Source: UNIVERSITY OF TENNESSEE submitted to
ALTERNATIVE POST-HARVEST WASHING SOLUTIONS TO ENHANCE THE MICROBIAL SAFETY AND QUALITY OF ORGANIC FRESH PRODUCE
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
OTHER GRANTS
Reporting Frequency
Annual
Accession No.
0230137
Grant No.
2012-51300-20005
Project No.
TEN02012-02247
Proposal No.
2012-02247
Multistate No.
(N/A)
Program Code
113.A
Project Start Date
Sep 1, 2012
Project End Date
Aug 31, 2017
Grant Year
2012
Project Director
Zhong, Q.
Recipient Organization
UNIVERSITY OF TENNESSEE
2621 MORGAN CIR
KNOXVILLE,TN 37996-4540
Performing Department
Food Science & Technology
Non Technical Summary
Production of organic fruits and vegetables relies on careful oversight and appropriate inputs at every step in the growth, harvesting, processing, packaging, storage, and transportation. Care must be taken at every point in the supply chain to minimize the risk of produce being contaminated with foodborne pathogens such as, Shiga-toxin producing Escherichia coli (e.g., O157:H7) and non-STEC, Listeria monocytogenes, and Salmonella. Because many fruits and vegetables are consumed with minimal processing, foodborne illnesses caused by these pathogens are threats to the wellbeing of consumers, especially the elderly, infants, fetuses of pregnant women, and the immune-suppressed. This integrated project proposal to the USDA AFRI Organic Agriculture Research and Extension Initiative Program addresses the third priority area to "develop and improve allowable food safety practices to reduce microbial contamination, while increasing shelf-life of organic fresh produce." The long-term goal of this project is to provide safe, alternative, sustainable and effective treatments to prevent or reduce human pathogen contamination of organic produce. To improve microbiological safety of organic produce, there is an urgent need to develop washing practices that not only enhance sanitization effectiveness but also fulfill the requirement of organic sustainability. In this proposal, integrated research and extension objectives are proposed to improve current sanitization/washing practices. These will include fundamental approaches to understand surface properties of fresh produce and implement permitted surfactants in washing solutions to overcome capillary forces to enable more efficacious use of chlorine. In addition, novel sanitization strategies are proposed using organic essential oils to sanitize produce with and without chlorine. Economic feasibility, impacts on shelf-life and sensory properties of sanitization practices will be evaluated. Effective practices developed through research will be rapidly disseminated through extension to organic producers using media, electronic outlets, and on-farm testing. Integrated extension activities will be an important component directly improving microbial safety and quality of organic produce products in two southeastern states. The successful integration of research and extension can be implemented in organic production in other states.
Animal Health Component
(N/A)
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
7121452117010%
7121452200010%
7121460117020%
7121460200010%
7121420117010%
7121420200010%
7121430117020%
7121430200010%
Knowledge Area
712 - Protect Food from Contamination by Pathogenic Microorganisms, Parasites, and Naturally Occurring Toxins;

Subject Of Investigation
1452 - Carrot; 1430 - Greens and leafy vegetables; 1460 - Tomato; 1420 - Melons;

Field Of Science
1170 - Epidemiology; 2000 - Chemistry;
Goals / Objectives
The efforts of this integrated project will be focused on developing alternative organic antimicrobials that can be incorporated into postharvest processing water. To increase sanitizer effectiveness, the research component of this proposal will include strategies to (1) improve the access of chlorine to microenvironments on produce surfaces and (2) develop and validate alternative sanitization agents and protocols. For the former (Objective 1), we will utilize surfactants allowed for organic production to overcome the capillary force in microenvironments on produce surfaces. For the latter (Objective 2), we will develop technologies to solubilize organic plant essential oils that have shown a wide array of antimicrobial activity in other food systems but have limited water solubility in their native state. The solubilized essential oil will be studied for sanitization alone or in combination with chlorine. Conditions optimized in Objectives 1 and 2 will be used for in-field testing in Objective 3. Impacts of improved and alternative sanitization conditions will be studied for shelf-life and sensory tests in Objective 4, while the economic feasibility will be analyzed in Objective 5. The extension activities include the engagement of stakeholders, with six organic producers in North Carolina and Tennessee serving a four-year period on a Board of Advisors, development and implementation of producer workshops, and development of multi-media extension materials.
Project Methods
The integrated project has research and extension components. The first research objective is to probe surface properties of organic fresh produce and develop strategies of improving sanitization effectiveness of washing solutions. Surfactants permitted for organic production will be studied for the potential of overcoming the capillary force on organic fresh produce and improving sanitization effectiveness of chlorine solutions. Cocktails of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella will be prepared from 5 strains associated with outbreaks due to consumption of contaminated fresh produce. The bacteria will be inoculated on organic carrots, cherry tomatoes, cantaloupes, and leafy greens (romaine lettuce and spinach), and the sanitization effectiveness will be evaluated after treatment, along with residual chlorine and surfactant concentrations. The second objective is to study technologies of dissolving plant-derived food antimicrobials as alternative sanitization agent. The solubilized organic essential oil (EO) will be studied for sanitization alone or in combination with chlorine. The third objective is to in-field test the strategies developed in Objectives 1-2. Three research stations with USDA certified organic sites will be used, one located in Tennessee and two in North Carolina, which will utilize organic production standards for growing one cultivar of tomatoes and lettuce. All treatments will be evaluated on site in year three and fully replicated in year four. The fourth objective is to characterize impacts of alternative sanitization agents on sensory and quality. Romaine lettuce and cherry tomato will be used as the test crops for top 6 antimicrobial combinations from Objective 1 (chlorine +surfactant) and top 6 antimicrobial combinations from Objective 2 (EO or EO + chlorine), with comparison to two controls of water only and 150 ppm chlorine. The fifth objective is to conduct economic analysis of the alternative washing solutions. Extension activities will be fully integrated into all aspects of the research, beginning with involvement of organic stakeholders through a Board of Advisors. Their input and guidance on research objectives, success criteria, review of outreach material and media will assure that the research and extension activities are appropriately targeted. The utility of these alternative antimicrobial systems will be shared in several media types to assure appropriate distribution and on-going use for those in the organic fruit and vegetable industry. Varying delivery and means of communication will facilitate a dialogue amongst organic fruit and vegetable industry members that will be ongoing part the project's timeline and emphasize the importance of appropriate food safety interventions during the processing of fresh organic produce.

