Effect of Different Pre-Cooling Methods on the Quality of Litchi During Cold Storage
Jenilton Gomes Da Cunha
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsDear,
The manuscript presents a relevant proposition for the postharvest fruit sector by comparing different pre-cooling methods for litchi. The justification is appropriate, the topic has industrial and agricultural applicability, and there is coherence between the stated objective and the analyzed variables. Moreover, in general, the manuscript is clearly written, with good structure and sufficiently recent bibliographical contextualization to inform the reader of current research and emerging technologies under evaluation.
However, the study presents methodological and interpretative limitations which, if addressed, may significantly enhance its scientific and technological contribution. In the methodology, although the detailed description of the cooling system and instrumentation is a positive aspect, essential information regarding the experimental design is lacking, particularly with respect to the rationale behind the experimental layout. It is important to highlight that the treatments involve two factors—pre-cooling method (forced-air vs. hydrocooling) and air velocities (3, 6 and 10 m/s)—and additionally include the evaluation period (0, 6 and 18 days), which clearly characterizes a multifactorial statistical problem. The manuscript treats these treatments as simple comparisons, whereas a factorial model would allow the exploration of interactions and provide better explanations for combined effects, strengthening physiological inferences as well. The adoption of a factorial ANOVA with mean comparison tests would therefore be more suitable and result in a considerably more robust analysis.
Regarding the analysis of postharvest variables, the selected parameters are appropriate; however, the physiological basis could be expanded, considering that cooling modulates processes such as respiratory rate, carbohydrate metabolism, tissue firmness, and enzymatic browning of the pericarp. The discussion of soluble solids, firmness, and moisture could be more directly connected to known physiological mechanisms—such as membrane permeability, respiratory consumption, and osmotic diffusion—thus enriching interpretation. In addition, the keywords should be revised, as they are highly similar to the title. Keywords should broaden the article’s scope and indexing reach, and should not repeat or closely reproduce the title.
Overall, the manuscript addresses a relevant topic and presents data that may contribute to advances in litchi postharvest handling. With improvements in the statistical analysis (preferably addressing the design as factorial), the article has potential for publication and for greater scientific and technical impact. Therefore, I suggest that if the authors provide a summary of the analysis of variance demonstrating lack of interaction among the factors, their current approach may be justified. Finally, I recommend that the conclusion section be summarized and that only the main findings be presented; there is no need to repeat results and discussion. The conclusion should clearly show whether the results adequately addressed the stated objective.
Author Response
Comments 1: In the methodology, although the detailed description of the cooling system and instrumentation is a positive aspect, essential information regarding the experimental design is lacking, particularly with respect to the rationale behind the experimental layout. It is important to highlight that the treatments involve two factors—pre-cooling method (forced-air vs. hydrocooling) and air velocities (3, 6 and 10 m/s)—and additionally include the evaluation period (0, 6 and 18 days), which clearly characterizes a multifactorial statistical problem. The manuscript treats these treatments as simple comparisons, whereas a factorial model would allow the exploration of interactions and provide better explanations for combined effects, strengthening physiological inferences as well. The adoption of a factorial ANOVA with mean comparison tests would therefore be more suitable and result in a considerably more robust analysis.
Response 1: We sincerely appreciate the reviewer’s professional and constructive suggestions regarding our experimental design and statistical approach. We fully agree that this study represents a multifactorial problem, and adopting a factorial model significantly strengthens the physiological inferences of the results.
To address the lack of essential information regarding the experimental layout and its rationale, we have implemented the following improvements in the revised manuscript:
Detailed Rationale in New Section 2.3 (Experimental Design): We have added a dedicated section (Lines 129–141) to clarify the logic of our experimental layout.
Innovation of the FAC Method: We have highlighted that our forced-air cooling (FAC) approach differs from conventional methods where fruits are directly exposed to cold air, which often leads to rapid desiccation in litchis. Instead, we utilized PET packaging to prevent direct air contact, aiming to balance rapid heat removal with moisture preservation.
Comparison and Optimization: The trial was designed to compare this packaged FAC at three distinct velocities (3, 6, and 10 m/s) against traditional hydro-cooling (soaking), which serves as the industry benchmark. The core objective (rationale) was to determine the optimal pre-cooling parameters that minimize field heat while maintaining postharvest quality, providing a practical reference for the litchi supply chain.
Summary Table of the Factorial Layout (Table 1): A new Table 1 has been added in Section 2.3. This table clearly outlines the 4×3 factorial arrangement (4 cooling treatments × 3 storage periods), ensuring the multifactorial nature of the study is transparent and the methodology is reproducible.
Adoption of Two-way Factorial ANOVA: As suggested, we have updated our statistical analysis from simple comparisons to a Two-way Factorial ANOVA (Treatment × Storage Time). This allows us to evaluate the main effects of cooling methods and storage duration, as well as their interactive effects (T×S).
