The Chemistry, Sensory Properties and Health Benefits of Aroma Compounds of Black Tea Produced by Camellia sinensis and Camellia assamica

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This review article has new and originality of a report of chemistry, sensory property, and formation mechanism of aroma compounds of black tea produced by Camellia sinensis and Camellia assamica. The reveiw also contains information about black tea; i.e, processing, chemical properties, and health benefits. The content is good and fits the aims and scope of horticulturae. I think this manuscript is publishable if authors revised this manuscript slightly like below.

1) Lines 73-75: According to the author, the article discusses sensory analysis methodologies and emphasizes the relevance of sensory analysis. As a result, more information about sensory evaluation is required.

2) Lines 326-332: Please double-check this section.

3) Lines 362-363: Please elaborate on the increase in phenolic compounds following fermenation.

4) Line 399: The term "polyphenols" is overused in the discussion of digestive tract protective properties. Please mention the active ingredient.

5) Many publications have been published on the effects of season, agricultural practices, growing areas and processing conditions on tea product quality. However, this paper does not provide much of this information.

Author Response

This review article has new and originality of a report of chemistry, sensory property, and formation mechanism of aroma compounds of black tea produced by Camellia sinensis and Camellia assamica. The reveiw also contains information about black tea; i.e, processing, chemical properties, and health benefits. The content is good and fits the aims and scope of horticulturae. I think this manuscript is publishable if authors revised this manuscript slightly like below.

• Lines 73-75: According to the author, the article discusses sensory analysis methodologies and emphasizes the relevance of sensory analysis. As a result, more information about sensory evaluation is required.

Response: Thank you for your comment. We have added the related information.

2) Lines 326-332: Please double-check this section.

Response: Thank you for your correction. We have revised it carefully.

3) Lines 362-363: Please elaborate on the increase in phenolic compounds following fermenation.

Response: Thank you for your comment. Tea leaves contain enzymes that catalyze the degradation of specific molecules, such as esters of hydroxycinnamic acid, to release free hydroxycinnamic acids. All things considered, the particular activities that take place during black tea fermentation are responsible for the rise in free hydroxycinnamic acids. These molecules are released and undergo transformation as a result of a number of biological events that take place throughout the fermentation process. The oxidation of catechins is one of the main processes leading to the rise in free hydroxycinnamic acids during fermentation. Catechins undergo enzymatic oxidation to produce theaflavins and thearubigins, which add flavor and color. Black tea's deep, malty flavor is enhanced by thearubigins, which are the byproduct of polymerization processes. The antioxidant qualities are enhanced by this rise in phenolic chemicals, which may have positive health effects.

4) Line 399: The term "polyphenols" is overused in the discussion of digestive tract protective properties. Please mention the active ingredient.

Response: Thank you for your comment. We have revised the sentence: “Tea aroma components, notably theaflavins, exhibit strong antioxidant action.”

• Many publications have been published on the effects of season, agricultural practices, growing areas and processing conditions on tea product quality. However, this paper does not provide much of this information.

Thank you for your suggestion. Because there are many articles about seasons, agricultural practices and growing areas, we are more concerned about the quality, chemical composition, and health benefits of black tea. We also add a paragraph about these researches, as your suggestions.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

I consider that the review is well done, sufficiently documented and well described. The information gathered is timely, extensive, the content is discussed with precision, although it lacks in indicating the paths for future research.

However, I suggest four aspects:

1) indicate the method for collecting the information (keywords, database consulted, information processing); this is important to verify that the data collection has been exhaustive.

2) The section titled "The Main Aroma Compounds of Black Tea" should be accompanied by a figure or analysis that indicates the molecules and their proportion that constitute the aromatic profile of the two varieties of black tea (perhaps a PCA analysis) , which would complement table 2 and allow the chemical differences to be visually seen; In that same sense, it would be nice to see some chemical structures of the most outstanding molecules.

3) In the section "2.1. The main processing technologies of black tea",  2.3. The variation of critical aroma compounds during processing and 2.4. The health benefits of critical aroma compounds of black tea" it should be indicated in which varieties the results described were detected.

4) The Conclusions section is very long and there are descriptions that should be in results, for example, lines 451 to 473 are more appropriate in section 2 "The Main Aroma Compounds of Black Tea"

 

Author Response

I consider that the review is well done, sufficiently documented and well described. The information gathered is timely, extensive, the content is discussed with precision, although it lacks in indicating the paths for future research.

However, I suggest four aspects:

• indicate the method for collecting the information (keywords, database consulted, information processing); this is important to verify that the data collection has been exhaustive.

