Nutritional Quality and Safety of Windowpane Oyster Placuna placenta from Samal, Bataan, Philippines^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study provides valuable baseline data on this underutilized species. However, after careful review, I believe that major revisions are needed to address important limitations in the study design, data analysis, and discussion of results. Below I provide detailed comments intended to help improve the scientific rigor and clarity of your manuscript.

- The manuscript does not present clearly outlined research questions or hypotheses.

- The study is based on samples collected from a single geographic location (Samal, Bataan) at three time points over nearly two years. This does not provide sufficient replication or spatial coverage to support conclusions about seasonal variation or safety of the species more broadly. Moreover: The statistical analysis is limited to t-tests and simple means. More appropriate statistical models (e.g., ANOVA, mixed models) should have been used to analyze seasonal or temporal variation; No correction for multiple comparisons was applied, increasing the risk of type I error.

- The text is overly descriptive and uncritical: there is no in-depth analysis of the impact of the heavy metals detected, nor discussion of the implications of variable levels of As;

- The study suggests food safety, but ignores the relevant variability of arsenic (above FSANZ standards in one sample) and does not discuss ways of mitigating or monitoring;

- The discussion of practical application and development of food products is speculative and lacks economic data or real tests of acceptance and technological feasibility;

- There is no adequate discussion of the limits of the study (e.g., limited scope of collection, lack of study of nutrient bioavailability);

- The tables could be reorganized for clarity (e.g., clearly separate data by season and analysis type).

 

Suggested Reading

Assessment of potentially toxic metals, metalloids, and non-metals in muscle and liver tissue of Two Fish Species (Mugil cephalus Linnaeus, 1758 and Odontesthes regia (Humboldt, 1821)) from the Coastal Area of Callao, Peru. REGIONAL STUDIES IN MARINE SCIENCE, 2024, p. 103423.

Comments on the Quality of English Language

Some problems

Page 2, lines 45–47:

“In particular, bivalves, in common with other molluscal shellfish, are rich sources of vitamin B12, choline, selenium, iron, and zinc [2]. In fact, with regards to omega-3 fatty acids, iron, selenium and zinc, the nutritional value value of some shellfish is superior to that of land-based protein sources, including beef, chicken, and pork [3].”

Issues: Repetition (“value value”); the sentence is unnecessarily long and could be split for clarity.

Page 3, lines 53–54:

“...from which the name windowpane oyster dervies and is a versatile material nows used to fashion handcrafted items and a wide range of materials...”

Issues: Typographical error (“dervies” → derives, “nows” → now); awkward construction with multiple conjunctions; should be split into two sentences.

Page 6, lines 170–171:

“DPPH-RSA = abs (blank-b) x vol (extract) x 0.25029 mg/umol x dilution factor (mg TE/g) slope x weight of sample”

Issues: The formula presentation lacks clarity; missing punctuation or line breaks make it difficult to follow.

Page 9, lines 332–334:

“The results from the antioxidant assay showed that extract of windowpane oyster can scavenge free radicals to a certain extent. Given the dietary importance of antioxidants and their utility in marketing, the present data should be a valuable asset in the development of marketable foods from the oyster meat.”

Issues: “...should be a valuable asset...” is awkward; passive voice and vague phrasing reduce clarity.

Page 14, lines 531–534:

“There is potential for introducing windowpane oyster meat into the food system of the Philippines and indeed elsewhere. Such a move would improve food security, nutrition and enhance the economic prospects of those associated with the windowpane oyster industry.”

Issues: The sentence is long and repetitive (“food security, nutrition and enhance the economic prospects” could be restructured for parallelism); overuse of connectors.

Author Response

Referee 1

“- The manuscript does not present clearly outlined research questions or hypotheses.”

We agree that in the submitted manuscript these were implicit rather than explicit. We have extensively modified the Abstract and the Introduction to bring the research questions to the fore, e.g., lines 14-17, 30-33, 258-264.

