Analysis of Pigments at the Surface of Fresh Beef With Reflectance Spectrophotometry

SUMMARY There is need for a nondestructive method of measuring the proportions of myoglobin derivatives in meat samples. Such a method was developed in which reflectance spectra are recorded on the absorbancy scale for samples of fresh beef containing predominantly myoglobin (Mb), oxymyoglobin (MbO 2 ), or met‐myoglobin (Mb + ) at the surface. The spectra are adjusted so that reflectance measured on the absorbancy scale (R A ), is 1.0 at 525 mμ, an isobestic point for the three derivatives. With this adjustment, the isobestic point for MbO 2 and Mb + at 474 μ and the isobestic point for Mb and MbO 2 at 571 mμ are reproducible, and the R A values at 474 mμ and 571 mμ are less variable. In that way, 100% reflectance values were established, but a model system was needed to determine intermediate reflectance values due to mixtures of myoglobin derivatives. The model system, containing known amounts of MbO 2 and Mb + , indicated that Beer's law was not followed, but the deviation was small. Some of the difficulties inherent in this type of study are discussed, and a hypothesis is proposed to explain the peculiarities of reflectance spectra.