Enhancing Calcium Transport in Table Grapes Using Sorbitol: A Sustainable Strategy for Promoting Fruit Quality

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This review manuscript presents a comprehensive and timely exploration of using sorbitol as a sustainable preharvest tool to enhance calcium transport and thereby improve the quality and storability of table grapes. The topic is highly relevant given the increasing regulatory and consumer pressure to find alternatives to conventional treatments like SO₂. The authors effectively build a compelling case by first outlining the major challenges in table grape production, then detailing the crucial role of calcium and its mobility limitations, and finally introducing polyols—specifically sorbitol—as an innovative solution.

The manuscript is well-structured, logically argued, and supported by an extensive and up-to-date bibliography. The manuscript is of high quality but would benefit from minor revisions to improve clarity and focus.

Specific points for revision:

1. Focus of Challenges Section: The initial section on the challenges of grape production and postharvest (Section 2) is comprehensive but could be more focused. To strengthen the narrative, the authors should more directly link these challenges (especially cracking, berry shattering, and fungal decay) to the underlying issue of calcium deficiency and the need for an effective calcium transport vector. This will create a more targeted lead-in to the proposed solution.

2. Discussion of Other Polyols: The review centers on sorbitol, but it would be valuable to briefly discuss the potential of other polyols (e.g., mannitol, xylitol) for similar complexation roles. A short comparative statement or a mention of existing research on other polyols as nutrient vectors would provide a broader context and highlight sorbitol's relative efficacy or uniqueness. The mention of inositol in wine grapes (Page 17) is a good start but should be integrated into this broader discussion.

3. Evidence for the Sorbitol-Calcium Complex: The proposed mechanism of calcium-sorbitol complexation is central to the review's thesis. This section (5.2) should be strengthened by:

Providing a more detailed review of the direct experimental evidence (e.g., spectroscopic data, stability constants) for the formation of these complexes in planta or in model systems.

Clarifying the specific mechanism of facilitated phloem transport. Does the complex prevent Ca²⁺ precipitation, mask its charge, or interact with specific transporters?

Author Response

Reviewer 1

This review manuscript presents a comprehensive and timely exploration of using sorbitol as a sustainable preharvest tool to enhance calcium transport and thereby improve the quality and storability of table grapes. The topic is highly relevant given the increasing regulatory and consumer pressure to find alternatives to conventional treatments like SO₂. The authors effectively build a compelling case by first outlining the major challenges in table grape production, then detailing the crucial role of calcium and its mobility limitations, and finally introducing polyols, specifically sorbitol, as an innovative solution.

The manuscript is well-structured, logically argued, and supported by an extensive and up-to-date bibliography. The manuscript is of high quality but would benefit from minor revisions to improve clarity and focus.

 

We sincerely appreciate the time and effort you dedicated to reviewing our manuscript. We are very grateful for your positive assessment, noting the manuscript’s high quality, comprehensive nature, and timely relevance to sustainable viticulture. Your constructive suggestions have guided us in implementing significant revisions to improve the clarity and focus of the narrative.

We have integrated your observations into the most recent version (NV) of the manuscript, titled: " Enhancing calcium transport in table grapes using sorbitol: A sustainable strategy for promoting fruit quality " (NV, Lines 2-3).

In addition to implementing the structural and content revisions detailed in our accompanying response letter, we want to assure you that the entire revised manuscript has undergone a meticulous review for English language, grammar, and flow. A native English speaker expert currently affiliated with our research center to ensure the highest level of clarity and readability throughout the text performed this comprehensive linguistic check.

Below is a point-by-point response detailing the revisions made based on your feedback:

 

Q1. Focus of Challenges Section: The initial section on the challenges of grape production and postharvest (Section 2) is comprehensive but could be more focused. To strengthen the narrative, the authors should more directly link these challenges (especially cracking, berry shattering, and fungal decay) to the underlying issue of calcium deficiency and the need for an effective calcium transport vector. This will create a more targeted lead-in to the proposed solution.

R1.1. We have performed a major structural revision to sharpen the focus. The original Chapter 2 was condensed and integrated into a new structure that immediately establishes the causal link to calcium:

• The manuscript now begins with a condensed Introduction (Section 1) that explicitly states that all major physiological problems are " All these physiological problems are closely related to calcium sufficiency in grape tissues." (NV, L. 59-60).
• The main body of the review now starts with Section 2: The Crucial Role of Ca in Fruit Quality at Harvest and Postharvest (NV, L. 175). This section is dedicated to detailing Ca²⁺ deficiency disorders, thereby directly connecting the quality issues to the need for enhanced Ca²⁺

We have enhanced the text describing the specific links (Lines 61-129):

• Fungal Decay: Ca²⁺-deficient fruits are more prone to fungal infestation since calcium is a key structural component of the cell wall.
• Cracking: Nutrient deficiencies, particularly Ca²⁺, increase the incidence of cracking, as calcium is essential for maintaining cell wall integrity.
• Shattering: Calcium deficiency is explicitly linked to the weakening of the abscission zone and a higher susceptibility to berry shattering, as Ca²⁺ bound to pectins reduces detachment.

 

Q2. Discussion of Other Polyols: The review centers on sorbitol, but it would be valuable to briefly discuss the potential of other polyols (e.g., mannitol, xylitol) for similar complexation roles. A short comparative statement or a mention of existing research on other polyols as nutrient vectors would provide a broader context and highlight sorbitol's relative efficacy or uniqueness. The mention of inositol in wine grapes (Page 17) is a good start but should be integrated into this broader discussion.

