Study on the Dynamics of Microflora during Natural Fermentation of Different Blueberry Wines
Round 1
Reviewer 1 Report
In this manuscript, the trends of fungal communities and the diversity of compositional structures of 3 blueberry wines were analyzed in different fermentation periods. Saccharomyces was the dominant genera in the middle and late fermentation stages of blueberry wine. However, the experimental data of the manuscript is too little to support the conclusions.
1. This study only examined the composition of the fungus. What about bacteria?
2. There 3 varieties of blueberry were used in this study. Whether these three blueberries are representative? How many varieties of blueberry are there in the Majiang production area of Guizhou? More information needs to be provided.
3. More information, such as physicochemical and sensorial properties, on blueberry wines needs to be provided.
4. More details about the production of blueberry wines are needed.
5. There are many errors in the “References”.
There are two numbers listed before each article.
The strain name needs to be italicized. Line 543, 549, et al.
Some articles have incomplete page numbers. Line 550, 558, et al.
Line 581, “H?Genauer“。
Line 582, “Rep 2013”.
Author Response
Response to Reviewer 1 Comments
Thank you very much for writing your valuable comments on the paper in your busy schedule. I have carefully revised each comment as follows:
Point 1: This study only examined the composition of the fungus. What about bacteria?
Response 1: Your question is particularly good. The reason that this study only examined the composition of the fungus is that blueberry wine is mainly fermented by yeasts, and bacteria do not take part in the alcoholic fermentation process. Bacteria are mainly involved in malolactic fermentation, which is a secondary fermentation after alcoholic fermentation, and their main role is to improve the flavor and mouthfeel of the wine and to reduce the acidity of the wine. This is also due to the lack of clarity in the introduction section of the main research component of my thesis, which has now been revised in the original draft to read" There have been very few studies on the changes in the microflora of blueberry wine, and studies on the fungal composition and changes in different varieties of blueberries and various stages of fermentation have not been reported." Meanwhile, I am very grateful to my teacher for providing me with new research ideas for further research on the flavor and texture of blueberry wine.
Point 2: There 3 varieties of blueberry were used in this study. Whether these three blueberries are representative? How many varieties of blueberry are there in the Majiang production area of Guizhou? More information needs to be provided.
Response 2: There are more than 10 varieties of blueberries in the production area of Majiang, Guizhou, but most of them are fresh blueberries and do not meet the conditions for brewing. There are three main types of blueberries in the local area, which are: rabbit-eye blueberries, southern highbush blueberries, and half-highbush blueberries. Among them, southern highbush blueberries and semi-highbush blueberries mainly belong to fresh blueberries, with larger grains and thicker skins, which are favorable for transportation and longer shelf life and are not suitable for brewing. The three blueberries used in the paper are all rabbit-eye blueberries. Rabbiteye blueberries have smaller grains, and higher sugar content, but thinner skin, are easy to break during picking and transportation, mainly used for deep processing, in which the anthocyanin content of rabbit-eye blueberries is higher than the other two types of blueberries, a combination of factors, the three blueberries selected have better winemaking characteristics, can maximize the characteristics of the local blueberries, and has a very good representation.
Point 3: More information, such as physicochemical and sensorial properties, on blueberry wines needs to be provided.
Response 3: It has been revised in the manuscript.
Point 4: More details about the production of blueberry wines are needed.
Response 4: It has been revised in the manuscript.
Point 5: There are many errors in the "References".
There are two numbers listed before each article.
The strain name needs to be italicized. Line 543, 549, et al.
There are many errors in the "References". There are two numbers listed before each article.
Some articles have incomplete page numbers. Line 550, 558, et al. Line 581, "H?Genauer". Line 582, "Rep 2013".
Response 5: It has been revised in the manuscript.
Reviewer 2 Report
Manuscript ID: fermentation-2627571
The manuscript Study on the dynamics of microflora during natural fermentation of different blueberry wines deals with the evaluation of the fungal communities of fermented blueberry wine samples from three Vaccinium ashei varieties, at different fermentation periods to assess the composition and abundance of fungal communities, as well as their potential role in the blueberry wine fermentation process. The manuscript is well written and clearly explained, and the topic has great interest in food biotechnology. The development of yeast starters cultures from native microflora is a crucial issue to the industrial production of fermented food, like blueberry wine, as inoculating with commercial yeasts, mainly Saccharomyces from winemaking industry lead to an average flavor profile that does not highlight the particular aroma and specific organoleptic characteristics of them.
