Environmental and Economic Life Cycle Assessment of Enzymatic Hydrolysis-Based Fish Protein and Oil Extraction

Round 1

Reviewer 1 Report

The manuscript, titled "Environmental and Economic Life Cycle Assessment of Enzymatic Hydrolysis-Based Fish Protein and Oil Extraction,” addresses the assessment of the environmental and economic value of fish protein hydrolysis using an enzymatic method, with the output being fish protein and oil. The authors conducted a life cycle assessment and a life cycle cost analysis for Atlantic mackerel by-products processing through enzymatic hydrolysis. They calculated the input investment and the return on investment. The authors commented that the results are influenced by the region and source of electricity production. Nevertheless, they claimed that the study might assist future research and decisions regarding the extraction of fish by-product ingredients. The study presents a promising approach for evaluating the environmental footprint of fish hydrolysate production. However, several grammatical errors and ambiguities need to be addressed before accepting the manuscript.

Specific comments:

1.      Abstract: “As global fish consumption rises, sustainable methods become more important to extract valuable ingredients from fish.” The sentence lacks coherence.  I do not find any justification with rising the fish consumption and important methods development for fish compounds extraction. Rewrite the sentence please.

2.      Please avoid we/ our in the scientific writing as written in Line: 16, 17, 21, 23. Rather write the sentences in passive form.

3.      The abstract should be written in past form (Line 19, 23, 25).

4.      In introduction, line 52-69; the authors discussed various methods for protein and oil extraction; however, the authors did not discuss about a modern green technique, subcritical water hydrolysis technique fort fish protein hydrolysis.

5.      Table 1; how did the authors determined the values?

6.      Did the author mention the purpose of production FPH and fish oil? In my view, the production process depends on the purpose of application.

7.      Table 3; the authors are requested to discuss the breakdown cost of FPH production.

8.      Table 5; In 3^rd column heading, Fish oil (per 1 g FPH) should be Fish oil (per 1 g fish oil).

9.      Figure 3; Our study should be replaced with “The present study”.

10.  Conclusion: Line 333; …FPH and fish oil ….. should be ……FPH and fish oil production…..

11.  Conclusion: Line 338; FPH by enzymatic method is a very old and established method…..how do the authors call this a novel technique?

12.  The conclusion should not contain more than 2/3 paragraphs. Please avoid reference in conclusion.

There are several grammatical errors and ambiguities need to be corrected.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors of this paper performed a life cycle and life cycle cost analysis for a process of enzymatically hydrolyzing fish waste parts into a fish protein hydrolysate (as main products) and fish oil (as by-product). Presented results will surely be of interest to the scientific community, are comparable to previously published data, and are compared in the paper. However, the structure of the paper is questionable, due to the fact that the Materials and Methods section and Results section are all mixed up, i.e. some results can be found the in the Materials and Methods section and some methodology explanations can be found in the results section. This is why I need to recommend a complete re-writing, rearrangement of the text, in order to clearly be divided into the named sections. Besides this main concern, I have some specific comments that also need to be addressed:
1. Please put one sentence in the introduction section about what represents the term "rest raw material", just to make it clear for the reader that is a by-product or waste of a fish processing facility.
2. In Table 1 the input and output quantity of fish rest raw material changed during preparation, however no explanation for it.
3. In Table 3 distilled water is referring to water from Table 1? These terms should be made uniform.
4. Energy in Table 3 has the value 2.47 kWh and in Table 2 it's 2.48 just for the hydrolysis part of the process.
5. If one run (lines 204-206) i.e. one batch takes 8 hours, it doesn't matter what's the size of the batch. You have to go through all the operations and processes in order to obtain 61 grams or 1 gram of product. If you need to hold the enzymatic process and 50 degrees for 60 minutes it doesn't matter if you get 1 gram or 61 grams. This only influences the amount of initial raw material and enzyme used. Or am I missing something?
6. How did you get 0.25 ml of cleaning detergent for 1 g of protein, if you experimentally used 250 mL of detergent for 61 g of protein?
7. Cleaning and sanitation has been omitted from the LCA midpoint results?