Progress 09/01/12 to 08/31/17

Outputs
Target Audience:Scientific community, growers, and the produce industry. Changes/Problems:In Objective 1, effects of adding surfactants in chlorine washes to improve disinfection efficacy were not pursued after the finding that adding gum arabic at 1% in 200 ppm chlorine solution actually reduced the efficacy of decontaminating Salmonella on cherry tomatoes. The research team decided to study an alternative water-based sanitizer, Citrox, that has been approved for organic production in UK but not yet in USA. In Objective 5, a true cost-benefit analysis of alternative washing solutions was not completed because of the limited availability of pricing information for commercialized products. What opportunities for training and professional development has the project provided?The project supported various personnel for different durations: two technicians, 4 post-doctoral researchers, 9 graduate students varying from 8 months to 4 years, and 20 undergraduate researchers as hourly workers. Three post-doctoral researchers after training were employed as faculty members in research universities in the United States and the fourth continued for post-doctoral training. Graduate students participated in the project continued for pre- and post-doctoral trainings or were hired by food and agricultural companies. Two undergraduate researchers are now in the graduate school. Three day-long workshops were offered in North Carolina and Tennessee for a total of eighty nine participants. A series of field presentations (Field Days) allowed for practical information to be presented to various audiences that include organic and conventional growers, regulators, scientists, students and natural conservation officials: Alternative Crops and Organics Field Tour, Mountain Horticultural Crops, Waynesville, NC (August 2015, 85 participants); Pick Tennessee Conference, Knoxville, TN (February 2016, 12 participants); Organic Field Day, Mountain Horticultural Crops, Waynesville, NC (August 2016, 105 participants); Mountain Horticultural Crops Research Station Field Days, Waynesville, NC (July 2016, 201 participants); Tomato Field Day, Mountain Horticultural Crops Research and Extension Center, Mills River, NC (August 2016). A symposium titled "Washing Your Produce-Sanitizing Solutions" was organized at the 2016 American Society for Horticultural Science Meeting in Atlanta, GA. How have the results been disseminated to communities of interest?Throughout the project, findings of research objectives have been disseminated through open access theses and dissertations, peer-reviewed journal publications, presentations in annual meetings of the Institute of Food Technologists, the American Institute of Chemical Engineers, the International Association of Food Protection, the American Society for Horticultural Science, and the OREI project directors' workshop, and the integrated extension activities. Through extension activities, project information was communicated with the Board of Advisors, field day participants that included organic and conventional growers, regulators, scientists, students and natural conservation officials, workshop participants, and free-access multi-media videos posted on YouTube and factsheets posted on the UT Extension website. A symposium titled "Washing Your Produce--Sanitizing Solutions" was delivered in the 2016 American Society for Horticultural Sciences annual meeting in Atlanta, GA, with the extension team presenting talks of "So Many Options, So Little Time: Selecting the Right Sanitizer for Your Operation," "Hitting the Mark for Food Safety and Organic Production in Postharvest," and "Filling the Pipeline: Considerations for Novel Sanitizers in Organic Production," followed by a panel discussion with speakers. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? In Objective 1, surfaces of spinach leaves were imaged, and contact angles of water droplets on cherry tomato, carrot, cantaloupe, lettuce leaf, and spinach leaf surfaces were determined and were reduced to <~25° by surfactants. For Salmonella on cherry tomatoes, gum arabic dissolved at 1% in 200 ppm chlorine solution lowered the decontamination efficacy. Studies on hydrophilic sanitizers were then focused on Citrox 14WP Pro Garda concentrate, an organically certified sanitizer in UK. A cocktail with five strains of Escherichia coli O157:H7 was inoculated on organic cherry tomatoes, baby spinach, Romaine lettuce, and cantaloupes, while a cocktail with five serovars of Salmonella enterica was inoculated on cherry tomatoes only. The inoculated samples were treated with aqueous solutions with 0.0%, 0.5%, and 0.75% v/v Citrox with and without 1.0% w/v organic load. Citrox treatments reduced pathogens up to 2 log more than the control and were similar to chlorine washes. Unlike chlorine, no transfer of bacteria to washing solutions and subsequent clean produce was observed for Citrox treatments that were also not significantly affected by the organic load. EPA approval is needed for use as a postharvest water sanitizing agent prior to utilization in the United States. In Objective 2, novel technologies of preparing plant essential oils (EOs) without specialized equipment such as a homogenizer were studied. Microemulsions using sucrose octanoate esters and lecithin had low loading of EOs. A technology was developed to readily prepare 1% EO emulsions using 1% whey protein concentrate, gum arabic, soybean lecithin, and their combinations by dissolving thyme oil, clove bud oil, or cinnamon oil in a hot alkaline solution and subsequently mixing with an aqueous emulsifier solution. Emulsions were prepared in several labs of the project team, demonstrating the ease and reproducibility of this technology. In tryptic soy broth, emulsions were generally similar to or more effective than free EOs