Chemical Analysis and Antioxidant Capacity of the Stages of Lignocellulosic Ethanol Production from Amazonian Fruit Industrial Waste
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1. The detail results of enzymatic hydrolysis for glucose should be added in the abstract.
2. There is none results or information of antioxidant capacity in the abstract.
3. Line 34, EL or LE?
4. Line 44-79, the latest references should be added.
5. The current situation of Amazonian fruit farming wastes should be more introduced in the introduction.
6. Did you concentrate the glucose liquor and then use to fermentation? What is the finals concentration of glucose in the liquor before fermentation?
7. The conclusion is verbose, it should be simplified.
Comments on the Quality of English Language1. The detail results of enzymatic hydrolysis for glucose should be added in the abstract.
2. There is none results or information of antioxidant capacity in the abstract.
3. Line 34, EL or LE?
4. Line 44-79, the latest references should be added. You can check the works in https://doi.org/10.1039/D3GC00271C; https://doi.org/10.1016/j.indcrop.2024.119374
5. The current situation of Amazonian fruit farming wastes should be more introduced in the introduction.
6. Did you concentrate the glucose liquor and then use to fermentation? What is the finals concentration of glucose in the liquor before fermentation?
7. The conclusion is verbose, it should be simplified.
Author Response
"Please see the attachment."
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
I believe this is a good piece of work, but there is still room for improvement. Below, I have included my suggestions.
Introduction
After the third paragraph (or after the penultimate paragraph), quantify the amount of residue produced annually. Indicate how this residue is managed and whether it is collected centrally in any manner, so that the reader can understand if the quantities produced are compatible with the requirements of a lignocellulosic ethanol production industry.
Towards the end of the introduction, justify the choice of acid hydrolysis with diluted sulfuric acid as the pretreatment method. Highlight the comparative advantages over other options for similar biomasses.
Materials and Methods
Specify whether the conditions used for hydrolysis with sulfuric acid were the optimal conditions from the referenced work, to justify why only these conditions were tested.
Explain why the liquid streams from the pretreatment, where glucose concentration is very low, were fermented, and why the hydrolysate fermentation was completed with still high levels of glucose, significantly higher than the glucose content in the liquid obtained from the pretreatment.
Identify which inhibitors were measured in the C18 column.
Results and Discussion
Present the characterization of the starting biomass to allow the calculation of yields for each process and present these values.
Express the sugar concentrations in the liquids obtained after treatment as a percentage of the starting biomass. Comparing concentrations in g/L when different solid/liquid ratios were used doesn't make much sense. Is greater removal achieved, or is it an effect of dilution? The reader can do the calculations, but it's clearer if this information is already presented in this manner.
The claim that it is possible to obtain compounds of great industrial interest will depend on whether such industrialization is feasible. Beyond the nature of the compound, if its concentration in the liquid is very low, the process required for its separation and purification may be so costly that it becomes unprofitable, making the industrial interest in such a liquid null.
It is unclear whether the results presented in Table 2 refer to the liquids obtained after fermentation (table title) or to the liquid fraction after pretreatment with diluted sulfuric acid (as stated in the text). Assuming it refers to the former, I suggest presenting the data in the order of the process and continuing with the presentation of the enzymatic hydrolysate data.
Comment on whether the ethanol concentrations achieved are suitable for subsequent concentration by distillation, as they initially appear to be low. Compare these concentrations with other values reported in the literature for different biomasses.
To complete the work, I suggest calculating the yield of each stage and the enzymatic activity and proposing a mass balance for the entire process.
Author Response
"Please see the attachment."
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe work fermentation-3192691 is devoted to a detailed analysis of the chemical composition of semi-finished products of bioethanol production from three lignocellulosic fruit wastes in Amazonia: açaí seeds, mango peel and peach palm peel.
The work is devoted to a relevant topic, and the relevance is well justified in the introduction. Standard analytical methods were used, the results seem reliable.
The following methodological comments are available:
1) The raw material sources used should be listed in the Abstract and in the introduction.
2) The chemical composition of the raw materials before and after treatment with sulfuric acid should be added. It is not clear why the fermentability of solid substrates significantly worsens with a load of 5% solids at the stage of chemical hydrolysis compared to using 15%? After all, both options were aimed at enzymatic hydrolysis with a load of 3%.
