Publications by authors named "Yaguang Luo"

57 Publications

Nondestructive multiplex detection of foodborne pathogens with background microflora and symbiosis using a paper chromogenic array and advanced neural network.

Biosens Bioelectron 2021 Jul 1;183:113209. Epub 2021 Apr 1.

Department of Biomedical and Nutritional Sciences, University of Massachusetts, Lowell, 01854, MA, USA. Electronic address:

We have developed an inexpensive, standardized paper chromogenic array (PCA) integrated with a machine learning approach to accurately identify single pathogens (Listeria monocytogenes, Salmonella Enteritidis, or Escherichia coli O157:H7) or multiple pathogens (either in multiple monocultures, or in a single cocktail culture), in the presence of background microflora on food. Cantaloupe, a commodity with significant volatile organic compound (VOC) emission and large diverse populations of background microflora, was used as the model food. The PCA was fabricated from a paper microarray via photolithography and paper microfluidics, into which 22 chromogenic dye spots were infused and to which three red/green/blue color-standard dots were taped. When exposed to VOCs emitted by pathogens of interest, dye spots exhibited distinguishable color changes and pattern shifts, which were automatically segmented and digitized into a ΔR/ΔG/ΔB database. We developed an advanced deep feedforward neural network with a learning rate scheduler, L regularization, and shortcut connections. After training on the ΔR/ΔG/ΔB database, the network demonstrated excellent performance in identifying pathogens in single monocultures, multiple monocultures, and in cocktail culture, and in distinguishing them from the background signal on cantaloupe, providing accuracy of up to 93% and 91% under ambient and refrigerated conditions, respectively. With its combination of speed, reliability, portability, and low cost, this nondestructive approach holds great potential to significantly advance culture-free pathogen detection and identification on food, and is readily extendable to other food commodities with complex microflora.
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http://dx.doi.org/10.1016/j.bios.2021.113209DOI Listing
July 2021

Salmonella inactivation and sponge/microfiber mediated cross-contamination during papaya wash with chlorine or peracetic acid as sanitizer.

Food Microbiol 2021 May 10;95:103677. Epub 2020 Nov 10.

Environmental Microbial and Food Safety Laboratory, USDA-ARS Beltsville Agricultural Research Center, Beltsville, MD, 20705, USA. Electronic address:

Imported papayas from Mexico have been implicated in multiple salmonellosis outbreaks in the United States in recent years. While postharvest washing is a critical process to remove latex, dirt, and microbes, it also has the potential of causing cross-contamination by foodborne pathogens, with sponge or other fibrous rubbing tools often questioned as potential harboring or transmitting risk. In this study, Salmonella inactivation and cross-contamination via sponges and microfiber wash mitts during simulated papaya washing and cleaning were investigated. Seven washing treatments (wash without sanitizer; wash at free chlorine 25, 50, and 100 mg/L, and at peracetic acid 20, 40, and 80 mg/L), along with unwashed control, were evaluated, using Salmonella strains with unique antibiotic markers differentially inoculated on papaya rind (serovars Typhimurium, Heidelberg, and Derby) and on wash sponge or microfiber (serovars Typhimurium, Newport, and Braenderup). Salmonella survival and transfer on papaya and on sponge/microfiber, and in wash water were detected using selective plating or enrichment. The washing and cleaning process reduced Salmonella on inoculated papayas by 1.69-2.66 and 0.69-1.74 log for sponge and microfiber cleaning, respectively, with the reduction poorly correlated to sanitizer concentration. Salmonella on inoculated sponge or microfiber was under detection limit (1.00 log CFU/cm) by plate count, but remained recoverable by selective enrichment. Transference of Salmonella from inoculated papaya to sponge/microfiber, and vice versa, could be detected sporadically by selective enrichment. Sponge/microfiber mediated Salmonella cross-contamination from inoculated to uninoculated papayas was frequently detectable by selective enrichment, but rendered undetectable by wetting sponge/microfiber in sanitizing wash water (FC 25-100 mg/L or PAA 20-80 mg/L) between washing different papaya fruits. Therefore, maintaining adequate sanitizer levels and frequently wetting sponge/microfiber in sanitizing wash water can effectively mitigate risks of Salmonella cross-contamination associated with postharvest washing, especially with regard to the use of sponge or microfiber wash mitts.
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http://dx.doi.org/10.1016/j.fm.2020.103677DOI Listing
May 2021

Alkynyl silver modified chitosan and its potential applications in food area.

Carbohydr Polym 2021 Feb 21;254:117416. Epub 2020 Nov 21.

Department of Nutrition and Food Science, College of Agriculture and Natural Resources, University of Maryland, College Park, MD 20742, United States. Electronic address:

Chitosan was modified by substituting alkynyl silver on chitosan (Ag-CS) through a two-step chemical modification to form a novel antimicrobial coating material. The physicochemical property, antimicrobial activity, cytotoxicity, and potential food applications of Ag-CS were systematically investigated. The Ag-CS presented a smooth sheet structure, and demonstrated stronger antimicrobial effects than either silver acetate (AgOAc) or silver nitrate (AgNO) against both Gram positive and Gram negative bacteria strains. Ag-CS also demonstrated a controlled release of Ag for over 5 days, whereas AgOAc or AgNO infused chitosan released over 90 % Ag within 4 h. Ag-CS coating on shrimps significantly extended their shelf-life. Overall, our results revealed that the newly developed Ag-CS antimicrobial coating material possesses strong antimicrobial efficacies with a sustained Ag release property, and its ability to slow down the spoilage rate of shrimps indicates its potential in the improvement of food quality and shelf life.
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http://dx.doi.org/10.1016/j.carbpol.2020.117416DOI Listing
February 2021

Factors Impacting Chemical and Microbiological Quality of Wash Water during Simulated Dump Tank Wash of Grape Tomatoes.

J Food Prot 2021 Apr;84(4):695-703

U.S. Department of Agriculture, Agricultural Research Service, Environmental Microbial and Food Safety Laboratory, 10300 Baltimore Avenue, Beltsville, Maryland 20705, USA (ORCID: https://orcid.org/0000-0001-6164-4318 [Y.L.]; https://orcid.org/0000-0001-6877-7527 [P.M.]).

