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Open AccessFeature PaperArticle
Peer-Review Record

Effects of Ultrasound on Fermentation of Glucose to Ethanol by Saccharomyces cerevisiae

Fermentation 2019, 5(1), 16; https://doi.org/10.3390/fermentation5010016
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Fermentation 2019, 5(1), 16; https://doi.org/10.3390/fermentation5010016
Received: 31 December 2018 / Revised: 24 January 2019 / Accepted: 27 January 2019 / Published: 29 January 2019
(This article belongs to the Special Issue Biomass Conversion: Fermentation Chemicals and Fuels)

Round  1

Reviewer 1 Report

The paper „Effect of ultrasound on fermentation of glucose to ethanol by Saccharomyces cerevisiae” is very interesting and investigates the effect of direct and indirect ultrasound treatment on the course and effectiveness of glucose fermentation as a model medium. In my opinion it is a good candidate to be published in Fermentation, however, some issues should be addressed:

1.       L 86 an L 91 – once authors use YP-glucose 5% and once YPD-glucose 5%, I think it should be unified

2.       L101-103 – I think that authors were mistaken if the total volume is 125 mL the volume of Erlenmeyer flasks should be more than 125 mL. Also, could you please explain in more detail what was the composition of the fermentation medium? Especially the part “…and 6.25 mL YP 10X

medium inoculated with 6.25 mL of yeast inoculum” is hard to follow.

3.       L123-124 – the HPLC conditions should be included (column, detector, temperatures, mobile phase, flow etc.)

4.       L130-136 – could you please explain on what basis were the ultrasound treatment conditions selected?

5.       L193-199 – I think that results should be also included in form of table or figure

6.       L194 – the authors wrote “If the value is larger than 1 the external mass transfer limitation is significant” while in the previous section (L148) there was “if CAs/CAb << 1, the external mass transfer limitation is significant due to a well-defined boundary layer”. Could you please explain which sentence is true?

7.       Figure 3 – data presented in this figure are basically the same as in figures 4 and 5, I suggest to remove this figure, especially that there is no discussion included

8.       There are also some issues regarding text editing:

-          Figure 1 – “a” and “b” (both, lower case and capital letters) should be checked, as they are inconsistent and do not match to the text description (L110)

-          L187-188 – the power “-10” and “-9” should be written in superscript

-          All subsections in section 3 (results and discussion) have the same number (3.1.)

-          L266 – “Treatment” unnecessarily starts with a capital letter

-          L267 and 271 – I think that authors meant “Figure 6”

Author Response

Reviewer 1

The paper „Effect of ultrasound on fermentation of glucose to ethanol by Saccharomyces cerevisiae” is very interesting and investigates the effect of direct and indirect ultrasound treatment on the course and effectiveness of glucose fermentation as a model medium. In my opinion it is a good candidate to be published in Fermentation, however, some issues should be addressed:

1.       L 86 an L 91 – once authors use YP-glucose 5% and once YPD-glucose 5%, I think it should be unified

Response: This was corrected and now it appears only as YP-glucose 5%.

2.       L101-103 – I think that authors were mistaken if the total volume is 125 mL the volume of Erlenmeyer flasks should be more than 125 mL. Also, could you please explain in more detail what was the composition of the fermentation medium? Especially the part “…and 6.25 mL YP 10X

medium inoculated with 6.25 mL of yeast inoculum” is hard to follow.

Response: There was a missing amount in the sentence; it was 112.5 mL of glucose (200 g/L). The total volume of the 125 mL Erlenmeyer flasks is actually 155 ml. This information was added to the revised manuscript (L106).

3.       L123-124 – the HPLC conditions should be included (column, detector, temperatures, mobile phase, flow etc.)

Response: This information has been added to the revised manuscript.

4.       L130-136 – could you please explain on what basis were the ultrasound treatment conditions selected?

Response: The conditions selected were chosen based on the ways ultrasound is applied (direct and indirect) and on the energy densities reported in previous studies. These were similar to studies where improvements in fermentation were reported. In some other studies, higher ultrasonic energy densities were applied that killed yeast cells. This information was added to the revised manuscript.

5.       L193-199 – I think that results should be also included in form of table or figure

Response: A table has been added with the results. See Table 2 in the revised manuscript.

