Sheep’s and Goat’s Frozen Yoghurts Produced with Ultrafiltrated Whey Concentrates
Round 1
Reviewer 1 Report
Despite the effort made by the authors to write the manuscript, due to numerous shortcomings, the manuscript cannot be published in this form and requires major revision.
Section - Introduction
It is far too long and needs to be shortened.
Line 37: please explain the abbreviation BOD and COD
Table 1: Why were guar and xanthan gum added in the production of the frozen dessert? I know that only in the experimental ice cream the addition of inulin was used; however, xanthan gum and guar gum were used in all products. Since there may be an interaction between these 3 stabilizers, the effect may be to increase the stabilizing properties of the emulsion. It seems reasonable to mention this issue in the submitted manuscript. Part of the discussion regarding the effect of inulin on ice cream stabilization, melting, etc., in my opinion, is speculation.
In the methods section - information on statistical analysis is missing. The authors probably show standard deviation, median or another parameter in the figures—however, each time, the reader has to wonder what the author had in mind.
The results presentation is correct. However, to increase the readability of the manuscript, I suggest combining this section with the discussion.
Discussion section:
First of all, it should explain why the authors obtained such findings. Discussion is that place in a publication where the authors should propose some mechanism to explain a phenomenon. Unfortunately, the authors very often focused only on comparing their results with others. In the discussion, the authors should also refer to all the research results presented in the publication.
You describe the effect of the addition of xanthan gum on the creaminess or sensory evaluation of the frozen yogurt. However, the methodology says that a different inulin additive was used to make the products. In my opinion, this discussion should be about the effect of inulin on sensory evaluation results and not about xanthan gum. It is often unclear who is results are meant, whether the authors of the manuscript or the authors of the cited publication (e.g., line 453-457). Line 472-478: Since DVS, encapsulated or immobilized cultures activity differ significantly, their uncritical comparison leads to erroneous conclusions.
Author Response
We have carefully read the comments and I am enclosing a list of our responses to the reviewer´s comments.
REVIEWER 1
Despite the effort made by the authors to write the manuscript, due to numerous shortcomings, the manuscript cannot be published in this form and requires major revision.
Section - Introduction
It is far too long and needs to be shortened.
We agree. Most of the information present in the introduction was transferred to the discussion.
In order to clarify the manuscript and to avoid repetitions, Introduction section has been reorganised and shortened.
Line 37: please explain the abbreviation BOD and COD
The abbreviations have been explained. Please see lines 36-37.
Table 1: Why were guar and xanthan gum added in the production of the frozen dessert? I know that only in the experimental ice cream the addition of inulin was used; however, xanthan gum and guar gum were used in all products. Since there may be an interaction between these 3 stabilizers, the effect may be to increase the stabilizing properties of the emulsion. It seems reasonable to mention this issue in the submitted manuscript. Part of the discussion regarding the effect of inulin on ice cream stabilization, melting, etc., in my opinion, is speculation.
Guar and xanthan gums were added in order to perform their functions with regard to the stabilization of the ice cream and avoidance of ice crystals growth. Inulin was added in order to evaluate its performance concerning body and texture of ice-cream formulations and as a prebiotic. In fact, all 3 ingredients may interact with each other in order to improve the stability of the emulsion. However, in the present work this feature was not evaluated.
The discussion was changed in order to avoid speculative sentences. The information regarding the effect of stabilizers derives from the literature revision and not from our experiments.
In the methods section - information on statistical analysis is missing. The authors probably show standard deviation, median or another parameter in the figures—however, each time, the reader has to wonder what the author had in mind.
It was a mistake. Statistical information is now included (lines 219-221). The meaning of data is indicated on top of the figures.
The results presentation is correct. However, to increase the readability of the manuscript, I suggest combining this section with the discussion.
Results and discussion sections were combined.
Discussion section:
First of all, it should explain why the authors obtained such findings.
We have tried to clarify the presentation of results.
Discussion is that place in a publication where the authors should propose some mechanism to explain a phenomenon. Unfortunately, the authors very often focused only on comparing their results with others. In the discussion, the authors should also refer to all the research results presented in the publication.
Possible explanations for the findings were included and, when possible, results obtained by other researchers were compared to ours.
You describe the effect of the addition of xanthan gum on the creaminess or sensory evaluation of the frozen yogurt. However, the methodology says that a different inulin additive was used to make the products. In my opinion, this discussion should be about the effect of inulin on sensory evaluation results and not about xanthan gum.
