Fingerprinting of Volatile Organic Compounds for the Geographical Discrimination of Rice Samples from Northeast China

Round 1

Reviewer 1 Report

Fingerprinting of volatile organic compounds for the geographical discrimination of rice samples from Northeast China

In the submitted paper, a non-targeted volatile compound (VOCs) metabolomics method was applied to research the phenotype of rice from Heilongjiang, Jilin, and Liaoning provinces using headspace gas chromatography mass spectrometry HS-SPME/GC-MS with multivariate pattern recognition analysis (unsupervised HCA, PCA and supervised PLS-DA), thereby identifying the potential variation markers of VOCs in rice.

This is an extensive research, with a lot of numerical analysis based on HS-GC–MS data.

Thematically the work is interesting for the researchers and professionals and the proposed  manuscript is relevant to the scope of the journal.

I found it appropriate for publication in the Foods journal, but only after some modifications and clarification from the Authors.

Abstract, title and references          

Abstract is concise and clearly written, with a good command of English, and clear representation of the aim of the paper. Containing exactly 200 words, it can be said that it does meet the demands of the journal Foods (200 max). Furthermore, it is adequately structured: background of the proposed research, the method used, and main conclusions were mentioned.

The title of the paper adequately reflects the subject under investigation in the proposed study.

The literature review is comprehensive and properly done. References are numbered in order of appearance in the text, as demanded by formatting rules of the journal. Although there is no limitation in the number of references, a reference list of 32 citations is completely sufficient to cover the topic proposed.

Introduction  

The authors clearly represented the importance of the issue described. In the final paragraphs of the introductory section the authors explain what the core of their research is. The novelty of the work must be more clearly demonstrated.

Materials and Methods        

The authors adequately described the sampling procedure and sample preparation, extraction of volatiles, optimization of the HS-SPME method, GC-MS parametes used, and mutlivariate data treatment.

Results and Discussion         

The meaning, relevance and importance of the obtained results are explained in the same section. Furthermore, they were adequately compared with previous studies.

The significance of the Work: Given the large number of analyzed data, this is an interesting study with a possible significant impact in this area.

Statistical interpretation of the analytical data must be more properly presented.

The verification of the model should be performed. Model validation is possibly the most important step in the model building sequence. Unfortunately, a high R² value does not guarantee that the model fits the data well. The residuals from a fitted model are the differences between the responses observed and the corresponding prediction of the response computed using the regression function. If the model fit to the data were correct, the residuals would approximate the random errors that make the relationship between the explanatory variables and the response variable a statistical relationship.

Conclusions   

Conclusions are clear and strongly supported by the results obtained.

This is an extensive research, with a lot of numerical analysis based on HS-GC–MS data.

Other Specific Comments: The work is properly presented in terms of the language. The work presented here is very interesting and well done; it is presented in a compact manner.
The results are presented in a logical sequence and the discussion and analysis of the results are properly elaborated.
The manuscript should be improved from technical/graphical viewpoint, as described in the pdf file.

Comments for author File: Comments.pdf

Author Response

Response: Thank you very much for your positive comments on our manuscript. According to your comments, the manuscript has been modified. Please check the revised manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

I enjoyed reading the manuscript entitled “Fingerprinting of volatile organic compounds for the geographical discrimination of rice samples from Northeast China”. Manuscript is very well organized but some proposed changes should be done. In my point of view, is minor comments.

 

My comments are as follow:

 

• In line 163, I tried to enter to http://www.metaboanalyst.cn/ but was no possible.
• At the end of the conclusion section, you stated: “The potential for establishing sample banks from other regions is obvious and may lead to changes in the authenticity of rice in the future.”. I suggest to include a sentence to stablish pros and cons related to applicate this methodology to another foods (fruits, vegetables, dairy, etc.).

.

