Copolyamide-Based Modified Atmosphere Packaging Attenuates Phenolic Degradation and Maintains Postharvest Quality of Rubus Berries

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

There are two huge problems with this paper. Any discussion or even description of the MAP packaging is not present, even though the title makes it clear this appears to be a novel material. The other major issue is that authors never state what the final CO2/O2 was in these bags. There are indications in some assays that there may be fermentative respiration at work, which would mean CO2 values are above 15%.  Some important details are skipped in the methods, such as standards used for total phenolics, etc. 

Also, method for TA is in no. 4 not no. 5. Not sure how one can accurately see a color change in 3 ml of juice (not diluted?).

This ms presents a good deal of biochemistry on the enzymes involved in various pathways in blackberry. Many of the tests are generic, rather than highly specific. This approach is ok, although in some cases more specific assays would be helpful such as identifying specific anthocyanins, phenolics that might be affected by MA.  

Elvira and Esparanza are fairly new blackberry and raspberry introductions from Driscoll. They are noted for high SSC and firm fruit. 

Check on the titratatable acidity method used. Color indicator is unusual. May be why they had quite a bit of juice for ssc and tacid though.

Why is the material used for map not discussed relative to the other studies. Also look up the map studies especially raspberry and see if materials and similar details on comp. discussed. I think we also had one on blackberry as a short paper?

Authors: Andew or Andrew?

Lines 10,  17. The study does not investigate or reveal. The researchers do the investigating and interpretation

Line 33 define short storage potential.  Or is it storage life?

Are ROS strictly due to postharvest or actually part of ripening and senescence regardless of postharvest phase?

Could use some introductory information on what a copolymide bag is, in contrast to what is commonly used for MAP.

Methods: what was the temperature at harvest and prior to MAP packaging of fruit? What was the model/source/type of plastic of control punnets? Were 100% full colored berries also firm or was ripeness just selected on berry color?  Assuming that berries were hand harvested, were these easily detached?

For respiration, 100-150 g fruit from each replicate were warmed for that particular interval? So each interval had 3 replicates of fruit used for respiration, x 3 readings? Or one replicate, measured with 3 readings?

What was average berry size here?

What was the final CO2/O2 content in polyamide bags? What was relative humidity of control and MAP treatments?  Assuming MAP is a sealed system, how much does increased relative humidity contribute to differences in berry biochemistry?

Were there signs of decay, berry cell collapse (as has been found on raspberry)?

What was the standard used for TPC? Gallic acid?

Author Response

Reviewer 1:

Comment: There are two huge problems with this paper. Any discussion or even description of the MAP packaging is not present, even though the title makes it clear this appears to be a novel material. The other major issue is that authors never state what the final CO2/O2 was in these bags. There are indications in some assays that there may be fermentative respiration at work, which would mean CO2 values are above 15%.  Some important details are skipped in the methods, such as standards used for total phenolics, etc. 

Reply: The packaging material used is a novel yet the literature has nearly no information about its effect on any horticultural produce. The details of the methods have been updated and highlighted as the red colour.

Comment: Also, method for TA is in no. 4 not no. 5. Not sure how one can accurately see a color change in 3 ml of juice (not diluted?).

Reply: The correction for citation has been made as suggested by the reviewer. The method used for TA calculation was based on where 3 mL of the juice without dilution was used to determine the colour change as an indication of titratable acidity. The colour modifications from red to purple were easily identifiable to measure TA.

Comment: This ms presents a good deal of biochemistry on the enzymes involved in various pathways in blackberry. Many of the tests are generic, rather than highly specific. This approach is ok, although in some cases more specific assays would be helpful such as identifying specific anthocyanins, phenolics that might be affected by MA. 

Reply: Thanks for suggestion. However, the authors have not determined the effect of MA on the individual or specific polyphenolics, flavonoids and anthocyanins. Yet we will consider this comment for our future studies.  

Comment: Elvira and Esparanza are fairly new blackberry and raspberry introductions from Driscoll. They are noted for high SSC and firm fruit. Check on the titratatable acidity method used. Color indicator is unusual. May be why they had quite a bit of juice for ssc and tacid though.

Reply: The authors believes that total volume of juice is not affecting the final calculation of total acids and the calculations are made in replication using composite samples which reduces the biasness in the mean data.   

Comment: Why is the material used for map not discussed relative to the other studies. Also look up the map studies especially raspberry and see if materials and similar details on comp. discussed. I think we also had one on blackberry as a short paper?

Reply: The material used is coplolyamide based multilayer packaging material and its efficacy has been discussed in some food materials including meat. However, the available information as per best of our knowledge and available literature, has been incorporated to the introduction (L77-88), while the discussion has also been updated according to the available literature and changes have been highlighted in red colour.  

Comment: Authors: Andew or Andrew?

Reply: The name has been modified. Thanks for correction.

Comment: Lines 10, 17. The study does not investigate or reveal. The researchers do the investigating and interpretation.

Reply: The statements have been rephrased as suggested by the reviewer.

Comment: Line 33 define short storage potential.  Or is it storage life?

Reply: The word “storage potential” has been replaced with “storage life” as suggested by the reviewer.

Comment: Are ROS strictly due to postharvest or actually part of ripening and senescence regardless of postharvest phase?

Reply: As suggested by the reviewer, ROS are the primary factors involved in the ripening process for fruits and vegetables. However, this study mainly focuses on the postharvest aspects of Rubus berries and senescence is directly affected by ROS accumulation and has a direct correlation with the senescence mechanism.

Comment: Methods: what was the temperature at harvest and prior to MAP packaging of fruit? What was the model/source/type of plastic of control punnets? Were 100% full colored berries also firm or was ripeness just selected on berry color?  Assuming that berries were hand harvested, were these easily detached?

