Olive Leaf Extracts as a Medicinal Beverage: Origin, Physico-Chemical Properties, and Bio-Functionality

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The topic is actual and the information is important, whether as a consolidation of the Mediterranean diet or as new alternatives to agreesive chemical treatments.

The work is extense. It had some defects in the writting process. The version that was submitted had corrections that should bave been deleted. There must have been work reoeganization and there was no appropriate change in references. Ex: I point 3 the references vary frim 146 to 153, but in point 2.6 the references vary from 164 to 184.  References 186 to 193 were not found in the text. 

 

Comments for author File: Comments.pdf

Author Response

DETAILED RESPONSE TO ACADEMIC EDITOR AND  REVIEWERS’ COMMENTS

The Academic Editor’s and Reviewers’ comments were constructive since these improved the overall quality of our review article. We thank all the reviewers for their comments. There has been an effort to cover adequately all comments. The changes in the review article are marked in red color.

Reviewer 1#

The topic is actual and the information is important, whether as a consolidation of the Mediterranean diet or as new alternatives to agreesive chemical treatments.

The work is extense. It had some defects in the writting process. The version that was submitted had corrections that should bave been deleted. There must have been work reoeganization and there was no appropriate change in references. Ex: I point 3 the references vary frim 146 to 153, but in point 2.6 the references vary from 164 to 184.  References 186 to 193 were not found in the text. 

Response

We thank the Reviewer for the evaluation of the study and his/her suggestions for improvements. All the previous corrections were deleted, and the revised version has now been tracked with changes in red color. We checked the references and these were corrected accordingly. In addition, new literature has been added.

Reviewer 2 Report

Comments and Suggestions for Authors

Olive leaf extracts as a medicinal beverage: Origin, physico-chemical properties,
and bio-functionality
Andreas Alexandros Panou and Ioannis Konstantinos Karabagias

Comments:
Comment 1: L10-11. That's a weird expression in the first sentence. Please rephrase.
Comment 2: L14-16. Start the sentence with a capital letter.
Comment 3: L 19. I suggest a different selection of keywords.
Comment 4: L 23-28. Start the sentence with a capital letter.
Comment 5: L 40. Dubious reference [12].
Comment 6. L 42-43. Start the sentence with a capital letter.
Comment 7: L 45. Decapitalize the S in sulphur.
Comment 8. L 55-56, Table 1. Why is green tea with broccoli by-product that important
to be cited here? In a broader perspective, please explain the selection of “herb species”
in Table 1.
Comment 9: L 67-69. Please define the term “tea”.
Comment 10: L 89-93. You specify only three olive-producing countries by name. Why?
Comment 11: L 95-98. Start the sentence with a capital letter.
Comment 12: L 95-98. And what about anorganic matter?
Comment 13: L 104. Typo in “luteolin-7- Oglucoside”
Comment 14: L 103-109. Maybe the references [40-41] are not the only valid references
for complex olive leaves biophenols composition? I miss more chemically valid
references dealing with olive leaves phenolics.
Comment 15: L 103-109. In addition, I miss the more complex review of the olive leaves'
molecules with bio-functional properties, based on terroir, cultivar, geographical
position, methods of drying and extraction, period of harvest, and standardization of
phenolic compound concentration, using valid and contemporary internationally
accepted methods in the olive sector, among others.
Comment 16: L 117. The highest AO? Among? Please define.
Comment 17: L 117. Start the sentence with a capital letter.
Comment 18: L 117-119. “Highest amounts”? Incomplete and incomprehensible
sentence.
Comment 19: L 117-148. Does the time of publication have any influence on the
presented data?
Comment 20: L 192. Typo in “acis”.
Comment 21: L 190:192. Please revive the oleuropein (and ligstroside) glucoside
decomposition or hydrolytic pathway in olive leaves before and after administration,
which is not directly comparable to the fate of oleuropein in olive oils.
Comment 22: L 203. Start the sentence with a capital letter.
Comment 23: L 222-223, 229-230, 233-236, 297-300, 303-305 deal with EVOO
biophenols, which could not be directly compared to olive leaves’ biophenols therefore
at least a critical interpretation of this data is missing. L 294-297 address the table
olives, which again is not the same matrix. And again: the exact speciation and
concentration of active phenolic compounds is missing.
Comment 24: L 265-266, Table 2. The explanation of the terms used in the table, the
legend, and the numeric tolerances are missing from the table.
Comment 25: L 274. Start the sentence with a capital letter.
Comment 26: L 280-282. You mention the oleacein, and you do not include it in the
oleuropein decomposition pathway; therefore, a reader cannot receive the correct
information about all oleuropeine decomposition molecules (as in Comment 21).
Oleacein is active only in good quality EVOO oils, but I could be mistaken, of course.
Comment 27: L 311-340. Inconsistency in the composition and concentration data of
phenolic molecules in cited references cannot provide a consistent picture; therefore,
the authors should make an additional effort to critically and historically elaborate on
them before simply quoting them.
Comment 28: L 357-358. Hydroxytyrosol oleate IS a fatty acid ester.
Comment 29: L 396-420. Mismatches in reference numeration. I suppose references
[146 to 153] should be corrected to [186 to 193].
Comment 30: L 422-454. I find that all the data presented should also be examined from
a concentration perspective.
Comment 31: L 460. Space is missing in naming Bacillus cereus and Bacillus subtilis.
Comment 32: L 469-471. The data provided are measured after exposure to EVOO
phenols, which are different from olive leaf phenols.
Comment 33: L 482. Start the sentence with a capital letter.
Comment 34: L 499. Reference [226] should probably be corrected to [236].
Comment 35: L 506-509. An overly simplified assertion from the perspective of different
phenolic species present in olive leaf extracts, which are not the ones typically found in
EVOO.