in inhibiting bacteria. Emulsions with 0, 0.2, or 0.5%w/v EO were used to decontaminate Salmonella enterica, E. coli O157:H7 and Listeria monocytogenes five strain/serovar cocktails inoculated on organically grown cantaloupes, cherry tomatoes, baby spinach, Romaine lettuce, baby carrots, and snacking peppers with up to 5% organic load. The decontamination efficacy varied with the bacterial species and produce variety and was higher at a higher level of EOs. When emulsions with 0.5% EO were studied, bacteria on produce were reduced by ~1 to 3.5 log CFU/g, and the disinfection efficacy was less affected by organic load than chlorine. Similar to Citrox, EO emulsions prevented transferring of bacteria to wash solutions and uninoculated produce more effectively than chlorine and free EOs. The results show the potential use of emulsified EOs as alternative washes to decontaminate fresh produce and prevent cross-contamination. In Objective 3, field trials in 2015 were conducted for Romaine lettuce (cv. Cos) and tomatoes (Mountain Magic) in two fields at respective Universities' Organic Farms (1 in TN, 1 in NC). Field trials were repeated in 2016 for organic tomatoes (Mountain Magic) and yellow lunchbox snacking peppers (HMX-15637). Treatments included emulsions with 0.2% and 0.5% w/v thyme oil or clove bud oil, 0.5% and 0.75% Citrox, water (control), and 200 ppm chlorine wash. Aerobic plate counts and yeast and mold counts were determined on day 0 (immediately after wash), 3 and 7 under typical commercial storage conditions for lettuce and on day 0, 7, and 14 for tomatoes and peppers. Lettuce was determined to be incompatible for all EO emulsion treatments due to cell death and darkening. The EO emulsions behaved similarly to chlorine and Citrox behaved similarly to water when examining their interaction with the natural microflora of tomatoes. Overall appearance and firmness and shelf-life of tomatoes and peppers were similar after all treatments. Effects of alternative washing treatments on quality and sensory properties were studied in Objective 4. Emulsions with 0.5% thyme oil, clove bud oil, or cinnamon leaf oil were used to spray freshly harvested tomatoes and cantaloupes in 2015. After air-drying and storage at room temperature or at 4 °C, produce products were rated for browning, pitting, color development, and other changes every 3-7 days. Respiration and ethylene, total vitamin C, and pigments were determined with GC, HPLC, and spectrophotometry respectively. EO emulsions caused browning (possible cell necrosis) of lettuce within 0 to 7 days at 4 °C. Cantaloupes treatments did not show significant differences in respiration and contents of ethylene, beta carotene, and vitamin C. The 'Mountain Magic' tomato cultivar was similar for all treatments, but the 'Mountain Belle' cultivar, a smaller cherry tomato, treated by cinnamon or clove bud oil emulsions developed visible differences during storage at 4 °C. In 2016, impacts on quality of produce were repeated for tomatoes and done on mini peppers (since lettuce did not respond well) after dipping in emulsions with 0.25 or 0.50% thyme oil or clove bud oil emulsified by gum arabic, water, or 200 ppm chlorine wash. Again, 'Mountain Magic' tomatoes after various treatments showed similar quality properties, with higher lycopene content (P < 0.05) for the thyme oil treatment. Mini peppers after the EO treatments had 3x higher ascorbic acid than other treatments. Malic and citric acid contents were also higher for the EO treatments, but this difference was not sustained over time. Sensory analysis was conducted in 2016 for organically grown tomatoes and snacking peppers harvested from Waynesville, NC and Knoxville, TN and repeated for grape tomatoes in 2017. Overall, appearance was not but flavor and aroma characteristics were affected by EO washes, which faded after storage at 13 °C for up to 6 days. These findings showed the barrier of EO aroma and flavor on acceptability of organic fresh produce post-washing. In Objective 5, the extension team determined the cost of EO emulsions was not able to be forecast as too many variables, such as decrease in cost of primary ingredients based upon commercial scale. Given the limited availability of pricing information that would reflect a commercialized product, a true cost-benefit analysis of alternative washing solutions was not possible. Three advisory board meetings were held throughout the duration of the project to inform the experimental design and extension activities as well as allow the group to report back on outcomes of the research. Collaborations from the research and extension teams have resulted in 1) a full day curriculum on safe postharvest washing of organic fruits and vegetables, 2) three videos published on the UT Good Agricultural Practices YouTube channel (Experimental Report Evaluating Essential Oils for Organic Wash Systems; Postharvest Basics; Postharvest Sanitizers for Organic Washing Systems), and 3) three factsheets. Eighty-nine individuals in the day-long workshops held in NC and TN increased their knowledge around food safety principles and practices for postharvest handling of organic fresh produce by 30.5%. The full curriculum is available to extension professionals in the United States. Factsheets were published on the University of Tennessee Extension: 1) How to Use and Monitor Chlorine in Fruit and Vegetable Washwater and on Equipment and Food Contact Surfaces (SP798-A.pdf), 2) Using Peroxyacetic Acid in Fruit and Vegetable Washing and Packing (SP798-B.pdf), and 3) Using Sanitizers on Organic Fruit and Vegetable Farms- Merging National Organic Program Guidelines with Good Agricultural Practices (SP798-C.pdf). The availability of these multi-media materials to the public will have a long-term impact on enhancing the microbial safety of organic fresh produce.