R2.2 We have added a new, dedicated technical subsection that provides a detailed comparison, justifying the specific selection of sorbitol:

• New Section: 3.2. Thermodynamic, Chemical, and Practical Rationale for Preferring Sorbitol as a Vector (NV, L. 370–424).
• Key Content Incorporated: This section compares sorbitol, mannitol, and xylitol based on critical factors.
• Solubility: Sorbitol is demonstrated to be exceptionally soluble (∼2350 g/L), contrasting sharply with mannitol (∼180–220 g/L), which is 10 to 20 times less soluble. This restricts mannitol's practical utility in concentrated solutions.
• Affinity/Stability: Quantitatively, the Ca²⁺ affinity order is confirmed as sorbitol > xylitol > mannitol.
• Complexation Geometry: Sorbitol's stereochemistry allows it to act as a polidentate tetradentate ligand, coordinating with four -OH groups, an advantage not fully matched by mannitol or xylitol due to steric restrictions.

 

Q3. Evidence for the Sorbitol-Calcium Complex: The proposed mechanism of calcium-sorbitol complexation is central to the review's thesis. This section (5.2) should be strengthened by:

Providing a more detailed review of the direct experimental evidence (e.g., spectroscopic data, stability constants) for the formation of these complexes in planta or in model systems.

Clarifying the specific mechanism of facilitated phloem transport. Does the complex prevent Ca²⁺ precipitation, mask its charge, or interact with specific transporters?

R2.3 The relevant section (now 3.3. Complexation Mechanism and Transport of Sorbitol, NV, L. 427–507) has been significantly reinforced with detailed mechanistic explanations and evidence:

1. Experimental Evidence (NV, L. 433–444):

• Spectroscopic Data: We include direct evidence from Multinuclear Nuclear Magnetic Resonance (¹H,¹³C,and ⁴³Ca NMR) confirming the complexation of Ca²⁺ with sorbitol in aqueous solution.
• Binding Sites: NMR studies identified the preferred binding sites on sorbitol as the O-H groups of C1, C2, C4, and C6, supporting a 1:1 tetradentate complex where the Ca²⁺ is partially enveloped.
• General Principle: We cite Angyal (1973), noting that the presence of cis sequences of hydroxyl groups is key for polyols to form stable metal complexes.

1. Mechanistic Hypotheses (NV, L. 457–507):

We have detailed the three primary hypotheses explaining how the Ca²⁺-sorbitol complex overcomes low phloem mobility:

1. Maintaining Solubility (Prevention of Precipitation): The complex maintains Ca²⁺ in a soluble form, preventing its precipitation as insoluble salts (e.g., oxalates or Ca-pectates) in the phloem sap, which is the major cause of Ca²⁺ immobilization.
2. Reduction of Electrostatic Interaction: By coordinating with multiple -OH groups, the neutral sorbitol ligand partially "wraps" the Ca²⁺ cation. This reduces its effective exposed positive charge, thereby minimizing its electrostatic interaction with the cell walls and cation exchange sites of the phloem and making it less likely to be sequestered by membrane transporters.
3. Use of Polyol Transport Systems: The Ca²⁺-sorbitol complex may utilize existing sorbitol transporters (like VvPLT1 in grape cells) as an "encapsulating vehicle" to move systemically with the flow of photoassimilates, analogous to the established mechanism for boron transport in sorbitol-producing species.

 

We believe these comprehensive revisions address all points raised and significantly enhance the scientific rigor and focus of the manuscript.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This comprehensive review manuscript, titled "Enhancing calcium transport with polyols in table grapes: A sustainable tool for agriculture," presents a well-structured and timely exploration of sorbitol as a novel preharvest treatment to improve calcium (Ca²⁺) translocation in table grapes. The authors effectively highlight the significant postharvest challenges faced by table grapes—such as fungal decay, berry cracking, shattering, and rachis browning—and critically discuss the limitations of conventional practices, including sulfur dioxide applications and hormone treatments. The central proposition of using sorbitol to form soluble complexes with calcium, thereby overcoming its inherent low phloem mobility, is compelling and supported by a thorough synthesis of recent research. The paper not only elucidates the mechanistic basis of calcium-polyol complexation and transport but also consolidates evidence of its beneficial effects on fruit firmness, disease resistance, antioxidant capacity, and overall storability. By positioning calcium-sorbitol treatments within the broader context of sustainable agriculture, the review makes a valuable contribution to the field and suggests promising directions for future research and application.

 

The paper extensively cites studies that have achieved positive results by using calcium-sorbitol complexes on various crops such as peanuts, potatoes, and blood oranges. Although this strongly indicates the universal potential of the technology, there is a logical leap when directly applying it to support the core argument regarding "table grapes". The authors need to more explicitly emphasize that these are supporting evidence, and the core evidence should come from studies on grapes themselves.

 

 

Specific comments：

 

1. Title：The meaning expressed in the first half of the title is very clear, but I think the purpose of the second half is not direct enough. It should directly focus on improving the quality of the fruit. For example：A sustainable strategy for enhancing fruit quality
2. Abstract：
3. Line 36-38, Although these beneficial substances in grapes are related to the pathways and genes listed by the author, this paper has little to do with the synthesis of nutritional components. Therefore, I suggest deleting this part of the content.
4. Line 55: “leading to an increase in enzymatic activity”, These physiological changes, as a form of stress, lead to an increase in ROS. But what exactly are the increases in enzyme activity caused by the authors in their article? Theoretically, if there is no resistance to the stress or no external treatment, the changes in the antioxidant enzyme system may not be particularly significant, which is why ROS levels rise and the fruit quality is affected. Please check the cited article.
5. Line 65: “The high moisture content of table grapes 65 makes the fruit particularly susceptible to fungal infections,” Is it the moisture within the grape fruit itself, or the moisture on the surface of the fruit?
6. Section 2.3 “Berry Shattering”, In this section, I did not find any relevant research on calcium elements. Berry Shattering, as a very influential factor affecting the quality of grapes, especially their appearance quality, should have some studies related to calcium elements added. However, if the author is only concerned with the nutritional quality of the fruit, should this section be deleted?
7. Section 2.4 This part also has corresponding issues. A few words can be added to describe the connection between this problem and the calcium element.
8. 5. Dehydration and Rachis Browning, This part mainly discusses the role of packaging in maintaining the quality of grapes. It seems to have deviated from the topic of calcium elements.
9. The third part (Current Strategies for Quality Control of Table Grapes) is what I believe is the core issue of the entire review. The third part seems to have independently reviewed how to improve the quality of grape fruits (including before and after harvest). However, the description of calcium element transportation in this entire part is relatively scarce, and it appears to be somewhat disconnected from the main topic. I suggest combining this part with the fourth part to discuss the application of calcium elements in different harvesting strategies.

