Comparison of Different Grades of Innovative Tanyang Congou Black Tea (Minkehong) Based on Metabolomics and Sensory Evaluation

Round 1

Reviewer 1 Report

Review this manuscript:

Manuscript ID: horticulturae-2929588

Title: Comparison of different grades of innovative Tanyang Congou black tea (Minkehong) on the basis of metabolomics and sensory evaluation
Authors: Zi-wei Zhou, Qing-yang Wu, Li-Qin Chen, Shu-ling Ruan, Zi-yu Yang, Yun Sun, and Reheman Aikebaer

General comments

In this investigation, the authors evaluated sensory properties of Minkehong black tea (an innovative Tangyang Congou black tea). In this tsudy, standard samples of MKH were used as material, and the results of sensory evaluation showed that the whole quality of MKH decreased along with the downgrading. They considered that the differences in quality of the tea have a directly correlation of the variation of content of some ester-type catechins and non- ester catechins, volatile compounds, amino acids and caffeine.

Comments:

1)      The abstract have some errors (line 21: both the contetnt of ester-tpe catechins, change for both the content of ester-type catechins;  line 24: acids like Thr, Leu, ASP, change for acids like Thr, Leu, Asp) and is repetitive.

2)       Errors in spacing, punctuation and alignment are observed throughout the text.

3)       Line 104: gallate (EGCG), (-)-epicatechin (ECG), caffeine, L-Theanine (L-Thea), Arginine. ECG correspond to (-)-epicatechin gallate

4)       2.5 Detection and analysis of non-volatile compounds by UPLC-MS

They carried out this analysis using a methanolic extract. Why don't they carry out this analysis on the same extract used for the sensory evaluation? This methanol extract is not representative of that people consume.

The authors do not justify why they carried out the study on this methanolic extract. I think it is more interesting to do the study over the aqueous extract.

5)       Line 246: The results indicated that the whole quality decreased as tea downgraded

This is a conclusion, before showing the result

6)       In the same case, the description of figures does not keep the order in which they appear: For example figure 2, the first description is for 2C not for 2A. Similar case for figure 4

7)       Figure 2 has very small print particularly 2D. Similar case for figure 4, impossible to read the Figure 4A and 4C. Similar case for figure 4, impossible to read the Figure 4A and 4C. Figure 5 have a lot of information, is a big figure. They need another distribution, impossible to read the Figure 5A, 5B, 5D and 5F.  

8)       Table 2: What do the subscripts a, b, c, etc. represent? Figure 3 too

9)       Line 303: The abbreviation must be defined the first time it appears

10)   The authors should do a literature review. New articles and reviews could be incorporated as referencesFor example: https://doi.org/10.1016/j.foodchem.2023.136601, https://doi.org/10.1016/j.foodres.2022.112169, https://doi.org/10.3390/foods13010144

Moderate editing of English language required

Author Response

1)      The abstract have some errors (line 21: both the contetnt of ester-tpe catechins, change for both the content of ester-type catechins;  line 24: acids like Thr, Leu, ASP, change for acids like Thr, Leu, Asp) and is repetitive.

Reply: Thank you for your reminder. We have made corrections to errors and duplicates in the abstract (Line 22 & Line 25). All the modified parts in the manuscript are highlighted in yellow, the same below.

2)       Errors in spacing, punctuation and alignment are observed throughout the text.

Reply: Thank you for your reminder. We have carefully proofread the entire text including the spacing, punctuation and alignment, among others.

3)       Line 104: gallate (EGCG), (-)-epicatechin (ECG), caffeine, L-Theanine (L-Thea), Arginine. ECG correspond to (-)-epicatechin gallate

Reply: Thank you for your reminder. We apologize for our carelessness, and we have completed the full name of ECG (Line 121).

4)       2.5 Detection and analysis of non-volatile compounds by UPLC-MS

They carried out this analysis using a methanolic extract. Why don't they carry out this analysis on the same extract used for the sensory evaluation? This methanol extract is not representative of that people consume

The authors do not justify why they carried out the study on this methanolic extract. I think it is more interesting to do the study over the aqueous extract.

Reply: Thank you for your question and suggestion , which is very close to the tea consumption. Due to  the methanol can  dissolve key catechins in tea product comprehensively, therefore, the detection results are more reliable.  Therefore, in this study, we applied national standard detection methods[1], which used methanol to identify catechins in tea samples so as other previous studies. What’s more, there is a lack of standards for extracting tea catechins with the tea liquid during sensory evaluation, and the ratio of tea to water is fail to be determined because the results usually positively correlated with the content of catechins in tea soup during sensory evaluation[2-3]. In future, we will consider more from the perspective of beverage to make it more closely related to sensory evaluation

Ref:

[1] GB/T 8313-2018, Determination of total polyphenols and catechins content in tea.[National standard]. Beijing: Standards Press of China.

