Recycling and Conversion of Yeasts into Organic Nitrogen Sources for Wine Fermentation: Effects on Molecular and Sensory Attributes

Round 1

Reviewer 1 Report

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Comments for author File: Comments.pdf

Author Response

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Reviewer 2 Report

Dear authors, I carefully read your manuscript and, while I find your work of interest, multiple improvements are required for it to be published in a peer reviewed journal. My primary concerns are related to the statistical analysis and, in turn, interpretation of the data. Please see the detailed comments below.

Statistical analysis of the results – It is unclear from this paragraph which analyses were undertaken and why. For example, in L. 175. It is stated ‘The characteristics of wines’; which characteristics are you referring to? The chemical parameters? Also, why is Student’s t-test used? Why is Friedman statistics and LSD described in such detail? PCA is not listed (how it was performed and using which dataset). To be fixed.

Figure 1. Datapoints for each treatment should be connected. Consider removing the symbols for better visibility of data. What is the reason for representing the data as both density and Brix (i.e., panels a and c, respectively)? This appears redundant.

L. 205-226 Insufficient information on the analytical parameters of the obtained wines. Please, expand and specify accordingly. Related to the figures 2 and 3, this data set is lacking statistical analysis and interpretation.

Figure 2. Was the statistical analysis performed on this dataset? The results of the statistical analysis for each parameter should be included in the data representation (e.g. letters to denote significance groups).

Figure 3. Same as per Figure 2.  

PCA analysis – what is the reason for performing separate Principal Component Analysis for higher alcohols and esters? Such approach seems invalid. Please re-analyse the entire dataset. Also, the font on the PCA biplots is too small and thus illegible. In the paragraph where the explanation of the plots is provided, improper terminology is used and this should be revisited (i.e. correlations). C

Table 1. This data is not directly related to the study and should either be excluded from the manuscript or, at best, moved into the supplementary data.

Table 2. This is a poor representation of the data, which could easily be integrated into the spider plot (Figure 6). Please revisit.

Figure 6. What does ‘paramterized’ mean? Change and also include the scale for the plots.

L. 294-306 The links between the chemical and sensory properties of the wines are not analysed in a proper manner (statistical analysis is missing). This is to be conducted and incorporated into the manuscript.

L. 319-320 ‘Similarly, the ethanol and glycerol production among the different nitrogen supplementations also agree with this hypothesis’. What are you referring to in particular? Specify as it is not clear.

L.330 ‘production of the volatiles was not only significant at a chemical level, but also noticed by a non-expert sensory panel’ This statement further reinforces the need for an integrative analysis of sensory and chemical data.

Author Response

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Reviewer 3 Report

Review for the manuscript entitled “Recycling and conversion of yeasts into organic nitrogen sources for wine fermentation: effects on molecular and sensorial profiles” (fermentation-1475999).

This manuscript presents a study about the use of yeast protein hydrolysate (YPH) as a nitrogen source for grape must fermentation. Generally, the manuscript is well written and the topic is interesting. However, there are a lot of information missing especially from M&M and Results sections and need to be addressed. In my opinion, after major revision it can be published in the Fermentation.

Here are some comments and questions to the Authors:

1)Title: “sensorial profiles” seems too far away from the type of sensory tests applied in the manuscript. Please rephrase the title, here is a suggestion: “sensory attributes”

2)Keywords: Please remove the keywords which are already used in the title. You can use the grape type, the analytical methods used, the sensory tests.

3)Introduction:

L36: As far as I know, pomace can be used as feed for animals also.

4)Materials and Methods:

4.1.) The material and methods section provides only partial information on the scientific activities. Specifically, authors should report some reliable references on the method used to empower the selected methods.

4.2.) I suggest providing a flow-chart with the different stages of study to improve and make clearer the visual presentation of the experimental design.

4.3) Reagents: please provide details about the producers of all reagents used in M&M.

4.4.) Apparatus: please provide details about apparatus used during experiments (producer, model, city, country)

L105: Agitator or shaker or vortex?

L107: autoclave

L113: Water bath

L116: autotitrator

L120: freezeer (+temperature used to freeze the samples)

L 140: densitometer, refractometer

L152: FTIR

L153: spectrophotometer

L157: GCMS

L200: Soxhlet

L 203: Centrifuge

4.5) Description of the methods per se: L151-160 the description of the methods is too vague. Please give more details to each one.

