Fruit Quality and Antioxidant Content in Durian (Durio zibethinus Murr.) cv. ‘Monthong’ in Different Maturity Stages

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comments and Suggestions for Authors

Comments

The manuscript titled “Influence of harvest maturity on fruit quality and antioxidant content in durian (Durio zibethinus) cv. Monthong from Sisaket, Thailand” by Yongyut et al. is informative which attempts to evaluate the influence of harvest maturity on the external and internal quality of durian. The article is well written and clearly expressed. However, it contains some issues, which are expected to be addressed. Minor comments are offered below for the authors to consider.

Minor comments:

1. Abstract

Explain why fruit size is maximum at 90 DAFB, and theoretically size should increase as the fruit grows.

2. Plant Materials

Clarify how Completely Randomized Design was implemented (number of replicates, randomization process). In addition, the age of trees and management methods need to be supplemented.

3. Figure 5

Clarify whether this figure belongs to the peel or pulp.

4. Lines 325-327， "N/cm²" instead of "Newton/cm²"
5. Normative citation.（g., Lines 129-130 "following the method described by [16]." instead of "following the method described by Sulaiman et al [16]."）.

Author Response

# Reviewer-1

Point 1: Explain why fruit size is maximum at 90 DAFB, and theoretically size should increase as the fruit grows.

Response 1: We thank the reviewer for pointing out this issue. We have revised that point.

Lines 23-24:

The results showed that fruit circumference and length increased progressively with age, with maximum fruit size observed at 90 - 135 DAFB.

 

Point 2: Clarify how Completely Randomized Design was implemented (number of replicates, randomization process). In addition, the age of trees and management methods need to be supplemented.

Response 2: We thank the reviewer for pointing out this issue. We have revised that point.

Lines 85-94:

Durian samples were harvested at nine distinct maturity stages, determined by days after full bloom (15, 30, 45, 60, 75, 90, 105, 120, and 135 days). The fruits were collected from an orchard in Baan Sam Khilek, Tambon Pran, Amphoe Khun Han, Si Sa Ket province, northeastern Thailand (14°32'49.4"N, 104°29'11.9"E). Healthy fruits were randomly selected during the 2024 growing season from four 8-year-old durian trees of similar size, cultivated at an 8 × 8 m spacing in silty clay Chok Chai and Si Sa Ket soil types. The experiment followed a completely randomized design (CRD). Fruit samples were collected at 15-day intervals, yielding 72 fruits across the nine maturity stages (8 fruits per stage, with 4 replications). The samples were then transported to the laboratory at Khon Kaen University and acclimatized overnight at 25 ± 2°C and 80 ± 5% relative humidity.

Lines 108-112:

Fruit growth was assessed based on fruit circumference, length, and fresh weight. Circumference was measured at the widest part of each fruit, while length was determined as the distance from the stylar end to the stem end, both recorded in centimeters (cm). Fresh weight was measured individually using a digital balance (AND, Tokyo, Japan) and recorded in grams (g).

Lines 125-126:

The durian samples from each fruit (three replicates per treatment) were homogenized for the analysis of total soluble solids (TSS) and titratable acidity (TA).

 

Point 3: Figure 5. Clarify whether this figure belongs to the peel or pulp. Lines 325-327， "N/cm²" instead of "Newton/cm²". Normative citation.（g., Lines 129-130 "following the method described by [16]." instead of "following the method described by Sulaiman et al [16]."

Response 3: We thank the reviewer for pointing out this issue. We have revised those three points.

Lines 400-401:

Figure 5. Radar spectra of peel color values of durian cv. ‘Monthong’ at various maturity days.

Lines 322-333:

Pulp firmness exhibited a general increasing trend from 15 to 120 DAFB, with the highest recorded value of 76.08 N/cm² at 105 DFAB. A significant drop in firmness was observed at 135 DAFB (1.62 N/cm²), suggesting that overripe fruit becomes much softer. This firmness is influenced by the structural integrity of the cell wall, which is primarily composed of polysaccharides such as cellulose. Cellulose microfibrils, interconnected by hydrogen bonds, provide the primary framework, while hemicellulose and pectin serve as additional structural components [24]. Hemicellulose functions to link microfibrils, whereas pectin facilitates the binding of cellulose and hemicellulose, thereby enhancing cell wall rigidity. However, after 120 DAFB, pulp firmness declined, reaching its lowest value of 1.62 N/cm² at 135 DAFB due to over-ripening. This softening process is attributed to the degradation of cellulose, pectin, and hemicellulose, which compromises the cell wall structure and facilitates fruit ripening [34].

