Progress 01/01/21 to 12/31/24
Outputs
Target Audience:Academics (e.g., faculty, students, and staff scientists), canners, canmakers, and manufacturers of packaging coatings for metal food containers, consumers of canned foods. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Since Fall 2024, the graduate student has been mentoring an undergraduate researcher in Food Science, who was trained on several characterization techniques available in the Food Materials Characterization Lab housed within the Department of Food Science at Penn State: differential scanning calorimetry (DSC) and electrochemical impedance spectroscopy (EIS). The undergraduate student has been working on an independent research project with the goal of monitoring changes in the barrier performance of non-BPA food can coatings during retort processing inside a can. For her pedagogical training in Fall 2024, the graduate student served as instructor of record for FDSC 411: Managing Food Quality, a senior-level course focused on using statistical tools for the control and improvement of food quality. Her advisor provided her with mentoring and educational training to support her teaching growth by attending her lectures and providing constructive feedback. 69% of her students completed the Student Educational Experience Questionnaire, which is Penn State's instrument for gathering student feedback at the end of a course. She also guest lectured FDSC 150: Food Science First Year Engagement, where she led a laboratory exercise making mayonnaise using different protein sources (i.e., egg protein, plant-based protein, and no protein) to determine their effect on the appearance, quality, and physical structure of mayonnaise. This was a "funducational" laboratory exercise to introduce first years in the food science program to process-structure-property relationships. Additionally, she was selected to participate in the Targeted Teaching Transformation (T3) program and a Course in Ethical Pedagogy through the Schreyer Institute for Teaching Excellence (SITE). Her T3 coach, who is an Associate Research Professor at SITE, met with her throughout the semester, providing her with resources for handling scenarios that arose in the classroom, including requests for accommodations. In the Course in Ethical Pedagogy, the graduate student gained exposure to and understanding of which critical pedagogies fit her best (e.g., engaged, equity, and relation pedagogy). With the course instructors' help, she was able to refine her teaching philosophy statement. How have the results been disseminated to communities of interest?Research updates are shared with a packaging coatings manufacturer monthly. A presentation titled "Interactions of food constituents and novel metal can coatings" was made on Thursday, December 12, 2024 for the Ermanoski research group at Arizona State University (virtual). A manuscript titled "In situ electrochemical impedance spectroscopy of non-BPA food contact coatings on electrolytic tinplate under retort conditions" was accepted for publication in Journal of Food Engineering. An abstract titled "Interactions between aggressive food ingredients and novel non-bisphenol A food can coatings" has been submitted to Gamma Sigma Delta, which is an honor society for agriculture and agricultural sciences at Penn State, to present a research poster at the 2025 Research Expo on Thursday, March 27, 2025. This poster will also be presented at the Annual MatSE Poster Competition hosted by the Penn State Department of Materials Science and Engineering, the Graduate Research Exhibition hosted by the Penn State J. Jeffrey and Ann Marie Fox Graduate School on Friday, March 28, 2025, and the Penn State Chapter of Phi Tau Sigma Food Science in Action on Wednesday, April 2, 2025. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
We fabricated a silver/silver chloride reference electrode to perform EIS measurements inside a can during retorting and compared it to a commercial silver/silver chloride reference electrode. We completed a set of experiments using a definitive screening design to identify the main and interaction effects of aggressive food ingredients (acetic acid, citric acid, paprika oleoresin, NaCl, KCl, and sulfur-containing amino acids), as identified by industry, on a legacy BPA-based epoxy phenolic coating (EP) and a non-BPA polyester phenolic coating (PE) after 2 and 7 days of storage in food simulants at 50 °C post-autoclave (121 °C for 30 min). There were 17 experimental conditions, each representing a specific combination of ingredient factor levels. We performed EIS on polymer-coated tinplate samples before and after autoclaving to compare the corrosion protection