Changes in tenderness of beef M. semitendinosus and modification of actomyosin mediated by Fe(III)-protoporphyrin IX, protoporphyrin IX and free iron

The objective of the present study was to explore the effect of Fe(III)-protoporphyrin IX (hemin), protoporphyrin IX (PPIX) and free iron on beef M. semitendinosus tenderness and its molecular mechanism. Hemin, PPIX and FeCl3 treatment of beef muscles under heating tremendously decreased shear force of beef meat by approximately 24%, 26%, and 30% respectively and weakened the association of actin-myosin. The protein carbonyl content increased and sulfhydryl content decreased significantly in FeCl3 and hemin treated groups, indicating the oxidative modification of actomyosin. The higher surface hydrophobicity and intrinsic fluorescence intensity demonstrated that hemin, PPIX and FeCl3 increased the unfolding of actomyosin, and the crosslinking was formed by hydrophobic interaction and disulfide bonds. Hemin treatment increased the α-helices/random coil and initiated more structural changes in actomyosin as compared to that of PPIX and FeCl3. These biochemical changes might contribute to the dissociation of actomyosin. The obtained results established a link between meat tenderness and porphyrins/free iron content, and gave new insights into the mechanism of how hemin and released PPIX and free iron affect the physicochemical properties of actomyosin.