Please find the comments in the attached file.

Comments for author File: Comments.pdf

Author Response

DETAILED RESPONSE TO ACADEMIC EDITOR AND  REVIEWERS’ COMMENTS

The Academic Editor’s and Reviewers’ comments were constructive since these improved the overall quality of our review article. We thank all the reviewers for their comments. There has been an effort to cover adequately all comments. The changes in the review article are marked in red color.

Reviewer 2#

Comments and Suggestions for Authors

Olive leaf extracts as a medicinal beverage: Origin, physico-chemical properties,
and bio-functionality
Andreas Alexandros Panou and Ioannis Konstantinos Karabagias

Comments:
Comment 1: L10-11. That's a weird expression in the first sentence. Please rephrase.

Response

Revised accordingly.

Comment 2: L14-16. Start the sentence with a capital letter.
Response

Done accordingly.

Comment 3: L 19. I suggest a different selection of keywords.
Response

Revised accordingly.

Comment 4: L 23-28. Start the sentence with a capital letter.
Response

Done.

Comment 5: L 40. Dubious reference [12].
Response

Dear Reviewer, there is  an Anonymous source in the research paper to be used. It has been done and in other studies. We believe that it does not affect the clarity of our review.

Comment 6. L 42-43. Start the sentence with a capital letter.
Response

Done.

Comment 7: L 45. Decapitalize the S in sulphur.
Response

Done.

Comment 8. L 55-56, Table 1. Why is green tea with broccoli by-product that important
to be cited here? In a broader perspective, please explain the selection of “herb species”
in Table 1.
Response

Dear Reviewer, as we stated in the table legend, the table presents some selected herbs and spices. The tea with broccoli by -product was selected as a novel herbal drink given the considerable content in polyphenols.

Comment 9: L 67-69. Please define the term “tea”.
Response

The term has now been generalized.

Comment 10: L 89-93. You specify only three olive-producing countries by name. Why?
Response

This was not for a special reason. We added the words ‘’ For example’’ for a better interpretation and to avoid any misunderstanding.

Comment 11: L 95-98. Start the sentence with a capital letter.

Response

Corrected accordingly.

Comment 12: L 95-98. And what about anorganic matter?
Response

Added accordingly with a new reference.

Comment 13: L 104. Typo in “luteolin-7- Oglucoside”
Response

Corrected accordingly.

Comment 14: L 103-109. Maybe the references [40-41] are not the only valid references
for complex olive leaves biophenols composition? I miss more chemically valid
references dealing with olive leaves phenolics.

Response

We agree with the Reviewer. We updated the citation with a new reference, no. 37.

Comment 15: L 103-109. In addition, I miss the more complex review of the olive leaves'
molecules with bio-functional properties, based on terroir, cultivar, geographical
position, methods of drying and extraction, period of harvest, and standardization of
phenolic compound concentration, using valid and contemporary internationally
accepted methods in the olive sector, among others.
Response

We agree again with the Reviewer and the relevant information has been updated. See lines 99-102.

