Understanding Wood Polysaccharide Depolymerization and Denaturation Under Different Toasting Conditions Through Analysis of Sugars Extracted from French Oak Chips

Round 1

Reviewer 1 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

Dear Authors, I have revised your manuscript “Effect of toasting temperature and duration on sugars extracted from French oak (Quercus petraea) chips into model wine solution”. The work made a generally positive impression on me, however, just a few points require my opinion and attention:

My first observation is if you want to emphasise the effect of the duration of toasting, considering the variable of water concentration in the wood. Why is it proposed to evaluate the effect of the duration of toast in chips with a dryness of only 103^oC until a constant mass was achieved? Between the range of 103 to 180^oC, did you consider a dryness or toasted? Seems that there are no statistical changes in the loss of weight until 200oC, and in Figure 3, the glucose, arabinose and galactose start with the maximum amount of monosaccharides.

Line 31: Why is it necessary oxidation? Is it not for ageing?

Lines 29 to 36: There is also an increase in tannins, could be more explanatory to write a mention about tannins in the first lines of the introduction.

Line 57: Please mention the reference to the previous studies, or at least describe the thickness or mesh of the chips.

 

Line 172: All Figures, related to temperature and duration, could be clarifier have the standard deviation or the table with all results.

Author Response

Dear Reviewer 1,

Thank you for your important review. We would like to reply for your comments as follow.

Dear Authors, I have revised your manuscript “Effect of toasting temperature and duration on sugars extracted from French oak (Quercus petraea) chips into model wine solution”. The work made a generally positive impression on me, however, just a few points require my opinion and attention:

My first observation is if you want to emphasise the effect of the duration of toasting, considering the variable of water concentration in the wood. Why is it proposed to evaluate the effect of the duration of toast in chips with a dryness of only 103°C until a constant mass was achieved? Between the range of 103 to 180°C, did you consider a dryness or toasted?

[A] "The toasting of oak chips" and "the measurement of moisture content in oak chips (drying at 103°C)" are independent experiments. Generally, freshly cut wood is not processed immediately but is instead thoroughly dried beforehand. If this drying step is omitted, the wood may warp or distort after processing. The drying of wood is generally carried out when producing barrels or chips as well. A temperature of 103°C is set for drying the wood in order to measure its moisture content, and this method is widely recognized in the field of wood science (JIS Z2101: 2009). In the environment where the experiment was carried out in Japan, the moisture content of the dried wood is approximately 15%. The experiment at 103°C was conducted to demonstrate that the wood used in the experiment had been sufficiently dried after being cut. On the other hand, toasting is typically performed using wood that has been sufficiently dried. Therefore, toasting at 180°C refers to heating "dried wood", which has been left at room temperature, to 180°C.

For the reasons mentioned above, the changes between 103 to 180°C were not considered. This explanation is provided in lines 135-140, 322-326.

 

Seems that there are no statistical changes in the loss of weight until 200oC, and in Figure 3, the glucose, arabinose and galactose start with the maximum amount of monosaccharides.

[A] As you pointed out, there was almost no change in weight within the 180 to 200°C. However, the extracted monosaccharide contents has changed significantly. It has been confirmed that the raw wood contains not only polysaccharides but also monosaccharides, which can be extracted into the model wine. However, it is speculated that these monosaccharides undergo structural changes due to toasting around 200°C, transforming into compounds that are not sugars. However, the amount of these compounds is considered negligible relative to the weight of the wood chips. Therefore, it is unlikely to be reflected in the weight change. These explanations are provided in lines 315-316, 360-369, 371-374.

 

Line 31: Why is it necessary oxidation? Is it not for ageing?

[A] The barrel is a porous material, known to allow the passage of small amounts of oxygen. It is well known that this moderate oxidation plays an important role in the aging of wine in barrels. Therefore, the term "oxidation" was used. However, to avoid any misunderstanding regarding the point you raised, "oxidation" has been removed (lines 30-31).

 

Lines 29 to 36: There is also an increase in tannins, could be more explanatory to write a mention about tannins in the first lines of the introduction.

[A] We have added a description regarding the tannins extracted from the barrel to the first line of the introduction (lines 33-35).

 

Line 57: Please mention the reference to the previous studies, or at least describe the thickness or mesh of the chips.

[A] We have added the reference related to "our previous study" in lines 58-60.

 

Line 172: All Figures, related to temperature and duration, could be clarifier have the standard deviation or the table with all results.

[A] We have included all the data and standard deviation in the tables as Table 1S, 2S, 3S, and 4S in the Supplemental Data section. Please refer to lines 481-485 and the Supplementary data (attached file) for these additional data.

Reviewer 2 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

The manuscript by Kainuma et al. study the effect of differences in toasting temperature and duration on polysaccharides in French oak chips. This revised manuscript incorporated a title modification as well as edits in the various sections. Despite these modifications, the context and the theme remain similar to the authors previous publication, with the the exception of the inclusion of toasting duration. I still don't believe the additional element of toasting duration is adequate for a full research article.

 

Author Response

Dear Reviewer 2,

Thank you for your important review. We would like to reply for your comments as follow.

