Capture: Verify the primary source for the '20% metmyoglobin → half of consumers reject' fresh-meat threshold

food-sciencemeatmyoglobinkubelka-munk-theoryquantitative-claimprimary-source-verificationunverified-quantcorroboration

This capture directly answers the open question raised while promoting claim-kubelka-munk-reflectance-theory-grades-meat-freshness-via-myoglobin (tracked as question-verify-metmyoglobin-20-percent-consumer-rejection-threshold in 50-questions/). That note carries the figure "when the proportion of MMb reaches 20% it has been found that the product is rejected by half of the potential consumers," flagged [unverified-quant] because the citing paper (PMC5223250) attributes the number secondhand ("it has been found that") rather than reporting its own data. The task here was to trace the citation to its primary home and read that source directly.

Claim: The figure is consistently traced, in the citing literature, to two named 20th-century studies — Hood & Riordan (1973) and Renerre & Mazuel (1985) — not invented or garbled by the modern paper that repeats it

Claim type: historical/bibliographic-attribution claim (what the citation trail says, not the underlying number itself) — Tier 1–2 required; met at Tier 1 via direct full-text reads of two independent papers.

PMC5223250 (Hernández, Sáenz, Alberdi & Diñeiro, 2016) attributes the figure inline to two references: "Hood DE, Riordan EB. Discolouration in pre-packaged beef: measurement by reflectance spectrophotometry and shopper discrimination. Int J Food Sci Technol. 1973;8:333–343" and "Renerre M, Mazuel JP. Relationships between instrumental and sensory measurement methods of meat color. Sci Alim. 1985;5:541–557." A second, independent paper by an overlapping author set — Hernández, Sáenz, Alberdi & Diñeiro, "Comparison between two different methods to obtain the proportions of myoglobin redox forms on fresh meat from reflectance measurements" (J Food Sci Technol 52(12):8212–8219, 2015; PMC4648909) — carries the identical sentence and the same citation pair, word for word:

"As the proportion of metmyoglobin increases meat color turns to brown, this induces a negative response in consumers and when the proportion of MMb reaches 20 % it has been found that the product is rejected by half of the potential consumers (Hood and Riordan 1973; Renerre and Mazuel 1985)."

Because this is the same author group reusing the same sentence and citations across their own two papers (not two independent research groups converging on the figure), it corroborates the citation trail — the figure reliably traces to these two 1973/1985 studies and not to some other or invented source — without corroborating the number itself. Both quotes were confirmed present verbatim in the archived primary texts (mcp__seek__quote_check, both grounded: true).

Provenance:

• source_url: https://pmc.ncbi.nlm.nih.gov/articles/PMC4648909/
• source_sha: baf432631dd9684527ec56a3c4e413b24d490469159f8ec239d77d7ac41a230d
• source_title: "Comparison between two different methods to obtain the proportions of myoglobin redox forms on fresh meat from reflectance measurements"
• source_author: "B. Hernández, C. Sáenz, C. Alberdi, J. M. Diñeiro"
• source_date: 2015-06-19
• source_venue: "Journal of Food Science and Technology 52(12):8212–8219 (PMC4648909)"
• source_quote: "this induces a negative response in consumers and when the proportion of MMb reaches 20 % it has been found that the product is rejected by half of the potential consumers (Hood and Riordan 1973; Renerre and Mazuel 1985)"
• source_tier: 1

Claim: Neither named primary source has been independently read this session — both are access-blocked, so the number itself is still not confirmed in the original authors' own words

Claim type: epistemic-status/access claim about a research gap — Tier 3–4 acceptable for reporting the gap itself; reported plainly.

Multiple routes to Hood & Riordan (1973) were attempted and blocked:

• Wiley Online Library, the DOI's home (10.1111/j.1365-2621.1973.tb01721.x) — HTTP 403.
• ResearchGate's listing for the paper — HTTP 403 (archive_page fallback also 403'd).
• No open-access copy located via web search on HathiTrust, Internet Archive, or CORE for either the 1973 Journal of Food Technology / International Journal of Food Science and Technology volume or the paper itself.

Renerre & Mazuel (1985, Sciences des Aliments) was not located online at all this session (no DOI or open host surfaced). A related, more accessible Renerre solo review — "Factors involved in the discoloration of beef meat," Int J Food Sci Technol 25:613–630 (1990), Oxford Academic — was tried as a possible secondary route to a fuller quotation of the 1973/1985 finding, but also returned HTTP 403 (archive_page).

Because of the fabrication-risk rule on quote provenance (search-result summaries are not sourced material, however specific), none of the paraphrases of Hood & Riordan's finding that surfaced in search snippets are recorded here as claims — see the next claim for why that distinction matters.

Provenance: access attempts only; no admissible quote obtained.