Abstract: Fresh and fresh-cut tomatoes are high in phytonutrients. However, illness outbreaks associated with contaminated tomatoes have significantly impacted public health and the economic well-being of the tomato industry. Scientific information is needed to develop an effective, practical food safety standard to reduce pathogen contamination. The aim of this study was to assess factors impacting the deterioration of the quality of tomato wash water and the proliferation of indigenous microorganisms during a simulated dump tank washing process. Freshly harvested grape tomatoes were sorted into four groups: prime, defective, underripe, and nontomato debris. Tomatoes with leaf or stem harvest debris, combined or separate, were washed in tap water with or without free chlorine. Water samples were analyzed for total dissolved solids, turbidity, chemical oxygen demand, and chlorine demand. Microbial populations in water and on tomatoes as impacted by chlorine concentration and water filtration (300 μm) were also quantified. Field debris and defective tomatoes were the major contributors to microbial populations in wash water. Field debris, although accounting for <1% of the total weight of harvested material, contributed 37.84% of total dissolved solids, 46.15% of turbidity, 48.77% of chemical oxygen demand, and 50.55% of chlorine demand in the wash water. Water quality deterioration was proportional to the cumulative quantity of tomatoes and debris washed, and free chlorine at ≥5 mg/L significantly reduced the Enterobacteriaceae, aerobic mesophilic bacteria, and yeast and mold populations. These results highlight the importance of minimizing field debris and defective fruits in harvested grape tomatoes to reduce the microbial load and prevent deterioration of wash water quality. This information will be useful for the development of data-driven harvesting and packinghouse food safety practices for grape tomatoes.

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http://dx.doi.org/10.4315/JFP-20-343DOI Listing
April 2021

Survival of Salmonella enterica and shifts in the culturable mesophilic aerobic bacterial community as impacted by tomato wash water particulate size and chlorine treatment.

Food Microbiol 2020 Sep 28;90:103470. Epub 2020 Feb 28.

U.S. Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Environmental Microbiology and Food Safety Laboratory, 10300 Baltimore Ave, Beltsville, MD, 20705, USA. Electronic address:

Particulates of harvest debris are common in tomato packinghouse dump tanks, but their role in food safety is unclear. In this study we investigated the survival of Salmonella enterica and the shifts in relative abundance of culturable mesophilic aerobic bacteria (cMAB) as impacted by particulate size and interaction with chlorine treatment. Particulates suspended in grape tomato wash water spanned a wide size range, but the largest contribution came from particles of 3-20 μm. Filtration of wash water through 330 μm, applied after 100 mg/L free chlorine (FC) wash, reduced surviving cMAB by 98%. The combination of filtration (at 330 μm or smaller pore sizes) and chlorinated wash also altered the cMAB community, with the survivors shifting toward Gram-positive and spore producers (in both lab-simulated and industrial conditions). When tomatoes and harvest debris inoculated with differentially tagged Salmonella were washed in 100 mg/L FC for 1 min followed by filtration, only cells originating from harvest debris survived, with 85 and 93% of the surviving cells associated with particulates larger than 330 and 63 μm, respectively. This suggests that particulates suspended in wash water can protect Salmonella cells from chlorine action, and serve as a vector for cross-contamination.
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http://dx.doi.org/10.1016/j.fm.2020.103470DOI Listing
September 2020

Direct Metatranscriptome RNA-seq and Multiplex RT-PCR Amplicon Sequencing on Nanopore MinION - Promising Strategies for Multiplex Identification of Viable Pathogens in Food.

Front Microbiol 2020 9;11:514. Epub 2020 Apr 9.

Department of Biomedical and Nutritional Sciences, University of Massachusetts, Lowell, MA, United States.

Viable pathogenic bacteria are major biohazards that pose a significant threat to food safety. Despite the recent developments in detection platforms, multiplex identification of viable pathogens in food remains a major challenge. A novel strategy is developed through direct metatranscriptome RNA-seq and multiplex RT-PCR amplicon sequencing on Nanopore MinION to achieve real-time multiplex identification of viable pathogens in food. Specifically, this study reports an optimized universal Nanopore sample extraction and library preparation protocol applicable to both Gram-positive and Gram-negative pathogenic bacteria, demonstrated using a cocktail culture of O157:H7, , and , which were selected based on their impact on economic loss or prevalence in recent outbreaks. Further evaluation and validation confirmed the accuracy of direct metatranscriptome RNA-seq and multiplex RT-PCR amplicon sequencing using Sanger sequencing and selective media. The study also included a comparison of different bioinformatic pipelines for metatranscriptomic and amplicon genomic analysis. MEGAN without rRNA mapping showed the highest accuracy of multiplex identification using the metatranscriptomic data. EPI2ME also demonstrated high accuracy using multiplex RT-PCR amplicon sequencing. In addition, a systemic comparison was drawn between Nanopore sequencing of the direct metatranscriptome RNA-seq and RT-PCR amplicons. Both methods are comparable in accuracy and time. Nanopore sequencing of RT-PCR amplicons has higher sensitivity, but Nanopore metatranscriptome sequencing excels in read length and dealing with complex microbiome and non-bacterial transcriptome backgrounds.
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http://dx.doi.org/10.3389/fmicb.2020.00514DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7160302PMC
April 2020

Microgreen nutrition, food safety, and shelf life: A review.

J Food Sci 2020 Apr 6;85(4):870-882. Epub 2020 Mar 6.

Dept. of Nutrition and Food Science, Univ. of Maryland, College Park, MD, 20740, U.S.A.

Microgreens have gained increasing popularity as food ingredients in recent years because of their high nutritional value and diverse sensorial characteristics. Microgreens are edible seedlings including vegetables and herbs, which have been used, primarily in the restaurant industry, to embellish cuisine since 1996. The rapidly growing microgreen industry faces many challenges. Microgreens share many characteristics with sprouts, and while they have not been associated with any foodborne illness outbreaks, they have recently been the subject of seven recalls. Thus, the potential to carry foodborne pathogens is there, and steps can and should be taken during production to reduce the likelihood of such incidents. One major limitation to the growth of the microgreen industry is the rapid quality deterioration that occurs soon after harvest, which keeps prices high and restricts commerce to local sales. Once harvested, microgreens easily dehydrate, wilt, decay and rapidly lose certain nutrients. Research has explored preharvest and postharvest interventions, such as calcium treatments, modified atmopsphere packaging, temperature control, and light, to maintain quality, augment nutritional value, and extend shelf life. However, more work is needed to optimize both production and storage conditions to improve the safety, quality, and shelf life of microgreens, thereby expanding potential markets.
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http://dx.doi.org/10.1111/1750-3841.15049DOI Listing
April 2020

Genome Sequences of Brevundimonas naejangsanensis Strain FS1091 and Bacillus amyloliquefaciens Strain FS1092, Isolated from a Fresh-Cut-Produce-Processing Plant.