Comment 16: L 117. The highest AO? Among? Please define.
Response

Defined accordingly.

Comment 17: L 117. Start the sentence with a capital letter.
Response

Corrected accordingly.

Comment 18: L 117-119. “Highest amounts”? Incomplete and incomprehensible
sentence.
Response

Yes, corrected.

Comment 19: L 117-148. Does the time of publication have any influence on the
presented data?
Response

Yes, but we tried to include in this review the past, the present and some future perspectives of the relevant literature the last decades.

Comment 20: L 192. Typo in “acis”.
Response

Corrected accordingly.

Comment 21: L 190:192. Please revive the oleuropein (and ligstroside) glucoside
decomposition or hydrolytic pathway in olive leaves before and after administration,
which is not directly comparable to the fate of oleuropein in olive oils.
Response

We did not find in these lines the intended meaning. We tried to improve the clarity of our review flow by introducing in lines 117-124 the biochemical pathway of oleuropein. Besides, in these lines (190-192) we addressed the potential attributes of oleuropein and its derivatives according to the literature. Kindly see through the new flow of the review.

Comment 22: L 203. Start the sentence with a capital letter.
Response

Corrected accordingly.

 

Comment 23: L 222-223, 229-230, 233-236, 297-300, 303-305 deal with EVOO
biophenols, which could not be directly compared to olive leaves’ biophenols therefore
at least a critical interpretation of this data is missing. L 294-297 address the table
olives, which again is not the same matrix. And again: the exact speciation and
concentration of active phenolic compounds is missing.
Response

The information regarding the specific concentration of active phenolics was added where available.

Comment 24: L 265-266, Table 2. The explanation of the terms used in the table, the
legend, and the numeric tolerances are missing from the table.

Response

Defined and revised accordingly. In addition, the found concentrations were given.

Comment 25: L 274. Start the sentence with a capital letter.
Response

Response

Corrected accordingly.

Comment 26: L 280-282. You mention the oleacein, and you do not include it in the
oleuropein decomposition pathway; therefore, a reader cannot receive the correct
information about all oleuropeine decomposition molecules (as in Comment 21).
Oleacein is active only in good quality EVOO oils, but I could be mistaken, of course.
Response

We agree with the Reviewer and a relative comment has been inserted.

Comment 27: L 311-340. Inconsistency in the composition and concentration data of
phenolic molecules in cited references cannot provide a consistent picture; therefore,
the authors should make an additional effort to critically and historically elaborate on
them before simply quoting them.
Response

Checked and revised accordingly.

Comment 28: L 357-358. Hydroxytyrosol oleate IS a fatty acid ester.
Response

Corrected accordingly.

Comment 29: L 396-420. Mismatches in reference numeration. I suppose references
[146 to 153] should be corrected to [186 to 193].
Response

Yes, corrected accordingly.

Comment 30: L 422-454. I find that all the data presented should also be examined from
a concentration perspective.
Response

Dear Reviewer, information on concentrations of active phenolics was added, if these where available in the cited literature.

Comment 31: L 460. Space is missing in naming Bacillus cereus and Bacillus subtilis.
Response

Corrected accordingly.

Comment 32: L 469-471. The data provided are measured after exposure to EVOO
phenols, which are different from olive leaf phenols.
Response

Yes, we agree with the Reviewer. The cited literature, however, is used for addressing/introducing this topic of interest, focusing on oleuropein and its’ aglycons that exist also (even in much lower amounts) in olive oil.

Comment 33: L 482. Start the sentence with a capital letter.
Response

Corrected accordingly.

Comment 34: L 499. Reference [226] should probably be corrected to [236].

Response

Yes, corrected accordingly

Comment 35: L 506-509. An overly simplified assertion from the perspective of different
phenolic species present in olive leaf extracts, which are not the ones typically found in
EVOO.

Response

A better clarification was provided.