• https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.1973.tb01721.x — HTTP 403
• https://www.researchgate.net/publication/229872005_Discoloration_in_pre-packaged_beef_measurement_by_reflectance_spectrophotometry_and_shopper_discrimination — HTTP 403
• https://academic.oup.com/ijfst/article/25/6/613/7867407 — HTTP 403

Claim: search-derived characterizations (not independently confirmed) describe Hood & Riordan's actual 1973 result as a sales-ratio finding, not literally "half of consumers reject" — a framing gap that remains open

Claim type: quantitative/mechanism nuance — Tier 1–2 required, not met. Recorded as [unverified-quant — needs primary] per the fabrication rule: this characterization comes only from WebSearch's own synthesized answer text over search snippets, not a direct fetch of the paper, so it is not admissible as a sourced claim — it is recorded here as the shape of the open question, not as a fact.

Search summaries (not independently verified against primary text) repeatedly described Hood & Riordan's actual finding as: a linear relationship between surface metmyoglobin (5–33% MMb) and the proportion of total beef sales that were discoloured, such that a 1:2 ratio of discoloured-to-bright-red beef sales was reached when surface MMb was about 20%. A sales ratio observed in a shop is not the same claim as "half of potential consumers reject the product" — the former is a market-level outcome (roughly a third of realized sales going to the discoloured category, if bright-red keeps outselling 2:1), the latter is framed as an individual consumer-acceptance threshold. Whether the "half of consumers reject" phrasing is a faithful restatement of Hood & Riordan's own framing, a conflation with the separate Renerre & Mazuel (1985) citation paired alongside it, or a drift introduced somewhere in the citation chain between 1973 and the 2015/2016 PMC papers, cannot be determined without reading the 1973 paper's own text — which remains blocked (previous claim).

Provenance: none admissible — WebSearch synthesis only, [unverified-quant — needs primary].

Central question status

Is the primary source for "20% metmyoglobin → half of consumers reject" verified? [unverified — could not confirm or deny after search]. The citation trail is now solidly established and doubly corroborated: two independent Tier-1 papers from the same research group both name Hood & Riordan (1973) and Renerre & Mazuel (1985) as the sources, using identical wording, which rules out the figure being a fabrication or citation error introduced by either PMC paper. But the primary documents themselves remain unread after genuine effort (Wiley, ResearchGate, and a related Oxford Academic review all returned HTTP 403; no open-access copy found on HathiTrust or Internet Archive), so the number's exact wording, sample, and methodology in the authors' own words is still unconfirmed — and search-derived hints suggest the commonly repeated "half of consumers reject" framing may not exactly match what the 1973 study itself measured (a sales ratio, per unverified secondary characterization). The existing vault note's [unverified-quant] flag on this figure should remain in place, now with a more specific next step: get inside Hood & Riordan (1973) itself, not just another paper that cites it.

Further leads

• Renerre, M. (1990). "Factors involved in the discoloration of beef meat." Int J Food Sci Technol 25:613–630 — Oxford Academic hosts it; 403'd this session but is the most promising secondary review to quote Hood & Riordan more fully if access can be obtained by another route.
• Faustman, C. (1990). "The Biochemical Basis for Discoloration in Fresh Meat: A Review." Journal of Muscle Foods — another candidate review from the same era, untried this session.
• Mancini, R.A. & Hunt, M.C. (2005). "Current research in meat color." Meat Science 71:100–121 — read in full this session (open PDF at meatscience.org, the American Meat Science Association's own site); notably does not cite Hood & Riordan or the 20%/50% figure anywhere in its text or reference list, despite being the field's standard five-year review — a negative data point on how load-bearing this specific figure actually is in current meat-color research.
• HathiTrust holds a catalog record for the journal "Food technology" (https://catalog.hathitrust.org/Record/001116099) — untried this session for a scanned 1973 volume.

Entity candidates

• D. E. Hood — person — co-author of Hood & Riordan (1973), the older, foundational study the whole "20%/half-rejected" figure traces back to; not yet independently read.
• E. B. Riordan — person — co-author of the same 1973 foundational study.
• M. Renerre — person — co-author of Renerre & Mazuel (1985), the second half of the citation pair every modern paper repeats alongside Hood & Riordan; also authored the 1990 review flagged above as a further lead.
• J. P. Mazuel — person — co-author of the 1985 study.
• B. Hernández — person — corresponding author (Universidad Pública de Navarra) of both 2015 and 2016 PMC papers that repeat the secondhand citation identically; the modern conduit for the figure, not its origin.
• American Meat Science Association (AMSA) — concept/organization — publisher of the "Meat Color Measurement Guidelines" (1991, 2012) both PMC papers cite as methodological standard; also publishes Mancini & Hunt (2005) on its own site.