In-depth Analysis of Interactions (Table 2): We added a new summary table (Table 2, Section 3.2) presenting F-values and significance levels. The analysis of interactions specifically benefited our interpretation of skin yellowness (b* value) and fruit firmness (FF), confirming that the superiority of a specific pre-cooling method is indeed time-dependent.
Comments 2: Regarding the analysis of postharvest variables, the selected parameters are appropriate; however, the physiological basis could be expanded, considering that cooling modulates processes such as respiratory rate, carbohydrate metabolism, tissue firmness, and enzymatic browning of the pericarp. The discussion of soluble solids, firmness, and moisture could be more directly connected to known physiological mechanisms—such as membrane permeability, respiratory consumption, and osmotic diffusion—thus enriching interpretation.
Response 2: Thank you for pointing this out, we have enriched the physiological discussion in Section 4. Specifically:
At the beginning of the discussion, we added a statement on how cooling modulates the respiratory rate.Revised text (see Lines 346-348 in the revised manuscript):Rapid pre-cooling modulates the respiratory rate of fresh litchi by quickly removing field heat, thereby suppressing the metabolic activity associated with nutrient depletion and quality deterioration.
We linked TSS/TA decline to respiratory consumption and carbohydrate metabolism.Revised text (see Lines 388-390 in the revised manuscript): During storage, the enzymatic reactions of fruit metabolism accelerates the respiratory consumption of TSS and TA as storage time increases. In this process, these substrates may be utilized in carbohydrate metabolism to support cellular activity, ...
We explained the correlation between a* and PMC using membrane permeability.Revised text (see Lines 395-400 in the revised manuscript): The variations between a* and PMC shows a strong positive correlation, suggesting that pericarp moisture retention may be essential for maintaining cell membrane permeability. Pericarp desiccation likely leads to a loss of cellular compartmentalization, which could allow oxidative enzymes to react with phenolic substrates, thereby potentially triggering enzymatic browning and the decline of redness (a*).
We clarified that the loss of firmness is driven by osmotic diffusion and loss of turgor pressure.Revised text (see Lines 403-407 in the revised manuscript): The variations in FF and WLR exhibit a positive correlation, which may be attributed to the simultaneous occurrence of transpiration and aerobic respiration. These processes drive the osmotic diffusion of water from the fruit tissue to the external environment, leading to a loss of cellular turgor and the subsequent degradation of fruit firmness.
Comments 3: In addition, the keywords should be revised, as they are highly similar to the title. Keywords should broaden the article’s scope and indexing reach, and should not repeat or closely reproduce the title.
Response 3: Thank you for pointing this out, keywords have been updated to avoid repetition of the title.The revised keywords are as follows: litchi; shelf-life; fruit quality; forced-air cooling; postharvest physiology.
Comments 4: Overall, the manuscript addresses a relevant topic and presents data that may contribute to advances in litchi postharvest handling. With improvements in the statistical analysis (preferably addressing the design as factorial), the article has potential for publication and for greater scientific and technical impact. Therefore, I suggest that if the authors provide a summary of the analysis of variance demonstrating lack of interaction among the factors, their current approach may be justified.
Response 4: We greatly appreciate the reviewer’s encouraging comments and the insightful suggestion regarding the statistical validation. Regarding your suggestion to check for the lack of interaction: We performed the Two-way ANOVA analysis as suggested. The results, summarized in Table 2, revealed that significant interactions (p<0.05) exist for certain key quality attributes, specifically b* and fruit firmness (FF).For other parameters (L*, a*, PMC, WLR, TSS, and TA), the interaction was not statistically significant. However, since the assumption of 'lack of interaction' was not met for all key parameters, we agree that a unified statistical approach is necessary. Therefore, we have adopted the Two-way Factorial ANOVA for the entire dataset to ensure consistency and a more robust physiological interpretation.
Comments 5: Finally, I recommend that the conclusion section be summarized and that only the main findings be presented; there is no need to repeat results and discussion. The conclusion should clearly show whether the results adequately addressed the stated objective.
Response 5: We sincerely appreciate the reviewer’s constructive suggestion on the Conclusion section. We realize that the original version contained redundant data and repetitive discussion, which detracted from the core message.Following your recommendation, we have completely rewritten and condensed the Conclusion section. The revised version now focuses strictly on the major findings and their practical implications.