 

Reviewer 3 Report

Comments and Suggestions for Authors

1. The main focus of the review is on olive leaf extracts, but the introduction section does not specifically mention them until much later, in the last item of Table 1. Instead, the introduction broadly discusses herbal drinks and their medicinal properties. While the general context provided on the significance of medicinal plants and herbal beverages is useful, the introduction would be stronger with an early mention of olive leaf extracts to guide the reader and maintain focus on the paper’s central theme.
2. The sentence in lines 60-62 is grammatically incorrect. It is suggested to revise it to: According to the World Health Organization, more than 80% of people in Africa and Asia use herbal medicines.
3. The general herbal tea consumption data provided in lines 66-67 is over ten years old. It would be more relevant to include more recent data to reflect the current trends in herbal tea consumption.
4. Many readers may not be familiar with the phenolic compounds found in olive leaves. It would be helpful if the authors could provide the chemical structures of some primary phenolic compounds, such as oleuropein and its hydrolyzed derivatives, to enhance the clarity and depth of the review.
5. In line 117, the highest antioxidant activity of olive leaves is mentioned, but it is unclear compared to what. 
6. In line 122, the authors highlight the significance of oleuropein concentration but do not provide detailed information on the effective concentration. Providing this information would offer a clearer understanding of its potency and potential applications.
7. The authors highlight the various beneficial effects of oleuropein in olive leaves. However, it would be helpful to include a quantitative comparison of oleuropein content in olive fruit, olive oil, and olive leaves. Additionally, providing information regarding the metabolism and bioavailability of oleuropein in the human gastrointestinal tract would be valuable to the readers.
8. In the conclusion, the authors state, "In this context, more extensive research studies are required in the near future." It would be beneficial if the authors could provide some insights into the current knowledge gaps and suggest specific future research directions.

  Comments on the Quality of English Language

In several places, the first characters of the sentences are not capitalized (e.g., lines 14, 23, 42, 117, 482, etc.). Please review the manuscript thoroughly to correct these capitalization errors.

Author Response

DETAILED RESPONSE TO ACADEMIC EDITOR AND  REVIEWERS’ COMMENTS

The Academic Editor’s and Reviewers’ comments were constructive since these improved the overall quality of our review article. We thank all the reviewers for their comments. There has been an effort to cover adequately all comments. The changes in the review article are marked in red color.

Reviewer 3#

Comments and Suggestions for Authors

1. The main focus of the review is on olive leaf extracts, but the introduction section does not specifically mention them until much later, in the last item of Table 1. Instead, the introduction broadly discusses herbal drinks and their medicinal properties. While the general context provided on the significance of medicinal plants and herbal beverages is useful, the introduction would be stronger with an early mention of olive leaf extracts to guide the reader and maintain focus on the paper’s central theme.
   
   

Response

       The Reviewer is right. We have now improved the flow of the Introduction section by adding a cross-linked text:  ‘’ The most popular herbal drinks are many species of tea and olive leaf extract. The olive leaf extract possesses a distinctive position in herbal drink category on account of its high antioxidant, anti-inflammatory, anticancer, anticholesterolemic, antihypertensive, antimicrobial and antiviral properties which are mentioned in section 2. ‘’

2. The sentence in lines 60-62 is grammatically incorrect. It is suggested to revise it to: According to the World Health Organization, more than 80% of people in Africa and Asia use herbal medicines.
   
   

Response

The reviewer is right again. The sentence has now been corrected accordingly.

The general herbal tea consumption data provided in lines 66-67 is over ten years old. It would be more relevant to include more recent data to reflect the current trends in herbal tea consumption.
Response

Yes, the section was flourished with the current trends. Kindly see lines 89-93.

4. Many readers may not be familiar with the phenolic compounds found in olive leaves. It would be helpful if the authors could provide the chemical structures of some primary phenolic compounds, such as oleuropein and its hydrolyzed derivatives, to enhance the clarity and depth of the review.
   Response

We added now a figure (Figure 1) showing the structures of oleuropein and its hydrolyzed derivatives according to the Reviewer’s suggestions.

5. In line 117, the highest antioxidant activity of olive leaves is mentioned, but it is unclear compared to what. 
   
   

Response

Defined accordingly. See lines 137-138.

6. In line 122, the authors highlight the significance of oleuropein concentration but do not provide detailed information on the effective concentration. Providing this information would offer a clearer understanding of its potency and potential applications.
   Response

Details on the concentration of oleuropein in olive leaves and olive oil for comparison has been added.