[2] Zeng, L.; Fu, Y.Q.; Liu, Y.Y.; Huang, J.S.; Chen, J.X.; Yin, J.F.; Jin, S.; Sun, W.J.; Xu, Y.Q. Comparative analysis of different grades of Tieguanyin oolong tea based on metabolomics and sensory evaluation. LWT-Food Sci. Technol. 2023, 174, 114423.

[3] Cabrera, Mica.; Taher, F.; Llantada, A.; Do, Q.; Sapp, T.; Sommerhalter, M. Effect of Water Hardness on Catechin and Caffeine Content in Green Tea Infusions. Molecules. 2021, 12, 3485.

5)       Line 246: The results indicated that the whole quality decreased as tea downgraded

This is a conclusion, before showing the result

Reply: Thank you. This statement does not conform to the writing logic, and we have made adjustments to it (Line 279).

6)       In the same case, the description of figures does not keep the order in which they appear: For example figure 2, the first description is for 2C not for 2A. Similar case for figure 4

Reply：Thank you for your correction. This was indeed illogical. We have adjusted the combination of Figure 2 and Figure 4 in sequence to match the text description (Line 300 & Line 380).

7)       Figure 2 has very small print particularly 2D. Similar case for figure 4, impossible to read the Figure 4A and 4C. Similar case for figure 4, impossible to read the Figure 4A and 4C. Figure 5 have a lot of information, is a big figure. They need another distribution, impossible to read the Figure 5A, 5B, 5D and 5F.  

Reply: Thank you for your reminder. We have uploaded clearer figures in the Word version. The review version was a PDF version (file size:~2 Mb), which has been converted from a Word version (file size:~20 Mb). This has led to difficulties and to be impossible to reading Figures 2 and Figure 4 the PDF version.  Figure 5 indeed had too much information. Thanks to your suggestion, we have decomposed it into Figure 5 and Figure 6. (Line 418 & Line 452).

8)       Table 2: What do the subscripts a, b, c, etc. represent? Figure 3 too

Reply: Thank you. We apologize for our carelessness, and we have supplemented the meaning of a, b, c, etc. in both Table 2 and Figure 3 (Line 320 & Line 357).

9)       Line 303: The abbreviation must be defined the first time it appears

Reply: Thank you for your suggestion. We apologize for our carelessness, and we have made corrections and removed "Aa" (Line 333).

10)   The authors should do a literature review. New articles and reviews could be incorporated as references.Forexample: https://doi.org/10.1016/j.foodchem.2023.136601, https://doi.org/10.1016/j.foodres.2022.112169, https://doi.org/10.3390/foods13010144

Reply: Thank you for your suggestion. We have carefully read and studied these three papers and related literature, especially the review section，We have added a a literature review and cited relevant literature (Line 85 to 99).

Comments on the Quality of English Language

Moderate editing of English language required

Reply: Thank you for your comments on the quality of English language. We have invited a native English speaker to thoroughly check the language of the text. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Commercial samples of Minkehong black tea, which is classified as Fu'an tea, were selected for analysis in this article. I have doubts whether this article is scientifically original. If the authors had collected the plant material themselves, prepared it for analysis and then compared the results with those of commercial samples, the research would have been original and scientific. This is how a commercial brand is advertised. I do not feel able to review this article and therefore apologise.
Best regards,

Author Response

Commercial samples of Minkehong black tea, whichis classified as Fu'an tea, were selected for analysis in this article. I have doubts whether this article is scientifically original. If the authors had collected the plant material themselves, prepared it for analysis and then compared the results with thoseof commercial samples, the research would have been original and scientific. This is how a commercial brand is advertised. I do not feel ableto review this article andthereforeapologise.
Best regards,

Reply: Thank you for your valuable feedback and concern for the tea industry in Ningde (Fu’an City) City. First of all, in terms of the material selection and scientificity of our research, we are sure that it is scientific and original. Researches on tea standard samples  of different grades has been investigated widely, such as Anxi Tiehuanyin[1], Xihu Longjing teas[2], Wuyi Rougui Tea[3], Sri Lankan white tea, green tea, and black tea[4]).  Therefore, here comes three reasons to convey research on MKH tea samples.

(1) MKH is a reference sample produced based on the group standard [5] formulated by the Fu'an Tea Association,which not used for commercial aims and only for science study or manufacturing reference. Therefore,  we had obtained these samples from the Fu'an Tea Association without  any cost.

(2) The Fu'an Tea Association organized and invited relevant experts to carry out the MKH standard samples (super, first, second, and thirdlevel) after releasing standards in 2019. However, the grading was only based on the sensory evolution and lacked of objective experimental data to support. For example,  the  difference in sensory perception from the super-grade to third MKH, and the  differences in metabolites, including volatile and non-volatile compounds, are still unknown. Therefore, we conduct metabolomics experimental analysis in order to find grade differences(objective) that are consistent with sensory evaluation (subjective ). In other words, we hope to discover labeled metabolites that are consistent with level changes.