This information was derived from the literature review (Soukoulis & Tzia, 2008).
It is often unclear who is results are meant, whether the authors of the manuscript or the authors of the cited publication (e.g., line 453-457).
The sentence was changed in order to clarify that the results mentioned are from the references indicated. The idea was to indicate these strategies as ways to improve the nutritional and sensory characteristics of UF concentrated whey frozen yoghurts. Please see from line 370.
Line 472-478: Since DVS, encapsulated or immobilized cultures activity differ significantly, their uncritical comparison leads to erroneous conclusions
In order to clarify the manuscript, we have deleted some references related to encapsulated cultures and we have modified a sentence related to these results (line 399).
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript entitled “Sheep’s and goat’s frozen yoghurts produced with ultrafiltrated whey concentrates” aims to evaluate the possibility of using goat’s and sheep’s cheese whey concentrated by ultrafiltration for the production of frozen yoghurts with or without different concentrations of inulin.
The originality and relevance of this study consist in the fact that there are no studies about the production of frozen yoghurts with goat’s and sheep’s liquid whey protein concentrates which have applications as functional products. Moreover, these products are an interesting alternative for the utilization of whey, a major by-product from the manufacture of cheese.
L161: Correct word “yogurst”.
L164-166: If possible, please describe the physicochemical parameters (chemical composition, pH value) of the used whey types.
L190-192: I suggest adding information on the producers of the ingredients used.
L196: What was the temperature of the freezing process?
L197: What type of packaging was used?
L212-218: How many repetitions were performed to measure pH and determine titratable acidity?
L242, 249: How many repetitions were performed to measure overrun and meltdown rate?
L264-271: “Consumer preference tests were conducted (…) within 6 days of storage” tests of yoghurts or frozen yoghurts? Why was sensory evaluation not performed at 1, 7, 14, and 21 days of frozen yoghurt storage? Please cite the sensory evaluation method.
L272: There is a lack of information on the statistical analysis methods used. What are statistical analysis methods used in this study?
L315: On what date was the chemical composition of the frozen yoghurts analyzed? Was it the 21st day of storage?
L328: Were the other samples refrigerated under different conditions, in different flasks? It is not clear.
L348: Why overrun and meltdown rate was only tested immediately after production?
L353: On what date were the color parameters of the frozen yoghurts analyzed? Was it the 21st day of storage? Why was this analysis not performed at 1, 7, 14, and 21 days of frozen yoghurt storage?
L408: The title of Figure 8 informs about the evaluation on the date of production. Line 264 states that the yoghurts were evaluated within 6 days of production. It is not clear. Please correct.
Author Response
The manuscript entitled “Sheep’s and goat’s frozen yoghurts produced with ultrafiltrated whey concentrates” aims to evaluate the possibility of using goat’s and sheep’s cheese whey concentrated by ultrafiltration for the production of frozen yoghurts with or without different concentrations of inulin.
The originality and relevance of this study consist in the fact that there are no studies about the production of frozen yoghurts with goat’s and sheep’s liquid whey protein concentrates which have applications as functional products. Moreover, these products are an interesting alternative for the utilization of whey, a major by-product from the manufacture of cheese.
L161: Correct word “yogurst”.
The word “yogurst” has been changed by “yoghurt” (now, line 82).
L164-166: If possible, please describe the physicochemical parameters (chemical composition, pH value) of the used whey types.
The physicochemical parameters of the used whey types have been described. Please see lines 230-231 and 291-292.
L190-192: I suggest adding information on the producers of the ingredients used.
We have added this information. Please see table 1 footnotes.
L196: What was the temperature of the freezing process?
As the referee suggests, we have added the sentence “Immediately after freezing, the temperature of frozen yoghurts was -6 ± 1 ºC”.. Please see line 121.
L197: What type of packaging was used?
The packaging was polypropylene boxes. It has been indicated in the text. Please see line 122.
L212-218: How many repetitions were performed to measure pH and determine titratable acidity?
Three repetitions were made. It has been added in the text. Please see line 145.
L242, 249: How many repetitions were performed to measure overrun and meltdown rate?
Three repetitions were made. It has been added in the text. Please see lines 186 and 193.
L264-271: “Consumer preference tests were conducted (…) within 6 days of storage” tests of yoghurts or frozen yoghurts? Why was sensory evaluation not performed at 1, 7, 14, and 21 days of frozen yoghurt storage? Please cite the sensory evaluation method.
