Comparison of Raspberry Ketone Production via Submerged Fermentation in Different Bioreactors

Round 1

Reviewer 1 Report

This manuscript by Li et al. compared the production of raspberry ketone by submerged fermentation in a flask, stirred-tank reactor (STR), panel bioreactor (PBR), and fluidized bed reactor (FBR). This work shows that bioreactor design has a significant effect on raspberry ketone production by fungal fermentation.

Please address the following comments prior to publication:

1.     I would suggest replacing titres with titers.

2.     Line 55: Please use the full name of S. cerevisiae.

3.     Suggestion for abbreviations: Initially, use the word in full, followed by the abbreviation in parentheses. Thereafter use the abbreviation only. Some abbreviations in this manuscript (e.g., RK, FBR, STR ……) were defined multiple times, and the full names were still used after the abbreviations were defined.

4. Figure 1: Was nutrient solution supplied to reactors during fermentation? Why figure1b has a nutrient solution bottle, while Figure 1a doesn’t?

5.     Was the dissolved oxygen monitored during fermentation？

Author Response

This manuscript by Li et al. compared the production of raspberry ketone by submerged fermentation in a flask, stirred-tank reactor (STR), panel bioreactor (PBR), and fluidized bed reactor (FBR). This work shows that bioreactor design has a significant effect on raspberry ketone production by fungal fermentation.

Please address the following comments prior to publication:

1. I would suggest replacing titres with titers.

Response: Thanks for the suggestion, in the revised manuscript the word ‘titres’ has been changed into ‘titers’, highlighted in Line 319, on Page 10.

2. Line 55: Please use the full name of  cerevisiae.

Response: Thanks for the careful review, the full name of Saccharomyces cerevisiae has been updated in the revised version, highlighted in Line 52 on Page 2.

3. Suggestion for abbreviations: Initially, use the word in full, followed by the abbreviation in parentheses. Thereafter use the abbreviation only. Some abbreviations in this manuscript (e.g., RK, FBR, STR ……)were defined multiple times, and the full names were still used after the abbreviations were defined.

Response: Thanks for the suggestion. The reviewer is correct, we have defined the abbreviations of stirred tank reactor, panel bioreactor using STR, PBR in the beginning part manuscript, no need to give the full names again afterwards. In the revised version, only the abbreviations are used after they are defined initially.

4. Figure 1: Was nutrient solution supplied to reactors during fermentation? Why figure1b has a nutrient solution bottle, while Figure 1a doesn’t?

Response: Thanks for the reviewer’s good questions. In Fig.1a PBR is a batch-mode fermenter where both agitation and aeration are used. The aeration is supplied by the air pump which provided the air to gas flowmeter (control the gas flowrates), then to gas filter (avoid gas contamination), humidifier bottle (containing sterilized ultrapure water, to humidify the air and prevent gas evaporation in the PBR vessel) and finally into the PBR to provide dissolved oxygen. After the PBR, the gas would enter into the gas exhausted bottle before going out to the environment.

In Fig 1b, the FBR is a continues-flow reactor that both gas and liquids flow through the vessel to suspend the pellets. In detail, the gas is also pumped by the gas bottle, filtered via gas filter and controlled using gas flowmeter, exhausted using the exhaust bottle. In comparison, the liquids namely nutrients media is pumped in using the peristaltic pump from the nutrients bottle to reactor and return back to the nutrients bottle, thus minimizing the substrate inhibition and promoting the RK transportation. 

Thus, PBR in Fig 1a has no nutrient bottle while FBR in Fig 1b does have one.

5. Was the dissolved oxygen monitored during fermentation？

Response: Thanks for the good question. In the current study, we haven’t monitored the dissolved oxygen during the fermentation because it’s hard to detect and may also result in fungal contamination. Especially in the flask and fluidized bed reactor, which have no designed ports for DO probe. Instead, we simply control the gas flowrate at the same level for different reactors and try to reduce the effects by DO. This is really a good question, we should definitely improve our experimental design and investigate the DO in the future study.

Reviewer 2 Report

Overall, this is a well-designed work with clear logic and confidential results. As the author mentioned, the present work provides the importance of bioreactor design to fungal fermentation, and offer new insights to highly effective production of valuable natural compounds. However, the current manuscript also have a large number of minor errors, which need to be corrected in the revision stage. Some of them are listed as below for reference, and the author should carefully check the whole manuscript for the potential mistakes.

