Progress 09/01/24 to 08/31/25
Outputs
Target Audience:Growers and packers of organic fruits and vegetables, and scientists that are interested in organic fresh produce safety. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Five graduate students (two at the University of Tennessee, two at University of Georgia, and one at Washington State University) and twopost-doctoral research associates at the University of Tennessee were trained in the project. How have the results been disseminated to communities of interest?We engaged our Board of Advisors about the project scope and objectives. The project overview, project objectives, team members, and advisory board are publicized on our project website:https://washable-antimicrobial-coatings.tennessee.edu/. What do you plan to do during the next reporting period to accomplish the goals?In the first objective, we will continue to formulate acidic emulsion coatings and reformulate a commercial organic coating by dissolving hydrocolloids and essential oils. These formulations will be evaluated for their physical properties and their activities against bacterial and fungi pathogens. We expect to identify 6 coating formulations that will be used for testing antimicrobial activities on fruits in Objectives 2 and 3. In objective 2, we will test the efficacy of each coating against uncoated and coated controls in order to assess differences in populations of foodborne pathogens and fungal decay causing organisms on model crops (apricot, blueberry, cantaloupe, pepper, and tomato). Foodborne pathogen survival will be determined using a standard challenge study approach, where the target organisms (L. monocytogenes and Salmonella) will be inoculated at a high population in order to model population dynamics over time. Additionally, native microflora (aerobic and mesophilic bacteria, yeast, molds) populations will also be evaluated. In Objective 3, we will evaluate the shelf life and quality of these 6 coatings, as well as an uncoated control and a commercial coating control, on five crops (apricot, blueberry, cantaloupe, pepper, and tomato) under ideal storage conditions and expected storage life for each crop. We expect to complete a literature review of consumer responses to organic fruits and vegetables production methods and packaging to support survey design in Objective 4. In Objective 5, we will conduct semi-structured interviews with organic produce stakeholders to identify knowledge gaps and education needs. Findings will guide targeted outreach materials, shared through digital platforms and refined with input from the Board of Advisors.
Impacts
What was accomplished under these goals?
During this reporting period, the primary focus was on the first objective, with additional work done on the third and fifth objectives. In the first objective, we screened the antibacterial activity of essential oils from cinnamon, clove, peppermint, rosemary, and thyme. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against 5-stain cocktails of Salmonella and Listeria monocytogenes were determined using the microtiter plate assay in tryptic soy broth at 37 °C and brain heart infusion broth at 32 °C, respectively. The broths were additionally acidified to pH 5.0 and 6.0 with HCl or lactic acid. For L. monocytogenes, the MIC and MBC were the same at all three pH conditions for cinnamon (0.05% v/v), clove (0.05% v/v), and thyme (0.03% v/v) oils. Peppermint and rosemary oils were less active, with the MIC being 0.25% w/v at all pH conditions and the MBCs being 0.25% v/v at pH 5.0 and 0.25% or 0.5% v/v at pH 6.0 and 7.0. For Salmonella, cinnamon oil was the most active, with the respective MIC being 0.02%, 0.04%, and 0.08% v/v and the respective MBC being 0.040%, 0.160%, and 0.080% v/v at pH 5.0, 6.0, and 7.0. The MIC and MBC of clove oil against Salmonella were both 0.100% v/v, while they were all 0.125% v/v for thyme oil. Except the MIC of 0.250% v/v at pH 5.0, the MIC and MBC were 1.000% v/v for rosemary oil. Peppermint oil was the least active against Salmonella, with the MIC and MBC being 2.000% v/v at pH 6.0 and 7.0 and 0.250% v/v at pH 5.0. The interactions among the five essential oils were also tested at pH 5.0, 6.0, and 7.0 using the checkerboard assay. The combination of cinnamon and clove oils showed synergistic activity against Salmonella at pH 5.0 and 7.0, while the interactions of other combinations were mostly