Author Response

I enjoyed reading the manuscript entitled "Fingerprinting of volatile organic compounds for the geographical discrimination of rice samples from Northeast China." Manuscript is very well organized but some proposed changes should be done. In my point of view, is minor comments. My comments are as follows:

1. Comment: English language and style are fine/minor spell check required.

Response: Thank you for your suggestions. Our native English speak colleague Amjad Sohail helped revise the English grammar in the manuscript. In the acknowledged part of the manuscript, we sincerely thanks him for his help. Please refer to the revised manuscript. Please refer to line 82.

 

2. Comment: In line 163, I tried to enter to http://www.metaboanalyst.cn/ but was no possible.

Response: Thank you for your suggestions. We apologize for a small error in the URL name and the correct web address, such as "https://www.metaboanalyst.ca/."The web page opened by this URL is shown in Figure S1. We provided the correct URL in the revised manuscript. Please refer to line 162.

Figure S1. Web of metaboanalyst

3. Comment: At the end of the conclusion section, you stated: “The potential for establishing sample banks from other regions is obvious and may lead to changes in the authenticity of rice in the future.”. I suggest to include a sentence to stablish pros and cons related to applicate this methodology to another foods.

Response: Thank you for your suggestions. We add the following content to the conclusion of the manuscript.“In addition, this method provides an effective way for the origin identification of other foods  (fruits, vegetables, dairy, etc.). Therefore, it can effectively avoid fake and shoddy favorite and high-quality agricultural products and geographical indication of agricultural products.” Please refer to lines 366-369.

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript is incomplete, several tables and figures are missing:
Line: 101: Table S1 is not available
Line: 214: Figure S1 is not available
Line: 215: Table S2 is not available
Lines: 274-285: Figure S2 is not available
Which makes it difficult to understand the reason for undertaking such research.
Please precisely define the purposefulness of the research undertaken. Despite numerous reports, it may not seem necessary to geographically identify the rice's origin if it does not entail health risks for consumers.  Knowledge gap as well as the work novelty must be highlighted before listing your objectives.
I cannot recommend this manuscript for printing in this version, although the chemical methods are clearly described and properly carried out. 

Author Response

Response to Reviewer 3 Comments

1. Comment: The manuscript is incomplete, several tables and figures are missing:
   Line: 101: Table S1 is not available
   Line: 214: Figure S1 is not available
   Line: 215: Table S2 is not available
   Lines: 274-285: Figure S2 is not available

Which makes it difficult to understand the reason for undertaking such research.

Response: Thank you for your suggestions. Table S1, Table S2, Figure S1, and Figure S2 were provided as SUPPLEMENTARY INFORMATION in this manuscript. We submitted SUPPLEMENTARY INFORMATION separately. We sincerely apologize for the SUPPLEMENTARY INFORMATION that was missing. Table S1, Table S2, Figure S1, and Figure S2 are as follows:

 

Table S1 Geographical origin of the rice samples

Samples	Variety	Region	Prefecture
1	Longjing 31	Heilongjiang	Qiqihar
2	Longjing 39	Heilongjiang	Qiqihar
3	Longjing 46	Heilongjiang	Qiqihar
4	Longjing 71	Heilongjiang	Qiqihar
5	Suijing 306	Heilongjiang	Suihua
6	Longke 3	Heilongjiang	Qiqihar
7	Jinyu 1	Heilongjiang	Qiqihar
8	Suijing 18	Heilongjiang	Suihua
9	Suijing 28	Heilongjiang	Suihua
10	Suijing 302	Heilongjiang	Suihua
11	Jijing303	Jilin	Changchun
12	Jijing525	Jilin	Changchun
13	Jijing816	Jilin	Changchun
14	Jijing 830	Jilin	Tonghua
15	Jiyang 1	Jilin	Tonghua
6	Jiyang 100	Jilin	Tonghua
17	Tonghe 877	Jilin	Tonghua
18	Tonghe 822	Jilin	Tonghua
19	Tongyuan 568	Jilin	Tonghua
20	Tongke 29	Jilin	Tonghua
21	Liaojing 212	Liaoning	Shenyang
22	Liaojing 436	Liaoning	Shenyang
23	Liaojing 433	Liaoning	Shenyang
24	Liaojing 419	Liaoning	Shenyang
25	Liaoxing 21	Liaoning	Shenyang
26	Yanjing 927	Liaoning	Panjin
27	Yanjing 337	Liaoning	Panjin
28	Yanfeng 47	Liaoning	Panjin
29	Yanjing 939	Liaoning	Panjin
30	Yanjing 219	Liaoning	Panjin

