Styrene Migration from Polystyrene for Food Contact: A Case Study on the Processing Chain of Yoghurt Pots

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents a case study along the processing chain of yoghurt pots and the migration of styrene. This is one more work to be published on the topic of Styrene Migration from Polystyrene for Food Contact, within which the authors have published several articles. The manuscript is acceptable but before accepted, it needs to be complemented with some information that I did not find in the document.   

 

Line 128. Justify why the 40°C/10 days condition was used if the real contact of yoghurt with pots is under refrigerated conditions. Authors mentioned that the conventional food simulant and test conditions specified in Regulation (EU) No 10/2011 for refrigerated dairy products is 50% ethanol for 10 days at 40 °C; however, this information was not found in the Regulation document. Please, specify where it is stated that.  Authors commented that this condition includes hot-fill simulation.  If yoghurt is hot-fill packed, inform the filling temperature industrially used for that stage. Later in the manuscript (line 380), authors discussed about “obtaining an unrealistically high migration levels” at this condition, which from my point of view, was something expected.

Regarding the 20% ethanol food simulant, it is not among the recommended for testing yoghurt in Regulation (EU) No 10/2011. It also needs a more solid justification.

Also, why the 3% acetic acid food simulant (established in the Regulation 10/2011) was not used if the yoghurt pH is lower than 4.5? Discuss the reported effect of acidic conditions on the migration of styrene from PS.

 Figure 1. Add standard deviation data to the bars.

Line 298. It seems that droop is not the proper word to express a decrease in migration. Verify.

Author Response

Comment 1.: The manuscript presents a case study along the processing chain of yoghurt pots and the migration of styrene. This is one more work to be published on the topic of Styrene Migration from Polystyrene for Food Contact, within which the authors have published several articles. The manuscript is acceptable but before accepted, it needs to be complemented with some information that I did not find in the document.   

Line 128. Justify why the 40°C/10 days condition was used if the real contact of yoghurt with pots is under refrigerated conditions. Authors mentioned that the conventional food simulant and test conditions specified in Regulation (EU) No 10/2011 for refrigerated dairy products is 50% ethanol for 10 days at 40 °C; however, this information was not found in the Regulation document. Please, specify where it is stated that.  Authors commented that this condition includes hot-fill simulation.  If yoghurt is hot-fill packed, inform the filling temperature industrially used for that stage. Later in the manuscript (line 380), authors discussed about “obtaining an unrealistically high migration levels” at this condition, which from my point of view, was something expected.

Regarding the 20% ethanol food simulant, it is not among the recommended for testing yoghurt in Regulation (EU) No 10/2011. It also needs a more solid justification.

Also, why the 3% acetic acid food simulant (established in the Regulation 10/2011) was not used if the yoghurt pH is lower than 4.5? Discuss the reported effect of acidic conditions on the migration of styrene from PS.

 Figure 1. Add standard deviation data to the bars.

Line 298. It seems that droop is not the proper word to express a decrease in migration. Verify.

Answers to Reviewer 1

Thank you for your positive opinion. Complementary information is given below and added in the manuscript.

Line 128. According to the Regulation (EU) 10/2011, migration experiments shall be performed tak-ing into account the most severe contact conditions of the material with food under foreseeable conditions of use (time/temperature conditions). The representative conditions shall be taken from Annex III, Table 2 (selection of proper food simulant) and Annex V (time/temperature conditions) of the Regulation. Therefore in this study, we used simulant D1 (50% ethanol), specified for yoghurt (ref. food category N. 07.02 in Table 2 of Annex III). As regard the temperatures industrially used for the production and filling of yoghurt, we described them in our previous paper (Foods, 2022. DOI 10.3390/foods11142120): in case of stirred yoghurt the temperature of contact between the PS containers and the yogurt does not exceed 20 °C in the first hours after packaging and remain below 5 °C during shelf life ( approx. 40 days); in case of set yogurt the fermentation process is made in the filled pot at approx. 40 °C for 8 h, after this it is cooled down at 5 °C and stored as the stirred yoghurt. We used the condition 10 days at 40 °C for testing which according Regulation 10/2011 (Annex V, chapter 2.1.4 (b)) shall cover all storage times at refrigerated and frozen conditions including hot-fill conditions and/or heating up to 70 °C ≤ T ≤ 100 °C for maximum t = 120/2^ ((T-70)/10) minutes.
These explanations were added in the manuscript.

