A Critical Review on the Role of Lactic Acid Bacteria in Sourdough Nutritional Quality: Mechanisms, Potential, and Challenges

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript presents a detailed and scientifically rich review of the nutritional impacts of lactic acid bacteria in sourdough fermentation. It critically synthesizes current knowledge on how LAB modulates cereal matrix properties, improves bioavailability of nutrients, generates bioactive compounds, and influences glycemic response, with emphasis on both mechanistic understanding and translational challenges. The topic is highly relevant for both academic research and functional food development. However, despite its strengths, several core issues and technical areas require revision to enhance clarity, thoroughness, and impact.

 

Here are my detailed comments and suggestions:

1. The abstract lacks quantitative highlights or specific study references. Include 2–3 key statistics (e.g., % phytate reduction, RS increase, GI decrease) to underscore significance. Clarify that the focus is both mechanistic and translational—this dual focus is a strength.

2. A graphical abstract or summary diagram illustrating the major mechanisms and translational hurdles could significantly enhance accessibility.
3. Some sections, particularly Section 3 (subsections 3.1 to 3.7), are very dense with technical information and could benefit from brief summary paragraphs or visual overviews to reinforce key takeaways.
4. Section 3.1 presents contradictory findings without a clear synthesis. Highlight how new techniques (e.g., isotopic labeling, transporter assays) might overcome current gaps.
5. Section 3.2 is highly informative but overloaded with overlapping concepts (proteolysis, digestibility, gluten). Separate into two distinct subsections: (A) Nutritional enhancement via proteolysis, (B) Gluten detoxification strategies.
6. The review could better explain how reclassification improves strain selection for functional outcomes. Elaborate on how new genera like Lactiplantibacillus or Fructilactobacillus differ in metabolic profiles or fermentation traits.
7. Suggest how this revised taxonomy can be operationalized for strain engineering or starter selection.
8. While methodological critique is present, a more structured framework like a table summarizing methodological limitations in different evidence types would be informative.
9. Multiple mechanisms (acid, fiber, RS, SCFAs) are discussed, but their individual contributions remain ambiguous. Include a summary table comparing studies on GI reduction, indicating fermentation type, LAB strain, flour type, and % GI reduction.
10. While the review critiques in vitro models, there is no unified discussion on methodological hierarchy or reliability. It would be interesting to include a table comparing in vitro, ex vivo, and in vivo models—their strengths, limitations, and translational value.
11. Summarize how different fermentation types (I, II, III) affect mannitol accumulation and final FODMAP load.
12. Emphasize the need for standardization of fermentation parameters to ensure reproducible low-FODMAP outcomes.
13. Use consistent terminology for fermentation types (I, II, III), strain names (use full genus and species), and nutritional metrics (e.g., use “bioaccessibility” vs. “bioavailability” with precision).

Author Response

For research article

 

 

