Comparative Study of the Chemical Composition of Root, Stem and Leaf Essential Oils from Synedrella nodiflora (L.) Gaertn

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this study, the comparison of the chemical composition of the essential oil isolated from the root, stem and leaf of the species Synedrella nodiflora is carried out. It is an interesting study, but before being published some aspects must be addressed.

Introduction

- As a general introduction to the species, a brief description of the botanical family and genus should be given.

- Indicate why this species is studied.

- Specify the aim of the study.

Materials and Methods

- The Materials used are not specified

- Specify the quantities of plant material collected

-The Retention indices (RI) must be calculated in the qualitative identification (GC-MS)

Results and Discussion

-Specify the amount of essential oil obtained and the yields of each part of the plant, the ranges can be used in discussion or conclusions.

- The results of the abundances in the chemical composition must be presented as the average of at least three repetitions and the standard deviation.

- In all chemical composition tables, the calculated RIs must be compared with the bibliography RIs, for which the bibliography RIs must be included.

- The experimental design must be improved. In addition to the part of the plant used, a new variable, the collection location, is introduced into the results.

-The locations and number of samples analyzed for each part of the species (Table 1-Table 3) do not coincide (root: two locations, three samples; stem: three locations, four samples; leaf: three locations, 7 samples) this presents A problem when comparing compositions, the locations and numbers of samples should be the same.

- The comparison of the composition of the essential oil should be for each location, location 1: root, stem and leaf; place 2: root, stem and leaf. If you want to compare between places, it should be from the same part of the plant, Example root from place 1, root from place 2, etc.

- The three clusters detected in the PCA correspond to the collection places. According to the title of the article, the composition of the different parts of the plant is being compared, therefore the analysis should be redone.

-The discussion must be rewritten according to the observations made.

Comments on the Quality of English Language

- Avoid the use of contractions ("It's leaves...") in scientific writing

Author Response

In this study, the comparison of the chemical composition of the essential oil isolated from the root, stem and leaf of the species Synedrella nodiflora is carried out. It is an interesting study, but before being published some aspects must be addressed.

Introduction

- As a general introduction to the species, a brief description of the botanical family and genus should be given.

We added some details concerning the botanical family.

- Indicate why this species is studied.

- Specify the aim of the study.

This study is part of a project between three universities of Côte d’Ivoire (Félix Houphouët-Boigny Abidjan, Nangui Abrogoua Abidjan, Peleforo Gon Coulibaly Korhogo) and the university of Corsica) on the chemical characterization of essential oils from Côte d'Ivoire. During twenty years, more than forty plants were investigated. In this manuscript, we choice S. nodiflora. The chemical composition of essential oil samples (stems and leaves) isolated from African S. nodiflora has been investigated. However, most papers reported the chemical composition of a unique oil sample. Herein, we choice three locations and three organs (roots, stems, leaves) and reported for the first time to our knowledge the chemical composition of roots essential.

We modified the last paragraph of introduction.

Materials and Methods

- The Materials used are not specified

- Specify the quantities of plant material collected

A table with amounts, yields, locations, has been added.

The Retention indices (RI) must be calculated in the qualitative identification (GC-MS)

We used, the same non-polar column for GC(RI) and GC/MS and the same conditions. Then the calculation of RIs on GC/MS is not mandatory.

Results and Discussion

-Specify the amount of essential oil obtained and the yields of each part of the plant, the ranges can be used in discussion or conclusions.

A table with amounts, yields, locations, elevations has been added (Table 1).

- The results of the abundances in the chemical composition must be presented as the average of at least three repetitions and the standard deviation.

A triplicate has been realized for one sample and no variation were noted. Then, we analyzed each sample only once.

- In all chemical composition tables, the calculated RIs must be compared with the bibliography RIs, for which the bibliography RIs must be included.

 RIs (2nd column) from literature were added in all tables.

- The experimental design must be improved. In addition to the part of the plant used, a new variable, the collection location, is introduced into the results.

A sentence concerning the influence of location was added in the results.

-The locations and number of samples analyzed for each part of the species (Table 1-Table 3) do not coincide (root: two locations, three samples; stem: three locations, four samples; leaf: three locations, 7 samples) this presents A problem when comparing compositions, the locations and numbers of samples should be the same.

Unfortunately, it is not possible to obtain the same numbers of samples. Indeed, the Adiopodoumé Forest Reserve is a relic of the little that remains of Côte d’Ivoire’s littoral forest and the sampling is restricted.

- The comparison of the composition of the essential oil should be for each location, location 1: root, stem and leaf; place 2: root, stem and leaf. If you want to compare between places, it should be from the same part of the plant, Example root from place 1, root from place 2, etc.