The revised conclusions is as follows: This study demonstrates that forced-air cooling with package treatment is a feasible alternative to hydro-cooling for litchi pre-cooling. The fruit temperature decreased faster under a higher air velocity, but the cooling effect slowed down after the air velocity increased to 10 m/s, which also resulted in a lower fruit moisture loss compared with other air velocities, indicating that further increases in air velocity are unnecessary for practical applications. Although hydro-cooling provided the fastest cooling and better retention of pericarp moisture and firmness, it resulted in lower total soluble solid content during storage and involves operational limitations such as water hygiene control and post-cooling handling risks. In contrast, forced-air cooling with package treatment maintained comparable appearance and internal quality during 18 d of cold storage, while offering advantages in system hygiene and operational flexibility. From an industrial perspective, an optimized forced-air cooling regime (≈10 m/s) can be recommended as a practical pre-cooling strategy for litchi, balancing cooling performance, quality preservation, and operational convenience. The observed correlations further indicate that water loss and respiration-related depletion are key drivers of texture softening and soluble solid variation, highlighting moisture management as a critical control point in postharvest handling. Future research should focus on optimizing packaging vent designs and conducting energy-consumption analyses to further enhance the sustainability and cost-effectiveness of forced-air cooling systems in large-scale industrial applications.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsReviewers report Agronomy
The research article titled " Effect of Different Pre-cooling Methods on the Fresh-keeping Quality of Litchi during Cold Storage” has been reviewed critically.
General comments
The research paper has a potential of contributing significantly to the body of knowledge as it aims to develop alternative technologies for preserving the quality of Litchis. The efficacy of different precooling methods has been successfully assessed as having a potential of preserving postharvest quality of Litchi fruit. The setup of the study and novelty is there, however, write-up is not well articulated. The document requires major correction to be made in order to improve and make it meet the standards of the journal.
Specific comments
Line = L
L2 – Delete “Fresh-keeping”
L20 – Add the M & M section i.e. Cultivar, experimental design, sampling, and parameters that were evaluated.
L23 – Only TSS? What about other parameters? Even in TSS it is not clear whetehr there was significant difference or not between the treatments?
L31 – Italicise scientific name
L35 – “.. have been conducted”
L35 – packaging. Insert ref at the end of this sentence
L36-37 – “..of maintaining quality of litchis”
L41 – ..compared with
L42 – Delete “moving..” and write “Removing”
L45-46 – Rephrase that sentance
L56 – field not flied
L58 – “..quality are various”
L59 – Replace “about” with “on”
L69 – conducted
L75 – Tell us about the labs used
L76 – What is full maturity?
L80– ..of what temperature?
L82 – “fruit were removed.. “
L118 – conducted
L131 – Describe the process used to crush, as well as the tool used.
L153 - wiped off using..? Was that precise in each fruit?
L166-16 - This does not belong in this section, move it just above 2.7
L185 – Delete “it can be seen that”
L187 – “It also can be seen that..” Delete
L200 – “The fruit..” was precooled with..
L201 – had
L203 - Delete “it can be seen that”
L209 – Insert the p-values in each graph
Fig 4B - This graph present no significant difference between the treatments and across different storage days, why did you plot it?
Fig 4c - On 18d of this graph, you have aabb, but treatment 10m/s is the smallest (indicated by first "b"), and Hydro-cooling is highest (indicated by second "b"). Something is wrong here, it can't be. Please check.
L225 - Was there a significant difference between the treatments?
L272 – Make sure that your discussion is more explaining the results instead of retaining it again.
L339 – delete “more”
L349 - So what?
What is the 'take home message" from this study? Any recommendations? and future prospects?
References – Be consistent with the chosen ref style and adopt it throughout.
Comments on the Quality of English Language
The language needs to be improved, the document has many grammatical errors.
Author Response
Comments 1: L2 – Delete “Fresh-keeping”
Response 1: Thank you for this valuable suggestion. The term “Fresh-keeping” has been removed from the title. The revised title is: Effect of Different Pre-cooling Methods on the Quality of Litchi during Cold Storage.
Comments 2: L20 – Add the M & M section i.e. Cultivar, experimental design, sampling, and parameters that were evaluated.
Response 2: Thank you for this valuable suggestion. We have revised the Abstract to include the Materials and Methods section as requested. Specifically, we added the litchi cultivar ('Guiwei'), the specific experimental treatments (air velocities of 3, 6, 10 m/s and hydro-cooling at 5 ℃), the storage conditions (3–5 ℃ for 18 days), and the key parameters evaluated (cooling efficiency, pericarp moisture, color, firmness, TSS, etc.).
Revised text (see Lines 20-24 in the revised manuscript): Specifically, ‘Guiwei’ litchi fruits were treated with forced air cooling at air velocities of 3, 6, and 10 m/s and hydro-cooling (5 °C), followed by storage at 3–5 °C for 18 days. Changes in cooling efficiency, pericarp moisture content, color, fruit firmness, weight loss, total soluble solids (TSS), and titratable acidity (TA) were monitored.
Comments 3: L23 – Only TSS? What about other parameters? Even in TSS it is not clear whetehr there was significant difference or not between the treatments?