Response to Reviewer 1 Comments
1. Summary
We would like to sincerely thank the Editor and Reviewer 1 for their time and for providing insightful and constructive feedback on our manuscript. We have found the comments to be extremely helpful and have carefully revised the manuscript accordingly. A point-by-point response to each comment is provided below, and all changes have been highlighted in the revised manuscript for ease of review.
2. Point-by-point response to Comments and Suggestions for Authors Note.  All changes in the manuscript have been marked using the 'Track Changes' feature. For ease of viewing, we suggest selecting the 'All Markup' view to see the specific additions highlighted in blue.
Comments 1: The abstract lacks quantitative highlights or specific study references. Include 2–3 key statistics (e.g., % phytate reduction, RS increase, GI decrease) to underscore significance. Clarify that the focus is both mechanistic and translational—this dual focus is a strength.
Response 1: We thank the reviewer for this constructive feedback, which has helped us to enhance the abstract's clarity and impact. In response to the specific points raised, we have made two key revisions: ·       Quantitative highlights have been incorporated to underscore the nutritional significance, specifically citing phytate reduction (up to 90%) and the comparative Glycemic Index (GI) of sourdough versus conventional bread (≈ 54 vs. ≈ 75). ·       The review's dual focus on both underlying mechanisms and translational challenges is now explicitly stated in the second sentence, reinforcing what we agree is a key strength of the manuscript.
Comments 2: A graphical abstract or summary diagram illustrating the major mechanisms and translational hurdles could significantly enhance accessibility.
Response 2: We thank the reviewer for this excellent suggestion. We fully agree that a graphical abstract significantly enhances the manuscript's accessibility. As suggested, we have included a graphical abstract with our resubmission. This diagram visually contrasts the in vitro potential and observed mechanisms of LAB in sourdough (e.g., nutrient enhancement) with the key in vivo and translational hurdles (e.g., high system variability, scarcity of clinical data). We believe this provides a clear, high-level summary of the manuscript's core arguments.       Comments 3: Some sections, particularly Section 3 (subsections 3.1 to 3.7), are very dense with technical information and could benefit from brief summary paragraphs or visual overviews to reinforce key takeaways.   Response 3 : The reviewer's feedback that Section 3 was dense with information and would benefit from clearer key takeaways was very perceptive. We have taken this excellent suggestion to heart and have systematically revised each subsection from 3.1 to 3.7 to improve readability and reinforce the main conclusions. Specifically, we have implemented the following improvements: ·       For sections discussing complex and sometimes contradictory findings (e.g., 3.1 Minerals, 3.2 Proteolysis, 3.4 Glycemic Index, 3.6 Vitamins, and 3.7 FODMAPs), we have added brief concluding summary paragraphs. These paragraphs are designed to synthesize the detailed information presented, providing the reader with a clear take-home message for each topic. ·       For sections that present a wide range of comparative data (e.g., 3.5 Bioactive Compounds and 3.6 Vitamins), we have introduced new summary tables. These tables serve as the "visual overviews" suggested by the reviewer, consolidating key mechanisms, outcomes, and challenges into an accessible, easy-to-reference format. We believe this combination of new summary paragraphs and tables has significantly improved the structure and impact of Section 3, making it much easier for the reader to navigate the technical information and grasp the key findings of our review.       Comments 4: Section 3.1 presents contradictory findings without a clear synthesis. Highlight how new techniques (e.g., isotopic labeling, transporter assays) might overcome current gaps Response 4: We appreciate the reviewer for raising a critical point regarding the synthesis of conflicting evidence in this section. We agree that this is a key challenge in the literature and have substantially revised the section to provide a clearer narrative and a forward-looking perspective. ·       To provide a clearer synthesis, we have restructured the argument throughout the section. We now introduce the discrepancy between phytate degradation and actual mineral uptake as a 'central theme' and conclude the discussion of contradictory findings by proposing a 'paradigm shift'—moving focus from what is removed (phytate) to what is produced or altered by the specific microbes. These new synthesizing statements can be found in the third and fourth paragraphs of Section 3.1. ·       Furthermore, to highlight how new techniques might overcome current gaps, we have added a new concluding paragraph to Section 3.1. This paragraph is specifically dedicated to this topic, discussing how advanced techniques, including the suggested stable isotopic labeling and in vitro models like Caco-2 cell assays (for mechanistic transporter studies), are essential to resolve the current discrepancies. We believe these revisions have transformed the section from a list of contradictory findings into a cohesive critical analysis that not only synthesizes the current challenges but also proposes a clear path forward for future research.       Comments 5: Section 3.2 is highly informative but overloaded with overlapping concepts (proteolysis, digestibility, gluten). Separate into two distinct subsections: (A) Nutritional enhancement via proteolysis, (B) Gluten detoxification strategies. Response 5: We agree with the reviewer that separating the concepts of general nutritional enhancement from the specific issue of gluten detoxification significantly improves the clarity of this section. This was an excellent suggestion for restructuring the argument. Accordingly, we have reorganized the original section into two distinct subsections as recommended: ·       3.2.1. Nutritional Enhancement through Sourdough Proteolysis: This subsection now focuses exclusively on the general nutritional benefits of proteolysis, such as the enrichment of free amino acids and improvements in overall protein digestibility. ·       3.2.2. Gluten Detoxification Strategies: This new subsection is dedicated to the more specific and complex topic of mitigating gluten immunogenicity, discussing the mechanisms, clinical evidence, and significant translational challenges. This new structure has allowed for a more logical and focused presentation of the evidence. To further enhance the synthesis requested by the reviewer, we have also added a new concluding paragraph at the end of the section to summarize and contrast the findings from both topics.

