Supercritical Carbon Dioxide Extraction, Antioxidant Activity, and Fatty Acid Composition of Bran Oil from Rice Varieties Cultivated in Portugal

Round 1

Reviewer 1 Report

The manuscript presents novel important data on the influence of SCE operating conditions (plant loading, CO₂ flow rate, temperature, and pressure) on the rice bran oil yield. Also, the fatty acid profile of RBO extracts was determined, and it was demonstrated that the oils are rich in unsaturated fatty acids like oleic and linoleic, and exhibit significant antioxidant activity.

A lot of good solid work was done by the authors, and the paper will be of interest to the readers of the Journal. Hence, it should be published provided some minor revision and editing is introduced, namely:

Line 91: In a first set of experiments, the influence of different SFE process parameters (plant loading, CO2 flow rate, temperature, and pressure) in the extraction yield of rice bran oil was evaluated to establish operating conditions.

Comment: The sentence should be revised. For example: “…. on the extraction yield … in order to determine the optimum operating conditions”)

Line 134: temperature (40, 60 and 80) ⁰C and pressure (20.0, 30.0, 40.0 and 60.0) MPa.

Comment and Question: Though it is understandable why the authors have chosen those temperature values, still it should be noted that many phenolic compounds are oxidized at higher temperatures. For example, it is demonstrated by some researchers that TPC in extracts might decrease when extraction temperatures exceed 333.15 K, while others argue that even temperatures above 343.15 K are very harmful as fast polyphenol degradation could be initiated.

In view of this it will be instructive for the readers if the authors could elaborate briefly on the influence of T on the TPC. Moreover that the yield of RBO at p = 40 bar and at T = 80 C was just very slightly higher than those at the lower temperatures.

Lines 340-342… At the lowest CO2 flow rate (0.5 L/min) ….., resembling to a solubility limited extraction curve in opposition to the steepest extraction curves at the highest flow rates (1 and 1.5 L/min),

Comment: The sentence should be revised (e.g. should be: “…. Resembling the behavior of a solubility….. in contrast to the ”)

Line 344 – should be: “…. as can be seen…

Lines 465-466:

Comment: Antioxidant activity vs antioxidant capacity – they are not synonyms and should not be used as such. In the present case it is the Reviewers belief that the correct term is – Antioxidant activity.

Line 468: These results are like in agreement with…., should be revised to read: These results are in agreement with....

Line 532: Should be: “….transition to a circular economy.”

FIGURES:

Figures comprehension can be approved considerably provided more intense colors are used

Author Response

Dear Reviewer.

We are grateful to the reviewers for their time and for their efforts to examine our manuscript so carefully.  We have examined very carefully their queries, addressed the points they have raised and prepared detailed answers.  In those instances where a suggestion is not completely accepted, we explain in detail why.

We remain with the hope that the revised manuscript in its present form will satisfy the high standards of Separations.

José Coelho

Author Response File: Author Response.pdf

Reviewer 2 Report

In the paper " Supercritical carbon dioxide extraction, antioxidant activity and fatty acid composition of bran oil from rice varieties cultivated in Portugal”, the authors analyzed the effect of extraction conditions on extraction efficiency of the brain oil. This work covers an interesting topic but has some significant back draws. My biggest concern goes to the lack of statistical analyses of the results. Therefore, I suggest 'major revision' so that this point can be addressed.

Here are the specific comments:

Introduction; line 55. after rice bran oil, add RBO in the bracket

Introduction; the novelty of the research is not clear. How this research differs from previously described researches?

Line 94: How is it applicable to use extraction conditions selected as optimum for one cultivar for extraction form different cultivars?

Materials and methods: Line 131. How were the extraction conditions selected? Were the experiments performed randomly or according to the design of the experiment? Please clarify. Were the experiments performed with replications?

Line 183: Were the TPC measurements performed with replications?

Line 220: Were the DPPH measurements performed with replications?

Line 246: Were the ABTS measurements performed with replications?

Line 271: Were the fatty acids profile measurements performed with replications?

Results and discussion: Table 1. Please include standard deviations of oil yield in the table. It would be also useful to perform MANOVA to define the effect of the individual process variable on the oil yield.

When analyzing the effects of multiple variables on the process efficiency it is recommendable to perform the experiment according to the design of the experiments taking into account all interactions between process variables that can influence the process efficiency.

Table 2. Please include standard deviations for all presented results. Are there statistical differences between the results regarding the rice variety?

Figure 8. The description of the figures includes logitlog regression, but axis values are not in the log form. Please clarify. Why was the only correlation between ABTS and DPPH analyze? What about TPC?

Table 3. Please include standard deviations for all presented results. Are there statistical differences between the results regarding the rice variety?

Table 4. Please include standard deviations for all presented results. Are there statistical differences between the results regarding the rice variety?

Author Response

Dear Reviewer.

We are grateful to the reviewers for their time and for their efforts to examine our manuscript so carefully.  We have examined very carefully their queries, addressed the points they have raised and prepared detailed answers.  In those instances where a suggestion is not completely accepted, we explain in detail why.

We remain with the hope that the revised manuscript in its present form will satisfy the high standards of Separations.

José Coelho

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors put an effort and answered most of my comments. But some corrections are still needed. My suggestion is minor revision.

1. Include this whole section in the manuscript “This study focuses on providing new data in supercritical carbon dioxide extraction and composition of rice bran oil obtained from 8 rice varieties (3 short-grain Japonica and 5 long-grain Indica) cultivated specifically in Sado river in Portugal. From the best we knowledge is the first study with these 8 rice varieties, and their characterization in fatty acid composition, as well as the characterization concerning the antioxidant activity to the different fractions collected with the extraction time and the discussion of the consequent increase of the antioxidant activity in the last collected fractions. A short paragraph was placed in the introduction to highlight the novelty of the study. “

2. Please include following explanation into manuscript

“Optimizing the extraction conditions for one variety of rice bran and extend it to all others was assumed because we are extracting the oil, which is mainly composed of triacylglycerols that in turn reflected in the fatty acid composition shown in Table 3. Considering the composition of the oil and knowing the behavior of either the initial solubility (initial phase of extraction) or at a later stage of extraction, where diffusion phenomena control the extraction of the oil from the matrix, there is no reason why similar rice bran matrices of the same type and region may behave differently in supercritical CO2. Since the solubility of the compounds is characterize, another factor that controls the extraction is the interaction with the matrix that, in this case, are similar.”

3. Please do not use x as the sign for multiplication

Author Response

Dear Reviewer.

We are grateful to the reviewers for their time and for their efforts to examine and discussion of our manuscript so carefully.  We have examined very carefully their queries, addressed the points they have raised and prepared answers. 

Sincerely yours,

José Coelho

Author Response File: Author Response.pdf