Novel Sustainable Alternatives for the Study of the Chemical Composition of Cork

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript submitted deals with important aspects related to cork characterization to achieve a reduction of time and use of problematic solvents. The methodology is well explained and experiments clearly described. The use of an experimental design and statistics for extraction optimization are interesting tools as is demonstrated in this work.  The results are clearly presented, and conclusion are based in the main findings. In my opinion, this work deserves be published after some minor points:

Typographic mistakes:

Separation of words in lines 142 and 218.

Final sentence: point between temperature. As in line 146

Subindex CHCl3 line 186

“Included” instead of “include” in line 231

Table 5 in line 271

Suberin in line 309

Figure 1. Text of figure should be in English.

Figure 2.  Washings are called “extraction” in text. I suggest using the same name and remove figure title.

Author Response

Dear reviewer,

I hope this message finds you well. I am writing to express my sincere gratitude for your invaluable contributions as a reviewer for MDPI Sustainability. Your insightful comments and meticulous revisions significantly strengthened the quality and depth of our manuscript previously titled “Novel sustainable alternatives for the study of the chemical composition of cork”.

Your meticulous attention to detail and constructive feedback not only enhanced the clarity of the content but also enriched the overall scientific rigor of the paper.

Here we will answer your comments:

1. The typographic mistakes: thank you for your comments, we have rewritten all of them.
2. Figure 1: Yes, you are totally right. We feel sorry of that mistake, and we translated into English.
3. Figure 2: thank you for the appreciation, we have renamed it.

I am truly appreciative of the time and effort you dedicated to thoroughly evaluating the manuscript. Please accept my deepest gratitude for your invaluable guidance and scholarly input.

We look forward to the possibility of future answers and interactions.

Your faithfully,

Maria Verdum and Patricia Jové

Fundació Institut Català del Suro

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Comments

In this paper, the authors explored two approaches (ASE and MAE) as alternatives to the classical methodology for determining the chemical composition of cork. The theme is definite and the logic is clear. However, there are still some issues to be addressed. The specific comments can be found as following:

1.    In abstract, there are too many introductions about the background part, and the key points should be pointed out concisely.

2.    For the chemical composition test of cork, is there only one traditional method of soxhlet extraction?

3.    Lines 105-107, on “sustainable practices” and “green chemistry”, should give some of the latest references, such as: Recent progress of biomass in conventional wood adhesives: a review.

4.    In line 184, “H₂O” was miswritten as “H₂0”.

5.    Pay attention to the writing of upper and lower marks, such as “CHCl₃” in line 186.

6.    There are two serial numbers 4 in Figure 1.

7.    Figure 3 is not clear, and the resolution of the image should be improved.

8.    Line 271, the order of this table should be “Table 5” instead of “Table 3”.

There are still some typos and grammar issues in the manuscript. Authors should carefully recheck the whole manuscript.

Comments on the Quality of English Language

Need to be polished.

Author Response

Dear reviewer,

I hope this message finds you well. I am writing to express my sincere gratitude for your invaluable contributions as a reviewer for MDPI Sustainability. Your insightful comments and meticulous revisions significantly strengthened the quality and depth of our manuscript previously titled “Novel sustainable alternatives for the study of the chemical composition of cork”.

Your meticulous attention to detail and constructive feedback not only enhanced the clarity of the content but also enriched the overall scientific rigor of the paper.

Here we will answer your comments:

1. In abstract, there are too many introductions about the background part, and the key points should be pointed out concisely.

Thank you for comment, we have rewritten the background part and pointed out the aims of the study.

2. For the chemical composition test of cork, is there only one traditional method of soxhlet extraction?
3. Thanks for your question, as explained in the introduction, there is one method that is the most accepted. This method is described in the introduction and we refer to that method as the traditional method.
4. Lines 105-107, on “sustainable practices” and “green chemistry”, should give some of the latest references, such as: Recent progress of biomass in conventional wood adhesives: a review.

Thank you for your comment. We completely share your option and we put a new reference.

5. In line 184, “H2O” was miswritten as “H20” and Pay attention to the writing of upper and lower marks, such as “CHCl3” in line 186.

Thank you for your highlighting, we have rewritten the miswritten upper and lower marks.

6. There are two serial numbers 4 in Figure 1.

Yes, you are totally right. We feel sorry of that mistake. We have corrected it.

7. Figure 3 is not clear, and the resolution of the image should be improved.

Thank you for comment. We understand that the resolution is not clear. We have made the figure again bigger and with best resolution.