Regarding the use of 20% ethanol food simulant, the Reviewer asks a more solid justification. We added the following:
According Regulation 10/2011 (Annex III) 20% ethanol (food simulant C) shall be  used for alcoholic foods with an alcohol content of up to 20 % and those foods which contain a  relevant amount of organic ingredients that render the food more lipophilic. While, 50% ethanol (food simulant D1) shall be used for alcoholic foods with an alcohol content of above 20% and for oil in water emulsions, including milk product (see Annex III Table 2 and 3 of the Regulation). However, for some substances listed in Annex I, Table 1 additional rules are given (column 11) that shall be respected on situations where there is a risk of non-compliance. Among these, the notes on verification of compliance N.22 states that “when used in contact with non-alcoholic foods for which Table 2 of Annex III assigns food simulant D1, food simulant C shall be used for verification of compliance instead of food simulant D1”. This recommendation followed an EFSA Scientific Opinion (https://doi.org/10.2903/j.efsa.2014.3866), in which it was noted when the compliance of polyethylene furanoate (PEF) polymer is verified with food simulant D1 in accordance with the food simulant assignments in Table 2 of Annex III, there is a risk of interaction between this food simulant and the plastic. As this interaction would not occur in contact with the non-alcoholic foods for which this food simulant is assigned, the use of food simulant D1 for verification of compliance would give unrealistic results in such cases. According to the Authority, therefore, when verifying whether the use of this substance complies with this Regulation, food simulant C should be used for non-alcoholic foods to which Table 2 of Annex III assigns food simulant D1.

Regarding the 3% acetic acid food simulant. it was not used in the present study, we added following explanations:
According Regulation 10/2011 (Annex III) the food simulant 3% acetic acid shall be used for those foods which have a pH below 4.5 (including milk product). Since this work focus on the specific migration of styrene the 3% acetic acid food simulant was not used. In fact, according chapter 5 of Annex III of the Regulation, by derogation from the assignments of food simulants, where testing with several food simulants is required, a single food simulant shall be sufficient if on the basis of evidence acquired using generally recognised scientific methods this food simulant is shown to be the most severe food simulant for the particular material or article being tested. Styrene, with a Log Kow of 2.95 dissolves only slightly in water. Contrary, it is soluble in alcohol. In the scientific Literature  is also reported that testing styrene migration from PS employing aqueous food simulants lead to under-estimation of the migration processes occurring in real food products, for example by :
-Till D. E., Ehntholt, D. J., Reid, R. C., Schwartz, P. S, Sidman, K. R., Schwope, A. D., & Whelan, R. H. Migration of styrene monomer from crystal polystyrene to foods and food simulating liquids. Ind. Eng. Chem. Prod. Res. Dev. 1982, 21, 161-168. https://doi.org/10.1021/i100006a010Murphy, P.G.; Macdonald, D.A.; Lickly, T.D. Styrene Migration from General Purpose and High Impact Polystyrene into Food Simulating Solvents. Food Chem. Toxicol. 1992, 30, 225–232.
-Choi, J.O.; Jitsunari, F.; Asakawa, F.; Sun Lee, D. Migration of styrene monomer, dimers and trimers from polystyrene to food simulants. Food Addit. Contam. 2007, 22, 693–699.
-Amirshaghaghi, Z.; Emam Djomeh, Z.; Oromiehie, A. Studies of Migration of Styrene Monomer from Polystyrene Packag-ing into the Food Simulant. Iran. J. Chem. Eng. 2011, 8, 43-49.
-Dawson, P.; Seydim, A.C.; Hirt, D. Styrene Monomer Migration from Expanded Polystyrene into Food Acids and Ethanol. J. Food Res. 2020, 9.
-Aja, A.; J’Bari, S.; Ononogbo, A.; Buonocore, F.; Bear, J.C.; Mayes, A.G.; Morgan, H. An Insight into the Growing Concerns of Styrene Monomer and Poly(Styrene) Fragment Migration into Food and Drink Simulants from Poly(Styrene) Packaging. Foods 2021, 10, 1136. https://doi.org/10.3390/foods10051136.

