Use of Fe (II) and H₂O₂ along with Heating for the Estimation of the Browning Susceptibility of White Wine

Round 1

Reviewer 1 Report

The manuscript presents physicochemical data about white wine browning under Fe-H₂O₂ accelerated oxidative conditions. The context of the study is well introduced. However, the manuscripts remains a compilation of standard assays measuring compound families related to wine antioxidant activity. The mechanistic link of these compounds with browning potential (independent from oxidation) was hardly discussed alongside their data.

Authors claim "it is possible to develop a rapid test for assessing the susceptibility of white wines to browning" while there's no browning data under normal storage conditions (e.g. from the same wines used in the study) to support their claims. 

Author Response

DETAILED RESPONSE TO REVIEWERS’ COMMENTS

Reviewer 1

Comments

The manuscript presents physicochemical data about white wine browning under Fe-H₂O₂ accelerated oxidative conditions. The context of the study is well introduced. However, the manuscripts remains a compilation of standard assays measuring compound families related to wine antioxidant activity. The mechanistic link of these compounds with browning potential (independent from oxidation) was hardly discussed alongside their data.

Authors claim "it is possible to develop a rapid test for assessing the susceptibility of white wines to browning" while there's no browning data under normal storage conditions (e.g. from the same wines used in the study) to support their claims. 

-Response

Firstly, we would like to thank Reviewer 1 for acknowledging that the context of the study is well introduced.

Regarding his comment about the assays used, we used the scientifically available assays to estimate the susceptibility of white wines to oxidation. Moreover, we introduce the assay of total free sulphydryls as a new potential index of white wine oxidative browning. In addition, we have introduced in the Supplementary material the UV/Vis spectra to give more info regarding changes during wine storage at 18 ^oC and 45 ^oC (See for your convenience the added Supplementary figures and comments within the revised article).

As far as the mechanistic link of these compounds with browning potential, the latter is given in details in the Introduction section, so the reader has clear information to follow further the experimental results.

Finally, regarding our perspectives for the development of a rapid test for assessing the susceptibility of white wines to browning, we studied the evolution of browning, i.e the absorbance at 420 nm, along with changes in the chemical composition of white wine during storage at both18 ^oC and 45 ^oC. So, there is a plethora of browning data at 45 ^oC and under normal storage conditions i.e. at 18 ^oC.

Reviewer 2 Report

1. at pag. 3, lines 133-136 please provide reference for the method;
2. at pag. 4, line 144 improve de physical unit for concentration and switch 5 g/l to 5 g/L according to the rules of BIPM;
3. at pag. 4, lines 144-145 please provide reference for pH 3.5 used in model medium, or justify the selected value compared with the pH for the selected wines;
4. at pag. 4, line 147 – according to 2.3. Equipment, the Perkin Elmer Lambda 35 UV/Vis spectrophotometer is a double channel spectrophotometer. Please refresh this statement, give a reference for calibration, or provide witch Instrument Performance Verification (IPV) tests are realised for instrument calibration;
5. at pag. 4, line 150 please provide reference for the method;
6. at pag. 4, line 166 first concentration of catechin in methanol is 0.4 or is 0 and 4 mg/L;
7. at pag. 10, lines 369-370 please rephrase statement;
8. at pag. 14, lines 509-510 provide reference code for method used.

Author Response

DETAILED RESPONSE TO REVIEWERS’ COMMENTS

We thank the Reviewers who evaluated our manuscript. The comments were constructive since these improved the quality of our manuscript. There has been an effort to cover adequately all comments. All changes are marked in red colour within the revised article/material.

Reviewer 2

Comments

1. at pag. 3, lines 133-136 please provide reference for the method;
2. at pag. 4, line 144 improve de physical unit for concentration and switch 5 g/l to 5 g/L according to the rules of BIPM;
3. at pag. 4, lines 144-145 please provide reference for pH 3.5 used in model medium, or justify the selected value compared with the pH for the selected wines;
4. at pag. 4, line 147 – according to 2.3. Equipment, the Perkin Elmer Lambda 35 UV/Vis spectrophotometer is a double channel spectrophotometer. Please refresh this statement, give a reference for calibration, or provide witch Instrument Performance Verification (IPV) tests are realised for instrument calibration;
5. at pag. 4, line 150 please provide reference for the method;
6. at pag. 4, line 166 first concentration of catechin in methanol is 0.4 or is 0 and 4 mg/L;
7. at pag. 10, lines 369-370 please rephrase statement;
8. at pag. 14, lines 509-510 provide reference code for method used.

 

-Response

1. A reference has now been added.
2. Corrected accordingly.
3. The relevant references of the adjustment of pH of the model medium to 3.5 have now been provided.
4. The statement has been refreshed and calibration practices have now been declared.
5. A reference has now been added.
6. Corrected accordingly. It is 0, 4,….mg/L.
7. A better statement has now been given.
8. In this page all references are coded. We did not see any problem here.

Reviewer 3 Report

The authors investigated the possibility to use Fe (II) and H2O2 along with heating for the estimation of the browning susceptibility of white wine, with the aim to develop a rapid test for the estimation of the browning susceptibility of white wines. The manuscript is quite well written and its thematic has an applicative value, but from the scientific point of view the thematic is outdated, it lacks novelty and the references used are quite old, with only two references from the last eight years (2015-2022). If the authors wish to publish the paper, it should be thoroughly rewritten, with newer references added, and the novelty of the thematic should be emphasized in the text. Also, the discussion should be improved, also using the newer references.