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The article is interesting because it shows the study with durian (Durio zibethinus), an important economic crop in Thailand, due to the great commercial interest and extensive cultivation in the north of the country. The results were interesting, demonstrating that the fruit reaches a greater weight, firmness, dry matter, total phenolics, flavonoids, β-carotene, lycopene and antioxidant activity at 120 DAFB, providing a valuable reference to optimize the harvest time and meet specific market and consumer preferences, contributing to the local economy. Despite having citations from 2024, 35% of the references listed are out of date and are more than 10 years old. The article may be published after the authors respond to the comments.

1-Language corrections (it is recommended that the manuscript be reviewed by a native English speaker).

2-Abstract:

Explain when first cited in the text:

-The terms FW, TA could be explained for better understanding by the reader.

3-Introduction

-Line 42: Add the name of the family to which the species belongs.

4-Materials and Methods

a) Determination of Color change, Pulp Firmness, Dry Matter, TSS, and TA

-Lines 109 and 110: How were the juices obtained for the determination of TSS and TA?

b) Determination of Vitamin C Content

-Line 123: How was the sample solution prepared?

c) Determination of Beta-Carotene Content and Determination of Lycopene Content

-Add more information for determination of beta-carotene content and lycopene content to facilitate repeatability of experiments.

5-Discussion

-There was no comparison with literature data for the content of phenolics, flavonoids, β-carotene, lycopene and antioxidant activity.

6-References: 35% of the listed references are outdated; please update them to not older than 2014.

Comments on the Quality of English Language

Language corrections (it is recommended that the manuscript be reviewed by a native English speaker).

Author Response

#Reviewer-2

Point 1: 1-Language corrections (it is recommended that the manuscript be reviewed by a native English speaker).

Response 1: We thank the reviewer for pointing out this issue. We used native English speaker services for proofreading our manuscripts.

 

Point 2: Abstract: Explain when first cited in the text:

-The terms FW, TA could be explained for better understanding by the reader.

Response 2: We thank the reviewer for pointing out this issue. The full terms of abbreviations FW and TSS have been provided in the revised manuscript.

Lines 26-30:

The values recorded at this stage were: fruit weight (3652.30 g), firmness (42.08 N/cm²), dry matter (37.13%), total phenolics (43.98 mg/100 g fresh weight (FW)), flavonoids (8.33 mg catechin/100 g FW), β-carotene (1.35 mg/100 g FW), lycopene (53.98 mg/100 g FW), and antioxidant activity (6.32 mg TE/100 g FW). The highest total soluble solids (TSS) content was observed at 135 DAFB, with values of 25 °Brix.

 

Point 3: Introduction

-Line 42: Add the name of the family to which the species belongs.

Response 3: We thank the reviewer for pointing out this issue. We have revised that point.

Lines 41-42:

Durian (Durio zibethinus Murr.) belongs to the Bombaceae family and often referred to as the "King of Tropical Fruits,".

 

Point 4: Materials and Methods. Determination of Color change, Pulp Firmness, Dry Matter, TSS, and TA. Lines 109 and 110: How were the juices obtained for the determination of TSS and TA?

Response 4: We thank the reviewer for pointing out this issue. We have revised that point.

Lines 116-133:

Pulp firmness was measured using a penetrometer (Daiichi-FG 520K, Japan) equipped with a 0.5 cm diameter cylindrical plunger. The force exerted (N/cm²) was recorded as the plunger penetrated the fruit pulp to a depth of 0.5 cm. A pulp sample was taken from the middle of two major lobes after removing the rind. The pulp was then chopped, thoroughly mixed, and a 20 g sample was dried in a hot-air oven at 70°C for 48 hours or until a constant weight was achieved [13]. The percentage of dry matter was computed based on (w1/w2) × 100, where w1 is the weight prior to drying and w2 is the weight following complete drying. That calculation followed the method described by Sulaiman et al. [13]. The durian samples from each fruit (three replicates per treatment) were homogenized for the analysis of total soluble solids (TSS) and titratable acidity (TA). A 20 g fresh pulp sample was oven-dried at 70°C for 48 hours until a constant weight was achieved. The total soluble solids (TSS) content of the filtered juice was measured using a digital hand-held pocket refractometer (ATAGO, PAL-1, Japan). The results were recorded in °Brix. Titratable acidity (TA) was determined by titrating 5 mL of juice with 0.1 N NaOH, using 1% phenolphthalein as an indicator. The results of the titratable acidity (TA) analysis are expressed as a percentage of malic acid, as it is the primary organic acid found in durian arils. The values were recorded as a percentage.

