Optical scattering, absorption and absorbance spectra were evaluated in beef psoas major and semitendinosus muscle samples heated to different temperatures. Corresponding Warner-Bratzler shear force values were also measured as an assessment of the tenderness property. The characteristic absorbing peaks of myoglobin and its derivatives were better resolved in the absorption spectra than in the conventional absorbance spectra. Optical scattering coefficients were susceptible to muscle structural changes induced by heating. Taken together with shear force measurements, our measurements suggest that myofibril and collagen components have different effects on the optical scattering properties of meat. These results provide insight into the complicated process of light-muscle interactions, which is essential for the development of optical techniques for muscle characterization. (C) 2007 Elsevier Ltd. All rights reserved.