Extraction of Essential Oils from Plants by Hydrodistillation with Pulsed Electric Fields (PEF) Pre-Treatment

Round 1

Reviewer 1 Report

The paper focuses the applicability of pulsed electric field for extraction off essential oils, where PEF serves as a pre-treatment methodology. I confirm that the topic has good actuality and industrial relevance, however, I am not convinced with the results of this study. 

In my opinion this study is superficial. Only two distillation times are selected, the treatment parameters are hardly discussed. It's not clear why these PEF parameters are chosen, why there is no optimisation at all. The Joule heating is not discussed and compared properly. There is no statistical analysis. The amount of experimental data in my opinion is not sufficient to justify a publication in the Journal (conference proceedings at best).

Finally, the reported yields and improvements are in most cases lost in the STDEV of data. It makes an impression that authors have chosen 4 random parameters for PEF instead of doing appropriate optimisation for yield maximisation. They could have adjusted the amplitude, number of pulses, duration, frequency - a lot of flexibility.

Based on the the criticism above, I can't recommend this paper for publication. I think it requires a lot more experiments and parametrical research. 

 

 

Author Response

Please see attached file!

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript must be improved for publication. These are my comments and suggestions

Review the manuscript and correct typo and grammar errors, i.e. line 41, 356. Lines 89-90,95-96, correct grammar.

Based on the similarity report, lines 95-100, lines 470-476 must be changed. These are similar to other references.

Abstract: Clarify the values for the extraction yields with and without PEF pretreatment.

How much was the polyphenol extraction, antioxidant capacity? What does quality mean? Report values.

Introduction: References are not updated about PEF applications. There are current contributions in the recent years.

It is written "Considering the potential of PEF, as a pre-treatment before HD, for increasing the EO extraction from plants and reducing the distillation time, the number of studies published, and plants investigated is still very limited." This sentence is not supported. Include the state of the art of the preceding sentence.

Lines 62-62. Avoid repetitive information, those sentences should be omitted.

Line 304-308, sentences are not a hypothesis. These describe the trends about figure 3. Therefore, a clear mechanism must be discussed to support the results (in particular 30 min). I could be possible to cite preceding results from literature. What is the basis to obtain different results at 30 min and after 60 min? these are almost similar.

Results are evident to be the same and no effect was found in the presence of PEF by considering vertical lines (it seems error bars). Therefore, what is the contribution of the present manuscript?

Figures 3,4, 5. How were estimated the vertical lines? Are these error bars or standard deviations or uncertainties? Provide a full description of this calculation. This parameter could be an additional tool to explain the associated errors, hence the yields. 

Lines 304-308 and lines 326-330 are so similar.

Line 335. It is not valid since the kinetics was not evaluated.

Lines 341-342, 370-371. The statement must include the energy cost of PEF. After that, provide the difference between EOs extracted with and without PEF.

Table 4 should be removed; this information was included in Fig. 5.

If possible, section 3.1 and 3.2 should be discussed by associating information from literature about extraction or distillation methods of leaves, stems, algae, etc. based on PEF as pretreatment.

Based on the distillation time. I disagree with the statement in lines 362-365 and it should be changed. Extraction time demonstrates that all the extract is obtained above 60 min.

 Lines 368-370 "the amount extracted is higher than after 120 minutes using the conventional method." It is not valid, remove it. The amount of extract increases with time. It could probably be associated to experimental errors. Consider the same for Table 5.

Lines 370-371. it is not clear how was estimated 25%.

Table 5. Report the material (thyme).

Table 6. Is the variation referred to std deviation? explain.

Table 7. Include the part of the material and particle diameter

Author Response

Please see attached file!

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

In my opinion motivation that the research is not complete due to COVID is not a good argument to get it published. Presenting results as "positive" without statistical significance is not scientific. Authors should make a claim: can we use PEF for EO extraction from the selected plants or not. In this paper it seems that not, because increase of the mean if it's not P<0.05 means nothing.

Authors should increase the parametric flexibility and find appropriate protocols, which will give statistically significant differences. Even if they don't get it (e.g., after increasing intensities, and/or other parameters still the changes are lost in stdev) appropriate discussion should be made about limited applicability of PEF for this specific application. So it would become a negative result paper, which is also fine. But it should be based on experiments to make an impression that optimization was done, but still unsuccessful. It's not like that currently.

Therefore, I am sorry but in my opinion the publication can't be published in the current state.

Author Response

The author's response are in the attached file.

Author Response File: Author Response.docx

Reviewer 2 Report

Corrections were addressed. The manuscript can be published.

Author Response

Authors thanks the reviewer for his willingness in improving the paper.

Round 3

Reviewer 1 Report

I am sorry, but as I have mentioned previously I can't recommend this paper for publication. In this review version authors try to perform statistical analysis, but at the same time they performed experiments only in duplicates. You can't draw statistics, or check for normality with just two repetitions.

What authors need to do is just finish this paper as intended. Repeat some experiments, perform adequate number of repetitions, do statistical analysis. If required adjust the PEF parameters to have higher yields or at least show data to prove that their current protocols are optimal with their setup and plant.

Author Response

The comments are in attached file.

Author Response File: Author Response.docx