The Effect of Concentrated Microwave Field (CMF) on Selected Physical and Rheological Properties of Liquid Egg Products

Round 1

Reviewer 1 Report

Microwave processing of food has several advantages over the conventionally used thermal methods. Application of pulsed concentrated microwave field (CMF) for biomaterials, such as food and food raw materials has great potential, but the detailed investigation of this process can provide useful data and experiences for science, and for industry practice, as well.

 Egg materials ( egg white, yolk and liquid whole egg) can be considered as a good raw material to test the efficiency of CMF process. Manuscript applsci-1086979 has therefore an interesting topic for the readers of Applied Sciences journal.

Manuscript is generally well written with a logic structure. Although the research is conducted by using of a prototype CMF reactor, but these investigations applying RSM method can provide useful data for scaling up the process.

Research motivations are well defined in the Introduction section. Materials and method are given clearly. ANOVA and RSM results are explained in details. Manuscript contains interesting and valuable results (based on a complete research work) but, unfortunately, the results are not fully discussed with references.

 

Comments, suggestions:

I suggest the authors to highlight why use rheology parameters, pH and colour as ‘control parameters’ to test CMF (relevance of these parameters in thechnology, food quality, for instance)

I suggest the authors to check the typing errors in manuscript (sub/superscript, for example ‘cm3’ in line 111, ‘20oC’ in line 119 etc).

It is not clearly given why used 480W power for CMF experiments. Please give the explanation (temperature ramp was similar to conventional heating, avoid the undesirable high temperature/hot-spot heating, for instance?)

I suggest the authors to consider to give the temperature increment curves for CMF experiments with different parameters.

The study resulted in interesting and valuable results. But, unfortunately the results (pH, color, rheology) are not discussed with references. In my opinion it is available relevant references in the scientific literature (change of color, pH and apparent viscosity of egg materials) I suggest the authors to discuss their own results with these references.

 

Author Response

The authors would like to thank you for the review received. As suggested by the reviewer, the authors supplemented the work with information on the use of selected factors, i.e. pH, color parameters and apparent viscosity. It resulted both from the final evaluation of the quality of liquid egg products as well as in the case of apparent viscosity - also for technological reasons. The authors checked the work in terms of editing and removed the errors noticed. The lower power of the device (480 W) was used due to the lower risk of uneven heating of the analyzed samples. This information was also supplemented in the work. The suggestion to place the heating curves is valuable, but due to the numerous figures related to the RSM, the authors abandoned this intention. However, in the next work on CMF, the authors will try to include such graphs if possible. As suggested by the reviewer, an additional chapter "Discussion" was added, in which the most important aspects of our work were discussed in relation to the literature of other authors.

Reviewer 2 Report

The authors use a microwave generator to influence egg white, yolk and liquid whole egg. After exposure, the temperature, pH, color and viscosity of egg liquids are measured. The main idea of the article is unstated. If microwave generator allows better food preservation, as discussed in the abstract and introduction, then it is not clear how the measured parameters relate to food preservation.
In fact, the submitted manuscript does not look like a scientific article, but appears as a report on the work had been done. The manuscript contains 32 figures(!!!) and 7 tables that makes it very difficult to read and understand. Small amount of experimental material (9 points of 2-3 measurements) describe in each figure. Most of the data needs to be moved to Supplementary materials. In general, the manuscript requires the major revision and its structure has to be reconsidered. The authors have to review the data presentation: more concentration on the pronounced results of the study.
The article does not have of describe parameters and no links to the microwave generator (frequency, antenna type, specific absorption rate). The term "concentrated microwave field" in the title of the article is used only by the authors in their previous works and physically incorrect. To describe microwave radiation, standard physical terms are sufficient, such as specific absorption rate, irradiance, amplitudes of E and H components, amplitude, time and frequency modulations.

Author Response

The authors would like to thank you for the review received. In line with the reviewer's suggestions, the structure of the paper was changed by supplementing the introduction as well as adding the section "Discussion". The authors hope that thanks to this, it was possible to better highlight the advisability of using alternative methods of food preservation, including the use of microwave technology. The purposefulness of the analysis of selected parameters (temperature increase, pH, color, apparent viscosity) is justified due to the final quality of liquid egg products and its assessment by consumers, as well as in the case of apparent viscosity and temperature increase - also for technological reasons. Additional information on this subject is provided in the paper.

