Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper reports a Lean Six Sigma (LSS) DMAIC case study in a Portuguese fish-processing plant. Using value-stream mapping to locate a bottleneck at packaging/labelling, the authors define three CTD (critical-to-delivery) indicators. The study also frames outcomes against SDGs 8, 9, 12, 14. The topic is timely and relevant. Empirical LSS studies in food processing—especially fish—remain comparatively scarce, and the manuscript’s explicit mapping to SDGs is a welcome angle. The practical detail (CTDs, OEE decomposition, work-hour reallocation) will interest both academics and practitioners.

Concerns and required revisions:

1) The manuscript states “all CTDs have significantly improved, having exceeded the corresponding target value”. Yet Table 7 reports CTD2 “new performance” = 20:44 and “baseline” = 20:10, implying deterioration, and CTD3 “new” = 37% vs “baseline” = 15% (also deterioration). These entries contradict earlier baseline targets (CTD2 baseline 20:44 with target < 20:30; CTD3 baseline 37% with target < 10%) and the trend shown in Fig. 7 (close time improving toward ~20:10).

2) The narrative suggests both maintenance and the pull-system change contributed, with the largest throughput gain after advance ordering. Provide a simple interrupted time-series or step-change analysis (even descriptive) to apportion effects (maintenance vs scheduling vs levelling). Confidence intervals or control chart limits for CTDs and OEE would strengthen causal inference.

3) The SDG mapping is logical, but quantitative environmental/social indicators are not reported (e.g., overtime hours reduced, rework rate, kg of waste avoided, estimated spoilage reduction, energy-or GHG-related proxies). Add at least indicative estimates (with assumptions) converting observed process gains (e.g., OEE, earlier starts, reduced WIP) into sustainability metrics (waste kg/day, overtime hours/week, € cost of defects avoided), or clearly state data limitations.

4) The improvement window (Oct 2018–Jan 2019) is visible in the plots. Seasonality, product mix, or the retailer's expansion plan could confound outcomes. Discuss seasonality and demand mix; indicate whether any parallel initiatives occurred; note limits to generalizing beyond this plant and describe prerequisites for replication.

5) Economic impact calculation needs clarification. The manuscript reports +140 kg/day and ~€250 k/year in additional sales, plus “~1 month of work” saved. Show the arithmetic (operating days/year; average selling price/kg; margin vs revenue; treatment of variable costs). If the figure is gross sales, say so.

6) OEE components are given, but the measurement window (number of shifts/days), treatment of planned vs unplanned downtime/quality escapes, and data capture method are not specified. Briefly document the data collection protocol for OEE and CTDs (period, sampling frequency, system of record), and whether Figure 6/7 values are raw means or smoothed.

7) Please fix “Lean Sis Sigma” in the Discussion.

Author Response

Comment 1

Reply: We thank the reviewer for spotting this inconsistency. CTD2 and CTD3 values in Table 7 were incorrectly transcribed. The correct post-improvement values are consistent with the targets and with Figures 6 and 7. We have corrected the table and the text.

 

Comment 2

Reply: We agree that distinguishing between effects of maintenance vs scheduling vs levelling clarifies attribution. We have now added descriptive text indicating the timing of interventions and their relative contributions, starting in line 569.

 

Comment 3

Reply: Since no numeric sustainability data was collected, we now make this explicit in the manuscript. Manuscript changes were performed in section 3.6, where we framed the lack of individual metrics for specific sustainability indicators was justified (line 557), and in section 5, in the text as well as in Table 8 (line 695). A mention to this reality was also added in the conclusions, as a limitation (line 718) but also better sustaining the role of LSS in opening the door for sustainability in operations-oriented projects (line 725).

 

Comment 4

Reply: We acknowledge the potential role of seasonality in operational results. We have now added a limitations paragraph noting this However, we argue that our theoretical result, focused on the inclusion of sustainability goals in operational improvement projects via the use of LSS, would be generalizable to a larger extent (line 725).

