Impact of Cation-Exchange Resin Treatment on Acidification and Quality of Monastrell Red Wine

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

The manuscript entitled “Impact of Cation-Exchange Resin Treatment on Acidification and Quality of Monastrell Red Wine” presents an interesting study on the effects of cation-exchange resin treatment on the acidification of Monastrel red wine, compared to traditional acidification using tartaric acid. As explained by the authors, this study is particularly relevant in the context of the Murcia region, where climatic conditions lead to a lack of acidity in wines.

The experimental design of the study is well performed; however, major revisions are needed in the manuscript for it to be considered for possible publication in Fermentation.

Introduction and Objectives:
I think that  the Introduction (State of the Art) section requires a careful revision to improve its clarity and depth. Additionally, revisions in both the Materials and Methods and Results sections are necessary to ensure consistency and strengthen the overall quality of the manuscript.

When considering microbial acidification, it is important to mention which non-Saccharomyces and Saccharomyces yeasts are capable of producing malic or succinic acid. In addition, Lachancea thermotolerans is nowadays commonly used in winemaking to acidify the must or wine. In this context, it has been described in the literature that this yeast species is capable of producing L-lactic acid. This fact should be added in the introduction of the manuscript.

Why was acidification with malic or lactic acid not considered in this study? Malic and lactic acids do not generally cause stability problems in wine. However, their impact on wine pH is lower, as they are weaker acids compared to tartaric acid. In my opinion, it is necessary to include some comments regarding this aspect in the manuscript.

Materials and Methods:

• The general parameters of grape must (Brix, pH, acidity), used for the elaboration of the wine, must be included in the manuscript.
• In section 2.2.3, entitled “Tannin determination by HPLC”:
  The term “tannin” should be replaced by “proanthocyanidins,” since this methodology (phloroglucinolysis) quantifies only proanthocyanidins. In this sense, the term tannin includes all families of tannins.

Results and Discussion:

• Table 1 should be modified to follow the same format as the other tables in the manuscript. In this sense, the sample names should be presented at the top of the table (as column headers), ensuring consistency in layout and facilitating easier comparison across tables.
• There are errors in the table footnotes. Specifically, different letters within the same row indicate statistically significant differences between treatments. However, you indicated that the letters refer to differences within the same column, which is incorrect.
• When discussing the results from the table 4, it should be considered and explicitly mentioned in the manuscript that a lower pH favors the formation of carbocations through the depolymerization of proanthocyanidins, which may consequently promote their re-polymerization—possibly explaining the higher mean degree of polymerization (mDP) observed.
  In this context, the following paper provides a detailed explanation of the effect of pH on phenolic composition and proanthocyanidin behavior:
  Influence of Wine pH on Changes in Color and Polyphenol Composition Induced by Micro-oxygenation, DOI: 10.1021/jf103038g
  The information provided in this paper could be used to support the discussion of the differences observed in this study regarding phenolic composition, including anthocyanins, tannins, and color parameters.
• Replace throughout the discussion section “epigallocatechin” with “(-)-epigallocatechin.”
• In my opinion, it is necessary to include in the manuscript that the percentage of galloylation corresponds to the proportion of (-)-epicatechin-3-O-gallate subunits.
• It should be clarified whether flavan-3-ol monomers were considered in the phloroglucinolysis method, as their inclusion is relevant for the accurate interpretation of the proanthocyanidin composition and mDP calculations.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors,

Congratulations on your work, a very important topic for the wine industry and very relevant in light of climate change.
Here are some suggestions:
- Missing keywords
- Therefore, a lower presence of copper, along with other metals in wines from must-treated with cation exchange resin, could justify the lower volatile acidity values found in these wines. Table 1 should be referenced beforehand.
- Table 3, for the PA treatment, is missing the statistical letters. Similarly, Table 4 is missing the TT treatment.
- Table 6, improve the formatting.

Best regards

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

After the suggested modifications made in the manuscript, I consider that this manuscript may be accepted for possible publication in Fermentation.