Response 3: Thank you for pointing this out. We realized that reporting only TSS was insufficient to represent the internal quality changes. We have checked the data again:
For Color: The results (Section 3.2) showed that hydro-cooling maintained better pericarp color (higher a* and b* values) compared to forced air cooling; For TA: The results (Section 3.3) showed no significant difference in Titratable Acidity (TA) between the treatments during storage.Therefore, we have revised the sentence in the Abstract to include Pericarp Color and TA, and clarified the statistical significance.
Revised text (see Lines 26-29 in the revised manuscript): Compared with forced air cooling, hydro-cooling treated fruit maintained better pericarp color, higher cooling rate, pericarp moisture content and fruit firmness, but presented a lower total soluble solids (TSS) content, with no significant difference in titratable acidity (TA).
Comments 4: L31 – Italicise scientific name
Response 4: Thank you for your careful correction. We have italicized the scientific name of litchi (Litchi chinensis) in the revised manuscript as requested.
Revised text (see Lines 36-37 in the revised manuscript): Litchi (Litchi chinensis Sonn.) is a popular fruit of high commercial value in the southern China.
Comments 5: L35 – “.. have been conducted”
Response 5: We apologize for the grammatical error. We have corrected the phrase "were conduct" to "have been conducted" in Line 35 as suggested.
Revised text (see Lines 39-40 in the revised manuscript): ..., a large number of fresh-keeping measurements have been conducted, ...
Comments 6: L35 – packaging. Insert ref at the end of this sentence
Response 6: We appreciate this correction. We have changed the term "package" to "packaging" as suggested. Furthermore, we have inserted the relevant references [1] at the end of the sentence to support the statement regarding fresh-keeping measures.
Revised text (see Line 40 in the revised manuscript): ..., such as refrigerated storage, packaging and coating.
Comments 7: L36-37 – “..of maintaining quality of litchis”
Response 7: Thank you for the grammatical correction. We have revised the phrase "for litchi quality maintaining" to "of maintaining the quality of litchis" to improve the sentence structure as suggested.
Revised text (see Lines 40-42 in the revised manuscript): Among them, refrigerated storage with low temperature is considered the most effective way of maintaining the quality of litchis.
Comments 8: L41 – ..compared with
Response 8: Thank you for the correction. We have corrected the grammatical error "compare to" to "compared with" in Line 41.
Revised text (see Lines 45-47 in the revised manuscript): On the other hand, refrigerated storage with coating is also been proved to be a significant method for delaying the pericarp browning of litchi and maintaining a better quality compared with other treatments.
Comments 9: L42 – Delete “moving..” and write “Removing”
Response 9: We agree with this correction. We have replaced the word "Moving" with "Removing" in Line 42.
Revised text (see Lines 47-49 in the revised manuscript): Removing the field heat and reducing respiration rate of fresh products is important not only for quality maintaining but also reducing the refrigerated load of the storage or transport facility.
Comments 10: L45-46 – Rephrase that sentance
Response 10: Thank you for the suggestion. We have rephrased this sentence to correct the subject-verb agreement error and improve readability.
Revised text (see Lines 51-52 in the revised manuscript): Air cooling and hydro-cooling are the most common pre-cooling methods for fresh products.
Comments 11: L56 – field not flied
Response 11: We apologize for the typographical error. We have corrected "flied heat" to "field heat" in Line 56.
Revised text (see Lines 61-62 in the revised manuscript): As the easy water loss of pericarp, air cooling which forces cool air to flow across the fruit surface and take away the field heat is considered not suitable for litchi.
Comments 12: L58 – “..quality are various”
Response 12: Thank you for correcting this expression. We have replaced the incorrect phrase "are various with" with "vary with".
Revised text (see Lines 63-64 in the revised manuscript): The pre-cooling time and quality vary with different cooling air velocity, ...
Comments 13: L59 – Replace “about” with “on”
Response 13: Thank you for the suggestion. We have replaced the preposition "about" with "on" in the sentence referring to Shilpa et al. We also corrected the verb "proposed" to "conducted" to better describe the cited work.
Revised text (see Lines 65-66 in the revised manuscript): Shilpa et al. conducted a study on the effects of different pre-cooling time ...
Comments 14: L69 – conducted
Response 14: Thank you for the grammatical correction. We have corrected the phrase "was conduct" to "was conducted" in the Introduction section. We also checked the surrounding text and corrected "was investigated" to "were investigated".
Revised text (see Lines 73-76 in the revised manuscript): In this paper, a forced air cooling system was built, based on which the effects of different air velocity on the cooling time and quality change during long-term storage were investigated. Additionally, a comparison was conducted on the pre-cooling performance between the forced air cooling and hydro-cooling.
