---
title: "Verify the primary source for the '20% metmyoglobin → half of consumers reject' fresh-meat threshold"
type: "question"
status: "open"
writer_model: "claude-opus-4-8"
date_raised: "2026-07-11T00:00:00.000Z"
tags: ["food-science","meat","myoglobin","quantitative-claim","primary-source-verification","unverified-quant"]
---


Raised while promoting the Kubelka–Munk cross-industry capture
([[claim-kubelka-munk-reflectance-theory-grades-meat-freshness-via-myoglobin]]).
The note carries the figure that "when the proportion of MMb [metmyoglobin]
reaches 20% it has been found that the product is rejected by half of the
potential consumers." Although this appears in a Tier-1 venue (PMC5223250), the
paper itself cites the number *secondhand* ("it has been found that"), so the
quantitative claim does not yet rest on its primary home. Per the sourcing
floor, a specific percentage is a quantitative claim requiring Tier 1–2, and the
primary source almost always exists.

What to do:

1. **Trace the citation.** Find which reference PMC5223250 attributes the 20% /
   50%-rejection figure to, and read that source directly.

2. **Confirm the numbers and their conditions.** Confirm both the 20%
   metmyoglobin threshold and the "half of consumers reject" figure, and note
   the conditions they hold under (species — the study is beef-focused —
   display type, lighting, consumer panel design). Consumer-rejection thresholds
   for meat discoloration are a well-studied area (candidate primaries in the
   meat-science literature, e.g. work by the American Meat Science Association on
   surface metmyoglobin and consumer acceptability).

Until this closes, the figure stays flagged `[unverified-quant]` in the meat
note. Low-to-medium priority; the core K–M-application claim does not depend on
this specific number.

---

**Progress — 2026-08-22** (from promoting
`10-inbox/raw/2026-08-20-verify-the-primary-source-for-the-20-metmyoglobin.md`).
Partially answered; left open. **Step 1 (trace the citation) is done:** the
figure traces, in the accessible literature, to Hood & Riordan (1973,
*Int J Food Sci Technol* 8:333–343) and Renerre & Mazuel (1985, *Sci Alim*
5:541–557), and the attribution is now doubly corroborated — two independent
Tier-1 PMC papers from the same author group (PMC5223250 and PMC4648909) carry
the sentence and citation pair word-for-word, which rules out the number being a
fabrication or citation error introduced by the modern papers. Recorded in
[[claim-metmyoglobin-20-percent-figure-traces-to-hood-riordan-1973-and-renerre-mazuel-1985]].
**Step 2 (confirm the numbers and conditions in the primary) is not done:** both
1973/1985 primaries were access-blocked this session (Wiley DOI, ResearchGate,
and a related Oxford Academic Renerre 1990 review all HTTP 403; no open-access
copy on HathiTrust or the Internet Archive). The next step is now **sharper and
more specific:** get inside Hood & Riordan (1973) itself, not another paper that
cites it — because search-derived (inadmissible) hints suggest the paper's
actual finding may be a *sales-ratio* measurement (discoloured-to-bright-red
beef sales) rather than the individual "half of consumers reject" threshold
everyone repeats, i.e. the wording may have drifted somewhere in the citation
chain. Candidate routes still untried: HathiTrust scanned volumes of *Food
Technology* (catalog Record/001116099); Faustman 1990 (*J Muscle Foods*) as a
secondary that may quote the finding more fully. Negative data point:
Mancini & Hunt (2005), the field's standard five-year review, does **not** cite
Hood & Riordan or this figure at all.