(3) Our research significance and purpose is to provide a grading basis for MKH related products produced by tea enterprises. At the same time, it also provides reference for the formulation of standards for similar tea products and the development of physical standard samples (The physical standard samples need to be replaced every 5 years).

      Thank you again for your suggestion. We will fully consider your suggestion in our future research.

      Best wishes.

Author Response File: Author Response.pdf

Reviewer 3 Report

The article ‘Comparison of different grades of innovative Tanyang Congou black tea (Minkehong) on the basis of metabolomics and sensory evaluation’ has been reviewed. The study is well-planned, and results are well-exploited. However, some minor details need to be corrected.

The number of samples is too low for a metabolomics analysis. Why did you only chose three for each type of sample? Is it a replicate of the same tea or different teas made with the same raw material? Please include it.

Line 20 you should not include abbreviations without explanation in the abstract, i.e. UPLC-MS

Line 20-25 Sentence too long, please short it.

Line 26 861 compounds were identified or detected???? Please verify.

Line 138 if you say once, you do not need to include times…

Line 140 Please add what activities did the panel trained during training?. Did they follow any ISO norm? Please include it.

Line 209 Is not 250ºC too high temperature for the fiber? Why did you use this temperature? Do you have any reference?

Line 210 What temperature?

Line 328 identified? Or tentative identification? Did you use standards for all of them? Please be carefully with the terms.  

Line 345 Figure 4C too small. Do you have the plot with QC samples? Please include it in the supplementary material or replace for figure 4B

Line 354 Please add the meaning of RI. Is it calculated or from the literature? Where from the odor descriptor was taken? Please include the references.

Author Response

The number of samples is too low for a metabolomics analysis. Why did you only chose three for each type of sample? Is it a replicate of the same tea or different teas made with the same raw material? Please include it.

Reply: Thank you again for your suggestion. Indeed, as you said, our sample size is relatively small. However, based on the MKH standard issued in 2019, there are only four levels, ranging from special to third, which is consistent with most premium teas, for example, Panyang Congou black tea[1], Tieguanyin tea[2], Baimudan tea[3].

      Each level was sampled three times, mainly in accordance with the requirements of biological replicability, to ensure the reliability of the data. We have added the reasons for selecting three physical standards in the materials section (Line 149). All the modified parts in the manuscript are highlighted in yellow, the same below.  

      We can be very certain that each repeated sampling was from the same batch of samples, as the standard samples are uniformly formulated by the Fu'an Tea Association based on standards (Physical standard samples need to be replaced every 5 years). Hence, there will be no significant deviation between the test materials.

Ref:

[1] Gao, C.; Huang, Y.; Li, J.; Lyu, S.; Wang, Z.; Xie, F.; Luo, Y.; Zhang, F.; Chen, Z.; Sun, W. Relationship between the Grade and the Characteristic Flavor of PCT (Panyong Congou Black Tea). Foods 2022, 11, 2815.

[2] Zeng, L.; Fu, Y.Q.; Liu, Y.Y.; Huang, J.S.; Chen, J.X.; Yin, J.F.; Jin, S.; Sun, W.J.; Xu, Y.Q. Comparative analysis of different grades of Tieguanyin oolong tea based on metabolomics and sensory evaluation. LWT-Food Sci. Technol. 2023, 174, 114423.

[3] GB/T 22291-2017, White tea. [National standard]. Beijing: Standards Press of China.

Line 20 you should not include abbreviations without explanation in the abstract, i.e. UPLC-MS

Reply: Thank you for your reminder. We have supplemented the explanation for UPLC-MS in the abstract, as well as GC-MS (Line 20 & Line 26).

Line 20-25 Sentence too long, please short it.

Reply: Thank you for your reminder. We have broken down and shortened the long sentence (Line 22 to 26).

Line 26 861 compounds were identified or detected???? Please verify.

Reply: Thank you for your reminder. It should only have been ‘detected’. Our wording was not rigorous enough, and we have corrected it (Line 27).

Line 138 if you say once, you do not need to include times…

Reply: Thank you for your reminder. We have made the correction and carried out the operation according to the national standard[1], so we have removed ‘once’(Line 157).

Ref:

[1] GB/T 23776-2018, Methodology for sensory evaluation of tea. [National standard]. Beijing: Standards Press of China.

Line 140 Please add what activities did the panel trained during training? Did they follow any ISO norm? Please include it.

Reply: Thank you for your question. We screen tea evaluators according to the relative standards[1-2]. Before the formal sensory evaluation, three sensory evaluators (all with national level tea evaluator professional qualifications) participating in the evaluation and scoring  discussed methods in detail, including black tea characteristics, flavor options, scoring methods, etc, At the same time, tea evaluator promised that they would operate completely independently and did not communicate with each other throughout the entire process (Line 159 to 164).

