E. Buchholz, M.K. James, N.O. Hall, E.T. Ryser, and B.P. Marks. 2017. Inoculation protocols influence the thermal resistance of Salmonella Enteritidis PT30 in fabricated almond, wheat and date products. J. Food Prot. 81:606-613.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Gustafson, R., and E.T. Ryser. 2017. Survival and growth of Listeria monocytogenes during production and storage of caramel apples. Food Control 79:234-238.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Ahmad, N.H., A. Singh, I.M. Hildebrandt, H. Thippareddi, B.P. Marks, and E.T. Ryser. 2018. Validation of Enterococcus faecium as a surrogate for thermal inactivation of Salmonella on date paste. USDA NIFA Food Processing and Manufacturing Technology Project Directors Meeting, Natick, MA August 14-15.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Ahmad, N.H., C Oztabak, B.P. Marks, and E.T. Ryser. 2018. Effect of talc on thermal resistance of Enterococcus faecium NRRL B-2354 in almond meal at 0.45 aw. USDA NIFA Food Processing and Manufacturing Technology Project Directors Meeting, Natick, MA August 14-15.
  • Type: Book Chapters Status: Published Year Published: 2018 Citation: Smolinski, H.S., and E.T. Ryser. 2018. Microbiology of fresh and processed vegetables, pp. 159-182. In: Handbook of Vegetables and Vegetable Processing, 2nd Edition. Sinha, N.K., and Y.H. Yui (eds.). Wiley-Blackwell, Ames
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Steinbrunner, P., E.T Ryser, K. Dolan, B.P. Marks, and S. Jeong. Modeling inactivation of Salmonella during spray drying. USDA NIFA Food Processing and Manufacturing Technology Project Directors Meeting, Natick, MA August 14-15.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Ahmad, N.H., A. Singh, I.M. Hildebrandt, H. Thippareddi, B.P. Marks, and E.T. Ryser. 2018. Validation of Enterococcus faecium as a surrogate for thermal inactivation of Salmonella on date paste. Abst. Ann. Mtg. Int. Assoc. Food Prot., Salt Lake City, UT, July 8  11.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Ahmad, N.H., C Oztabak, B.P. Marks, and E.T. Ryser. 2018. Effect of talc on thermal resistance of Enterococcus faecium NRRL B-2354 in almond meal at 0.45 aw. Abst. Ann. Mtg. Int. Assoc. Food Prot., Salt Lake City, UT, July 8  11.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Steinbrunner, P., E.T Ryser, K. Dolan, B.P. Marks, and S. Jeong. Modeling inactivation of Salmonella during spray drying. Abst. Ann. Mtg. Int. Assoc. Food Prot., Salt Lake City, UT, July 8  11.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Alnughaymishi, H., and E.T. Ryser. 2018. Quantification of Listeria monocytogenes transfer during slicing of fresh produce based on inherent product characteristics. Abst. Ann. Mtg. Int. Assoc. Food Prot., Salt Lake City, UT, July 8  11.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Mower, A., M. Parish, E.T. Ryser, and M. Zweitering. 2018. The grey area of science: Predatory publishers and questionable conferences. Ann. Mtg. Int. Assoc. Food Prot., Salt Lake City, UT, July 8  11.
  • Type: Journal Articles Status: Submitted Year Published: 2018 Citation: Kearns, E., Gustafson, R., S. Magana, D. Lim, and E.T Ryser. 2018. Rapid concentration/detection of Escherichia coli O157:H7 and Listeria monocytogenes from lettuce wash waters generated in commercial scale facilities. Food Control (submitted).
  • Type: Journal Articles Status: Under Review Year Published: 2018 Citation: Oladimeji, V., S. Jeong, E. Almenar, B. P. Marks, K. L. Vorst, W. Brown, and E. T. Ryser. 2018. Predictive modeling of Listeria monocytogenes and Salmonella Typhimurium growth in diced celery, onions, and tomatoes during simulated commercial transport, retail storage and display. Intern. J. Food Microbiol. (in revision).
  • Type: Theses/Dissertations Status: Published Year Published: 2018 Citation: Hamoud Al Nughaymishi. 2018. Dissertation: Listeria monocytogenes transfer during slicing as impacted by intrinsic characteristics of fresh produce.


Progress 10/01/16 to 09/30/17

Outputs
Target Audience:This project addresses the fresh-cut produce and low moisture food industries with the results disseminated to industry, government and academia through various meetings sponsored by the International Association for Food Protection and other professional organizations. The impact of this work will result in altered behaviors among processors, distributors and retailers of fresh-cut produce and low moisture foods such as almonds, flour, peanut butter and dates with the end-result being enhanced safety and shelf-life. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Three M.S. students completed their degrees related to 1) transfer of Listeria during slicing of cantaloupe, 2.) concentration of E. coli and Listeria in produce wash water (study 2 above) and redistribution of Salmonella during pilot-scale processing of baby spinach and cilantro in 2017. Two of my Ph.D. students are assessing 1) various factors that impact pathogen transfer during preparation of fresh-cut produce (study 1 above) and 2) use of Enterococcus faecium as a surrogate for Salmonella during thermal processing of low moisture foods (study 3 above). A new Ph.D student also joined my laboratory to work on a USDA-funded project related to the redistribution of nanoparticles during simulated commercial processing of fresh-cut produce. How have the results been disseminated to communities of interest?These findings have been presented at various annual meetings including the International Association for Food Protection and the Institute of Food Technologists as well as to various commodity groups. What do you plan to do during the next reporting period to accomplish the goals?Work on the safety of low moisture foods will continue and a new project assessing the redistribution of nanoparticles during simulated commercial production of fresh-cut produce is now beginning.