Due to the limitations imposed by the amount of work to be performed in the experimental work, and due to the restrictions resulting from the Covid epidemy, it was decided to perform just one sensory test session. Since frozen yoghurts are conventionally consumed immediately after production or within a short storage period, it was decided to perform the test by the end of the first week of storage.
L272: There is a lack of information on the statistical analysis methods used. What are statistical analysis methods used in this study?
This was a mistake. Statistical information is now included. Please see lines 219-221.
L315: On what date was the chemical composition of the frozen yoghurts analyzed? Was it the 21st day of storage?
No. Frozen yoghurts were analyzed at the first day after production, exception made to overrun and meltdown rate that were performed immediately after freezing.
L328: Were the other samples refrigerated under different conditions, in different flasks? It is not clear.
No. All samples were refrigerated under the same conditions. We just wanted to emphasize that, although the target pH to stop fermentation was 4.5, microorganism’s activity was maintained during the cooling period, what led to pH values below 4.2 at day 1.
L348: Why overrun and meltdown rate was only tested immediately after production?
As referred, frozen yoghurts are normally served in a short period after freezing. Besides, immediately after freezing, the temperature of frozen yoghurts (-6 ± 1 ºC) allowed to perform the test without affecting significantly its structure. Over storage at - 21 ºC, the hardness of frozen yoghurts increased significantly and did not allow to perform the test without affecting significantly the structure. It was impossible to adequately measure the desired volume of frozen yoghurts in order to compare their weight with the one of the unfrozen yoghurt.
L353: On what date were the color parameters of the frozen yoghurts analyzed? Was it the 21st day of storage? Why was this analysis not performed at 1, 7, 14, and 21 days of frozen yoghurt storage?
Although the color parameters have been evaluated alongside the storage period, we decided to present the results obtained at the first day of storage in order to avoid excess of information. It must be mentioned that these values did not change significantly over storage and particularly between the first and 7th days of storage, when they were submitted to sensory evaluation.
L408: The title of Figure 8 informs about the evaluation on the date of production. Line 264 states that the yoghurts were evaluated within 6 days of production. It is not clear. Please correct.
It was an mistake. The legend of Fig.8 was corrected.
Author Response File: Author Response.docx
Reviewer 3 Report
It is good work!
Only a few grammar or other mistake can be found. The aims are clear, used reasearch plan and selected methods ar excellent.
I have only a few comment.
line 38: not tones but tons.
line 69-70: suggested sentence: Fermentation of lactose produces lactic acid, which acts on milk protein giving the texture and characteristics of yogurt.
Line 83: What does it mean:"residual taste"? Aftertaste?
Bigger pattern could be used for better identification of samples in some figures e.g. Fig. 1, 3, 4, 5, 6, 7.
Stronger axis lines and curve lines had to be used in Fig 2. improving the visibility.
line 309-312: If the samples were average samples and were homogenized, this explanation may be false partially.. I suggest taking into account the composition of the original whey and the properties of the components. For example the higher fat content of goat LWC (and yogurt.. and frozen yogurt) is coming from the higher whey fat content, considering same volume reduction rate... Furthermore, higher fat content of goat cheese whey resulted due to the significantly smaller goat milk fat globule size.
Difference in protein content of LWC-s can com from the different original protein content of wheys and teh different protein composition of goat milk. I suggest to give the composition of goat's and ewe's whey.
I suggest the evaluation of color stimulus difference, (not only the color coordinates) 'cause it can help the evaluation of sensory propeties in case of colour.
What is the reason of significant difference between the melting rate of 2.5 and 5% added inulin in goat LWC frozen yogurt samples?
After minor revision I suggest to publish this article.
Author Response
The manuscript entitled “Sheep’s and goat’s frozen yoghurts produced with ultrafiltrated whey concentrates” aims to evaluate the possibility of using goat’s and sheep’s cheese whey concentrated by ultrafiltration for the production of frozen yoghurts with or without different concentrations of inulin.
The originality and relevance of this study consist in the fact that there are no studies about the production of frozen yoghurts with goat’s and sheep’s liquid whey protein concentrates which have applications as functional products. Moreover, these products are an interesting alternative for the utilization of whey, a major by-product from the manufacture of cheese.
L161: Correct word “yogurst”.
The word “yogurst” has been changed by “yoghurt” (now, line 82).
L164-166: If possible, please describe the physicochemical parameters (chemical composition, pH value) of the used whey types.
The physicochemical parameters of the used whey types have been described. Please see lines 230-231 and 291-292.