“- The study is based on samples collected from a single geographic location (Samal, Bataan) at three time points over nearly two years. This does not provide sufficient replication or spatial coverage to support conclusions about seasonal variation or safety of the species more broadly. Moreover: The statistical analysis is limited to t-tests and simple means. More appropriate statistical models (e.g., ANOVA, mixed models) should have been used to analyze seasonal or temporal variation; No correction for multiple comparisons was applied, increasing the risk of type I error.”

We opted to provide the data without the suggested statistical analyses for two reasons. Firstly, regarding multiple comparisons, it is true that the problem becomes acute for large numbers of comparisons but, for more modest numbers, the risk remains relatively small. For example, comparisons in Table 2 for which there are six possible, would provide a risk of a type I error of just over 0.2 (See Figure 1 in J. Thora. Dis. (2017) 9, 1725 for the relationship between number of comparisons and probability of a type I error). Secondly, other data, e.g., Tables 4 and 6 do perhaps invite such comparisons. However, from the perspective of the oyster environment data, as noted by the reviewer these data are rather sparse. They are sufficient to demonstrate the oyster meat is nutritious and safe to consume (the objective of the work), but a robust analysis of the effects of environment on such parameters is outwith the scope of the present manuscript and would require a greater data density in time and location.

“- The text is overly descriptive and uncritical: there is no in-depth analysis of the impact of the heavy metals detected, nor discussion of the implications of variable levels of As;”

- The study suggests food safety, but ignores the relevant variability of arsenic (above FSANZ standards in one sample) and does not discuss ways of mitigating or monitoring;”

We accept these points and have re-written some sections. In particular, we address the issue of the As content and of other minerals more critically and we have incorporated the reference provided as well as other additional references into the modified text. This includes a reference to a document from WHO (WHO (2018)) highlighting the difference between inorganic and organic As; the latter being commonly associated with shellfish and considered to be less toxic. Additional discussion [lines 416-419 and 552-562] has been provided, together with relevant references regarding toxicity (Int J Environ Res Public Health (2023) 20, 2197 and Biometals (2006) 19, 555).

The reference provided by the referee was also a useful source of the levels of other elements in the tissue of fish for comparison and, we note that for the more common elements Ca, K, P and Mg, the order is similar and a comment on the levels has been added. The major difference resides in the heavier elements, Zn, Fe and Cu, which are more concentrated in the bivalve case although still within safety limits. This is discussed, lines 416-419 and includes two additional references.

“- The discussion of practical application and development of food products is speculative and lacks economic data or real tests of acceptance and technological feasibility;”

The practical application and development of new food products is in the context of the data in this manuscript indeed speculative at this stage, as it is outside the scope of the present investigation. We have added comments relating to the fact that there already exist dishes prepared from the meat, albeit limited mainly to fishermen’s families, and that pilot products have been produced and tested with two focus groups (lines 27-30 and 581-585).

“- There is no adequate discussion of the limits of the study (e.g., limited scope of collection, lack of study of nutrient bioavailability);”

The limitations regarding absence of the tracing of toxins prior to collection are mentioned (lines 571-573).

“- The tables could be reorganized for clarity (e.g., clearly separate data by season and analysis type).”

Given that there are only one set of data per season, we feel that keeping the current organisation enables the reader to capture the data at a glance.

 

Suggested Reading

Assessment of potentially toxic metals, metalloids, and non-metals in muscle and liver tissue of Two Fish Species (Mugil cephalus Linnaeus, 1758 and Odontesthes regia (Humboldt, 1821)) from the Coastal Area of Callao, Peru. REGIONAL STUDIES IN MARINE SCIENCE, 2024, p. 103423.

 

Comments on the Quality of English Language

Some problems

“The entire document has been edited thoroughly to make the writing clearer and more direct. All of the problems noted below have been corrected at their appropriate locations.”

Page 2, lines 45–47:

“In particular, bivalves, in common with other molluscal shellfish, are rich sources of vitamin B12, choline, selenium, iron, and zinc [2]. In fact, with regards to omega-3 fatty acids, iron, selenium and zinc, the nutritional value value of some shellfish is superior to that of land-based protein sources, including beef, chicken, and pork [3].”

