A Novel Method for the Evaluation of the Long-Term Stability of Cream Formulations Containing Natural Oils

Round 1

Reviewer 1 Report

As a scientist, I have major problems evaluating this manuscript. There is no question in my mind that this report may be important to some people in the cosmetics industry but, certainly, not to the scientific community. More specifically, this manuscript is a technical report that may be interesting to some people. It does not contain a scientific analysis. Since I am not familiar with the journal Cosmetics, I am refraining from the recommendation of the outright rejection of this manuscript.

Author Response

We believe that our article is of value to the Cosmetics industry.

Reviewer 2 Report

The manuscript needs a complete revision of its grammar and style.

Given the objectives of the paper, the Introduction should have included the rationale behind the relevance of the changes in water mass as an indicator of the long-term stability of cosmetic products. The methodology followed in the ICH guidelines uses different parameters to assess stability, namely phase separation resistance, pH, microscopic size analysis, globule size, zeta potential, conductivity and microbial challenge evaluation. How can the DVS system aspire to provide such a broad set of informations regarding a cosmetic formulation?

In the Introduction on jojoba oil, authors indicate that “ in the medical and pharmaceutical industry, the oil is used (…) as an anaesthetic for severe pain e.g. childbirth,”. A reference to support this sentence should be added.

Regarding the materials and methods, the main physico-chemical characteristics of the active ingredient should have been be disclosed, since they are crucial to the interpretation of the putative differences in the results obtained for formulations coded as A or B.

Overall, the results section is presented in a very tedious manner, often with extensive descriptions of the data that is already shown in the numerous tables or figures, which must be reduced in order to make the paper more objective. For example, regarding the data in tables 1 and 2 and throughout pages 15 and 16 extensive descriptive paragraphs were written. Often, a subjective analysis was made, like in the paragraph starting in line 197. What do the authors mean by "high" deviation? Only statistical analysis should be used to support conclusions on the pH stability under different conditions. The paper contains 6 pages of microscopic images of the different formulations! Do these images add much value, since globule size and zeta potential were also measured, thus enabling a quantitative analysis of this parameter? In my opinion, the entire data interpretation in section 3.1.3 is based in subjective terms.

A qualitative analysis combining the results provided by determination of globular size and zeta potential is presented in tables 3, 4 and 5. This approach doesn't seem to make much sense, since it doesn't take into account variations from the globule size and zeta potential at time 0, or variations between storage at different temperatures. For example, formulation IIIb is classified as excellent, despite having a globule size of 6184 nm at 40 ºC. Additionally, its globule size varies with temperature between 1579 nm and 6184 nm.

In the Discussion of the DVS results, an adequate revision of the literature has not been conducted. The results obtained in this should study should be compared with those of other works.

The conclusion of this study is too optimistic that the methodology “can be universally applied in the food, cosmetic and pharmaceutical industries to determine the long-term stability of semi-solids”. In my opinion, the authors have not yet established its relevancy, specially to cosmetic products with a more lipophilic nature, such as W/O emulsions.

Author Response

Dear Reviewer, thank you for your comments. The changes we have done to the revised paper based on your comments are highlighted in yellow colour.

 

The manuscript needs a complete revision of its grammar and style.

We have now revised the manuscript in terms of grammar & style.

Given the objectives of the paper, the Introduction should have included the rationale behind the relevance of the changes in water mass as an indicator of the long-term stability of cosmetic products. The methodology followed in the ICH guidelines uses different parameters to assess stability, namely phase separation resistance, pH, microscopic size analysis, globule size, zeta potential, conductivity and microbial challenge evaluation. How can the DVS system aspire to provide such a broad set of informations regarding a cosmetic formulation?

The introduction has been revised, please see changes on paper highlighted in yellow colour.

The DVS method was applied to the samples after their short-term stability evaluation at 25C with the aim to investigate if the stability "ranking" observed via the short-term stability protocol would agree with the stability ranking observed using the DVS.

 

 

In the Introduction on jojoba oil, authors indicate that “ in the medical and pharmaceutical industry, the oil is used (…) as an anaesthetic for severe pain e.g. childbirth,”. A reference to support this sentence should be added.

This statement has been deleted.

 

Regarding the materials and methods, the main physico-chemical characteristics of the active ingredient should have been be disclosed, since they are crucial to the interpretation of the putative differences in the results obtained for formulations coded as A or B.

The study is part of a wider study involving the design of a novel cream and active (which has not yet been exploited) for an aesthetic condition that the authors do not wish to disclose at the moment.