Publications

  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Zhang, L., F. Critzer, P.M. Davidson, and Q. Zhong. 2014. Formulating essential oil microemulsions as washing solutions for organic fresh produce production. Food Chemistry. 165: 113118.
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Luo, Y., Y. Zhang, K. Pan, F. Critzer, P.M. Davidson, and Q. Zhong. 2014. Self-emulsification of alkaline-dissolved clove bud oil by whey protein, gum arabic, lecithin, and their combinations. Journal of Agricultural and Food Chemistry. 62(19): 44174424.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Zhang, Y., Q. Ma, F. Critzer, P.M. Davidson, and Q. Zhong. 2016. Organic thyme oil emulsion as an alternative washing solution to enhance the microbial safety of organic cantaloupes. Food Control. 67: 31-38.
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Zhang, Y., H. Chen, F. Critzer, P.M. Davidson, and Q. Zhong. 2017. Potential of cinnamon oil emulsions as alternative washing solutions of carrots. Journal of Food Protection. 80(6): 9941001.
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Jiang, C., P. Perkins-Veazie, G. Ma, and C. Gunter. 2017. Muskmelon Fruit Quality in Response to Postharvest Essential Oil and Whey Protein Sprays. Horticultural Science 52:887-891.
  • Type: Theses/Dissertations Status: Published Year Published: 2015 Citation: Harness III, M.L. 2015. Sanitization Effectiveness of Alkaline-Dissolved Essential Oils as Organic Produce Washing Solutions. MS thesis, University of Tennessee - Knoxville.
  • Type: Theses/Dissertations Status: Published Year Published: 2015 Citation: Simmons, E.R. 2015. Evaluation of a natural antimicrobial-based sanitizer as an alternative to chlorine for reducing foodborne pathogenic bacteria on organic produce. MS thesis, University of Tennessee - Knoxville.
  • Type: Theses/Dissertations Status: Published Year Published: 2016 Citation: Jiang, C. 2016. Postharvest quality of vegetables after application of essential oils as innovative sanitizers. PhD Dissertation, North Carolina State University.
  • Type: Theses/Dissertations Status: Awaiting Publication Year Published: 2017 Citation: Dunn, L. 2017. A Transcriptomic Analysis of Salmonella enterica Newport In Planta and after Postharvest Sanitization. PhD Dissertation, University of Tennessee-Knoxville.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Zhang, L., F.M. Critzer, P.M. Davidson, and Q. Zhong. 2013. Formulation of essential oil microemulsions to enhance the microbial safety of organic fresh produce. The 2013 IFT Annual Meeting, July 13-16, Chicago, IL. Paper #255-168.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Luo, Y., Y. Zhang, K. Pan, F. Critzer, P.M. Davidson, and Q. Zhong. 2014. Self-emulsification of alkaline-dissolved clove bud oil by whey protein, gum arabic, lecithin, and their combinations. The 2014 AIChE Annual Meeting, Nov. 16-21, Atlanta, GA. Paper 364033.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Zhang, Y., F. Critzer, P.M. Davidson, and Q. Zhong. 2014. Application of self-emulsified organic thyme oil as washing solution to enhance the microbial safety of cantaloupes. The 2014 NIFA Organic Programs Project Directors Meeting, Oct. 21-22, Washington, DC.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Zhang, Y., F. Critzer, P.M. Davidson, and Q. Zhong. 2015. Organic thyme oil emulsion as an alternative washing solution to enhance the microbial safety of organic cantaloupes. The 2015 IFT Annual Meeting, July 11-14, Chicago, IL. Paper # 125-076.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Gann, L., M. Harness, P.M. Davidson, Q. Zhong, and F. Critzer. 2015. Utilization of Emulsified clove bud oil and thyme oil to inactivate Salmonella on cherry tomatoes and Escherichia coli O157:H7 on baby spinach. The 2015 Annual Meeting of the International Association for Food Protection, July 25-28, Portland, OR. Paper #P3-210.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Simmons, E., F. Critzer, Q. Zhong and P.M. Davidson. 2015. Efficacy of a commercial antimicrobial agent on organic produce against Escherichia coli O157:H7 and Salmonella enterica. The 2015 Annual Meeting of the International Association for Food Protection, July 25-28, Portland, OR. Paper #P3-116.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Jiang, C., and P. Perkins-Veazie. 2015. Postharvest quality of leafy green crops with essential oil application-a natural antimicrobial for food safety. The 2015 Annual Meeting of the American Society for Horticultural Science. Aug. 2-7, New Orleans, LA.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Jiang, C., P. Perkins-Veazie, C. Gunter, L. Quesada, E. Gutierrez. 2015. Essential oils as a chlorine alternative for produce safety: Effects on postharvest quality of cherry tomatoes. HortScience 51:S105.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Perkins-Veazie, P., Gorman, S., Davis, J., Ducharme, D., Wszelaki, A., Critzer, F. 2016. Essential oil disinfectant on appearance and composition of organically grown tomatoes HortScience 52:S250.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Dunn, L., M. Harness, D. Smith, S. Gorman, A. Hamilton, P.M. Davidson, Q. Zhong, and F. Critzer. 2017. Essential oil nanoemulsions as post-harvest wash solutions on snacking peppers. The 2017 Annual Meeting of the International Association for Food Protection, July 9-12, Tampa, FL. Paper #P1-198.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Zhang, Y., H. Chen, F. Critzer, P.M. Davidson, and Q. Zhong. 2017. Application of self-emulsified cinnamon oil as washing solution to enhance the microbial safety of baby carrots. The 2017 IFT Annual Meeting & Food Expo, June 25-28, Las Vegas, NV. Paper #P06-052.


Progress 09/01/15 to 08/31/16

Outputs
Target Audience:Organic and conventional growers, regulators, scientists, students and natural conservation officials. Changes/Problems:No major changes are expected. We expect to complete research and extension objectives after being given one-year no-cost extension. What opportunities for training and professional development has the project provided?The project thus far has trained 2 MS and 1 PhD students on produce microbiological safety, 1 PhD student on fresh produce quality, 2 MS students and 4 post-doctoral students on produce surface properties and essential oil emulsions. Three post-doctoral students involved in the project have now taken assistant professor positions in research universities in the USA. Additionally, a series of field presentations (Field Days) allowed for practical information to be presented to various audiences that include organic and conventional growers, regulators, scientists, students and natural conservation officials. Alternative Crops and Organics Field Tour, Mountain Horticultural Crops, Waynesville, NC. August 2015 (85 participants) Organic Field Day, Mountain Horticultural Crops, Waynesville, NC. August 2016 (105 participants) Mountain Horticultural Crops Research Station Field Days, Waynesville, NC. July 2016 (201 participants) Tomato Field Day, Mountain Horticultural Crops Research and Extension Center, Mills River, NC. August 2016. How have the results been disseminated to communities of interest?In the past year, we presented our research findings in the 2016 American Society for Horticultural Sciences annual meeting in Atlanta, GA (August 16-18). During this meeting a symposium with three talks (outlined below) and one poster presentation titled "Essential Oil Disinfectant on Appearance and Composition of Organically Grown Tomatoes" were shared. The symposium titled "Washing Your Produce--Sanitizing Solutions" was led by four speakers from our Extension team: 1. So Many Options, So Little Time: Selecting the Right Sanitizer for Your Operation-Diane Ducharme, North Carolina State University 2. Hitting the Mark for Food Safety and Organic Production in Postharvest- Annette Wszelaki, University of Tennessee 3. Filling the Pipeline: Considerations for Novel Sanitizers in Organic Production- Laurel Dunn, University of Tennessee 4. Panel Discussion with Speakers - Diane Ducharme, Annette Wszelaki, and Laurel Dunn In addition, one refereed research article, 1 PhD dissertation, and two MS theses have been published. What do you plan to do during the next reporting period to accomplish the goals?In the next reporting period, field trials will be adjusted to use tomatoes and peppers, rather than tomatoes and lettuce, due to the poor response of lettuce to essential oils. Composition of treated and stored fruit is finishing up with data analysis from both growing seasons (tomatoes) and single growing seasons (lettuce and peppers) taking priority in the coming year.