Impacts
What was accomplished under these goals? Study 1. The Effect of Pear Firmness on the Transfer of Salmonella during Mechanical Slicing Numerous studies have examined the extent of microbial cross-contamination during preparation of fresh-cut produce; however, few investigators have assessed the impact of specific processing parameters on pathogen transfer. This study aimed to evaluate the impact of pear firmness on transfer of Salmonella during mechanical slicing. Based on triplicate experiments, samples from the 1st , 9th, and 15th firm pears yielded average Salmonella populations of 2.4±0.1, 0.8±0.5, and 0.4±0.1 log CFU/cm2, respectively, which were significantly lower (P < 0.05) than medium (3.1±0.2, 1.2±0.4, and 0.6±0.1 log CFU/cm2) and soft pears (3.6±0.1, 1.5±0.2, and 1.1±0.3 log CFU/cm2). In addition, the total number of Salmonella cells transferred was statistically higher for firm (P < 0.05) as compared to medium and soft pears. Consequently, the extent of cross-contamination of fresh produce during slicing is affected by firmness. These findings should prove useful in developing improved predictive models for bacterial transfer and expanding current risk assessments across a wider range of products. Study 2. Rapid Concentration/Detection of Escherichia coli O157:H7 and Listeria monocytogenes from Lettuce Wash Waters Generated in Commercial Scale Facilities Our previously developed dead end ultrafiltration concentration (DEUF-C) sampling method demonstrated increased detection probability of pathogens in lettuce wash water (LWW) during pilot-scale testing. This study investigated the use of DEUF-C in commercial-scale tests through the following two objectives: 1) comparison of pathogen detection probabilities using DEUF-C versus standard grab sampling in LWWs generated from a processing test line and 2) assessment of DEUF-C to concentrate pathogens spiked into commercially generated flume and centrifugation LWWs. In objective 1, Escherichia coli and Listeria monocytogenes were detected in 100% of DEUF-C samples (n = 14) compared to 6.7% and 20%, respectively, in standard grab samples (n = 15). In objective 2, total filterable volumes for flume water were higher (n = 4; 30.6+9.9 L) than those for centrifugation water (n = 4; 9.9+2.0 L) (P=0.029, Mann-Whitney U Test). E. coli and L. monocytogenes were detected in 100% of DEUF-C samples compared to 11.1% and 16.7%, respectively, in standard grab samples. Therefore, while DEUF-C offers improved probability of detection for E. coli and Listeria, the total filterable volume for commercial produce wash water needs to be further improved. Study 3 - Utilization of Enterococcus faecium as a Salmonella spp. Surrogate for Thermal Treatment in Selected Low-moisture Food Products Composition and structure of low moisture foods may affect Salmonella thermal resistance. Therefore, it is important to qualify the appropriateness of surrogates prior to use in validating preventive controls. This study aimed to compare thermal resistance of Enterococcus faecium and Salmonella in peanut butter, almond meal, wheat flour, nonfat dried milk powder, date paste, and ground black pepper; and to determine reproducibility of results across five laboratories. Salmonella showed lower (P < 0.05) thermal resistance than E. faecium in almond meal, peanut butter, and nonfat dried milk powder. Although almond meal and peanut butter have a similar fat content, E. faecium and Salmonella showed less thermal resistance in almond meal (D90°C Ef: 8.55±0.13 min; D90°C Sal : 7.24±0.08 min at 0.45 aw) than in peanut butter (D90°C Ef: 21.17±0.21; D90°C Sal: 11.45 ± 0.25 min at 0.25 aw). Milk powder, at 0.25 aw , showed greater thermal resistance of E. faecium(D90°C: 25.20 ± 0.94 min) and less thermal resistance for Salmonella (D90°C: 6.69±0.13 min at aw0.25) than in almond meal and peanut butter. Overall, E. faecium appears to be a robust surrogate for Salmonella spp. across multiple low moisture products (with multiple cross-laboratory validations); however, product characteristics significantly impact that relationship. It is therefore necessary to consider product composition when validating thermal processes for low aw foods.