performance of the two can coatings exposed to food simulants. The individual and combined effects of coating type and food simulant had a significant effect on the low-frequency impedance modulus from EIS (where higher values represent greater resistance against the flow of ions through coatings) and on the glass transition temperature (Tg) measured by DSC (where a higher Tg generally leads to better barrier properties by restricting the movement of molecules through the coating). Ester linkages, which are not typically present in epoxy phenolic resins but are present in the polyester phenolic coating, are susceptible to hydrolysis degradation, especially when there are acids present to catalyze the reaction, resulting in Tg depression. Paprika oleoresin (PAP) had the largest effect on Tg, plasticizing the coatings and facilitating polymer degradation by acids and salts. In both coating systems, PAP increased the polymer film thickness, as measured by optical profilometry. As a plasticizer, PAP inserts itself between polymer chains, reducing the intermolecular forces and creating more free volume within the polymer matrix that can facilitate the absorption of solvents to result in swelling. The Tg of pristine coatings (i.e., coatings prior to exposure to food simulants) was lower than the Tg of some coatings after the ageing test, suggesting that plasticizers in the coating systems leached into the electrolyte solution after immersion and autoclaving. This is also evidenced by peaks present in solution-state nuclear magnetic resonance (NMR) spectra after autoclaving free films in deionized water. From X-ray fluorescence (XRF) analysis of food simulants during the ageing test, we observed more Fe dissolution at the 7 d time point than at 2 d, as additional time and exposure to food simulants at 50 °C allowed corrosion processes to continue. Acetic acid (AA) and PAP increased Fe dissolution in EP, whereas citric acid (CA) increased Fe dissolution in PE. This suggests the mechanism of polymer degradation leading to corrosion is different between the two coating systems (e.g., compatibility of PAP with the polymer, acid attack, chelating ability of CA, and the tendency of CA to form a passivation film on the metal surface). A manuscript using these data is in preparation. The surface roughness of the coating and metal surfaces was measured using optical profilometry. Sa is the arithmetic mean height used to evaluate surface roughness, with higher values corresponding to greater variations in height across the surface. Sq is the root-mean-square height or standard deviation of heights. In EP, AA and CA decrease Sa, while NaCl increases Sa. AA, PAP, and PRO increase the Sq of the coating, while KCl and NaCl decrease Sq. While the mean height of the peaks and valleys on the coating surface is becoming smaller, the overall variation in height between those peaks and valleys is increasing, indicating a rougher surface texture based on Sq. In PE, AA and PAP increase Sq on the metal surface, where a rougher surface texture may serve as localization sites for oxygen transport to the tinplate, increasing the corrosion rate. AA, CA, their interaction, and PRO affected the pH of the food simulant after the ageing test. This makes sense, as these ingredients can donate protons to the solution to lower the pH. KCl, NaCl, AA, and PAP increases Sn dissolution. There is an interaction effect between CA and PAP, where Sn dissolution is maximized when there is no CA and the highest concentration of PAP. This may be explained by the ability of CA to chelate metal ions near the metal surface and create a protective oxide layer that resists corrosion. In other words, CA may provide protection against corrosion in some food formulations. The interaction between NaCl and AA increases the Cl concentration in the polymer-coated tinplate (i.e., the migration of Cl into the coating). In acidic environments, H+ readily reacts with the metal surface, disrupting the protective oxide layer and allowing Cl- to penetrate more easily, initiating localized corrosion (e.g., pitting corrosion). These results are used to understand the individual and combined effects of food ingredients and their interactions with novel food can coatings.
Publications
- Type:
Peer Reviewed Journal Articles
Status:
Published
Year Published:
2025
Citation:
Stiphany T. Tieu, Elzbieta Sikora, Ali Tuncay Ozyilmaz, Luke A. Wolfe, Helene Hopfer, Gregory R. Ziegler,
In situ electrochemical impedance spectroscopy of non-BPA food contact coatings on electrolytic tinplate under retort conditions,
Journal of Food Engineering,
Volume 395,
2025,
112541,
ISSN 0260-8774,
https://doi.org/10.1016/j.jfoodeng.2025.112541.
