Determination of Diffusion Coefficients of Bisphenol A (BPA) in Polyethylene Terephthalate (PET) to Estimate Migration of BPA from Recycled PET into Foods

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The research manuscript written Mladen Juric, Roland Franz and Frank Welle outlines the determination of diffusion coefficients of bisphenol A in polyethylene terephthalate (PET) to estimate migration of bisphenol A from recycled PET into foods. It is a study of great significance and relevance to our daily lives.

In overall, the manuscript is well-written and organized, with an applicable experimental design and methodology. Furthermore, the formatting of the experimental data is helpful. However, I noticed a lack of comparison with already published studies. This summarized information might even be included in support materials, but there must be an argument in the text for this analysis.

The article's weakest part is the characterization of used PET bottle samples. There is no information about chemical and physical characteristics that distinguish different PET bottle batches. The authors might complete their study by given for further information about bottles chemical or physical characterization. There are a lot of characterization techniques that could help for this propose, such as: NMR, ss-NMR, FTIR, and TGA, and even Mechanical properties such as tensile strength or elongation.

The migration kinetics of bisphenol A is extensive and well-presented. Several criteria were investigated, including diffusion coefficients and activation energies of diffusion, and migration modelling on statistical analysis.

I recommend this work for acceptance, but I believe that some relevant points should be clarified and completed prior to acceptance:

1. Is it possible to provide further information about used PET bottles chemical or physical characterization? The authors didn’t make effective use of the Supplementary Material. Further data should be included herein, such as providing extensive NMR, FTIR, and TGA figures and detailed discussion for sample characterization.

2. Line 164. More information should be provided about the 50 bottles made from low-quality recycled PET? What is meant by "low quality"? What chemical and physical characteristics distinguish these two batches (good vs low quality)?

3.     Were the bottle samples all colorless?

4.    The study of different solvents and temperatures is quite complete. However, a few additional criteria could have been explored. What is the effect of UV/Vis radiation-induced degradation?

Author Response

Reviewer 1

The research manuscript written Mladen Juric, Roland Franz and Frank Welle outlines the determination of diffusion coefficients of bisphenol A in polyethylene terephthalate (PET) to estimate migration of bisphenol A from recycled PET into foods. It is a study of great significance and relevance to our daily lives.

In overall, the manuscript is well-written and organized, with an applicable experimental design and methodology. Furthermore, the formatting of the experimental data is helpful. However, I noticed a lack of comparison with already published studies. This summarized information might even be included in support materials, but there must be an argument in the text for this analysis.

The article's weakest part is the characterization of used PET bottle samples. There is no information about chemical and physical characteristics that distinguish different PET bottle batches. The authors might complete their study by given for further information about bottles chemical or physical characterization. There are a lot of characterization techniques that could help for this propose, such as: NMR, ss-NMR, FTIR, and TGA, and even Mechanical properties such as tensile strength or elongation.

The migration kinetics of bisphenol A is extensive and well-presented. Several criteria were investigated, including diffusion coefficients and activation energies of diffusion, and migration modelling on statistical analysis.

I recommend this work for acceptance, but I believe that some relevant points should be clarified and completed prior to acceptance:

Response of the authors: Thank you very much for this valuable review.

 

1. Is it possible to provide further information about used PET bottles chemical or physical characterization? The authors didn’t make effective use of the Supplementary Material. Further data should be included herein, such as providing extensive NMR, FTIR, and TGA figures and detailed discussion for sample characterization.

Response of the authors: The PET bottles analyzed were all commercial materials that entered the European market during the period under investigation. These are commercially available PET materials. No characterization was carried out, as this would have no influence on the project results. In particular due to the very large number of samples (375 samples), the effort involved would have been very high. Unfortunately, most of the samples are no longer available because most of them were analyzed some years ago. As an accredited testing laboratory, the samples only have to be stored for 6 months. Subsequent measurements are therefore no longer possible. A paragraph on the sample materials would be included in the manuscript.

2. Line 164. More information should be provided about the 50 bottles made from low-quality recycled PET? What is meant by "low quality"? What chemical and physical characteristics distinguish these two batches (good vs low quality)?

Response of the authors: "Low quality" means a recyclate with a very high concentration of BPA. "Low quality" is indeed not a good description of the material used. The paragraph has been changed accordingly.

3. Were the bottle samples all colorless?

Response of the authors: The majority of the bottles were clear, but also green or blue. No influence of the colors on the result of the bisphenol A concentrations was found. The paragraph was supplemented with regard to the colors of the PET bottles.