 

 

Comment 5

Reply: We clarified the arithmetic and explicitly state that this represents gross sales. The increase in production capacity of ~140 kg/day, when multiplied by the number of operating days per year and the average selling price per kilogram, corresponds to an estimated gain of approximately €250k/year in gross sales (Table 8 and line 601).

 

Comment 6

Reply: We added description on the data collection protocol (line 397).

 

Comment 7

Reply: Corrected the typographical error.

Reviewer 2 Report

Comments and Suggestions for Authors

The below suggestions for your reference:

1. The paper emphasizes integrating sustainability goals (such as waste reduction and improved working conditions) through Lean Six Sigma (LSS), but it focuses primarily on short-term operational and financial metrics (like production capacity and time savings) without assessing the long-term cultural transformation or the sustainability practices' persistence. For example, while the authors mention that sustainability could become part of the organizational culture, they do not provide data or evidence to demonstrate whether this shift has occurred or how it can be quantified. Specifically, in Section 5 "Summary, conclusions, and suggestions for future research," it clearly states: "However, while the short-term impacts on performance and resource efficiency were measurable, the long-term cultural effects—namely whether sustainability becomes embedded in the organization’s mindset and routines—can only be assessed over time and thus remained outside the scope of this project" (lines approximately 610-621). Additionally, in Section 4 "Discussion of the case study results," the discussion focuses on short-term gains (such as time savings and capacity increases) but does not extend to cultural or behavioral changes (lines approximately 570-590). This limits the depth of the research, as integrating sustainability is inherently a long-term process. The lack of a tracking mechanism in the case study (such as follow-up interviews or indicator monitoring) leads to conclusions that lack persuasiveness, affecting the theoretical contribution of the paper to sustainability transformation in industrial practice.

2. The case study is limited to the internal operations of the fish processing plant (such as packaging and labeling phases), without addressing upstream (such as fishery supply) or downstream (such as retail distribution) aspects. This neglects the overall optimization of the supply chain, whereas sustainability goals (like SDG 12 on responsible consumption and production) require a holistic view. For instance, the paper mentions waste reduction but does not analyze food loss outside the processing stage (like during transportation or retail). In Section 5 "Summary, conclusions, and suggestions for future research," it explicitly states: "The research was also developed under a constrained timeframe and limited to the processing stage. While operational and financial impacts were successfully validated within the plant, a broader optimization of the fishmonger’s department would require an extension of the analysis to retail operations" (lines approximately 625-628). In Section 3.1 "Problem statement," the focus on delays within the processing plant (like truck arrivals) is not linked to impacts on the retail side (such as stockouts), implying a limited scope (lines approximately 244-250).

3. The literature review (Section 2) lists existing studies but does not critically assess the shortcomings of integrating LSS with sustainability, particularly regarding the specifics of the food industry. For example, Section 2.3 mentions that research on LSS applications in the food industry is scarce but does not analyze the reasons (such as industry characteristics like product perishability) or compare methodological differences across studies. In Table 1, while summarizing the literature, most scholars did not focus on sustainability ("Sustainability perspective?" is marked as "No"), but the authors do not explain the implications or gaps this presents for their research. In Section 2.3 "Lean Six Sigma, Sustainability, and the food industry," it states: "The number of existing researches regarding the inclusion of a sustainability perspective in Lean Six Sigma application remains scarce" (lines approximately 156-157), but it does not expand on the implications of this scarcity. Table 1 shows that most case studies (like Besseris 2014, Desai 2015) did not integrate a sustainability perspective, but the authors only state this fact without linking it to their own study's innovations or limitations (lines approximately 180-217). This weakens the theoretical foundation of the paper. The literature review should be a critical synthesis, but the authors primarily provide descriptive lists without highlighting how their research fills existing gaps (such as through SDG integration). As a result, the contribution statement in Section 1 appears weak, lacking sufficient justification for why this case can advance the field.

