Effect of the Addition of Soy Beverage and Propionic Bacteria on Selected Quality Characteristics of Cow’s Milk Yoghurt Products

Round 1

Reviewer 1 Report

Overview and general recommendation:

The main objectives of the study were to analyze the effect of the addition of a soya beverage to cow’s milk in different proportions, and to evaluate selected quality parameters of the fermented yoghurt-type beverages obtained. The resulting milk, milk–soya and soya yoghurts displayed a pH value in the correct range and a stable bacterial population for 21 days during refrigerated storage. The article is well conceived. It contains all the necessary chapters.

The introduction is written correctly and provides enough data to understand the goal of the research.

The Material and methods are well explained. The methods are described correctly.

The results are presented in Tables, are logical and can be followed with understanding. The results are discussed with the results of similar studies.

Specific comments:

L 281 Table 1 shows the decrease in pH which was mostly gradual during storage of yoghurt beverages. How do you interpret the sudden drop in pH after 7 days of storage in soya beverage samples? Maybe I missed the interpretation.

In the part of material and methods please make a detailed explanation on formulation of yoghurt. What based different formulas?

Why the authors did not perform the sensory evaluation test of the product It is very important to judge the extent of consumer acceptance of the product

The conclusion section is very long, so please make it shorter and clearer

Comments for author File: Comments.pdf

Author Response

Author's Reply to the Review Report (Reviewer 1)

 

Authors response:

Thank you for performing a review of our manuscript. We appreciate the reviewer's helpful recommendations on how we can improve the presentation of our research. Below are our point-by-point responses and/or how we addressed the reviewer's recommendations in the revised manuscript.

 

Reviewer 1:

Overview and general recommendation:

The main objectives of the study were to analyze the effect of the addition of a soya beverage to cow’s milk in different proportions, and to evaluate selected quality parameters of the fermented yoghurt-type beverages obtained. The resulting milk, milk–soya and soya yoghurts displayed a pH value in the correct range and a stable bacterial population for 21 days during refrigerated storage. The article is well conceived. It contains all the necessary chapters.

The introduction is written correctly and provides enough data to understand the goal of the research.

The Material and methods are well explained. The methods are described correctly.

The results are presented in Tables, are logical and can be followed with understanding. The results are discussed with the results of similar studies.

Authors response:

We appreciate the reviewer for these heartening comment.

 

Reviewer 1:

Specific comments:

L 281 Table 1 shows the decrease in pH which was mostly gradual during storage of yoghurt beverages. How do you interpret the sudden drop in pH after 7 days of storage in soya beverage samples? Maybe I missed the interpretation.

Authors response:

We thank the reviewer for the suggestion. The pH value of soya beverage fermented by yoghurt bacteria increased during the first 7 days of cold storage and then began to decrease to a level statistically comparable to time "0". During fermentation, lactose (milk sugar) is converted into lactic acid by yoghurt bacteria, lowering the pH values of the fermented beverages, but during refrigerated storage of yoghurt products the pH can change in both directions: decrease or slightly increase. Other researchers have also observed such changes in the pH of yoghurts (see: Hilal Colakoglu and Oguz Gursoy. Effect of lactic adjunct cultures on conjugated linoleic acid (CLA) concentration of yogurt drink. J. Food. Agricult. Environ. 2011, 9, 60-64). Unfortunately, very often researchers do not comment on these changes and do not look for scientific justification for them. In our opinion, these changes may be caused by the varying buffering capacity of the yoghurt products and, therefore, both the transformation of the protein fraction and the acid profile, which is a result of both acidifying and enzymatic activities of the yoghurt bacteria still present under the refrigerated storage conditions of the beverage samples. The proteolytic activity of yoghurt bacteria during refrigerated storage of yoghurt samples is found in researchers' studies (see: O. Ben Moussa M. Boulares, M. Chouaibi, M. Mzoughi and M. Hassouna. Effects of lactulose levels on yoghurt properties. Ital. J. Food Sci. 2019, 31, 782-799). We presume that in the case of our samples, already after the completion of the actual fermentation of the soya beverage by the yoghurt bacteria, the postacidification changes were not fully stopped and only after 7 or more days of sample storage was the pH stabilized. We do not know the reason only in these yoghurt product samples this phenomenon has been observed. Unfortunately, we did not conduct detailed research in this direction, so we do not wish to elaborate on this topic in the manuscript. We have therefore added the following comment to the manuscript:

“It is worth noting the pH value of the soya beverage fermented by yoghurt bacteria, which increased during the first seven days of storage the yoghurt product samples at low temperature and then began to decrease to a level statistically comparable to the time immediately after fermentation. Such changes in the pH of yoghurt products are the result of the post-fermentation changes (resulting in different buffering capacity of samples due to changes in the protein fraction and acid content), which have not been completely stopped after the end of fermentation and continued during the first week of cold storage of the samples.”

 

Reviewer 1:

In the part of material and methods please make a detailed explanation on formulation of yoghurt. What based different formulas?

Authors response:

We appreciate the reviewer for the suggestion. To make the yoghurt recipes clearer, we have prepared a tabular summary of the sample layout in the Materials and Methods section (Table 1):

Beverages received	Variants 1: yoghurt bacteria fermented beverages	Variants 2: yoghurt and propionic bacteria (1:1) fermented beverages	Variants 3: propionic bacteria fermented beverages
cow's milk	x	x	x
milk–soya (2:1)	x	x	x
milk–soya (1:1)	x	x	x
milk–soya (1:2)	x	x	x
soya beverage	x	x	x

For this reason, we have renumbered further tables in the manuscript.

 

Reviewer 1:

Why the authors did not perform the sensory evaluation test of the product It is very important to judge the extent of consumer acceptance of the product

Authors response:

The reviewer's comment is true. Sensory evaluation of a product is especially important for assessing consumer acceptance. To conduct such an evaluation would have required us to use larger quantities of raw materials and materials, as well as to pay for an application to the university's ethics committee agreeing to conduct tests with human subjects. Unfortunately, the financial budget allocated to our research did not allow us to conduct such an evaluation, or even an organoleptic evaluation, and to prepare a proposal to the university ethics committee.

However, some of us are vegetarians and semivegans who have organoleptically tasted the resulting fermented beverages themselves. In our subjective opinion, fermented soya beverages are more organoleptically appealing than non-fermented soya beverage. The fermented mixtures of cow's milk and soya beverage also had interesting organoleptic characteristics, especially flavor. These would be good products for promoting these functional beverages by people consuming fermented milk beverages. The addition of propionic bacteria did not impair the organoleptic characteristics of the functional cow's milk and soya beverages obtained, and certainly improved their nutritional value. We did not mention this in the manuscript due to the lack of an opinion from the university's ethics committee.

It is very possible that in the future we will continue our research on the obtained fermented beverages with organoleptic evaluation, as well as the determination of nutritional parameters (e.g., B vitamin levels and protein digestibility).

We have added the following sentences at the end of the manuscript:

“The research results presented do not exhaust the research scope of scientific or applied interest. For the development of new products, sensory or organoleptic evaluation is extremely important. In this research, such an evaluation has not been conducted. Although there are indications that the addition of propionic bacteria did not impair the organoleptic characteristics of the functional milk, milk-soy and soy fermented yoghurt products obtained in these studies and improved their nutritional value. For the future, it is necessary to continue this research in terms of organoleptic evaluation, as well as the nutritional parameters (e.g., B vitamin levels and protein digestibility).”

 

Reviewer 1:

The conclusion section is very long, so please make it shorter and clearer

Authors response:

We appreciate the reviewer for the suggestion, we have shortened this part of the manuscript and simplified the text. the current version is as follows:

“This work, to the authors' knowledge, represents one of the only studies on the use of P. freudenreichii for the fermentation of milk or its mixture with soya beverage to produce yoghurt products. It is possible to obtain various functional yoghurt products based on cow's milk, as well as a milk–soya blend, using a mixture of yoghurt and propionic starter cultures. The use of propionic bacteria requires a longer fermentation time and a slightly higher process temperature. It was possible to demonstrate that the use of lactic acid bacteria in the form of a yoghurt starter culture, a yoghurt starter in combination with propionic bacteria, as well as a propionic bacteria starter culture alone, maintains the correct pH in in cow’s milk, milk–soya and soya yoghurt products during 21 days of refrigerated storage. The survival rate of S. thermophilus, L. delbrueckii subsp. bulgaricus and P. freudenreichii in yoghurt products depends on the type of starter used and changes during storage. The use of propionic acid fermentation bacteria allows the full attenuation of glucose, stachyose and verbascose in soya yoghurts. However, refrigerated storage time, as well as the type of starter used, do significantly determine the quality characteristics of milk, milk–soya and soya yoghurt products such as firmness, adhesiveness, and water-holding capacity.”

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript is interesting. The use of soybeans in the manufacture of yogurt is known. The authors attempted to innovate soy yoghurt by the addition of appropriate strains. 

I have a few comments:

1.In the introduction, we should describe the relevance of the study in more detail.

2. Addition of literature references to the methodology.

3.Remove spaces from tables.

Author Response

Author's Reply to the Review Report (Reviewer 2)

 

Reviewer 2:

The manuscript is interesting. The use of soybeans in the manufacture of yogurt is known. The authors attempted to innovate soy yoghurt by the addition of appropriate strains. 

Authors response:

Thank you for performing a review of our manuscript. We appreciate the reviewer's helpful recommendations on how we can improve the presentation of our research. Below are our point-by-point responses and/or how we addressed the reviewer's recommendations in the revised manuscript.

 

Reviewer 2:

I have a few comments:

1.In the introduction, we should describe the relevance of the study in more detail.

Authors response:

We appreciate the reviewer for the suggestion, we have added our commentary to the presented research objective to emphasize the relevance of the study. The current version is as follows:

“Therefore, the aim of the study was to evaluate the effect of the addition of a soy beverage and the application of propionic bacteria on selected quality characteristics of cow’s milk yoghurt products. This will open the possibility of producing innovative functional dairy yoghurt products with plant-based ingredients, such as soya beverages with symbiotic lactic acid bacteria and propionic acid bacteria.”

 

Reviewer 2:

2. Addition of literature references to the methodology.

Authors response:

We would like to thank the reviewer for this suggestion, this suggestion has been considered in the individual methodology points in the manuscript.

 

Reviewer 2:

3.Remove spaces from tables.

Authors response:

Done, we have removed all spaces from tables.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Review of the article applsci-2080463-peer-review-v1

Effect of the addition of soy beverage and propionic bacteria on selected quality characteristics of cow's milk set–type yoghurts

The article is very well written, both scientifically and linguistically. Only minor corrections need to be made:

1) The terms "fermented beverage" and "set-type yoghurt" are used interchangeably and are often used together, as "set-type yoghurt beverage". However, the first term means drinkable product, while the second is soft solid or spoonable product. The differentiation between beverage and set type could possibly be made according to the measured hardness: low for the former, high for the latter. Nevertheless, I recommend using a single term for all samples: fermented product, yoghurt product or yoghurt, even in the title of the article.

2) The text should be written in the third person passive voice and not in the first person active voice (delete 26 “we” and “our”).

3) Line 132: Instead of “textrometer”, write “texturometer”.

4) Line 150-151: Instead of “x g”, write “× g” (symbol × and g in italics).

5) Line 155: Instead of “* 100%”, write “× 100%”.

6) Line 171: Write “thermophilus” in italics.

7) Line 178-181: Write “Enterobacteriaceae” in italics (twice).

8) Line 194: Instead of “x g”, write “× g”.

9) Line 253: Delete “and standard deviations”.

10) Line 412: Instead of “yogurt”, write “yoghurt”.

11) Line 444: Write “Enterobacteriaceae” in italics.

12) Organoleptic (sensory) evaluation is missing, which is very important for a new food product. At the end of the conclusions, this should be highlighted as a suggestion for future research.