The manuscript by Kainuma et al. study the effect of differences in toasting temperature and duration on polysaccharides in French oak chips. This revised manuscript incorporated a title modification as well as edits in the various sections. Despite these modifications, the context and the theme remain similar to the authors previous publication, with the the exception of the inclusion of toasting duration. I still don't believe the additional element of toasting duration is adequate for a full research article.

[A] In our previous paper, we reported that sugars are extracted from oak chips and that this extraction varies with the toasting temperature. Based on these results, we hypothesized that the polysaccharides in the oak chips might undergo denaturation or fragmentation, these process that could be elucidated through sugar analysis, and carried out further experiments. It was found that toasting temperature has a critical role in both sugar fragmentation and denaturation, while toasting duration has a significant effect specifically on denaturation. The denaturation of sugars is a critical reaction directly linked to the formation of “aroma compounds” derived from the oak chips; thus, the results gained from this study hold a distinctly different significance from those of the previous results. On the other hand, in the toasting process of barrels and chips by cooperage, the degree of toasting is often assessed by the change in color. If the toasting color is deemed insufficient, it is likely that the toasting process will be extended. Therefore, we have added the change in the color of the chips as a new element (Fig. 1, Table 1, lines 122-128, 181-202, 306-313). This addition clarifies the relationship between the toasting process by cooperage and the chemical changes in wood polysaccharides, thereby enhancing the value of this paper.

Reviewer 3 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

According to the revised manuscript emailed on Oct 30th, 2024, by the editor, this manuscript has been substantially revised by the authors and can be considered for publication.

Author Response

Dear Reviewer 3,

 Thank you very much for your careful review. In response to requests from other referees, we have revised the manuscript by adding data on changes in chip color and modifying the title accordingly.

 

Round 2

Reviewer 2 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

The authors previous publication did identify that, an increase in temperature does contribute to denaturation. With the new revision of the current manuscript, the title was modified to emphasize on "understanding wood polysaccharide fragmentation and denaturation...". However, there is no deep insight given regarding this. For the manuscript to be publishable, I suggest that the authors to briefly include additional information in the discussion, highlighting or speculating how this fragmentation and denaturation happen. For example, relating the structural makeup of the polysaccharide and fragmentation behavior. Also, relate structure or functionality of the monosaccharides with their resistance or propensity to denature.

Author Response

[Comment] The authors previous publication did identify that, an increase in temperature does contribute to denaturation. With the new revision of the current manuscript, the title was modified to emphasize on "understanding wood polysaccharide fragmentation and denaturation...". However, there is no deep insight given regarding this. For the manuscript to be publishable, I suggest that the authors to briefly include additional information in the discussion, highlighting or speculating how this fragmentation and denaturation happen. For example, relating the structural makeup of the polysaccharide and fragmentation behavior. Also, relate structure or functionality of the monosaccharides with their resistance or propensity to denature.

[Response] Thank you very much for your suggestion. We agree with your suggestion and have added descriptions regarding the reactions induced within the oak chips by the thermal decomposition of wood polysaccharides (lines 440–448). There are many research on the thermal decomposition of wood polysaccharides, we believe that incorporating this information has enhanced the academic value of this paper. Thank you for your valuable comments. As far as our investigation shows, two technical terms, "fragmentation" and "depolymerization," are used to describe the breakdown of polysaccharides into smaller molecules. On the other hand, in the field of wood science, many studies use the term "depolymerization" instead of "fragmentation" to describe the thermal decomposition of wood polysaccharides (cellulose and hemicellulose). Therefore, to avoid any misunderstanding, we have decided to modify the terminology for the thermal decomposition of wood polysaccharides to "depolymerization." Furthermore, we have added information regarding the structure and propensity to denaturation of monosaccharides related to sugar denaturation (lines 382-385).

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript by Kainuma et al. study the effect of toasting temperature and time on extracted sugars from French oak chips into a model wine solution. The manuscript is well written, however, i have the comment below for the authors to address.

 

·       Based on authors previous publication, (Quantitative analysis of sugars extracted from French oak (Quercus petraea) chips: Effect of toasting temperature) https://doi.org/10.20870/oeno-one.2024.58.2.7755, I find these manuscripts very similar except for the incorporation of toasting duration. Understanding the changes in sugar content and composition associated with varying toasting temperature and duration is valuable in the winery industry. However, I don't believe the additional element of toasting duration is adequate for a full research article.

Reviewer 2 Report

Comments and Suggestions for Authors

Please refer to the attachment.

Comments for author File: Comments.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors, I have revised your manuscript titled “Effect of toasting temperature and duration on sugars extracted from French oak (Quercus petraea) chips into model wine solution”. The work made a generally positive impression on me, however, just a few points require my opinion and attention:

My first observation is if you want to emphasize the effect of the duration of toasting, considering the variable of water concentration in the wood. Why is proposed to evaluate the effect of the duration of toast in chips with a dryness of only 103^oC until a constant mass was achieved? Between the range of 103 to 180^oC, did you consider a dryness or toasted?

In my concern, could help to characterize the toast experimental design by showing the concentration of oxygen, and for further studies different thicknesses and different durations of toasting.

 

The use of 6 grams of chips per litre model wine, which is the reason? I think to clarify, could be interesting to develop why is used this concentration of wood chips per litre.