Microbiol Resour Announc 2020 Jan 23;9(4). Epub 2020 Jan 23.

Beltsville Agricultural Research Center, USDA Agricultural Research Service, Beltsville, Maryland, USA

The complete genome sequences of strain FS1091 and strain FS1092, which were isolated from a commercial fresh-cut-produce-processing facility, were determined. Both FS1091 and FS1092 have one circular chromosome of approximately 3.15 and 4.24 Mb, respectively.
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http://dx.doi.org/10.1128/MRA.01448-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6979307PMC
January 2020

Salmonella inactivation and cross-contamination on cherry and grape tomatoes under simulated wash conditions.

Food Microbiol 2020 May 6;87:103359. Epub 2019 Nov 6.

Environmental Microbial and Food Safety Laboratory, USDA ARS, Beltsville, MD, 20705, USA. Electronic address:

Washing in chlorinated water is widely practiced for commercial fresh produce processing. While known as an effective tool for mitigating food safety risks, chlorine washing could also represent an opportunity for spreading microbial contaminations under sub-optimal operating conditions. This study evaluated Salmonella inactivation and cross-contamination in a simulated washing process of cherry and grape tomatoes. Commercially harvested tomatoes and the associated inedible plant matter (debris) were differentially inoculated with kanamycin resistant (KanR) or rifampin resistant (RifR) Salmonella strains, and washed together with uninoculated tomatoes in simulated packinghouse dump tank (flume) wash water. Washing in chlorinated water resulted in significantly higher Salmonella reduction on tomatoes than on debris, achieving 2-3 log reduction on tomatoes and about 1 log reduction on debris. Cross-contamination by Salmonella on tomatoes was significantly reduced in the presence of 25-150 mg/L free chlorine, although sporadic cross-contamination on tomatoes was detected when tomatoes and debris were inoculated at high population density. The majority of the sporadic cross-contaminations originated from Salmonella inoculated on debris. These findings suggested that debris could be a potentially significant source of contamination during commercial tomato washing.
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http://dx.doi.org/10.1016/j.fm.2019.103359DOI Listing
May 2020

Microbiome convergence following sanitizer treatment and identification of sanitizer resistant species from spinach and lettuce rinse water.

Int J Food Microbiol 2020 Apr 23;318:108458. Epub 2019 Nov 23.

Environmental Microbiology and Food Safety Laboratory, USDA ARS, Beltsville, MD, United States of America. Electronic address:

Fresh produce, as a known or suspected source of multiple foodborne outbreaks, harbors large populations of diverse microorganisms, which are partially released into wash water during processing. However, the dynamics of bacterial communities in wash water during produce processing is poorly understood. In this study, we investigated the effect of chlorine (FC) and peracetic acid (PAA) on the microbiome dynamics in spinach and romaine lettuce rinse water. Treatments with increasing concentrations of sanitizers resulted in convergence of distinct microbiomes. The resultant sanitizer resistant microbiome showed dominant presence by Bacillus sp., Arthrobacter psychrolactophilus, Cupriavidus sp., and Ralstonia sp. Most of the FC and PAA resistant bacteria isolated from spinach and lettuce rinse water after sanitation were gram positive spore forming species including Bacillus, Paenibacillus, and Brevibacillus spp., while several PAA resistant Pseudomonas spp. were also isolated from lettuce rinse water. Inoculation of foodborne pathogens altered the microbiome shift in spinach rinse water under PAA treatment, but not in lettuce rinse water or FC treated samples. These inoculated foodborne pathogens were not isolated among the sanitizer resistant strains.
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http://dx.doi.org/10.1016/j.ijfoodmicro.2019.108458DOI Listing
April 2020

Dynamic changes in the physicochemical properties of fresh-cut produce wash water as impacted by commodity type and processing conditions.

PLoS One 2019 26;14(9):e0222174. Epub 2019 Sep 26.

U. S. Department of Agriculture, Agricultural Research Service, Beltsville Agricultural, Research Center, Environmental Microbiology and Food Safety Laboratory, Beltsville, MD, United States of America.

Organic materials in fresh-cut produce wash water deplete free chlorine that is required to prevent pathogen survival and cross-contamination. This research evaluated water quality parameters frequently used to describe organic load for their fitness to predict chlorine demand (CLD) and chemical oxygen demand (COD), which are major needs identified by the industry-led produce food safety taskforce. Batches of romaine lettuce, iceberg lettuce, or carrot of different cut sizes and shapes were washed in 40 liters of water. Physicochemical properties of wash water including CLD, COD, total organic carbon (TOC), total suspended solids (TSS), total dissolved solids (TDS), turbidity, total sugar content, and pH, were monitored. Results indicate that pH is primarily commodity dependent, while organic load is additionally impacted by cutting and washing conditions. Significant linear increases in COD, TOC, CLD, TDS, and turbidity resulted from increasing product-to-water ratio, and decreasing cut size. Physicochemical parameters, excluding pH, showed significant positive correlation across different cut sizes within a commodity. High correlations were obtained between CLD and COD and between COD and TOC for pooled products. The convenient measurement of TDS, along with its strong correlation with COD and CLD, suggests the potential of TDS for predicting organic load and chlorine reactivity. Finally, the potential application and limitation of the proposed models in practical produce processing procedures are discussed extensively.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0222174PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6762053PMC
March 2020

Impact of routine sanitation on the microbiomes in a fresh produce processing facility.

Int J Food Microbiol 2019 Apr 2;294:31-41. Epub 2019 Feb 2.

Environmental Microbiology and Food Safety Laboratory, USDA ARS, Beltsville, MD, United States. Electronic address:

Indigenous bacterial populations in fresh-cut produce processing facilities can have a profound effect on the survival and proliferation of inadvertently contaminating foodborne pathogens. In this study, environmental samples were collected from a variety of Zone 3 sites in a processing plant before and after daily routine sanitation. Viable mesophilic aerobic bacteria population was evaluated using both culturing method and quantitative real-time PCR (qPCR) after propidium monoazide treatment. Zone 3 surface microbiota were analyzed using 16S rRNA gene amplicon sequencing with the Qiime2 bioinformatic pipeline. Over 8000 bacterial species across 4 major phyla were identified in Zone 3 microbiomes in the processing facility. Overall, effective bacterial reduction was observed at the sampling sites on the production floor, while sanitation effect on peripheral surfaces was less evident. Effective sanitation resulted in both quantitative and qualitive shifts of Zone 3 microbiota. Several species were highly abundant at multiple sample sites for both winter and summer samplings. Based on the spatial and temporal distribution of the most abundant species, a Zone 3 core microbiome in the processing facility was tentatively described to included Cupriavidus sp., Pseudomonas sp., Ralstonia sp., Arthrobacter psychrolactophilus, Pseudomonas veronii, Stenotrophomonas sp., and an unknown species of the family Enterobacteriaceae.
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http://dx.doi.org/10.1016/j.ijfoodmicro.2019.02.002DOI Listing
April 2019

Impacts and interactions of organic compounds with chlorine sanitizer in recirculated and reused produce processing water.