Figure 1. standard deviation data to the bars were added

Line 298. corrected

Reviewer 2 Report

Comments and Suggestions for Authors

It is important to ensure that food contact materials (FCM) comply with applicable legal requirements at every stage of the supply chain. However, the methods involved in the relevant standards usually use "simulants" to describe the migration of the hazard. The manuscript uses five general purpose polystyrene (GPS-1, GPS-2, GPS-3, HS-1, HS-2) and three types of thermoformed tanks (PS-P-11, PS-P-22, PS-P-32) as target samples. The residue level and migration of styrene monomer in polystyrene packaging materials from food contact materials to food simulants and real yogurt foods were studied. The paper studies the migration of food contact materials in actual food, which is very meaningful.

However, there are still some problems with this manuscript, as follows:

1. The introduction to the European Commission's Regulation (EU) 10/2011 on Plastics in contact with Food, currently revised (EU) 2023/1442), should provide a detailed description of this situation.

2. The detection of styrene uses GC-FID, Headspace GC-FID, P&T GC, and dynamic headspace (purge & trap) GC-MS, and relevant chromatographic diagrams should be added to the document.

3. The sample material is characterized by scanning electron microscope (SEM), and the electron microscope characterization diagram should be added to the document.

4. There is a situation that the GC-FID analysis method cannot detect the styrene concentration below 0.1ppm. If this situation is encountered, how to deal with it?

5. The extraction solvents of styrene are dichloromethane, methanol, ethyl acetate and acetone, etc., but only acetone was used in this paper. The comparison results of the extraction effect of different solvents on styrene should be increased.

6. The extraction methods of styrene in polystyrene materials include solution-headspace method and solution-precipitation method, etc. In order to verify the feasibility of the method, the recovery experiment is essential.

Comments on the Quality of English Language

Minor editing of English language required.

Author Response

Review Report (Reviewer 2)

It is important to ensure that food contact materials (FCM) comply with applicable legal requirements at every stage of the supply chain. However, the methods involved in the relevant standards usually use "simulants" to describe the migration of the hazard. The manuscript uses five general purpose polystyrene (GPS-1, GPS-2, GPS-3, HS-1, HS-2) and three types of thermoformed tanks (PS-P-11, PS-P-22, PS-P-32) as target samples. The residue level and migration of styrene monomer in polystyrene packaging materials from food contact materials to food simulants and real yogurt foods were studied. The paper studies the migration of food contact materials in actual food, which is very meaningful. However, there are still some problems with this manuscript, as follows:

1. The introduction to the European Commission's Regulation (EU) 10/2011 on Plastics in contact with Food, currently revised (EU) 2023/1442), should provide a detailed description of this situation.
2. The detection of styrene uses GC-FID, Headspace GC-FID, P&T GC, and dynamic headspace (purge & trap) GC-MS, and relevant chromatographic diagrams should be added to the document.
3. The sample material is characterized by scanning electron microscope (SEM), and the electron microscope characterization diagram should be added to the document.
4. There is a situation that the GC-FID analysis method cannot detect the styrene concentration below 0.1ppm. If this situation is encountered, how to deal with it?
5. The extraction solvents of styrene are dichloromethane, methanol, ethyl acetate and acetone, etc., but only acetone was used in this paper. The comparison results of the extraction effect of different solvents on styrene should be increased.
6. The extraction methods of styrene in polystyrene materials include solution-headspace method and solution-precipitation method, etc. In order to verify the feasibility of the method, the recovery experiment is essential.

Answers to Reviewer 2

Thank you for your positive opinion. Complementary information is given below and added in the manuscript.

1. We added a more detailed description on the requirements of Regulation 10/2011 in the introduction in lines 44-80 and lines 294-347.
2. Relevant chromatograms (exemplary) were added in the supplementary materials for the detection of styrene with: a. GC-FID (in acetone extracts of the PS materials), b. HS GC-FID (in 20% and 50% food simulants), c. dynamic headspace (purge & trap) GC-MS (in yoghurt after migration experiment)
3. The SEM pictures were given in the supplementary material as separate images (in order to guarantee optimal resolution).
4. A detection limit of 0.1 ppm correspond to 100 ppb. Currently, a precautionary specific migration limit for styrene of 40 ppb has been proposed by the EU Commission. Therefore an analytical method with a detection limit of 0.1ppm would not be considered suitable for the purpose. The GC-FID method used in our study for analysis of the food simulants has a detection limit of 1.3 ppb in 20% ethanol and of 3.2 ppb in 50% ethanol. We added these data in the manuscript (see section methods).