Publications

  • Type: Journal Articles Status: Submitted Year Published: 2017 Citation: Bhalsod, G.D., Y.-H. Chung, S. Jeon, W. Gui, H. Li, E.T. Ryser, A.K. Gruber, and W. Zhang. 2017. Uptake and accumulation of pharmaceuticals in overhead- and surface-irrigated greenhouse lettuce. J. Ag Food Chem.
  • Type: Journal Articles Status: Submitted Year Published: 2017 Citation: Casulli, K.E., F.J Garces-Vega, K.D. Dolan, E.T. Ryser, L. J. Harris, and B.P. Marks. 2017. Impact of process temperature, humidity, and initial product moisture on thermal inactivation of Salmonella Enteritidis PT30 on pistachios during hot-air heating. J. Food Prot.
  • Type: Journal Articles Status: Submitted Year Published: 2017 Citation: Limcharoenchat, P., S.E. Buchholz, M.K. James, N.O. Hall, E.T. Ryser, and B.P. Marks. 2017. Effects of inoculation protocol on thermal resistance of Salmonella Enteritidis PT30 in fabricated almond, wheat and date products. J. Food Prot.
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Gustafson, R., and E.T. Ryser. 2017. Survival and growth of Listeria monocytogenes during production and storage of caramel apples. Food Control.
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Davidson, G.R., C.N. Kaminski-Davidson, and E.T. Ryser. 2017. Persistence of Escherichia coli O157:H7 during pilot-scale processing of iceberg lettuce using flume water containing peroxyacetic acid-based sanitizers and various organic loads. Intern. J. Food Microbiol. 248:22-31
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Singh, P., M. Silva, E.T. Ryser, S. Ha, and I. Kang. 2017. Recovery of associated and internalized Salmonella in broiler skin by stomaching and grinding. Food Control 73:883-888
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Wegert, S.L., T.G. Aw, E.T. Ryser, and J.B. Rose. 2017. Postharvest reduction of coliphage MS2 from romaine lettuce during simulated commercial processing with and without a chlorine-based sanitizer. J. Food Prot. 80:220-224
  • Type: Theses/Dissertations Status: Published Year Published: 2017 Citation: Ryann E. Gustafson  M.S. 2017. Rapid concentration/detection of Escherichia coli O157:H7 and Listeria monocytogenes from lettuce wash water
  • Type: Theses/Dissertations Status: Published Year Published: 2017 Citation: Haley S. Smolinski  M.S. 2017. Salmonella Typhimurium LT2 transfer and redistribution on baby spinach and cilantro during pilot scale processing
  • Type: Theses/Dissertations Status: Published Year Published: 2017 Citation: Rocky Patil  M.S. 2017. Transfer of Listeria monocytogenes during cutting, slicing, dicing and subsequent storage of cantaloupe and honeydew melons
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Defrain, L., H. Alnughaymishi, and E.T. Ryser. 2017. Survival and growth of foodborne pathogens in fruit juice. Abst. Ann. Mtg. Int. Assoc. Food Prot., Tampa, FL July 9 - 12.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Ahmad, N.H., H.-C. Tsai, I,M. Hildebrandt, M.-J. Zhu, J. Tang, E.T. Ryser, and B.P. Marks. 2017. Validation of Enterococcus faecium as a Salmonella surrogate for isothermal treatment of almond meal. Abst. Ann. Mtg. Int. Assoc. Food Prot., Tampa, FL July 9 - 12
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Ahmad, N.H., I.M. Hildebrandt, S. Pickens, S. K. Lau, X. Xu, S. Liu, H.-C. Tsai, A.M. Rincon, J. Subbiah, H. Thippareddi, M.-J. Zhu, J. Tang, N.M. Anderson, E.M. Grasso-Kelley, E.T. Ryser, and B.P. Marks. 2017. Multi-laboratory comparison of E. faecium and Salmonella thermal resistance in selected low-moisture food products. Abst. Ann. Mtg. Int. Assoc. Food Prot., Tampa, FL July 9 - 12
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Alnughaymishi, H., and E.T. Ryser. 2017. The effect of pear firmness on transfer of Salmonella during mechanical slicing. Abst. Ann. Mtg. Int. Assoc. Food Prot., Tampa, FL July 9  12.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Gustafson, R., S. Magana, E. Kearns, D. Lim, and E.T Ryser. 2017. Rapid concentration/detection of Escherichia coli O157:H7 and Listeria monocytogenes from lettuce wash waters generated in commercial scale facilities. Abst. Ann. Mtg. Int. Assoc. Food Prot., Tampa, FL July 9  12
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Suehr, Q.J., B.P. Marks, E.T. Ryser and S. Jeong. 2017. Quantification of adhesion force of Salmonella attached to food grade surfaces in low moisture environments. Abst. Ann. Mtg. Int. Assoc. Food Prot., Tampa, FL July 9 - 12
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Liu, S., N.H. Ahmad, J. Xu, E.T. Ryser, M.-J. Zhu, B.P. Marks and J. Tang. 2017. Enterococcus faecium as a surrogate for Salmonella in thermal treatment of non-fat milk powder. Abst. Ann. Mtg. Int. Assoc. Food Prot., Tampa, FL July 9 - 12
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Carroll, J.M., Q.J. Suehr, P. Steinbrenner, B.P. Marks, E.T. Ryser and S. Jeong. 2017. Direct comparison of the modes of cross-contamination associated with Salmonella during almond processing. Abst. Ann. Mtg. Int. Assoc. Food Prot., Tampa, FL July 9 - 12
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Gustafson, R., S. Magana, E. Kearns, D. Lim, and E.T Ryser. 2017. Rapid concentration/detection of Escherichia coli O157:H7 and Listeria monocytogenes from lettuce wash waters generated in commercial scale facilities. USDA-NIFA Project Directors Meeting, Tampa, FL July 8
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Lopez, K., J.A. Fehlberg, M. Ghasemlou, M.B. Oglesby, E.T. Ryser, J. Harte, S. Chob, M. Rubino, and E. Almenar 2017. Development of a novel antimicrobial pouch made of polyethylene terephthalate coated with a UV-curable formulation containing 2-(E)-hexanol and its effects on blueberry shelf life. Abst. Ann. Meeting Inst. Food Technol. Las Vegas, NV, June 25  28
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Lopez, K., J.A. Fehlberg, M. Ghasemlou, M.B. Oglesby, E.T. Ryser, J. Harte, S. Cho, C.L. Lee, M. Rubino, and E. Almenar. 2017. Novel antimicrobial pouch to extend produce shelf life: A case study on blueberry. Ann. Mtg. United Fresh, Chicago, IL, June 13  15.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Ryser, E.T. 2017. Assessing the risk of pathogen cross-contamination during postharvest washing of fresh-cut produce. Ann. Mtg. Int. Assoc. Food Prot., Tampa, FL July 9 - 12
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Ryser, E.T. 2017. Impact of commercial processing on the microbiological safety of fresh produce. Ann. Edu. Conf. Upper Peninsula Environ Health Assoc., Escanaba, MI, Feb 22
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Ryser, E.T. 2017. Quantification of Salmonella and E. coli O157:H7 transfer and redistribution on leafy greens during pilot-scale processing. Tech. Forum on Produce Safety for FDA Funded Research, Greenbelt, MD, Feb. 9.