  Due to the large amount of text in the overall review, the third part is the content that needs to be revised in particular. If possible, it should be combined with the fourth part, and only the content related to calcium should be retained.

10. 1. Ca as a Structural Component, Signaling Agent, and Its Mobility in the Plant, This part involves too many molecular mechanisms. Although calcium is involved in many physiological processes, it is not necessary to elaborate on it in detail here. Especially in the third paragraph (Signaling is regulated by elemental components that control the magnitude and duration of……This enzyme is key to the formation of various polyphenolic compounds in plants, including flavonoids, lignins, and other phenylpropanoids, which contribute to structural integrity and stress), it is recommended to delete it and only retain the potential molecular mechanisms related to the improvement of grape fruit quality.
11. Section 6.1, 6.1. Enhancing Ca Transport and Other Nutrients. The title of this section is 6.1. Enhancing Ca Transport and Other Nutrients. There might be relatively less research on Calcium-Sorbitol Complexes. Therefore, the author has included some studies on other elements such as boron complexes. However, I think this is somewhat inappropriate. The content about boron complexes can be simplified and led to the discussion of calcium.
12. If possible, a supplementary section can be added to the paper to specifically discuss the potential limitations of this technology, the optimal application conditions (concentration, timing, environmental factors), and the possible variation responses in different grape varieties. This will make the argument more comprehensive and credible.

Author Response

Reviewer 2

This comprehensive review manuscript, titled "Enhancing calcium transport with polyols in table grapes: A sustainable tool for agriculture," presents a well-structured and timely exploration of sorbitol as a novel preharvest treatment to improve calcium (Ca²⁺) translocation in table grapes. The authors effectively highlight the significant postharvest challenges faced by table grapes, such as fungal decay, berry cracking, shattering, and rachis browning, and critically discuss the limitations of conventional practices, including sulfur dioxide applications and hormone treatments. The central proposition of using sorbitol to form soluble complexes with calcium, thereby overcoming its inherent low phloem mobility, is compelling and supported by a thorough synthesis of recent research. The paper not only elucidates the mechanistic basis of calcium-polyol complexation and transport but also consolidates evidence of its beneficial effects on fruit firmness, disease resistance, antioxidant capacity, and overall storability. By positioning calcium-sorbitol treatments within the broader context of sustainable agriculture, the review makes a valuable contribution to the field and suggests promising directions for future research and application.

The paper extensively cites studies that have achieved positive results by using calcium-sorbitol complexes on various crops such as peanuts, potatoes, and blood oranges. Although this strongly indicates the universal potential of the technology, there is a logical leap when directly applying it to support the core argument regarding "table grapes". The authors need to more explicitly emphasize that these are supporting evidence, and the core evidence should come from studies on grapes themselves.

 

We sincerely appreciate the time and detailed attention you dedicated to reviewing our manuscript. Your specific comments and suggestions regarding the manuscript's focus, structure, and clarity have been instrumental in preparing the revised version.

We concur with your overall assessment that the original manuscript required a clearer emphasis on the central role of calcium and polyols, particularly in relation to table grapes, to strengthen the narrative flow.

We confirm that we have implemented major structural and content revisions in new version (NV), aligning the document more closely with its primary objective: enhanced calcium transport as a sustainable strategy for fruit quality improvement.

In addition to implementing the structural and content revisions detailed in our accompanying response letter, we want to assure you that the entire revised manuscript has undergone a meticulous review for English language, grammar, and flow (NV Blue letter color). A native English speaker expert currently affiliated with our research center to ensure the highest level of clarity and readability throughout the text performed this comprehensive linguistic check.

Below is a detailed response outlining how each of your specific comments has been addressed in the revised manuscript:

 

General Comment (Evidence Focus)

You correctly pointed out the necessity of clearly distinguishing supporting evidence from other crops versus core evidence from grape studies, given the central argument regarding table grapes.

The  structure of the manuscript has been revised (following your suggestion and those of other reviewers) to focus immediately on the challenges in table grapes as manifestations of calcium deficiency (New Version “NV”, L. 59, 164-174). The Abstract now clearly states the focus on table grapes. The main section on applications (Section 4) prioritizes the application of calcium-sorbitol complexes in table grapes (NV, L. 615-617), while using data from other crops (e.g., potato, peanut, blood orange) as supporting evidence demonstrating the broad applicability of the chelation technology (NV, L. 592-614).

 

Q1. Title：The meaning expressed in the first half of the title is very clear, but I think the purpose of the second half is not direct enough. It should directly focus on improving the quality of the fruit. For example：A sustainable strategy for enhancing fruit quality

R2.1. Accepted and Resolved. The title has been revised to: "Enhancing calcium transport in table grapes using sorbitol: A sustainable strategy for promoting fruit quality" (NV, L. 2-3)

 

Q2. Abstract (L. 36-38): Suggest deleting content related to the synthesis of nutritional components (pathways and genes) as it is not the paper's main focus. Abstract：

R2.2. Accepted and Resolved. The Abstract in NV has been thoroughly revised and condensed. The specific sentences relating complex molecular mechanisms (genes and pathways not directly related to Ca transport) have been deleted, ensuring the Abstract focuses solely on the rationale, mechanism, and outcomes of Ca-sorbitol complexation.