Impacts
What was accomplished under these goals? In the fourth project year, research objectives have been mostly completed. The efforts in the first and second objectives have been focused on disseminating results, with a paper published and others getting ready for submission. In Objective 3, the 2nd year of field trials continued with two fields at respective Universities (1 in TN, 1 in NC) with two crops of organic tomatoes (Mountain Spring) and peppers (yellow Lunchbox snack peppersfrom Johnny's Selected Seeds). Snacking peppers were substituted for Romaine lettuce, which was shown to be unmarketable through work in Objective 4 in the first year of field trials. Tomatoes and snacking peppers were exposed to wash solutions consisting of emulsified thyme oil and clove bud oil as well as Citrox and were compared to control treatments of water and 200 ppm chlorine wash for their applicability in the field setting. Produce was sampled at day 0 (immediately after treatment), 7, and 14 from each location. Microbiological data analysis is still on-going, but indicates that the performance of emulsified essential oils is similar if not better than that of 200 ppm chlorine and better than water alone in reducing populations of yeast, molds, and bacteria that cause spoilage for both tomatoes and peppers on day 0. However, these populations were similar across all treatments by day 14. In the fourth objective, tomatoes and snacking peppers were exposed to the alternative wash solutions as well as the water and chlorine controls. Generally, 'Mountain Magic' tomatoes treated with essential oils had few changes compared to water or chlorine. Total lycopene content was highest at all storage days in tomato fruit treated with thyme oil. Total phenolic content decreased over storage time for most treatments but was slightly higher in tomatoes treated with thyme oil. Analysis of lettuce indicated a loss of total phenolic and chlorophyll content in those treated with cinnamon or clove oil, which is consistent with the immediate browning reaction (possible cell necrosis) of lettuce to essential oils. In control (water, chlorine) treatments, total phenolic content increased with storage time. Sensory Studies started with July & August 2016 harvests from Waynesville, NC and Knoxville, TN. Descriptive sensory analysis with 100 panelists was conducted for peppers and tomatoes utilizing emulsified thyme, clove bud, and cinnamon oil in addition to Citrox and the controls of water or chlorine. Sensory testing occurred 18-24 hr after washes were applied and demonstrated that all alternative washes were liked similarly to chlorine and water controls with respect to appearance. However the emulsified essential oils were liked less than the water and chlorine controls with respect to the following parameters: overall liking, flavor liking, texture liking, and freshness intensity. Based on this feedback, we recommend conducting sensory testing at intervals past 18hr post-wash to see if these same results hold true since it is unlikely that any produce would be consumed this soon after washing given typical distribution channels. Educational development: The TN and NC Extension Team meet with the Advisory Board members in late February 2016 to provide updates on progress of research and extension efforts and to ask for assistance in getting into existing venues for outreach activities. The Extension team continues communication efforts through out the year with 2-hr. conference calls to further development of resources. Seven modules for delivery of curriculum continue development activities. Learning objectives have been reviewed and accepted by all team members as well as a template being developed for modules. Modules have been developed and been delivered in several existing venues (see below). Several conference presentation requests had been made without success; additional requests have been made for the upcoming fall/winter meetings. The project was highlighted in North Carolina on Dr. Davis's blog and during the August 20 Alternative Crops and Organics Field Tour. During this event, progress on the project was shared with many visitors to the field including scientists, students, and growers. Extension factsheets are developed on the use of organic sanitizers (PAA), postharvest care, and use of sanitizers approved for NOP and how to use chlorine effectively. Factsheets are currently under peer review and will be submitted to University for publication. A private videographerwas secured to develop 3 short educational videos. Scripts were written, recommendations for photographic shots to capture visual content, and peer review of content was completed by late fall. Video shots were staged at a local packinghouse during the 3rd week of March 2016. Drafts of videography are currently in review by Extension team. Three titles include: 1) Postharvest Sanitizers for Organic Wash Systems; 2) Fresh Produce Postharvest Basics; 3) Evaluating Essential Oils for Organic Wash Systems. These videos will be used in the workshops, posted on the website (https://ncfreshproducesafety.ces.ncsu.edu/) as well as have the potential to be extended to an eXtension webinar. Finally, a 12 question survey was sent to organic growers on the following topics: good agricultural practices (GAP) implementation, produce washing procedures, commodities washed, wash quality, type of sanitizers used and where used, and interest in essential oils that could reduce the risk of foodborne pathogens. Results from survey will be used to build an Excel-based interactive tool comparing each alternative to chlorine and the costs associated with that decision is being developed for deployment in fall 2016.

Publications

  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Zhang, Y., Q. Ma, F. Critzer, P.M. Davidson, and Q. Zhong. 2016. Organic thyme oil emulsion as an alternative washing solution to enhance the microbial safety of organic cantaloupes. Food Control. 67: 31-38.
  • Type: Theses/Dissertations Status: Published Year Published: 2016 Citation: Jiang, C. 2016. Postharvest quality of vegetables after application of essential oils as innovative sanitizers. PhD Dissertation, North Carolina State University.
  • Type: Theses/Dissertations Status: Published Year Published: 2015 Citation: Harness III, M.L. 2015. Sanitization Effectiveness of Alkaline-Dissolved Essential Oils as Organic Produce Washing Solutions. MS thesis, University of Tennessee - Knoxville.
  • Type: Theses/Dissertations Status: Published Year Published: 2015 Citation: Simmons, E.R. 2015. Evaluation of a natural antimicrobial-based sanitizer as an alternative to chlorine for reducing foodborne pathogenic bacteria on organic produce. MS thesis, University of Tennessee - Knoxville.


Progress 09/01/14 to 08/31/15

Outputs
Target Audience:Scientific community and produce industry. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has trained 2 MS and 1 PhD students on produce microbiological safety, 1 PhD student on fresh produce quality, 2 MS students and 2 post-doctoral students on produce surface properties and essential oil emulsions. Two post-doctoral students involved in the project have now taken assistant professor positions in two major research universities. How have the results been disseminated to communities of interest?In the past year, we presented our research findings in the 2015 Annual Meetings of the Institute of Food Technologists in Chicago, IL (one poster) and the International Association of Food Protection in Portland, OR (two posters) and at the 2015 Annual Meeting of the American Society for Horticultural Science (one poster). We invited members of our Board of Advisors to attend our project annual meeting in Waynesville, NC and received valuable feedbacks on our research findings and extension plans. What do you plan to do during the next reporting period to accomplish the goals?In the next reporting period, we plan to repeat field trials (Objective 3). We will continue Objective 5 (cost analysis) and other extension activities as proposed.