 The numbering of samples has been modified as follow:

1 = Adiopodoumé forest

2 = Yapo-Abbé forest

3 = Korhogo

R = roots; S = stems, L = leaves

Comparison between places was made for the same part of the plant in the sections 3.1 (roots), 3.2 (stems) and 3.3 (leaves) in order to show the influence of harvest site on the chemical composition. Then, in section 3.4, comparison between the three organs was made and the clusters obtained are related to the organs (Cluster I: leaves, Cluster II: stems and Cluster III: roots). Therefore it could be stated that in a same location, root, stem and leaf essential oils exhibit different chemical compositions. For example, samples R1 (root), S1 (stem) and L1a, L1b (leaf) from Adiopodoumé forest are distributed among the three clusters, confirming different chemical compositions. Discussion was improved in this way.

- The three clusters detected in the PCA correspond to the collection places. According to the title of the article, the composition of the different parts of the plant is being compared, therefore the analysis should be redone.

The three clusters detected in the PCA correspond to the three organs: (Cluster I: leaves, Cluster II: stems and Cluster III: roots).

-The discussion must be rewritten according to the observations made.

The discussion was modified.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Well-written article. No comments!

Comments on the Quality of English Language

Looks good

Author Response

Thank you for the comments

Reviewer 3 Report

Comments and Suggestions for Authors

Observation 1

2.1 section. In addition to knowing the geographic coordinates of the location of the plants, it would be good to have data on the average altitude of the harvesting sites

Observation 2

In section 2.5, the identification of compounds using two column systems: non-polar and polar, however, in section 2.3, there are no data on the characteristics of the polar column, nor on the conditions of analysis of this assay. It should be specified which polar column was used and the GC and MS spectrometer conditions.

Observation 3

section 2.4.

It is not clear when all the spectra are mentioned, nor which samples were analyzed in NMR equipment.

Were the whole oils analyzed, or did the NMR analyze pure molecules previously separated in a chromatographic system.

If the whole oils were analyzed (oil fingerprint), how was it possible to find the signals of the molecules that are in low percentages?

Please describe this section better and include the NMR spectra obtained as supplementary material outside the manuscript.

Author Response

Observation 1. 2.1 section. In addition to knowing the geographic coordinates of the location of the plants, it would be good to have data on the average altitude of the harvesting sites

A table with vegetal amounts, yields, locations, elevations has been added.

Observation 2. In section 2.5, the identification of compounds using two column systems: non-polar and polar, however, in section 2.3, there are no data on the characteristics of the polar column, nor on the conditions of analysis of this assay. It should be specified which polar column was used and the GC and MS spectrometer conditions.

Two columns non-polar and polar were used for GC(RI) and one column for GC-MS. The non-polar column is exactly the same for GC(RI) and GC/MS.

Observation 3. section 2.4. It is not clear when all the spectra are mentioned, nor which samples were analyzed in NMR equipment.

The 14 samples were analyzed by NMR. We modified the first sentence of paragraph 2.4.

Were the whole oils analyzed, or did the NMR analyze pure molecules previously separated in a chromatographic system.

If the whole oils were analyzed (oil fingerprint), how was it possible to find the signals of the molecules that are in low percentages?

Please describe this section better and include the NMR spectra obtained as supplementary material outside the manuscript.

We added one paragraph and two references to explain the identification of individual components using ¹³C NMR spectroscopy developed by the university of Corsica and reported in several articles.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript has been improved, however the inconsistency with the PCA analysis still remains. The authors wrote "The three clusters detected in the PCA correspond to the three organs: (Cluster I: leaves, Cluster II: stems and Cluster III: roots)." This is an error, it is clear that essential oils extracted from different parts are different, therefore, should not be considered as Clusters. The chemical composition of each part of the plant (leaves, stems and roots) should be analyzed in the different places. Also consider that there are not enough samples of roots and stems to perform a PCA, since there are only 3 samples.

Comments on the Quality of English Language

Minor editing of English language required, example: "The essential oil samples and were analyzed with..."

Author Response

The manuscript has been improved, however the inconsistency with the PCA analysis still remains. The authors wrote "The three clusters detected in the PCA correspond to the three organs: (Cluster I: leaves, Cluster II: stems and Cluster III: roots)." This is an error, it is clear that essential oils extracted from different parts are different, therefore, should not be considered as Clusters. 

We modified the text paragraph 3.4. The sentences dealing with “three organs-three clusters” have been deleted. We replaced “cluster” by “group”.

The chemical composition of each part of the plant (leaves, stems and roots) should be analyzed in the different places. The discussion is modified and focused on the chemical characterisation of each organ and the influence of the location. The sentences which compared the chemical composition of each organ have been deleted.

Also consider that there are not enough samples of roots and stems to perform a PCA, since there are only 3 samples.

We agree that the use of PCA is questionable but wanted to perform a comprehensive statistical analysis including PCA and HCA.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is Ok

Author Response

Thank you for the comments

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript has been improved, all suggestions have been taken into account and errors corrected. I consider that it can be published in the present form.