L190-192: I suggest adding information on the producers of the ingredients used.
We have added this information. Please see table 1 footnotes.
L196: What was the temperature of the freezing process?
As the referee suggests, we have added the sentence “Immediately after freezing, the temperature of frozen yoghurts was -6 ± 1 ºC”.. Please see line 121.
L197: What type of packaging was used?
The packaging was polypropylene boxes. It has been indicated in the text. Please see line 122.
L212-218: How many repetitions were performed to measure pH and determine titratable acidity?
Three repetitions were made. It has been added in the text. Please see line 145.
L242, 249: How many repetitions were performed to measure overrun and meltdown rate?
Three repetitions were made. It has been added in the text. Please see lines 186 and 193.
L264-271: “Consumer preference tests were conducted (…) within 6 days of storage” tests of yoghurts or frozen yoghurts? Why was sensory evaluation not performed at 1, 7, 14, and 21 days of frozen yoghurt storage? Please cite the sensory evaluation method.
Due to the limitations imposed by the amount of work to be performed in the experimental work, and due to the restrictions resulting from the Covid epidemy, it was decided to perform just one sensory test session. Since frozen yoghurts are conventionally consumed immediately after production or within a short storage period, it was decided to perform the test by the end of the first week of storage.
L272: There is a lack of information on the statistical analysis methods used. What are statistical analysis methods used in this study?
This was a mistake. Statistical information is now included. Please see lines 219-221.
L315: On what date was the chemical composition of the frozen yoghurts analyzed? Was it the 21st day of storage?
No. Frozen yoghurts were analyzed at the first day after production, exception made to overrun and meltdown rate that were performed immediately after freezing.
L328: Were the other samples refrigerated under different conditions, in different flasks? It is not clear.
No. All samples were refrigerated under the same conditions. We just wanted to emphasize that, although the target pH to stop fermentation was 4.5, microorganism’s activity was maintained during the cooling period, what led to pH values below 4.2 at day 1.
L348: Why overrun and meltdown rate was only tested immediately after production?
As referred, frozen yoghurts are normally served in a short period after freezing. Besides, immediately after freezing, the temperature of frozen yoghurts (-6 ± 1 ºC) allowed to perform the test without affecting significantly its structure. Over storage at - 21 ºC, the hardness of frozen yoghurts increased significantly and did not allow to perform the test without affecting significantly the structure. It was impossible to adequately measure the desired volume of frozen yoghurts in order to compare their weight with the one of the unfrozen yoghurt.
L353: On what date were the color parameters of the frozen yoghurts analyzed? Was it the 21st day of storage? Why was this analysis not performed at 1, 7, 14, and 21 days of frozen yoghurt storage?
Although the color parameters have been evaluated alongside the storage period, we decided to present the results obtained at the first day of storage in order to avoid excess of information. It must be mentioned that these values did not change significantly over storage and particularly between the first and 7th days of storage, when they were submitted to sensory evaluation.
L408: The title of Figure 8 informs about the evaluation on the date of production. Line 264 states that the yoghurts were evaluated within 6 days of production. It is not clear. Please correct.
It was an mistake. The legend of Fig.8 was corrected.
Reviewer 4 Report
Review ID: applsci-1258419
The reviewed Ms ID: applsci-1258419 (Sheep’s and goat’s frozen yoghurts produced with ultrafiltrated whey concentrates) is quite interesting and contributes to update the literature with information on the possibility of producing new yoghurt-type products and processing surplus whey production. Manuscript is really good organized. The experiment had been good planned and executed. Authors have obtained very interesting results, which are presented generally, in a clear and transparent way.
Unfortunately, I have some major and minor objections to this work. The most urgent is that no information on statistical analysis is provided in the paper, so the validity of the results obtained cannot be verified.
Main comments
- Introduction is valuable but too protracted: please condense and simplify so as to inform the reader of current research findings in this area and demonstrate the novelty of the experiment undertaken. Much of the information presented can be used later in the discussion.
- The authors need to supplement the Materials and methods chapter with a comprehensive statistical section.
Other remarks
L205-206: please insert reference for ash content determination
L215-216: please provide condition of pH calibration
L220-222: please provide a complete methodology (sampling, an illuminant, observer, area of viewing aperture) with appropriate literature method
L237-241: texture parameters should be listed and described
L261: the dilution must be precisely stated
L263: please provide appropriate reference for sensory analysis
The significant differences should be included in figures.