 

 

Comments 6: The review could better explain how reclassification improves strain selection for functional outcomes. Elaborate on how new genera like Lactiplantibacillus or Fructilactobacillus differ in metabolic profiles or fermentation traits.

 

Response 6:

The reviewer raises an excellent point. A deeper explanation of the practical benefits of the new taxonomy indeed strengthens the manuscript's core argument. We have therefore revised Chapter 2 to build a more cohesive narrative.

To address the reviewer's specific points, we have made the following revisions:

• In Section 2.1, we inserted two new paragraphs that explain how the new framework is functionally predictive. We do this by contrasting the distinct metabolic strategies of key genera (Lactiplantibacillus vs. Fructilactobacillus) and providing further examples for other important genera.
• To further reinforce this link between taxonomy and function, we also revised Section 2.2 (Relevant Metabolism and Acidification). The discussion of metabolic pathways in this section now explicitly refers back to the new genera, strengthening the connection and providing a more integrated explanation. For instance, the paragraph on metabolic flexibility was rewritten to better illustrate these principles using the key species as examples.

We are confident that these revisions across both sections now clearly demonstrate the value of the new taxonomy by providing the specific examples and elaborations the reviewer requested.

 

 

 

Comments 7: Suggest how this revised taxonomy can be operationalized for strain engineering or starter selection.

 

Response 7:

We thank the reviewer for this excellent suggestion to connect our taxonomic discussion to real-world applications. We agree this is a crucial point that enhances the impact of the review.

To address this, we have added a new concluding paragraph to Section 2.1. This paragraph is specifically dedicated to discussing how the revised taxonomy can be operationalized. It details the framework's direct applications in:

• The bioengineering of strains for improved functional traits.
• The rational design of complementary, multi-strain starter cultures.

This addition successfully demonstrates the practical utility of the new taxonomic framework, as requested.

 

 

 

Comments 8: While methodological critique is present, a more structured framework like a table summarizing methodological limitations in different evidence types would be informative

Response 8:

This is an excellent suggestion to help synthesize the methodological critiques scattered throughout the manuscript. To provide the structured framework requested, we have designed and added a new summary table (Table 8) in the Conclusion. This table summarizes the key strengths, limitations, and overall translational value of the different types of evidence discussed (in vitro, animal in vivo, and human in vivo models), directly addressing the need for a clearer overview of methodological limitations.

 

 

 

Comments 9: Multiple mechanisms (acid, fiber, RS, SCFAs) are discussed, but their individual contributions remain ambiguous. Include a summary table comparing studies on GI reduction, indicating fermentation type, LAB strain, flour type, and % GI reduction.

 

Response 9 :

The reviewer's comment was particularly insightful, highlighting that while we discussed multiple mechanisms for GI reduction, we did not adequately synthesize the ambiguity surrounding their individual contributions. To address this, we have made two major revisions to this section:

1. Synthesis of Ambiguity: We have added a new concluding paragraph to Section 3.4.2 that explicitly frames this ambiguity as a "primary scientific challenge." This new text synthesizes the discussion on the various mechanisms and serves as a direct bridge from the mechanistic hypotheses to the empirical data.
2. New Summary Table: As suggested, we have created and introduced a new summary table (Table 4). This table compares key experimental studies on GI reduction, detailing the flour type, specific intervention (including fermentation type and strains where available), and the reported glycemic impact, directly providing the comparative overview the reviewer requested.

 

 

Comments 10: While the review critiques in vitro models, there is no unified discussion on methodological hierarchy or reliability. It would be interesting to include a table comparing in vitro, ex vivo, and in vivo models—their strengths, limitations, and translational value.

 

Response 10:

We agree with the reviewer on the value of such a summary, which aligns with their earlier comment (#8). As detailed in our response to Comment #8 above, we have added a new comprehensive table (Table 8) to the Conclusion. This table directly compares in vitro, animal (in vivo), and human (in vivo) models, outlining their respective strengths, limitations, and translational value, as suggested. We believe this new table provides the unified discussion and methodological hierarchy the reviewer was looking for.