 

 

Table S2 VOCs identified in the rice sample with GC–MS. (μg/kg)

NO	Compound	CAS	Molecular Formula	RI	Heilongjiang	Jilin	Liaoning
1	Decane	124-18-5	C10H22	1000	0.58−3.24	0.35−5.42	0.28−0.62
2	Undecane	1120-21-4	C11H24	1100	1.78−6.59	0.71−12.97	2.29−3.43
3	2-methyl-decane	6975-98-0	C11H24	1064	0.46−7.14	2.1−32.98	15.02−15.21
4	Dodecane	112-40-3	C12H26	1200	8.87−22.41	4.72−28.37	17.45−59.48
5	Tridecane	629-50-5	C13H28	1300	3.15−27.48	2.98−26.78	56.34−64.59
6	Tetradecane	629-59-4	C14H30	1400	28.91−119.44	49.2−115.99	153.71−246.26
7	Hexadecane	544-76-3	C16H34	1600	2.44−9.72	2.28−19.27	12.26−16.56
8	2,6,10,14-tetramethyl-hexadecane	638-36-8	C20H42	1792	2.69−7.93	4.85−14.85	8.06−15.51
9	Styrene	100-42-5	C8H8	1254	3.27−13.22	2.13−15.29	23.17−45.29
10	2,6-dimethyl-decane	13150-81-7	C12H26	1112	1.15−7.54	2.49−10.35	6.43−23.0
11	2-methyl-dodecane	1560-97-0	C13H28	1264	6.89−129.06	9.33−33.9	158.78−204.51
12	2,6,10-trimethyl-dodecane	3891-98-3	C15H32	1366	8.72−138.3	8.13−43.86	54.8−286.06
13	Heptanal	111-71-7	C7H14O	1182	8.70−8.70	4.70−9.75	n.d.
14	(E,E)-2,4-nonadienal	5910-87-2	C9H14O	1216	9.71−71.91	0.58−12.93	28.31−61.67
15	Nonanal	124-19-6	C9H18O	1104	8.29−17.85	2.51−44.89	n.d.
16	(E)-2-heptenal	18829-55-5	C7H12O	1334	5.03−5.03	81.48−277.59	289.36−374.42
17	Decanal	112-31-2	C10H20O	1206	1.18−18.40	7.69−12.53	8.94−47.46
18	Pentadecanal	316249	C15H30O	1715	1.59−6.82	0.46−18.36	2.36−2.88
19	Hexadecanal	629-80-1	C16H32O	1817	0.52−2.10	1.44−2.84	0.81−0.88
20	(E) 6, I0-dimethyl-5,9 undecadien-2-one	3796-70-1	C13H22O	1876	4.79−15.45	12.62−29.42	11.50−19.01
21	6,10-dimethyl-2-undecanone	1604-34-8	C13H26O	1408	13.76−25.85	6.99−20.19	12.11−19.78
22	Hexanol	626-93-7	C6H14O	1211	3.90−24.12	1.71−27.2	19.03−51.06
23	1-octanol	111-87-5	C8H18O	1558	0.42−4.66	1.28−8.39	6.22−24.36
24	n-heptadecanol	1454-85-9	C17H36O	1984	0.27−0.85	1.26−3.46	1.49−1.69
25	2-hexyl-1-decanol	2425-77-6	C16H34O	1504	8.10−32.28	12.09−24.13	21.35−37.47
26	3,7,11-trimethyl-1-dodecanol	6750-34-1	C15H32O	1571	1.88 −5.75	1.13−7.99	12.54−49.56
27	Octanoic acid	124-07-2	C8H16O2	2050	0.14 −0.40	0.27−5.78	0.26−0.31
28	n-Hexadecanoic acid	57-10-3	C16H32O2	1968	1.05 −2.03	2.02−8.28	1.58−2.38
29	Hexanoic acid	142-62-1	C6H12O2	1849	0.09 −0.09	n.d.	0.42−0.42
30	Nonanoic acid	112-05-0	C9H18O2	2173	0.48 −1.52	0.85−2.92	0.95−8.01
31	Benzyl alcohol	100-51-6	C7H8O	1877	1.89 − 6.22	3.61−5.57	3.85−5.21
32	Toluene	108-88-3	C7H8	1036	0.88 −11.29	0.61−3.05	1.17−1.96
33	2-butyl-1-octanol	735273	C12H26O	1277	11.95−80.42	6.69−41.94	55.07−79.89

