Preharvest Application of Hexanal as a Surface Treatment Improved the Storage Life and Quality of Mango Fruits

Round 1

Reviewer 1 Report

Dear Authors, dear Editor,

draft article “coatings-1387372-peer-review-v1 Preharvest Application of Hexanal…” refers on the conservation of mango fruits sprayed with hexanal solution on the fruit surface to delay post-harvest ripening. The Authors measure an array of fruit quality indicators in treated and untreated-control fruits of four cultivars, and conclude that treatment with hexanal, together with cold storage, has merits for application.

While it is true that the experiment core is a surface treatment, it is also to consider the niche application as of agricultural or food science significance. I cannot judge whether this research is meaningful in its specific field. In any case, the research is performed with appropriate methods and result reporting. One aspect that I am unable to understand, as a time-to-time layman Western eater of supermarket-grade mangoes is the connection of the measured indicators to “fruit quality” as perceived by the consumer. It would be of a great help to non-professional readers (there will be many, given the power of indexing services) if photos can give visual hint of the effect of the measured parameters on the aspect of the fruits.

Another more technical aspect is to understand whether application of hexanal (which is itself a sweetish-smelling substance, with a not particularly pleasant odour, at least as a laboratory chemical) has an effect on fruit smell.

Section 2.1. The hexanal stock solution for preharvest spray was prepared using 0.2% (v/v) hex-83 anal dissolved in equal volume of tween 20 the surfactant, and ethanol. The spray solution 84 was prepared prior to application, by mixing 1 part of stock in 4 part of water (v/v). The 85 hexanal concentration in final spary solution is 0.02%. Is this calculation right? It should be 0.04%. Stock is 20 mM, that applied is 1:5, so being 4 mM, which is not little! Did you check how much solution, and hexanal, was in fact deposited on fruit surface, and how much went inside? Did it photo-oxidize when the solution dried out on the fruits in the field?

Sampling and statistical analysis, as reported, are not simple to understand. It is conceived that each fruit underwent a complete set of measurements and that all chemical and enzymatic measurements were performed on homogenized fruit flesh. All this can only be imagined, since it is not reported. How many fruits were tested for each parameter and sampling time (Table 1 note adds to confusion)? Please, put yourself in another lab-man’s shoes! There is a lot of mistyping, however it don’t jeopardize understanding. Just check, please.

Tables and Figures (bar plots) are a mess to follow. DBH (days before harvest) means that measurements are taken with the fruit still on the mango tree. This is not apparent from any description, and only derives from my imagination and a bit of expertise in field measurement. I imagine that evolution of gases (CO2 for respiration rate and ethylene for ripening) are measured by placing the fruit and its branch in a plastic bag with a pipe that leads to the measuring device. Is it the case? You can put a photo to show. Lettering of the statistical tests floats in the figures, so that readers get lost.

By the way, is hexanal treatment authorized? This is something agricultural experts will ask.

This is an interesting, curious piece of work and I suggest that you valorize the efforts of the research team and of the field workers, by making it appreciated by many more readers than you can conceive. Most work is clumsily reported to the point that reader’s imagination is strained to figure out what really your team did. I would recommend that you edit this draft and add most of the missing descriptions and explanations. Figures and photos would greatly help readers to get the best of this work. I suggest a major revision but a positive judgement on research

Best regards

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This a well written manuscript the quality of which can further improve prior to its publication. Please see attached a few recommendation of the reviewer

Comments for author File: Comments.docx

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors, dear Editor,

I have examined the revised version of “coatings-1387372-peer-review-v2 Preharvest Application of Hexanal…”. This update sheds more light on the interesting work performed, by reporting more information and better explaining some points. However, the text is still cumbersome to study for interested readers. Some sparse suggestions:

The description of the methods is still difficult to follow. I understand now that CO2 and ethylene were measured post-harvest, on collected fruits placed in some box or whatever, in the cold and at RT, for some sampling time in different days. This may be greatly improved, for example by using a GANTT or some similar sketch of activities over time. I can’t understand whether the same fruits were used for all the determinations (as I would expect, in order to correlate parameters from the same fruit).

For all the information that is in the supplementary, you may crop one example for the main text and refer to the supplementary for the complete set.

You may crop a pair of GC-MS traces from the supplementary and report in the relevant section to show that treatment with hexanal modifies the profile of volatiles. In Tables 3-6, what is “probability”? is it the match of library search? (I hope not!) by the way: “The base peak of each 186 spectrum was compared with the base peak of the chemical components in the NIST 187 Ver.2011 MS data library through on-line and comparing the spectrum obtained through 188 GC/MS.” What does it mean? I am a >30yr practitioner of mass spectrometry, know the Thermo instrument you use and did a lot of GC-MS fingerprinting, but I can’t make it. I wouldn’t report GC-MS results as in these tables, because they are difficult to match. Given the list of all considered volatiles in all samples, you can make the column list of levels in the different cultivars and untreated vs. treated. Just to give you an example of this kind of data presentation, you may see this (doi:10.1016/j.mambio.2012.01.003 and its Supplementary information file).I notice that you did not add an internal standard for extraction, so you cannot compare quantitatively the profiles of volatiles. I find this an operational bias, since you can’t run Principal Component Analyses on your rich dataset.

Since hexanal is GRAS, state it clearly in the introduction, since I could not find this key information until a couple of words in the discussion.

2.2.7.1. Sample selection and solvent extraction this is a title without paragraph?

I still suggest a major revision and stay with my positive judgement on the research.

Best regards

Author Response

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Author Response File: Author Response.docx