Progress 10/01/15 to 09/30/16

Outputs
Target Audience:This project addresses the fresh-cut produce industry with the results disseminated to industry, government and academia through various meetings sponsored by the International Association for Food Protection, Institute of Food Technologists, and United Fresh. The impact of this work will result in altered behaviors among processors, distributors and retailers of fresh-cut fruits and vegetables with the end result being enhanced safety and shelf-life. In addition these findings will also help to guide governmental food safety policies and decision-makingthrough risk assessments. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Three new M.S. students joined my laboratory in 2015 with two of these students having completed the work on transfer of E. coli O157:H7 and Salmonella during pilot-scale processing of fresh-cut Romaine lettuce, baby spinach and cilantro at different inoculation levels and inoculated:uninoculated product ratios with this work part of an FDA contact. My other new MS student completed a short study on Listeria growth in caramel apples and is currently working on a rapid detection systemfor foodborne pathogens in produce wash water as part of a USDA-funded project. The end result of this work will be a same day test for detection of E. coli O157:H7 and Listeria in produce wash water that can be used by industry to better ensure end-product safety. I also currently have 2 Ph.D. students in my laboratory - one focused on Study 1 described above and the other assessing the feasibility of using a non-infectious surrogate bacterium in place of Salmonella in a series of thermal inactivation trials involving low moisture foods such as nuts, flour, peanut butter, almonds and date paste. How have the results been disseminated to communities of interest?These findings have been presented at various annual meetings including the International Association for Food Protection and the Institute of Food Technologists as well as to various commodity groups. What do you plan to do during the next reporting period to accomplish the goals?The work will continue as detailed above withfinalization and publication ofstudies 1 and 2 above in addition to other work addressing Listeria in caramel apples, and cross-contamination during production of fresh-cut tomatoes, onions and cantaloupe. Hence, at least 6 abstracts and 8 peer-reviewed publications are anticipated in 2016-2017. Three new M.S. students joined my laboratory in 2015 with two of these students having completed the work on transfer of E. coli O157:H7 and Salmonella during pilot-scale processing of fresh-cut Romaine lettuce, baby spinach and cilantro at different inoculation levels and inoculated:uninoculated product ratios with this work part of an FDA contact. My other new MS student completed a short study on Listeria growth in caramel apples and is currently working on a rapid detection systemfor foodborne pathogens in produce wash water as part of a USDA-funded project. The end result of this work will be a same day test for detection of E. coli O157:H7 and Listeria in produce wash water that can be used by industry to better ensure end-product safety. I also currently have 2 Ph.D. students in my laboratory - one focused on Study 1 described above and the other assessing the feasibility of using a non-infectious surrogate bacterium in place of Salmonella in a series of thermal inactivation trials involving low moisture foods such as nuts, flour, peanut butter, almonds and date paste.