 

Overall, the results section is presented in a very tedious manner, often with extensive descriptions of the data that is already shown in the numerous tables or figures, which must be reduced in order to make the paper more objective. For example, regarding the data in tables 1 and 2 and throughout pages 15 and 16 extensive descriptive paragraphs were written. Often, a subjective analysis was made, like in the paragraph starting in line 197. What do the authors mean by "high" deviation? Only statistical analysis should be used to support conclusions on the pH stability under different conditions. The paper contains 6 pages of microscopic images of the different formulations! Do these images add much value, since globule size and zeta potential were also measured, thus enabling a quantitative analysis of this parameter? In my opinion, the entire data interpretation in section 3.1.3 is based in subjective terms.

Paragraphs 3.1.2, 3.1.3 & 3.1.4 have all been revised.

The microscopic images have been removed.

 

A qualitative analysis combining the results provided by determination of globular size and zeta potential is presented in tables 3, 4 and 5. This approach doesn't seem to make much sense, since it doesn't take into account variations from the globule size and zeta potential at time 0, or variations between storage at different temperatures. For example, formulation IIIb is classified as excellent, despite having a globule size of 6184 nm at 40 ºC. Additionally, its globule size varies with temperature between 1579 nm and 6184 nm.

The short-term stability study was performed in accordance with the International Council for Harmonization (ICH) guidelines for cosmetic formulations, where physical (appearance, odor, color, phase separation resistance, globule size) and chemical properties (pH, zeta potential measurement), and microbial changes were assessed after 8 days, 14 and 28 days of sample storage at 4 ± 1 °C in the refrigerator, 25 ± 1 °C ambient room temperature and 40 ± 1 °C in an incubator.

Regarding Formulation IIIb that was indeed an oversight as both globule size and zeta potential parameters influences stability.  It has been corrected in the revised paper.

 

In the Discussion of the DVS results, an adequate revision of the literature has not been conducted. The results obtained in this should study should be compared with those of other works.

Please see introductory section as these changes have already been made. Also, a similar study has been previously conducted using the rheological technique, oscillatory amplitude sweep test with LVR determination to measure stability i.e. the longer the LVR (linear viscosity region), the more stable or structured the cream, and vice-versa.

 

The conclusion of this study is too optimistic that the methodology “can be universally applied in the food, cosmetic and pharmaceutical industries to determine the long-term stability of semi-solids”. In my opinion, the authors have not yet established its relevancy, specially to cosmetic products with a more lipophilic nature, such as W/O emulsions.

The study involved the use of Dynamic Vapour Sorption test to determine long-term stability. The authors believe the technique can be applied to cosmetic samples containing water or with the ability to absorb moisture. In essence, the method can be applied to liquid and semi-solid cosmetic products.

 

Reviewer 3 Report

 

The manuscript “A Novel Method for the Evaluation of the Long-Term Stability of Cream Formulations Containing Natural Oils” presents the DVS method as tool for the evaluation of the long-term stability of cream formulations which is an interesting idea but I suggest to change the title because, even if he results are promising, the method needs more data for validation to be used. Also the DVS method is only a minor part of the paper making the title improper in my view

Overall, the article is well structured and has an easy to follow presentation.

Regarding redaction I noticed some small things that can be changed:

• the botanical plants names should be written in Italic, see row 39 (Simmondsia Chinensis), row 51, (Adansonia digitate), row 67 (Cocos nucifera)
• please correct on row 117 ”8days” and on 119 28days
• on row 118 check ”at an rpm of 3000 for 15 minutes”
• at 2.2.2.2. pH determination change the HCL with HCl
• table 3, the ”4” is missing
• figure 4 has the legend incomplete

Another suggestions is to make the data presentation more clear, for this point of view, please check the following:

3.1.2. pH Determination

 ”Nearly all creams stored at 25°C room temperature, exhibited very low pH deviations (<0.1) i.e. there was no significant difference in pH values after 8, 14 and 28 days, and only products IIB and IVB showed low deviations of 5.32/±0.1 and 5.45/±0.08. However, all products stored under 40 °C after the end of the 4 weeks’ measurement showed very high deviations. This implies that all products with each oil combinations stored at room temperature had very good shelf-life or stability and could be safe for use.” 

This paragraph is confusing, please reformulate it.

If the purpose of the pH determination is to observed the changings please justify the purpose of table 2.

3.1.4. Globule Size and Zeta Potential Measurement

The authors said: In this study, an emulsion with average globule size ≥6000nm was classified as having poor stability. Charges >-25was termed poor stability, −25 to −29.9 as average stability, −30 to −44.9 was said to have good stability and ≤-45 indicated excellent stability.

So, in table 3, at formulation IIIB is an average size of 6184/±1651.9 and the Zeta potential of -47.1 and the report quality is excellent. Does not both parameters influence the stability? Why you consider the quality excellent if you have an average size above the limit?

I suggest all the data presented in the table not be repeated in the text (rows 305-386), those comments can be rephrased without numeric values to make them easier to read.

3.1.5. Microbial Challenge Evaluation

Figure 5: the pictures used are the same as those on the manufacturer's website and I advise to eliminate them. Thus the whole figure 5 can be removed.

