Egg By-Products: Composition, Bioactive Potential, and Utilization in the Circular Economy

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The review manuscript provides a comprehensive and up-to-date synthesis on the composition, processing, and valorization of egg by-products within the context of the circular economy. The text covers solid (eggshell and membrane) and liquid (technical albumen) by-products in detail, discussing technological, nutritional, pharmaceutical, and environmental aspects. The topic is highly relevant to the scope of Biomass due to its emphasis on sustainable resource use and valorization of agri-food residues. However, the authors should clarify some issues to improve and strengthen the manuscript. Below are specific comments:

Abstract: Add a brief mention of key limitations and a concise closing statement.

Introduction: Please emphasize the novelty of this review over previous reviews.

Introduction: Explicitly state objectives and research gaps.

Methodology, first mention: The authors state in the abstract that the manuscript is a systematic review. However, I have not found the search criteria or databases used. Provide a detailed database search strategy and inclusion/exclusion criteria.

Composition section, eggshell subsection: Include a table summarizing chemical variability.

Composition section, membrane subsection: Expand discussion on functional properties variability.

Processing technologies: Please include a critical comparison of extraction methods (yield, cost, barriers).

Processing technologies: Suggest summarizing valorization routes in a figure or table.

Application section: Highlight prominent emerging applications with a more critical perspective.

Liquid by-products: Provide a more detailed analysis of the challenges, especially those related to liquid by-products.

The sections "solid by-products" and "liquid by-products" have the same numbering (4.1). Please verify.

Conclusion: Add an explicit summary of the knowledge gaps and a direction for future work.

Author Response

Dear reviewer, thank you for your valuable feedback and the opportunity to enhance our manuscript.

You will find all the corrections done according your comments marked in the manuscript. 

Comment 1: Abstract: Add a brief mention of key limitations and a concise closing statement.

Response 1: Thank yоu for pointing this out. We agree with this comment. We changed the text in line 14-16, and the sentences are: For this reason, restrictions have been introduced on their use after disposal, to bioactive applications in medical, cosmetic and pharmaceutical products, as well as feed. The shells are subject to special conditions for processing and use.

Comment 2: Introduction: Please emphasize the novelty of this review over previous reviews.

Response 2: Thank yоu for pointing this out. We agree with this comment. We changed the text in line 100-104, and the sentences i added are: The focus of this review will be on the bioactive application of these wastes in the food, feed, medical, cosmetic and pharmaceutical industries. The article describes the composition of all by-products and covers methods and techniques for their processing into usable raw materials and products in the context of the circular economy.

Comment 3: Introduction: Explicitly state objectives and research gaps

Response 3: Thank yоu for pointing this out. We agree with this comment. We change the text in line 98-100.

Comment 4: Methodology, first mention: The authors state in the abstract that the manuscript is a systematic review. However, I have not found the search criteria or databases used. Provide a detailed database search strategy and inclusion/exclusion criteria.

Response 4: Thank yоu for pointing this out. W agree with this comment. we change the text in line 30. The presented manuscript is a literature review not a systematic. The word “systematic” is a mistake during translation.

Comment 5: Composition section, eggshell subsection: Include a table summarizing chemical variability.

Response 5: Thank yоu for pointing this out. We agree with this comment. We insеrted Table 1. Biomineralized composite of eggshell.

Comment 6: Composition section, membrane subsection: Expand discussion on functional properties variability.

Response 6: Thank yоu for pointing this out. We agree with this comment. We added the text in line 186-191, 482-484

Comment 7: Processing technologies: Please include a critical comparison of extraction methods (yield, cost, barriers).

Response 7: Thank yоu for pointing this out. We agree with this comment, but not all authors investigate the purity of the obtained extract. In this way we would compare the yield and value of obtained extract with different purity, which in my opinion is not appropriate.

Comment 8: Processing technologies: Please include a critical comparison of extraction methods (yield, cost, barriers).

Response 8: Thank yоu for pointing this out. We agree with this comment. It would be good to make such a comparison, but data on the purity of the extracted materials is not available, and the value depends on this factor.

Comment 9: Application section: Highlight prominent emerging applications with a more critical perspective.

Response 9: Thank yоu for pointing this out. We agree with this comment. We added the text in line 613-620

Comment 10: Liquid by-products: Provide a more detailed analysis of the challenges, especially those related to liquid by-products.

Response 10: Thank yоu for pointing this out. We agree with this comment. We change the text in line 806-811, 926

Comment 11: The sections "solid by-products" and "liquid by-products" have the same numbering (4.1). Please verify.

Response 11: Thank yоu for pointing this out. We agree with this comment. We change the text in line 762, 763, 809, 854

Comment 12: Conclusion: Add an explicit summary of the knowledge gaps and a direction for future work.