Impacts
What was accomplished under these goals? The primary focus of the current research in my laboratory is assess the extent of cross-contamination that can occur during slicing and dicing of fresh fruits and vegetables with this information needed for improved risk assessments that will impact both government policies and future federal funding in the area of produce safety. During the time period for this report, three major studies were conducted as summarized below. Study 1. Impact of Cutting Speed on Listeria monocytogenes transfer during slicing of zucchini squash and cucumbersto better ensure the safety of fresh-cut fruits and vegetables from the point of commercial processing through retail sale. Increased consumption fresh-cut produce has led to heighted food safety concerns as evidenced by on-going recalls and outbreaks. Using cucumbers and zucchini squash as model products based on their inherent compositional differences, this study aimed to evaluate the impact of mechanical slicing speed on Listeria transfer. In this work zucchini squash and cucumbers were contaminated with Listeria and then slicedwith a commonly used supermarket/kitchen slicer at different speedsfollowed by uninoculatedzucchini and cucumbers to determine the extent of cross-contamination. The extent of fresh produce cross-contaminationwas affected by slicing speed with less cross-contamination seen for cucumbers regardless of slicing speed compared to zucchini due to the different physical characteristics of the two products.These findings should prove useful in developing improved predictive models for bacterial transfer based on product composition and expanding current risk assessments across a wider range of products. Study 2. Spread ofEscherichia coliO157:H7during Flume Washing and Drying of Fresh-Cut Romaine Lettuce In this study,low levels of E. coli O157:H7 contamination(0.1 to 1000 cells per leaf)and different amounts of contaminated and uncontaminated Romaine lettuce (10:100, 5:100, 1:100 and 0.5:100)were used in combinationto assess the spread of E. coli O157:H7 during simulated commercial washing and drying. In this study, lower inoculation levels led to decreased E. coli O157:H7 transfer to romaine lettuce during processing. Within the same inoculation level, the amount of contaminated product processed did not have a significantly impact the extent of cross-contamination. Washing of fresh-cut produce in water containing a sanitizer also did not eliminate E. coli O157:H7. These findings are critical for predicting the extent of cross-contamination under more realistic conditions and will help to improve the exposure assessment in risk assessments for leafy greens. Study 3. Quantifying the redistribution of Salmonella Typhimurium LT2 during simulated commercial production of fresh-cut baby spinach and cilantro Using the same design in Study 2 above, Salmonella was substituted for E. coli O157:H7 and baby spinach and cilantro for Romaine lettuce. These results again showed that Salmonella transfer between the inoculated and uninoculated products decreased astheinitial inoculation level decreased.In addition, the amount of contaminated product processedhad less of an impact on cross-contamination than the level of pathogen contamination. Adding 60 ppm free chlorine to the flume tank generally failed to decrease the extent ofcross-contamination during washing and drying. These data will again be used to refine current risk assessments designed to predict the likelihood of illness from consumption of fresh-cut leafy greens.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Gustafson, R., and E.T. Ryser. 2016. Survival and growth of Listeria monocytogenes during production and storage of caramel apples. Abst. Ann. Mtg. Int. Assoc. Food Prot., St. Louis, MO, July 31  August 3.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Alnughaymishi H., and E.T. Ryser. 2016. Impact of cutting speed on Listeria monocytogenes transfer during slicing of zucchini squash and cucumbers. Abst. Ann. Mtg. Int. Assoc. Food Prot., St. Louis, MO, July 31  August 3.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Buchholz, S., P. Limcharoenchat, N. O. Hall, S. Jeong, E. T. Ryser, and B P. Marks. 2016. Effects of temperature, water activity, and structure on thermal resistance of Salmonella in dates and date paste. Abst. Ann. Mtg. Int. Assoc. Food Prot., St. Louis, MO, July 31  August 3.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Smolinski, H. S., S. Wang, L. Ren, Y. Chen, B. Kowalcyk. E. Thomas and E.T. Ryser. 2016. Quantifying redistribution of Salmonella Typhimurium LT2 during simulated commercial production of fresh-cut baby spinach and cilantro. Abst. Ann. Mtg. Int. Assoc. Food Prot., St. Louis, MO, July 31  August 3.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Wang, S., H. S. Smolinski, L. Ren, Y. Chen, B. Kowalcyk, E. Thomas, and E. T. Ryser. 2016. Spread of Escherichia coli O157:H7 during flume washing and drying of fresh-cut Romaine lettuce. Abst. Ann. Mtg. Int. Assoc. Food Prot., St. Louis, MO, July 31  August 3.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Lim, D.M., E.T. Ryser, S.M. Castillo, E.A. Kearns, and R. Gustafson. 2016. Rapid concentration/detection of E. coli O157:H7 and Listeria monocytogenes from produce wash water. Abst. USDA NIFA Project Directors Meeting, St. Louis, MO July 30.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Marks, B.P., J. Tang, E.T. Ryser, S. Wang, and S. Jeong. 2016. Factors affecting pasteurization efficacy for Salmonella in low moisture foods. Abst. USDA NIFA Project Directors Meeting, St. Louis, MO July 30.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Chopra, S., S. Dhumal, P. Abeli, E.T. Ryser, R Beaudry and E. Almenar. 2016. Moisture regulation to control microbial growth on packaged produce. United Fresh, Chicago, IL, June 20-22.
  • Type: Theses/Dissertations Status: Published Year Published: 2016 Citation: Siyi Wang  M.S. 2016. Spread of Escherichia coli O157:H7 during flume washing and drying of fresh-cut Romaine lettuce. Michigan State University, East Lansing, MI
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Caballero, O., S. Alles, S., L. Quynh-Nhi, R.L. Gray, E. Hosking, L. Pinkava, P. Norton, J. Tolan, M. Mozola, J. Rice, Y. Chen, J. Odumeru, and E. Ryser. 2016. Validation of modifications to the ANSR Listeria method for improved ease of use and performance. J. AOAC Intern. 99:98-111.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Caballero, O., S. Alles, S., L. Quynh-Nhi, R.L. Gray, E. Hosking, L. Pinkava, P. Norton, J. Tolan, M. Mozola, J. Rice, Y. Chen, E. Ryser, and J. Odumeru. 2016. Validation of the ANSR Listeria monocytogenes method for detection of Listeria monocytogenes in selected food and environmental samples. J. AOAC Intern. 99:112-123
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Wang, H., and E.T. Ryser. 2016. Quantitative transfer of Salmonella during mechanical slicing of tomatoes as impacted by multiple processing variables. Intern. J. Food Microbiol. 234:76-82.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Scollon, A.M., H. Wang, and E.T. Ryser. 2016. Transfer of Listeria monocytogenes during mechanical slicing of onions. Food Control. 65:160-167.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Page, N., J. Gonz�lez-Buesa, E.T. Ryser, J. Harte, and E. Almenar. 2016. Interactions between sanitizers and packaging gas compositions and their effects on the safety and quality of fresh-cut onions (Allium cepa L.). Intern. J. Food Microbiol. 208:105-113.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Kok, A., W. Brown, K.L. Vorst, E.T. Ryser, and L. Gorman. 2016. Transit temperatures experienced by fresh-cut leafy greens during cross-country shipment. Food Control 61:146-155.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Benoit, A., B.P. Marks, E.T. Ryser, S. Jeong, and P. Crandall. 2016. Image analysis of a fluorescent physical surrogate for quantifying Listeria monocytogenes transfer between delicatessen meats and product contact surfaces. Appl. Eng. Agr. 31:


Progress 10/01/14 to 09/30/15

Outputs
Target Audience:This project addresses the fresh-cut produce industry with the results disseminated to industry, government and academia through various meetings sponsored by the International Association for Food Protection, Institute of Food Technologists, United Fresh and the European Controlled and Modified Packaging Industry. The impact of this work will result in altered behaviors among processors, distributors and retailers of fresh-cut fruits and vegetables with the end result being enhanced safety and shelf-life. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project is providing valuable training for2 PhD and3 MS students in my own laboratory as well as severalother graduate students working with my co-investigators. How have the results been disseminated to communities of interest?These findings have been presented at various annual meetings including the International Association for Food Protection and the Institute of Food Technologists as well as to various commodity groups. What do you plan to do during the next reporting period to accomplish the goals?The work will continue as detailed above with completion of the FDA contract and the other USDA-funded project on rapid detection of pathogens in produce wash water. At least 6 abstracts are anticipated for professional meetings next summer. Several grant proposals to continue the above work are also pending.

Impacts
What was accomplished under these goals? Three new M.S. students joined my laboratory in 2015 with two of these students now assessing the transfer of E. coli O157:H7and Salmonella during pilot-scale processing of fresh-cut Romaine lettuce, baby spinach and cilantro at different inoculation levels and inoculated:uninoculated product ratios with this work part of an FDA contact. These findingswill be critical to refining the current FDA risk assessment for fresh-cut leafy greens.My other new MS student completed a short study on Listeria growth in caramel apples and has now begun working on Objective 3 above. The end result of this work will be a same day test for E. coli O157:H7 and Listeria in produce wash water that can be used by industryto better ensure end-product safety.