Indeed, placing 32 figures, and after adding one photo a total of 33 figures, may seem unnecessary, but in the papers in the field of food technology related to the optimization of technological processes (using RSM) it is not uncommon practice. The essence of optimization of technological processes with the use of RSM often boils down to a tedious analysis of the simulation of the variability of the analyzed factors in order to obtain the optimal final product. For this reason, the authors decided not to remove the RSM figures, especially since only those that were statistically significant were included. The advantage of the RSM method is the use of relatively few "input" measurement points (for example, 9 resulting from the use of two variables in the 3x3 model) with 2 or 3 repetitions and obtaining "output" precise simulations of the analyzed discriminants. For this reason, this method is used in food technology and in many scientific works related to this discipline.

As suggested by the reviewer, the work supplemented the information related to the microwave generator (including information about the frequency equal to 2.45 GHz and details of the waveguide) and supplemented the text on the use of microwave treatment in food technology. With regard to the name "concentrated microwave field" used by the authors, we agree that it may not be very strict, but it has been used in our country for almost 20 years and was given in the manual of the microwave reactor by the manufacturer, i.e. Plazmatronika. In international literature, the technology we use is most often referred to as "single-mode-type microwave heating". Due to the traditional definition of this technology as CMF in our country, we decided to leave this nomenclature at work. Explanations related to this were also included in the work. We were not able to indicate all the parameters of microwave interactions specified by the reviewer. We focused on input variables important from the point of view of food technology and information related to this was included in the work. We hope it will be sufficient from a practical point of view.

It is worth noting that the thermal effect obtained from the use of microwave technology is parallel to the so-called CMF non-thermal effect in the process of microbial inactivation. We obtained a synergistic effect of the „hurdle technology” here, which we checked in previous studies. The impulse CMF treatment turns out to be significant, as it is more effective in its latal effect against the microorganisms contained in the liquid egg materials compared to the classic continuous mode of microwave treatment. For this reason, after previous experience on the effectiveness of microwave impulse treatment in our current work, we focused on the analysis of technological (temperature increase, apparent viscosity) and qualitative (pH, color, but also apparent viscosity) discriminants, which may be of practical use in the food industry.

Reviewer 3 Report

The article concerns one of the new methods that may be of potential importance in the preservation of food products - concentrated microwave field (CMF). According to the text, a certain limitation is its application to liquid products.

My questions and comments to the text:

Abstract: in the abstract The Authors mention "modified microwave reactor", but in next part of manuscript there is no information on what the modification was about and who was its author. Please explain.

Methodology:

1. Is the method of preparing the yolk, egg white and mixed egg samples developed by the Authors or is it a method described in the literature? There is no reference to any methodologies in this part of the text (other publications of the Authors were also not included in the methodology).
2. The Authors determined the color parameters L*a*b* How was the measurement performed with the Minolta in a liquid test? Please explain. Would it not be advisable in this case to calculate the total color difference ∆E? It may be more expressive to the reader if the differences in color between the standard and the sample are reported as the difference between these numbers in relation to the sample and the standard.
3. On what basis were the CMF parameters determined? Previously conducted experiments? Please clarify this information.
4. Determination of mean values: what are the result of two repetitions in the determination of pH and three - in three? What was it caused by?

Results:

I understand that there are not many similar studies to discuss with them the results obtained in the experiment, but the results without discussion do not show the advantage of the applied solution. The reader will conclude that this is a forward-looking process only if he compares with the results obtained for other methods. I kindly ask that the Authors include a reference to other methods with the results of their research.

Correlation: the correlations that occur between the different examined discriminants were indicated, but there was no explanation as to how they translate into the interpretation of the obtained results. There was also no discussion of the results obtained here.

Conclusions: needs to be reworded, as this is a fairly extensive summary at the moment. The sentence summarizing this chapter is not a well-formulated conclusion, nor does it indicate the applicability of this method. There is also no indication of advantages and benefits of its use in the case of the tested samples.

References: standardize the way of writing literature items and follow editorial requirements - at the moment there are different writing styles. The self-citation is also puzzling - as many as 4 of the 16 listed literature items are by the main Author.

Author Response

The authors would like to thank you for the review received. The original method of preparing liquid egg raw materials has been used in our laboratory in a similar way for many years. Supplementary information on this subject has been included in the work.

The method of color measurement was detailed in the work. The suggestion of using one color parameter (ΔE) instead of three (L*a*b*) is valuable, but due to the specificity of the color of the yolk and LWE, the authors decided to leave the color parameters as L*a*b*. Most of the works on egg raw material are based on three color parameters, although in the next works the authors will consider the possibility of adding also the ΔE parameter.