5.and6. In a previous paper we reported about recovery experiments of different model substances (including styrene and styrene oligomers) using the extraction method with acetone. Additionally we tested different methods for the extraction of styrene in polystyrene materials including solution-headspace method, solution-precipitation method, swelling; according our results, the swelling method using acetone is enough exhaustive. We added these considerations in the present manuscript (see section methods).

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript reports about the gas chromatographic (GC) determination of the quantity (micrograms/kg) of monomer (styrene) released from commercial polystyrene (PS) blends used for food packaging. In particular, the tested polymeric blends consisted of high impact polystyrene (HI-PS) and general purpose polystyrene (GP-PS) mixtures, recovered at different processing stages (i.e., extruded sheets and thermoformed pots). Water-ethanol (i.e., 20% ethanol and 50% ethanol) and yoghurt have been used as food simulants. The PS blends were exposed to ethanol/H₂O food simulants for 10 days at 20°C and 40°C and to yoghurt for 50 days at 8°C. Such food simulant conditions have been selected according to the EU plastic regulation. The total amount of monomer in the thermoformed pots, extruded sheets and the two types of pellets has been extract by acetone and chromatographically determined, as shown in Table 1. The GC determinations in food simulants are given in Table 2 and compared in a cumulative histogram (see Figure 1). Monomer release in yoghurt from extruded sheets resulted higher than from the thermoformed pots.

This manuscript does not constitute a real scientific study but it is a sort of technical report concerning a product of the plastics industry. The study is aimed uniquely to establish the plastic material capability to exceed the European regulations in terms of migration of styrene monomer into food simulants. Also the Reference Section is mostly a list of European regulations about plastic materials and articles intended to come into contact with food. In addition, the commercial material described in this report is actually unknown because for confidentiality reasons, the Company name that provided the PS samples is not given; therefore, the provided information is of no practical use for readers. Although the very lengthy Discussion Section (rich of obvious considerations) and Introduction Section, very few data are provided, indeed the Results Section is extremely short (only few lines) and all presented data are in one histogram (Table 2 contains the same experimental data of the histogram in Figure 4 with standard deviations). Useless SEM-micrographs of the scratches present on the surfaces of extruded and thermoformed samples are also provided in the Supplementary Material. Finally, this technical report does not satisfy the minimal requirements of a scientific investigation and cannot be accepted for publication in a scientific journal.

Author Response

Review Report (Reviewer 3)

The manuscript reports about the gas chromatographic (GC) determination of the quantity (micrograms/kg) of monomer (styrene) released from commercial polystyrene (PS) blends used for food packaging. In particular, the tested polymeric blends consisted of high impact polystyrene (HI-PS) and general purpose polystyrene (GP-PS) mixtures, recovered at different processing stages (i.e., extruded sheets and thermoformed pots). Water-ethanol (i.e., 20% ethanol and 50% ethanol) and yoghurt have been used as food simulants. The PS blends were exposed to ethanol/H2O food simulants for 10 days at 20°C and 40°C and to yoghurt for 50 days at 8°C. Such food simulant conditions have been selected according to the EU plastic regulation. The total amount of monomer in the thermoformed pots, extruded sheets and the two types of pellets has been extract by acetone and chromatographically determined, as shown in Table 1. The GC determinations in food simulants are given in Table 2 and compared in a cumulative histogram (see Figure 1). Monomer release in yoghurt from extruded sheets resulted higher than from the thermoformed pots.

This manuscript does not constitute a real scientific study but it is a sort of technical report concerning a product of the plastics industry. The study is aimed uniquely to establish the plastic material capability to exceed the European regulations in terms of migration of styrene monomer into food simulants. Also the Reference Section is mostly a list of European regulations about plastic materials and articles intended to come into contact with food. In addition, the commercial material described in this report is actually unknown because for confidentiality reasons, the Company name that provided the PS samples is not given; therefore, the provided information is of no practical use for readers. Although the very lengthy Discussion Section (rich of obvious considerations) and Introduction Section, very few data are provided, indeed the Results Section is extremely short (only few lines) and all presented data are in one histogram (Table 2 contains the same experimental data of the histogram in Figure 4 with standard deviations). Useless SEM-micrographs of the scratches present on the surfaces of extruded and thermoformed samples are also provided in the Supplementary Material. Finally, this technical report does not satisfy the minimal requirements of a scientific investigation and cannot be accepted for publication in a scientific journal.

