The effects of ultrasound‐assisted extraction (UAE) and microwave‐assisted extraction (MAE) methods on molecular and physicochemical characteristics of the resultant gelatin were examined. Before extraction procedure, we investigated the optimum pH for swelling of Common carp by‐products, which is an important pretreatment for gelatin production. The highest swelling yield was achieved at pH 13 among pH 1–14 with unit intervals. Results indicated that the UAE gelatin has a higher gel strength, viscosity, melting point, and gelling point. The power and time of sonication showed a reverse relation with these characteristics. In addition, as the time of microwave heating was raised, the gel strength, viscosity, melting point, and gelling point were decreased. The FT‐IR spectra showed similar peaks but the Amide B in UAE gelatin slightly vanished. The electrophoretic pattern also revealed the higher gel strength and viscosity of UAE gelatin due to the higher intensity of α and β chains compared to MAE gelatin. It can be concluded from all of the results of this study that the produced gelatin using these procedures can be a good source of gelatin in food and drug industries.

Oil extracted from fish waste is considered as a value‐added product. The effect of postmortem processing times (0, 3, 6, and 9 hr) and blanching methods (sodium chloride, pH shift, and high temperature) on the extracted oil from rainbow trout viscera was studied. Blanching was applied six hours prior to oil extraction to counteract the effects of delayed processing time and increasing the oil stability. Autolysis by digestive enzymes is main culprit of higher contents of free fatty acids, lipid oxidation, saponified compound, and saturation degrees in case of postponed oil extraction. Results showed that PV was increased after pH shift and high temperature blanching, while there were no significant differences by using salt blanching. The lowest amount of TBA, AV, Totox, and saponification index was observed in salt blanched treatment. The colorimetric values including L*, b*, and whiteness index were decreased after pH shift, whereas redness was increased. Unfavorable coloration could be attributed to the lipid oxidation process that giving rise nonvolatile decomposition products with carbonyl groups. Our results indicated that salt blanching could reduce the effects of delayed processing time and lead to higher quality value‐added product from rainbow trout viscera.

The effects of Maillard Reaction Products (MRPs) obtained from fish gelatin hydrolysates and D-glucose conjugation on the techno-functional characteristics of fish gelatin films were investigated, and the antioxidant effects were measured. MRPs were added to a gelatin solution at different concentrations (5-30% of the gelatin weight). The results revealed that the addition of the MRPs changed the film thickness from 0.15 mm (control) to 0.199 mm (film containing 30% MRPs). Some parameters including density, opacity, and color (ΔE) of the films were directly related to the MRPs concentration. Unlike these parameters, the solubility of the samples was not significantly altered, and the degree of swelling was indirectly changed owing to the MRPs addition. The results also indicated that the MRPs could dramatically decrease the water vapor permeability and oxygen permeability. The viscosity and mechanical properties of the films were increased as the MRPs concentration increased. The UV protective and the DPPH radical scavenging activities of the films were positively related to the MRPs concentration. The control sample (8.71 mg/mL) and the sample containing 30% MRPs (IC50 at 1.72 mg/mL) showed the lowest and highest antioxidant activities, respectively. The results of this study revealed that a fish gelatin film containing MRPs could be used as an active film in food packaging.