The Influence of Cryogrinding on Essential Oil, Phenolic Compounds and Pigments Extraction from Myrtle (Myrtus communis L.) Leaves

Round 1

Reviewer 1 Report

The Original Research Article “The influence of cryogrinding on essential oil, phenolic com- 2 pounds and pigments extraction from myrtle (Myrtus communis L.) leaves” represents a well presented investigation relevant to the assigned tasks.

The aim of this study was to investigate the influence of cryogrinding pretreatment on the recovery of essential oil, phenolics and pigments from myrtle leaves. This is one of the first studies to examines the effect of cryogrinding and distillation time on the yield of myrtle EO.

Since EOs contain highly volatile and thermolabile compounds that can be lost at classical grinding temperatures due to evaporation or oxidation, grinding at -196 °C using nitrogen as a cryogen, i.e. cryogrinding, can avoid such undesirable losses and changes. In this way, it is possible to preserve the flavour, colour and nutritional value of ground herbs, having a finer and more uniform size which in turn also increases the yield of distillation/extraction.

Since, as a rule, the yield of myrtle essential oils is very low and rarely exceeds 1%, 3-minute cryopreservation significantly increases the yield and concentration of volatile essential oil compounds and reduces the distillation time to 30 minutes, and 9-minute cryogrinding pretreatment and 15-minute extraction lead to an increase in the concentration of phenolic compounds and pigments on the 40%. The results obtained by the authors are important for the complete extraction of substances from the leaves of Myrtus communis L.

The work has been done at a good scientific level and ready for publication.

Author Response

We thank the reviewer for the time and effort and also for finding our work suitable for publication.

Reviewer 2 Report

Well written but old technique of GC was used.

Comments for author File: Comments.pdf

Author Response

We thank the reviewer for the time and effort. Please see the attachment for the point-by-point response to the remarks raised.

Author Response File: Author Response.pdf

Reviewer 3 Report

Lines 161-162: Please specify which compounds in which no standards were available and also indicate the compound from the same chemical group that was used instead.

Line 188: How reliable is quantification completed in this way? Can you support this with the literature?

Line 201-206: Why were the standards for these compounds not used? In a quick search I found standards for:

 myricetin-3-O-galactoside (https://www.caymanchem.com/product/36467/myricetin-3-galactoside).

myricetin-3-O-rhamnoside (https://www.wilshiretechnologies.com/product/myricetin-3-o-rhamnoside/)

quercetin-3-glucoside (https://www.sigmaaldrich.com/US/en/substance/quercetin3glucoside46438482359)

apigenin (https://www.sigmaaldrich.com/US/en/product/sigma/10798?gclid=EAIaIQobChMIjojnrcOc-wIVQSatBh3RoQZBEAAYASAAEgKXSfD_BwE&gclsrc=aw.ds)

epicathechin (https://www.sigmaaldrich.com/US/en/product/sigma/e1753?gclid=EAIaIQobChMIhsHfzsOc-wIVMRqtBh2KiwNpEAAYASAAEgJ6jPD_BwE&gclsrc=aw.ds)

It is concerning that actual standards for the two most abundant phenols extracted in this study, myricetin 3-O-galactoside and myricetin 3-O-rhamnoside, were not used for quantification and qualification. The authors must explain why actual standards were not used and support this method with literature references.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors state in their response that they have included the following references: 

Martins, C. C., Rodrigues, R. C., Mercali, G. D., & Rodrigues, E. (2022). New insights into non-extractable phenolic compounds analysis. Food Research International, 111487.

Tomaz, I., & Maslov, L. (2016). Simultaneous determination of phenolic compounds in different matrices using phenyl-hexyl stationary phase. Food Analytical Methods, 9(2), 401–410.

But neither of these references could be found in the updated manuscript. Please be sure to include them along with the statement they provided:

The myricetin 3-O-galactoside and myricetin 3-O-rhamnoside, were not used for quantification and qualification because it was not possible to obtain the specified standards from the supplier at the time the analyses were performed due to the COVID crisis. According to various authors, if standards are not available, compounds with similar structure or representatives of a family of phenolic compounds can be used for quantification of the phenolic compounds and the results expressed as equivalents (Martins et al., 2022; Tomaz & Maslov, 2016).

Author Response

We thank the reviewer for the following comment which was now also addressed in the manuscript.

The authors state in their response that they have included the following references: 

Martins, C. C., Rodrigues, R. C., Mercali, G. D., & Rodrigues, E. (2022). New insights into non-extractable phenolic compounds analysis. Food Research International, 111487.

Tomaz, I., & Maslov, L. (2016). Simultaneous determination of phenolic compounds in different matrices using phenyl-hexyl stationary phase. Food Analytical Methods, 9(2), 401–410.

But neither of these references could be found in the updated manuscript. Please be sure to include them along with the statement they provided:

The myricetin 3-O-galactoside and myricetin 3-O-rhamnoside, were not used for quantification and qualification because it was not possible to obtain the specified standards from the supplier at the time the analyses were performed due to the COVID crisis. According to various authors, if standards are not available, compounds with similar structure or representatives of a family of phenolic compounds can be used for quantification of the phenolic compounds and the results expressed as equivalents (Martins et al., 2022; Tomaz & Maslov, 2016).

Answer: The sentence and references were included in the manuscript as suggested. 

 

Author Response File: Author Response.pdf