 

Q3. Line 55: “leading to an increase in enzymatic activity”, These physiological changes, as a form of stress, lead to an increase in ROS. But what exactly are the increases in enzyme activity caused by the authors in their article? Theoretically, if there is no resistance to the stress or no external treatment, the changes in the antioxidant enzyme system may not be particularly significant, which is why ROS levels rise and the fruit quality is affected. Please check the cited article.

R2.3. The introductory text now states that physiological disorders and fungal infections disrupt homeostasis, triggering "increased enzymatic activity and the generation of reactive oxygen species (ROS)" (NV, L. 52-60). The specific types of enzymes—such as Polygalacturonase and Cellulase—are later detailed in Section 2.3 ("Effect of Ca Application on Fruit Quality") and Section 2.4 ("Effect of Ca Application on Table Grapes Quality") as being involved in cell wall breakdown (NV, L. 209, 235–238, 248–249)

 

Q4. Line 65: “The high moisture content of table grapes 65 makes the fruit particularly susceptible to fungal infections,” Is it the moisture within the grape fruit itself, or the moisture on the surface of the fruit?

R2.4. While the original phrasing is maintained, the following sentences explicitly link fungal susceptibility to calcium deficiency because Ca is a " are more prone to fungal infection since calcium is a key structural component of the cell wall " (NV, L. 65-66). This focuses the discussion on the internal structural integrity (cell wall strength) of the fruit, rather than solely on surface moisture.

 

Q5. Section 2.3 “Berry Shattering”, In this section, I did not find any relevant research on calcium elements. Berry Shattering, as a very influential factor affecting the quality of grapes, especially their appearance quality, should have some studies related to calcium elements added. However, if the author is only concerned with the nutritional quality of the fruit, should this section be deleted?

R2.5. This section (now integrated into the Introduction) was retained and strengthened by adding explicit links between calcium deficiency and the disorder: "Calcium deficiency, which compromises cell wall integrity, is frequently linked to the weakening of the abscission zone and, consequently, to a higher susceptibility to berry shattering. Conversely, calcium bound to pectins within the abscission zone was found to reduce berry detachment from the clusters" (NV, L. 94-98)

 

Q6. Section 2.4 This part also has corresponding issues. A few words can be added to describe the connection between this problem and the calcium element.

R2.6. The connection is now explicit in the Introduction: "In this regard, calcium has also been shown to stimulate the biosynthesis of anthocyanins, making its deficiency an important factor contributing to colour loss" (NV, L. 113-115)

 

Q7. Dehydration and Rachis Browning, This part mainly discusses the role of packaging in maintaining the quality of grapes. It seems to have deviated from the topic of calcium elements.

R2.7. This section is also integrated into the Introduction. We clarify the link between Ca²⁺ and rachis quality: "In this context, preharvest calcium applications in vineyards have been shown to effectively preserve rachis freshness by reducing water loss and chlorophyll degradation (Sabir and Sabir, 2017). Moreover, calcium has been reported to suppress the formation of brown pigments" (NV, L. 123-125).

 

Q8. The third part (Current Strategies for Quality Control of Table Grapes) is what I believe is the core issue of the entire review. The third part seems to have independently reviewed how to improve the quality of grape fruits (including before and after harvest). However, the description of calcium element transportation in this entire part is relatively scarce, and it appears to be somewhat disconnected from the main topic. I suggest combining this part with the fourth part to discuss the application of calcium elements in different harvesting strategies.

R2.8. As suggested by multiple reviewers, the entire original Chapter 3 has been condensed and integrated into the Introduction (Section 1) (NV, L. 130–151). This revised structure eliminates the disconnected feeling by serving as background that immediately precedes the Introduction of calcium mobility limitations (NV, L. 1152-163) and the proposed sorbitol solution (NV, L. 164-174). The main body of the review now starts with the focused topics: Ca²⁺ role (Section 2) and Polyols (Section 3)

 

Due to the large amount of text in the overall review, the third part is the content that needs to be revised in particular. If possible, it should be combined with the fourth part, and only the content related to calcium should be retained.

 

Q9. 4.1. Ca as a Structural Component, Signaling Agent, and Its Mobility in the Plant, This part involves too many molecular mechanisms. Although calcium is involved in many physiological processes, it is not necessary to elaborate on it in detail here. Especially in the third paragraph (Signaling is regulated by elemental components that control the magnitude and duration of……This enzyme is key to the formation of various polyphenolic compounds in plants, including flavonoids, lignins, and other phenylpropanoids, which contribute to structural integrity and stress), it is recommended to delete it and only retain the potential molecular mechanisms related to the improvement of grape fruit quality.

R2.9. The section corresponding to the molecular mechanisms (now V2, Section 2.1) has been significantly revised. The detailed third paragraph of the original text (which discussed CDPKs, PAL, and ABA signaling pathways) has been deleted to maintain focus on the structural role of Ca and its mobility constraints, which are most relevant to the Ca-sorbitol mechanism (NV, L. 177-196).

 

Q10. Section 6.1, 6.1. Enhancing Ca Transport and Other Nutrients. The title of this section is 6.1. Enhancing Ca Transport and Other Nutrients. There might be relatively less research on Calcium-Sorbitol Complexes. Therefore, the author has included some studies on other elements such as boron complexes. However, I think this is somewhat inappropriate. The content about boron complexes can be simplified and led to the discussion of calcium.