Impacts
What was accomplished under these goals? In the third project year, the proposed research objectives were being further progressed. In the first objective, a commercial citrus-based natural antimicrobial, Citrox, was also evaluated for its efficacy in rinse water to inactivate five-strain cocktails of Escherichia coli O157:H7 or Salmonella enterica on cantaloupes, as well as Listeria monocytogenes on either organically grown cherry tomatoes, baby spinach, Romaine lettuce, or cantaloupes. Studies on the transfer of bacteria to rinse water and clean produce were completed for the three bacteria and the four produce products. Results from the past reporting period confirmed that (1) Citrox was an effective inhibitor of the Gram negative and Gram positive bacteria and (2) Citrox sanitizing solutions stopped transfer, or cross contamination, from inoculated produce to un-inoculated produce when tested at 0.5% and 0.75%. The absence of cross-contamination is beneficial in large-scale distribution of organic produce since all the tomatoes, leafy greens and cantaloupes will share one large dump tank during post-harvest processing. Citrox contains organic compounds so using it as a sanitizing agent on organic produce allows the produce to remain organic. In the second objective, we completed studies on essential oils self-emulsified by whey protein concentrate (WPC), gum arabic, or their combination as alternative washing solutions to reduce pathogens on organically grown produce by expanding produce varieties to baby spinach, baby carrots, and green onions. Continuing from the last reporting period, the recovery of Salmonella and L. monocytogenes cocktails on whole cantaloupes after washing by 0.2% free or emulsified thyme oil (TO) was studied during the subsequent ambient (21 °C) storage for up to 14 days. The populations of Salmonella and L. monocytogenes reduced in all treatments during storage, and were consistently the lowest after washing by the TO emulsion and storage up to 10 days, while no significant difference between free and emulsified TO treatments was observed on day 14. For baby carrots inoculated with Salmonella, E. coli O157:H7, or L. monocytogenes, cinnamon oil (CO, with the major component being eugenol) emulsified by gum arabic or the combination of WPC and gum arabic was studied at 0.2% or 0.5%, which was compared to rinsing with water only or the same concentration of free CO. The reduction of bacteria on baby carrots was generally more effective at 0.5% CO than at 0.2% CO, and the emulsified CO was slightly (~0.5 log CFU/m2) more effective than free CO. 0.5% emulsified CO eliminated cross-contamination and was not affected by 2% and 5% organic loads (OLs). Similarly, 0.5% emulsified CO was more effective than free CO for green onions inoculated with pathogens but caused tissue damages. Without OL, chlorine at 200 ppm was the most effective with over a 4 log reduction of E. coli O157:H7 on baby spinach compared to emulsified TO and clove bud oil (CBO). However, 0.5% (v/v) TO was the second most effective, with a 3 log reduction of E. coli O157:H7, and seemed completely invulnerable to OL while chlorine with 1% OL was significantly less effective than all emulsified TO. Results from testing for E. coli O157:H7 transfer were much the same, with chlorine being the most effective but significantly hindered by the presence of organic matter. The results to date indicate potential of emulsified essential oils for use as post-harvest rinses for fresh produce, as they consistently showed more resilience against OL than chlorine. In Objective 3, field trials commenced for Romaine lettuce and tomatoes. Wash solutions consisting of emulsified TO and CBO as well as Citrox were compared to a water and 200ppm chlorine wash. Lettuce were sampled on day 0 (immediately after wash), 3 and 7 under typical commercial storage conditions for aerobic plate counts (APC) and yeast and mold (YM) counts, while tomatoes were sampled on day 0, 7, and 14. Similar populations for all wash treatments were observed on YM and APC and increased similarly throughout the 7 day holding period for lettuce. Our alternative wash solutions did not result in any different bacterial populations than chlorine or water only treatments which are more commonly used amongst small and medium organic growers to prepare produce for market. Data collection is just being completed for tomatoes. All field trials will be replicated once more during the next growing season. In the fourth objective, essential oil formulations were tested on field lettuce and tomatoes. Organically grown romaine lettuce from Waynesville, NC was harvested, cooled, and shipped to Knoxville TN or to Kannapolis NC. Lettuce were dipped in formulations of 0.25 or 0.50% CO or CBO emulsified by gum arabic or in 200 ppm chlorine or water, drained, and held at 4 C for 3 to 10 days. Heads were weighed and rated at days 3, 7, and 10 and green color determined at the leaf apex. CO and CBO treatments had negative effects on quality, causing browning that appeared within 0 to 7 days depending on percent oil. Tomatoes were dipped in oil formulations of the same concentration and are currently being evaluated. Additionally, similar effects of essential oils on lettuce were observed for freshly harvested and store-bought Romaine lettuce. An attempt to further explain this phenomenon is being undertaken at a more cellular level. Extension activities have been initiated in the third project year. Starting in January, an Advisory Board Meeting was held to provide updates on the alternative organic antimicrobials, discussion on results and introduction of the field and Extension portions of this project. Field Studies: For the field testing of the alternative antimicrobial washes, two fields have been secured at respective Universities (1 in TN, 1 in NC) with two crops (Cherry tomato 'Mountain Magic' and Romaine lettuce 'Parris Island Cos'). Organic seeds were grown in greenhouses (February - March) and transplanted to organic certified fields in spring 2015 (April - May). Romaine lettuce were harvested two times (end of April - May) and tomatoes harvested one time (July). These products were used in field studies as detailed above and assessed for shelf-life (weight and color assessments). Educational development: Extension efforts centered on economic feasibility, workshop and resource development, and video/still photography capture. An economic feasibility to capture costs associated with existing antimicrobials used within the fruit and vegetable industry (chlorine and PAA), as well as any viable alternative with costs acquired. A survey is being developed to capture specifics on uses/costs and a webinar is to be developed as well as workshop content. Brainstorms on workshop content, locations and venues were done with internal committee as well as Advisory Board; several existing shorter venues (30 min. - 1 hr.) were applied to for workshop delivery (2016). An agenda for a day workshop with assignments to committee members for the development of learning modules, identification of resource needs, hands-on activities, and methods of evaluation are currently in place. Resource materials defined include hands-on activities and ordering of materials, factsheet development, Webinar, and videos. Video/still photography was captured for both the field and laboratory experiments and will be incorporated into the delivery of workshops. Additionally, a "grower's kit" will be utilized and given to participants at the workshops.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Zhang, Y., F. Critzer, P.M. Davidson, and Q. Zhong. 2015. Organic thyme oil emulsion as an alternative washing solution to enhance the microbial safety of organic cantaloupes. The 2015 IFT Annual Meeting, July 11-14, Chicago, IL. Paper #125-076.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Gann, L., M. Harness, P.M. Davidson, Q. Zhong, and F. Critzer. 2015. Utilization of Emulsified clove bud oil and thyme oil to inactivate Salmonella on cherry tomatoes and Escherichia coli O157:H7 on baby spinach. The 2015 Annual Meeting of the International Association for Food Protection, July 25-28, Portland, OR. Paper #P3-210.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Simmons, E., F. Critzer, Q. Zhong and P.M. Davidson. 2015. Efficacy of a commercial antimicrobial agent on organic produce against Escherichia coli O157:H7 and Salmonella enterica. The 2015 Annual Meeting of the International Association for Food Protection, July 25-28, Portland, OR. Paper #P3-116.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: Jiang, C., and P. Perkins-Veazie. 2015. Postharvest quality of leafy green crops with essential oil application-a natural antimicrobial for food safety. The 2015 Annual Meeting of the American Society for Horticultural Science. Aug. 2-7, New Orleans, LA.


