Extraction and Analysis of Compounds with Antibacterial Potential from the Red Alga Grateloupia turuturu

Round 1

Reviewer 1 Report

In my opinion, the paper “Extraction and Analysis of Compounds with antibacterial Potential from the Red Alga Grateloupia turuturu”, cannot be accepted mainly because it doesn’t provide novelty in its field, both in chemical and biological analysis. As it is reported even in the conclusion, it has been already reported in some studies the extract activity of this alga as well as the polysaccharides composition. Although the biological activity show a dose depended and increase with the enrichment that has been done with the second extraction, it is not so relevant (extracts have moderate activity) and I believe that you cannot associate the activity to the polysaccharides without further investigation. Further study on resistant bacterial strains, for example, and further chemical purification to identify compounds can improve the work.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors described that they obtained an ethanol fraction extracted with ethanol from Grateloupia turuturu (two life cycle individuals) and a polysaccharide (carrageenan) fraction further extracted with hot water. Using these extract fractions, the cell growth inhibitory activity of E. coli and S. aureus was performed, and they described that the inhibitory ability increases with the concentration. In addition, FTIR-ATR measurement of each fraction is carried out, and it is stated that the composition of each fraction extracted from two life cycle individuals was not different. And, it has been confirmed that each contains carrageenan.

 

1) As can be seen from Figures 2 and 3, the hot water extract fraction shows stronger cell growth inhibitory activity than the ethanol extract fraction. This difference seems to be due to the difference in the concentration of carrageenan, as can be seen from Figure 4. (In Figure 4, we can see that the ethanol extract fraction also contains carrageenan.) It may be that the hot water extract fraction rich in carrageenan showed stronger growth inhibitory activity and the ethanol extract fraction less carrageenan showed only weak activity. Evidence should be given if the activity of the ethanol extract fraction is not due to carrageenan.

 

2) The authors describe "fatty acids (palmitoleic acid, oleic acid ...), glycosides and alkaloids, are associated in fact with the antibacterial capacity observed against these two strains" in the discussion. However, the FTIR-ATR results only show that carrageenan is contained in all extracted fraction. Evidence should be given if it is due to effects other than carrageenan.

 

3) The authors also state from the results of FTIR-ATR that "the presence of a hybrid kappa / iota / theta carrageenan with some vestigial presence of agar." However, the peaks at 741 and 790 cm-1, which are the basis for the presence of agar, are difficult to read from Figure 4. Therefore, it is also doubtful that there is agar.

4) There is no legend unit in Figures 2 and 3.

Author Response

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Round 2

Reviewer 1 Report

The paper “Extraction and Analysis of Compounds with antibacterial Potential from the Red Alga Grateloupia turuturu” has been significantly improved as clarity of the contents and quality of presentation. Some minor errors in text editing are still present and should be carefully checked.

Author Response

Thank you for your comment. We have taken into consideration your opinion and based on that (and on what we thought that should be improved) we’ve made some corrections to our article where we tried to improve our explanation of the research design and to better connect the results and conclusion. We hope that with this review everything becomes clear.

Reviewer 2 Report

The authors obtained ethanol extract and polysaccharide extract, but I still can not understand that only polysaccharide extracts were measured by FTIR-ATR. As you mentioned, if there is no polysaccharide in the ethanol extract, it may be important that ethanol extracts are also measured by FTIR-ATR and show that they do not absorb at 1012 cm -1 and 1217 cm -1. These two peaks are strong and are typical for sulfate of agar/carrageenan. The need for this additional experiment is up to the editor.

 

Please make the following corrections.

Fig. 4: tretasporophyte → tetrasporophyte

tretasporophyte polysaccharide → tetrasporophyte polysaccharide

Author Response

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Author Response File: Author Response.pdf