R2.10. The discussion of boron (B) has been maintained (NV, L. 558-588) because it serves as a critical mechanistic analogy for polyol-assisted transport. The text clarifies that the B-polyol mechanism demonstrates how sorbitol facilitates the phloem mobility of typically immobile nutrients like B (which forms neutral complexes) and, by analogy, Ca [500–501]. The section now explicitly introduces the Ca²⁺-sorbitol complex as a direct extension of this established B mechanism (NV, L. 587-588).

 

Q11. If possible, a supplementary section can be added to the paper to specifically discuss the potential limitations of this technology, the optimal application conditions (concentration, timing, environmental factors), and the possible variation responses in different grape varieties. This will make the argument more comprehensive and credible.

R2.11. Your suggestion (about adding a supplementary section on limitations, optimal conditions, and varietal responses) has been addressed by integrating this critical information, both in the proposed text and through existing details already present in NV, thereby increasing the comprehensiveness and credibility of the argument.

The new text you proposed for is scientifically relevant and highly appropriate for inclusion (Lines 640-652).

Section 4.3. Potential Limitations and Application Considerations

Although Ca–sorbitol applications show promising results, their effectiveness is conditioned by several physiological and agronomic factors. Calcium has intrinsically low phloem mobility, and its movement into berries decreases sharply after veraison due to reduced xylem functionality and transpiration [56,127,170]. Therefore, application timing is critical, with the highest efficiency reported when foliar sprays are applied between fruit set and veraison [56]. Likewise, environmental conditions strongly influence uptake, since factors such as humidity, surface wetness, and stomatal behavior determine foliar absorption [146]. Although Ca–sorbitol complexes improve Ca solubility and mobility [70], application dose must be carefully managed, as excessive polyol sprays may adversely affect leaf physiology [119]. Finally, varietal differences in cuticle traits, transpiration rate, and sensitivity to cracking result in heterogeneous responses among cultivars; consequently, Ca-based treatments may require variety-specific adjustment [8,34].

 

We believe these comprehensive revisions address all points raised and significantly enhance the scientific rigor and focus of the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

While reading the manuscript entitled “Enhancing calcium transport with polyols in table grapes: A sustainable tool for agriculture”, I noticed the absence of a table of contents, which would help the reader navigate the extensive text more effectively.

More importantly, I found that up to Chapter 4, the manuscript does not specifically address the central topic announced in the title namely, the role of calcium and polyols in table grape physiology and postharvest quality. Chapters 1 to 3 mainly provide background information on table grape composition, general postharvest disorders, and existing pre and postharvest management strategies. Although these sections are well documented, they read more as a general overview of viticultural practices rather than a focused review of calcium dynamics or polyol-mediated transport.

For this reason, I believe that the first three chapters should be substantially condensed and integrated into a single, comprehensive introduction.

From Chapter 4 onwards, the manuscript clearly becomes a true review article, addressing calcium’s physiological role, its limited phloem mobility, and the potential of sorbitol as a transport vector. This part is well aligned with the stated objectives and should therefore form the core of the review.

In summary, I recommend a major structural revision in which:

1. Chapters 1–3 are merged and rewritten as a concise introduction (approximately 4–6 pages).
2. The main body of the review starts from the current Chapter 4 (“The crucial role of Ca in fruit quality at harvest and postharvest”).
3. A Table of Contents is added to improve readability and organization.

This reorganization would make the manuscript more coherent with its title, strengthen its scientific focus, and enhance its overall readability.

 

Author Response

Reviewer  3

 

 While reading the manuscript entitled “Enhancing calcium transport with polyols in table grapes: A sustainable tool for agriculture”, I noticed the absence of a table of contents, which would help the reader navigate the extensive text more effectively.

More importantly, I found that up to Chapter 4, the manuscript does not specifically address the central topic announced in the title namely, the role of calcium and polyols in table grape physiology and postharvest quality. Chapters 1 to 3 mainly provide background information on table grape composition, general postharvest disorders, and existing pre and postharvest management strategies. Although these sections are well documented, they read more as a general overview of viticultural practices rather than a focused review of calcium dynamics or polyol-mediated transport.

For this reason, I believe that the first three chapters should be substantially condensed and integrated into a single, comprehensive introduction.

From Chapter 4 onwards, the manuscript clearly becomes a true review article, addressing calcium’s physiological role, its limited phloem mobility, and the potential of sorbitol as a transport vector. This part is well aligned with the stated objectives and should therefore form the core of the review.

 

We sincerely appreciate the time you dedicated to reviewing our manuscript. Your insightful comments and suggestions have been invaluable in enhancing the clarity, structure, and scientific precision of our New Version (NV) work. We entirely agree that the original version lacked clear focus at the beginning, and your recommendation for condensation has allowed the manuscript to center more effectively on the core topic of polyol-mediated calcium transport.

We have integrated your observations into the most recent version of the manuscript, titled "Enhancing calcium transport in table grapes using polyols: A sustainable strategy for enhancing fruit quality" (NV, Lines 2-3), which now incorporates major structural modifications and provides a more coherent and direct presentation.

In addition to implementing the structural and content revisions detailed in our accompanying response letter, we want to assure you that the entire revised manuscript has undergone a meticulous review for English language, grammar, and flow (NV Blue letter color). A native English speaker expert currently affiliated with our research center to ensure the highest level of clarity and readability throughout the text performed this comprehensive linguistic check.

We address your specific comments point by point below:

 

In summary, I recommend a major structural revision in which:

Q1. Chapters 1–3 are merged and rewritten as a concise introduction (approximately 4–6 pages).

R3.1. We have performed a major restructuring of the manuscript, successfully merging the content of Chapters 1, 2, and 3 of the original document into a single, substantially condensed Introduction (Section 1) (V2, Lines 44–174), as you recommended. This new structure establishes the context more efficiently:

• It presents the table grape industry and its quality challenges (fungal infections, cracking, berry shattering).
• It quickly establishes the causal link between these challenges and the inefficiency of calcium nutrition in grape tissues.
• It briefly discusses current preharvest and postharvest control strategies (such as girdling, elicitors, and SO₂ treatments).
• It culminates with a clear presentation of the limitation of low Ca²⁺ phloem mobility and proposes sorbitol as the "vector" designed to overcome this specific transport problem.