Reply: The harvesting was performed in the early morning between 7-8 am where the temperature is relative low. However, the authors didn’t record the temperature at harvest and before the MAP storage as it was not the main factor during this study.

Moreover, the controls were stored in the commercial plastic punnets (L × W × H = 0.16 × 0.12 × 0.06 m) with cushion material, perforations at the bottom and without lids.

The harvesting was manual and berries were easily detachable. The harvesting of the blackberries and raspberries at full colour development stage was performed as it is the commercial practice for the local Australian markets due to no colour development after harvest in both berries. The firmness of blackberries is relatively higher at full colour development stage as compared to raspberries; however, the firmness was not determined during this study.

Comment: For respiration, 100-150 g fruit from each replicate were warmed kept at room temperature (20°C) for 2 hours for that particular interval. So each interval had 3 replicates of fruit used for respiration, x 3 readings? Or one replicate, measured with 3 readings?

Reply: For respiration, each replication contained one reading making three readings per treatment.

Comment: What was average berry size here?

Reply: Thanks for comment. However, the authors didn’t measure the size of berries in this study.

Comment: What was the final CO₂/O₂ content in polyamide bags? What was relative humidity of control and MAP treatments?  Assuming MAP is a sealed system, how much does increased relative humidity contribute to differences in berry biochemistry?

Reply: The authors provided respiration rates and CO₂/O₂ ratios were not given as the retention capacity of the packaging is 6-8% CO₂ and 10-12% O₂ as communicated by the manufacturer. However, the impact of different relative humidity levels on the berry biochemistry was not identified.

Comment: Were there signs of decay, berry cell collapse (as has been found on raspberry)?

Reply: The signs of decay and berry collapse were more visible in the raspberries. However, the drupelets leakage and juice leakage were the main indication of decay in the blackberries.

Comment: What was the standard used for TPC? Gallic acid?

Reply: L150: Gallic acid standard curve was used to quantify the total phenolic and has been added to the revised manuscript.

Thanks for suggestions and corrections.

Reviewer 2 Report

Comments and Suggestions for Authors

In this manuscript, the authors employed modified atmosphere packaging for attenuating phenolic degradation and maintaining postharvest quality of Rubus berries during storage. The author obtained some research results, which had a certain effect on the quality of blackberry and raspberry. However, there are still some parts of the manuscript that need to be revised, as follows:

 

1. Lin 93: MAP bags: its parameters and characteristics, such as the permeability of gases, water and other substances, are not provided.

2. line 285-287: Statistical analysis should be explained better.

3. Line 282: Change “U g^-1” to “U g^-1 protein”.

4. Line 232: “… expressed as U mg-1 protein”, the “-1” requires superscripts.

5. Fou the unit of enzyme, some are expressed by U g^-1 protein, some are expressed by U mg^-1 protein, it is recommended to unify.

6. line 528: … DHAR enzyme (GSSG), … : this is wrong.

7. The oxidised glutathione and dehydroascorbate are also important parameters in ascorbate-glutathione pathway, why not measured?

8. Conclusion section is weakly formulated. It should be improved with the inclusion of most important research outcomes. So suggest its needs to be revised and should give some future insight in it.

9. If possible, please provide a mechanism diagram in this study to better illustrate the impacts of modified atmosphere packaging on the quality of blackberry and raspberry.

Author Response

Reviewer 2:

In this manuscript, the authors employed modified atmosphere packaging for attenuating phenolic degradation and maintaining postharvest quality of Rubus berries during storage. The author obtained some research results, which had a certain effect on the quality of blackberry and raspberry. However, there are still some parts of the manuscript that need to be revised, as follows:

Comment: Line 93: MAP bags: its parameters and characteristics, such as the permeability of gases, water and other substances, are not provided.

Reply: Thanks for comment. However, this is a commercial product (MAP bags) and the manufacturer didn’t provide extended details about the packaging properties.

Comment: line 285-287: Statistical analysis should be explained better.

Reply: The detail of statistical analysis has been added as suggested by the reviewer.

Comment: Line 282: Change “U g^-1” to “U g^-1 protein”.

Reply: The change suggested by the reviewer has been incorporated throughout the manuscript.

Comment: Line 232: “… expressed as U mg-1 protein”, the “-1” requires superscripts.

Reply: L233: The correction has been made as suggested by the reviewer. Thanks for correction.

Comment: For the unit of enzyme, some are expressed by U g^-1 protein, some are expressed by U mg^-1 protein, it is recommended to unify.

Reply: The difference in the unit of CAT enzyme is based on its molar extinction coefficient value which is in “M^-1 cm^-1” as compared to all other enzymes where values is in “mM^-1 cm^-1”. In case to determine the value of CAT in “U g^-1”, this value is very high and that’s why authors presented this in “mg^-1”.

Comment: line 528: … DHAR enzyme (GSSG), … : this is wrong.

Reply: L 571: The sentence has been rephrased. Thanks for corrections.

Comment: The oxidised glutathione and dehydroascorbate are also important parameters in ascorbate-glutathione pathway, why not measured?

Reply: Thanks for suggestion. The authors determined only the total glutathione and ascorbic acid. However, the authors will consider determining both these parameters also in future investigations. 

Comment: Conclusion section is weakly formulated. It should be improved with the inclusion of most important research outcomes. So suggest its needs to be revised and should give some future insight in it.

Reply: The authors have improved the conclusion section and also added the future prospects in the revised manuscript as suggested by the reviewer.

Comment: If possible, please provide a mechanism diagram in this study to better illustrate the impacts of modified atmosphere packaging on the quality of blackberry and raspberry.

Reply: Thanks for the suggestion. However, the results for both berries are different from each other making it quite difficult to draw one mechanistic diagram for both berries.

Thanks for suggestions and corrections.