Underutilized Malaysian Agro-Industrial Wastes as Sustainable Carbon Sources for Lactic Acid Production

Round 1

Reviewer 1 Report

This manuscript represents a review of the possibility of utilizing Malaysian agro-industrial wastes for lactic acid production. The data on published results concerning lactic acid production is collected and systematized well, so I think it would interest the scientific community. However, I recommend a major revision to reorganise the manuscript to make it even more tractable to the average reader.

The following represents a list of my suggestions:

1. The manuscript should be reorganized in terms of the following sections: 1 Introduction (without subsection headings 1.1 and 1.2), 2 Feedstocks or use the subsection 1.1 heading for this, and then use subsection 2.1 for coconut waste, 2.2 Oil Palm Waste, etc., 3 Production of Lactic Acid or the subsection 1.2 heading for this, and finally 4 Challenges, etc. In the Lactic Acid Production section, I would recommend making tables with data on pretreatment, hydrolysis, and fermentation conditions as well as producing strains together with the final yield of lactic acid (something like tables 2 and 3 but this time for all wastes)

2. In the last paragraph of the introduction section the process of lactic acid production is divided into three phases: pretreatment, hydrolysis and fermentation. There is no mention of product separation and purification, so maybe this could be added as a fourth phase, and additionally some data on that as a separate section in the manuscript.

3. Use the abbreviations adequately. Either use it from the first mention in the text and then use the abbreviation till the end of the manuscript, or don't use it at all. Also, I would recommend avoiding abbreviations in the abstract and then begin using them in the remaining text of the manuscript. At the first mention, please put the abbreviations in brackets (just as you did for lactic acid bacteria) because the abbreviation for lactic acid is missing.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

Reviewer comments:

The manuscript should be reorganized in terms of the following sections: 1 Introduction (without subsection headings 1.1 and 1.2), 2 Feedstocks or use the subsection 1.1 heading for this, and then use subsection 2.1 for coconut waste, 2.2 Oil Palm Waste, etc., 3 Production of Lactic Acid or the subsection 1.2 heading for this, and finally 4 Challenges, etc. In the Lactic Acid Production section, I would recommend making tables with data on pretreatment, hydrolysis, and fermentation conditions as well as producing strains together with the final yield of lactic acid (something like tables 2 and 3 but this time for all wastes)

Response:

The manuscript has been reorganised as suggested by the reviewer as follow:

1. Introduction

1.1 Underutilised Malaysian Agro-Industrial Waste

1.2 Production of Lactic Acid from Agro-Industrial Waste

2. Potential Agro-Industrial Waste as Feedstock for Lactic Acid Production

2.1 Coconut Waste

2.2 Oil palm Waste

2.3 Rice Waste

2.4 Bagasse

3. Challenges, Limitation and Future Works

Thank you for your suggestion to improve the manuscript by adding one more table. However, we believe that the current number of 6 figures and 3 tables (in total) is quite high for a review paper. In addition, all data have been included in each subsection of the waste.

 

Reviewer comments:

In the last paragraph of the introduction section the process of lactic acid production is divided into three phases: pretreatment, hydrolysis and fermentation. There is no mention of product separation and purification, so maybe this could be added as a fourth phase, and additionally some data on that as a separate section in the manuscript.

Response:

Thank you for your suggestion. The information on separation and purification phases (phase 4) have been added in the revised manuscript text and in Figure 2.

 

Reviewer comments:

Use the abbreviations adequately. Either use it from the first mention in the text and then use the abbreviation till the end of the manuscript, or don't use it at all. Also, I would recommend avoiding abbreviations in the abstract and then begin using them in the remaining text of the manuscript. At the first mention, please put the abbreviations in brackets (just as you did for lactic acid bacteria) because the abbreviation for lactic acid is missing.

Response:

Thank you for your suggestion. We have updated the abbreviation of LAB in the manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript entitled as “Underutilised Malaysian Agro-Industrial Wastes as Sustainable Carbon Sources for Lactic Acid Production” (Manuscript ID- fermentation-2606079), takes Malaysia’s agricultural wastes as a typical case study to discuss the potential of untapped Agro-Industrial Wastes from four major kinds of crops of coconut, oil palm, rice, and sugarcane to be used as sustainable carbon sources for Lactic Acid (LA) production. Detailed analysis and discuss are provided with the summary of latest related literature in state of the art, focusing on the topics of chemical and nutritional composition of the wastes biomass for fronds, bran, husk, shell, straw, trunks, flesh, kernel, bagasse, and Empty Fruit Bunches (EFB) etc. from the crops processing, the potential for LA fermentation with specific microorganisms (microbial strains as bacteria, fungi, and yeast, biological enzyme etc) for valorization of Agro-Industrial Wastes biomass in this comprehensive review.