This change allows the manuscript to proceed directly to the scientific justification of the central proposal, meeting the expectation for a focused review article.

 

Q2. The main body of the review starts from the current Chapter 4 (“The crucial role of Ca in fruit quality at harvest and postharvest”).

R3.2. Following the condensation of the initial chapters into the new Introduction (Section 1), the main body of the manuscript now begins with the central topics you identified:

• The new Section 2 is titled "The Crucial Role of Ca in Fruit Quality at Harvest and Postharvest" (NV, Line 175).
• The subsequent core Section 3 is titled "Polyols as Physiological Tools and Nutrients Vector" (NV, Line 294).

This reorganization ensures that the focus of the review shifts immediately to calcium's role and the polyols' function right after setting the agronomic background in the Introduction.

Furthermore, we strengthened the justification for selecting sorbitol over other polyols (a related concern from Reviewer 1) by incorporating new technical details:

• New text incorporated: Section 3.2. Thermodynamic, Chemical, and Practical Rationale for Preferring Sorbitol as a Vector (NV, Lines 370–424).
• New Content: This subsection includes a comparison of sorbitol, mannitol, and xylitol, emphasizing that sorbitol is preferred due to its exceptionally high aqueous solubility (approximately 10 to 20 times greater than mannitol) and its ability to form slightly more stable complexes with Ca²⁺, following the affinity order: sorbitol > xylitol > mannitol. This justifies its superior role in stabilizing Ca²⁺ in solution and preventing precipitation.

 

Q3. A Table of Contents is added to improve readability and organization.

R3.3. We have added a Table of Contents at the beginning of the manuscript (NV, Lines 29–42), which enhances reader navigation through the re-structured sections of the text.

These fundamental structural changes significantly improve the manuscript's focus and coherence with the title, strengthening its rigor as a focused review article on polyol-assisted calcium transport.

 

We believe these comprehensive revisions address all points raised and significantly enhance the scientific rigor and focus of the manuscript.

 

Reviewer 4 Report

Comments and Suggestions for Authors

Please find my comments in the attached manuscript.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Please find my comments on the grammar issues in the attached manuscript.

Author Response

Reviewer 4

We sincerely appreciate the time you dedicated to reviewing our manuscript. Your comments and suggestions have been invaluable in enhancing the clarity, structure, and scientific accuracy of the work.

We have integrated your observations into the most recent version of the manuscript, titled: ""Enhancing calcium transport in table grapes using polyols: A sustainable strategy for enhancing fruit quality"". This version already incorporates major structural modifications requested by Reviewers 1, 2, and 3 (specifically, the condensation of the introductory material).

 

In addition to implementing the structural and content revisions detailed in our accompanying response letter, we want to assure you that the entire revised manuscript has undergone a meticulous review for English language, grammar, and flow (NV Blue letter color). A native English speaker expert currently affiliated with our research center to ensure the highest level of clarity and readability throughout the text performed this comprehensive linguistic check.

 

We address your specific comments point by point below:

 

Q1. The manuscript title emphasizes enhancing calcium transport with polyols as a sustainable approach. However, Section 2 primarily discuss challenges in grape production, which do not directly address calcium transport or polyol-mediated mechanisms. The authors should clarify how these preharvest strategies relate to calcium transport or consider refocusing the title to reflect the content more accurately.

R4.1. We agree on the importance of establishing the thematic connection early on. Following the suggestions of Reviewers 2 and 3, the former "Section 2. Main challenges..." has been integrated and condensed into the Introduction (Section 1). We have ensured that the relevance of calcium becomes evident immediately after listing these challenges: "All these physiological problems are closely related to calcium efficiency in grape tissues" (lines 58–59). Therefore, the content is now directly linked to the central thesis on calcium transport, and the revised (now more descriptive) title has been retained.

 

Q2. While the abstract provides a clear rationale for studying calcium transport and the potential role of sorbitol in table grapes, it does not explicitly state that this is a review paper or outline the scope of the review. I recommend revising the abstract to briefly indicate what aspects of the topic are reviewed (e.g., current understanding, recent studies, mechanisms, and future directions). This would help readers immediately recognize the nature and cove

R4.2. The Abstract in the revised version now explicitly includes these elements. The revision begins with the sentence:

"This comprehensive review synthesizes the current scientific understanding and recent studies regarding calcium dynamics..." (lines 13–14). “The review thoroughly discusses the mechanistic hypotheses by which” (lines 17–19), “Finally, we outline future directions for investigation, aiming to” (lines 23–24), thereby clearly defining the scope of the article.

 

Q3.  Lines 26-27. The introductory paragraph is generally informative but contains several grammatical and stylistic issues that affect readability. For example, the sentence “Grapes are the fruit of the Vitis genus which grows in clusters of berries” is grammatically incorrect, and “pigments and, and anthocyanins” includes a repeated word. In addition, some phrases (e.g., “are required to be harvested”) could be simplified for smoother flow.

R4.3.  We have revised and improved the flow of the Introduction (lines 45–52). The sentences were corrected to be more precise and natural, eliminating the redundancy and adjusting the grammatical structure at the beginning.

 

Q4. If so, I recommend that the title explicitly mention sorbitol to accurately reflect the main focus of the review, improve clarity, and attract readers interested in this specific intervention.

R4.4. We have considered this suggestion, have decided to include "Sorbitol" in the title.