 

 

 

Comments 11: Summarize how different fermentation types (I, II, III) affect mannitol accumulation and final FODMAP load.

 

Response 11:

The reviewer makes an excellent point that a direct comparison of different sourdough types was missing from the original text. To address this, we have added a new paragraph within Section 3.7.1 (specifically, the second paragraph of this subsection). This new text is dedicated to summarizing how fermentation type influences FODMAP outcomes. It now explicitly contrasts traditional Type I sourdoughs, which often lead to mannitol accumulation by heterofermentative LAB, with controlled Type II sourdoughs, where selected strains can be used to maximize fructan degradation while minimizing polyol synthesis.

 

This focused addition now provides the clear, comparative summary the reviewer requested.

 

 

 

Comments 12: Emphasize the need for standardization of fermentation parameters to ensure reproducible low-FODMAP outcome

Response 12:

We agree with the reviewer's important suggestion to emphasize the need for process control for reliable outcomes. We have therefore added a new paragraph immediately following the one discussed above (now the third paragraph of Section 3.7.1) that directly addresses this. The new text explicitly states that "reproducible production of low-FODMAP sourdough products necessitates strict standardization of fermentation parameters" and highlights the key variables (time, temperature, and flour composition) that require rigorous control. This reinforces the translational challenges and strengthens the manuscript's conclusions regarding the application of this technology.

 

 

 

Comments 13: Use consistent terminology for fermentation types (I, II, III), strain names (use full genus and species), and nutritional metrics (e.g., use “bioaccessibility” vs. “bioavailability” with precision).

 

Response 13:

The reviewer's point about terminological consistency is well-taken. We recognize that precision in language is critical for the manuscript's clarity, and we have performed a thorough proofread of the entire manuscript to address every aspect of this comment.

Specifically, we have standardized the following:

• Fermentation Types: We have ensured that the terminology for sourdough types (e.g., 'Type I', 'Type II') is now used consistently throughout the text, tables, and figures.
• Strain Names: We have reviewed all mentions of microbial species to ensure they follow the standard scientific convention (full name at first mention within the text, and abbreviated thereafter).
• Nutritional Metrics: We have carefully reviewed and corrected the use of "bioaccessibility" and "bioavailability" throughout the manuscript. The term "bioaccessibility" is now consistently used for findings from in vitro digestion models, while "bioavailability" is reserved for outcomes from in vivo (animal or human) studies, ensuring these critical terms are used with the precision they require.

We are grateful to the reviewer for highlighting the importance of this consistency, and we believe the manuscript is now much stronger and more precise as a result of this comprehensive check.

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Reviewer 2 Report

Comments and Suggestions for Authors

This review addresses the beneficial role of LAB in sourdough bread production. The work is clear, well-organized, and well-written. However, some minor comments should be corrected prior to publication.

Remove underscores from the following lines: 64, 216, 222, 223, 248, 278, 249, 250, 252, 260, 278, 281, 303, 362, 429, 723, 734.

Table 1: The name of the microorganisms should be in italics and the species in lowercase.

For L. rhamnosus are mention prebiotics effect, but for table 1 only probiotic effect could be mentions and prebiotics action (by production of EPS or other) could be explain in other section

 

Line 199: delbrueckii in italic

Line 179: plantarum in italic

Line 140-144, 258-260 and other setences:  deleted italic

Line 145 and a lot of sentences of manuscripts deleted type in bold

Line 223-223 explain Ca and Re

Line 253: check that proteolitic activity also could be in the membrane and cell wall

Line 264, 272, check abbreviations: AAs, FAA???

line 595, deleted script

Line 671: check format of references (Komstantinidis et al)

Line 671: what is ALE?

Line 710: What does Type I refer to?

 Line 746: remove underline

The conclusions should highlight that some of the properties attributed to sourdough bread have not been verified (absorptions of minerals and consumption by celiac), while others, such as a decrease in the glycemic index, have been. However, further studies are needed to further understand the benefits of consuming this bread compared to bread fermented with yeast.

