Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Please refer to the attachment for detailed information！

Comments for author File: Comments.pdf

Author Response

The authors thank the reviewer for their close reading and constructive comments. The suggested changes are highlighted in blue. Please note that some text may appear in a different color, if it addresses overlapping feedback from another reviewer.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The study is potentially valuable, but substantial methodological, modelling, and interpretive issues should be addressed before publication.  Therefore, I recommend major revision.

1. The Introduction should better justify foam-mat drying over alternative techniques, explain the rationale for infrared drying, clearly identify the research gap, and state the novelty of the study.
2. The reported optimal conditions contain 0% egg white albumen, meaning that they are not foam-mat drying conditions. The authors should reconcile this result with the title, objectives, and conclusions or revise the scope of the manuscript.
3. Provide complete reagent information and self-contained descriptions of the DPPH and HPLC methods, including reagent concentrations, volumes, incubation conditions, equipment settings, calibration procedures, and validation details.
4. Describe purée and foam preparation more thoroughly, including thawing and seed-removal procedures, batch size, blending time and speed, actual whipping speed, mixer attachment, and the standardized folding procedure.
5. Justify the use of egg white as the sole foaming agent, the absence of a stabilizer, and the selection of 5% and 10% concentrations. Clarify whether fresh egg white or purified albumin was used and how the percentages were calculated.
6. Foam density, expansion or overrun, stability, drainage, and preferably bubble-size distribution should be reported. Without these measurements, explanations based on air incorporation, foam collapse, or foam instability remain speculative.
7. Provide photographs or schematics of both dryers and report all fixed operating parameters, including air velocity, tray dimensions and position, sample area, relative humidity where available, preheating conditions, and actual product temperature. For the infrared dryer, specify the emitter type, wavelength range, power density, emitter-to-sample distance, and operating principle.
8. Report the grinding speed, time, batch mass, and particle-size or sieving conditions, as these factors may affect the measured powder properties.
9. Clarify the moisture-content basis and correct or verify the drying equations and units. In particular, check the sign of the drying-rate equation, the Midilli equation notation, the percentage factor in the Carr index, and the units of the Hausner ratio. In Equation 10, define L according to the actual drying geometry; for symmetric two-sided slab drying, it is the half-thickness.
10. Briefly justify the selection of the seven drying models and include residual analysis or another assessment of model adequacy. Relationships between temperature, egg-white concentration, and the parameters of the selected model should also be developed, or the model should be presented as valid only for the tested conditions.
11. Figure 2 should emphasize the practically relevant drying period and report the time required to reach a defined target moisture content. The criterion for “constant mass” should be stated. The 30-minute measurement interval may also be too long to characterize the rapid initial drying stage adequately.
12. Justify the comparison between fresh wet purée and dried powder colour. Report sample depth, powder compaction, holder, background, aperture, calibration, and replication. Each powder should preferably be compared with its corresponding pre-drying formulation containing the same egg-white concentration.
13. Reporting L*, a*, and b* is useful, but optimizing all individual and derived colour responses may be redundant. The optimization should focus on meaningful quality criteria such as total colour difference, hue angle or browning index, drying time, bioactive retention, and powder properties.
14. Bioactive-compound results should account for dilution caused by adding egg white. Retention should be calculated relative to the corresponding initial formulation, fruit-solid content, and powder yield. The authors should also clarify whether egg white acts only as a foaming agent or is intended to act as an encapsulant, and avoid unsupported claims of protection.
15. Clarify whether triplicates represent three independent drying experiments or repeated analyses from one drying batch. Explain how the standard deviations and centre-point results were calculated, and simplify the lowercase and uppercase superscript definitions in the tables.
16. A complete audit of the data and calculations is required. Examples include discrepancies between Table 3 and the text, inconsistent HPLC totals, the questionable increase in initial moisture after egg-white addition, and the non-symmetric Pearson correlation matrix in Table S4.  
17. The supplementary material should be reformatted, with aligned values, repeated table headers, consistent symbols and units, and higher-resolution figures.
18. Claims concerning economic viability, shelf stability, enhanced bioavailability, or protective effects should be removed or qualified unless supported by energy analysis, storage or water-activity data, microbial testing, or bioavailability measurements.

Author Response

The authors thank the reviewer for their close reading and constructive comments. The suggested changes are highlighted in red. Please note that some text may appear in a different color, if it addresses overlapping feedback from another reviewer.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript deal with the drying of wild blackthorn puree using hot-air convective drying and infrared drying at temperature of 50, 60, and 70 °C, with egg albumin added at 0, 5, or 10% as a foaming agent. The manuscript evaluates drying kinetics using seven thin-layer drying models and report that the Midilli and Page models provide the best fit for moisture-ratio evolution. Effective moisture diffusivity and activation energy is also determined. It is concluded that IR drying generally increases moisture diffusivity compared with convective drying. The manuscript examines powder bulk density, tapped density, Carr index, Hausner ratio, colour parameters, browning index, total colour difference, total anthocyanin content, total phenolic content, total flavonoid content, and DPPH antioxidant activity. Response surface methodology is applied to optimise colour-related parameters as a function of drying temperature and egg albumin concentration. PCA is applied to explore relationships between technological, colourimetric, flowability, and phytochemical variables. HPLC profiling is used to identify and quantify selected components. In my opinion, the applied methods are appropriate. The manuscript has a logic structure and contains interesting and valuable results, but need significant revision to make it clear and complete (see my comments&suggestions).