 

Point 5: Materials and Methods. Determination of Vitamin C Content. Line 123: How was the sample solution prepared?

Response 5: We thank the reviewer for pointing out this issue. However, in the original draft, we have provided a clear and detailed explanation of the sample solution preparation for determining vitamin C content (Lines 135-148).

 

Point 6: Materials and Methods. Determination of Beta-Carotene Content and Determination of Lycopene Content. Add more information for determination of beta-carotene content and lycopene content to facilitate repeatability of experiments

Response 6: We thank the reviewer for pointing out this issue. We have provided more detailed information regarding the determination of beta-carotene content and lycopene content to facilitate repeatability of experiments.

Lines 168-188:

The beta-carotene content in durian extracts was determined using the method described by Volker et al. [16], with modifications to ensure consistency and reproducibility. A 1.5 g sample of durian extract was accurately weighed using an analytical balance and transferred into a clean, dry test tube. Care was taken to ensure that all samples were prepared under identical conditions to minimize variability. To facilitate the extraction of beta-carotene, a solvent mixture consisting of 1.5 mL of hexane, 0.75 mL of ethanol, and 0.75 mL of acetone was added to the sample. The selection of these solvents was based on their ability to dissolve beta-carotene efficiently while preventing oxidation. The mixture was then vortexed at a high speed for 1 min to ensure thorough homogenization of the sample and solvent system. Following vortexing, the sample was subjected to centrifugation at 5000 rpm for 10 min at a controlled temperature of 25 °C. The centrifugation process facilitated the separation of the solvent-extracted beta-carotene from solid residues, ensuring a clear upper phase for subsequent analysis. After centrifugation, 0.3 mL of the clear upper phase was carefully pipetted out and transferred into a clean test tube. To ensure accurate absorbance readings, the extract was diluted with 2.7 mL of hexane, resulting in a total volume of 3.0 mL. The dilution step helped in maintaining the absorbance values within the linear range of the spectrophotometer, thereby preventing deviations due to high analyte concentrations. The absorbance of the diluted extract was then measured at 449 nm using a UV-Vis spectrophotometer. A blank solution consisting of pure hexane was used to calibrate the spectrophotometer before each measurement to eliminate background interference.

Lines 190-212:

                The lycopene content in durian extracts was determined following the method described by Volker et al. [16]. In this procedure, a 1.5 g sample of durian pulp or extract was carefully weighed and placed into a suitable container. To this sample, 1.67 mL of hexane, 1 mL of ethanol, and 0.33 mL of distilled water were added. The hexane serves as a non-polar solvent to extract the lipophilic lycopene, while ethanol and water assist in breaking down any emulsions and help to maintain phase separation during the extraction process. Once the solvents were added, the mixture was vortexed vigorously for 1 min to ensure thorough mixing and extraction of lycopene from the sample matrix. After vortexing, the sample was subjected to centrifugation at 5000 rpm for 10 min at 25 °C. This step facilitates the separation of the mixture into two distinct phases: the upper hexane layer containing the extracted lycopene and other non-polar compounds, and the lower aqueous phase, which contains polar substances. Following centrifugation, the upper hexane phase was carefully separated using a micropipette or syringe, ensuring that the lower aqueous phase was not disturbed. A 0.3 mL aliquot of this upper hexane phase was then transferred into a clean vial and combined with 2.7 mL of hexane. This dilution was necessary to bring the extract into a concentration range suitable for spectrophotometric analysis. The prepared sample was analyzed using a spectrophotometer set to a wavelength of 472 nm, which corresponds to the absorption maximum of lycopene. The absorbance value obtained at this wavelength is directly proportional to the concentration of lycopene present in the extract. A standard calibration curve of known lycopene concentrations was used to quantify the lycopene content in the durian extract, allowing for accurate measurement of the compound’s concentration based on the recorded absorbance.

 

Point 7: Discussion. There was no comparison with literature data for the content of phenolics, flavonoids, β-carotene, lycopene and antioxidant activity.

Response 7: We thank the reviewer for pointing out this issue. Additional discussion and respective references have been provided in the revised manuscript.

Lines 504-511:

Previous studies have shown that extending harvest maturity significantly enhanced the levels of carotenoids (from 22.3 μg/g FW to 122.0 μg/g FW), lycopene (from 5.9 μg/g FW to 47.1 μg/g FW), phenolics (from 65.1 μg GAE/g FW to 125.0 μg GAE/ FW), and flavonoids (from 29.1 μg CE/g FW to 50.9 μg CE/g FW) in tomatoes. However, beta-carotene levels exhibited fluctuations with extended maturity, ranging from 0.81 μg/g FW to 2.12 μg/g FW. Additionally, antioxidant activity increased with extended maturity, as evidenced by the rise in DPPH values (from 25.7% to 85.6%) and FRAP values (from 1.38 μmol/g TE FW to 3.35 μmol/g TE FW) [54].