1.      The information for the list of co-authors is missed.

2.      In abstract, some of the abbreviations are introduce twice (like RK), but some of them are without the necessary explanation, such as RA.

3.      In general, most of the cited references are outdated, which may weaken the novelty of this work. Please update them.

4.      In Table 1, the source of the collected data should be included. Also, Table 2 should be revised as three-line table similar to Table 1.

5.      In Fig. 2, the words are too small, and the format of these bars in Fig. 2(c) and Fig. 2(f) should be unified. Similar problems can be found in Fig, 5.

6.      The Manuscript has many textual problems and the quality of the English must be improved. In addition to occasional syntax/grammar issues, the authors have a loose and confusing text composition style, all these aspects make the Manuscript difficult to read.

7.      In fact, the part of Discussion should be merged into that of Results, so that the relevant discussion can be corresponded to the specific results for better understand. Otherwise, the part of Discussion is more like a detailed Conclusion.

8.      In the current revision, the Conclusion is relatively simple, please emphasize the main findings with the specific data in here, so as to make a comprehensive conclusion.

1.   The Manuscript has many textual problems and the quality of the English must be improved. In addition to occasional syntax/grammar issues, the authors have a loose and confusing text composition style, all these aspects make the Manuscript difficult to read.

Author Response

Overall, this is a well-designed work with clear logic and confidential results. As the author mentioned, the present work provides the importance of bioreactor design to fungal fermentation, and offer new insights to highly effective production of valuable natural compounds. However, the current manuscript also have a large number of minor errors, which need to be corrected in the revision stage. Some of them are listed as below for reference, and the author should carefully check the whole manuscript for the potential mistakes.

1. The information for the list of co-authors is missed.

Response: Thanks for the comments, the info of co-authors have been improved in the revised manuscript, highlighted in Line 5-Line 15 on Page 1.

2. In abstract, some of the abbreviations are introduce twice (like RK), but some of them are without the necessary explanation, such as RA.

Response: Thanks the reviewer for pointing out the issue, explanation for RA (raspberry ketone) has been added in the revised abstract, highlighted in Line 26.

3. In general, most of the cited references are outdated, which may weaken the novelty of this work. Please update them.

Response: Thanks for the good suggestion, more newly published work related to raspberry ketone and bioproduction have been updated in the revised manuscript, such as those highlighted in Line 35, Line 38, Line 44, etc.

4. In Table 1, the source of the collected data should be included. Also, Table 2 should be revised as three-line table similar to Table 1.

Response: Thanks for the reviewer’s comments. Table 1 summarized the main operating parameters that we manually designed for different bioreactor systems, which is aimed to help the readers to understand the different fungal fermentation conditions, so that the data were from the experimental design, no specific source for them. Regarding the format of Table 2, we have changed it into a three-line table similar to Table 1 as reviewer suggested, highlighted in Line 286-Line 288, on Page 8.

5. In Fig. 2, the words are too small, and the format of these bars in Fig. 2(c) and Fig. 2(f) should be unified. Similar problems can be found in Fig, 5.

Response: Thanks for the good suggestion. The words illustrated in Fig.2 and Fig.5 have been enlarged. Besides, the formats of figures have been also improved in the revised manuscript.

6. The Manuscript has many textual problems and the quality of the English must be improved. In addition to occasional syntax/grammar issues, the authors have a loose and confusing text composition style, all these aspects make the Manuscript difficult to read.

Response: Thanks for the careful review and pointing out the issues. In the revised manuscript, we have tried to correct some typing and grammar errors, to improve the quality of the whole content.

7. In fact, the part of Discussionshould be merged into that of Results, so that the relevant discussion can be corresponded to the specific results for better understand. Otherwise, the part of Discussion is more like a detailed Conclusion.

Response: Thanks to the reviewer’s good comments. We have combined the Sections of Results and Discussion together in the revised manuscript. Besides, the Conclusion section is also improved to emphasize the importance and novelty of this stuy.

8. In the current revision, the Conclusionis relatively simple, please emphasize the main findings with the specific data in here, so as to make a comprehensive conclusion.

Response: Thanks for the good suggestion. We have rewritten the Conclusion part and provided the key findings using essential data, the importance of this study has also been emphasized, highlighted in Line 445-457, on Page 13.