Food gels were obtained using fish protein isolate recovered from Atlantic cod (Gadus morhua) by-products using the isoelectric solubilisation/precipitation method. The use of low temperatures (not exceeding 10 °C) at the alkaline solubilisation stage resulted in the production of a fish protein isolate with high-molecular mass (FPI-1), while the use of high temperatures (24 °C) resulted in the production of a fish protein isolate with low-molecular mass (FPI-2). The isolates demonstrated excellent gelling and nutritional properties based on their amino acid profiles. The denaturation temperatures of FPI-1 and FPI-2 determined by DSC were 163.0 and 158.5 °C. The secondary structure of FPI-1 demonstrated a high α-helix content and a low random coil content compared to FPI-2. The high-molecular isolate formed stronger gels than the low-molecular isolate, which is explained by the formation of a dense gel network with small pores of about 250 nm. The recovered cod protein isolates can be successfully used as food ingredients or food additives in the production of gel-like/enriched products.

Synthetic food packaging remains a looming environmental hazard. Biodegradable alternatives from renewable natural raw materials may be a solution to this problem. Edible packaging films can be produced from fish waste gelatin and seaweed sodium alginate. They combine environmental benefits with the functional characteristics required by the food industry. This article introduces a new environmentally friendly packaging film and its physicochemical profiles depending on the ratio of cold-water fish waste and sodium alginate. The experiment also included selecting the optimal type and concentration of plasticizer for safe and long food storage. The experimental films consisted of different mixes of cold-water fish skin gelatin, brown algae sodium alginate, and glycerol or sorbitol. The films were tested for thickness, moisture content, vapor permeability, moisture absorption, tensile strength, flexibility, and thermal properties. Optical microscopy, IR spectroscopy, and differential scanning calorimetry made it possible to analyze the structure, physicochemical properties, and thermal stability. The statistical processing relied on the Student’s t-test method. An optimal ratio of components yielded films with improved mechanical and barrier properties, low hygroscopicity, low vapor permeability, and high melting temperatures (135–138 °C). The samples with sorbitol as plasticizer demonstrated a more uniform structure, resulting in low vapor permeability (829–1,122 g/m2), reduced moisture absorption (≤ 98%), and high tensile strength. The samples with glycerol had better plasticizing properties, but higher vapor permeability (1,572–1,895 g/m2) and moisture absorption (114–179%). The established patterns may help to control the properties of industrial biopolymer compositions by adjusting the type of plasticizer and the concentration and ratio of components to obtain novel food films with improved mechanical characteristics and low hygroscopicity.