PLoS One 2018 12;13(12):e0208945. Epub 2018 Dec 12.

U. S. Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Environmental Microbiology and Food Safety Laboratory, Beltsville, Maryland, United States of America.

Water conservation and economics dictate that fresh produce processors reuse/recirculate the process water. However, the ensuing accumulation of organic matter in water depletes the chlorine sanitizer required for food safety. In this study, we comprehensively investigated chemical compounds that are responsible for water quality in relation to chemical oxygen demand (COD) and chlorine demand (CLD), the two most critical factors associated with water treatment and chlorine replenishment. Simulating commercial fresh-cut wash operations, multiple batches of diced cabbage (0.3 x 0.3 cm2) were washed in the same tank of water. The major components were isolated from the wash water and analyzed by HPLC. Sugars were the predominant compounds (82.7% dry weight) and the major contributor to COD (81.6%), followed by proteins/peptides (7.3% dry weight, 5.3% COD), organic acids (6.2% dry weight, 3.6% COD), and phenolics (0.5% dry weight, 0.5% COD). By repeated time course measures, the effect of these chemicals on CLD are dependent on the chemical structure, concentration in the wash water, and their rate of reaction. Proteins/peptides accounted for about 50% of the total CLD over a 120-min period and phenolics was 21% at 5 min, but diminished with time. The contribution by organic acids and sugars increased continuously, reaching 22% and 16% of total CLD at 120 min of chlorination, respectively. Collectively, these compounds represented 86% of the CLD in cabbage wash water at 5 min and greater than 94% CLD afterwards. This is the first systematic report on the source of COD and CLD during fresh produce washing. It provides essential information for the produce processors to develop safe, effective, and economical wash water treatment/reuse and chlorine replenishment strategies.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0208945PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6291160PMC
May 2019

An entrapped metal-organic framework system for controlled release of ethylene.

J Colloid Interface Sci 2019 Jan 21;533:207-215. Epub 2018 Aug 21.

Food Quality Laboratory, United States Department of Agriculture, Agricultural Research Service, Beltsville, MD 20705, USA. Electronic address:

A novel gas storage and release system was developed for ethylene, an exogenous plant hormone that regulates fruit ripening and senescence. This system consists of a metal organic framework (MOF) core and an alginate-based shell. The MOF comprises a coordination complex of Al and [btc] ligands, which formed hexagonal structure (P6/mmc) with unit cell of 14.28 × 14.28 × 31.32 Å, as revealed by the X-ray diffraction analysis. Ethylene absorption isotherm exhibited an absorption capacity of 41.0 cm/g MOF at 25 °C and 101.3 kPa. After charging with ethylene, the MOFs are further entrapped in a close-knit bead formed with alginate-Fe(III) matrix, observed under a scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). The alginate shell is degraded by exposing to 200 mM sodium citrate aqueous solution, triggering a continuous release of ethylene. With 20 mg of MOF, ethylene concentration reached 0.41-0.46 mg/L per mg MOF after 2.5 h. This is the first report regarding a controlled release of ethylene through degrading alginate-Fe(III) matrix rather than by changing the interfacial pore size of MOF under extreme conditions. This technology can enable precisely controlled and targeted applications of ethylene for food processing and agricultural applications.
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http://dx.doi.org/10.1016/j.jcis.2018.08.057DOI Listing
January 2019

Shifts in spinach microbial communities after chlorine washing and storage at compliant and abusive temperatures.

Food Microbiol 2018 Aug 4;73:73-84. Epub 2018 Jan 4.

Environmental Microbiology and Food Safety Laboratory, USDA ARS, Beltsville, MD, United States. Electronic address:

Fresh produce, like spinach, harbors diverse bacterial populations, including spoilage and potentially pathogenic bacteria. This study examined the effects of produce washing in chlorinated water and subsequent storage on the microbiota of spinach. Baby spinach leaves from a commercial fresh-cut produce processor were assessed before and after washing in chlorinated water, and then after one week's storage at 4, 10, and 15 °C. Microbial communities on spinach were analyzed by non-selective plating, qPCR, and 16S rDNA amplicon sequencing. Bacterial populations on spinach, averaging 6.12 ± 0.61 log CFU/g, were reduced by 1.33 ± 0.57 log after washing. However, populations increased by 1.77-3.24 log after storage, with larger increases occurring at higher temperature (15 > 10 > 4 °C). The predominant phylum identified on unwashed spinach leaves was Proteobacteria; dominant genera were Pseudomonas and Sphingomonas. Bacterial communities shifted significantly after chlorine washing and storage. Several Proteobacteria species, such as Stenotrophomonas sp. and Erwinia sp., were relatively tolerant of chlorine treatment, while species of Flavobacterium and Pedobacter (phylum Bacteroidetes) grew rapidly during storage, especially at abusive temperatures. Cupriavidus sp. and Ralstonia sp. showed significant increases after washing. After storage, microbial communities on spinach appeared to shift back toward the pre-washing distributions.
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http://dx.doi.org/10.1016/j.fm.2018.01.002DOI Listing
August 2018

Investigation on chlorine-based sanitization under stabilized conditions in the presence of organic load.

Int J Food Microbiol 2018 Feb 1;266:150-157. Epub 2017 Dec 1.

Department of Nutrition and Food Science, University of Maryland, 0112 Skinner Building, College Park, MD 20742, United States. Electronic address:

Chlorine, the most commonly used sanitizer for fresh produce washing, has constantly shown inferior sanitizing efficacy in the presence of organic load. Conventionally this is attributed indirectly to the rapid chlorine depletion by organics leading to fluctuating free chlorine (FC) contents. However, little is known on whether organic load affects the sanitization process directly at well-maintained FC levels. Hereby, a sustained chlorine decay approach was employed to study the inactivation of Escherichia coli O157:H7 under stabilized washing conditions. Chlorine solution was first incubated with organic load for up to 4h, modeling the chlorination in produce washing lines. The FC level was then stabilized at five targeted values for sanitization study. Our study showed decreased sanitizing efficacy as the organic load increased. At 5s residence time and pH6.5, a minimum of 0.5 and 7.5mg/L FC were needed to achieve a 5 log reduction at 0 and 900mg/L chemical oxygen demand (COD), respectively. The decrease was more pronounced at lower FC, higher COD, higher pH, and shorter residence time values. The organics-associated interference with FC measurement and disruption of chlorine/bacteria interaction, together with the chlorine demand of concentrated inoculum per se, collectively resulted in inadequate sanitization. Finally, our results were compared with existing studies conducted under dynamic conditions in the context of different experimental settings. This study provided a feasible method for studying the bacteria/sanitizer interaction while ruling out the confounding effect from fluctuating FC levels, and it indicated the direct, negative impact of organic load.
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http://dx.doi.org/10.1016/j.ijfoodmicro.2017.11.027DOI Listing
February 2018

Association between bacterial survival and free chlorine concentration during commercial fresh-cut produce wash operation.

