Use of Apple Pomace as Substrate for Production of Lactiplantibacillus plantarum Malolactic Starter Cultures

Round 1

Reviewer 1 Report

This article offers some interesting insights about the potential of utilizing an agro-industrial by-product as a low cost substrate for biomass production, particularly for two native strains of Lactiplantibacillus plantarum with oenological potential as starter cultures.

The manuscript is clear and scientifically sound, but it would be recommended to proofread the whole text, possibly by a native English speaker, as extensive polishing is necessary. Some very long phrases must be broken down in at least two sentences and rewritten, as the understanding is impaired in some cases. In particular, Lines 48-52, 53-58, 80-85.

Furthermore, there are some specific points to be addressed as suggested below:

1. You could use Lpb. plantarum as the abbreviation for Lactiplantibacillus plantarum, to differentiate from Lb. in the former classification, which is used now for the genus Lactobacillus.
2. In Lines 60-61, you mention that Lpb. plantarum can be inoculated in wine without previous acclimation, but then in Lines 75-76 it is said that acclimation is necessary. Do you already have results of your strains in comparison between acclimated and non-acclimated cultures in winemaking? Or do you plan carrying out new experiments in the future for this matter?
3. Could you please describe the preparation of the pre-inoculum for the trials? After activation of the frozen cultures in MRS for 48 h, how were the cells prepared for inoculation in the different media? Which inoculation rate?
4. In Lines 98-99, I did not understand what the authors mean by “For spectrophotometric determination, AP medium was centrifugated at 5000 g for 20 min and the clarified supernatant was used”. How can you measure cellular growth by OD after centrifuging the medium?
5. In Line 100, it is indicated that 1% w/v of yeast extract was used, while in Line 197 there is 0.5%. Also, it might be better to use sAP or mAP when referring to the supplemented AP, to avoid confusion with regular AP.
6. Why you did not use MRS at pH 4.5 for the synthetic wine trials?
7. In terms of biomass produced, did you measure the g/L of cells or CFU/mL that were obtained after the growth in AP or MRS? As you mention that the initial bacterial concentration is crucial for the success of fermentation, it would be necessary to know the maximum carrying capacity of the proposed medium, to evaluate its feasibility for starter production.
8. It is sometimes said in the literature that a population of 10⁶ cells/mL is necessary to perform MLF, but actually the studies regarding this claim are very scarce. Could you please include a broader discussion on this topic? It was interesting that even large populations of 10⁷ and 10⁸ cells/mL in your trials were not sufficient to complete the MLF, possibly due to a lack of acclimation as you suggested. You could also implement a discussion about the different behaviors in Merlot and Pinot Noir. Did you observe similar results before?

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors, the paper is fine and simple, but I repute that some more results should be produced in the sight of a revised version. For example, more cases to the dataset. The methodology has to be improved and the results will benefit from such additional analyses. For example a microbial control should have been employed, or some other experimental conditions. You could add some microbiological featuers, such as metabolites production. What if on applle pomace detrimental compounds are produced? More over you should revise the abstract, improve the introduction writing about the importance to conduct your study, give more details in regard.

Please find in the pdf some revisons that you should address in the revised version. 

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear, thanks for your revision. By my side the paper can now be accepted.