Comments, suggestions:

The title emphasises foam-mat drying, but the reported optimum conditions (for polyphenol content and BI) are 0% egg albumin for both convective and infrared drying (line 860-862). Authors also concluded that ’Egg white albumen as a foaming agent did not confer substantial protection of bioactive compounds, as expected’ (line 867-868). These mean that the optimised samples are not truly foam-mat samples. Therefore, I suggest reconsidering the title of the manuscript, or make clearer the conclusions.

A foam-mat drying study should characterise the foam as well. Essential parameters are missing: foam density (before drying), foam expansion/stability, viscosity, bubble-size distribution, and collapse behaviour during drying, for examples.

In the Introduction, the principles of foam mat drying and the experience gained with this method to date (advantages, limitations, applicability, etc.) should have been explained in more detail.

The description of the drying conditions is superficial. In addition, the humidity levels, the wavelength of the infrared radiators, IR lamp-sample distance, air-circulation properties, the selection criteria of drying temperature, the location of temperature measurements within the material, the temperature rise, and temperature inhomogeneities are not specified.

An analysis of the energy efficiency of the two drying methods is also missing (specific energy consumption vs. removed water, for example). Therofore, for example, the statement that foam-mat drying is “economically viable” is unsupported because no cost, energy-consumption, productivity, or scale-up analysis was performed.

The surface properties of the sample (e.g., “smoothness” of surface, surface moisture distribution, and the temperature/pH-dependent behavior of individual components) can also influence light reflection and, consequently, the measured color coordinates. How was this taken into account during the color measurement?

Figure 2, 3, 4 and 5 has poor visibility (mainly axis titles, labels). Please improve the visibility of these figures.

Both significant and nonsignificant terms are included in the model equations. If the main text of the manuscript does not include the ANOVA table, these equations (Eq. 19-32) may be misleading in this form.

The drying-rate equation is written as moisture at time t + Δt minus moisture at time t, divided by 30 min. Since moisture decreases during drying, this expression should give negative values.

In Fickian diffusion equation the characteristic length is commonly half-thickness, depending on the equation form. The manuscript defines L as the thickness of the material. In my opinion, the drying method and conditions used in the study justify this choice; I would just ask that you make this clear in the manuscript.

Based on its current content, Chapter 2.9 (HPLC Analysis) is either unnecessary as a separate subsection or its content needs to be amended (detailed description of the method).

The manuscript states that all experiments were performed in triplicate, but it is unclear whether these were independent drying batches or only analytical/technical replicates. The RSM model appears to be fitted to only two variables with repeated centre points, but the manuscript calls it a “3-Level Factorial Design” and reports 13 runs. It needs clearer explanation. A full 3 × 3 factorial design contains 9 combinations; 13 runs imply additional centre-point replicates. The authors should state the number of true replicated centre points, whether runs were randomised. etc.

The citation style is inconsistent (full/abbreviated journal titles; Ref22-author names). Furthermore, in line 307’ Rajkumar et al. (2007) [25]’ is mentioned but Ref25 appears to be a different Rajha et al. paper on grape by-product extraction. Please check the numbering of the references in the whole manuscript.

Comments on the Quality of English Language

Author Response

The authors thank the reviewer for their close reading and constructive comments. The suggested changes are highlighted in dark green. Please note that some text may appear in a different color if it addresses overlapping feedback from another reviewer.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Issue 1: After revision, the Results and Discussion sections are merged into Part 3; however, Part 3 contains only one subsection, 3.1, with no Part 4, and directly transitions to Part 5, the Conclusions. The formatting still requires further adjustment.It is recommended to modify the paper framework as follows: 1 Introduction → 2 Materials and Methods (or Theory/Model) → 3 Results and Discussion (with 3.1) → 4 Conclusion.

Issue 2: The Conclusions section should include a summary of the findings regarding the effects of drying temperature and phycocyanin concentration on color.

Author Response

The authors thank reviewer to a close reading and appropriate comments, aiming to improve our work. The suggested changes are highlighted in blue.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript has been improved. However, the authors are strongly recommended to provide photographs or schematic diagram of two dryers. After this minor revision, the manuscript can be accepted for publication.

Author Response

The authors thank reviewer to a close reading and appropriate comments, aiming to improve our work. The suggested changes are highlighted in red.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In accordance with the reviewers’ recommendations, the authors have thoroughly and carefully revised and expanded the manuscript; they have also provided detailed responses to the reviewers’ comments. As a result of the additions and revisions made in the “Introduction,” “Methodology,” and “Results” sections, the manuscript’s completeness and clarity have improved. The revised title now better reflects the content of the article. 

Author Response

The authors thank reviewer to a close reading and appropriate comments, aiming to improve our work.