54. Cheng, W.; Li, S.; Bao, F.; Xu, Z.; Li, T. The changes of antioxidant contents and antioxidant activities of the tomato cultivar Fentailang during the maturity stages. J. Oleo Sci. 2023, 72(6), 577-583. DOI: 10.5650/jos.ess22326

Point 8: References: 35% of the listed references are outdated; please update them to not older than 2014.

Response 8: We thank the reviewer for pointing out this issue. We have updated the references, ensuring that outdated citations (pre-2014) now make up less than 35% of the total. However, we retained certain older references due to their critical findings and original protocols.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

all comments and suggestions have been included in the attached file.

Comments for author File: Comments.pdf

Author Response

# Reviewer-3

Point 1: Cultivar names should be enclosed in single quotation marks, even when the term cultivar is used. Therefore, in the title and body of the article, single quotation marks should be added to the cultivar name where they are missing.

Response 1: We thank the reviewer for pointing out this issue. We have revised that point by adding the single quotation marks to the cultivar name (example: ‘Monthong’) throughout the revised manuscript.

 

Point 2: Title. In my opinion it should be restructured.

Response 2: We thank the reviewer for pointing out this issue. We have revised the title of the manuscript, following the reviewer’s suggestions.

Lines 2-3:

Fruit quality and antioxidant content in durian (Durio zibethinus Murr.) cv. ‘Monthong’ in different maturity stage.

 

Point 3: Keywords. There are too few of them, besides, it should be rather avoided to give the same keywords as are already included in the title of the article. While the name of the species or cultivar is acceptable here (even if it is in the title), the other words should be different.

Response 3: We thank the reviewer for pointing out this issue. We have revised the list of keywords as the reviewer suggested.

Line 38:

Keywords: antioxidants activity; dry matter; fruit quality; harvest maturity; polyphenol content

 

Point 4: Abstract. Line 30: the first time the abbreviation TA appears there. in which case (as in TSS, which has been explained), this abbreviation should be clarified and it should be stated that titratable acidity is meant.

Response 4: We thank the reviewer for pointing out this issue. We have removed the abbreviation “TA” from the abstract in the revised manuscript.

 

Point 5: The word “variety” should be replaced bu “cultivar”.

Response 5: We thank the reviewer for pointing out this issue. We have replaced the term “variety” with “cultivar” throughout the revised manuscript.

 

Point 6: Methodology

- there is no mention of the growing conditions - whether it is organic, conventional, how the trees were grown - in what spacing, , in what form, soil conditions, how old the trees are, etc.

- It is not stated how many fruits were taken for testing at what phases, were the fruits divided into repetitions, how many repetitions were there and how many fruits were in a repetition?

Response 6: We thank the reviewer for pointing out this issue. We have provided additional information regarding the growing conditions, cultural practices, the age of the durian trees, soil conditions, the number of replications, and the sample size.

Lines 85-94:

Durian samples were harvested at nine distinct maturity stages, determined by days after full bloom (15, 30, 45, 60, 75, 90, 105, 120, and 135 days). The fruits were collected from an orchard in Baan Sam Khilek, Tambon Pran, Amphoe Khun Han, Si Sa Ket province, northeastern Thailand (14°32'49.4"N, 104°29'11.9"E). Healthy fruits were randomly selected during the 2024 growing season from four 8-year-old durian trees of similar size, cultivated at an 8 × 8 m spacing in silty clay Chok Chai and Si Sa Ket soil types. The experiment followed a completely randomized design (CRD). Fruit samples were collected at 15-day intervals, yielding 72 fruits across the nine maturity stages (8 fruits per stage, with 4 replications). The samples were then transported to the laboratory at Khon Kaen University and acclimatized overnight at 25 ± 2°C and 80 ± 5% relative humidity.

 

Point 7: Methodology

- data relating to measurements of fruit growth and development are missing from the methodology. What specific parameters were taken into account here? What were they measured with, how and in what units? How were fruit length, weight and circumference measured? How were the results counted - was an mean taken, from how many replicates/fruits?

- the methodological descriptions are missing the units in which the results of the studies are reported.

Response 7: We thank the reviewer for pointing out this issue. We have provided additional information regarding the measurements of fruit growth and development and the respective measurement units.