Response: Thank you for your comment. We used a thorough strategy with targeted keywords and reviewed multiple databases to achieve a thorough data collection process. The following keywords were utilized, either single or in combination: processing, fermentation (enzymatic oxidation), black tea, aroma, molecular sensory, quantitative descriptive analysis, aroma extraction dilution analysis, and aroma production mechanism. These keywords were chosen because they were pertinent to the subject of our study and the particular goals we had in mind. The electronic bibliographic databases PubMed, ScienceDirect (Elsevier), Springer, and Nature yielded 466 articles when searched; after removing duplicates, the number of entries was reduced to 389. 108 records remained after the 389 records were sifted using preset inclusion criteria. These databases were chosen because they have a history of holding top-notch research articles on the topics, we are interested in. Within these databases, we used advanced search capabilities and search filters to focus our search and find the most pertinent articles. To make sure that our information processing was accurate and consistent, we used standardized data extraction methodologies. We are sure that our strategy has allowed us to gather an extensive and thorough dataset to back up the research results.

2) The section titled "The Main Aroma Compounds of Black Tea" should be accompanied by a figure or analysis that indicates the molecules and their proportion that constitute the aromatic profile of the two varieties of black tea (perhaps a PCA analysis) , which would complement table 2 and allow the chemical differences to be visually seen; In that same sense, it would be nice to see some chemical structures of the most outstanding molecules.

Response: Thank you for your suggestion. We have added a figure in the section "The Main Aroma Compounds of Black Tea".

3) In the section "2.1. The main processing technologies of black tea",  2.3. The variation of critical aroma compounds during processing and 2.4. The health benefits of critical aroma compounds of black tea" it should be indicated in which varieties the results described were detected.

Response: Thank you for your valuable suggestion. We have added some information appropriately.

4) The Conclusions section is very long and there are descriptions that should be in results, for example, lines 451 to 473 are more appropriate in section 2 "The Main Aroma Compounds of Black Tea"

Response: Thank you for your suggestion. We have rearranged positions of description.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

General comments

 

The manuscript presents a very interesting information. However, for being a review it is important to provide more information mentioning previous studies. For example, in processing technologies not only is necessary to mention the occurred changes but also mention the way that each process is generally done because it affects the final compounds. In addition, it would be very useful to include previous studies considering variables in each one of them. I mention below some aspects to consider:

 

 

1.       In the introduction section I highly recommend including a figure with the varieties used, with a short information regarding the morphological differences between them.

 

2.       When mentioning the processing technologies of black tea give more information, for example, in whitering, specify how much the moisture content decreases (line 70). Which enzymes break down the materials? (line 70).

 

3.       In the same line that the comment before, describe how the rolling process is done. A flow chart for the the main processing technologies of black tea could help.

 

4.       Specify PPO and abbreviations the first time they are mentioned (line 188). TFs and TRs (line 206).  (FADVs, AADVs, VTs, or CDVs) (line 162).

 

5.       Give detailed information regarding fermentation in black tea.

 

6.       Line 197. “The decision to conclude fermentation at the right moment is pivotal” Prove criteria to conclude fermentation at the right moment.

 

7.       Drying. Lines 215-217. Authors mention that some researchers investigated the effects of different drying techniques and micro-218 wave treatment exhibited the most favorable outcomes. At least it is necessary to include the conditions in the process were carried out. 

 

8.       Which drying technology is more commonly used? Which are their conditions? E.g. if it is hot air drying, which temperatures are commonly used?

 

9.       2.3. The variation of critical aroma compounds during processing. I recommend putting the information together with 2.1 section when defining the stages of the process.

 

10.   Line 309. Which temperatures?

 

11.   Line 328. “high temperatures and for longer” it is relative, please provide at least a range of temperature and processing times, according to previous researchers.

 

12.   When mentioning the health benefits, please mention the specific compounds that are related to each benefit. Which compounds are related to Neuro-regulation effects? Anti-microbial effects?  

 

13.   Reference the tables and figures within the manuscript.

 

14.   Conclusion section gprovide a lot of theoretical information. Notice that conclusions should be mainly drawn from the methodology and results. Authors could add information specifying the future applications for the obtained results.

 

15.   Finally, I also recommend to change the tittle because there is no information regarding the “formation mechanisms”, it will be necessary to include the reactions, not only mention the pathways in different contexts.

Author Response

The manuscript presents a very interesting information. However, for being a review it is important to provide more information mentioning previous studies. For example, in processing technologies not only is necessary to mention the occurred changes but also mention the way that each process is generally done because it affects the final compounds. In addition, it would be very useful to include previous studies considering variables in each one of them. I mention below some aspects to consider:

In the introduction section I highly recommend including a figure with the varieties used, with a short information regarding the morphological differences between them.

Response: Thank you for your suggestion. We have added.

When mentioning the processing technologies of black tea give more information, for example, in whitering, specify how much the moisture content decreases (line 70). Which enzymes break down the materials? (line 70).

Response: Thank you for your suggestion. First withered by being exposed to air, having their moisture content decreased from 76 to 60–62%.

Enzymes (phenol oxidase) in the tea leaves break down materials, including proteins and polyphenols, during withering and producing volatile compounds. Phenol oxidase, or the primary enzyme in the manufacturing of tea, and its catalase and hydroxylase activities are in charge of the primary transformation of phenol molecules, which affects the product's quality.

3. In the same line that the comment before, describe how the rolling process is done. A flow chart for the the main processing technologies of black tea could help.

