Characterization of Gelatin and Hydrolysates from Valorization of Farmed Salmon Skin By-Products

Round 1

Reviewer 1 Report

On request of Polymers, I have revised the manuscript titled “Characterization of gelatin and hydrolysates from valorisation of farmed salmon skin by-products”, by José Antonio Vázquez and co-workers.

The main scope of this study was to develop a system to valorise by-products coming from Salmon processing which commonly involves the skinning of fish, and that need to be handled for avoid accumulation. Indeed, skin residues contain insoluble and little exploitable collagen which could be a valuable source of gelatin, which, being soluble, represents a more tractable material that has found many applications in the food, pharmaceutical, and biomedical industries The authors have herein proposed firstly the recovering of gelatin by thermal extraction of collagen preceded by different chemical treatments that allowed to obtain similar materials for extraction yields but with different rheological properties. Secondly, the subsequent proteolysis of skin residues allowed to achieve hydrolysates with maximized digestibility and antihypertensive activity, accompanied by the sharpest reduction in molecular weight and higher content of essential amino acids.

The present manuscript is well written, easy to read, and English is fine. Considering a worldwide scenario, where modern societies increasingly demand convenience food, such as fish fillets, the by-products of the fishing industry may pose environmental problems as its volume expands along with growing consumption of fish. Often they are discarded or used to produce low-value fish feed, while they may turn into raw materials for gelatine extraction in place of using pig and cattle bones, skins, and hides. Although many other studies exist concerning the extraction and properties of gelatine from a wide range of fish species, salmon included, the overall merit of this study was having extracted gelatine from farmed salmon skin using different methods and studied for the first time the molecular weight distributions of each material by gel permeation chromatography (GPC) with light scattering detection.

The rheological properties of gelatine have been discussed considering GPC information, along with amino acid profiling. Additionally, the authors have developed a method to completely valorise of salmon skin with the production protein hydrolysates from the solids remaining from gelatine extraction.

General comments

In my opinion, this research will attract the attention of a wide audience among Polymers’ readers, and the appealing results obtained in this study are worthy to be published, but some minor issues must be addressed mainly concerning some typos.

Along all manuscript all headings and sub-headings must contain words with their first letter in capital format.

Line 53 and line 270. After the ref [7] and Ref [37] respectively, there are too many spaces.

Line 63. Please put ref 13 and 14 within the same square bracket, separated by a comma.

Sections 2.2. and 2.3. In these sections, the authors provided a list of experimental procedures both for protocols P1-P5 and for the obtainment of collagen hydrolysates. I suggest inserting the reaction conditions in Tables (Table 1 for Section 2.2. and Table 2 for Section 2.3.) and shorten the text.  Please, along all manuscript, in the main text use Figure and not Fig.

In Figure 4, panel a, Transmittance is incorrect. Please correct accordingly.

Table 4 does not respect the Polymers’ template. Please correct accordingly.

Although not mandatory for Polymers I suggest the authors to separate the last part of discussion in a new paragraph of conclusions.

I ask for minor revisions.

Author Response

We thank the reviewer for the time dedicated to read our paper and the kind comments. We have made all the changes suggested, except for the addition of a conclusions paragraph, as we believe these are sufficiently clear as is.

Reviewer 2 Report

Dear Authors,

Your manuscript described the characterization of gelatin and derivatives from salmon skin by-products. This approach is of utmost relevance nowadays and the content was very adequately presented. If I may, the suggestions would be to reinforce the use of antihypertensive method and consider to consult this new reference from fish bioactives (10.19277/bbr.18.1.256).

Author Response

We thank the reviewer for their comments, however it is not clear to us what he means by “reinforce the use of antihypertensive method”. As far as the reference, interesting as it may be, we see no relationship with the presented work since we did not used n-butanol in the extraction process. Consequently, we have made no changes in the manuscript.