Lines 108-112:

Fruit growth was assessed based on fruit circumference, length, and fresh weight. Circumference was measured at the widest part of each fruit, while length was determined as the distance from the stylar end to the stem end, both recorded in centimeters (cm). Fresh weight was measured individually using a digital balance (AND, Tokyo, Japan) and recorded in grams (g).

 

Point 8: Methodology

- in the methodological description of the color measurements, only the color of the fruit peel was included, but it was not mentioned that the color of the pulp was also measured.

Response 8: We thank the reviewer for pointing out this issue. We have clarified that the color of the pulp was also measured.

Lines 114-115:

The color properties of fruit peel and pulp were measured in terms of L, a, and b* values using a Color Meter (HunterLab MiniScan EZ 1043).

 

Point 9: Methodology

- it is not indicated how the firmness of the fruit was measured - was the peel removed, was the measurement taken on one or both sides of the fruit, in which part of the fruit was the firmness checked (the upper part, the middle?), what kind of stem was used (diameter), at what speed did the stem move, what units?

Response 9: We thank the reviewer for pointing out this issue. We have provided additional information regarding the measurement of firmness parameter.

Lines 116-119:

Pulp firmness was measured using a penetrometer (Daiichi-FG 520K, Japan) equipped with a 0.5 cm diameter cylindrical plunger. The force exerted (N/cm²) was recorded as the plunger penetrated the fruit pulp to a depth of 0.5 cm.

 

Point 10: Methodology

- the notation of citation should be changed.

Response 10: We thank the reviewer for pointing out this issue. We have revised the notation of citation following the reviewer’s suggestions. The changes have been made throughout the revised manuscript.

 

Point 11: Methodology

- there is no description of how the fruit samples were prepared for chemical analyses, how many fruit were taken for such analyses, were they previously frozen - if so, at what temperature and for how long were they stored, were the fruit here divided into replicates, how many replicates, etc.?

Response 11: We thank the reviewer for pointing out this issue. We have provided additional information regarding the sample preparation and conditions for chemical analysis.

Lines 119-133:

A pulp sample was taken from the middle of two major lobes after removing the rind. The pulp was then chopped, thoroughly mixed, and a 20 g sample was dried in a hot-air oven at 70°C for 48 hours or until a constant weight was achieved [13]. The percentage of dry matter was computed based on (w1/w2) × 100, where w1 is the weight prior to drying and w2 is the weight following complete drying. That calculation followed the method described by Sulaiman et al. [13]. The durian samples from each fruit (three replicates per treatment) were homogenized for the analysis of total soluble solids (TSS) and titratable acidity (TA). A 20 g fresh pulp sample was oven-dried at 70°C for 48 hours until a constant weight was achieved. The total soluble solids (TSS) content of the filtered juice was measured using a digital hand-held pocket refractometer (ATAGO, PAL-1, Japan). The results were recorded in °Brix. Titratable acidity (TA) was determined by titrating 5 mL of juice with 0.1 N NaOH, using 1% phenolphthalein as an indicator. The results of the titratable acidity (TA) analysis are expressed as a percentage of malic acid, as it is the primary organic acid found in durian arils. The values were recorded as a percentage.

 

Point 12: Statistical analysis

- it should be added that a one-way analysis of variance was used. This information is missing from the description. It is also essential to indicate which exactly results of the study were statistically analyzed.

- not all characteristics were statistically analyzed by the Authors (e.g. hue, chroma, lenght, circumference).

- what specific level of significance of differences was used in the study.

Response 12: We thank the reviewer for pointing out this issue. We have provided additional information regarding a one-way ANOVA and the confidence level for the LSD test.

Lines 234-238:

The data were analyzed using a one-way analysis of variance (ANOVA) in Statistix version 10. A one-way ANOVA with the least significant difference (LSD) test was conducted to determine significant treatment differences (P ≤ 0.01) at each maturity stage. Additionally, correlation coefficients were calculated to assess the relationship between maturity stages and dry matter content.

 

Point 13: table number 1 should be the second.

Response 13: We thank the reviewer for pointing out this issue. We have changed table number 1 should be the table number 2. And changed table 2 to table1.

 

Point 14: the Newton unit should be written as N.

Response 14: We thank the reviewer for pointing out this issue. We have revised the term “Newton” with “N” throughout the revised manuscript.

 

Point 15: the Authors do not refer to Table 3 in the text. - there are no references to tables in many of the paragraphs in which the results are presented. There is not a single reference to tables in subsection 3.4!

Response 15: We thank the reviewer for pointing out this issue. We have mentioned Table 3 in the revised manuscript, especially in subsection 3.4.