Progress 09/01/13 to 08/31/14

Outputs
Target Audience: Scientific community. Changes/Problems: No changes. What opportunities for training and professional development has the project provided? Trained 2 MS and 1 PhD students on produce microbiological safety, 1 PhD student on fresh produce quality, 2 MS students and 2 post-doctoral students on produce surface property and essential oil emulsions. One post-doctoral student is now on faculty in a major research university. How have the results been disseminated to communities of interest? In the past year, we gave an oral presentation about self-emulsification technology at the 2014 Annual Meeting of the American Institute of Chemical Engineers (Atlanta, GA) and a poster presentation at the OREI project directors’ workshop (Washington, DC). We also published two research articles based on findings in the past two years. What do you plan to do during the next reporting period to accomplish the goals? In the next reporting period, we will continue to study research Objectives 1, 2 and 4 to identify formulations that are effective in inactivating Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella on organic produce and cause minimal quality defects. The identified formulations will be used for Objective 3 for field trials and Objective 5 for cost analysis in years 3 &4. We will also begin extension activities as proposed.

Impacts
What was accomplished under these goals? In the current reporting period, we continued to study the proposed research objectives and planned extension activities to be initiated next year. For the first objective, because we found the ineffectiveness of chlorine in reducing bacteria on cherry tomatoes with the presence of organic matter, we studied an alternative aqueous sanitizer, Citrox 14WP Pro Garda concentrate that is an organically certified sanitizer in UK. The efficacy of Citrox in inhibiting foodborne pathogens on organic cherry tomatoes, baby spinach, and romaine lettuce and the prevention of cross-contamination were studied. The foodborne pathogens were cocktails of five strains of Escherichia coli O157:H7 or five serovars of Salmonella enterica (on cherry tomatoes only). The Citrox was tested at 0.0% (control), 0.5%, and 0.75% v/v in aqueous solutions, with and without 1.0% % w/v organic load. The reduction of bacteria by Citrox was up to 2 log lower than the control. The transfer of bacteria to washing solution and subsequent clean produce was significant for the control but not detected for Citrox treatments. The organic load had no significant effect on Citrox treatments. For the second objective, we continued to study the novel technology developed in the previous year that self-emulsifies essential oils using whey protein concentrate 34 (WPC-34), gum arabic, soybean lecithin, and their combinations as emulsifiers. We have characterized structure and stability of emulsions prepared from clove bud oil (CBO), thyme oil, cinnamon oil, and vanilla oil and the minimum inhibitory (MIC) and bactericidal concentrations (MBC) of these emulsions against cocktails/serovars of Salmonella enterica, Escherichia coli O157:H7 and Listeria monocytogenes. Vanilla extract and pure vanilla were ineffective against these pathogens. The MIC and MBC of thyme oil were the lowest among the essential oils, followed by CBO. Based on the physical stability and antimicrobial activity, one emulsion each of thyme oil and CBO was chosen as alternative washing solutions. Thyme oil self-emulsified with gum arabic was compared with free thyme oil dissolved in 5% ethanol for their antimicrobial activities against Salmonella enterica, Escherichia coli O157:H7 and Listeria monocytogenes inoculated on organically grown cantaloupes. After treatment by 0.1%, 0.2%, 0.5% emulsified or free thyme oil for 2 min, the emulsified thyme oil exhibited significantly better inhibition against the three bacteria than free thyme oil. The efficacy of thyme oil at different organic loads (2% and 5%) was also evaluated. The organic load showed no effects on the antimicrobial efficacy of emulsified thyme oil but a slight improvement on the inhibition activity of free thyme oil. Thyme oil (0.2% and 0.5%) self-emulsified with gum arabic, CBO (0.2% and 0.5%) self-emulsified with WPC-34, and CBO (0.2% and 0.5%) self-emulsified with WPC-34 and gum arabic combination were tested against Salmonella serovars on the surfaces of cherry tomatoes and compared to the efficacy of chlorine at 200 ppm. 0.5% CBO self-emulsified with WPC-34 and WPC-34/gum arabic combination showed a significantly greater reduction than chlorine at 200 ppm. These emulsions were significantly less effective in the presence of 1% organic load but were still as effective as the chlorine treatment. 0.5% thyme oil emulsified with gum arabic was just as effective as chlorine at 200 ppm and showed no significant difference in the presence of 1% organic load. Overall, 0.5% CBO emulsified with WPC-34 was the most effective at reducing levels of Salmonella on cherry tomato surfaces, while 0.5% thyme oil emulsified with gum arabic was the least susceptible to the presence of organic compounds. For the fourth objective, effects of essential oil emulsions on postharvest quality and shelf life of cherry tomato, cantaloupe, and Romaine lettuce were evaluated. Emulsions of thyme oil, CBO, and cinnamon leaf oil were prepared with WPC-34, adjusted to pH 6.5, and diluted with water to a final oil concentration of 0.5%. Freshly harvested tomatoes and cantaloupes were sprayed with the emulsions, air-dried, and stored at room temperature or at 4 °C. Subjective ratings for browning, pitting, color development, and other changes were made every 3-7 days. Respiration and ethylene were measured by GC and total vitamin C assayed by HPLC. Pigment content (mostly beta carotene in cantaloupe and lycopene in tomatoes) was assayed by hexane extraction and absorbance at 450 and 503 nm by spectrophotometry. In cantaloupe, some brown spotting was found, but least with the thyme oil emulsion. No differences in respiration, ethylene content, beta carotene, or vitamin C content were found among treatments. In tomato, two cultivars were used. ‘Mountain Magic’ had no adverse symptoms and no differences were found among treatments for assays of color, ratings, respiration, or vitamin C. ‘Mountain Belle’, a smaller cherry tomato, showed some pitting and delayed color development when held at 4 C following treatment with cinnamon or clove oil emulsions.