Comments 15: L75 – Tell us about the labs used
Response 15: Thank you for the suggestion. We have specified the detailed laboratory information in Section 2.1, at the same time, "Chonghua" has been changed to "Conghua".
Revised text (see Lines 81-83 in the revised manuscript): The research was carried out at the Key Laboratory of Southern Agricultural Machinery and Equipment (Ministry of Education), South China Agricultural University, Guangzhou, China. 50 kg litchi fruit (cultivar ‘Guiwei’) with full maturity was harvest in the orchard located at Conghua, Guangzhou, ...
Comments 16: L76 – What is full maturity?
Response 16: Thank you for the question. We have clarified the definition of maturity in the revised manuscript. The fruits were harvested at commercial maturity, which is characterized by a bright red pericarp surface.
Revised text (see Lines 83-85 in the revised manuscript): 50 kg litchi fruit (cultivar ‘Guiwei’) at commercial maturity (characterized by a bright red pericarp) were harvest in the orchard located at Conghua, Guangzhou, ...
Comments 17: L80– ..of what temperature?
Response 17: Thank you for pointing out the missing information. We have added the initial fruit temperature (21 ± 1 ℃) in Section 2.1 to clarify the starting condition of the experiment.
Revised text (see Lines 86-87 in the revised manuscript): Upon arrival, the initial fruit core temperature was approximately 21 ± 1 ℃.
Comments 18: L82 – “fruit were removed.. ”
Response 18: Thank you for the correction. We have improved the sentence structure and usage. We changed "the fruits removed" to "the fruit were removed" and ensured a parallel structure for the subsequent actions (removed, dried, and packed).
Revised text (see Lines 91-93 in the revised manuscript): After that, the fruits were removed from the cooling container, dried with blotting paper, and packed with PET packages (about 0.5 kg in one package).
Comments 19: L118 – conducted
Response 19: We apologize for the grammatical error. We have corrected "was conduct" to "was conducted" in the sentence regarding quality evaluation.
Revised text (see Lines 124-127 in the revised manuscript): After that, all the fruits treated by forced air cooling and hydro-cooling were placed to another fresh-keeping container as shown in Fig. 1 for 18 d long-term storage under 3~5℃ environment and quality evaluation was conducted at the 6 d and 18 d.
Comments 20: L131 – Describe the process used to crush, as well as the tool used.
Response 20: Thank you for the comment. We have added the details regarding the juice extraction process. We clarified that the fruits were pitted and manually squeezed in the bags to extract the juice.
Revised text (see Lines 154-157 in the revised manuscript): The litchi fruits were peeled and pitted (seeds removed). The arils were put into clean packaging bags and manually squeezed/crushed to extract the juice. The juice was filtered through gauze, poured into beakers, and shaken evenly.
Comments 21: L153 - wiped off using..? Was that precise in each fruit?
Response 21: Thank you for this critical question regarding the methodology. To ensure the accuracy of the weight loss measurement, it is necessary to remove the surface condensation caused by the temperature difference.
In our experiment, we used soft gauze to gently blot the water droplets on the fruit surface without rubbing the pericarp. This method was performed consistently for all samples to minimize experimental error and avoid damaging the fruit surface. We have revised the description in Section 2.6 to be more specific.
Revised text (see Lines 177-179 in the revised manuscript): After the storage, the fruit was taken out from the fresh-keeping area, and the surface condensation was gently blotted with soft gauze to ensure consistency, and the weight was recorded as Mn.
Comments 22: L166-16 - This does not belong in this section, move it just above 2.7
Response 22: Thank you for the suggestion. We have moved the description and calculation formulas for Half-cooling time (HCT) from the 'Statistical analysis' section to a new section '2.7. Evaluation of cooling efficiency' (lines 167-177 in the original manuscript). The 'Statistical analysis' section (now Section 2.8) now only contains details regarding experimental design and statistical tests.
Revised text (see Line 176 and 188in the revised manuscript): 2.8. Evaluation of cooling efficiency; 2.9. Statistical analysis.
Comments 23: L185 – Delete “it can be seen that”
Response 23: Agreed. We have deleted this phrase to make the sentence more concise.
Revised text (see Lines 216-217 in the revised manuscript): From Fig. 3A, the fruit temperature decreases faster under a higher air velocity.
Comments 24: L187 – “It also can be seen that..” Delete
Response 24: Agreed. We have deleted the redundant phrase and rephrased the sentence to improve conciseness and grammatical accuracy.
Revised text (see Lines 218-219 in the revised manuscript): From Fig. 3B, the temperature in the package decreased faster as the air velocity increased.
Comments 25: L200 – “The fruit..” was precooled with..
Response 25: We sincerely appreciate this suggestion. We have replaced the general expression "The fruit treated by..." with the more precise "Fruit precooled with..." throughout Section 3.2 to better reflect the experimental process. We have also corrected related grammatical errors and improved the sentence structures in this section.