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

In this contribution, the authors propose a study on the sustainability and economic aspects of enzymatic hydrolysis for extracting protein ingredients and oils from fish waste. They offer environmentally friendly and economically viable practices, providing an integration of Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) methods that offer a robust framework for evaluating both the environmental and economic aspects of the process. The topic is both impressive and timely. Results regarding the climate change impact and cost of producing Fish Protein Hydrolysate (FPH) offer valuable insights into the sustainability and economic viability of this extraction method. Moreover, the sensitivity analysis highlights the importance of considering regional and electricity source variations, ensuring a more accurate assessment.

In general, the paper is solid and conclusions are consistent with experimental data.

Therefore, the manuscript may be of interest for publication in Resources journal, but the following points need to be addressed before the publication:

1.    Introduction section, beyond economic and sustainable aspects, lacks of key references on valorization of fish waste to obtain value-added products (see some recent papers published on this topic: Reviews in Aquaculture, 2023, 15(3), 1115-1141; Sustainability, 2021, 13(5), 2428; Frontiers in Chemical Engineering, 2022, 4,1072761)

2.    Some english polishing to correct typos and mistakes is needed.

3.    Some references must get the right formatting.

Some english polishing to correct typos and mistakes is needed.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for improving the manuscript.

Author Response

Dear reviewer 

The corresponding author, on behalf of all co-authors, would like to appreciate your time and effort put into reviewing our manuscript. 

There have been minor changes in the next version of our manuscript. Figure 1 has been replaced with a new one, to improve the clarity of the process. There have been some additions in the text to make the process even more clear.

With best regards,

Reviewer 2 Report

The authors really put an effort into correcting the paper and making it more attractive for publishing. They addressed all the of the points from the previous review. Now, that the manuscript has been rearranged, I could understand the matter even better, which is good for the audience that will be reading it. However, this brought up some new question that I would like to be answered:

1. After hydrolysis, enzyme inactivation was performed at 90 degrees Celsius. Didn't that inactivate the proteins as well or is that not important? The authors did, however, mentioned in the introduction section that subcritical water hydrolysis is disadvantageous due to thermal degradation of heat-sensitive compounds and proteins must certainly are that type of compounds.

2. After centrifugation how was the protein and oil rich fractions obtained, i.e. separated? Decanting? And what about the solid leftover fraction? It is not explained in the Material and Methods section, it doesn't appear on the the block diagram in Figure 1, but it does in Table 1, where it is clear that bones and sludge are also present besides the proteins, oil and water. If these are in the oil phase it should be made clear and explained how is the oil separated from this phase. And how due these bones and sludge affect the LCA?

3. In Figure 1 please add processing residue in the block with Atlantic mackerel, because in this way it seems that the entire fish and not its processing waste is the raw material for protein extraction.

4. If the production cost for 1 gram of protein is 3.68 euros (Line 307), and the selling price is 0.0077 euros (Table 2), how is this profitable, i.e., economically viable, in order to make the "industry stakeholders decide towards this more environmentally friendly practice"?

5. What's the reason for not performing a compositional analysis of the raw material, but using previously published results shown in Table 8?

6. Also If we use the lower value for protein content (18%) from Table 8 on the 15.951 g fish processing residue (raw material) from Table 1, that gets us 2.87 g of protein, and the 1 g obtained or extracted represents only 35%, which is a really low yield. More protein can be found in the side stream than in the main product stream.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Authors have revised the manuscript thoroughly, according to reviewers' comments and suggestions. I recommend this paper for publication in Resources journal.

Minor editing of English language required

Author Response

Dear reviewer 

The corresponding author, on behalf of all co-authors, would like to appreciate your time and effort put into reviewing our manuscript. 

There have been minor changes in the next version of our manuscript. Figure 1 has been replaced with a new one, to improve the clarity of the process. There have been some additions in the text to make the process even more clear.

With best regards,

Round 3

Reviewer 2 Report

Authors made all of the needed changes to the paper and answered to all of my questions accordingly, so I can happily recommend it for publication.