Monitoring In Vitro and In Vivo Aroma Release of Espresso Coffees with Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry

Round 1

Reviewer 1 Report

It is a pleasure for me to review the manuscript on the discrimination of three coffees in head- and nosespace by Andrea Romano et al.

In general, the manuscript is very well written and based on very well designed and executed research. Additionally, the topic of in vitro and in vivo aroma release from coffee is of high importance to the food and flavor research community. Thus, I definitely recommend this paper for publication in Applied Sciences with only some minor remarks and suggestions for improvement.

The following comments are not in the order of importance, but following the manuscript.

The introduction is very concise, gives a good overview about the topic and focuses on relevant information concerning the present study.

(minor) I would slightly re-organize 2 as information about providing the coffee samples to the panelists is included in 2.1 (should be 2.3) whereas information about the samples for headspace is correctly placed in 2.4.

(minor) Strictly speaking, in 2.2 a multitude of mass spectra are integrated for 1s.

In 2.4 an autosampler coupled to the PTR-MS device is mentioned. This coupling should be elaborated in somewhat more detail (I also could not find further information in [10]) as it is no standard setup for PTR-MS. Was it static or dynamic headspace? Was the headspace directly injected or diluted in some carrier gas? Maybe even a whole paragraph under 2.2 could be written about this.

(minor) In 2.5.1 Th and mass-to-charge ratio should be avoided and m/z used according to IUPAC (correct throughout the rest of the manuscript).

Fig. 1 and particularly 2: The authors should think of a way to deal with the overlaps as it is very difficult to read.

Tab. 2 (and S3): Aren't total compound concentrations around 100 ppmv (sum in S3) well above the instrument's upper dynamic range limit? And are e.g. 5 ppmv on m/z 97.028 causing detector saturation effects? Assuming about 100 cps/ppbv sensitivity, this would mean 500,000 cps. Maybe the authors could discuss this.

Tab. 2 and 3: Could the authors elaborate in more detail about the superscripts (a, b, c)?

Line 180: "…total amount of a specific mass peak released in the nose." should be rewritten (colloquial).

Fig. 3 and lines 196ff: The purpose of this figure is quite difficult to understand for someone not used to this type of diagrams. Could the authors elaborate about the key message of Fig. 3? Furthermore, the area of the respective compound classes in the diagrams represents the number of compounds detected rather than the concentration compared to the total VOCs released. By having a quick look at the diagrams it seems being the other way round. This misinterpretation is also supported by line 208 "Figure 3 … carbonyls dominated the HS and NS with more than 50% of total peak area". Therefore, some more explanation or different wording would help.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

This study is related to the analysis of the aroma release of espresso coffees by PTR-ToF-MS headspace and nosespace. In this study, for sample discrimination, only 3 coffee samples with different roasting degrees were used and only 3 panelists were used, which were the major drawbacks in this study, in my opinion. Also, more support and comparison with literature should be included. More specific details can be seen in the attached PDF file. 

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have improved the quality of the manuscript, by addressing all the reviewers comments.