Line 411:

The relationship between total soluble solids (TSS) at harvest maturity and the quality of ‘Monthong’ durian showed statistically significant changes in the fruit’s chemical composition. TSS exhibited a general increasing trend, ranging from 2.80 to 25.00 °Brix. The highest TSS value (25.00 °Brix) was recorded at 135 DAFB, though it was not significantly different from the TSS at 120 DAFB (23.36 °Brix) (Table 3).

Line 432:

Titratable acidity (TA) followed a distinct trend, reaching its peak (2.67%) at 105 DAFB before declining to 1.02% and 0.78% at 120 and 135 DAFB, respectively (Table 3).

Line 447:

Vitamin C content exhibited a rising trend throughout fruit development, peaking at 105 DAFB (512.33 mg/100 g FW) before decreasing to 283.00 mg/100 g FW at 120 DAFB and 166.17 mg/100 g FW at 135 DAFB (Table 3).

Line 463:

Our study demonstrates that durian sweetness, measured as total soluble solids (TSS), increases with maturity, reaching its peak at 135 DAFB (Table 3).

 

Point 16: Conclusions: As mentioned at the beginning of this review, I consider that in this type of research one-year results are not sufficient to be able to recommend something. This can of course be some indication, but the Authors should emphasize that these are one-year results and further studies/observations are needed to confirm them.

Response 16: We thank the reviewer for pointing out this issue. In conclusion, our one-year results should be regarded as a preliminary study. Further research involving multi-environmental trials across multiple years and locations is necessary to confirm the presence of G × E interactions.

Lines 525-527:

However, our one-year results should be regarded as a preliminary study. Further research involving multi-environmental trials across multiple years and locations is necessary to confirm the presence of G × E interactions.

 

Point 17: references (links, DOI) to the cited publications are missing from the literature entries.

Response 17: We thank the reviewer for pointing out this issue. The links/DOI of each reference (if any) have been provided in the revised manuscript (Lines 545-665).

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The Authors have adequately revised much of the manuscript, but there are still some issues that remain unresolved by the authors and they are of some concern, especially as the authors did not address them in their response to the review. Details are in the attached file.

Comments for author File: Comments.pdf

Author Response

We appreciate your valuable suggestions for further improving the manuscript. Therefore, the manuscript has been revised as your suggestions. Where modifications for the reviewer 3 were made, the highlights are red. The details of the revision are given below.

 

# Reviewer-3

Point 1: According to the authors - for the study of the physical properties of the fruits, 8 fruits were taken on each measurement date and divided into 4 repetitions. So 1 repetition is only 2 fruits and all measurements on a given date were taken on only 8 fruits? Don't the Authors think this is too few? In my opinion, using only 8 fruits per measurement date is far too limited. Such a small sample size is insufficient to reliably determine the characteristics evaluated by the authors. Ideally, a minimum of 8 fruits should constitute one replicate, with at least three replicates in total. Furthermore, it remains unclear how many fruits were used to analyze the content of biologically active compounds. This important detail has not yet been provided. I also question whether 8 fruits per measure date would yield a sufficient amount of material for comprehensive chemical analyses. It remains unclear how many fruits were chemically analyzed, what the weight of the sample replicates was, how many replicates were included, or whether replicates were used at all. This crucial information is still missing.

Response 1: We thank the reviewer for pointing out this issue. We used 16 fruits per measurement date, with 4 fruits per replicate. The same fruits used for physiological measurements were subsequently utilized for chemical analyses, ensuring consistency across data sets. The sample quantity was sufficient for comprehensive chemical analysis, as each assay required only 5 g of material—except for beta-carotene and lycopene, which required 1.5 g each. In the revised manuscript, we have included additional information and clarifications to address this point.

Lines 91-94:

Fruit samples were collected at 15-day intervals, yielding 144 fruits across the nine maturity stages (16 fruits per stage, with 4 replications). The samples were then transported to the laboratory at Khon Kaen University and acclimatized overnight at 25 ± 2°C and 80 ± 5% relative humidity.

Lines 95-103:

Following the physical assessment, the same fruits from each maturity stage—16 fruits per measurement date, with 4 fruits per replicate—were used to analyze the content of biologically active compounds. The fruits were chopped and homogenized in liquid nitrogen using a high-speed blender for 1 minute. A weighed portion (100–150 g) was lyophilized for 48 hours, after which the dry weight was recorded. The lyophilized samples were then ground to pass through a 0.5 mm sieve and stored at −20 °C until further analysis. Each chemical analysis in the biological samples was performed in triplicate using a 5 g sample, except for the determinations of lycopene and beta-carotene, which required only 1.5 g.

