Utilization of Blackmouth Catshark (Galeus melastomus) Skins as an Alternative Source of Gelatin: Extraction and Physicochemical Characterization in Comparison to Porcine Skin Gelatin

Round 1

Reviewer 1 Report

The paper compares the physicochemical characterization of gelatin obtained from blackmouth catshark skins extracted using a combined alkaline and acidic process to porcine skin gelatin. In doing so, the authors claim a relatively high yield of dry gelatin obtained from the extraction method, with high protein and low moisture and ash content, better color properties, and similar gel strength and viscosity than pork-derived gelatin.

The study is well thought out and conducted logically to compare blackmouth catshark skin-derived and pork-derived gelatin's physicochemical properties. The authors conclude that the skins from blackmouth catshark can be potentially used as an alternative raw material for gelatin manufacture, fulfilling the needs of a more diverse market that does not consume pork or cow- derived products.

The conclusions are consistent with the presented evidence and results.

Overall, the paper is very well written, with easy-to-follow figures that enhance the study's importance.

Comments

1.       The reported measurements for gelatin yield presented were only conducted twice (n=2). To further substantiate their claim that “the yield of gelatin found in this study was significantly higher than that previously reported for gelatin extracted,” more measurements are suggested to increase reliability. It would seem that the extraction process utilized has several steps where product can be lost, and a duplicate measure would fail to account for this properly,

2.       The most recent reference included is from 2016, with the vast majority being from the early 2000s or before. Have there been no advances in the field in the past eight years?

3.       Double-check the reference formatting: The bolding of the publication tear and page number does not match in all. 

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted in red-colored text in the revised manuscript.

1. The reported measurements for gelatin yield presented were only conducted twice (n=2). To further substantiate their claim that “the yield of gelatin found in this study was significantly higher than that previously reported for gelatin extracted,” more measurements are suggested to increase reliability. It would seem that the extraction process utilized has several steps where product can be lost, and a duplicate measure would fail to account for this properly. Authors: If gelatin was lost in the side streams of the various processing steps, then that would have led to a large standard deviation. Many research studies in this field present gelatin yield without a standard deviation or standard error. In our study, however, the standard deviation of gelatin yield for n=2 is provided and was found 0.61 (Line:240), which means that the co-efficient of variation (CV) is 4.37%, which is very low. A low CV means that the measurement is precise and in many experiments is used for repeatability. Therefore, were believe that no further measurements are required, despite the fact that the process comprised of several processing steps.
2. The most recent reference included is from 2016, with the vast majority being from the early 2000s or before. Have there been no advances in the field in the past eight years? Authors: Four additional recent research studies have been added in the manuscript. Please see references [12], [13], [14] and [54].
3.  Double-check the reference formatting: The bolding of the publication tear and page number does not match in all. Authors: We agree with the comment. References have been checked and changes have been made in the References section.

Reviewer 2 Report

Keywords: should be in alphabetic order

Materials: Line 82: please correct the unit of degree centigrade ( -20oC). infact correct it in the entire manuscript

Q:  Line 110: The Gelatin Yield was on dry weight basis? please mention it below the formula.

If possible please add some new references as most the references are quite old.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted in red-colored text in the revised manuscript.

Materials: Line 82: please correct the unit of degree centigrade ( -20oC). infact correct it in the entire manuscript. Authors: Thank you for noticing. Changes have been made throughout the manuscript.

Q:  Line 110: The Gelatin Yield was on dry weight basis? please mention it below the formula. Authors: Yes, it is expressed as g dry gelatin/100 g original fish skins. Please check line 126 in the revised manuscript.

If possible please add some new references as most the references are quite old.

Authors: Four additional research studies have been added in the introduction section. Please check references [12], [13], [14] and [54] in the references section.

Reviewer 3 Report

The characterization procedure and results are clearly presented. But Figure 2 is missing.

" In this manuscript, authors extracted gelatin from blackmouth catshark using a patent method and characterized the properties of extracted gelatin including molecular weight analysis, amino acid analysis, gelling properties. Overall, the characterization procedure and results are presented appropriately. I think the manuscript can be published in present format. But authors should consider following aspects to improve the manuscript further: 1. The activated carbon treatment method should be presented in line 103. How was the odor removal extent evaluated? 2. The boom strength of fish gelatin was reported to be around 100g for cold-water fish and 200g for warm-water fish (Derkach SR, Voron'ko NG, Kuchina YA, Kolotova DS. Modified Fish Gelatin as an Alternative to Mammalian Gelatin in Modern Food Technologies. Polymers (Basel). 2020 Dec 19;12(12):3051. doi: 10.3390/polym12123051.) Can authors explain why the gelatin extracted from blackmouth catshark has such high strength? 3. Authors should briefly introduce how widely fish gelatin has been applied in commercial food products (e.g., Paskesz Marshmallows) and the disadvantage of fish gelatin. "

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted in red-colored text in the revised manuscript.

1. The activated carbon treatment method should be presented in line 103. How was the odor removal extent evaluated? Authors: We agree with the comment. This is actually based on the patented process cited in the manuscript (Karayannakidis et al. [22] in revised manuscript), where the activated carbon treatment is described. Basically, the gelatin extract is passed through a column filled with granular activated carbon. This processing step was found to be critical in order to obtain gelatin from various fish skins (including blackmouth catshark, sole, salmon etc.) free of the unpleasant fishy odor. The odor was assessed by a group of panelists, but not in this study. Please refer to lines:114-116 of the revised manuscript, where we describe how the treatment was done.
2. The boom strength of fish gelatin was reported to be around 100g for cold-water fish and 200g for warm-water fish (Derkach SR, Voron'ko NG, Kuchina YA, Kolotova DS. Modified Fish Gelatin as an Alternative to Mammalian Gelatin in Modern Food Technologies. Polymers (Basel). 2020 Dec 19;12(12):3051. doi: 10.3390/polym12123051.) Can authors explain why the gelatin extracted from blackmouth catshark has such high strength? Authors: There are numerous research studies where a high gel strength gelatin is obtained from fish skins (e.g., 401 g gel strength for gelatin extracted from Alaska pollock skins in the study of Zhou, P., and Regenstein, J. M. 2005. Effects of alkaline and acid pretreatments on Alaska pollock skin gelatin extraction. J. Food Sci. 70: C392–C396). In the study that you mention the authors attribute the inferior gel strength of fish gelatin to the lower imino acid content only (Pro and HyPro content). However, the physical properties of gelatin, such as gel strength, are also affected by the MW distribution and the proportion of a-chains (e.g., https://doi.org/10.1007/s12393-014-9096-5). As you can see in our electrophoretic study, BC skin gelatin showed higher proportion of a-chains than porcine gelatin.  
3. Authors should briefly introduce how widely fish gelatin has been applied in commercial food products (e.g., Paskesz Marshmallows) and the disadvantage of fish gelatin. " Authors: Please read lines 59-69 in the revised manuscript.

Reviewer 4 Report

Dear author, please respond to my comments on the pdf file attached and please care about using most recent references in your meterial and method sections. Also, please care about putting commas where it is possible

Comments for author File: Comments.pdf

Please care about putting commas where it is possible

Author Response

Dear reviewer, thank you very much for taking the time to review this manuscript. Please download the attached pdf file that you asked for with our responses. All changes to your suggestions have been made with one exception, the first comment on page 12 in the conclusions section. We did not modify the sentence and we would like to leave it as it is. The changes are higlighted in red colored-text in the revised manuscript. Again, thank you for yor time.

The authors.

Author Response File: Author Response.pdf