Answers to Reviewer 3

Thank you for your opinion.

We strongly disagree on the comment stating that our manuscript does not constitute a real scientific study but it a sort of technical report concerning a product of the plastics industry aimed uniquely to establish the plastic material capability to exceed the European regulations in terms of migration of styrene.
Oppositely, we think that our paper is an interesting case study from the perspective of it showing the challenges in measuring styrene migration around the proposed 40ppb level (an analytical challenge) and that there are many factors that may influence actual migration levels measured at different stages within the supply chain of FCMs (which is relevant for the different stakeholders).
Styrene has been classified by EFSA in 2020 into the ‘high priority group’, a list of substances to be re-evaluated in order to determine whether a specific migration limit is required and, following this, a precautionary specific migration limit of 40 ppb has been proposed by the EU Commission. The Authority (EFSA) is currently evaluating available studies to exclude a concern over the genotoxicity potential of styrene in plastic FCMs and the publication of a scientific opinion is expected in summer 2024. The styrene SML is expected in one of the next Amendments of Regulation 10/2011, in 2024 or 2025. Therefore, the topic of our paper is actual and important. In addition, EFSA noted in a recent assessment  (https://doi.org/10.2903/j.efsa.2020.6247) that when the compliance of PS polymers is verified with food simulants (especially 50% ethanol), there is a risk of interaction between this food simulant and the plastic. As this interaction would not occur in contact with the non-alcoholic foods, the use of food simulants for verification of compliance would give unrealistic results in such cases. Because of these findings, the EC currently proposes to demonstrate compliance of styrene, testing in food instead of simulants. For this, analytical methods shall be developed and assessed in terms of reliability and sensitivity. For the Industry (from the resins producers to the converters and the food industry, like dairy producers), which normally tests the material using simulants, this is a big task and causes uncertainty about the applicable methods. Scientific information on the suitable analytical methods to test compliance of styrene is necessary. Therefore, the topic studied in our work which focus on actual migration levels measured at different stages within the supply chain of FCMs (in simulants and as comparisons in real food) is relevant and interesting for the different stakeholders.

Regarding the Reference Section, we strongly disagree on the negative comment stating that it is mostly a list of European regulations about plastic materials and articles intended to come into contact with food. In fact, we listed the relevant EU Regulations (3 in total) as background information and different scientific article (total of 25) which specifically deal with the migration of styrene from PS in food simulants and foods.

Regarding the comment on the sample material studied, we disagree that the provided information is of no practical use for readers. Commercial names are not reported (as in many scientific publications for confidentiality reasons) because the aim of the study was not to report on specific materials properties, but to look at different materials which are widespread used for the manufacturing of FCMs, particularly in this case for dairy product packaging. They were provided by the Styrenics Steering Committee of Plastics Europe (which is one of the leading European trade associations and represent the majority of the production capacity of PS) in order to be representative of standard industrial materials used in the European market for food contact applications. Not only one material was investigated but, five types of pellets, three types of extruded sheets and three types of thermoformed pots (manufactured by two different converters).

About the comment on the Results Section (extremely short) and all presented data are in one histogram: We follow the instruction for authors for this journal, according which this section should provide a concise and precise description of the experimental results. We discuss the results and how they can be interpreted from the perspective of previous studies and of the working hypotheses in the section Discussion. The findings and their implications were discussed in the broadest context possible.  In the revised version of the manuscript we add one table (Table 3) and one figure (Figure 2) extending the interpretation of the results related to the relative migration of styrene.

About the comment on useless SEM-micrographs: Microscopy was tentatively used in order to explain the difference observed in the monomer release from sheets and pots, even if no clear explanations could be obtained, these results shall be shown and we discuss the possibility to use further analytical techniques to better identify the morphological differences of the materials..