Food Microbiol 2018 Apr 22;70:120-128. Epub 2017 Sep 22.

U. S. Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Environmental Microbiology and Food Safety Laboratory, 10300 Baltimore Ave, Beltsville, MD 20705, USA.

Determining the minimal effective free chlorine (FC) concentration for preventing pathogen survival and cross-contamination during produce washing is critical for developing science- and risk-based food safety practices. The correlation between dynamic FC concentrations and bacterial survival was investigated during commercial washing of chopped Romaine lettuce, shredded Iceberg lettuce, and diced cabbage as pathogen inoculation study during commercial operation is not feasible. Wash water was sampled every 30 min and assayed for organic loading, FC, and total aerobic mesophilic bacteria after chlorine neutralization. Water turbidity, chemical oxygen demand, and total dissolved solids increased significantly over time, with more rapid increases in diced cabbage water. Combined chlorine increased consistently while FC fluctuated in response to rates of chlorine dosing, product loading, and water replenishment. Total bacterial survival showed a strong correlation with real-time FC concentration. Under approximately 10 mg/L, increasing FC significantly reduced the frequency and population of surviving bacteria detected. Increasing FC further resulted in the reduction of the aerobic plate count to below the detection limit (50 CFU/100 mL), except for a few sporadic positive samples with low cell counts. This study confirms that maintaining at least 10 mg/L FC in wash water strongly reduced the likelihood of bacterial survival and thus potential cross contamination of washed produce.
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http://dx.doi.org/10.1016/j.fm.2017.09.013DOI Listing
April 2018

Silver Nanocluster-Embedded Zein Films as Antimicrobial Coating Materials for Food Packaging.

ACS Appl Mater Interfaces 2017 Oct 25;9(40):35297-35304. Epub 2017 Sep 25.

Department of Nutrition and Food Science, College of Agriculture and Natural Resources, University of Maryland , College Park, Maryland 20740, United States.

Highly efficient antimicrobial agents with low toxicity and resistance have been enthusiastically pursued to address public concerns on microbial contamination in food. Silver nanoclusters (AgNCs) are known for their ultrasmall sizes and unique optical and chemical properties. Despite extensive studies of AgNCs for biomedical applications, previous research on their application as antimicrobials for food applications is very limited. Here, for the first time, by incorporating AgNCs (∼2 nm in diameter) into zein films that are widely used as food packaging materials, we developed a novel coating material with potent antimicrobial activity, low toxicity to human cells, and low potential to harm the environment. In addition, we systematically evaluated the antimicrobial activities and cytotoxicity of AgNCs-embedded zein films and compared them to zein films embedded with AgNO or Ag nanoparticles with diameters of 10 and 60 nm (AgNP10 and AgNP60, respectively). At equivalent silver concentrations, AgNCs and AgNO solutions exhibited considerably higher antimicrobial activities than those of AgNP10 and AgNP60 solutions. Moreover, AgNCs exhibited less cytotoxicity to human cells than AgNO, with a half maximal inhibitory concentration (IC) of 34.68 μg/mL for AgNCs, compared to 9.14 μg/mL for AgNO. Overall, the novel AgNCs coating developed in this research has great potential for antimicrobial applications in food packaging materials due to its high antimicrobial efficacy, ultrasmall size, and low cytotoxicity.
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http://dx.doi.org/10.1021/acsami.7b08152DOI Listing
October 2017

Red Cabbage Microgreens Lower Circulating Low-Density Lipoprotein (LDL), Liver Cholesterol, and Inflammatory Cytokines in Mice Fed a High-Fat Diet.

J Agric Food Chem 2016 Dec 28;64(48):9161-9171. Epub 2016 Nov 28.

Diet, Genomics and Immunology Laboratory, Beltsville Human Nutrition Research Center, ARS, U.S. Department of Agriculture , Beltsville, Maryland 20705, United States.

Cardiovascular disease (CVD) is the leading cause of death in the United States, and hypercholesterolemia is a major risk factor. Population studies, as well as animal and intervention studies, support the consumption of a variety of vegetables as a means to reduce CVD risk through modulation of hypercholesterolemia. Microgreens of a variety of vegetables and herbs have been reported to be more nutrient dense compared to their mature counterparts. However, little is known about the effectiveness of microgreens in affecting lipid and cholesterol levels. The present study used a rodent diet-induced obesity (DIO) model to address this question. C57BL/6NCr mice (n = 60, male, 5 weeks old) were randomly assigned to six feeding groups: (1) low-fat diet; (2) high-fat diet; (3) low-fat diet + 1.09% red cabbage microgreens; (4) low-fat diet + 1.66% mature red cabbage; (5) high-fat diet + 1.09% red cabbage microgreens; (6) high-fat diet + 1.66% mature red cabbage. The animals were on their respective diets for 8 weeks. We found microgreen supplementation attenuated high-fat diet induced weight gain. Moreover, supplementation with microgreens significantly lowered circulating LDL levels in animals fed the high-fat diet and reduced hepatic cholesterol ester, triacylglycerol levels, and expression of inflammatory cytokines in the liver. These data suggest that microgreens can modulate weight gain and cholesterol metabolism and may protect against CVD by preventing hypercholesterolemia.
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http://dx.doi.org/10.1021/acs.jafc.6b03805DOI Listing
December 2016

Survival and Growth of Listeria monocytogenes on Fresh-Cut "Athena" and "Rocky Ford" Cantaloupes During Storage at 4°C and 10°C.

Foodborne Pathog Dis 2016 11 22;13(11):587-591. Epub 2016 Aug 22.

2 Environmental Microbial and Food Safety Laboratory, United States Department of Agriculture, Agricultural Research Service , Beltsville, Maryland.