additive or indifferent for both pathogens. We formulated 152 acidic emulsions in the first objective. Emulsifiers were tested for lecithin and gum arabic at 1-5% w/v. Hydrocolloids (xanthan gum, carrageenan, alginate, gellan gum, and native corn starch) were incorporated individually and in combination in the aqueous phase at 0.5-1.0% w/v. Vegetable oil was used at 20-60% v/v. Emulsions were prepared using a shear homogenizer at 20,000 rpm for 5 min, and the pH was adjusted to 3.0-6.0 using 10% w/v lactic acid. The stability of emulsions was visually inspected during ambient storage for 30 days. It was observed that lecithin alone and gum arabic alone were unable to form stable emulsions. Alginate alone and gellan gum alone did not improve emulsion stability. Combinations of gum arabic with the hydrocolloids also did not stabilize the emulsions. The stable emulsions were added with 1.0% w/v glycerin as a plasticizer and were cast in petri dishes for drying at room temperature for 48 h to evaluate their film forming properties. Formulations containing 20% v/v vegetable oil, 3-5% w/v lecithin, and 1.0% w/v hydrocolloids (xanthan gum, carrageenan, and native corn starch) exhibited film-forming properties, while other formulations showed free oil after drying. The visually stable and film-forming formulations were further incorporated with 1.5% v/v or 3.0% v/v cinnamon or thyme oil and were adjusted to pH 3.0-5.0 using 10% w/v lactic acid. The survival of L. monocytogenes in the coating was evaluated after 1, 2, and 24 h of incubation at 21 °C. The pH 3.0 coating with and without 1.5% v/v cinnamon oil both achieved >5.5 log reductions within 1 h, while no significant reduction was observed after 2 h for other treatments. The visually stable and film-forming formulations were also preliminarily evaluated for their effectiveness in inhibiting growth of native molds and weight loss of tomatoes during ambient storage for 7 days. Each tomato was sprayed with about 1.0 mL of coating, and 6 tomatoes were used for each formulation in comparison with the uncoated control. Two formulations containing 3.0% v/v cinnamon oil showed promising results. After 7 days, the formulation prepared with 3% w/v lecithin, 0.5% w/v xanthan gum, and 0.5% w/v carrageenan had a weight loss of 3.13%, and the other formulation containing 5% w/v lecithin, 0.5% w/v xanthan gum, and 1.0% w/v native corn starch had a weight loss of 4.55%, both of which were lower than 7.37% of the uncoated control. One moldy tomato was observed for both formulations, compared to three moldy tomatoes for the uncoated control. In the third objective, we established a protocol of determining the residual cinnamon oil content on tomatoes using high performance liquid chromatography (HPLC) with a C-18 column. Tomatoes were immersed in 150 mL of 80% v/v aqueous ethanol and stirred overnight to extract residual cinnamon oil. The extracts were filtered with a 0.45 mm filter, and the permeate was analyzed using a mobile phase consisting of 80% acetonitrile and 20% water (containing 0.1% orthophosphoric acid) at a flow rate of 1 mL/min. Preliminary tests showed the impact of coating drying conditions on the residual cinnamon oil content on tomatoes and the removal of more than 50% cinnamon oil after washing the coated tomatoes. In the fifth objective, we had our first Board of Advisors meeting in September 2024 and a progress meeting in May 2025. We launched our project website (https://washable-antimicrobial-coatings.tennessee.edu/ or https://wacs.tennessee.edu), X (Twitter) account, and YouTube channel. To further engage stakeholders, we conducted an in-person discussion with the Washington produce industry to characterize the challenges associated with organic produce production and postharvest practices. This activity served as a tool to identify educational needs and gaps in available resources. The feedback is being used to guide the design of upcoming semi-structured interviews, which will provide more detailed, context-specific insights into stakeholder priorities, barriers to adoption, and areas where targeted training or outreach materials may have the greatest impact. The independent project evaluator, Dr. George Chitiyo, conducted his evaluation of the project. He concluded the project is progressing well according to the proposed timeline in year 1.
Publications
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