Author Response

Dear Reviewer, Thank you for your comments. The changes based on your comments are highlighted in green colour in the revised manuscript.

The manuscript “A Novel Method for the Evaluation of the Long-Term Stability of Cream Formulations Containing Natural Oils” presents the DVS method as tool for the evaluation of the long-term stability of cream formulations which is an interesting idea but I suggest to change the title because, even if he results are promising, the method needs more data for validation to be used. Also the DVS method is only a minor part of the paper making the title improper in my view

The title of the manuscript does not mention the DVS method. In our opinion it is an accurate title considering we specify the samples used (creams containing natural oils)

We are happy to consider alternative title suggested by the Reviewer.

 

Overall, the article is well structured and has an easy to follow presentation.

Regarding redaction I noticed some small things that can be changed:

• the botanical plants names should be written in Italic, see row 39 (Simmondsia Chinensis), row 51, (Adansonia digitate), row 67 (Cocos nucifera)

Done

• please correct on row 117 ”8days” and on 119 28days

Done

• on row 118 check ”at an rpm of 3000 for 15 minutes”

This experiment was conducted using an automated centrifuge after 8 days of product formulation at 3000rpm for 15 minutes.

• at 2.2.2.2. pH determination change the HCL with HCl

Done

• table 3, the ”4” is missing

It has now been added.

• figure 4 has the legend incomplete

This has now been corrected. "Globule size measurement after 8, 14 and 28 days at 4, 25 and 40 °C".

 

Another suggestions is to make the data presentation more clear, for this point of view, please check the following:

3.1.2. pH Determination

 ”Nearly all creams stored at 25°C room temperature, exhibited very low pH deviations (<0.1) i.e. there was no significant difference in pH values after 8, 14 and 28 days, and only products IIB and IVB showed low deviations of 5.32/±0.1 and 5.45/±0.08. However, all products stored under 40 °C after the end of the 4 weeks’ measurement showed very high deviations. This implies that all products with each oil combinations stored at room temperature had very good shelf-life or stability and could be safe for use.” 

This paragraph is confusing, please reformulate it.

All this paragraph has now been re-written.

 

If the purpose of the pH determination is to observed the changings please justify the purpose of table 2.

Table 2 was inserted to observe changes or variations in samples stored under the same conditions after the end of 28 days. The mean and standard deviation was calculated, and the SD used to indicate reproducibility.

 

3.1.4. Globule Size and Zeta Potential Measurement

The authors said: In this study, an emulsion with average globule size ≥6000nm was classified as having poor stability. Charges >-25was termed poor stability, −25 to −29.9 as average stability, −30 to −44.9 was said to have good stability and ≤-45 indicated excellent stability.

So, in table 3, at formulation IIIB is an average size of 6184/±1651.9 and the Zeta potential of -47.1 and the report quality is excellent. Does not both parameters influence the stability? Why you consider the quality excellent if you have an average size above the limit?

Yes, indeed both parameters influence stability. This has now been corrected.

 

I suggest all the data presented in the table not be repeated in the text (rows 305-386), those comments can be rephrased without numeric values to make them easier to read.

All these paragraphs have now been rephrased.

 

3.1.5. Microbial Challenge Evaluation

Figure 5: the pictures used are the same as those on the manufacturer's website and I advise to eliminate them. Thus the whole figure 5 can be removed.

Figure 5 has now been removed.

 

Reviewer 4 Report

The manuscript submitted for publication deals with the evaluation of the long-term stability of four oil-in-water creams from naturally sourced oil ingredients such as jojoba, baobab and coconut oil, proposing its assessment by Dynamic Vapor Sorption system. The results achieved were compared with the short-term stability experiments carried out before.

The selected topic is pertinent, and the structure and the content of the manuscript are convincing. Furthermore, the paper is well-written.

However, I suggest that this manuscript should be accepted for publication after the revision.

 

Some of the points are as below:

- Remove the abbreviation “O/W” in the Abstract.

- Page 2, line 44 – please give some examples of skin diseases that could benefit from the use of jojoba oil;

- At the end of the Introduction, when it is referred to the long-term assessment, it must be added the traditional way to perform it and also to complete the reference to high-performance liquid chromatography methods. Furthermore, when it is used the abbreviation HPLC-DAD-MS, be careful, as it in this form it seems that the HPLC is coupled to both DAD and MS detectors. Please improve it;

- In subsection 2.1. Materials, the reference to the article of the authors ([28]) is unnecessary.

- In the subjection 2.2.2.2. pH Determination, please check the storage solution of pH electrode. Are you sure that is used HCl solution? Usually, it is used a 3 M KCl solution.