Cantaloupes, marketed as "Rocky Ford," were implicated in the U.S. multistate outbreak of listeriosis in 2011, which caused multiple fatalities. Listeria monocytogenes can survive on whole cantaloupes and can be transferred to the flesh of melons. The growth of L. monocytogenes on fresh-cut "Athena" and "Rocky Ford" cantaloupe cultivars during refrigerated storage was evaluated. Fresh-cut cubes (16.4 cm) from field-grown cantaloupes were each inoculated with 5 log CFU/mL of a multi-strain mixture of L. monocytogenes and stored at 4°C or 10°C. Inoculated fresh-cut cubes were also: (1) continuously stored at 4°C for 3 days; (2) temperature-abused (TA: 25°C for 4 h) on day 0; or (3) stored at 4°C for 24 h, exposed to TA on day 1, and subsequently stored at 4°C until day 3. L. monocytogenes populations on fresh-cut melons continuously stored at 4°C or 10°C were enumerated on selected days for up to 15 days and after each TA event. Brix values for each cantaloupe variety were determined. L. monocytogenes populations on fresh-cut cantaloupe cubes stored at 4°C increased by 1.0 and 3.0 log CFU/cube by day 7 and 15, respectively, whereas those stored at 10°C increased by 3.0 log CFU/cube by day 7. Populations of L. monocytogenes on fresh-cut cantaloupes stored at 10°C were significantly (p < 0.05) greater than those stored at 4°C during the study. L. monocytogenes showed similar growth on fresh-cut "Athena" and "Rocky Ford" cubes, even though "Athena" cubes had significantly higher Brix values than the "Rocky Ford" fruit. L. monocytogenes populations on fresh-cut cantaloupes exposed to TA on day 1 and then refrigerated were significantly greater (0.74 log CFU) than those stored continuously at 4°C for 3 days. Storage at 10°C or exposure to TA events promoted growth of L. monocytogenes on fresh-cut cantaloupe during refrigerated storage.
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http://dx.doi.org/10.1089/fpd.2016.2160DOI Listing
November 2016

Survival and growth of Listeria monocytogenes on whole cantaloupes is dependent on site of contamination and storage temperature.

Int J Food Microbiol 2016 Oct 25;234:65-70. Epub 2016 Jun 25.

United States Department of Agriculture, Agricultural Research Service, Environmental Microbial and Food Safety Laboratory, Beltsville, MD 20705, USA. Electronic address:

Whole cantaloupes (Cucumis melo L.), marketed as 'Rocky Ford', were implicated in a large multi-state outbreak of listeriosis in the United States in 2011; however, survival and growth of Listeria monocytogenes on whole cantaloupes remains relatively unexplored. The research presented here evaluated three different storage temperatures, two sites of contamination of cantaloupes, and two cantaloupe varieties to determine their effect on the survival of L. monocytogenes. 'Athena' and 'Rocky Ford' cantaloupe cultivars were grown in soil and harvested, and individual melons subsequently received a multi-strain inoculum of L. monocytogenes (6 log CFU/melon), which were then stored at 4°C, 10°C, and 25°C. Changes in L. monocytogenes populations on the rinds and stem scars of cantaloupes stored at each temperature were determined at selected times for up to 15days. An analysis of variance revealed that inoculation site and storage temperature significantly affected survival of L. monocytogenes on cantaloupes during storage (p<0.05), but cultivar did not influence L. monocytogenes (p>0.05). Populations of L. monocytogenes on stem scars of cantaloupes stored at 25°C increased by 1-2 log CFU/melon on day 1, and were significantly greater than those on cantaloupes stored at 4°C or 10°C (p<0.05), which remained constant or increased by approximately 0.3 log CFU/melon, respectively, over the same time period. A decrease of 2-5 log CFU/melon of L. monocytogenes occurred on the rinds of cantaloupes during storage by day 7, and were not significantly different at the three different storage temperatures (p>0.05). In trials performed in rind juice extracts, populations of L. monocytogenes decreased by 3 log CFU/mL when stored at 25°C by day 3, but grew by 3-4 log CFU/mL when stored at 4°C over 7days. Overall, site of contamination and storage temperature influenced the survival of L. monocytogenes on cantaloupes more than cantaloupe cultivar type.
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http://dx.doi.org/10.1016/j.ijfoodmicro.2016.06.030DOI Listing
October 2016

Development of Metal-Organic Framework for Gaseous Plant Hormone Encapsulation To Manage Ripening of Climacteric Produce.

J Agric Food Chem 2016 Jun 20;64(25):5164-70. Epub 2016 Jun 20.

Environmental Microbial and Food Safety Laboratory, Agricultural Research Service, ‡Food Quality Laboratory, Agricultural Research Service, and ∥Electron and Confocal Microscope Unit, Agricultural Research Service, United States Department of Agriculture , Beltsville, Maryland 20705, United States.

Controlled ripening of climacteric fruits, such as bananas and avocados, is a critical step to provide consumers with high-quality products while reducing postharvest losses. Prior to ripening, these fruits can be stored for an extended period of time but are usually not suitable for consumption. However, once ripening is initiated, they undergo irreversible changes that lead to rapid quality loss and decay if not consumed within a short window of time. Therefore, technologies to slow the ripening process after its onset or to stimulate ripening immediately before consumption are in high demand. In this study, we developed a solid porous metal-organic framework (MOF) to encapsulate gaseous ethylene for subsequent release. We evaluated the feasibility of this technology for on-demand stimulated ripening of bananas and avocados. Copper terephthalate (CuTPA) MOF was synthesized via a solvothermal method and loaded with ethylene gas. Its crystalline structure and chemical composition were characterized by X-ray diffraction crystallography, porosity by N2 and ethylene isotherms, and morphology by electron microscopy. The MOF loaded with ethylene (MOF-ethylene) was placed inside sealed containers with preclimacteric bananas and avocados and stored at 16 °C. The headspace gas composition and fruit color and texture were monitored periodically. Results showed that this CuTPA MOF is highly porous, with a total pore volume of 0.39 cm(3)/g. A 50 mg portion of MOF-ethylene can absorb and release up to 654 μL/L of ethylene in a 4 L container. MOF-ethylene significantly accelerated the ripening-related color and firmness changes of treated bananas and avocados. This result suggests that MOF-ethylene technology could be used for postharvest application to stimulate ripening just before the point of consumption.
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http://dx.doi.org/10.1021/acs.jafc.6b02072DOI Listing
June 2016

Proliferation of Escherichia coli O157:H7 in Soil-Substitute and Hydroponic Microgreen Production Systems.

