---
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.