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Progress 01/01/23 to 12/31/23
Outputs
Target Audience:Academics (e.g., faculty, students, and staff scientists), can makers, and manufacturers of packaging coatings for metal containers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The graduate student participated in the three-day Can Manufacturing and Processing Course presented by Silgan Containers from May 16 to 18, 2023. The curriculum included background on manufacturing processes, an in-depth discussion from receiving cans to labeling and shipping, and training to develop skills necessary to evaluate the integrity of double seams and their importance to food can safety. The graduate student was trained on several advanced materials characterization techniques available at Penn State: Fourier-transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance spectroscopy (ssNMR), X-ray diffractometry (XRD), and X-ray fluorescence (XRF). FTIR and ssNMR will be used to study polymer degradation in food can coatings after exposure to food simulants. XRD will provide information on the varying corrosion phenomena of the metal substrate (e.g., preferential dissolution of iron or tin on electrolytic tinplate) in response to different food ingredients and based on the oxygen content inside the electrochemical cells. XRF will be used for elemental analysis of coated metal coupons to identify which (if any) food components have migrated into the coatings after exposure. The graduate student was also trained on the autoclaves (or steam sterilizers) in the Media Preparation Room of the Erickson Food Science Building for use as an alternative cooking (or sterilization) method to retorting. On February 28-29, 2024, the graduate student participated in a full audit of the Allpax pilot-scale retort that is housed in the Wet Pilot Plant within the Penn State Department of Food Science.The graduate student attended the Fall 2023 Data Management and Research Reproducibility in R Workshop Series hosted by the Research Informatics and Publishing department at Penn State University Libraries. The series provided hands-on training in fundamental coding skills, data management strategies in R to support research reproducibility, and data visualization. The graduate student also attended the Schreyer Institute's Workshops on "Writing Your Diversity/Diversity, Equity, and Inclusion Statement" on January 30, 2024 and "Writing Your Teaching Philosophy Statement" on January 31, 2024. How have the results been disseminated to communities of interest?Research updates are shared with a packaging coatings manufacturer monthly. A poster presentation titled "In situ electrochemical impedance spectroscopy measurements of organic coatings on food cans under retort conditions" was made on Thursday, October 12th at the 2023 College of Earth and Mineral Sciences Graduate Research Showcase and on Thursday, October 26th at the 2023 Materials Day hosted by Penn State Materials Research Institute. A manuscript titled "In situ electrochemical impedance spectroscopy of organic coatings on electrolytic tinplate under retort conditions" was completed and submitted to Progress in Organic Coatings for publication in a peer-reviewed scientific journal. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we plan to complete experiments using a definitive screening design to investigate the corrosivity of select food ingredients (acids, paprika oleoresin, salts, and sulfur-containing amino acids) and their interactions. These ingredients have been identified to be especially aggressive (or problematic) by anecdata from industry partners and in the literature. We will perform electrochemical impedance spectroscopy (EIS) on coated metal panels before and after retort sterilization to compare the corrosion protection performance of BPA-based epoxy phenolic and BPA-NI polyester phenolic coatings exposed to electrolyte solutions of varying composition. Samples will be evaluated by atomic force microscopy, differential scanning calorimetry, EIS, FTIR, optical profilometry, oxygen sensing, XRD, and XRF coupled at two time points in an accelerated ageing test: 14 d and 28 d after storage in respective food simulant solutions at 50 °C post-retort. Data will be used to probe interactions between food ingredients and food can coatings, specifically the (synergistic) effects of food ingredients and polymer degradation mechanisms. In a different set of experiments, we will simulate the bead patterns on steel food cans using a tube wringer to compare the barrier performance of coated metal panels subjected to mechanical deformation with coated metal flat sheets. We will use characterization techniques discussed previously. In another set of experiments, steel food cans with BPA-based epoxy phenolic and BPA-NI polyester phenolic coatings will be used to investigate the effect of headspace level and oxygen content on degradation and corrosion mechanisms. The cans will be filled to different fill volumes of food simulants. Additionally, we will pull varying amounts of vacuum during can seaming. The cans will be evaluated using the characterization techniques discussed previously.
Impacts
What was accomplished under these goals?
