The Use of Reflectance Spectrophotometry for the Assay of Raw Meat Pigments

TLDR

Reflectance spectrophotometry has been applied to meat pigments, but the literature lacks comprehensive reviews and standardized methods for measuring total pigments and metmyoglobin content. This study proposes improved spectrophotometric methods to quantify total pigments and the percent metmyoglobin in raw meat using reflectance data. The authors use reflectivity at the 525‑nm isobestic point, convert reflectance to K/S ratios, and establish linear relationships between K/S and total pigment extracted with acidified acetone, while determining metmyoglobin from the K/S 572/K/S 525 ratio with defined limits for 0 % and 100 % metmyoglobin. They found that lowering meat pH reduced the K/S value, likely due to increased scattering from texture changes.

Abstract

SUMMARY The literature on reflectance spectrophotometry, as it applies to meat pigments, is critically reviewed, and improved methods are suggested for determination of total pigments and of the percent metmyoglobin from reflectance data on raw meat. The suggested method for total pigment was based on reflectivity of the meat samples at 525 mμ, the isobestic point for myoglobin, oxymyoglobin, and metmyoglobin. The reflectivity data, when calculated as the corresponding ratios of the absorption coefficient K to the scattering coefficient S were linearly related to total pigment extract from the meat with acidified acetone. K/S values of pigment‐free (peroxide‐treated) samples were obtained as a base line. Lowering the pH of the meat decreased the K/S value. This was attributed to changes in texture which increased S. Metmyoglobin was determined from the ratio K/S 572 mp/K/S 525 mμ. Limiting values for the ratio were established for meat containing 100% and 0% metmyoglobin, and a linear relation was assumed between the ratios and intermediate amounts of metmyoglobin.