J Food Prot 2015 Oct;78(10):1785-90

Environmental Microbial and Food Safety Laboratory, U.S. Department of Agriculture, Agricultural Research Service, Beltsville, Maryland 20705, USA.

Radish (Raphanus sativus var. longipinnatus) microgreens were produced from seeds inoculated with Escherichia coli O157:H7 by using peat moss-based soil-substitute and hydroponic production systems. E. coli populations on the edible and inedible parts of harvested microgreen plants (7 days postseeding) and in growth medium were examined. E. coli O157:H7 was shown to survive and proliferate significantly during microgreen growth in both production systems, with a higher level in the hydroponic production system. At the initial seed inoculation level of 3.7 log CFU/g, E. coli O157:H7 populations on the edible part of microgreen plants reached 2.3 and 2.1 log CFU/g (overhead irrigation and bottom irrigation, respectively) for microgreens from the soil-substitute production system and reached 5.7 log CFU/g for those hydroponically grown. At a higher initial inoculation of 5.6 log CFU/g seeds, the corresponding E. coli O157:H7 populations on the edible parts of microgreens grown in these production systems were 3.4, 3.6, and 5.3 log CFU/g, respectively. Examination of the spatial distribution of bacterial cells on different parts of microgreen plants showed that contaminated seeds led to systematic contamination of whole plants, including both edible and inedible parts, and seed coats remained the focal point of E. coli O157:H7 survival and growth throughout the period of microgreen production.
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http://dx.doi.org/10.4315/0362-028X.JFP-15-063DOI Listing
October 2015

A mathematical model for pathogen cross-contamination dynamics during produce wash.

Food Microbiol 2015 Oct 27;51:101-7. Epub 2015 May 27.

Department of Mathematics, Cleveland State University, Cleveland, OH, USA. Electronic address:

One of the main challenges for the fresh-food produce industry is to ensure that the produce is free from harmful pathogens. A potential area of risk is due to cross-contamination in a sanitizing chlorine wash-cycle, where the same water is used to wash contaminated as well as non-contaminated produce. However, this is also an area where effective intervention strategies are possible, provided we have a good understanding of the mechanism of cross-contamination. Based on recent experimental work by Luo, Y. et al. A pilot plant scale evaluation of a new process aid for enhancing chlorine efficacy against pathogen survival and cross-contamination during produce wash, International Journal of Food Microbiology, 158 (2012), 133-139, we have built mathematical models that allow us to quantify the amount of cross-contamination of Escherichia coli O157:H7 from spinach to lettuce, and assessed the efficacy of the associated wash-cycle protocols.
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http://dx.doi.org/10.1016/j.fm.2015.05.010DOI Listing
October 2015

Growth of Salmonella enterica and Listeria monocytogenes on Fresh-Cut Cantaloupe under Different Temperature Abuse Scenarios.

J Food Prot 2015 Jun;78(6):1125-31

Environmental Microbial and Food Safety Laboratory, U.S. Department of Agriculture, Agricultural Research Service, Beltsville, Maryland 20705, USA.

Effective cold chain management is a critical component of food safety practice. In this study, we examined the impact of commonly encountered temperature abuse scenarios on the proliferation of Salmonella enterica and Listeria monocytogenes on fresh-cut cantaloupe. Inoculated fresh-cut cantaloupe cubes were subjected to various temperature abuse conditions, and the growth of S. enterica and L. monocytogenes was determined. During 1 week of storage, Salmonella cell counts on fresh-cut cantaloupe increased by -0.26, 1.39, and 2.23 log units at 4 °C (control), 8 °C, and 12 °C (chronic temperature abuse), respectively, whereas that of L. monocytogenes increased by 0.75, 2.86, and 4.17 log units. Under intermittent temperature abuse conditions, where storage temperature fluctuated twice daily to room temperature for 30 min, Salmonella cell count increased by 2.18 log units, whereas that of L. monocytogenes increased by 1.86 log units. In contrast, terminal acute temperature abuses for 2 to 4 h resulted in upwards to 0.6 log unit for Salmonella, whereas the effect on L. monocytogenes was less significant compared with L. monocytogenes on cut cantaloupe stored at 4 °C. Significant deterioration of produce visual quality and tissue integrity, as reflected by electrolyte leakage, was also observed under various temperature abuse conditions.
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http://dx.doi.org/10.4315/0362-028X.JFP-14-468DOI Listing
June 2015

Inactivation dynamics of Salmonella enterica, Listeria monocytogenes, and Escherichia coli O157:H7 in wash water during simulated chlorine depletion and replenishment processes.

Food Microbiol 2015 Sep 2;50:88-96. Epub 2015 Apr 2.

Department of Nutrition and Food Science, University of Maryland, 0112 Skinner Building, College Park, MD 20742, USA.

Maintaining effective sanitizer concentration is of critical importance for preventing pathogen survival and transference during fresh-cut produce wash operation and for ensuring the safety of finished products. However, maintaining an adequate level of sanitizer in wash water can be challenging for processors due to the large organic load in the wash system. In this study, we investigated how the survival of human pathogens was affected by the dynamic changes in water quality during chlorine depletion and replenishment in simulated produce washing operations. Lettuce extract was added incrementally into water containing pre-set levels of free chlorine to simulate the chlorine depletion process, and sodium hypochlorite was added incrementally into water containing pre-set levels of lettuce extract to simulate chlorine replenishment. Key water quality parameters were closely monitored and the bactericidal activity of the wash water was evaluated using three-strain cocktails of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes. In both chlorine depletion and replenishment processes, no pathogen survival was observed when wash water free chlorine level was maintained above 3.66 mg/L, irrespective of the initial free chlorine levels (10, 50, 100 and 200 mg/L) or organic loading (chemical oxidation demand levels of 0, 532, 1013 and 1705 mg/L). At this free chlorine concentration, the measured ORP was 843 mV and pH was 5.12 for the chlorine depletion process; the measured ORP was 714 mV and pH was 6.97 for the chlorine replenishment process. This study provides quantitative data needed by the fresh-cut produce industry and the regulatory agencies to establish critical operational control parameters to prevent pathogen survival and cross-contamination during fresh produce washing.
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http://dx.doi.org/10.1016/j.fm.2015.03.004DOI Listing
September 2015

A novel microfluidic mixer-based approach for determining inactivation kinetics of Escherichia coli O157:H7 in chlorine solutions.

Food Microbiol 2015 Aug 10;49:152-60. Epub 2015 Feb 10.

The Environmental Microbial and Food Safety Lab, Agricultural Research Service, The United States Department of Agriculture, Beltsville, MD 20705, USA.