 

Some other specific comments are the following:

 

Lines 27-28: Change ‘Present results’ to ‘The results’.

Lines 30-31: The text ‘Results also show that the levels flavanols is a suitable index to…’ should be improved to make it clearer.

Lines 39-86 (and on several other places in the manuscript): The text should be divided in paragraphs.

Lines 89-91: Why is this in italic? Also, on other places in the text the styles of writing differs considerably and they should be uniform throughout the manuscript.

Line 218: Delete ‘of the mixture’ as it is repeated twice.

Line 223-224: do not write both ‘p=0.040’ and ‘<0.05’ because it is enough to write one value from these two. Chose the approach and then use it consistently throughout the manuscript.

Line 233 (and other places where this is mentioned below the figures): do not write the abbreviation (A420 nm) but the full name (absorbance at 420 nm).

Lines 392-393: Rewrite the text ‘Glutathione, the main thiol of wines, it has been proposed to…’.

Lines 425-428: Rewrite the conclusions to be more detailed and concise.

Author Response

DETAILED RESPONSE TO REVIEWERS’ COMMENTS

We thank the Reviewers who evaluated our manuscript. The comments were constructive since these improved the quality of our manuscript. There has been an effort to cover adequately all comments. All changes are marked in red colour within the revised article/material.

Reviewer 3

Comments

The authors investigated the possibility to use Fe (II) and H2O2 along with heating for the estimation of the browning susceptibility of white wine, with the aim to develop a rapid test for the estimation of the browning susceptibility of white wines. The manuscript is quite well written and its thematic has an applicative value, but from the scientific point of view the thematic is outdated, it lacks novelty and the references used are quite old, with only two references from the last eight years (2015-2022). If the authors wish to publish the paper, it should be thoroughly rewritten, with newer references added, and the novelty of the thematic should be emphasized in the text. Also, the discussion should be improved, also using the newer references.

 -Response

We would like to thank Reviewer 3 for acknowledging that the article has an applicative value and is quite well written.

Regarding the novelty of the present study, we should stress that for the first time in the relevant literature, the addition of Fe II + H₂O₂ along with heating to estimate the susceptibility of white wine to browning. Moreover, we introduce the assay of total free sulphydryls as a new potential index of white wine oxidative browning.

The novelty of the present study has now been given in Abstract and Conclusion sections, so the reader understands quite clear the new amendments and applications of the present study. In addition, there has been an effort to improve the discussion section by introducing the newest and most relevant studies. See through the revised text and reference list.

Some other specific comments are the following:

Lines 27-28: Change ‘Present results’ to ‘The results’.

-Response

Done.

Lines 30-31: The text ‘Results also show that the levels flavanols is a suitable index to…’ should be improved to make it clearer.

-Response

The sentence was improved.

Lines 39-86 (and on several other places in the manuscript): The text should be divided in paragraphs.

-Response

The whole text has now been divided into paragraphs.

Lines 89-91: Why is this in italic? Also, on other places in the text the styles of writing differs considerably and they should be uniform throughout the manuscript.

-Response

Lines 89-91 have now been set without italic. There has been an effort to keep consistent the type of writing through the main text.

Line 218: Delete ‘of the mixture’ as it is repeated twice.

-Response

Done.

Line 223-224: do not write both ‘p=0.040’ and ‘<0.05’ because it is enough to write one value from these two. Chose the approach and then use it consistently throughout the manuscript.

-Response

Corrected. We used only the p-value. Kindly see through the revised text.

Line 233 (and other places where this is mentioned below the figures): do not write the abbreviation (A420 nm) but the full name (absorbance at 420 nm).

-Response

Corrected according to Reviewer’s suggestions.

Lines 392-393: Rewrite the text ‘Glutathione, the main thiol of wines, it has been proposed to…’.

-Response

The text has now been modified to be clearer.

Lines 425-428: Rewrite the conclusions to be more detailed and concise.

-Response

The conclusion section has now been more detailed and concise. See through the revised conclusion section.

Round 2

Reviewer 1 Report

The manuscript is now considerably improved after making connections with recent studies and adding mechanistic discussions.

Author Response

We tried to improve the manuscript.

Reviewer 3 Report

Although some changes have been made to the manuscript and it improved in some extent, the improvement was not enough to qualify for the publication in the Applied Sciences journal. From the scientific point of view the thematic remains outdated and it lacks novelty. Also, there is a quite large number of self-citation (a total of 11 references), which should be reduced. In my opinion, if the authors wish to publish the paper, it should be more thoroughly rewritten. One additional information, if the p value is 0,000, it is usually written in the text as p<0.001.

Author Response

We tried to improve the manuscript.

It is truth that this work is applied research and its scope is the development of an easy, rapid, and reliable test to evaluate the browning susceptibility of white. This is of global interest. Moreover, referee 3 says that this work lacks novelty. Our work is not basic research and does not provide new scientific knowledge, even though our results indicate that total free sulphydryls may be a suitable index to follow white wine oxidation. Our work shows that similar changes occur in white wine by adding or not Fe (II) and H₂O₂ (Fenton reaction) at 18 or 45 ^oC and indicates that an easy, rapid, and reliable test to evaluate the browning susceptibility of white can be developed / standardized.

 

My groups through that time published several significant original research works in the thematic of wine oxidation and we used several of them. We tried to exclude some of self-citations.

Regarding comment info of referee 3 concerning the p value we corrected this point.