Fig. 4 there is lack of results for ash
Author Response
The reviewed Ms ID: applsci-1258419 (Sheep’s and goat’s frozen yoghurts produced with ultrafiltrated whey concentrates) is quite interesting and contributes to update the literature with information on the possibility of producing new yoghurt-type products and processing surplus whey production. Manuscript is really good organized. The experiment had been good planned and executed. Authors have obtained very interesting results, which are presented generally, in a clear and transparent way.
Unfortunately, I have some major and minor objections to this work. The most urgent is that no information on statistical analysis is provided in the paper, so the validity of the results obtained cannot be verified.
Main comments
- Introduction is valuable but too protracted: please condense and simplify so as to inform the reader of current research findings in this area and demonstrate the novelty of the experiment undertaken. Much of the information presented can be used later in the discussion.
- The authors need to supplement the Materials and methods chapter with a comprehensive statistical section.
We have modified the manuscript as the referee indicated. Introduction has been condensed. Statistical information is now included (lines 219-221). On top of figures are indicated the meaning of data. It was also introduced in the legends of the figures.
Other remarks
L205-206: please insert reference for ash content determination.
It has been added the reference. Please, see line 132.
L215-216: please provide condition of pH calibration
It has been corrected as proposed. Please, see lines 141-142.
L220-222: please provide a complete methodology (sampling, an illuminant, observer, area of viewing aperture) with appropriate literature method.
It has been corrected as proposed. Please, see lines 149-151.
L237-241: texture parameters should be listed and described.
It has been corrected as proposed. A reference was added (line 181).
Phadungath, C. Basic measurement for food texture. Texture Technologies Corp - Texture Profile Analysis. 2010. Retrieved from https://texturetechnologies.com/resources/texture-profile-analysis
L261: the dilution must be precisely stated.
It has been corrected as proposed. All 3 dilutions were inoculated in triplicate. Please, see line 202.
L263: please provide appropriate reference for sensory analysis
A reference on affective tests was included. Please, see line 208.
Stone H., Sidel J. Sensory Evaluation Practices (3dEdition). Food Science and Technology. 2004, 247-277. New York. Academic Press.
The significant differences should be included in figures.
It has been corrected in all figures when appropriate.
Fig. 4 there is lack of results for ash
It has been corrected.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The revised manuscript is much more readable and interesting. However, in my opinion, repeating the experiment in another laboratory does not guarantee the same results. The main problem of the manuscript is the statistical interpretation of the results. From the description, the reader knows that the experiment was performed only once and each analysis was performed three times, i.e., for each analysis n=3. To apply parametric tests (e.g., One-way ANOVA, Tukey HSD), the distribution of results must be normal. The statistical program will count everything, but does the obtained p-value mean that the results are significantly different from each other? Otherwise, non-parametric tests should be used. Therefore, please provide the exact procedure for selecting statistical tests.
Author Response
Please find attached our responses to reviewers. Thank you for your valuable comments and suggestions.
Author Response File: Author Response.docx
Reviewer 4 Report
This is the second review of Ms ID: applsci-1258419 (Sheep’s and goat’s frozen yoghurts produced with ultrafiltrated whey concentrates). In all honesty I must say that authors have improved the manuscript as well as they could, taking into account almost all my comments and suggestions. Unfortunately, there is a one objection (see previous review, Main comments, second point) to be explained at length, because authors answer was, however, unsatisfactory. The data/results presented in figures and tables indicate on one, two or three factors (species, products (species and inulin), and storage). Therefore the statistical analysis should include a detailed description of each together with interactions. These analyses are necessary to ensure appropriate discussion and inference.
Other remarks
Dry matter should be replace with ‘total solids’ (see L128) throughout the text
L68-69 & L212-213: one sentence in not a paragraph
L91 & L93: bar and MPa, is it possible to unify pressure units?
L198: section 2.4. remains unchanged; the dilution must be precisely stated, Values -5, -6 and -7 are misleading, please use ‘serial decimal dilutions (1:10)’ or ‘serial 10-fold dilutions’ or 10-fold, 100-fold etc. or 10-3, 10-4, etc.
L311: the L* is lightness or darkness of any color (not whiteness), please do not confuse the terms
Author Response
Please find attached our responses to reviewers. Thank you for your valuable comments and suggestions.
Author Response File: Author Response.docx
Round 3
Reviewer 4 Report
The authors in the second round of review took into account all comments and suggestions so I do not raise any objections to the presented results. Best regards