Publications

  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Zhang, L., F. Critzer, P.M. Davidson, and Q. Zhong. 2014. Formulating essential oil microemulsions as washing solutions for organic fresh produce production. Food Chemistry. 165: 113118.
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Luo, Y., Y. Zhang, K. Pan, F. Critzer, P.M. Davidson, and Q. Zhong. 2014. Self-emulsification of alkaline-dissolved clove bud oil by whey protein, gum arabic, lecithin, and their combinations. Journal of Agricultural and Food Chemistry. 62(19): 44174424.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Luo, Y., Y. Zhang, K. Pan, F. Critzer, P.M. Davidson, and Q. Zhong. 2014. Self-emulsification of alkaline-dissolved clove bud oil by whey protein, gum arabic, lecithin, and their combinations. The 2014 AIChE Annual Meeting, Nov. 16-21, Atlanta, GA. Paper 364033.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2014 Citation: Zhang, Y., F. Critzer, P.M. Davidson, and Q. Zhong. 2014. Application of self-emulsified organic thyme oil as washing solution to enhance the microbial safety of cantaloupes. The 2014 NIFA Organic Programs Project Directors Meeting, Oct. 21-22, Washington, DC.


Progress 09/01/12 to 08/31/13

Outputs
Target Audience: Scientific community. Changes/Problems: No changes. What opportunities for training and professional development has the project provided? Trained 1 MS and 2 PhD students on produce microbiological safety, 1 PhD student on fresh produce quality, 1 MS student and 1 post-doctoral student on produce surface property and essential oil emulsions. How have the results been disseminated to communities of interest? A poster presentation about formulating microemulsions of essential oils was given at the 2013 Annual Meeting of the Institute of Food Technologists (Chicago, IL). What do you plan to do during the next reporting period to accomplish the goals? In the next reporting period, we will continue to study research Objectives 1 and 2, focusing on microbiological experiments to indentify formulations effectively inactivate Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella on organic produce. The findings will be used for Objectives 3 and 4 in years 3 &4. We will also begin planning extension activities and field trials to take place in years 3 & 4.

Impacts
What was accomplished under these goals? In the current reporting period, we had our first Board of Directors (BOA) meeting on February 12, 2013. For the first objective, we evaluated the ability of surfactants to improve the interaction of chlorine with target microorganisms when Salmonella was inoculated onto cherry tomatoes. The recovered Salmonella, 7.19 log CFU/~20g sample, was similar for the untreated group, those dipped into a wash liquid containing only deionized water or 200 ppm chlorine and 1% gum arabic (P>0.05). The recovered Salmonella was significantly reduced (P<0.05) when dipped in 200 ppm chlorine and 0.1% gum arabic or only 200 ppm chlorine, corresponding to 5.66 or 4.96 log CFU/~20g sample, respectively. In addition, samples that followed the washing treatments of contaminated tomatoes were analyzed to test for the amount of Salmonella transferring onto clean tomatoes. Water was the least effective of these with an average of 4.57 log CFU/~20g Salmonella transferred. All chlorinated treatment washes were similarly effective at preventing the transfer of Salmonella, with numbers from 1.08 (chlorine + 0.1% gum arabic) to 1.24 (chlorine) up to 1.53 (chlorine + 1% gum arabic) log CFU/~20g sample. For the second objective, we continued to study formulations using sucrose octanoate esters (SucraShield®) and lecithin to dissolve essential oils. Surface tension on four produce products - cherry tomato, carrot, cantaloupe, lettuce leaf, and spinach leaf was significantly reduced by the microemulsion with dissolved essential oils when compared to deionized water. Because SucraShield may be too expensive for practical applications, we studied another method to self-emulsify essential oils using whey protein concentrate 34 (WPC-34), gum arabic, soybean lecithin, and their combinations as emulsifiers. This was enabled by the deprotonation under alkaline conditions to dissolve essential oils, addition of emulsifier(s), and neutralization. Deprotonation conditions were optimized for the capacity to produce stable essential oil emulsions after self-emulsification. Physicochemical properties, including particle size, entrapment efficiency, stability, and particle morphology of emulsions were characterized. Several essential oils were tested, and clove bud oil was found to be the most suitable for this self-emulsification technique. WPC and equal mass of WPC and gum arabic were the most feasible emulsifiers, showing 1% biopolymer capable of emulsifying 1% clove bud oil and no significant changes in mean particle dimension during 7-day storage at ambient conditions. Based on high performance liquid chromatography, the major component of clove bud oil, eugenol, showed a similar elution profile before and after self-emulsification. When tested against Listeria monocytogenes Scott A, Escherichia coli O157:H7 ATCC 43895 and Salmonella Enteritidis, the emulsions showed similar or lower minimum inhibitory (MIC) and bactericidal concentrations (MBC) than clove bud oil dissolved in ethanol. Similar observations were found when emulsions and free oils were studied for growth kinetics of bacteria in tryptic soy broth. For the fourth objective, postharvest rating systems for cherry tomato, Romaine lettuce, and cantaloupe were developed to follow subjective changes during storage after application of developed products, and criteria for bioactives of interest were established.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Zhang, L., F.M. Critzer, P.M. Davidson, and Q. Zhong. 2013. Formulation of essential oil microemulsions to enhance the microbial safety of organic fresh produce. The 2013 IFT Annual Meeting, July 13-16, Chicago, IL. Paper #255-168.