Revised text (see Lines 243-244, 248-250 and 254-255 in the revised manuscript):
The variation of pericarp color and weight loss rate of fruit precooled with different methods during storage is shown in Fig. 4.
Fruit precooled with hydro-cooling showed higher a* and b* values during storage. Fruit precooled with forced air at 6 m/s (FAC 2) exhibited had slightly higher L*, b*, and PMC, but lower a* values.
However, the 10 m/s treatment had the shortest cooling time, and fruit precooled with this velocity showed lower moisture loss compared with other air velocities.
Comments 26: L201 – had.
Response 26: We sincerely appreciate the reviewer's professional suggestion regarding the tense. We realize that according to academic writing conventions, experimental results should be reported in the past tense. Therefore, we have thoroughly revised the "Results" section, changing the present tense (e.g., "has", "is", "decrease") to the past tense (e.g., "had", "was", "decreased") to ensure consistency and accuracy.
Revised text (see Lines 243-256 in the revised manuscript): The variation of pericarp color and weight loss rate of fruit precooled with different methods during storage is shown in Fig. 4. Basically, the L* color and PMC of all the fruits decreased along the storage time. Notably, no significant changes in a* values were observed throughout the 18-day storage period for all treatments (Fig. 4B), indicating that the degradation of anthocyanins was effectively inhibited by the pre-cooling treatments and subsequent cold storage. Fruit precooled with hydro-cooling showed higher a* and b* values during storage. Fruit precooled with forced air at 6 m/s (FAC 2) exhibited had slightly higher L*, b*, and PMC, but lower a* values. The a* value of the fruit pericarp was 23.8, 2.4, 22.8, 2.3, 23.1 and 24.4, respectively. Hydro-cooling helped delay pericarp moisture loss during storage (Fig. 4D). Increasing cooling air velocity improved the pre-cooling rate of fruit but promoted the risk of moisture loss. However, the 10 m/s treatment had the shortest cooling time, and fruit precooled with this velocity showed lower moisture loss compared with other air velocities. PMCs for forced-air and hydro-cooled fruit were 69.01%, 66.51%, 68.73%, and 71.49%, respectively.
Comments 27: L203 - Delete “it can be seen that”
Response 27: Agreed. We have removed the redundant phrase to improve the conciseness of the manuscript. The sentence has been rephrased to directly state the observation.
Revised text (see Lines 251-252 in the revised manuscript): Hydro-cooling helped delay pericarp moisture loss during storage (Fig. 4D).
Comments 28: L209 – Insert the p-values in each graph
Response 28: Thank you for this constructive suggestion. We have now inserted the results of the two-way ANOVA (represented by significance levels) into the top right corner of each sub-figure in Figure 4 and Figure 5. These indicators show the main effects of Treatment (T), Storage Time (S), and their Interaction (T × S). Furthermore, we have updated the figure captions to define the significance symbols (e.g., ns for p>0.05, * for p<0.05, and *** for p<0.001). These results are consistent with the data presented in the newly added ANOVA summary table (Table 2).
Comments 29: Fig 4B - This graph present no significant difference between the treatments and across different storage days, why did you plot it?
Response 29: Thank you for your valuable comment regarding Figure 4B. We understand the reviewer's concern that the lack of statistical significance might appear to provide limited information. However, we believe that including this data is scientifically essential for the following reasons:
1.Criticality of the a* value for litchi: The a* value represents the redness of the litchi pericarp, which is the most important sensory attribute and the primary indicator of browning. Since litchi is highly perishable and typically browns within 2–3 days at room temperature (as noted in the Introduction), the fact that no significant decrease in a* was observed across all treatments over the 18-day storage period is a significant finding. It demonstrates that all tested pre-cooling methods, combined with cold storage, were highly effective in stabilizing anthocyanins and maintaining the characteristic red color.
- Reporting a "Null Result" as evidence of stability: In postharvest research, a "no significant difference" result can be as informative as a significant one. In this case, it indicates the robustness of the cold chain treatment in preserving color, regardless of the specific pre-cooling air velocity used. It confirms that the limiting factor for litchi shelf-life in this study was not the loss of redness (a*), but rather other factors like weight loss or moisture content (as shown in other figures).
- Completeness of the L*, b* and a* color space: It is standard academic practice to report L*, b* and a* values together to provide a comprehensive evaluation of chromaticity. Removing a* would leave an incomplete picture of the color changes occurring during storage.
To address your concern, we have added a sentence in the revised manuscript (Lines 244-248) to explicitly highlight that the maintenance of a* values across all treatments underscores the effectiveness of the pre-cooling and cold storage strategy in inhibiting browning.