 

Q5. Line 52. The manuscript title emphasizes enhancing calcium transport with polyols as a sustainable approach. However, Section 2 primarily discuss challenges in grape production, which do not directly address calcium transport or polyol-mediated mechanisms. The authors should clarify how these preharvest strategies relate to calcium transport or consider refocusing the title to reflect the content more accurately.

R 4.5. We greatly appreciate your highly valuable comment regarding the structure of the original manuscript, specifically pointing out the perceived lack of direct connection between the general challenges discussed in former Section 2 (Line 52) and the central theme of calcium transport enhancement via polyols, as emphasized in the title.

We confirm that your suggestion has been thoroughly addressed through a major structural revision implemented in the new version of the document. This revision ensures that the narrative flow immediately links the quality challenges to the specific nutritional problem that the proposed polyol technology is designed to solve.

 

Detailed Resolution of Structural Coherence:

1. Shifted Focus and Reorganization: In the original submission, the challenges were presented in the standalone Section 2: Main Challenges in Table Grape Production and Postharvest. Following recommendations to condense initial sections and sharpen the focus, this structure was fundamentally changed in new versión. The main body of the review now starts with Section 2: The Crucial Role of Ca in Fruit Quality at Harvest and Postharvest (L. 175). The physiological disorders (the original "challenges") are now discussed explicitly within this framework, particularly under the subsection 2.2. Physiological Disorders Associated with Ca Deficiency (L. 197).

 

2. Explicit Link to Calcium Deficiency and Transport: The revised manuscript now clearly establishes that the challenges presented are direct manifestations of inefficient calcium management in grape tissues:

• The Foundational Problem: The Introduction concludes by confirming that all major physiological problems—including fungal infections, cracking, and berry shattering—are "closely related to calcium efficiency in grape tissues" (L. 59–60).
• Calcium Mobility Limitation: The core hypothesis is introduced early: Calcium (Ca²⁺) is a vital macronutrient essential for cell wall integrity and resistance, but its inherent low mobility in the phloem restricts its effective delivery to developing sink organs, especially after veraison (L. 17, 156, 160). This low mobility leads to Ca deficiencies in distal organs like fruits, even when mature leaves contain sufficient Ca.
• Fungal Decay and Cracking: The susceptibility of grapes to fungal infection (e.g., Botrytis cinerea) is linked to nutrition, as calcium-deficient fruits are more prone to infestation because Ca is a key structural component of the cell wall and acts as a signaling agent (L. 65–67). Similarly, deficiencies in calcium increase the incidence of cracking because Ca is essential for maintaining cell wall integrity (L. 79–80). Calcium treatments mitigate cracking by reducing enzyme activity (PG and Cx) that degrades the cell wall, thereby increasing peel integrity (L. 247–249).
• Berry Shattering: We highlight that Ca²⁺ deficiency compromises cell wall integrity, which is frequently linked to the weakening of the abscission zone and higher susceptibility to berry shattering (L. 94–96).
•  

3. Justification of the Polyol Solution: The necessity for the sorbitol-mediated transport mechanism is introduced as the direct solution to the mobility constraint described in Section 2:

• Sorbitol as a Vector: The review proposes using sorbitol, a natural sugar alcohol, as a carrier that forms stable and soluble calcium–sorbitol complexes (L. 164–165). This mechanism is designed to overcome the low phloem mobility of Ca²⁺, allowing the nutrient to reach the fruit more efficiently to strengthen the cell wall and mitigate the aforementioned quality challenges.
• Mechanistic Detail: The justification is further detailed in Section 3: Polyols as Physiological Tools and Nutrients Vector, which includes discussions on the thermodynamic and chemical rationale for preferring sorbitol, such as its superior solubility and higher affinity for Ca²⁺ compared to mannitol or xylitol.
• By repositioning the discussion of table grape challenges as direct evidence of the need for enhanced calcium transport, the revised manuscript achieves a greater alignment between the core content and the title, thereby satisfying the reviewer's important comment.

 

Q6. Lines 53-54. This sentence conflates fungal infections (biotic stress) with physiological disorders, then attributes the effects on ROS and cell integrity to “these physiological disorders.” I recommend clearly distinguishing biotic (fungal) and physiological issues to avoid confusion and maintain scientific accuracy.

R4.6. We have revised the wording in the Introduction (NV, lines 55–59) to improve this distinction and the scientific accuracy in attributing the effects on ROS and cell integrity.

 

Q7. line 60-63- The introduction already clearly states  (lines 45 and 46) the focus and purpose of the review in an earlier sentence: “This review proposes and explores the potential of polyols, particularly sorbitol, as an innovative agricultural tool to enhance Ca transport in table grapes…” The later sentence, “The purpose of this review is to delve into the potential of sorbitol, Ca, and calcium-sorbitol complexes…,” is redundant. I recommend removing or consolidating this second statement to avoid repetition and improve clarity.

R4.7. We appreciate this observation. This sentence has been removed from the revised manuscript as a result of the restructuring and condensation of the Introduction, thereby resolving the redundancy

 

Q8. line 80.

R4.8. "breaking" (line 68)

 

Q9. lines 85-86. The sentence uses quotation marks around “serious limitations in profitable grape production.” It is unclear whether this is a direct quotation from a reference or the authors’ own wording. If it is not a direct quote, the quotation marks should be removed and the sentence rephrased for clarity. If it is a quote, a proper citation should be included immediately after the quotation.

R4.9. The quotation marks have been removed in the revised manuscript (NV, lines 72–75). The assertion is now presented as paraphrased text supported by the corresponding citation, thereby resolving the ambiguity regarding whether the phrase was a direct quote or the authors' own wording.

 

Q10. line 89. The term “vegetal hormones” in point 3 is incorrect. The authors should replace it with “plant hormones” or “phytohormones” to use standard terminology in plant science.