The manuscript can be accepted with a minor revision. Suggestion for the typos and manuscript modification are as follows:

1. Page 3, line 91: “is” is deleted.

2. Page 6, line 167: the last “d” in “to produced” is deleted.

3. Page 7, line 176: “at” is deleted.

4. References section, page 19, lines 614-615: add the volume, issue, pages information in reference no.22

5. References section, page 20, lines 639-640: reference no 33 is deleted for repeated citation with reference no 31.

6. References section, page 20, lines 652: complete the reference no 39.

7. References section, page 21, lines 694-695: complete the reference no 59. 

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

Reviewer comments:

 

1. Page 3, line 91:“is” is deleted.
2. Page 6, line 167: the last“d” in “to produced” is deleted.
3. Page 7, line 176:“at” is deleted.

Response:

All correction have been made in the revised manuscript as suggested by reviewer.

 

Reviewer comments:

1. References section, page 19, lines 614-615: add the volume, issue, pages information in reference no.22
2. References section, page 20, lines 639-640: reference no 33 is deleted for repeated citation with reference no 31.
3. References section, page 20, lines 652: complete the reference no 39.
4. References section, page 21, lines 694-695: complete the reference no 59. 

Response:

Reference information have been updated in the revised manuscript.

 

Author Response File: Author Response.docx

Reviewer 3 Report

The research deals with the production of lactic acid by microbial fermentation of agro-industrial waste with an emphasis on underutilised Malaysian waste. I consider the title relevant in the field.

Authors should improve the following:

Paragraph 1.2. Production of Lactic acid from Agro-Industrial Waste should be improved by adding information on:

What properties the lactic acid has besides antimicrobial properties and for what purposes LA is used other than as a food additive?

Mention that there are other microorganisms that produce lactic acid (besides bacteria), and which ones?

Which bacterial strains are most commonly used or are most effective in lactic acid production?

 

Which parameters are crucial in the fermentation process besides the strain of the microorganism?

What are the challenges of producing lactic acid by bacteria from lignocellulosic waste, and what are the challenges of purification, i.e., obtaining the final product?

 

 

It would also be desirable to enrich the work with more recent publications in this field, for example:

Ojo, A.O.; de Smidt, O. Lactic Acid: A Comprehensive Review of Production to Purification. Processes 2023, 11, 688. https://doi.org/10.3390/pr11030688

 

Line 149 - "Coconut husk, also referred to as coir..." - delete word "to".

Line 264, 274, 491 - g/L/h correct to g/L h (also in Table 2.).

Line 521 - "...yield (around 0.5) of lactic acid." correct to (around 0.5 g/g).

Line 584, 586, 664, 687, 743, and 750 - the name of the microorganisms should be written in italic.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

Reviewer comments:

Paragraph 1.2. Production of Lactic acid from Agro-Industrial Waste should be improved by adding information on:

What properties the lactic acid has besides antimicrobial properties and for what purposes LA is used other than as a food additive?

Response:

Other properties / roles of lactic acid in food application are as acidulant and coagulant. The information on the other roles of lactic acid in food applications has been added in the revised manuscript.

 

Reviewer comments:

Mention that there are other microorganisms that produce lactic acid (besides bacteria), and which ones?

Which bacterial strains are most commonly used or are most effective in lactic acid production?

Response:

Other microorganisms are fungi such as Rhizophus oryzae can also produced lactic acid. The information on other microorganisms that produced lactic acid and the effective strains has been added in the revised manuscript.

 

Reviewer comments:

Which parameters are crucial in the fermentation process besides the strain of the microorganism?

Response:

The information on the crucial factor such as temperature, pH, agitation speed, substrate concentration and presence of inhibitor have been added in the revised manuscript.

 

Reviewer comments:

What are the challenges of producing lactic acid by bacteria from lignocellulosic waste, and what are the challenges of purification, i.e., obtaining the final product?

Response:

The information has been added in the revised manuscript.

 

Reviewer comments:

It would also be desirable to enrich the work with more recent publications in this field, for example:

Ojo, A.O.; de Smidt, O. Lactic Acid: A Comprehensive Review of Production to Purification. Processes 2023, 11, 688. https://doi.org/10.3390/pr11030688

Response:

The suggested paper has been included in the revised version of the manuscript.

 

Reviewer comments:

Line 149 - "Coconut husk, also referred to as coir..." - delete word "to".

Line 521 - "...yield (around 0.5) of lactic acid." correct to (around 0.5 g/g).

Line 584, 586, 664, 687, 743, and 750 - the name of the microorganisms should be written in italic.

Response:

Corrected as suggested by reviewer.

 

Reviewer comments:

Line 264, 274, 491 - g/L/h correct to g/L h (also in Table 2.).

Response:

This unit refers to lactic acid productivity in one hour. To avoid confusion, we change the unit to g/L h^-1.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have adequately addressed all of the points for the initial review, so I can only recommend it for publication in the present form. Congrats!