About the comment on the very few data provided and on the conclusions that our paper does not satisfy the minimal requirements of a scientific investigation and cannot be accepted for publication in a scientific journal. We believe that, even if our work does not report results of a long basic research study, it is original, concise and effectively conveys our findings. According to the roadmap for EU FCM policy revision, recently published by the EU Commission’s DG SANTE, the assessment of FCM shall better address the safety of the final product and the exchange of information across the supply chain shall be improved. To the knowledge of the authors, no literature data is available on migration levels measured at different stages along the processing chain of yoghurt pots (especially with a focus on styrene). Therefore, our research findings, even if no extensive, are original, relevant and interesting for the different stakeholders. In conclusions, in our case study, we used scientific methods and knowledge to attain practical information related to the specific topic of chemicals migration from plastic FCMs. For this reasons we believe that our paper satisfy the requirements of a scientific investigation and shall be accepted for publication in the journal “Applied Science” special Issue “Analysis of Migrating Chemicals and Residues from Plastic, Bioplastic and Recycled Food Contact Materials (FCM) in Food Matrices”.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The author has revised the manuscript one by one as required. However, there is still a problem that extracts in headspace GC-FID chromatogram, especially b2-b7, are not well separated, and further improvements are needed.

Comments on the Quality of English Language

Minor editing of English language required.

Author Response

Responses to the referees’ comments

Review Report (Reviewer 2)

The author has revised the manuscript one by one as required. However, there is still a problem that extracts in headspace GC-FID chromatogram, especially b2-b7, are not well separated, and further improvements are needed.

Answers to Reviewer 2

Figures b2-b7 in the supplementary material show the HS/GC-FID chromatograms obtained for the migration solutions from PS. The styrene peak (analyte of interest in this study, at RT 14.7 min) is well separated and it was integrated always in the same way in all the HS/GC-FID chromatograms. Probably the Reviewer means that near the m-xylene peak (at RT 14.02 min) other two small peaks can be seen; m-xylene is the internal standard used in this study. The peak before it is ethylbenzene which was present in the migration solution and also in the standard mix used for calibration. It was not quantified in this study but it resulted well separated from m-xylene. The peak after m-xylene is an impurity (probably an isomeric form) present in the m-xylene standard. It is much smaller than the m-xylene peak and it also well separated from it. In order to facilitate the interpretation of these considerations we added some figures in the supplementary material (see Figures b1b and b1c).

Reviewer 3 Report

Comments and Suggestions for Authors

I respect the opinion of Authors and thank them very much for carefully replying to all my considerations; however, they should understand that a manuscript to become a scientific article adequate for publication on an international scientific journal, as Applied Science, must have a certain originality content. To ensure the compliance with European regulations for an industrial product, cannot be considered as a scientific target worthy of publication. Unfortunately, owing to such a lacking of originality, many modest ‘quality-control’ reports, organized in form of scientific articles, do not pass the peer reviewing stage and do not become scientific articles. ALSO THE IMPOSSIBILITY TO IDENTIFY THE STUDIED MATERIAL MAKES ABSOLUTELY UNUSEFUL TO PUBLISH RESULTS CONCERNING AN UNKNOWN INDUSTRIAL PRODUCT AND IN ADDITION THE PROVIDED RESULTS CANNOT BE VERIFIED BY OTHER SHOLARS INVOLVED IN THE SAME RESEARCH FIELD. IS THIS STUDY TRUE? HOW CAN RESULTS BE VERIFIED WITHOUT A SURE IDENTIFICATION BASED ON THE PRODUCT TRADE NAME AVAILABILITY? Finally, the negligible originality content of the submitted article and the anonymized trade names of the object of study and consequent impossibility to verify the truthfulness of the communicated results suggest me to decline for its publication on Applied Science.

Author Response

Review Report (Reviewer 3)

I respect the opinion of Authors and thank them very much for carefully replying to all my considerations; however, they should understand that a manuscript to become a scientific article adequate for publication on an international scientific journal, as Applied Science, must have a certain originality content. To ensure the compliance with European regulations for an industrial product, cannot be considered as a scientific target worthy of publication. Unfortunately, owing to such a lacking of originality, many modest ‘quality-control’ reports, organized in form of scientific articles, do not pass the peer reviewing stage and do not become scientific articles. ALSO THE IMPOSSIBILITY TO IDENTIFY THE STUDIED MATERIAL MAKES ABSOLUTELY UNUSEFUL TO PUBLISH RESULTS CONCERNING AN UNKNOWN INDUSTRIAL PRODUCT AND IN ADDITION THE PROVIDED RESULTS CANNOT BE VERIFIED BY OTHER SHOLARS INVOLVED IN THE SAME RESEARCH FIELD. IS THIS STUDY TRUE? HOW CAN RESULTS BE VERIFIED WITHOUT A SURE IDENTIFICATION BASED ON THE PRODUCT TRADE NAME AVAILABILITY? Finally, the negligible originality content of the submitted article and the anonymized trade names of the object of study and consequent impossibility to verify the truthfulness of the communicated results suggest me to decline for its publication on Applied Science.