6.       L194 – the authors wrote “If the value is larger than 1 the external mass transfer limitation is significant” while in the previous section (L148) there was “if CAs/CAb << 1, the external mass transfer limitation is significant due to a well-defined boundary layer”. Could you please explain which sentence is true?

Response: The sentence discussing the external mass transfer limitation was referring not referring to the Thiele modulus, not CAs/CAb << 1. Both sentences were correct, but perhaps could have been better written since they refer to two different things. We have rewritten them for clarity.

7.       Figure 3 – data presented in this figure are basically the same as in figures 4 and 5, I suggest to remove this figure, especially that there is no discussion included

Response: The data in Figure 3 are important to show the behavior of the treatments over time. We have added a discussion statement about these data in the Results and Discussion section (line 220). 

8.       There are also some issues regarding text editing:

-          Figure 1 – “a” and “b” (both, lower case and capital letters) should be checked, as they are inconsistent and do not match to the text description (L110)

-          L187-188 – the power “-10” and “-9” should be written in superscript

-          All subsections in section 3 (results and discussion) have the same number (3.1.)

-          L266 – “Treatment” unnecessarily starts with a capital letter

-          L267 and 271 – I think that authors meant “Figure 6”

Response: Those editing mistakes have been corrected.

Reviewer 2 Report

This manuscript dewscribed a simple experiment whwre ultrasound was used as a means to improve fermentation for biofuels production. The manuscript is well written and presented.  For this reviewer I would like to have seen the research was about biofueld when readign the title.

For the abstract, it wasn't clear what the research question/s was and if there was question/s was the questions answered. Its seems a reaonsable experiment to conduct but would also seem there was conflicting reports on the benefits of ultasound. L74 states a hypothesis but I wanted to see something similar in the abstract and not wait until the end of th eIntroduction. Also senetence stating the hypothesis is burried in that long paragraph. Please have a separate paragraph to atstae the aim and ways the experiment will be conducted.

One strain of S. cerevisiae is used. Would the results change if a different yeast or yeast strain was used?

The results are clear and reasonably concise. It did seem the yeast was slow to produce ethanol. Previous reports relative to brewing indicted ethanol can be produced very quickly and more than 1% in 24 hrs. 

The remainder of the manuscript requires minor spelling and grammar checking.

Author Response

Reviewer:

This manuscript dewscribed (sic) a simple experiment whwre (sic) ultrasound was used as a means to improve fermentation for biofuels production. The manuscript is well written and presented.  For this reviewer I would like to have seen the research was about biofueld (sic) when reading the title. For the abstract, it wasn't clear what the research question/s was and if there was question/s was the questions answered. Its seems a reaonsable (sic) experiment to conduct but would also seem there was conflicting reports on the benefits of ultasound. L74 states a hypothesis but I wanted to see something similar in the abstract and not wait until the end of th eIntroduction (sic). Also senetence (sic) stating the hypothesis is burried (sic) in that long paragraph. Please have a separate paragraph to atstae (sic) the aim and ways the experiment will be conducted.

Response: The abstract was improved and the hypothesis and more info about the purpose of the study was added. A statement regarding the focus on biofuel ethanol production was also added to the Abstract. The term "biofuel" was also added to the keywords. The paragraph in the Introduction that contained the objective and hypothesis has been broken into two to more clearly highlight the hypothesis.

One strain of S. cerevisiae is used. Would the results change if a different yeast or yeast strain was used?

Response: We do not know how the results would change if different yeast were used. The strain that was selected for the study is widely used in the dry mill corn ethanol industry for fuel ethanol production. Thus the results would apply to commonly used industrial fermentation.

The results are clear and reasonably concise. It did seem the yeast was slow to produce ethanol. Previous reports relative to brewing indicted (sic) ethanol can be produced very quickly and more than 1% in 24 hrs.  

Response: We observed much more than 1% ethanol production in 24 hours. In fact, ethanol concentration reached between 5 and 7%, depending on the treatment, after 24 hours. Therefore we do not understand this question.

The remainder of the manuscript requires minor spelling and grammar checking.

Response: Spelling and grammar have been checked, improved and corrected.

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