Lactic Acid Fermentation of Carrageenan Hydrolysates from the Macroalga Kappaphycus alvarezii: Evaluating Different Bioreactor Operation Modes

Round 1

Reviewer 1 Report

In this article, the authors have explored the potential of Kappaphycus alvarezii, a type of seaweed, as a sustainable raw material for lactic acid production. They have experimented with different feeding strategies to optimize lactic acid fermentation of K. alvarezii hydrolysates using Lactobacillus pentosus and discussed the regeneration of activated charcoal used for detoxification. I have some minor comments and queries related to the article.

 1.     line 396: It would be helpful to provide more explanation on why these results are significant, especially for the general reader who may not be as familiar with the subject area.

2.     A few minor typographical and grammatical errors are present in the text, a thorough proofreading will help ensure your paper is polished and professional.

3.     Can you provide further insight into how the activated charcoal regeneration process works? What specific conditions are required to ensure close to 100% efficiency?

4.     Regarding the statement in line 354 about the successful removal of HMF from solutions during charcoal regeneration, could you explain why the selectivity reduction becomes significant only after the third regeneration?

5.     You mentioned thermal treatment of activated carbon results in reduced selectivity (line 357). Could you provide more details on the nature and extent of this selectivity reduction?

6.     Line 361 suggests using biomass for activated carbon production. Could you elaborate on how efficient this method is compared to conventional sources of activated carbon?

7.     Line 383-388 suggests batch fermentations with cell mass recycling could achieve higher lactic acid production rates. Could you provide more information about the factors influencing the efficiency of these sequential batch fermentations?

8.     You mention the use of feedstocks for lactic acid production in biorefineries (line 392). How does the choice of feedstock impact the yield and quality of the lactic acid produced?

9.     Can you provide additional information on how K. alvarezii hydrolysates' detoxification can be improved to further reduce operational costs?

10.  Line 408 states that pulse fed-batch is less preferable than extended continuously fed-batch operation. Can you explain the main reasons for this preference?

11.  Could you elaborate more on the future research directions you envision for improving lactic acid production from K. alvarezii biomass? 

English is fine, proofreading needed.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The article titled "Lactic Acid Fermentation of Carrageenan Hydrolysates from 2 the Macroalga Kappaphycus alvarezii Evaluating Different Bio-3 reactor Operation Modes”. This study shows the potential of applying feeding strategies for augmenting yield and final concentrations in lactic acid fermentation of K. 404 alvarezii hydrolysates with L. pentosus. Simple fed-batch cultivation produced high titers and yields of lactic acid. Hence the study contributes new information to reader.

1.      Provide the novelty, objectives and aims of study in the introduction.

2.      The Introduction has too many paragraphs, combine and shorten some paragraphs.

3.      “The hydrolysate fermentation media was inoculated with 100% (v/v) of cellular mass produced in the last step of the acclimation procedure”. Can authors explain 100% cellular mass in this sentence? 100% (v/v) of inoculum is required? It is high. Also, cellular mass is not suitable term, please rephrase.

4.      Why the feeding started in pulse fed-batch and extended fed-batch was different? The batch fermentation period should be similar for both right?

5.      Table 1 missing the result of 5-hydroxymethylfurfural (HMF) concentrations.

6.      The analytical methods in methodology need to be improved by elaborating the methods of HPLC.

The language and grammars need to be improved.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Different fermentation mode was evaluated for lactic acid production from Kappaphycus alvarezii hydrolysates, and some useful information was obtained. My concerns are as follows:

1, Focus on the topic of this study, and tighten the introduction part.

2, Besides HMF, what other impurities detected in the hydrolysates? 

3, During the fermentation, did the dissolved oxygen controlled?

4, I'm not sure, whether or not the 400g/L galactose was compeletly consumed. How did the author give a yield of over 1g/g (132.6/400) in the manuscript?

5, Compared with other hydrolasates from different macroalga, to highlight the advantages of Kappaphycus alvarezii hydrolysates used in this study.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I am happy with the revision and article can be accepted for possible publication.

Did not check English in the revised version.

Reviewer 2 Report

The corrections have been made accordingly.

Reviewer 3 Report

I'm ok for the revised manuscript.