Study on the Effect of Different Concentrations of SO₂ on the Volatile Aroma Components of ‘Beibinghong’ Ice Wine

Round 1

Reviewer 1 Report

The authors aim to investigate the impact of increasing SO2 levels on the aromatic profile of 'Beibinghong' ice wine. The topic might be of interest, nevertheless, there is a key point related to the experimental section that needs to be clarified.

The whole experimental apparatus is based on the addition of a few tens of μg /L during vinification, identifying an optimum corresponding to 30 μg /L. However, it is not clear what is the scientific significance and technological feasibility of adding such low concentrations of SO2 as a vinification aid. The authors state that differences in the order of tents μg /L make the difference in the fermentation rates, which is pretty unrealistic. Moreover, it is hard to understand how the authors relate the legal limits for overall SO2 addition in wines (hundreds of mg/L) and the significantly lower concentration (tens of μg/L) added in grape juices in the present study. In lines 98-99 authors state that: “The addition of SO2 to red wines, depending on the fruit's health and composition, should not exceed 60 μg/L”; nevertheless, this regulation/recommendation is not either mentioned or discussed based on scientific evidence.

Was it an approach based on preliminary studies? Authors state that “few studies have investigated the effects of different SO2 additions on the aroma of 'Beibinghong' ice wines and identified the volatile compounds that play a crucial role in the different SO2 additions” (Lines 110-112); however, these studies have not been mentioned making it difficult to evaluate the contribute and innovation proposed here.

In my opinion, the authors must provide adequate justification for their experimental plan in terms of SO2 addition, which is the key aspect of the experiment, also considering the technological feasibility of the approach they propose and explicitly mentioning the studies previously conducted on the subject.

In general, all statements need to be supported by adequate references or explained in the context of the experimental results.

I am adding additional comments below:

·         SO2: subscript. Correct all over the manuscript

·        the same concept (understanding the effect of SO2 on the fermentation of 'Beibinghong' ice wine) is repeated redundantly; please make the abstract/introductory/conclusion parts more concise and informative

·         The role of SO2 in wine protection and the molar balances of reactions involved need to be critically discussed. Are the dosages investigated sufficient to ensure the protection and consistent to identify differences attributable to the SO2 concentration?

·         Vitis amurensis Rupr: Italic

·         Recommended SO2 levels in wines are reported without any Regulatory reference. In Europe, for instance, the updated legal limits are 150 and 200 mg/L, respectively, and not 160 mg/L and 210 mg/L as stated by the authors; please clarify your sources.

Author Response

Thank you very much for your comments on my paper, which benefited me a lot. The replies to your comments are attached to the following one by one, please have a look. Thank you again for your criticism and correction.

Author Response File: Author Response.pdf

Reviewer 2 Report

In the present study the authors investigated the effects of SO₂ addition on the fermentation process and volatile aroma compounds of 'Beibinghong' ice wine. I found the article very well written and organized. Th work is presented in details and in an understandable manner. I have some minor observations only.

In case of SO2, the number 2 should be subscript. Please correct in the whole manuscript

The abstract is too long and containing a lot of detailed information that is not needed in an abstract. Please write a brief abstract that can highlight the state of the art in the field, what you did, why you did, what you obtained and maybe a very short conclusion.

The introduction is well documented, well written and organized. I have no comments.

Line 186 – is G.A.S the manufacturer of the GC-IMS instrument? If yes more details are needed (city, country, etc).

The quality of the figures is not good enough and especially the text of the figures cannot be read. Please improve it.

Author Response

Thank you very much for your comments on my paper, which greatly benefited me. The replies to your comments are attached to the following individually; please look at them. Thank you again for your criticism and correction.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear authors,

I have analyzed the manuscript and I would like to make some recommendations:

1.The Abstract should be rewritten bearing in mind that it must have a more synthetic form and reproduce only that research result that is considered novel and the most important. Separate the listing of the analysis methods used from the results. Correctly write the chemical formula of sulfur dioxide with the number 2 as a subscript.

2. Rewrite the title, the wording is not too synthetic.

3. Rewrite the keywords: the same words as in the title must not be repeated.

4. Please detail the process of obtaining the wine samples from section 1.3: what chemical characteristics did the must have prepared for fermentation, what type of yeasts were used, in what concentration, etc. It is not clear whether the samples were repeated to analyze possible errors.

5. Please comment on the results presented in section 2.1 with arguments and bibliographical references. Likewise, in sections 2.2, 2.3, 2.4.

 6. In table 5, where the sensory characteristics of some identified compounds are presented, please mention for each compound, the bibliographic indication from which the correlation with the sensory descriptors can be found.

7. For the entire results and discussions section, please provide explanations and argue the results obtained by comparison with the specialized literature, so add relevant bibliographic references.

8. You must convey the novelty and relevance of the study.

9. The conclusions are not concise and the most relevant.

Author Response

Thank you very much for your comments on my paper, which greatly benefited me. The replies to your comments are attached to the following individually; please look at them. Thank you again for your criticism and correction.

Author Response File: Author Response.pdf

Reviewer 4 Report

Line 15 Asbtract extremely long. Should be 150-200 words, as the journal suggests.

Line 29-31 Same information twice

Line 31-39 too much explanation of m&m section, you should reduce. 

Line 50 Keywords should be significant, change aroma presenting substances by other name, such as aroma, aromatic compounds, aromatic components…

Line 63-64 same Beibinghong?? The second Beibinghong what? Standardized wine?

Line 90 Point instead of coma or lowercase letter ‘such’

Line 93 Add reference

Line 119 100 μg/L is written twice. Is that correct?

Line 300 Figure 3 do not include extra information compared with Fig 2 , include it in supplementary material.

Line 330 Can you include the RT time in min instead of seconds? In the list there are some letters in Chinese. Please change it.

Line 399 Can you please include the PCA with the QC samples?

Line 500 Conclusions too long, please short it

Author Response

Thank you very much for your comments on my paper, which greatly benefited me. The replies to your comments are attached to the following individually; please look at them. Thank you again for your criticism and correction.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Line 148 Add the unit mg/L to 10

How did you manage to reach 100 mg/L SO2 in fermentation? Was it appropriate to ensure the yeasts' metabolism? And what about the risk of developing off-flavors due to sulfur compounds? Once again, does the SO2 addition strategy make sense on a technological prospect? Possibly this high concentration affected the yeast activity. 

Author Response

Thank you, Professor, thank you very much for your review. I have attached my response in the attached file; good luck with your work, and thanks again!

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear authors,

I reviewed the updated document and I would like to point out that you did not solve all the points as I mentioned in the first analysis.

Section 2, results and analyses, is a string of results, without motivating the discoveries made and without finding any scientific explanations for the statements according to references or other published works ( the number of which is very high regarding the use of sulfur dioxide). You also failed to explain the relevance and novelty of the study that motivates the publication, because the number of works published on this topic is very large (and is not found in the cited bibliography - too few bibliographic references).

The content of table 5 has not been fixed. There is a need for a bibliographic reference for each volatile compound and the descriptors with which it is correlated. See in the example or in the published literature.

I recommend revising the manuscript according to the observations.

Author Response

Thank you, Professor, thank you very much for your review. I have attached my response in the attached file; it is hard for you to check it again; good luck with your work, and thanks again!

Author Response File: Author Response.pdf

Reviewer 4 Report

The authors changed all the suggestions I made. 

You should consider QC samples for metabolomics studies in further experiments.

Author Response

Thank you, Professor, thank you very much for your review. I have attached my response in the attached file; good luck with your work, and thanks again!

Author Response File: Author Response.pdf