- In subsection 2.2.2.5. Microbial Challenge Test (Page 4, line 146), when is mentioned “left for 72 h to allow optimum fungi growth”, I think it is also missing “bacteria”;

- Figure 1 is not referred to in the text;

- Page 5, lines 197-209 (subsection 3.1.2. pH Determination) – the text did not match with the data of Table 2. Furthermore, check the data of Table 2 marked in bold;

- Please check the legend of Table 2: it appears to be “Average Cumulative pH Values/Deviation after 28 days for each Product Stored at 4 °C, 25 °C and 40 °C;

- Figure 2 is not referred to in the text;

- In my opinion, Figure 3 could be provided as Supplementary File;

 - Page 16, line 371 – It misses “872.9nm/−47.0mV, after 8 days”;

- Page 17, lines 416-418 – This information was already given in the Material and Methods section;

- Figure 5 is not referred to in the text;

- Page 18, line 340 – Please check the meaning of the sentence “Model IVA stored at 25 °C room temperature, Figure 6 showed a total plate count”;

 - Figures 7 and 8 are not referred to in the text;

 

With thanks and best wishes,

The Reviewer

Author Response

Dear Reviewer,

Thank you very much for your comments. The changes based on your comments are highlighted in blue colour in our revised manuscript.

 

The manuscript submitted for publication deals with the evaluation of the long-term stability of four oil-in-water creams from naturally sourced oil ingredients such as jojoba, baobab and coconut oil, proposing its assessment by Dynamic Vapor Sorption system. The results achieved were compared with the short-term stability experiments carried out before.

The selected topic is pertinent, and the structure and the content of the manuscript are convincing. Furthermore, the paper is well-written.

However, I suggest that this manuscript should be accepted for publication after the revision.

 

Some of the points are as below:

• Remove the abbreviation “O/W” in the Abstract.

Done

• Page 2, line 44 – please give some examples of skin diseases that could benefit from the use of jojoba oil;

Jojoba oil can be used to treat eczema and seborrheic dermatitis. Other skin conditions include acne, sores and inflammation.

Please see the revised sentence in the manuscript.

 

• At the end of the Introduction, when it is referred to the long-term assessment, it must be added the traditional way to perform it and also to complete the reference to high-performance liquid chromatography methods. Furthermore, when it is used the abbreviation HPLC-DAD-MS, be careful, as it in this form it seems that the HPLC is coupled to both DAD and MS detectors. Please improve it;

We have now revised the Introduction considering your comment. Please see this revised part in the manuscript.

 

• In subsection 2.1. Materials, the reference to the article of the authors ([28]) is unnecessary.

It has now been removed.

 

• In the subjection 2.2.2.2. pH Determination, please check the storage solution of pH electrode. Are you sure that is used HCl solution? Usually, it is used a 3 M KCl solution.

That is correct as HCl is also used to recondition the electrode. Please see below:

https://www.chromservis.eu/i/cleaning-reconditioning-ph-electrodes/g/physical-properties-measurement-hints-and-tips

 

• In subsection 2.2.2.5. Microbial Challenge Test (Page 4, line 146), when is mentioned “left for 72 h to allow optimum fungi growth”, I think it is also missing “bacteria”;

It takes a period of 24 h to observe any bacterial growth and a total of 72 h for fungal growth. Nevertheless, the experiment was closely monitored on a daily basis and observations were recorded.

 

• Figure 1 is not referred to in the text;

Reference to Figure 1 has now been added.

 

• Page 5, lines 197-209 (subsection 3.1.2. pH Determination) – the text did not match with the data of Table 2. Furthermore, check the data of Table 2 marked in bold;

The text on subsection 3.1.2 has now been revised.

 

• Please check the legend of Table 2: it appears to be “Average Cumulative pH Values/Deviation after 28 days for each Product Stored at 4 °C, 25 °C and 40 °C;

Thank you, this has now been corrected.

 

• Figure 2 is not referred to in the text;

Figure 2 is now referred in the text.

 

• In my opinion, Figure 3 could be provided as Supplementary File;

We decided to remove Figure 3 from the manuscript based on another Reviewer's comment.

 

 - Page 16, line 371 – It misses “872.9nm/−47.0mV, after 8 days”;

This part of the manuscript has been re-written for better clarity.

 

• Page 17, lines 416-418 – This information was already given in the Material and Methods section;

We mention it again here just for clarity when viewing Figure 4.

 

• Figure 5 is not referred to in the text;

This Figure has now been removed based on another Reviewer's comment.

 

• Page 18, line 340 – Please check the meaning of the sentence “Model IVA stored at 25 °C room temperature, Figure 6 showed a total plate count”;

All this paragraph has been revised for clarity.

 

 - Figures 7 and 8 are not referred to in the text;

They are now referred as Figures 5 & 6 in the revised paper. 

Round 2

Reviewer 2 Report

The authors have modified the manuscript accordingly.