Comparative Nutritional and Healthy Values of Macro- and Microelements in Edible and Non-Edible Tissues of Raw and Processed Common Octopus (Octopus vulgaris)

The macroelement (Na, Mg, P, S, K, and Ca) and microelement (Mn, Fe, Co, Cu, Zn, As, Cd, Sn, Ba, and Pb) composition of edible (arm and mantle) and non-edible (viscera) tissues of octopus (Octopus vulgaris) was studied. Three different size groups were considered separately (1-2, 2-3, and 3-4 kg per specimen). Additionally, the effect of cooking processing (40 min at 90 °C) and frozen storage (4 months at -18 °C) was determined. All raw tissues depicted the following increasing sequence for the macroelement content (p < 0.05): Ca < Mg < P ≈ K < Na ≈ S; regarding microelements, the raw viscera tissue showed a higher level (p < 0.05) than the counterpart edible tissues. The cooking process led to a general decrease in macroelement values (p < 0.05) in arm and mantle tissues; for microelements, no effect (p > 0.05) was observed for Co, Mn, and Sn content, but an average increase was obtained for Cd, Cu, and Pb values. The frozen storage did not lead to element content changes in the arm tissue (p > 0.05); in contrast, general content increases and decreases were detected for mantle and viscera, respectively. In spite of level changes detected, this study proves that viscera, a common waste of commercial processing, can be considered a valuable source of essential elements.