Water extractability of the zinc protoporphyrin IX–myoglobin complex from Parma ham is pH-dependent

•In Parma ham, 30–50% of zinc protoporphyrin IX (ZnPP) was water-insoluble.•The water extraction ratio of ZnPP positively correlated with the muscle pH.•The higher pH increased the water extractability of ZnPP from Parma ham.•Water-insoluble ZnPP binds to myoglobin (Mb) and hemoglobin.•The water solubility of Mb at pH 5.5–6.0 decreased by binding to ZnPP. The bright red color of Parma ham is mainly derived from zinc protoporphyrin IX (ZnPP), which exists in both water-soluble and insoluble states. Water-soluble ZnPP mainly binds to hemoglobin, however, the presence of water-insoluble ZnPP remains unexplained. Therefore, we aimed to elucidate how ZnPP exists in a water-insoluble state by focusing on its binding substance. Depending on the skeletal muscle, water-insoluble ZnPP comprised 30–50% of total ZnPP. The ZnPP water extractability was positively correlated with muscle pH. Water-insoluble ZnPP was extractable with a high-pH solution and existed as a complex with myoglobin or hemoglobin; nevertheless, myoglobin-binding ZnPP was more abundant. Furthermore, the water solubility of the myoglobin globin moiety at pH 5.5–6.0 was reduced by ZnPP binding. These results suggest that water-insoluble ZnPP mainly exists as a ZnPP–Mb complex, with low solubility attributed to the low pH of the ham.