What was accomplished under these goals? We completed the set of experiments using our novel experimental EIS setup (modified pressure canner and paint test cell) and method that was described in a previous report to probe polymer-coated metal samples in situ under retort conditions (121 °C for 90 min, 15 psi). Coated metal panels (BPA-based epoxy phenolic and BPA-NI polyester phenolic coatings with three levels of phenolic loading to control the glass transition temperature) were exposed to 1% NaCl electrolyte solution and evaluated by EIS before, during, and after retorting. Electrochemical impedance measurements were coupled with visual inspection of the coatings at two time points during the accelerated ageing test: 1 and 28 d of storage in 1% NaCl electrolyte solution at 50 °C post-retort. We put together a manuscript titled "In situ electrochemical impedance spectroscopy of organic coatings on electrolytic tinplate under retort conditions" based on the findings from this set of experiments and submitted the manuscript to Progress in Organic Coatings for publication in a peer-reviewed scientific journal. FTIR results comparing pristine versus degraded (retorted then aged in 1% CaCl2 for 28 d at 50 °C post-retort) BPA-NI coatings showed ester hydrolysis may be the polymer degradation mechanism in our accelerated ageing tests. ssNMR spectra for pristine versus degraded (retorted then aged in 1% CaCl2 for 28 d at 50 °C post-retort) BPA-NI coatings showed promise for using this characterization technique to elucidate degradation behavior of hydrothermally-aged food can coatings.
Publications
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Progress 01/01/22 to 12/31/22
Outputs
Target Audience:Academics (e.g., faculty, students, and staff scientists), can manufacturers, and manufacturers of packaging coatings for metal containers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?To thermally process the coated metal samples, the graduate student was trained to operate the Allpax pilot-scale retort that is housed in the Wet Pilot Plant within the Penn State Department of Food Science. In August 2022, the graduate student attended a group demo session for optical profilometry. This was followed by an individual demo session, where the graduate student brought her own sample (corroded coated metal sample) to run on the Keyence VK-X3100 3D Surface Profiler that is housed in the Materials Characterization Lab at Penn State. An undergraduate student researcher was trained on high-performance liquid chromatography and fluorescence spectroscopy to identify and quantify acetic acid and capsaicin that migrate into the coatings from the food simulant. How have the results been disseminated to communities of interest?Presentations were made at the 2022 AFRI Novel Foods and Innovative Manufacturing Technologies Annual Grantees' Conference on July 8, 2022 and to the Can Manufacturers Institute on October 21, 2022. Research updates are shared with a manufacturer in packaging coatings on a monthly basis. An oral presentation was given at the 2022 PPG Elevator Pitch Competition on May 5th. A poster presentation titled In situ electrochemical impedance spectroscopy measurements of organic coatings on food cans under retort conditions was made on October 20-21 at the 2022 Materials Day hosted by Penn State Materials Research Institute. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we expect to complete experiments comparing bisphenol A (BPA)-based epoxy and BPA non-intent (BPA-NI) polyester coatings using the in-situ electrochemical impedance spectroscopy (EIS) setup for a manuscript. This will allow us to characterize changes in the coatings during thermal processing under retort conditions. In consultation with a provider of metal food packaging, we identified a highly problematic (i.e., aggressive) canned food product. We are currently accelerating its degradation/failure by storage at 50 °C. In a month, we will perform a visual inspection of the food cans, determine which food components have migrated into the coating, and characterize the polymer-coated metal system using EIS. These results will be compared to those obtained for the food cans stored at ambient temperature (ca. 21 °C). We plan to use these data to inform food simulant formulations for EIS studies by identifying aggressive food components and generating an understanding of the interaction effects of ingredients. Additionally, we will perform EIS on coated metal samples (BPA-based epoxy and BPA-NI polyester) before and after thermal processing to assess how changes induced during retorting affect the barrier properties of can coatings exposed to different electrolytes. Samples will be monitored and evaluated using EIS coupled with visual inspection for a month at specified intervals. To better represent actual food systems, we will use some combination of a protein cocktail containing cysteine, methionine, and/or taurine; acid (e.g., acetic, citric, and malic), sodium nitrate, sodium thiosulfate, and calcium-magnesium phytate for the electrolyte system. We will control the pH using the acids of interest and develop a protocol to control the oxygen content. We plan to use atomic force microscopy (AFM) and optical profilometry (OP) to characterize the surface roughness and visualize the surface morphology of coated metal samples exposed to the different electrolytes and to retort processing.