 

 

Point 2: The separation of the Results and Discussion chapters was not commented on. In my opinion, these chapters should be separated.

Response 2: We thank the reviewer for pointing out this issue. We have separated the Results and Discussion sections. The Results section now appears in lines 248–381, while the Discussion section is presented in lines 382–537.

 

Point 3: The results given in the paragraphs: 312 - 317 and 247 - 251 are repeated. Why did the Authors not remove the repeated data or even explain why they should remain in this form in the manuscript? The Authors also didn't address the comment of unnecessary repetition in the text of the exact data from the referenced tables. Simply quoting the full data from the tables in the description of the results may not be a major shortcoming, but in my opinion the text definitely loses its fluidity by quoting numbers in too much detail.

Response 3: We thank the reviewer for pointing out this issue. We have revised the Results section to reduce the level of numerical detail. Instead, we focus on key findings, overarching trends, and their implications within each sub-section.

Lines 248-381:

3. Results

3.1. Growth and Development of ‘Monthong’ Durian Fruit from 15 to 135 Days After Full Bloom

A marked and consistent increase in fruit circumference was observed (Figures 3 and 4). Starting at approximately 20 cm at 15 DAFB, the circumference expanded rapidly, reaching around 55 cm by 60 DAFB, indicating vigorous growth during early fruit development. Thereafter, growth decelerated, plateauing at approximately 60 cm. From 90 DAFB onward, circumference values remained relatively stable, suggesting that the fruit had attained its maximum girth.

Likewise, fruit length exhibited a gradual increase, rising from approximately 12 cm at 15 DAFB to about 28 cm by 75 DAFB (Figures 3 and 4). Continued but slower elongation was recorded, peaking at roughly 35 cm by 105 DAFB. A slight decline in length was noted after this point, potentially attributable to post-maturity shrinkage.

These findings suggested that ‘Monthong’ durian underwent rapid dimensional growth—particularly in girth—during the first 60 days post-bloom. Between 90 and 105 DAFB, growth rates stabilized, signaling the transition toward physiological maturity. Notably, circumferential growth was more pronounced than longitudinal growth, underscoring a dominant lateral expansion pattern.

3.2. Dry Matter Accumulation, Fruit Weight, and Firmness Dynamics in ‘Monthong’ Durian Across Different Maturity Stages

The scatter plot (Figure 5) revealed a strong positive linear relationship between days after full bloom (DAFB) and dry matter (DM) content. As DAFB increased, the percentage of DM also rose, indicating progressive maturation and the accumulation of solids such as sugars and fibers in the fruit or plant tissue. During the initial growth phase (15–60 DAFB), DM content remained relatively low. A marked increase was observed between 75 and 120 DAFB, after which the rate of accumulation began to plateau around 135 DAFB.

Fruit weight increased steadily with days after full bloom (DAFB) (Table 1). Specifically, it rose from 137.35 g at 15 DAFB to a maximum of 3,652.30 g at 120 DAFB. The highest fruit weight was recorded between 105 and 135 DAFB. Fruit firmness also increased during early and mid-development stages, reflecting structural maturation, but declined markedly by 135 DAFB—indicative of softening associated with full ripeness. Dry matter content, a critical parameter for evaluating durian quality, showed a continuous upward trend from 15 to 135 DAFB, increasing from 5.75% to 37.31%. A statistically significant peak was observed at 120 DAFB, where dry matter content reached 37.13%.

These findings suggest that the optimal harvest window lies between 105 and 120 DAFB, offering a favorable balance among fruit weight, firmness, and dry matter content. Harvesting at 90–105 DAFB may preserve maximal firmness, which is advantageous for storage and transport. In contrast, fruit harvested at 135 DAFB—although suitable for immediate consumption due to peak ripeness—exhibits diminished firmness and dry matter content, rendering it less ideal for postharvest handling.

3.3. Color Changes in ‘Monthong’ Durian Peel and Pulp at Different Harvest Maturity Stages

Peel color exhibited marked changes throughout fruit development, as reflected by variations in brightness (L*), green-red (a*), and blue-yellow (b*) color parameters (Table 2). The L* value followed a non-linear trend, reaching a maximum of 29.36 at 45 days after full bloom (DAFB), followed by a consistent decline. This pattern indicates progressive darkening of the peel, particularly after 60 DAFB. The a* value remained low and relatively stable (generally below 1.5) between 15 and 75 DAFB, then increased sharply to a peak of 1.92 at 135 DAFB. This suggests a gradual reduction in green hue and an onset of red pigmentation during later stages of maturity, especially after 105 DAFB. Meanwhile, the b* value increased steadily from 15 to 120 DAFB, peaking at 18.37, and then slightly declined. This trend indicates an intensification of yellow coloration with ripening, with the most pronounced color development occurring near full maturity.