3) The desire to extract phenolic compounds after fermentation is methodologically unclear. If these are valuable compounds, they should be extracted from plant material by CO2 extraction or ethanol extraction. Lignocellulosic ethanol is a technical product. It is impossible to extract food phenolic substances from a technical product. Therefore, the stages should be reversed: first, extract phenolic substances, then carry out alcoholic fermentation.
4) If the authors plan to use phenolic substances after fermentation for some technical purposes, this must be justified.
5) It is necessary to add a calculation of how much the content of phenolic substances increases after fermentation. This is a very modest figure. But it must be indicated if the authors wish to include the increase in the content of phenolic substances in the conclusions.
6) Please explain what is new about this work compared to reference 17? The reference is not available globally.
7) There is very little sugar in the liquid fractions of acid hydrolysates. Their processing into ethanol is economically unprofitable. Suggest ways to use them or ways to utilize them.
Author Response
"Please see the attachment."
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsMost of my comments were taken into account and corrections were made in the proposed direction.
I would have liked some results not to be expressed in concentrations (g/L), but in relation to the original solid, to be independent of the quantity of liquid used in the pretreatment. In any case, I understand that the results can be presented in this way.
Author Response
"Please see the attachment."
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have greatly improved the manuscript by adding the chemical composition of the raw materials.
1) Table 5 is currently unreadable and the terminology is confusing. Please put a period or comma in the numerical values ​​as required by the journal without strikethroughs or red marks, as this greatly impairs comprehension.
The following data should be provided:
a) Chemical composition of raw materials (available, this is table 1)
b) Chemical composition of the products of processing raw materials with 1% sulfuric acid (with a load of 5% and 15%) (SHOULD BE ADDED!!!)
c) Chemical composition of the liquid fraction after processing raw materials with 1% sulfuric acid (available, this is table 2)
d) Chemical composition of enzymatic hydrolysates (available, this is table 4)
e) Chemical composition of mash (is this table 3 or table 5? It is not clear)
2) From the authors' answer to question No. 2, it seemed that during enzymatic hydrolysis the load was 5% and 15%, but in the materials and methods the authors write that a load of 3% was used for enzymatic hydrolysis.
So, the options differed in the load of raw materials during chemical preliminary treatment: 5% and 15%. In this case, the higher the water modulus and the more dilute sulfuric acid is used, the deeper the pre-treatment is, i.e. 5% should provide better removal of non-cellulose impurities than 15%, because the higher the water modulus, the better the mass transfer.
The authors then separate the liquid fraction from the solid, and in both cases the dry matter load during enzymatic hydrolysis is 3% or 30 g/l. Therefore, the explanation "The worsening of fermentability observed with the 5% solids load can be attributed to a lower solids density, which results in a lower concentration of enzymes in contact with the substrate during subsequent enzymatic Hydrolysis" is not suitable, the dry matter density was the same for 5% and 15%, namely 3%.
So, it is fundamentally important how the chemical composition of the raw material changed after treatment with a 1% sulfuric acid solution, this data must be added in order to understand for ourselves and explain to readers the difference in the enzymatic hydrolysis of the obtained substrates. This is directly related to the article and without this data the article is illogical.
3) It is also necessary to add a calculation of what is the yield of fermentable sugars from the mass of the substrate when using 5% and 15%. I will give an example from Table 4.
Mango peel, 5%, the sum of monosaccharides is 12.95 + 0.21 = 13.16 g / l, then the yield is 13.16 x 100 / (30 / 0.9) = 39.5%
Mango peel, 15%, the yield is 76.2%.
4) It is interesting that despite the fact that the mass fraction of hemicelluloses in acai seeds is 39%, which is quite a lot, very little xylose was found in both the waste liquids and the enzymatic hydrolysates. How can this be explained?
5) In the conclusions, reflect which raw material you consider the best for obtaining ethanol? All types of raw materials have low levels of fermentable sugars.
6) The detailed chemical analysis of the fractions is an advantage of this work. However, with a substrate loading of 3%, these details are not very important for future production, since the concentrations of ethanol and phenolic substances are very low, which is due to the low substrate loading. In the future, the authors may conduct enzymatic hydrolysis of priority raw materials at high substrate concentrations.
Comments on the Quality of English LanguageI have no complaints about the quality of the English language
Author Response
"Please see the attachment."
Author Response File: Author Response.pdf