 

Author Response

For research article

 

 

Response to Reviewer 2 Comments
1. Summary
We sincerely thank Reviewer 2 for their positive assessment of our work and for their meticulous proofreading. We appreciate the careful attention to detail, and we have addressed each of the suggested corrections point-by-point below. All changes in the manuscript have been marked using the 'Track Changes' feature. For ease of viewing, we suggest selecting the 'All Markup' view to see the specific additions highlighted in blue
2. Point-by-point response to Comments and Suggestions for Authors     Comments 1: Remove underscores from the following lines: 64, 216, 222, 223, 248, 278, 249, 250, 252, 260, 278, 281, 303, 362, 429, 723, 734. Response 1: We thank the reviewer for their careful proofreading and keen attention to detail. We have gone through the entire manuscript and have removed all extraneous underscores as requested.   Comments 2: Table 1: The name of the microorganisms should be in italics and the species in lowercase. Response 2: We thank the reviewer for their valuable suggestions to improve the clarity and accuracy of Table 1. We have made the following corrections as recommended:       Comments 3: For L. rhamnosus are mention prebiotics effect, but for table 1 only probiotic effect could be mentions and prebiotics action (by production of EPS or other) could be explain in other section Response 3: This is an excellent point for clarity. We have amended the entry for L. rhamnosus in Table 1 to focus on its probiotic role, as suggested.     Comment 4: Line 199: delbrueckii in italic Response 4: Corrected.   Comment 5: Line 179: plantarum in italic Response 5: Corrected.   Comment 6: Line 140-144, 258-260 and other setences: deleted italic Response 6: Corrected. All instances of incorrect italics have been fixed.   Comment 7: Line 145 and a lot of sentences of manuscripts deleted type in bold Response 7: Corrected. All instances of unnecessary bolding have been removed.     Comment 8: Line 223-223 explain Ca and Re Response 8: Thank you for noting this. We have now explicitly defined these starter culture abbreviations (Carla (Ca) and Rebola (Re)) in the text for improved clarity.   Comment 9: Line 253: check that proteolitic activity also could be in the membrane and cell wall Response9: This is an excellent and important point. We have revised the sentence to accurately state that the proteolytic system of LAB includes both cell envelope-associated proteinases and intracellular peptidases.   Comment 10:Line 264, 272, check abbreviations: AAs, FAA??? Response 10: Thank you. We have reviewed the manuscript and ensured that all abbreviations, including AA (amino acids) and FAA (free amino acids), are defined upon their first use.   Comment 11: line 595, deleted script Response 11: This has been corrected. The extraneous text at this location has been deleted.   Comment 12: Line 671: check format of references (Komstantinidis et al) Response 12: Thank you for pointing this out. We have checked this reference and all others to ensure they are correctly formatted according to the journal's guidelines.     Comment 13: Line 671: what is ALE? Response 13: Thank you for highlighting this. We have now defined the abbreviation ALE (Adaptive Laboratory Evolution) at its first mention in the text.   Comment 14: Line 710: What does Type I refer to? Response 14: This is a crucial point for clarity. We have revised the text, particularly in Section 3.7.1, to explicitly define the different sourdough fermentation types and their characteristics, including a clear description of traditional Type I sourdoughs.     Comment 15: Line 746: remove underline Response 15: Corrected. The underline has been removed.     Comment 16: The conclusions should highlight that some of the properties attributed to sourdough bread have not been verified (absorptions of minerals and consumption by celiac), while others, such as a decrease in the glycemic index, have been. However, further studies are needed to further understand the benefits of consuming this bread compared to bread fermented with yeast. Response 16: We thank the reviewer for this important suggestion to refine the conclusions. We agree that highlighting the varying levels of evidence for different health claims and calling for specific comparative studies strengthens the final summary of our review. We have revised the Conclusion section to incorporate these key points: The first paragraph now explicitly differentiates between the more established benefits (e.g., lower glycemic index) and those that still require more robust clinical validation (e.g., mineral absorption, benefits for celiac disease). In the paragraph outlining future research priorities, we have specified the need for comparative trials that assess sourdough bread against yeast-leavened bread. Furthermore, to provide a structured critique of the evidence base as suggested in the reviewer's other comments, we have also introduced Table 8. This table establishes a clear hierarchy of evidence by comparing the strengths and limitations of the primary experimental models in the field. We are confident these comprehensive revisions provide the nuanced and forward-looking conclusion the reviewer suggested.