Effect of Molecular Weight of Tilapia (Oreochromis Niloticus) Skin Collagen Peptide Fractions on Zinc-Chelating Capacity and Bioaccessibility of the Zinc-Peptide Fractions Complexes in Vitro Digestion
Round 1
Reviewer 1 Report
In this work, the authors investigated the effect of the molecular weight of tilapia skin collagen peptides on their zinc chelation capacity and the bioaccessibility of their zinc complexes, by evaluating the zinc-chelating ability of three different molecular weight peptides (P1,P2,P3), their solubility and the stability of the Peptides-Zn(2+) complexes during simulated in vitro digestion.
The work is interesting, but in my opinion the peptides-Zinc interaction deserves a more accurate investigation. I am especially mesmerised by the hypothesised formation of Zn-N bond with N atoms of the peptide bonds, based on the shift of amide A bands (page 10, lines 247 - 254). Are there other evidences (XPS, XAS at Zn absorption edge, or other spectroscopic studies) of the formation of a Zn-N bond? Have the authors considered that the stability of C=O and COO- FT-IR features could be explained with the substitution of C=O...H-N hydrogen bonds with Zn(2+)/carbonyl or carboxyl groups interactions; the breaking of H-bonds could justify the Amide A band shift. This is just an hypothesis, but I expect that the authors introduce a more accurate discussion of their N-Zn bond formation hypothesis.
In addition, there is a number of minor/medium corrections that should be considered:
1) page 3, line 103: how was the pH maintained at 6? did you use a buffered solution? please give details.
2) page 4, line 111: please give a more detailed description of the atomic absorption spectrometry measurements (sample preparation, etc).
3) page 5, line 133: again, what buffer did you use? please insert a detailed description (chemicals, concentrations, pH checking procedure).
4) page 5, line 148: how did you check that pH = 7.5? to put the same amount of HCl and NaOH could not be an accurate procedure, usually a phosphate buffer is used to obtain such pH-stable solutions.
5) page 10, lines 251-252: "electron" (not "election").
6) page 11, line 268: "FTIR results demonstrate....". The term "demonstrate" is not appropriate. I suggest to use "suggest".
7) page 12, line 299: "small particle size". Did you perform morphological characterisation? no SEM images are presented in the paper.
8) page 13, line 324: "The results showed that P1 exhibited stronger zinc chelation capacity due to the higher net negative charge on its surface". But your hypothesis is that amide groups bond Zn ions through N-Zn bonds. No negative charge (COO- groups, usually, in peptides) are involved in Peptide-Zn interactions in your hypothesis.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
- Line 100. In general, weak alkali conditions are better suited to create charge-charged conditions for Zinc-binding peptides. Why did you proceed at pH 6.0 to prepare zinc peptide?
- Line 163. Zinc-chelating capacity of the peptide
The authors cite that surface hydrophobicity is important. Why did the surface hydrophobicity of collagen peptides p1, p2, and p3 not show the measurement results?
- Line 317-319. What is the evidence for improved bioavailability of zinc peptides?
Table 3 shows the results of only zinc release by digestive enzymes. The bioavailability when compared to inorganic zinc is unknown as a result.
Minor revision
Line 131. The zinc solubility à The solubility
Lone 134, 135. 37 ℃ --> 37℃, 20 ℃ --> 20℃, Please confirm all (oC and % units must be pasted with the previous word)
Line 158. SPSS --> Mark manufacturer and country of origin behind SPSS
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors considered all my suggestions, and the manuscript was carefully revised. I think that this paper is now suitable for publication, after the following minor corrections:
1) at page 5, line 139 the word "buffer" is repeated twice in the same sentence. Please correct.
2) the sentence at page 5, line 154 "and maintain that stability of the pH value of the system" is not clear, please reformulate it.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Some of the requests for revision were not reflected, but the paper is accepted at the present level.
Author Response
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Author Response File: Author Response.pdf