Publications

  • Type: Theses/Dissertations Status: Published Year Published: 2015 Citation: Wang, H. 2015. Quantifying transfer and inactivation of Salmonella during post-harvest processing of tomatoes. PhD Dissertation. Michigan State University.
  • Type: Theses/Dissertations Status: Published Year Published: 2015 Citation: Oladimeji, V. 2015. Fate of Listeria monocytogenes in diced onions and celery, and Salmonella Typhimurium in diced tomatoes packaged under modified atmosphere during simulated commercial storage. MS Thesis. Michigan State University.
  • Type: Theses/Dissertations Status: Published Year Published: 2014 Citation: Ren, L. 2014. Impact of selected unit operations on the spread of Escherichia coli O157:H7 during pilot-scale production of fresh-cut lettuce. MS Thesis. Michigan State University
  • Type: Theses/Dissertations Status: Published Year Published: 2014 Citation: Scollon, A. 2014. Transfer and survival of Listeria monocytogenes during slicing, dicing and storage of onions. MS Thesis. Michigan State University
  • Type: Book Chapters Status: Published Year Published: 2014 Citation: Ryser, E.T., and A. Wesche. 2014. Recovery of sublethally injured bacteria. In Compendium of Method for the Microbiological Examination of Foods, 5th Edition. American Public Health Assoc., Washington, DC
  • Type: Book Chapters Status: Published Year Published: 2014 Citation: Ryser, E.T., and J. Schuman. 2014. Aerobic plate count. In Compendium of Method for the Microbiological Examination of Foods, 5th Edition. American Public Health Assoc., Washington, DC
  • Type: Book Chapters Status: Published Year Published: 2014 Citation: Ryser, E.T., and C.W. Donnelly. 2014. Listeria. In Compendium of Method for the Microbiological Examination of Foods, 5th Edition. American Public Health Assoc., Washington, DC.
  • Type: Journal Articles Status: Submitted Year Published: 2015 Citation: Wang, Z., and E.T. Ryser. 2015. Quantitative transfer of Salmonella during mechanical slicing of tomatoes as impacted by multiple processing variables. Intern. J. Food Microbiol. (submitted).
  • Type: Journal Articles Status: Submitted Year Published: 2015 Citation: Page, N., J. Gonz�lez-Buesa, E.T. Ryser, J. Harte, and E. Almenar. 2015. Interactions between sanitizers and packaging gas compositions and their effects on the safety and quality of fresh-cut onions (Allium cepa L.). Intern. J. Food Microbiol. (submitted).
  • Type: Journal Articles Status: Submitted Year Published: 2015 Citation: Kok, A., W. Brown, K.L. Vorst, E.T. Ryser, and L. Gorman. 2015. Transit temperatures experienced by fresh-cut leafy greens during cross-country shipment. Food Control (submitted)
  • Type: Journal Articles Status: Awaiting Publication Year Published: 2015 Citation: Benoit, A., B.P. Marks, E.T. Ryser, S. Jeong, and P. Crandall. 2015. Image analysis of a fluorescent physical surrogate for quantifying Listeria monocytogenes transfer between delicatessen meats and product contact surfaces. Appl. Eng. Agr.
  • Type: Journal Articles Status: Published Year Published: 2015 Citation: Sansawat, T., H.C. Lee, L. Zhang, E.T. Ryser, and I. Kang. 2015. Antilisterial effects of different hop acids in combination with potassium acetate and potassium diacetate at 7 and 37oC. Food Control 59:256-261
  • Type: Other Status: Published Year Published: 2014 Citation: Wang, H., and E.T. Ryser. 2014. Microbiological safety of fresh-cut produce from the processor to your plate. Food Safety Magazine. August/September p. 64-70
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Wengert, S., T.G. Aw, E.T. Ryser, and J.B. Rose. 2015. Post-harvest reduction of coliphage MS2 from Romaine lettuce during simulated commercial processing with and without a chlorine-based sanitizer. Abst. Ann. Mtg. Int. Assoc. Food Prot., Portland, OR, July 25-28
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Alnughaymishi H., and E.T. Ryser. 2014. Listeria monocytogenes transfer during slicing of cucumbers, zucchini squash and onions as impacted by product density. Abst. Ann. Mtg. Int. Assoc. Food Prot., Portland, OR, July 25-28
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Dhinga, D., S. Chopra, E.T. Ryser and E. Almenar. 2015. Microbial quality and safety of tomatoes (Solanum lycopersicum L.) as affected by sanitization, packaging atmosphere and their interactions during storage at 7oC. Abst. Ann. Mtg. Inst. Food Technol., Chicago, IL, July 11-14
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Charles, A., H. Wang, E.T. Ryser and D.W. Schaffner. 2014. Modeling Salmonella transfer during tomato slicing. Ann. Mtg. Soc. Risk Analysis, Denver, CO, Dec 7-10
  • Type: Conference Papers and Presentations Status: Other Year Published: 2015 Citation: Ryser, E.T. 2015. Research update on Listeria in fresh produce  postharvest processing, packaging and distribution. USDA/GMA Workshop: Evaluation of risk factors for foodborne listeriosis. College Park, MD, June 16-18
  • Type: Conference Papers and Presentations Status: Other Year Published: 2015 Citation: Ryser, E.T. 2015. Listeria: Characteristics and control in food facilities. Food Safety Workshop for Apple Packing Facilities, Grand Valley State University, Grand Rapids, MI, April 22
  • Type: Conference Papers and Presentations Status: Other Year Published: 2014 Citation: Ryser, E.T. 2014. Food safety on celery packing and processing lines. Great Lakes Fruit, Vegetable and Farm Market Expo. Grand Rapids, MI, Dec. 10


Progress 07/01/14 to 09/30/14

Outputs
Target Audience: This project addresses the fresh-cut produce industry with the results disseminated to industry, government and academia through various meetings sponsored by the International Association for Food Protection, Institute of Food Technologists, United Fresh and the European Controlled and Modified Packaging Industry. The impact of this work will result in altered behaviors among processors, distributors and retailers of fresh-cut fruits and vegetables with the end result being enhanced safety and shelf-life. . Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? One Ph.D. and two M.S. students will bejoining my laboratory in January 2014. These new students will be invoved in validadting two FDA risk assesments for fresh-cut lettuce and tomatoes using our unique pilot-scale processing line which has attracted considerable attention nationally. See www.youtube.com/watch?v=8mSKdjxauTw How have the results been disseminated to communities of interest? The findings have been presented at variousannual meetings including the International Association for Food Protection and the Institute of FoodTechnologists as detailed in the Products section of this report. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Since this project began July 1, 2014, the accomplishments have been limited with one Ph.D. andfour M.S. students aiming to finish their degrees from the previous project in December of 2014.