Comments for author File: Comments.pdf

Author Response

Author's Reply to the Review Report (Reviewer 3)

 

Reviewer 3:

Review of the article applsci-2080463-peer-review-v1

Effect of the addition of soy beverage and propionic bacteria on selected quality characteristics of cow's milk set–type yoghurts

Authors response:

Thank you for performing a review of our manuscript. We appreciate the reviewer's helpful recommendations on how we can improve the presentation of our research. Below are our point-by-point responses and/or how we addressed the reviewer's recommendations in the revised manuscript.

 

Reviewer 3:

The article is very well written, both scientifically and linguistically. Only minor corrections need to be made:

1) The terms "fermented beverage" and "set-type yoghurt" are used interchangeably and are often used together, as "set-type yoghurt beverage". However, the first term means drinkable product, while the second is soft solid or spoonable product. The differentiation between beverage and set type could possibly be made according to the measured hardness: low for the former, high for the latter. Nevertheless, I recommend using a single term for all samples: fermented product, yoghurt product or yoghurt, even in the title of the article.

Authors response:

We thank the reviewer for the suggestion, this suggestion has been incorporated throughout in the manuscript. We have chosen to use the term 'yoghurt products ' suggesting that they are yoghurt-type products. We introduced this term in the title of the manuscript, the abstract and the entire manuscript.

 

Reviewer 3:

2) The text should be written in the third person passive voice and not in the first person active voice (delete 26 “we” and “our”).

Authors response:

We have made these corrections in our manuscript: we changed “we” and “our” to the third person passive voice.

 

Reviewer 3:

3) Line 132: Instead of “textrometer”, write “texturometer”.

4) Line 150-151: Instead of “x g”, write “× g” (symbol × and g in italics).

5) Line 155: Instead of “* 100%”, write “× 100%”.

6) Line 171: Write “thermophilus” in italics.

7) Line 178-181: Write “Enterobacteriaceae” in italics (twice).

8) Line 194: Instead of “x g”, write “× g”.

9) Line 253: Delete “and standard deviations”.

10) Line 412: Instead of “yogurt”, write “yoghurt”.

11) Line 444: Write “Enterobacteriaceae” in italics.

Authors response:

We appreciate the reviewer for the suggestion, we have made these corrections in the manuscript.

 

Reviewer 3:

12) Organoleptic (sensory) evaluation is missing, which is very important for a new food product. At the end of the conclusions, this should be highlighted as a suggestion for future research.

Authors response:

The reviewer's comment is true. Sensory evaluation of a product is particularly important for assessing consumer acceptance. To conduct such an evaluation would have required us to use larger quantities of raw materials and materials, as well as to pay for an application to the university's ethics committee agreeing to conduct tests with human subjects. Unfortunately, the financial budget allocated to our research did not allow us to conduct such an evaluation, or even an organoleptic evaluation, and to prepare a proposal to the university ethics committee.

However, some of us are vegetarians and semivegans who have organoleptically tasted the resulting fermented beverages themselves. In our subjective opinion, fermented soya beverages are more organoleptically appealing than non-fermented soya beverage. The fermented mixtures of cow's milk and soya beverage also had interesting organoleptic characteristics, especially flavor. These would be good products for promoting these functional beverages by people consuming fermented milk beverages. The addition of propionic bacteria did not impair the organoleptic characteristics of the functional cow's milk and soya beverages obtained, and certainly improved their nutritional value. We did not mention this in the manuscript due to the lack of an opinion from the university's ethics committee.

It is very possible that in the future we will continue our research on the obtained fermented beverages with organoleptic evaluation, as well as the determination of nutritional parameters (e.g., B vitamin levels and protein digestibility).

Regarding the conclusions in the manuscript, we have added the following sentences at the end: “The research results presented do not exhaust the research scope of scientific or applied interest. For the development of new products, sensory or organoleptic evaluation is extremely important. In this research, such an evaluation has not been conducted. Although there are indications that the addition of propionic bacteria did not impair the organoleptic characteristics of the functional milk, milk-soy and soy fermented yoghurt products obtained in these studies and improved their nutritional value. For the future, it is necessary to continue this research in terms of organoleptic evaluation, as well as the nutritional parameters (e.g., B vitamin levels and protein digestibility).”

 

Author Response File: Author Response.pdf