Effect of extracting time and temperature on yield of gelatin from different fish offal

The aim of the study was to determine the optimal conditions for preparing gelatin from different kinds of fish offal: heads and backbones of Baltic cod, skins of fresh and cold-smoked salmon, and skins of salted and marinated herrings. The yield of gelatin extraction at 45 °C was 71–75% for fresh salmon skins or cod backbones, and 86%, for smoked salmon skins. When heating marinated herring skins for 15 min or salted herring skins for 45 min, about 100% of collagen was converted to gelatin. For fish skins, 45 °C and 15–60 min extraction time, depending on the kind of skins, were established as optimal conditions for preparing gelatin. The yield of gelatin extraction from the cod heads did not exceed 70%, even when a three stages process was used. In the case of backbones, 100% of collagen in the form of gelatin was isolated using this procedure. SDS-PAGE analysis showed that gelatin from fish skins was much less degraded than gelatin from pigskins.