8. Line 271, the order of this table should be “Table 5” instead of “Table 3”.

Thank you for appreciation. We feel sorry of that mistake. We have renamed it.

9. Typo and grammar issues and Quality of English Language

Yes, your right. English is not our mother tongue. For that reason, we submitted the manuscript to a MDPI English revision, and we changed the mistakes. The Author Services certifies the manuscript.

I am truly appreciative of the time and effort you dedicated to thoroughly evaluating the manuscript. Please accept my deepest gratitude for your invaluable guidance and scholarly input.

We look forward to the possibility of future answers and interactions.

Your faithfully,

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Manuscript is well defined, easy to understand. The language is appropriate and understandable. The topic is compatible with the journal’s scope.

The overview of the given results is significant and relevant, presented in a well-structured way. Data and analyses presented appropriately.

Tables containing the parameters and chemical composition are clear and concise. The figures (1 to 4) are appropriate.

The data presented in the chapters Results and Discussion are very significant and relevant, presented in a well-structured way.

Conclusions justified consistent with the evidence and arguments presented.

The main contribution of this manuscript is to confirm the importance of a new approach to the study of the chemical composition of cork using sustainable techniques, providing accurate results without compromising the integrity of the environment. For the determination of the chemical composition of cork, two alternatives to the classic methodology are presented, one of which is optimized and validated and which shortens the test time and the amount of solvent.

Accept manuscript with minor changes:

Line 8, 14, 17, 21: The Abstract is without headings for the sections.

Line 26: Is it necessary to mention the same word "cork" twice as a keyword?

Line 30: Add a reference/references.

Line 40: Add a reference/references.

Line 57: Add a reference/references for the traditional method.

Line 271: Is Table 3 label actually Table 5?!

Line 346: The reference cite according to the journal s propositions.

Line 378: The reference cite according to the journal s propositions.

Author Response

Dear reviewer,

I hope this message finds you well. I am writing to express my sincere gratitude for your invaluable contributions as a reviewer for MDPI Sustainability. Your insightful comments and meticulous revisions significantly strengthened the quality and depth of our manuscript previously titled “Novel sustainable alternatives for the study of the chemical composition of cork”.

Your meticulous attention to detail and constructive feedback not only enhanced the clarity of the content but also enriched the overall scientific rigor of the paper.

Here we will answer your comments:

1. Line 8, 14, 17, 21: The Abstract is without headings for the sections.

Thank you for comment, we have put the headings in italics to make the sections clearer.

2. Line 26: Is it necessary to mention the same word "cork" twice as a keyword?

Thanks for your question. The first cork is from “cork extractives” and refers to a part of chemical composition process of cork. And the second “cork” refers to the cork material itself (cork as the outer bark of cork oak tree). We changed the position of the keywords to avoid misunderstanding.

3. Lines 30, 40 and 57 add a reference/references

Thank you for appreciation. We completely share your option and we put references.

4. Line 271: Is Table 3 label actually Table 5?!

the order of this table should be “Table 5” instead of “Table 3

Thank you for question. We feel sorry of that mistake. We have renamed it.

5. Line 346 and 378: The reference cites according to the journal s propositions.

Thank you for your highlighting, we have rewritten them.

I am truly appreciative of the time and effort you dedicated to thoroughly evaluating the manuscript. Please accept my deepest gratitude for your invaluable guidance and scholarly input.

We look forward to the possibility of future answers and interactions.

Your faithfully,

Maria Verdum and Patricia Jové

Fundació Institut Català del Suro

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The work presents an interesting study about the cork analysis sequence presenting a possible faster alternative to the classical approach maintaining most of the analysis philosophy. Nevertheless, the explanation of the methodology and results presentation is confuse and needs to be improved.

General Comments

Results presentation are confuse. The use of where and in what determinations MAE and ASE where used is confuse. The sequence of operations for the determination of extractives, suberin, lignin and sugars should be clarified, perhaps with a scheme.

 As explained in chapter 2.5 suberin was determined by classical methodology but, in tables 3 two values are presented for suberin content? Why? Material and methods are not clear about the sequential analysis of cork and what methods are used in sequence. What kind of heating was used for suberin determination in each sequence?

 

 Why to present MAE if the solvent extraction results are confuse and very far from the classical? Why both tables 3 (?) give different results for classical suberin and polysaccharides?

