Recovery of Bound Phenolic Compounds from Rice Hulls via Microwave-Assisted Alkaline Hydrolysis

Round 1

Reviewer 1 Report

The paper describes a new methodology to optimise the recovery of bound phenolic antioxidants from rice hulls using microwave assisted alkaline hydrolysis.

The paper is exceptionally written and presents novel information. The Introduction is clear and includes useful and relevant information. The experimental design is robust and the statistical analysis is suitable. The methods are described to a very good detail. The tables and figures are clear and informative.

This new methodology developed by the authors allows to recover higher amounts of antioxidants from rice hulls at a significantly shorter time compared to the existing literature. This work should be of high interest to academics and industry. For these reasons, I recommend the paper to be accepted for publication after the below minor comments have been addressed.

Minor comments:

·       Lines 208-209: Please adjust the title of this section to include the ultrasound extraction too.

·       Section 2.7: Please add a brief description of how the temperature was measured during/after ultrasound assisted extraction.

·       Line 398: replace higher with longer.

·       Line 413: the values obtained were higher (not the results) – please revise the sentence.

·       Line 423: you mentioned that the results are superior. I believe that what you are trying to say is that  theantioxidant levels you obtained were higher compared to the Wanyo et al., 2014. Please re-write the sentence to ‘’The levels reported in this study are also higher to the those reported by...’’ or something similar.

Author Response

Responses to Reviewer #1
Comments and Suggestions for Authors

Comment: The paper describes a new methodology to optimise the recovery of bound phenolic antioxidants from rice hulls using microwave assisted alkaline hydrolysis.

The paper is exceptionally written and presents novel information. The Introduction is clear and includes useful and relevant information. The experimental design is robust and the statistical analysis is suitable. The methods are described to a very good detail. The tables and figures are clear and informative.

This new methodology developed by the authors allows to recover higher amounts of antioxidants from rice hulls at a significantly shorter time compared to the existing literature. This work should be of high interest to academics and industry. For these reasons, I recommend the paper to be accepted for publication after the below minor comments have been addressed. Response:
We thank Reviewer #1 for appreciation of our work and for proposing our manurscipt to be accepted for publication after minor revision. All the points raised are now answered one by one below.

Comment: Lines 208-209: Please adjust the title of this section to include the ultrasound extraction too.
Response: The title of the section has been now changed to “Application of optimum conditions to rice hull samples of different varieties and comparison to ultrasound-assisted alkaline hydrolysis” according to Reviewer’s suggestion (lines 222-223 of the revised manuscript)

Comment: · Section 2.7: Please add a brief description of how the temperature was measured during/after ultrasound assisted extraction.
Response: A description about how the temperature was measured during ultrasound-assisted hydrolysis is now added to the revised manuscript according to Reviewer’s suggestion (lines 231- 232 of the revised manuscript)

Comment: · Line 398: replace higher with longer.
Response: Done according to Reviewer’s suggestion (line 397 of the revised manuscript)

Comment: · Line 413: the values obtained were higher (not the results) – please revise the sentence.
Response: The sentence has been now revised to “The values of the present study are also higher compared to those reported for rice hulls of the Greek variety..” according to Reviewer’s suggestion (line 412 of the revised manuscript)

Comment: · Line 423: you mentioned that the results are superior. I believe that what you are trying to say is that the antioxidant levels you obtained were higher compared to the Wanyo et al., 2014. Please re-write the sentence to ‘’The levels reported in this study are also higher to the those reported by...’’ or something similar.

Response: The sentence has been now modified to “The levels reported in the present study are also higher than those reported by Wanyo et al...” according to Reviewer’s suggestion (lines 422- 423 of the revised manuscript).

Reviewer 2 Report

The present study investigates the effect of various microwave-assisted alkaline hydrolysis conditions (duration, temperature, solvent: solid ratio) on the total phenol content, antioxidant activity, and the concentration of two major phenolic compounds, namely p-coumaric and ferulic acids. The study focuses on ethyl acetate extracts derived from hulls originating from a Greek rice-milling industry.

Introduction:

-The authors should elaborate more on the reasons why enzymatic techniques alone are not as effective in obtaining phenolic compounds with antioxidant capacity.

-Only one study is cited, why? They should show the gap more forcefully and make it clear why the microwave-assisted alkaline hydrolysis technique is the most effective solution.

Materials and Methods

The methodology employed is in my opinion appropriate and the experimental design is well executed.