In addition, this work is well done, performing an adequate set of experiments, and describes a large data set reporting new findings, so it deserves to be published. However, the potential capacity as starter cultures of the main fungal communities and of the more specific yeast species found in blueberry wines should have been studied. In particular, the authors could have confirmed the technological and sensory aptitudes of the yeasts from the wine samples that presented the best organoleptic characteristics, Powderblueberry, in an experimental batch.
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer 2 Comments
Thank you very much for writing your valuable comments on the paper in your busy schedule, and for recognizing and praising my experiment, I will continue to work hard! Next, I will respond to the comments you gave me:
Point 1: “……the potential capacity as starter cultures of the main fungal communities and of the more specific yeast species found in blueberry wines should have been studied.”
Response 1: This suggestion from the teacher is particularly good! It is a highly significant study to screen out winemaking yeasts with local characteristics. This study is mainly basic research on the fungal changes in each fermentation stage during the natural fermentation of three kinds of blueberry wines, from which the fungal flora that dominates the fermentation is identified, and at the same time, the fungal changes in three different blueberry wines are used to determine the flora composition law in the pre-fermentation period, the mid-fermentation period and the post-fermentation period. in the next step of the study, based on the results of the current study, I will carry out in-depth research on the native yeasts of blueberries to open up such as a Comparison of fermentation power, activation degree, and fermentation effect of screened yeasts with commercial yeasts, etc. The next stage will be the study of the fermentation potential of screened indigenous strains.
Point 2: “……could have confirmed the technological and sensory aptitudes of the yeasts from the wine samples that presented the best organoleptic characteristics, Powderblueberry, in an experimental batch.”
Response 2: I am very grateful to my teacher for pointing out the direction of my experiment! In this experiment, the Powderblueberry wine samples showed outstanding advantages, and in the later experiments, I domesticated the screened strains and optimized the brewing process as well as carried out a detailed test on the aroma composition of blueberry wine, while making comparisons with the commercial yeast, and using sensory evaluation of the product to illustrate the detailed research. Due to the large amount of data content, this thesis mainly focuses on the basic research of blueberry wine flora, so not all the data are shown.
Round 2
Reviewer 1 Report
There is only a table in “3.1”. The results and discussions must be supplemented.
Author Response
The alcohol content of the three blueberry wines is constantly changing during different fermentation periods, and there are differences in alcohol content between the different blueberry varieties. In the pre-fermentation period, the alcoholic strengths of Gardenblue and Powderblue were closer to each other, and Britewell had a higher alcoholic power. As the fermentation process advances, blueberry wine decreases in alcohol content in the middle of the fermentation period. This is because the yeast has a greater intake of nutrients when its growth rate is at its maximum, and the process of alcohol synthesis is inhibited. Reaching the end of fermentation, the alcohol content increased, and the lower alcohol content of the Gardenblue, compared to the Powderblue and the Britewell, reflected the weaker yeast population of the Gardenblue. Britewell was too high in the pre-fermentation period, approaching the alcohol tolerance value of the yeast, which tends to inhibit yeast growth. Initial brix, total sugar, and dry leachate primarily influence the potential for alcohol production during the fermentation of blueberry wines, which can be visualized here using the value of the alcoholic strength. Total acid is mainly used for sensory evaluation and has no major influence on the bacterial flora of the wine, while malic acid - lactic acid is an essential component of total acid, which influences the taste and the flavor of the wine. Volatile acid provides an important basis for aroma composition, but too much volatile acid can affect the quality of the wine. Of the three samples, the Powderblue Blueberry had the lowest level of Volatile acid, which allows the blueberry wine to provide aroma and enhance the wine quality. pH was close to the same level, which is necessary for the growth of yeast, and helps the yeast's biochemical reactions, which are ultimately reflected in the Alcoholic strength. The Total SO2 of Gardenblue and Britewell fluctuates greatly during the first, middle, and late stages of fermentation, which may be due to the release of from the yeast during the cell wall cracking during the fermentation, and the large fluctuation of SO2 can easily inhibit the activity of the yeast and affect the progress of the fermentation. The total SO2 of Powderblue increases gradually during the fermentation process, which ensures that the yeast can adapt to the fermentation process and is not affected by the fluctuation of total SO2 in the early and middle stages of the fermentation. Therefore, overall, the Powderblue blueberry wine samples had good physicochemical indexes, which were favorable for carrying out the following experiments.