Response 12: Thank yоu for pointing this out. We agree with this comment. We changed whole Conclusion section line 935

 

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

This systematic review examines the composition and utilization of egg processing by-products eggshells, eggshell membranes, and technical albumen, within the circular economy framework. Eggshells, comprising 95% inorganic calcium carbonate, is valuable for agriculture, food, and medicine. One​‍​‌‍​‍‌ percent of the eggshell membrane is the part of the egg, which consists of collagen and hyaluronic acid, and can be used in cosmetics and tissue engineering. Technical albumen is a liquid by-product that has been banned for human consumption (Regulation 853/2004) but is rich in ​‍​‌‍​‍‌proteins.

 In my opinion, this article brings added value, if you answer or clarify the following aspects, the article can be published:

What specific functional properties differentiate eggshell membrane components (collagen, keratin) from eggshell inorganic substance?

How do the reported yields from different membrane separation techniques contrast regarding industrial applicability?

In what ways do the documented bioactive potentials of technical albumen proteins contradict scarcity of relevant literature?

Considering the circular economy goal, how might the varied calcium supplement dosages affect long-term consumer acceptance?

Author Response

Dear reviewer, thank you for your valuable feedback and the opportunity to enhance our manuscript.

You will find all the corrections done according your comments marked in the manuscript. 

Comment 1: What specific functional properties differentiate eggshell membrane components (collagen, keratin) from eggshell inorganic substance?

Response 1: Thank yоu for pointing this out. We agree with this comment. We changed the text in line 276-279, 935 To make the chemical composition of the shell more visible, We inserted Table 1. Biomineralized composite of eggshell.

Comment 2: How do the reported yields from different membrane separation techniques contrast regarding industrial applicability?

Response 2: Thank yоu for pointing this out. We agree with this comment. We changed the text in line 322-325

Comment 3: In what ways do the documented bioactive potentials of technical albumen proteins contradict scarcity of relevant literature?

Response 3: Thank yоu for pointing this out. We agree with this comment. We changed the text in line 927-930.

Comment 4: Considering the circular economy goal, how might the varied calcium supplement dosages affect long-term consumer acceptance?

Response 4: Thank yоu for pointing this out. We agree with this comment. We changed the text in line 365-368.

Reviewer 3 Report

Comments and Suggestions for Authors

The presented manuscript (3990695) presents a well-structured review of the sustainable utilization of egg-processing by-products - a topic of considerable importance in the context of circular economic principles and the global effort to reduce industrial waste. The review is based on an extensive body of literature comprising 255 sources, which underscores the depth and thoroughness of the authors’ analytical work.

The manuscript thoroughly examines the composition and biological value of solid (eggshell and membrane) and liquid (technical albumin) by-products that are generated in significant quantities. The text summarizes existing methods for processing these materials - including mechanical, chemical, and enzymatic approaches - and outlines a wide range of potential applications across the food, feed, medical, pharmaceutical, and cosmetic industries. This clearly highlights the cross-sectoral relevance and practical significance of the topic.

The subject matter is relevant to a broad community of stakeholders, including industry practitioners, researchers, and end-users of food products.

Although the review holds significant scientific value, I recommend that the authors revise and refine the manuscript before publication.

Comments and Recommendations for Improvement

1. The purpose of the review should be articulated more clearly in the Introduction. The aim would benefit from being more specific, focused, and aligned with the structure of the paper.
2. The Conclusions require substantial revision. Currently, this section focuses mainly on directions for future research (particularly regarding the sustainable use of liquid products), whereas it should first summarize the key findings of the review. The conclusions must correspond to the stated aim and highlight the main insights, outcomes, and identified research gaps.
3. It is recommended to expand the discussion on the use of solid by-products - especially eggshells - as efficient adsorbents for wastewater treatment. This is an important and rapidly developing application area that deserves more detailed coverage.

Author Response

Dear reviewer, thank you for your valuable feedback and the opportunity to enhance our manuscript.

You will find all the corrections done according your comments marked in the manuscript. 

Comment 1: The purpose of the review should be articulated more clearly in the Introduction. The aim would benefit from being more specific, focused, and aligned with the structure of the paper.

Response 1: Thank you for pointing this out. We agree with this comment. We changed the text in line 98-104.

Comment 2: The Conclusions require substantial revision. Currently, this section focuses mainly on directions for future research (particularly regarding the sustainable use of liquid products), whereas it should first summarize the key findings of the review. The conclusions must correspond to the stated aim and highlight the main insights, outcomes, and identified research gaps.

Response 2: Thank you for pointing this out. We agree with this comment. We changed whole Conclusion section line 934.

Comment 3:  It is recommended to expand the discussion on the use of solid by-products - especially eggshells - as efficient adsorbents for wastewater treatment. This is an important and rapidly developing application area that deserves more detailed coverage.

Response 3: Thank you for pointing this out. We agree with your comment that eggshells are effective absorbents, and this is a developing area of science. The focus of this review is the bioactive potential with an emphasis on food, pharmaceutical, medical and cosmetic applications, as well as concluding the most recent knowledge. The utilization of eggshells has its novelties but it was already extensively reported.