Ref:

[1] GB/T 24710-2009. Production of geographical indication_Tanyang Congou black tea[Geographical Indication]. Beijing: Standards Press of China. (in Chinese).

[2] T/FACX-2018. Tanyang Gongfu Tea with Flowery-fruity Flavour Minkehong Black Tea[Group standard]. Fu'an: Tea Industry Association of Fu'an City. (in Chinese)

[1] GB/T 23776-2018, Methodology for sensory evaluation of tea. [National standard]. Beijing: Standards Press of China.

Line 209 Is not 250ºC too high temperature for the fiber? Why did you use this temperature? Do you have any reference?

Reply: Thank you for your question. We have reviewed the original report again and found that 250℃ is indeed the analytical temperature, which was performed after extraction (60℃). The extraction head was aged for 5 minutes at 250 ℃ in the Fiber Conditioning Station, which was the step before extraction. We have commissioned Metware Co. to complete the detecting in this part, and the relevant references [1-3] were all pre-extracted using the same method and parameters for GC-MS. We have made some errors in the manuscript, and we have rewritten this section and added references (Line 234 to 238).

Ref:

[1] Liu,H.; Chen, W.; Chai, Y.; Liu, W.; Chen, H.; Sun, L.; ... & Huang, C.Terpenoids and their gene regulatory networks in Opisthopappus taihangensis ‘Taihang Mingzhu’ as detected by transcriptome and metabolome analyses. Frontiers in Plant Science, 2022, 13, 1014114.

[2] Shi,Y.; Zhu, Y.; Ma, W.; Shi, J.; Peng, Q.; Lin, Z.; Lv, H. Comprehensive investigation on non-volatile and volatile metabolites in four types of green teas obtained from the same tea cultivar of Longjing 43 (Camellia sinensis sinensis) using the widely targeted metabolomics. Food chemistry, 2022, 394, 133501.

[3] Du, Z.; Jin, Y.; Wang, W.; Xia, K.; Chen, Z. Molecular and metabolic insights into floral scent biosynthesis during flowering in Dendrobium chrysotoxum. Frontiers in Plant Science, 2022, 13, 1030492.

[4] Wu, Q.Y.; Zhou, Z.W.; Zhang, Y.N.; Huang, H.Q.; Ou, X.X; Sun, Y. Identification of key components responsible for the aromatic quality of Jinmudan black tea by means of molecular sensory science. Foods 2023, 12, 1794.

Line 210 What temperature?

Reply: Thank you for your reminder. The temperature should be 250℃. However, the extraction head we used is not brand new, so we have deleted the content of this section (Line 238).

Line 328 identified? Or tentative identification? Did you use standards for all of them? Please be carefully with the terms.  

Reply: Thank you for your reminder. We apologize for our lack of rigor. It should be tentative identification rather than identified. The GC-MS section did not use standards for identification, but was based on the results of the NIST library comparison. Therefore, we have made modifications (Line 360).  

Line 345 Figure 4C too small. Do you have the plot with QC samples? Please include it in the supplementary material or replace for figure 4B

Reply: Thank you for your reminder. Figure 4 has been remade, possibly due to formatting (PDF), resulting in low clarity in Figure 4. We have also made some adjustments, and in the latest uploaded Word version, Figure 4 was very clear. We have conducted QC sample testing and analysis, which was overlooked in the previous drawing. We have reflected the relevant results of QC in the PCA scatter plot (Line 379).

Line 354 Please add the meaning of RI. Is it calculated or from the literature? Where from the odor descriptor was taken? Please include the references.

Reply: Thank you for your reminder. We have added an explanation of RI below Table 2, as well as CAS number. The RI value was obtained from the NIST database, so we have changed the column to ‘NIST RI’. Odor descriptor was mainly taken from reference[1,2], and we have supplemented it into the table (Line 389).

Ref：

[1] Wang, D.; Liu, Z.; Chen, W.; Lan, X.; Zhan, S.; Sun, Y.; Su, W.; Lin, C.; Ni,  Comparative study of the volatile fingerprints of roasted and unroasted oolong tea by sensory profiling and HS-SPME-GC-MS. Curr Res. Food Sci. 2023, 6, 100442.

[2] Xiao, Y.; Huang, Y.; Chen, Y.; Xiao, L.; Zhang, X.; Yang, C.; Li, Z.; Zhu, M.; Liu, Z.; Wang, Y. Discrimination and characterization of the volatile profiles of five Fu brick teas from different manufacturing regions by using HS–SPME/GC–MS and HS–GC–IMS. Curr Res. Food Sci. 2022, 5, 1788-1807.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

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Author Response

Thank you for your suggestion.