Issues: Repetition (“value value”); the sentence is unnecessarily long and could be split for clarity.

Page 3, lines 53–54:

“...from which the name windowpane oyster dervies and is a versatile material nows used to fashion handcrafted items and a wide range of materials...”

Issues: Typographical error (“dervies” → derives, “nows” → now); awkward construction with multiple conjunctions; should be split into two sentences.

Page 6, lines 170–171:

“DPPH-RSA = abs (blank-b) x vol (extract) x 0.25029 mg/umol x dilution factor (mg TE/g) slope x weight of sample”

Issues: The formula presentation lacks clarity; missing punctuation or line breaks make it difficult to follow.

Page 9, lines 332–334:

“The results from the antioxidant assay showed that extract of windowpane oyster can scavenge free radicals to a certain extent. Given the dietary importance of antioxidants and their utility in marketing, the present data should be a valuable asset in the development of marketable foods from the oyster meat.”

Issues: “...should be a valuable asset...” is awkward; passive voice and vague phrasing reduce clarity.

Page 14, lines 531–534:

“There is potential for introducing windowpane oyster meat into the food system of the Philippines and indeed elsewhere. Such a move would improve food security, nutrition and enhance the economic prospects of those associated with the windowpane oyster industry.”

Issues: The sentence is long and repetitive (“food security, nutrition and enhance the economic prospects” could be restructured for parallelism); overuse of connectors.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The review report for fishes-3702943 below.

Title: Nutritional quality and safety of windowpane oyster Placuna 2 placenta from Samal, Bataan, Philippines

 

• What is the main question addressed by the research?

The aim of  the present study was to determine the nutritional quality of windowpane oyster meat which is a by-product of this bivalve, to inform future decisions as to how the oyster could be utilized as a raw material for the production of valuable food products. In tandem, the safety, in terms of microbial content and the concentration of common heavy metals, was also investigated.

 

• What specific improvements should the authors consider regarding the methodology?

The methodology is understandable.

 

• Do you consider the topic original or relevant to the field? Does it address a specific gap in the field? Please also explain why this is/ is not the case.

Several studies have been conducted to assess the nutritional value of oysters and other molluscs but very little information pertains to the nutritional benefits of Placuna placenta.

 

• What does it add to the subject area compared with other published material?

In the Philippines the Food Nutrition and Research Institute of the Department of Science and Technology included windowpane oyster in the Philippine Food Composition Table. Although proximate composition and other nutrient contents of this oyster have been determined, as discussed extensively the information is incomplete in terms of its nutritional quality.

Thus, it would be beneficial to undertake a thorough investigation of the biochemical characteristics of this bivalve to establish its processing potential and safety for human consumption. This is particularly relevant from an economic perspective, as the oyster harvesters are on the bottom two income deciles and uplifting their income would be of great benefit.

 

• Are the conclusions consistent with the evidence and arguments presented and do they address the main question posed? Please also explain why this is/is not the case.

 

 

The data in the present paper provide more in-depth information covering both nutritional and safety aspects of the meat. The analyses demonstrate that windowpane oyster meat is a useful

source of protein, as well as fatty acids and antioxidants; both carotenoids and phenolics contributing to the latter. Importantly, whereas the meat is a good source of minerals, it was not found to be contaminated significantly with heavy metals.

 

• Are the references appropriate?

All 34 references cited in this manuscript are appropriate and relevant to this research.

Some titles of cited publications in References were written in full name, others in abbreviations (E.g.:verse 630, 638).

In some places the abbreviated names of the pages and volumes are given (E.g.:verse 608, 620, 648), in others they are not. It is recommended to standardize it.

 

• Any additional comments on the tables and figures.

The tables are understandable.

Adding a photo of Placuna placenta to the manuscript would make the work more attractive.

Author Response

We have checked the references, particularly as some citations were not correct. 

The graphical abstract does contain photos of the oysters and the oyster meat.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Ok