Effect of Commercial and Autochthonous Bioprotective Cultures for Controlling Listeria monocytogenes Contamination of Pecorino Sardo Dolce PDO Cheese

Round 1

Reviewer 1 Report

The manuscript entitled ‘Effect of commercial and autochthonous bioprotective cultures for controlling Listeria monocytogenes contamination on Pecorino Sardo Dolce PDO cheese’ falls under the scope of the journal. However, it requires significant modifications before further processing. Kindly address the following comments:

General comments:

There is a need to work on grammatical mistakes.

The name of the bacterium in the title i.e., Listeria monocytogenes should be italic.

Specific comments

Abstract:

Line 15: Replace ‘chemical-physical characteristics’ with ‘physicochemical characteristics’.

Provide the full form of PDO.

Line 18-19: Reframe this sentence for better understanding.

Line 22: Do not start a sentence with a number. Rectify it.

Line 25: tested? or tests? Kindly check. Moreover, kindly check the number i.e., 0,3 or 0.3 and 1,8 or 1.8. What is the meaning of UFC/g? Correct it.

Line 26: Better to write ‘no previous study was’ instead of ‘no previous researches’.

 

Keywords: Avoid using the keywords which are already present in the title.

 

Introduction:

Line 49: The authors did not mention that L. monocytogenes is a Gram-positive bacterium found in spoiled milk and milk products. Amend this information.

Line 57: Apart from LAB, what are the other control measures used to mitigate contamination in such products? Kindly describe.

Line 58: Name a few antimicrobial compounds of LAB.

 

Materials and methods:

It has not been mentioned the quantity of procured milk. When was it procured? How was it procured and processed? Provide all this information. Overall, the methodology of the experiments is very confusing.

Line 83: From where the freeze-dried culture was purchased/procured. Provide the details.

Line 93: Provide the complete details about the location of cheese cheese-making plant.

Line 108: Provide the experimental conditions of the shelf life study.

Line 112-118: If the procedure is self-explanatory by the given figure, why the authors have repeated the same thing in the text? Better to provide this part as supplementary material.

Figure 1. Receiving raw sheep milk: Provide the quantity to be used in this study.

Table 3: Why comma has been used in the entire dataset instead of a decimal?

 This study lacks an important parameter i.e., texture analysis during the shelf life study, which is required in such products.

 

 

There is a requirement to thoroughly check the MS for grammatical errors.

Author Response

Dear reviewer, thanks for the useful comments and cues of reflection. The manuscript has been revised and english language revision was carried out by a native speaker. You can find the detailed response in the attached file.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors have delivered a relevant work for Listeria management. Different from most challenge studies, the L. monoocytogenes was inoculated already in the milk, then the cheese was made, and then the cheese was stored at different temperatures. Inclusion of the cheese making part is both a quality and a draw back in this work. On one hand, it gives information about early contamination, and a representative picture of the growth and survival in the interior of the cheese. It also makes it possible to include the adaptation process, if any, before storage. In the guidelines for challenge studies, the inoculation is done in ready made products, and this has been considered as a draw back in cases where the contamination is likely to occure at earlier stages. On the other hand, contamination of cheese is also likely to happen during maturation, and then the contamination will be on the rind. By inoculating at earlier steps, the effect of contamination on the surface will be less focused. Therefore, the design of the study is good for early stage contamination.

The study is well described, but some points need to be considered:

1.       The Listeria strains applied are reference strains or local strains. This is in line with the guidelines, but the reference strains are not among the recommended strains in the guidelines. Reference strains should be characterised for their ability to grow under the conditions in the food, in order to ensure that the measured growth rate is related to the food matrix and storage conditions rather than to an untypical strain with low growth rate. Such tests can be done in growth medium with adjusted pH and water activity, but with no added starter culture. If the strains have been used in other challenge studies, it is normally enough to refer to these works.

2.       The inoculation concentration was 100 cfu/ml, according to the description, but the concentration appear not to have been measured. This is a drawback, as the work is rather a study of inactivation than a study of growth. After “braking curd” and “curd schrinking” (Table 3), all samples are below the detection level for qualitative and quantitative analyses. It would be useful to do a parallel experiment with higher inoculation level to explore the survival effect in general, and the effect of starter cultures in particular. This would not be in conflict with the guidelines for challenge studies, as these guidelines are prepared for studies of growth, not for survival. A discussion of what the choice of inoculation level, in retrospect after seeing the results, would increase the quality of the paper.

3.       The authors conclude that the starter cultures reduces the end concentration of Listeria. I do not agree in this conclusion. The control cheeses without a starter culture and the the ones with starter cultures give the same results, so the contribution from starter culture compared to the contribution from other microbes in the cheese to supress growth of L. monocytogenes is not shown. On the contrary, the concentration of LAB before storage is as high or higher in the control cheeses as in the ones produced with starter culture. I do agree with the authors that use of starter cultures is a mean to increase the control of L.monocytogenes growth in general, but I can not see that it is proven from the reported data in this paper. That said, I agree that the use of starter cultures is proven not to have negative effects.

The authors are encouraged to assess the three points above.

Author Response

Dear reviewer, thanks for the useful comments and cues of reflection. The manuscript has been revised and english language revision was carried out by a native speaker. You can find the detailed response in the attached file.

Author Response File: Author Response.docx

Reviewer 3 Report

1. This is an interesting piece of work but it is limited in several respects.

2. The replication is limited. As a result, this is a feasibility study with positive results. The authors need to recognise and discuss this!

3. Bioprotective cultures are not novel, their use in cheese is not novel. This work while commercially relevant and important has limited scientific interest.

4. Will the authors make Lactobacillus delbrueckii 84 subsp. sunkii (LS) available so that its action can be investigated?

5. The main factor limiting the growth of listeria in most cheeses is the concentration of undissociated lactic acid. The authors have not provided the data on undissociated lactic acid. This should be provided and integrated into the discussion. 

 

Author Response

Dear reviewer, thanks for the useful comments and cues of reflection. The manuscript has been revised. You can find the detailed response in the attached file.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

All the comments have been addressed. It can be accepted now.