Answers to Reviewer 3

We also thank the Reviewer for the provided reply.

Regarding the originality content of our manuscript: we would like to remark that in this study styrene migration levels were evaluated at several levels of the processing chain of yoghurt pots (from pellets, sheets to pots), which is a particular and original aspect in the context of migration from FCMs. In fact, we previously studied styrene migration from PS materials and published some articles looking at the migration levels detectable in real products taken from the supermarket and compared them with the results of simulated migration testing in food simulants. However, migration data along the processing chain of PS materials for food contact applications and comparisons between starting-intermediate-final materials are not yet available in the scientific literature. The observation that sheets show an (unexpectedly) different behavior from the final pot materials, concerns us since longer and we were searching for scientific explanations. Therefore, we started this study with direct comparisons of sheet and pot and corresponding pellet material. The scope of the study is not the ensure the compliance for an industrial product (as stated by the Reviewer) but is to look at the differences in the migration behavior between PS sheets (intermediate material) and PS pots (final material) along the processing chain. Therefore, we consider that our submitted manuscript deals with an interesting and very original aspect worthy of publication.

About the comment on the anonymized trade names of the studied materials, we would like to remark that they were provided by our Industrial partner (which is one of the leading European trade associations and represents most of the production capacity of PS) to be representative of standard industrial materials used in the European market for food contact applications, especially for packaging of yoghurt. We must respect the confidentiality agreement with our Industrial partner who does not allow us to identify the studied materials in the publication with their trade names. Nevertheless, we added in the revised manuscript some comments which describe their main technical properties. The sample were not bought by the authors but were directly taken from the processing chain of yoghurt pots (at the converting stage) by members of the association. Therefore, it must be recognized that the study is true and look at real industrial materials which are adequate to be evaluated in our applied research study (a case study along the processing chain of yoghurt pots). The properties of different grades vary, as the data of our study show, but we expect that the principal differences between sheet and pot material will be reproducible with any other PS material for dairy products.

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

Experimental data included in this work have been increased compared to starting version by adding the product migration kinetics in food; however, the work remains quite poor of technical information. In addition, a big European industry of PS produces a very large variety of PS products; the product trade name MUST be revealed also in the case the performance of this product is not good enough! The Authors should deepen the study of the ‘Galilean method’ in the part that concerns the need to be able to reproduce scientific experiments, which is the basis of all experimental sciences.

 

 

Author Response

Responses to the referees’ comments

Review Report (Reviewer 3)

Experimental data included in this work have been increased compared to starting version by adding the product migration kinetics in food; however, the work remains quite poor of technical information. In addition, a big European industry of PS produces a very large variety of PS products; the product trade name MUST be revealed also in the case the performance of this product is not good enough! The Authors should deepen the study of the ‘Galilean method’ in the part that concerns the need to be able to reproduce scientific experiments, which is the basis of all experimental sciences.

Answers to Reviewer 3

Thank you for recognizing the improvement in our revised manuscript.

About the comment on the investigated sample materials: The study was initiated and financially supported from the Styrenics Steering Committee of Plastics Europe, which represents the relevant manufacturers of styrene polymers. According to the guidelines of pre-competitive studies within the framework of Plastics Europe, trade names of the polymers used may not be mentioned. The companies involved in the Styrenics Steering Committee selected representative materials for the yoghurt sector for this study. We added this explanation in the section “material and methods”.

Additionally, in the same section we added the main technical properties of the PS materials which allow the reproducibility of the scientific experiments.

In this work (as anticipated in the title “…a case study along the processing chain of yoghurt pots”) sample materials were taken from a converter company who process the pellets to sheet and pots specifically for the food contact application “yoghurt pot”. These materials are therefore actual PS products used by different dairy producers to pack and distribute their products in the market. For these reasons we consider the investigated PS products adequate to be evaluated in a research study on FCMs.