4. The case study is based on a single entity (a Portuguese fish processing plant) and does not involve comparisons across multiple plants or industry diversity. This limits the generalizability of the conclusions, as there are significant variations within the food processing industry (e.g., meat vs. fish). Additionally, the application of DMAIC tools (like VSM and OEE) does not discuss external factors (such as market fluctuations or policy changes), which may lead to results that are not replicable in dynamic environments. In Section 5 "Summary, conclusions, and suggestions for future research," it states: "Future work should explore how similar Lean Six Sigma initiatives can be applied in other fresh food processing contexts" (line approximately 625), indirectly acknowledging the sample limitation. Section 3 "Case Study" provides an overall description of a single plant case but does not reflect on sample bias in the discussion (such as the impacts of plant size or geographical location) (lines approximately 225-565). The single-case design is a common limitation, but the authors do not quantify its impact (e.g., through sensitivity analysis). This makes the paper's recommendations (such as LSS as a sustainability platform) potentially applicable only to similar contexts, lacking broader applicability. Combined with the constraints of the timeframe mentioned in Section 5, the methodology appears rushed.

Author Response

Comment 1

Reply/notes to reviewer: We acknowledge that our study emphasizes short-term operational outcomes. The company’s primary aim was operational improvement, and our research approach deliberately built on that focus to introduce sustainability considerations in a way that was acceptable to the organization. In other words, sustainability was integrated through the operational improvement efforts that the company was already willing to pursue. This approach successfully allowed sustainability concerns to become part of the project, even if long-term cultural embedding was beyond the scope of this case. We have reinforced this stance both in the intro (line 71) and in the conclusions (line 718).

 

Comment 2

Reply/notes to reviewer: We agree the scope was limited to the internal processing stage. This was a boundary condition of the project, and this reality is highlighted in the text, and the metrics that were used for improvement were essentially internal operations metrics. Nevertheless, we reinforced this perspective in the conclusions (lines 738 to 746).

 

Comment 3

Reply/notes to reviewer: We recognize that the limited literature on Six Sigma in the food industry, and in particular in the fish processing industry, is a research gap that we explored and that we should better highlight. We have revised the article to stress that the scarcity of sustainability-oriented LSS studies in the food industry highlights a gap that this case addresses, though further work is required to broaden theoretical foundations. (lines 223 and 711).

 

Comment 4

Reply/notes to reviewer: We acknowledge the potential role of seasonality in operational results. We have now added a limitations paragraph noting this However, we argue that our theoretical results, focused on the inclusion of sustainability goals in operational improvement projects via the use of LSS, would be generalizable to a larger extent (line 725).

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The paper presents a Lean Six Sigma (LSS) DMAIC case study in a Portuguese fish-processing plant, combining value-stream mapping with OEE analysis to relieve a packaging/labelling bottleneck. The manuscript explicitly frames operational outcomes against SDGs 8, 9, 12, and 14, and reports capacity/time improvements with practical measures (maintenance, advance ordering, workload levelling). The updated version clarifies the data protocol and acknowledges seasonal/demand-mix limitations, strengthening transparency of methods and external validity. 
 
1) Table 7 is now internally consistent: CTD2 improves from 8:44 p.m. to 8:10 p.m. (meeting the “before 8:30 p.m.” target), while CTD3 improves from 37% to 15%. However, the narrative still states that all CTDs exceeded their targets, which is not supported if CTD3’s target remains “< 10%”. Please revise the claim to “CTD1 and CTD2 met targets; CTD3 improved substantially (37%→15%) but fell short of the < 10% goal.” 
 
2) The manuscript now clarifies that the €250k/year figure represents gross sales potential derived from the ~140 kg/day gain. To complete the transparency, please add the assumed operating days/year and the average selling price per kg (or provide a range-based sensitivity, e.g., €/kg in [X–Y] with N operating days). 

Author Response

Thank you for your careful review, pointing out the remaining inconsistencies in the text. They have now been adressed:

Regarding the Targets for the CTDs, we have revised teh etxt and clarified that CTD3 has fallen short, altough only slightly, of the proposed target. This has been reviewed in line 534.

As for the financial gains, we have clarified the number of operating day a year, base don the information already contained in the text, and accounting for holidays: ~290 operating days a year.

Thank you for the opportunity and help to improve our work.