Impacts
What was accomplished under these goals?
What was accomplished under these goals? We carried out in situ EIS measurements under retort conditions using the pressure canner and paint test cell (PTC) we modified. We successfully obtained impedance data on corroding and degrading coated metal samples. The in-situ setup was updated to allow for thicker feedthrough wires that are properly shielded and insulated to minimize errors in data collection. Coated metal samples were exposed to 1% NaCl or 1% CaCl2 food simulant solutions, which served as the electrolyte for EIS. We compared impedance data for BPA-based epoxy coatings and BPA-NI polyester coatings with three levels of phenolic loading before and after heating under retort conditions (121 °C for 90 min). Visual inspection was implemented in tandem with EIS to provide kinetic and mechanistic information on coating degradation and underlying corrosion processes. Data obtained with coated metal samples subjected to retorting were compared with those without thermal processing. All samples were incubated at 50 °C over the course of four weeks to accelerate coating degradation/failure. They were evaluated by EIS and visual inspection 0, 1, 2, 5, 7, 14, 21, and 28 days after setting up the PTCs. Differential scanning calorimetry revealed the glass transition temperature (Tg) of BPA-NI polyester coatings was lower than that of the BPA-based epoxy control and increased on increasing phenolic loading. Parameters (e.g., coating capacitance and conductivity) extracted from equivalent circuit models fitted to EIS data showed enhanced corrosion protection performance with increasing glass transition temperature. Additionally, thermal processing of the coated metal samples appeared to improve the corrosion protection performance of coatings (possibly by mode of relaxation of the polymer networks). From the demo session of the Keyence VK-X3100 3D Surface Profiler, we obtained a 3D rendering of a corroded coated metal sample's surface morphology and characterized its surface roughness.
Publications
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Progress 01/01/21 to 12/31/21
Outputs
Target Audience:Graduate students, can manufacturers, and can coating manufacturers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The graduate student spent one week on-site at an industrial partners site learning how to maufacture and characterize coated metal samples. The co-investigators and the graduate student have visited can manufacturing sites and coating manufacturers research facilities to learn of significant practical problems. How have the results been disseminated to communities of interest?One presentation was made to the Can Manufacturers Institute on October 6, 2021. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we expect to have the in-situ EIS setup operational. This will allow us to characterize changes in the coatings during thermal processing. Additionally, we will perform EIS on coated metal samples before and after thermal processing to assess how changes induced during retorting affects the barrier properties of can coatings in contact with different electrolytes. To better represent actual food systems, we will add complexity to the electrolyte by adding other salts in EIS experiments. In the next phase of our study, we aim to develop a fundamental understanding of the different types of corrosion mechanisms caused by the food matrices and simulants of interest in response to different coating formulations to characterize the interactions between food components, the polymer linings, and the metal substrates.
Impacts
What was accomplished under these goals?
We set up our electrochemical impedance spectroscopy (EIS) equipment and developed testing methodology to test coated metal samples. We worked with an industry partner to prepare coated metal flat sheets for EIS testing, from coating formulation to application to performance testing. We started EIS testing of samples with different types of coatings (varying polymer systems and glass transition temperatures) and different metal substrates (electrolytic tinplate and tin free steel) to characterize intact coatings and coatings with defects using equivalent circuit modeling. We introduced defects, either superficial scribes or those exposing the metal substrate, to determine their effects on the EIS response. Working with our industry partners, we narrowed down aggressive commercial food products (i.e., those most likely to induce corrosion in food cans) to simulate and to use as the electrolyte in EIS experiments. We plan to start with food simulants, specifically 1% brine, before systematically adding complexity to account for real food systems. The graduate student has learned and developed methodology for materials characterization, including differential scanning calorimetry to determine thermal transitions in polymeric materials (e.g., glass transition) and scanning electron microscopy to examine coating surfaces on the nanoscale. We designed and built a setup (autoclavable electrochemical cell and pressure canner) for EIS testing under retort conditions (121 C, 15 psi, 90 min) to monitor changes in the coating in-situ.
Publications
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