Revised text (see Lines 244-248 in the revised manuscript): Basically, the L* color and PMC of all the fruits decreased along the storage time. Notably, no significant changes in a* values were observed throughout the 18-day storage period for all treatments (Fig. 4B), indicating that the degradation of anthocyanins was effectively inhibited by the pre-cooling treatments and subsequent cold storage.
Comments 30: Fig 4c - On 18d of this graph, you have aabb, but treatment 10m/s is the smallest (indicated by first "b"), and Hydro-cooling is highest (indicated by second "b"). Something is wrong here, it can't be. Please check.
Response 30: We sincerely apologize for this serious oversight in the statistical labeling of Figure 4C. The reviewer is absolutely correct that the assignment of significance letters was logically inconsistent in the original version.
We have thoroughly re-examined the raw statistical data and the multiple comparison results (p<0.05). The error occurred because the significance letters were misassigned and reversed during the final figure preparation stage. We have now corrected Figure 4C following the standard academic convention: the group with the highest mean value is assigned the letter "a", and subsequent letters (b, c, etc.) are assigned to groups with significantly lower values.
In the revised Figure 4C, at 18d, the Hydro-cooling group (the highest mean value) is now correctly labeled with "a", and the 10 m/s group (the lowest mean value) is labeled with "b", which accurately reflects the statistical ranking and significant differences.
Furthermore, we conducted a comprehensive self-check of all other figures in the manuscript to ensure total accuracy. We identified a similar inconsistency in the significance labeling of Figure 5A (Fruit weight loss rate) and have corrected it accordingly. In the revised Figure 5A, the 18d group (highest weight loss) is now correctly assigned the letter "a", while the 6d group is assigned "b".
We believe these corrections resolve the logical inconsistencies and appreciate the reviewer's keen eye in identifying this error.
Comments 31: L225 - Was there a significant difference between the treatments?
Response 31: We thank the reviewer for this question. To clarify the statistical differences, we have performed a Two-way Factorial ANOVA (Treatment × Storage Time) for all quality indices, as summarized in the Table 2.
Specifically for Weight Loss Rate (WLR), the ANOVA results indicated that while storage time had a highly significant effect (p<0.001), there was no significant difference among the four pre-cooling treatments (F=1.25,p>0.05), nor was there a significant interaction (F=0.68,p>0.05). This is further illustrated in Figure 5A, where the mean comparison letters (a, b) show significant changes over time but no statistical difference between treatment groups on the same storage day.
We have revised the text (Lines 271–287 in the revised manuscript) to explicitly state these findings and ensure clarity for the reader.
Revised text (see Lines 271–287 in the revised manuscript): The two-way ANOVA results (Table 2) showed that storage time (S) had a dominant and highly significant effect on all measured quality indices, confirming the progressive senescence of litchi fruit. Regarding the interaction between pre-cooling treatment and storage time (T × S), a significant effect was observed for fruit firmness (FF) (p<0.05), indicating that the impact of pre-cooling methods on texture softening changed over the storage duration. However, no significant interactions were detected for WLR, TSS, and TA (p>0.05), suggesting that these parameters followed a consistent variation trend across all treatment groups during the 18-d period. As shown in Fig. 5A, the fruit WLR increased throughout the storage period, reaching approximately 4% by day 18. In alignment with the ANOVA results, no significant differences were observed among the four pre-cooling treatments at either the 6d or 18d intervals (p > 0.05), reflecting that while pre-cooling is essential, the specific method did not significantly alter the overall weight loss rate under these storage conditions. As shown in Fig. 5B, although the interaction was not significant, the pre-cooling treatment had a significant main effect on TSS (Table 2). At the end of storage (18 d), the TSS values for the 3, 6, 10 m/s FAC and hydro-cooling treatments were 15.6%, 16.5%, 16.4%, and 15.5%, respectively, with the 6 and 10 m/s FAC groups maintaining slightly higher levels.
Comments 32: L272 – Make sure that your discussion is more explaining the results instead of retaining it again.
Response 32: Thank you for this suggestion. We have revised Section 3.4 to avoid a simple point-by-point repetition of the correlation coefficients. Instead, we have synthesized the data to describe the synergistic and synchronized variation patterns among different quality indicators. This modification provides a more comprehensive summary of the observed trends while maintaining the objectivity of the Results section.
Revised text (see Lines 325-337 in the revised manuscript): As shown in Figure 6, the litchi quality indicators exhibited highly integrated and synchronized variation patterns throughout the storage period. Specifically, the variation in fruit brightness (L*) was synergistic with internal chemical markers, showing high positive correlations with TSS (0.77) and TA (0.86), suggesting that surface color fading was closely linked to changes in soluble solids and organic acids. Similarly, pericarp redness (a*) was closely associated with moisture status, as indicated by its strong positive correlation with PMC (0.85).Regarding quality degradation, strong inverse relationships were observed between WLR and TSS (−0.85), indicating that weight loss was synchronized with the depletion of soluble solids during storage. Finally, fruit firmness (FF) was closely coupled with the moisture status of the fruit, showing a positive correlation with PMC (0.80) and a strong negative correlation with WLR (−0.74), indicating that fruit softening was closely associated with changes in moisture status during the storage process.