4. The study of different solvents and temperatures is quite complete. However, a few additional criteria could have been explored. What is the effect of UV/Vis radiation-induced degradation?

Response of the authors: The bottles were analyzed before they came onto the market. The analyzed samples were therefore not exposed to UV radiation. An influence of UV radiation on the results or on the degradation can therefore be ruled out. The paragraph was supplemented with the note that the samples were analyzed before the bottles were placed on the market.

Reviewer 2 Report

Comments and Suggestions for Authors

The research article titled "Determination of diffusion coefficients of bisphenol A (BPA) in polyethylene terephthalate (PET) to estimate migration of BPA from recycled PET into foods" primarily addresses the critical issue of BPA contamination in food contact materials, particularly focusing on recycled PET (rPET). The study is significant as it measures the precise diffusion coefficients for BPA in PET and applies migration modeling to predict BPA concentrations, which is crucial given the stringent new limits proposed by the European Food Safety Authority (EFSA).

One of the original contributions of this paper is the detailed quantification of BPA diffusion coefficients and the activation energies of diffusion in different food simulants. This data is not readily available in the existing literature, making it a valuable addition. Moreover, the study's use of migration modeling to establish maximum allowable BPA concentrations in rPET under different conditions fills a significant gap. This approach is particularly relevant given the analytical challenges posed by the new, extremely low TDI (tolerable daily intake) set by EFSA.

The research adds substantial value to the subject area by providing a methodology that combines experimental data with predictive modeling. This methodology not only helps in assessing compliance with new regulatory limits but also aids in understanding the migration behavior of BPA from rPET into foods under various storage conditions. Compared to other published material, this study offers a robust framework for indirectly controlling BPA levels in PET by focusing on measurable concentrations in the material itself rather than in the food.

However, the methodology could be improved in several ways. Firstly, the authors should consider increasing the number of samples and replicates to ensure more statistically significant results. Additionally, further controls should include a broader range of temperatures and storage durations to better simulate real-world conditions. Including a comparison with more types of food simulants and actual food products would also strengthen the study's applicability.

The tables and figures in the paper are clear and well-organized, providing a comprehensive view of the data. The quality of the data appears to be high, supported by rigorous analytical methods. However, the number of references is relatively low, and the authors should consider citing more studies to better contextualize their findings and confront their results with existing literature.

The conclusions of the paper are generally consistent with the evidence presented. The experimental data on diffusion coefficients and migration kinetics align well with the predictive models used. However, the study could benefit from a clearer discussion on the variability observed in BPA concentrations among different rPET samples and how this impacts overall migration predictions.

In summary, while the study is a valuable contribution to the field of food safety and material science, there are areas for improvement. Enhancing the robustness of the methodology and expanding the range of conditions tested would provide a more comprehensive understanding of BPA migration from rPET. Increasing the number of references would also bolster the credibility and depth of the study. Overall, this paper provides critical insights but could be strengthened by addressing these suggestions.

Comments on the Quality of English Language

The quality of English in the manuscript is generally good but can be improved for better clarity and readability. Ensure consistent terminology and correct minor grammatical errors. Simplify complex sentences, explain technical jargon briefly when first introduced, and improve transitions between sections. Using active voice and avoiding redundancies will make the text more engaging. Clear and concise descriptions for figures and tables are also recommended. Overall, these adjustments will enhance the manuscript's communication and readability.

Author Response

Reviewer 2

The research article titled "Determination of diffusion coefficients of bisphenol A (BPA) in polyethylene terephthalate (PET) to estimate migration of BPA from recycled PET into foods" primarily addresses the critical issue of BPA contamination in food contact materials, particularly focusing on recycled PET (rPET). The study is significant as it measures the precise diffusion coefficients for BPA in PET and applies migration modeling to predict BPA concentrations, which is crucial given the stringent new limits proposed by the European Food Safety Authority (EFSA).

One of the original contributions of this paper is the detailed quantification of BPA diffusion coefficients and the activation energies of diffusion in different food simulants. This data is not readily available in the existing literature, making it a valuable addition. Moreover, the study's use of migration modeling to establish maximum allowable BPA concentrations in rPET under different conditions fills a significant gap. This approach is particularly relevant given the analytical challenges posed by the new, extremely low TDI (tolerable daily intake) set by EFSA.