7. The authors highlight the various beneficial effects of oleuropein in olive leaves. However, it would be helpful to include a quantitative comparison of oleuropein content in olive fruit, olive oil, and olive leaves. Additionally, providing information regarding the metabolism and bioavailability of oleuropein in the human gastrointestinal tract would be valuable to the readers.
   Response

Kindly see the above response and lines 125-134 in the revised manuscript.

8. In the conclusion, the authors state, "In this context, more extensive research studies are required in the near future." It would be beneficial if the authors could provide some insights into the current knowledge gaps and suggest specific future research directions.
   Response

Added accordingly. Thank you.

 

Comments on the Quality of English Language

In several places, the first characters of the sentences are not capitalized (e.g., lines 14, 23, 42, 117, 482, etc.). Please review the manuscript thoroughly to correct these capitalization errors.

Response

The whole manuscript has been improved concerning the English language.

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript has formatting errors and the presence of words deleted throughout the text. In addition, the English could be improved.
The review article lacks scientific relevance and is poor in content, and the manuscript has 219 references, some of which are not related to the study subject and others are too old for a review article.

Author Response

DETAILED RESPONSE TO ACADEMIC EDITOR AND  REVIEWERS’ COMMENTS

The Academic Editor’s and Reviewers’ comments were constructive since these improved the overall quality of our review article. We thank all the reviewers for their comments. There has been an effort to cover adequately all comments. The changes in the review article are marked in red color.

Response to Reviewer 4#

We thank the Reviewer for his/her suggestions to improve our manuscript. There has been an effort to improve the clarity of the review article, dismiss any errors, and connect better the topic information. We hope the revised manuscript fits with your standards. Thank you.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The work present great improvement.

Table 2  is still on two pags, but I think this is a publisher problem.

Author Response

We thank the Reviewer for acknowledging the improvement of our study. Yes, the table can be reformulated on one page by the Editorial office. We also attempted to include it on one page.

 

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for your reply. Please find the three tiny comments in the file attached.

Comments for author File: Comments.docx

Author Response

-Reviewer 2 reply: Yes, thank you, I understand. However, you might consider presenting this reference solely as an example of different uses rather than as a scientifically valid reference like the others.

Response

We have now deleted this reference and added a new one.

-Reviewer 2 reply: Yes, thank you. However, you could introduce it with a brief comment.

Response

Done accordingly. Kindly see lines 53-56.

-Reviewer 2 reply: I still miss a short description of olive phenolics: tree (branches or twigs) – leaves – drupes (olives) – (EV)OO. This is to inform the reader and avoid distraction because your paper’s title deals with OLIVE LEAF extracts AND NOT with (EV)OO.

Response

Yes, the Reviewer is right. Added accordingly. Kindly see lines 113-116.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed my comments.

Author Response

Thank you for acknowledging our effort to improve the manuscript.

Reviewer 4 Report

Comments and Suggestions for Authors

The text and formatting of the manuscript have been improved, however, there are still some points to be observed:

- the English can still be improved;

- please review the references, as not all of them are relevant and some are very old (for a review study, consider more recent works);

- the objective and justification of the study must be included in the last paragraph of the manuscript introduction;

- pg 13, lines 545-547: avoid using the expression "must develop"; please consider changing the sentence to "Therefore, the food and beverage industry should consider olive leaf extracts as an excellent ingredient in the development of new fortified beverages that strengthen the immune system and longevity."

Comments on the Quality of English Language

The English can still be improved.

Author Response

Comments and Suggestions for Authors

The text and formatting of the manuscript have been improved, however, there are still some points to be observed:

Response

Thank you for acknowledging our effort to improve the manuscript.

- the English can still be improved;

Response

There has been an additional effort to improve the English language.

 

 

 

 

- please review the references, as not all of them are relevant and some are very old (for a review study, consider more recent works);

Response

We deleted the old references and hold the newer ones to maintain the quality and the basic information presented in the study. Kindly see through the reference list.

- the objective and justification of the study must be included in the last paragraph of the manuscript introduction;

Response

The reviewer is right. Kindly see lines 88-92 in the Introduction section.

- pg 13, lines 545-547: avoid using the expression "must develop"; please consider changing the sentence to "Therefore, the food and beverage industry should consider olive leaf extracts as an excellent ingredient in the development of new fortified beverages that strengthen the immune system and longevity."

Response

Thank you for your advice. Added accordingly.