RI: retention index.

n.d.: not detected.

 

Figure S1. Total ion chromatogram of VOCs profile of Heilongjiang, Liaoning, and

Jilin rice samples were obtained from HS-SPME-GC-MS.

Figure S2. Significant differences in VOCs profile of Heilongjiang, Jilin, and Liaoning rice samples A) PLS-DA scores plot for the first component (76.6%) Vs second component (18.6%), indicating discrimination between Heilongjiang (red color), Jilin (green color), and Liaoning (blue color) rice samples. B) Three-dimensional PLS-DA scores plot. C) Three-dimensional PLS-DA loading plot. D) PLS-DA classification using the different number of components. Bar plots show the three performance measures (prediction accuracy, R², and Q²) using different components. The red '*' indicates the best values of the currently selected measures (Q²). E) PLS-DA model validation by permutation tests based on the separation distance. The p-value based on permutation is P< 0.001 (0/1000).

2. Comment: Please precisely define the purposefulness of the research undertaken. Despite numerous reports, it may not seem necessary to geographically identify the Rice's origin if it does not entail health risks for consumers. Knowledge gap as well as the work novelty must be highlighted before listing your objectives.

Response: Thank you for your suggestions. As described in the preface to the manuscript, Rice with a geographic origin label in China, such as Wuchang Rice in Heilongjiang, Panjin rice in Liaoning, and Baijinxiang rice in Jilin, are considered high-quality Rice and favored by consumers [1]. While there are significant differences in rice quality and composition across regions, it seems impossible to discriminate Rice's geographic origin by appearance or regular analysis [2]. In addition, volatile organic compounds (VOCs) are the diagnostic aspects of rice quality that can determine consumers' acceptance. They are also essential indicators of geographical origins. Therefore, in the current study, a non-targeted VOCs metabolomics method was applied to research the phenotype of Rice from Heilongjiang, Jilin, and Liaoning provinces. Specifically, HS-SPME and GC-MS and multivariate pattern recognition analysis identified the potential variation markers of VOCs in rice.

1. Dong KL.; Mo C.; Lee DK.; Long NP.Kwon SW. Non-Destructive Profiling of Volatile Organic Compounds Using Hs-Spme/Gc–Ms and its Application for the Geographical Discrimination of White Rice. J Food Drug Anal. 2018, 26,260.DOI:10.1016/j.jfda.2017.04.005
2. Suzuki Y.; Chikaraishi Y.; Ogawa NO.; Ohkouchi N.Korenaga T. Geographical Origin of Polished Rice Based On Multiple Element and Stable Isotope Analyses. Food Chem. 2008, 109,470-475.DOI:10.1016/j.foodchem.2007.12.063
3. 
   Comment: I cannot recommend this manuscript for printing in this version, although the chemical methods are clearly described and properly carried out. 

Response: First of all, thank you very much for your affirmation of the writing of this manuscript. Since the absence of the attached materials SUPPLEMENTARY INFORMATION makes you confused about the article, we have supplemented the SUPPLEMENTARY INFORMATION and further modified and adjusted the grammar and writing standards of the article in detail.

Author Response File: Author Response.docx