Characterization of fish gelatin from surimi processing wastes: Thermal analysis and effect of transglutaminase on gel properties

Fish gelatin extraction from wastes of fish Herring species (Tenualosa ilisha) was carried out by a series of pretreatment with 0.2 M Ca(OH)(2) followed by 0.1 M citric acid and final water extraction at 50 degrees C for 3 h. The resulting fish gelatin preparation was evaluated for its dynamic viscoelastic properties, gelling and melting temperatures and gel strength. The gelling and melting temperatures of gelatin samples (at 6.67%, w/v) were obtained from differential scanning calorimetry and theological studies. The melting temperature of extracted fish gelatin (EFG) obtained ranged from 16.2 to 16.7 degrees C compared to that of commercial fish gelatin gel (CFG), from 23.7 to 25.6 degrees C and halal bovine gelatin (HBG), from 26.5 to 28.7 degrees C. On the other hand, gelling temperatures of EFG, CFG and HBG ranged from 5.1 to 5.2 degrees C, 11.9 to 17.46 degrees C, and 12.6 to 19.33 degrees C, respectively. EFG gave gels with a considerably lower G' values than CFG and HBG. The bloom strength of EFG gels at 6.67% (w/v) was 69.03 g which was much lower than HBG (336.2 g) and CFG (435.9 g). Enzyme transglutaminase was added in the amounts of 0.5, 1.0, 3.0 and 5.0 mg/g gelatin to modify the gel properties of the extracted fish gelatin. The modified EFG gels obtained had higher gel strengths of 101.1 g and 90.56 g with added transglutaminase of 1.0 and 3.0 mg/g, respectively. However with addition of 5.0 mg/g enzyme the gel strength increased only up to 75.06 g. SDS-PAGE of extracted gelatin gel showed protein band intensities for alpha 1-chains and 53 kDa but in gels added with higher concentration of transglutaminase, these Protein band intensities seemed to disappear. (C) 2008 Elsevier Ltd. All rights reserved.