Publications

  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Wang, H., and E.T. Ryser. 2014. Efficacy of various sanitizers against Salmonella during simulated commercial packing of tomatoes. J. Food Prot. (in press).
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Zhang, L., Z. Yan, J.M. Gillett, A.C. Schilder, E.J. Hanson, and E.T. Ryser. 2014. Efficacy of chlorine dioxide gas and freezing rate on the microbiological quality of frozen blueberries. Food Control (in press).
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: 16. Davidson, G.R., C.N. Kaminski, and E.T. Ryser. 2014. Impact of organic load on Escherichia coli O157:H7 survival during pilot-scale processing of iceberg lettuce with acidified sodium hypochlorite. J. Food Prot. (in press)
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Buchholz, A.L., G.R. Davidson, B.P. Marks, E.C.D. Todd, and E.T. Ryser. 2014. Tracking an Escherichia coli contaminated batch of leafy greens through a pilot-scale processing line. J. Food Prot. 77:1487-1494.
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Magana, S., S.M. Schlemmer, G.R. Davidson, E.T. Ryser and D.V. Lim. 2014. Laboratory and pilot-scale dead-end ultrafiltration of sanitizer-free and chlorinated lettuce wash water for improved detection of Escherichia coli O157:H7. J. Food Prot. 77-1260-1268.
  • Type: Other Status: Published Year Published: 2014 Citation: Wang, H., and E.T. Ryser. 2014. Microbiological safety of fresh-cut produce from the processor to your plate. Food Safety Magazine July/August 64-70.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Alnughaymishi H., and E.T. Ryser. 2014. Listeria monocytogenes transfer during slicing of cucumbers, zucchini squash and onions as impacted by product density. Abst. Ann. Mtg. 17th World Congress Food Sci. Technol (IUFoST). Montreal, Canada, Aug. 17-21
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Wang, H., and E.T. Ryser. 2014. Effect of four commercial sanitizers against Salmonella on two conveyor belt systems during conveyance of diced tomatoes. Abst. Ann. Mtg. Int. Assoc. Food Prot., Indianapolis, IN, August 3  6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Wang, H., and E.T. Ryser. 2014. Salmonella attachment and biofilm formation on tomatoes and equipment surfaces as impacted by organic load, pH and temperature. Abst. Ann. Mtg. Int. Assoc. Food Prot., Indianapolis, IN, August 3  6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Scollon, A., N. Page, E. Almenar and E.T. Ryser. 2014. Effect of sanitizers and in-package atmosphere on Listeria monocytogenes growth in diced yellow onions. Abst. Ann. Mtg. Int. Assoc. Food Prot., Indianapolis, IN, August 3  6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Scollon, A., and E.T. Ryser. 2014. Transfer of Listeria monocytogenes during pilot-scale dicing of onions. Abst. Ann. Mtg., Int. Assoc. Food Prot., Indianapolis, IN, August 3  6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Patil, R.D., J.C. Thorns and E.T. Ryser. 2014. Quantitative transfer of Listeria monocytogenes during mechanical slicing of cantaloupe and honeydew melon. Abst. Ann. Mtg. Int. Assoc. Food Prot., Indianapolis, IN, August 3  6
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Ren, L., B. Mazon, B.P. Marks, and E.T. Ryser. 2014. The effect of water flow rate on Escherichia coli O157:H7 transfer from inoculated lettuce to wash water in closed pipe system. Abst. Ann. Mtg. Int. Assoc. Food Prot., Indianapolis, IN, August 3  6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Jeong, S., B.P. Marks, and E.T. Ryser. 2014. Minimizing Salmonella attachment to dry surfaces through use of high-frequency nano-amplitude mechanical vibration. Abst. Ann. Mtg. Int. Assoc. Food Prot. Indianapolis, IN, August 3  6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Hildebrandt, I.M., B.P. Marks, E.T. Ryser, R. Villa-Rojas, J. Tang, and S. Bucholz. 2014. Impact of inoculation procedures on thermal resistance of Salmonella in wheat flour and associated repeatability of results. Abst. Ann. Mtg. Int. Assoc. Food Prot. Indianapolis, IN, August 3  6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Mazon, B., B.P. Marks, L. Ren, and E.T. Ryser. 2014. Effects of physical variables on Salmonella transfer from produce to stainless steel. Abst. Ann. Mtg. Int. Assoc. Food Prot. Indianapolis, IN, August 3  6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Gonzalez-Buesa, J., N. Page, C. Kaminski, E.T. Ryser, R. Beaudry and E. Almenar. 2014. Interactions between atmospheres and sanitizers and their effect on the quality and safety of packaged fresh-cut celery (Apium graveolens L.) Abst. Ann. Mtg. Amer. Soc. Hort. Sci. Orlando, FL, July 28  31.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Suehr, Q., S. Jeong, B.P. Marks, and E.T. Ryser. 2014. Discrete element modeling of bacterial cross-contamination during almond processing. Abst. Ann Mtg. Canadian Society for Bioengineers/American Society of Agricultural and Biological Engineers, Montreal, Quebec, Canada, July 13-16.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Jayeola, V.O., and E.T. Ryser. 2014. Modeling growth of Listeria monocytogenes in sanitizer-treated diced onions, tomatoes and celery. Abst. Ann. Mtg. Int. Assoc. Food Prot. Indianapolis, IN, August 3  6.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Wang, H., and E.T. Ryser. 2014. Transfer and sanitizer inactivation of Salmonella during simulated commercial dicing of tomatoes. Abst. Ann. Mtg. Inst. Food Technol., New Orleans, LA, June 21-24.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Jeong, S., B.P. Marks and E.T. Ryser. 2014. Effect of almond product structure on x-ray inactivation kinetics of Salmonella. Abst. Ann. Mtg. Int. Assoc. Food Prot. Indianapolis, IN, August 3  6.