L152 FTIR work parameters, software used to interpret the data.

L153: Describe the Folin Ciocalteu method, the concentrations of the standards the standard equation curve, r2 value. Please provide reference also.

L158: Please specify sample preparations and how were the higher alcohols and esters identified? Did you use a library of spectra or internal standards (in this case please provide their names and the producer, the standard equation curve, r2 value)?

4.6.) Sensory evaluation:

Evaluators: On what basis were the panellists selected? (What were the criteria for their selection?)

What ages were the sensory panellists (average ± standard deviation, minimum, maximum)? How many females and male?

How many sessions of training were performed? How many hours lasted each session?

In first and second stage were used water solutions or wine solutions? This should be specified.

Third stage: were samples coded? How? What was the order of the presentation of the samples? What kind of glasses did you use during experiments? How did the organisers address the potential for sensory fatigue? Did panellists have breaks between the samples? Were panellists provided with water or something else as a palate cleanser? 

Tests applied. It seems that there is a confusion about the sensory tests, and it is not clear for the authors what is the purpose of which sensory test.  

Preference test is a test used to assess the preference between two or several samples (so it is a forced choice test), which means that from all the samples tested, one is preferred based on subjective criteria. Please revise L171 “indicate their preference for each sample”.

Ranking test is a method of classification in which a series of samples is placed in order of intensity or degree of some specified attribute.

“Sensory profile” (from the title and throughout the manuscript) is a descriptive test and is much more complex than the tests presented by the authors.

Sensory attributes evaluated.

L163. Authors state that the following flavors of wine were evaluated: sweetness, acidity and astringency. Sweetness and sour (acidity) are tastes (they are perceived through the gustatory receptors found on the tongue) and astringency is a trigeminal sensation, so none of them is flavor. Flavour is a perception in the mind, and is the result of simultaneous combination of taste, retronasal olfaction and trigeminal inputs. Therefore, flavor and taste have different definitions. Please correct throughout the whole manuscript.  

5)Results:

L292: Figure 6

Firstly, since preference and ranking test are different and give different results, it is not correct to insert the results of the preference test in the same chart with ranking test.

Secondly, the size of the axis is not given.

Thirdly, maybe you would like to consider changing it into a table format. Then it is possible to add the statistical significance also. Please provide p-value.

L303. No correlation was done between the analytical part and sensory perception. Astringency is mainly due to the polyphenols, however in the manuscript there is no correlation between the data.

The authors have invested so much effort in performant analytical techniques to evaluate the volatiles, however, they did not record the aroma perception from the sensory panel. This could’ve been very interesting.  

L305-306: Since the product is wine, are you sure that “sweetness is desirable by a great number of consumers”?? In case the evaluators were only students, then it may be so… however, wine is appreciated for other sensory attributes.  

Author Response

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Round 2

Reviewer 1 Report

The manuscript has extensively improved. Two more comments that could help the manuscript in clarity is how significance at p<0.05 is presented in tables and figures (try to use letters to show ranking between treatments a, b, c, etc..) ** and * can be a little it confusing.

The same applies to supplementary material. (also check spelling of gallic acid) in the calibration curve in the supplementary material.

Author Response

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Reviewer 2 Report

Dear authors, 

Upon multiple revisions, your article has considerably improved in quality. 

Author Response

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Reviewer 3 Report

Dear Authors, the revised version of the manuscript was much improved and carefully redrafted. I do appreciate all the effort made by the Authors for improving the quality of the presented work. In my opinion, the revised manuscript meets the journal requirements and is suitable for publication after including some minor corrections listed below.

L185: Sensory evaluation

L187: “volunteers, not selected” what do you mean by not selected? At least they should be wine consumers…

L166, 183, 206: Folin – Ciocalteu method, and please correct throughout the text also.

Figure 7. Please change it into a Table. I have already given this recommendation in the previous review. It is NOT correct to insert in the same chart the preference and ranking of sensory attributes. They are two different sensory tests, meaning that the panel is going through a different cognitive process of evaluation, therefore, the results CAN NOT be displayed on the same chart.  

Author Response

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