Comments 33: L339 – delete “more”
Response 33: Thank you for pointing out this grammatical error. We have deleted "more" before "faster" as suggested. We have also updated the verbs to the past tense to ensure consistency throughout the manuscript.
Revised text (see Lines 414-417 in the revised manuscript): The fruit temperature decreased faster under a higher air velocity, but the cooling effect slowed down after the air velocity increased to 10 m/s, which also has a lower fruit moisture loss compare to other air velocities, ...
Comments 34: L349 - So what?
Response 34: We appreciate the reviewer's insightful question. We realize that the previous conclusion was merely a summary of data rather than an interpretation of the study's practical value. We have completely rewritten the Conclusions section. The revised version now clearly defines the optimal air velocity (10 m/s), provides a balanced comparison between forced-air and hydro-cooling, and offers a specific recommendation for the industry.
Revised text (see Lines 413-429 in the revised manuscript): This study demonstrates that forced-air cooling with package treatment is a feasible alternative to hydro-cooling for litchi pre-cooling. The fruit temperature decreased faster under a higher air velocity, but the cooling effect slowed down after the air velocity increased to 10 m/s, which also resulted in a lower fruit moisture loss compared with other air velocities, indicating that further increases in air velocity are unnecessary for practical applications. Although hydro-cooling provided the fastest cooling and better retention of pericarp moisture and firmness, it resulted in lower total soluble solid content during storage and involves operational limitations such as water hygiene control and post-cooling handling risks. In contrast, forced-air cooling with package treatment maintained comparable appearance and internal quality during 18 d of cold storage, while offering advantages in system hygiene and operational flexibility. From an industrial perspective, an optimized forced-air cooling regime (≈10 m/s) can be recommended as a practical pre-cooling strategy for litchi, balancing cooling performance, quality preservation, and operational convenience. The observed correlations further indicate that water loss and respiration-related depletion are key drivers of texture softening and soluble solid variation, highlighting moisture management as a critical control point in postharvest handling.
Comments 35: What is the 'take home message" from this study? Any recommendations? and future prospects?
Response 35: Thank you for this constructive feedback. We have revised the Conclusion section to explicitly address these three points:
Take-home message: Forced-air cooling with packaging is a viable and "cleaner" alternative to traditional hydro-cooling, maintaining comparable quality during 18 d of storage.
Recommendations: An optimized air velocity of approximately 10 m/s is recommended for industrial applications to balance cooling efficiency with moisture retention.
Future prospects: We have added a forward-looking statement suggesting that future studies should investigate packaging vent optimization and energy efficiency to improve the economic sustainability of the system.
Revised text (see Lines 429-432 in the revised manuscript):
Future research should focus on optimizing packaging vent designs and conducting energy-consumption analyses to further enhance the sustainability and cost-effectiveness of forced-air cooling systems in large-scale industrial applications.
Comments 36: References – Be consistent with the chosen ref style and adopt it throughout.
Response 36: Thank you for pointing out the formatting issues in the Reference section. We have now meticulously revised all references to strictly adhere to the MDPI Agronomy citation style, as seen in the latest published articles. Specifically, we have unified the author name format (Surname, Initial), bolded the publication year, italicized the journal titles and volume numbers, and ensured that all Latin species names are italicized. The punctuation and abbreviations have also been standardized throughout the manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsI confirm that the comments have been addressed as recommended, and the manuscript has been improved significantly .
I support the acceptance of the current version of the manuscript after minor improvements like:
Line 88 - change harvest to harvested, and,
Proofreading
Author Response
Comments 1: I support the acceptance of the current version of the manuscript after minor improvements like: Line 88 - change harvest to harvested, and, Proofreading
Response 1: We sincerely thank the reviewer for the positive feedback and for the supportive recommendation regarding the acceptance of our manuscript. In accordance with your suggestions, we have carefully revised the text and performed a thorough proofreading to improve the linguistic quality. The specific changes are as follows:
As suggested, we have changed "harvest" to "harvested" (now in Line 84) to ensure the correct use of the passive voice.
Beyond the specific line mentioned, we have conducted a comprehensive check of the entire manuscript to rectify typographical and grammatical errors. Key corrections include changing "promotes" to "promote" (Line 59), "was conduct by" to "was conducted by" (Line 70), and "well know" to "well-known" (Line 340). Additionally, the term "forced air cooling" has been standardized to "forced-air cooling" throughout the manuscript.
Author Response File: Author Response.pdf