Results

In the methodology, the authors indicate that they are going to compare the mean values obtained by microwave- and ultrasound-assisted alkaline hydrolysis a paired comparison student's t-test was performed. However, in line 395 when they compare the results, they do not use a t-test for it. This comparison in which part was performed. It is not clear. I suggest reviewing and clarifying it.

Conclusions

The conclusions should be rewritten to make them clearer; there are some vague sentences that force the reader to go back to the document. The optimal operating conditions found in the study should be indicated, specifying their numerical values.

For example, in the sentence: "The short duration of microwave treatment along with high temperature and solvent: solid ratio were found to favor the release of these valuable compounds and consequently their effective recovery", it is not indicated by way of conclusion what is a "short duration", high temperature and desirable value of the solvent: solid ratio.

I suggest improving this section.

The proposed article is interesting, experimentally rigorous, and provides technical knowledge for the future development of the antioxidant sector. The article has some elements of improvement that I will specify in my evaluation to the authors and I hope they can improve it before giving my approval for publication. Thank you for taking me into account in the review.

Author Response

Response to Reviewer #2

 

Comments and Suggestions for Authors

 

Comment: The present study investigates the effect of various microwave-assisted alkaline hydrolysis conditions (duration, temperature, solvent: solid ratio) on the total phenol content, antioxidant activity, and the concentration of two major phenolic compounds, namely p-coumaric and ferulic acids. The study focuses on ethyl acetate extracts derived from hulls originating from a Greek rice-milling industry.

Response:

We thank Reviewer #2 for appreciation of our work. All the points raised are now answered one by one.

 

Comment: Introduction: -The authors should elaborate more on the reasons why enzymatic techniques alone are not as effective in obtaining phenolic compounds with antioxidant capacity.

Response: We thank Reviewer for his/her comment. A more elaborated discussion about both chemical and enzymatic hydrolysis as well as on the reasons why enzymatic hydrolysis is not as effective in obtaining phenolic compounds along with two more relevant references are now added in lines 46-57 of the revised manuscript. 

 

Comment: -Only one study is cited, why? They should show the gap more forcefully and make it clear why the microwave-assisted alkaline hydrolysis technique is the most effective solution.

 

Response: We have now added three more references regarding the use of microwave-assisted extraction from various plant materials to highlight the gap existing in literature about the use of microwaves for the liberation of bound phenolics from rice hulls (lines 83-86 of the revised manuscript). Moreover, an additional reference is now added in lines 87-89 of the revised manuscript to make clear the effectiveness of microwave-assisted alkaline hydrolysis. 

 

 

Comment: Materials and Methods

The methodology employed is in my opinion appropriate and the experimental design is well executed.

Response: We thank Reviewer #2 for appreciation of our design and execution of experiments.

 

Comment: Results

In the methodology, the authors indicate that they are going to compare the mean values obtained by microwave- and ultrasound-assisted alkaline hydrolysis a paired comparison student's t-test was performed. However, in line 395 when they compare the results, they do not use a t-test for it. This comparison in which part was performed. It is not clear. I suggest reviewing and clarifying it.

Response: We thank Reviewer for his/her comment. We have now modified section 2.8 “Statistical analysis” in lines 241-243 of the revised manuscript as well as the respective Table 6 along with a relevant footnote to make clear that two-tailed paired t-tests were carried out to compare the mean values obtained by microwave- and ultrasound-assisted alkaline hydrolysis.

 

Comment: Conclusions

The conclusions should be rewritten to make them clearer; there are some vague sentences that force the reader to go back to the document. The optimal operating conditions found in the study should be indicated, specifying their numerical values. For example, in the sentence: "The short duration of microwave treatment along with high temperature and solvent: solid ratio were found to favor the release of these valuable compounds and consequently their effective recovery", it is not indicated by way of conclusion what is a "short duration", high temperature and desirable value of the solvent: solid ratio.

I suggest improving this section.

Response: The optimum microwave-assisted alkaline hydrolysis conditions found in the study have now been added in the conclusions section according to Reviewer’s suggestion (lines 441-442 of the revised manuscript). Moreover, the mean values derived from the various assays as well as p-CA and FA contents upon microwave- and ultrasound- assisted alkaline hydrolysis have been now added in lines 446-450 of the revised manuscript. Additionally, the range of values regarding the p-CA and FA content found in the present study have been also added (lines 451-452 of the revised manuscript).

 

Round 2

Reviewer 2 Report

The authors addressed all the observations raised in the first point-by-point review. This new version of the manuscript is ready for publication. I approve.

Thanks to the authors for their willingness to improve the suggested aspects.