 Particular Comments

 12, 51, 320

Wrong sentence. Suberin, that can reach 60% of cork solvent extracted mass, is the main cork structural component and cellulose is perhaps the lowest. Suberin don’t exist in wood, no wood methodology could be adapted for its analysis. Cork research was developed for more than two centuries, was the responsible for the born of the word “Cell” and cannot be regarded as a secondary field of wood research. It is natural that the same methodologies are adopted to analyze the same components, lignin and polysaccharides, otherwise it would be absurd. This cannot be interpreted as wrong or a bad scientific approach.

 57

What traditional method? For analysis of what?

 59-61

Time of extraction depends of many factors. Time is the necessary to achieve a “complete extraction” or reaction. Time depends of heating “force”, depends of soxhlet dimension, depends of solvent volume in real circulation, depends of particle size, depends of material compression and mass, depends of real temperature in the soxhlet, depends of solvent diffusivity in the material, … So, time means nothing, number of cycles are more trustworthy but higher cycle times decrease diffusivity problems . Experience is an important key in this operation and we cannot use the same time for a soxhlet extraction if the conditions used are not the same. Authors should clarify how they ensured that the time used was sufficient to guarantee complete extraction.

 13-16, 69-84, …

Authors give the idea that cork quality can be inferred by a rapid analysis methodology. The authors' intention is understandable but, as is too common, the most important aspect of the chemical analysis of cork, the sample preparation, i.e., crushing, sieving and selection of the fraction, is neglected. A very good cork plank and a very bad one can give the same chemical analysis. Bad cork planks are thinner, or has more holes or more pores, if I select in the milling the pure suberized tissue, I will not observe any substantial chemical difference. The vast majority of the researchers systematically overlooks this important part of the analytical sequence, it is invisible in the published work, with some exceptions no one talks about it. The crushing and selection of fraction for analysis directly and significantly interferes with the analytical results of extraction with solvents and the quantitative result of the components. If I select a good fraction I will not see the composition of the fines where are the harder tissues coming from more woody cells.  It would be beneficial for the reader if the text were clearer considering this aspect.

 176-178

Wrong reference. Original work of the methodology is reference 16.

Marques, A.V., Pereira, H. (1987). On the determination of suberin and other structural components in cork from Quercus suber L. Anais do Instituto Superior de Agronomia (Lisboa)

 202

unnecessary precision of Bp.

 211

“Optimization cork chemical composition”

Chapter 3.2 referes to analysis of solvent extraction. The text presented do not optimizes all the cork composition determination, only time of extraction.

 

Figure 3: figures size matters

19

In the abstract suberin is presented has a 45% content with MAE. MAE is presented as Microwave Assisted Extraction but, in reality, it is a rapid heating device for anything, including solvent extraction and suberin depolymerization, and works differently and in dependency of compounds polarity. The use of the word extraction in MAE definition is confuse in the context of the unit operation “extraction” and in suberin depolymerization context. As a suggestion, if MHA, Microwave Heating Assistance, is used instead of MAE the word “extraction” will not be confuse anymore and is promptly associated with inert solvent extraction.   

 305

“ASE and traditional methodologies did not present statistical differences”. Not entirely true, in the case of ASE, CH2Cl2 and EtOH extractives results are 75-77% shorter than the classical and water result compensate it for a similar global extraction result. In the case of MAE the results cannot be compared, microwave heating is very dependent of solvent polarity and in the case of complex materials its effect on bond breaking, due to vibrational excitation, may be underestimated. The underestimated value of water extraction by MAE is strange, it should be higher, the consequence was an overestimation of polysaccharides. Tables, results and their analysis should be more clear in the comparison.

Comments on the Quality of English Language

English language, punctuation and grammatical construction must be improved, Ex:

Lines 41, 45, 55, 63, 143, 184-186, 201, 218, 226, 236, figure 1, tables, 2, 3, 4.

Author Response

Dear reviewer,

I hope this message finds you well. I am writing to express my sincere gratitude for your invaluable contributions as a reviewer for MDPI Sustainability. Your insightful comments and meticulous revisions significantly strengthened the quality and depth of our manuscript previously titled “Novel sustainable alternatives for the study of the chemical composition of cork”.

Your meticulous attention to detail and constructive feedback not only enhanced the clarity of the content but also enriched the overall scientific rigor of the paper.

Here we will answer your comments:

1. General comments: Results presentation are confuse. The use of where and in what determinations MAE and ASE where used is confuse. The sequence of operations for the determination of extractives, suberin, lignin and sugars should be clarified, perhaps with a scheme.