A brief explanation of this issue was also completed in the work. CMF parameters were carefully selected based on numerous (but not always published) previous experiments. Information on this topic was also completed in the work. The double determination of the pH, not the triple one, was dictated by the minimal variability of this parameter. In many works, pH, but also temperature measurements, are performed in duplicate as being sufficiently accurate. Nevertheless, in the next works the authors will consider the possibility of unifying the number of repetitions for all determinations.

As suggested by the reviewer, an additional chapter "Discussion" was added, in which the most important aspects of our work were discussed in relation to the literature of other authors. Selected results in terms of their correlation with other factors were also included in the discussion. As suggested by the reviewer, the conclusions were changed and shortened to the most important ones. General considerations on the usefulness of the CMF method have been supplemented and included in other parts of the work. In connection with the supplemental text, citations of another 23 new papers were added to the total number of 39 papers. The citations of our earlier work in this context seem to be proportionate. The authors also attempted to standardize the cited literature.

Round 2

Reviewer 1 Report

Manuscript applsci-1086979 has an interesting topic and it contains valuable results.

After the revision the manuscript is well structured, research motivations and the novelties of study are clear. Authors have revised the manuscript according to reviewers’ comments and suggestions.

Amendments, rephrasing, corrections, additional information and references contributed to achieve a higher scientific quality of the manuscript and made it more clear and complete.

I accept all modifications and answers and recommend applsci-1086979 for publishing.

Author Response

The authors thank the reviewer for comments and help in improving the text. The final shape of the work was slightly changed at the request of reviewer 2, which should make it easier for the reader to perceive the figures, the number of which has been reduced. A fragment of the discussion concerning the so-called the effect of non-thermal inactivation of microorganisms was added. Two conclusions were also added (numbers 5 and 6).

Reviewer 2 Report

The authors made a great job for improve of the manuscript. However, they did not fulfill the main requirement after the first review. The main requirement is reduction of the number of figures and tables in the manuscript.

 

The author’s argument “papers in the field of food technology related to the optimization of technological processes (using RSM) it is not uncommon practice” does not stand up to criticism. Since average number of figures is 4-5 in the articles which the authors refer and in the other works in WoS (theme RSM in FOOD SCIENCE TECHNOLOGY).

Transfer most of the results to “supplementary materials”, leave only the most important results at the base of the article and combine several figures into one. This is desirable to do to do because a single graph in itself does not carry a lot of information, since it is built on 9 points.

 

Figures with “Pareto chart” can also be removed and replaced with one large table.

 

Make captions and numbers on figures comparable in size to the main text.

 

The authors added physical parameters of their device. This has certainly improved the understanding of the physical process in the experiment.

 

However, the authors continue to insist on the non-thermal phenomena of CMF processing: “It is worth noting that the thermal effect obtained from the use of microwave technology is parallel to the so-called CMF non-thermal effect in the process of microbial inactivation”.  I do not deny that there is a possibility of non-thermal effects of EMF in the gigahertz range. However, in order to obtain such effects, it is necessary to work with a power density <10-100 mW/cm2. With the specified power of 480 W and “inner dimensions of waveguide opening were 86.36 mm × 43.18 mm”, it is wrong to talk about non-thermal effects.

 

The efficiency of the pulsed mode at such powers does not indicate non-thermal effects, but only confirms the well-known thesis that value of the biological effects are not always proportional to tissue heating. It is important where the EMF energy is absorbed, next to DNA or other vital molecules and how quickly the local heating is leveled off.

 

The main thing is not said in the conclusion, which of the tested regimes turned out to be optimal from the point of view of preserving nutritional properties and from the point of view of protection against microorganisms.

 

Author Response

The authors thank the reviewer for the comments and help in improving the text. As suggested by the reviewer, all Pareto figures have been removed. Pareto coefficients are listed in the appropriate tables. The individual RSM charts were also deleted, leaving the most important ones. For each egg raw material, the 4 most important physical and rheological discriminants (as RSM diagrams) were selected and combined into three separate figures with 4 sub-diagrams each. As suggested by the reviewer, this will simplify the analysis of the results and facilitate the comparison of selected discriminants separately for egg white, yolk or liquid whole eggs.

At the end of the discussion, a part of text was added to try to explain the so-called non-thermal influence of microwave treatment on the inactivation of microorganisms. We hope that the reader will be able to form an opinion on other possible causes of microbial inactivation than thermal effects.

As suggested by the reviewer, at the end of the description of the results for egg white, yolk and LWE, general suggestions were added regarding the use of the best parameters of the microwave treatment process in the overall technological and consumer perspective. Conclusions 5 and 6 related to this issue have also been added.