Response: Thank you for your suggestion. We have added. Tea leaves that have withered are ruptured during the rolling process, which also damages the tea cells and releases oxidase, which initiates oxidation. The oxidation of the green tea leaves causes them to become bright copper in color while rolling. This technique determines the black tea's curled.

4. Specify PPO and abbreviations the first time they are mentioned (line 188). TFs and TRs (line 206). (FADVs, AADVs, VTs, or CDVs) (line 162).

Response: Thank you for your correction. We have specified all the abbreviations in the paper where they first appeared: PPO in section 2.1.2; TFs in section 2.1.2; TRs in section 2.1.3; FADVs, AADVs, VTs, or CDVs in section 2.2.

5. Give detailed information regarding fermentation in black tea.

Response: Thank you for your suggestion. We have added the detailed information in section 2.1.3.

6. Line 197. “The decision to conclude fermentation at the right moment is pivotal” Prove criteria to conclude fermentation at the right moment.

Response: Thank you for your correction. We have corrected it.

7. Drying. Lines 215-217. Authors mention that some researchers investigated the effects of different drying techniques and micro-218 wave treatment exhibited the most favorable outcomes. At least it is necessary to include the conditions in the process were carried out.

Response: Thank you for your comment. The material being treated is affected by microwave technology in both thermal and nonthermal ways. The heat generated within the treated materials increases internal temperature and evaporates moisture. The quick migration of moisture is accelerated by the pressure created by evaporation, which gives the treated material its distinctive properties of high heat transfer, high drying rate, high efficiency, and high quality. When black tea was microwave dried, the highest levels of polyphenols, catechins, and theaflavins were discovered. The fermented leaves were heated in a 700 W microwave for 6 minutes (leaf temperature: 91–8 °C), cooled for 1 hour outside the oven, heated again for 4 minutes (leaf temperature: 106–6 °C), cooled for 30 minutes outside the oven, and heated again for 2 minutes (leaf temperature: 115–3 °C).

8. Which drying technology is more commonly used? Which are their conditions? E.g. if it is hot air drying, which temperatures are commonly used?

Response: Thank you for your comment. Traditional drying techniques using hot air provide benefits such as ease of use and low cost, but drawbacks such as extended drying times and significant nutritional loss. drying for about 20 minutes at 150 °C, then cooling outside of the drying apparatus for an hour, and finally drying for about 100 minutes at 90 °C.

9. 2.3. The variation of critical aroma compounds during processing. I recommend putting the information together with 2.1 section when defining the stages of the process.

Response: Thank you for your recommendation. We have revised according to your recommendation.

10. Line 309. Which temperatures?

Response: Thank you for your comment. The volatility of black tea may be affected by the temperature of the fermenting process. The relative volatile content might be more volatile at higher fermentation temperatures, including alcohols and alkenes at 31 °C, esters and alkanes at 28 °C. 

11. Line 328. “high temperatures and for longer” it is relative, please provide at least a range of temperature and processing times, according to previous researchers.

Response: Thank you for your comment. The quality of the finished black tea is mostly determined by the fermentation stage of the processing. The primary oxidized polyphenolic components that affect black tea's quality characteristics are TF and TR. Typically, orthodox tea or crush, tear, and curl (CTC) black tea require a temperature range of 24-29°C for 2-4 hours or 55-110 minutes, respectively, during the fermentation process. During fermentation, a relative humidity of 95–98% and a sufficient supply of oxygen should be maintained. Thus, to guarantee the health advantages of black tea and its different sensory quality parameters (color, fragrance, taste, and flavor), the fermentation stage must be closely monitored.

12. When mentioning the health benefits, please mention the specific compounds that are related to each benefit. Which compounds are related to Neuro-regulation effects? Anti-microbial effects?

Response: Thank you for your comment. Black tea contains polyphenolic substances called thearubigins and flavonoids. Numerous researchers used general term “polyphenolic substances”, which have a variety of health benefits, including immune-regulatory, anti-inflammatory, antioxidant, anti-cancer, cardiovascular, anti-diabetic, anti-obesity, and hepatoprotective properties.

Black tea's caffeine and L-theanine related for neuro regulation effects.

Certain tea fragrance components, such as catechins and theanine, have been discovered to have antibacterial activities.

Theaflavins and flavonoids (black tea) exhibit strong antioxidant action. In the digestive system, they can aid in scavenging dangerous free radicals that can cause cell damage and raise the possibility of developing digestive problems like gastric ulcers and colorectal cancer.

13. Reference the tables and figures within the manuscript.

Response: Thank you for your suggestion. We have added.

14. Conclusion section provide a lot of theoretical information. Notice that conclusions should be mainly drawn from the methodology and results. Authors could add information specifying the future applications for the obtained results.

Response: Thank you for your professional advice. We have made some modifications to the conclusion and removed some theoretical information to make it more concise.

15. Finally, I also recommend to change the tittle because there is no information regarding the “formation mechanisms”, it will be necessary to include the reactions, not only mention the pathways in different contexts.

Response: Thank you for your valuable suggestion. We have removed the 'formation mechanism' and appropriately modified the title.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Thanks for adding the suggested information. Accept in present form