Thank you for comment. The manuscript is focus on describe two possible method as a alternative method of the used one. For that reason, the determination method via ASE is described in section 3.1, 3.2 and 3.3 and the determination method via MAE in 3.4. The figure 1 describe the sequence operation for the determination of extractives, suberin, lignin and holocellulose. The sequence is also described in the manuscript (line 64-75). As it described, the chemical analysis method of cork is based on serial extraction, this sequence is the same used for the proposal methods ASE and MAE. We base our research of changing Soxhlet reactor to ASE or MAE.

 

2. General comments: As explained in chapter 2.5 suberin was determined by classical methodology but, in tables 3 two values are presented for suberin content? Why? Material and methods are not clear about the sequential analysis of cork and what methods are used in sequence. What kind of heating was used for suberin determination in each sequence?

Thanks for your question. Suberin determination via ASE is not possible as it is explain for that reason after the extractive determination via ASE the suberin content was determined by classical methodology. Table 3 compered the whole chemical composition of cork by classical methodology with the extractive determination via ASE follow by the suberin determination by classical methodology. Table 3 has a footnote detailing this.

The chemical analysis method of cork is based on serial extraction, this sequence is the same used for the proposal methods ASE and MAE. As we are previously explained, we base our research of changing Soxhlet reactor to ASE or MAE extractions.

 

3. General comments: Why to present MAE if the solvent extraction results are confuse and very far from the classical? Why both tables 3 (?) give different results for classical suberin and polysaccharides?

Thank you for your question. You are totally right the MAE methodology needs to be optimized in the future as it is said in the article. There is two table 3 in the manuscript we revised and renamed it. The table 3 refers to the comparison of the whole chemical composition of cork by classical methodology with the extractive determination via ASE follow by the suberin determination by classical methodology. The table 5 refers to the comparison of the whole chemical composition of cork by classical methodology with the whole chemical composition of cork via MAE. The results of the classic composition are different because there were different baches form the same sample. The classic method has little reproducibility as explained in the article, for this reason we believe that it is important to look for new alternatives to this methodology.

 

4. Lines 12, 51, 320:

Thank you for your highlighting, we have rewritten them.

 

5. Line 57 What traditional method? For analysis of what?

Thank you for your question. It refers to the traditional method for analysis cork. We specified to avoid mistakes.

 

6. Lines 59-61:

You are totally right and the 59-61 date refers to the studies 3 and 5 of the bibliography. The authors of these studies described the number of cycles. In our research the number of cycles has also been studied. However, our response variables selected were the milligrams of extract obtained and the extraction ratio or yield as g extract/g raw cork·100, as it is explained.

 

7. Lines 13-16, 69-84

Thank you for your comment. We totally share your point of view. The intention of the article is to help decision-making about samples of cork granulated or cork stoppers in the factory to guide their quality. And, as you mention, the sample should be processed in the same way to avoid misinterpretation. We explained the samples preparation in section 2.1.

 

8. Lines 176-178: Wrong reference

Thank you for your highlighting. We feel sorry of that mistake. We have renamed it.

 

9. Line 202: unnecessary precision of Bp.

Thank you for your appreciation, we have rewritten them.

 

10. Line 211. “Optimization cork chemical composition”

Thank you for comment, as it is explained four factors were optimized: temperature and times extraction, sample quantity, and the number of extractions. It is explained in section 3.1.

 

11. Figure 3: figures size matters

Thank you for comment. We understand that the resolution is not clear. We have made the figure again bigger and with best resolution.

 

12. Line 19:

Thank you for your comment. The percentage of suberin presented in the abstract was explain in the sections 2.4 and 3.4 and the results were presented in table 5. We understand the appreciation about MAE and MHA, we used the same device for doing extraction of dichloromethane, ethanol and water and the depolarization of suberin for this reason we talked about MAE without differentiation of progradation or usages.

 

13. Line 305: “ASE and traditional methodologies did not present statistical differences”.

Thank you for your comment. The results presented in table 3 were statistical analyzed. The comparison of the two methodologies showed no significant differences (p_value >0.05) in all the categories (section 3.3). Results obtained via MAE were not statistical analyzed as it is explained in text.

 

14. Typo and grammar issues and Quality of English Language

Yes, your right. English is not our mother tongue. For that reason, we submitted the manuscript to a MDPI English revision, and we changed the mistakes. The Author Services certifies the manuscript.

I am truly appreciative of the time and effort you dedicated to thoroughly evaluating the manuscript. Please accept my deepest gratitude for your invaluable guidance and scholarly input.

We look forward to the possibility of future answers and interactions.

Your faithfully,

Maria Verdum and Patricia Jové

Fundació Institut Català del Suro

Author Response File: Author Response.pdf