The research adds substantial value to the subject area by providing a methodology that combines experimental data with predictive modeling. This methodology not only helps in assessing compliance with new regulatory limits but also aids in understanding the migration behavior of BPA from rPET into foods under various storage conditions. Compared to other published material, this study offers a robust framework for indirectly controlling BPA levels in PET by focusing on measurable concentrations in the material itself rather than in the food.

Response of the authors: Thank you very much for this valuable review.

However, the methodology could be improved in several ways. Firstly, the authors should consider increasing the number of samples and replicates to ensure more statistically significant results.

Response of the authors: We analyzed a total of 375 PET bottles over 5 years. This should be statistically significant. For the kinetics, three samples per kinetic point were broad in contact with the simulant. The concentration in the migration solutions was then measured twice per migration solution using HPLC. The six values were then averaged and the standard deviation determined. This is also a typical approach for migration kinetics which is typically considered statistically significant. This information has been added to the manuscript

Additionally, further controls should include a broader range of temperatures and storage durations to better simulate real-world conditions. Including a comparison with more types of food simulants and actual food products would also strengthen the study's applicability.

Response of the authors: The maximum temperature that is possible with dichloromethane (40 °C) was used for the extraction. The extraction was exhaustive. Further temperatures are therefore not required for the extraction of the PET bottles. Four temperatures between 30 °C and 60 °C were used for the migration kinetics. Below 30 °C the migration is very slow, so that the concentrations of BPA are below the detection limits and therefore no diffusion coefficient can be determined. The glass transition temperature of PET is between 60 and 70 °C. Therefore, 60 °C was chosen as the highest temperature for the migration experiments. Four temperatures were chosen to show that the Arrhenius plot is linear. Diffusion coefficients at other temperatures can therefore be predicted from the activation energies of diffusion. No changes were made in manuscript regarding this point.

The tables and figures in the paper are clear and well-organized, providing a comprehensive view of the data. The quality of the data appears to be high, supported by rigorous analytical methods. However, the number of references is relatively low, and the authors should consider citing more studies to better contextualize their findings and confront their results with existing literature.

Response of the authors: To the best of our knowledge, we have cited all scientific papers on bisphenol A in PET. Bisphenol A appears in many publications, also in connection with beverages in PET bottles. However, most publications have not quantified BPA in PET. It is therefore unclear where the BPA in beverages comes from. BPA is ubiquitous and can enter the beverage via many contamination routes. Therefore, only the relevant publications that have quantified BPA in PET were analyzed. Citing other studies that have not quantified BPA in PET does not provide any additional knowledge and would only dilute the results of the study. Nevertheless, we have added some publications.

The conclusions of the paper are generally consistent with the evidence presented. The experimental data on diffusion coefficients and migration kinetics align well with the predictive models used. However, the study could benefit from a clearer discussion on the variability observed in BPA concentrations among different rPET samples and how this impacts overall migration predictions.

Response of the authors: With the BPA concentrations, we wanted to provide an overview of how much BPA can be determined in beverage bottles via the recycling of PET bottles. As expected, the concentrations in the 375 bottles analyzed show a broad variation. Under given migration conditions, the migration of BPA into the beverage is directly proportional to the concentration of BPA in the PET bottle wall. In order to minimize the migration of BPA, the concentration in the bottle wall can therefore be minimized. This paragraph was added to the manuscript.

In summary, while the study is a valuable contribution to the field of food safety and material science, there are areas for improvement. Enhancing the robustness of the methodology and expanding the range of conditions tested would provide a more comprehensive understanding of BPA migration from rPET. Increasing the number of references would also bolster the credibility and depth of the study. Overall, this paper provides critical insights but could be strengthened by addressing these suggestions.

Response of the authors: We have tested the migration conditions and simulants typical for PET beverage bottles. Extending the contact conditions does not provide any insight into the migration of BPA from PET bottles into beverages. The use of 50% ethanol and 95% ethanol as simulants, for example, leads to changes in the PET due to swelling so that diffusion coefficients can no longer be determined. Therefore, these simulants were not used in our study.

 

 

Comments on the Quality of English Language

 

The quality of English in the manuscript is generally good but can be improved for better clarity and readability. Ensure consistent terminology and correct minor grammatical errors. Simplify complex sentences, explain technical jargon briefly when first introduced, and improve transitions between sections. Using active voice and avoiding redundancies will make the text more engaging. Clear and concise descriptions for figures and tables are also recommended. Overall, these adjustments will enhance the manuscript's communication and readability.

Response of the authors: These are very general references without specific cases. It is therefore difficult to go into these points in detail.