R4.10 "Plant hormones" (line77)

 

Q11. line 110. The sentence “Colour is highly determinant in consumer acceptance” contains a grammatical issue. The word “determinant” is a noun, but an adjective is required here. Consider revising to “Colour is highly determinative in consumer acceptance” or “Colour is highly important for consumer acceptance.”

R4.11. Corrected. The sentence has been rewritten in NV to improve flow and grammar to "Colour is a key factor in consumer acceptance" (line 108)

 

Q12. line 127.

R4.12. The specific sentence that contained the quotation marks has been eliminated, and the content has been rewritten in a more concise form, thereby resolving the issue of ambiguity/citation (NV, Lines 71–74, in the previous version).

 

Q13. line 136-153. The paragraph currently lacks references to support the statements made. Please provide appropriate citations for the claims or data presented, as the current text appears unsubstantiated. Each factual assertion or previously published finding should be properly referenced to maintain scientific rigor and credibility.

R4.13. Thank you for your comment regarding the lack of references in lines 136-153 of the original manuscript.

This observation has been fully addressed in the revised manuscript.

The content of the original paragraph (former Section 3: Current Strategies for Quality Control) was removed as a separate section (following structural revisions requested by other reviewers) and was condensed into the Introduction (Lines 139–162). All assertions detailing preharvest (e.g., girdling, elicitors) and postharvest strategies (e.g., SO₂​, MAP) in this reorganized text are now fully substantiated with appropriate citations, ensuring scientific rigor.

 

Q14. line 280. Please refer to my comment in line 89.

R4.14. As a result of the restructuring and condensation of the initial sections, the content has been rewritten more concisely and integrated into the revised narrative. This ensures that the relevant information is presented as paraphrased text and is properly supported by the corresponding citations, thereby resolving any issues of ambiguity or citation that might have existed in line 280 of the previous version.

 

Q15. Line 294-296. The sentence is somewhat confusing. It is not clear whether the detrimental effects are due to the ‘effective doses’ themselves or the resulting aromas/off-odors. Consider rephrasing to clearly separate the cause (high dose) from the observed effects (persistent aroma or off-odor), so readers can easily understand the point.

R4.15. This paragraph, which was previously Chapter 3 in previous version, has been restructured and integrated into the Introduction (lines 139–148). The text now includes numerous citations to support each statement related to pre- and postharvest management strategies, as requested (e.g., on girdling, elicitors, MAP, and SO₂).

 

Q16. line 466. The word “stated” sounds vague and passive. Consider using a more precise verb, such as “reported,” “documented,” or “found,” to convey scientific evidence more clearly.

R4.16. We accept the suggestion to improve accuracy. We have replaced “stated” with “reported” in NV, line 304: “Furthermore, polyols have been repeatedly reported to be naturally present in higher plants.”

 

Q17. Lines 581-588. The manuscript uses chemical symbols such as P, Zn, F, Mn, and K without defining them. For clarity, it is recommended to provide the full names at first mention, e.g., “phosphorus (P), zinc (Zn), iron (Fe), manganese (Mn), and potassium (K)”. This will help readers unfamiliar with the symbols follow the text more easily.

R4.17.  We have defined the symbols at their first mention in Section 4.1 (NV, lines 535–539). Based on the agronomic context of nutrient restriction in alkaline soils, we have assumed that “F” referred to “Fe” (iron), as it is a common micronutrient with availability issues. Revision in NV, lines 530–534 (conceptual):
“…phosphorus (P) solubility can be significantly restricted, whereas in alkaline soils, the availability of micronutrients such as zinc (Zn), iron (Fe), and manganese (Mn) is often diminished. Under arid conditions… macronutrients like potassium (K) are limited.”.".

 

Q18. Line 641- 646.  The section is titled “Effects on Fruit Quality and Stress Resistance”, but the text started with potato tubers. It may be helpful to either adjust the section title to reflect tuber/root crops or ensure that the discussion focuses on fruit crops, to maintain consistency with the section heading.

R4.18. We have retained the title (NV, Section 4.2), as the main focus of the manuscript is grape (fruit) quality, and tuber crops serve as crucial supporting evidence for the efficacy of the Ca–sorbitol complex. However, we have revised the opening sentence of the section to clearly contextualize these studies. Revision in lines 592–593:

"4.2. Effects on Fruit Quality and Stress Resistance. Evidence from other crops demonstrates the broad applicability of calcium-sorbitol complex treatments: In potatoes, chelated calcium-sorbitol fertilizer revealed better performance...".

 

Q19. Lines 679 – 680. The table uses the “+” and “–” symbols to indicate changes in plant parameters, but their meaning is not explicitly defined. For clarity, it is recommended to include a note or legend explaining that “+” indicates an increase or improvement and “–” indicates a decrease or reduction in the respective trait.

R4.19. We have added a note or legend below Table 2 to define the symbols, ensuring clarity: “Note: The symbol ‘+’ indicates an increase or improvement, and ‘–’ indicates a decrease or reduction in the respective trait.” (line 631).

 

Q 20. Lines 698–704 repeat the idea that calcium-sorbitol treatments improve shelf-life, yield, sustainability, and fruit quality.

R4.20. We have revised the Conclusions section (NV, lines 658–675). While the conclusions must summarize the key findings (which inevitably involves some repetition), we have refined the wording so that the final lines focus on synergy, sustainability, and future perspectives (NV, lines 664–670), in accordance with the expected standard for this section.

 

Q21 Other indicated changes:

“Botrytis cinerea” has been corrected to “B. cinerea.”

 

 

We believe these comprehensive revisions address all points raised and significantly enhance the scientific rigor and focus of the manuscript.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

No further commments.

Reviewer 2 Report

Comments and Suggestions for Authors

I think the author has revised the article to perfection after a major overhaul, and it can well highlight the topic and logic. There are no other opinions.