Determination of the minimum free chlorine concentration needed to prevent pathogen survival/cross-contamination during produce washing is essential for the development of science-based food safety regulations and practices. Although the trend of chlorine concentration-contact time on pathogen inactivation is generally understood, specific information on chlorine and the kinetics of pathogen inactivation at less than 1.00 s is urgently needed by the produce processing industry. However, conventional approaches to obtain this critical data have been unable to adequately measure very rapid responses. This paper reports our development, fabrication, and test of a novel microfluidic device, and its application to obtain the necessary data on pathogen inactivation by free chlorine in produce wash solution in times as short as 0.10 s. A novel microfluidic mixer with the capability to accurately determine the reaction time and control the chlorine concentration was designed with three inlets for bacterial, chlorine and dechlorinating solutions, and one outlet for effluent collection. The master mold was fabricated on a silicon wafer with microchannels via photopolymerization. Polydimethylsiloxane replicas with patterned microchannels were prototyped via soft lithography. The replicas were further assembled into the micromixer on glass via O2 plasma treatment, and the inlets were connected to a syringe pump for solution delivery. To determine the kinetics of free chlorine on pathogen inactivation, chlorine solutions of varying concentrations were first pumped into the micromixer, together with the addition of bacterial suspension of Escherichia coli O157:H7 through a separate inlet. This was followed by injection of dechlorinating solution to stop the chlorine-pathogen reaction. The effluent was collected and the surviving bacteria cells were enumerated using a modified 'Most Probable Number' method. Free chlorine concentration was determined using a standard colorimetric method. The contact time was experimentally set by adjusting the solution flow rate, and was estimated by computational fluid dynamics modeling. Results showed that 1) pathogen inactivation was significantly affected by free chlorine concentration (P < 0.0001) and subsecond reaction time (P < 0.0001) and their interactions (P < 0.0001); and 2) the current industry practice of using 1.0 mg/L free chlorine will require more than 1.00 s total contact to achieve a 5-log10 reduction in an E. coli O157:H7 population, whereas a 10.0 mg/L free chlorine solution will achieve 5-log10 reduction in as little as 0.25 s. Information obtained from this study will provide critical insight on kinetics of bacterial inactivation for a broad range of sanitizers and produce wash operational conditions, thus facilitating the development and implementation of science-based food safety regulations and practices for improving food safety.
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http://dx.doi.org/10.1016/j.fm.2015.01.013DOI Listing
August 2015

Metabolomic assessment reveals an elevated level of glucosinolate content in CaCl₂ treated broccoli microgreens.

J Agric Food Chem 2015 Feb 5;63(6):1863-8. Epub 2015 Feb 5.

Beltsville Human Nutrition Research Center, Food Composition and Methods Development Laboratory, and §Beltsville Agricultural Research Center, Food Quality Laboratory, U.S. Department of Agriculture, Agricultural Research Service , Beltsville, Maryland 20705, United States.

Preharvest calcium application has been shown to increase broccoli microgreen yield and extend shelf life. In this study, we investigated the effect of calcium application on its metabolome using ultra-high-performance liquid chromatography with mass spectrometry. The data collected were analyzed using principal component analysis and orthogonal projection to latent structural discriminate analysis. Chemical composition comparison shows that glucosinolates, a very important group of phytochemicals, are the major compounds enhanced by preharvest treatment with 10 mM calcium chloride (CaCl2). Aliphatic glucosinolates (glucoerucin, glucoiberin, glucoiberverin, glucoraphanin, pentyl glucosinolate, and hexyl glucosinolate) and indolic glucosinolates (glucobrassicin, neoglucobrassicin, and 4-hydroxyglucobrassicin) were increased significantly in the CaCl2 treated microgreens using metabolomic approaches. Targeted glucosinolate analysis using the ISO 9167-1 method was further employed to confirm the findings. Results indicate that glucosinolates can be considered as a class of compounds that are responsible for the difference between two groups and a higher glucosinolate level was found in CaCl2 treated groups at each time point after harvest in comparison with the control group.
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http://dx.doi.org/10.1021/jf504710rDOI Listing
February 2015

Fabrication of biomimetically patterned surfaces and their application to probing plant-bacteria interactions.

ACS Appl Mater Interfaces 2014 Aug 4;6(15):12467-78. Epub 2014 Aug 4.

Environmental Microbial and Food Safety Lab, Agricultural Research Service, United States Department of Agriculture , Beltsville, Maryland 20705, United States.

We have developed a two-step replica molding method for rapid fabrication of biomimetically patterned plant surfaces (BPS) using polydimethylsiloxane (PDMS-BPS) and agarose (AGAR-BPS). Beyond providing multiple identical specimens that faithfully reproduce leaf surface microstructure, this approach also offers unique chemical, physical, and biological features. PDMS-BPS provide good structural durability for SEM examination, have surface wettability comparable to plant surfaces for coating development, and allow for real-time monitoring of biosynthesis through incorporation into microfluidic devices. AGAR-BPS are compatible with bacterial growth, recovery, and quantification, and enable investigation of the effects of surface topography on spatially varying survival and inactivation of Escherichia coli cells during biocide treatment. Further development and application of these biomimetically patterned surfaces to study (and possibly modify) other aspects of plant-bacteria interactions can provide insight into controlling pathogen contamination in a wide range of applications.
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http://dx.doi.org/10.1021/am502384qDOI Listing
August 2014

Whole-head washing, prior to cutting, provides sanitization advantages for fresh-cut Iceberg lettuce (Latuca sativa L.).

Int J Food Microbiol 2014 Jun 21;179:18-23. Epub 2014 Mar 21.

Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. Electronic address:

The efficacy of two leafy produce wash methods, the traditional cutting-before-washing process and a new washing-before-cutting method, on reduction of Escherichia coli O157:H7 inoculated on Iceberg lettuce was compared. The washing tests were conducted in a pilot-scale washer using combinations of water, chlorine, peroxyacetic acid, and ultrasound. The washing-before-cutting process recorded an E. coli O157:H7 count reduction 0.79-0.80 log₁₀ CFU/g higher than that achieved with the cutting-before-washing process in treatments involving only a sanitizer. When ultrasound was applied to the washing-before-cutting process, a further improvement of 0.37-0.68 log₁₀ CFU/g in microbial count reduction was obtained, reaching total reductions of 2.43 and 2.24 log₁₀ CFU/g for chlorine and peroxyacetic acid washes, respectively.
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http://dx.doi.org/10.1016/j.ijfoodmicro.2014.03.018DOI Listing
June 2014