Pulp color exhibited marked changes throughout fruit maturation, as reflected in the brightness (L*), green-red (a*), and blue-yellow (b*) color parameters (Table 2). The L* value increased from 74.31 at 15 days after full bloom (DAFB) to 82.78 at 105 DAFB, followed by minor fluctuations, suggesting a progressive brightening of the pulp during ripening—potentially indicative of increased moisture content and reduced cellular opacity. The a* value declined consistently from 6.41 at 15 DAFB to 0.26 at 60 DAFB, before rising slightly, indicating a transition from green to a more neutral or yellow tone, consistent with chlorophyll degradation and carotenoid development. The b* value showed a pronounced increase from 27.27 at 15 DAFB to a peak of 49.90 at 135 DAFB, signifying an intensification of yellow pigmentation—a characteristic commonly associated with ripening-related biochemical changes, including sugar accumulation.

3.4. Fruit Quality Dynamics in ‘Monthong’ Durian Across Different Maturity Stages

Total Soluble Solids (TSS) exhibited a progressive increase with fruit maturation, rising from 2.80 °Brix at 15 days after full bloom (DAFB) to a maximum of 25.00 °Brix at 135 DAFB (Table 3), reflecting a consistent accumulation of sugars as the fruit ripened. Titratable acidity (TA) followed a biphasic trend, increasing to a peak of 2.67% at 105 DAFB before declining sharply to 0.78% at 135 DAFB. This pattern suggests a mid-maturation acid peak, followed by substantial deacidification during the later stages of ripening. Correspondingly, the TSS/TA ratio—a key indicator of the balance between sweetness and acidity—increased markedly from 0.46 at 15 DAFB to 32.05 at 135 DAFB. Low ratios during early development are indicative of dominant acidity, whereas high ratios at later stages highlight the predominance of sweetness. Vitamin C content displayed a non-linear trajectory, peaking at 512.33 mg/100 g fresh weight (FW) at 105 DAFB before declining to 166.17 mg/100 g FW by 135 DAFB. This suggests that vitamin C accumulation is optimized around mid-maturity.

3.5. Antioxidant Profiles and Dynamics in ‘Monthong’ Durian Across Different Maturity Stages

Total phenolic content increased significantly with fruit maturation, reaching its peak at 120 days after full bloom (DAFB) with 43.98 mg/100 g FW, followed by a slight decline to 39.00 mg/100 g FW at 135 DAFB. A pronounced accumulation of phenolics was observed post-90 DAFB, indicating enhanced biosynthesis during the later stages of development. Similarly, total flavonoid content exhibited a gradual increase, peaking at 120 DAFB (8.33 mg catechin equivalents/100 g FW), before declining markedly at 135 DAFB (4.22 mg catechin equivalents/100 g FW).

Beta-carotene levels demonstrated a consistent upward trend, attaining the highest concentration at 120 DAFB (1.35 mg/100 g FW), followed by a reduction to 0.89 mg/100 g FW at 135 DAFB. Lycopene content also increased progressively with maturation, peaking at 53.98 mg/100 g FW at 120 DAFB and slightly decreasing to 48.80 mg/100 g FW thereafter. These patterns suggest active carotenoid and lycopene biosynthesis during late maturation stages, coinciding with visible pigment development.

ABTS radical-scavenging activity exhibited a distinct peak at 90 DAFB (5.89 mg Trolox equivalents [TE]/100 g FW), followed by a significant decline, indicating that antioxidant potential as measured by ABTS is not directly correlated with total phenolic content, implying the involvement of additional antioxidant contributors. In contrast, DPPH radical-scavenging activity increased with maturity, reaching its maximum at 120 DAFB (6.32 mg TE/100 g FW), and declined marginally thereafter. Notably, DPPH activity showed a stronger correlation with total phenolic accumulation.

These findings indicate that the overall antioxidant capacity, particularly via DPPH and ABTS assays, is highest between 90 and 120 DAFB. The concentrations of phenolics, flavonoids, carotenoids, and lycopene also culminate at 120 DAFB, with most parameters either plateauing or declining by 135 DAFB, likely due to over-ripening or compound degradation. Therefore, 120 DAFB represents the optimal harvest maturity for maximizing antioxidant properties and bioactive compound content in durian cv. 'Monthong'.

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