Fish skin gelatin, as a waste product of sea bream, was used to obtain fish gelatin hydrolysate (FGH) with the treatment of alcalase (alc) and savinase (sav). The functional properties of FGHs and their usage possibilities in frozen dough bread making were investigated. FGH treated with alc showed a higher emulsifying stability index (189 min), while FGH treated with sav showed greater foaming capacity (27.8%) and fat-binding capacity (1.84 mL/g). Bread doughs were produced using two FGHs (alc and sav) and their combination (FGH-alc + FGH-sav). Using FGH treated with these enzymes individually was more effective than their combination in terms of polyacrylamide gel electrophoresis (SDS-PAGE) results and bread quality (specific volume and hardness). The addition of FGH into bread dough showed no significant effect on bread dough viscoelasticity (tan δ), while the increment level of tan δ value for control dough was higher than the dough containing FGH after frozen storage (−30 °C for 30 days). The highest freezable water content (FW%) was found in control dough (33.9%) (p < 0.05). The highest specific volume was obtained for control fresh bread and bread with FGH-alc, while the lowest volume was obtained for fresh bread containing FGH-sav (p < 0.05). After frozen storage of the doughs, the bread with FGH-alc showed the highest specific volume. FGH addition caused a significant reduction in the L* (lightness) value of fresh bread samples when compared to control bread (p < 0.05). This study suggested that usage of FGH-alc in bread making decreased the deterioration effect of frozen storage in terms of the specific volume and hardness of bread.

Fish gelatins are increasingly recognized as sustainable biopolymers for food, packaging, and biomedical applications; however, their functional performance often requires improvement. In this study, the effects of transglutaminase (TG) modification on the physicochemical and structural properties of trout (T) and sea bass (SB) gelatins were systematically investigated. TG treatment enhanced gel strength in a species- and concentration-dependent manner, with trout increasing from 100 g (control) to 108 g at 0.04% TG and SB reaching a maximum of 163 g at 0.01% TG. Rheological measurements confirmed improved viscoelastic behavior, particularly in trout samples (G′ > G″). Emulsifying activity was optimized at 0.02–0.04% TG in trout, while excessive cross-linking reduced interfacial activity; nevertheless, emulsion stability was improved in both species. Foaming capacity and stability reached 195% and 148%, respectively, in trout, whereas higher TG concentrations led to reductions in SB foaming performance. Scanning electron microscopy revealed denser and more homogeneous networks in TG-modified gels, correlating with their enhanced rigidity. Transparency remained high, while zeta potential shifted toward more negative values, indicating improved colloidal stability. FTIR, UV–Vis, and DSC analyses confirmed conformational rearrangements and thermal stabilization after cross-linking. Minor decreases in oil-binding capacity and slight color changes were also observed. Overall, TG cross-linking significantly enhanced the functional and structural properties of fish gelatins in a source-dependent manner, supporting their potential as versatile and sustainable biopolymers for diverse industrial applications.

The increasing global interest in fish consumption leads to a greater generation of fish waste. Fish waste, rich in nutrients such as protein, bioactive compounds, and vitamins, is attracting growing attention for its potential applications in food. In this study, gelatin hydrolysate obtained from fish skin waste was utilized as a stabilizer and/or emulsifier in ice cream production. It was found that gelatin hydrolysate significantly increased the protein content of the ice cream samples. The K and n values in different ice cream compositions varied between 0.009 and 1.012 Pa.sⁿ and 0.356 and 0.863, respectively. The consistency coefficients of samples D1 (sahlep and mono-diglyceride) and D3 (sahlep and gelatin hydrolysate) were almost the same, indicating that the mono-diglyceride was replaced by an equivalent amount of gelatin hydrolysate. All the ice cream mixtures tested showed non-Newtonian, pseudoplastic flow, as indicated by their n values being less than 1. All mixtures demonstrated greater elasticity than viscosity, as their storage modulus (G′) was higher than their loss modulus (G″). In the third interval of 3-ITT, all ice cream mixtures displayed thixotropic behavior, indicating that their viscoelastic properties could be restored after a sudden deformation. The overrun levels of the samples ranged from 9.55% to 21.74%; the use of gelatin hydrolysate resulted in a statistically significant increase (p < 0.05). The highest hardness and stickiness values in the samples were determined in the specific sample containing equal amounts of emulsifier, stabilizer, and gelatin hydrolysate. Furthermore, gelatin hydrolysate prolonged the first dripping time and melting rate of the samples.

The invasive fish Atherina boyeri constitutes an ecologically disruptive yet underexploited biomass with strong potential for transformation into value-added biofunctional ingredients. This study investigates the functional, antioxidant, and antimicrobial properties of protein hydrolysates that were produced from fish collected in the Hirfanlı and Yamula reservoirs using three commercial proteases (alcalase, bromelain, and flavourzyme). Bromelain produced the highest degree of hydrolysis, yielding higher proportions of low-molecular-weight peptides and greater radical-scavenging activity. Flavourzyme hydrolysates exhibited the most favorable emulsifying properties, Alcalase hydrolysates produced the highest foaming capacity and stability. All hydrolysates showed high absolute zeta-potential values across pH 3–9, demonstrating strong colloidal stability. Protein solubility remained above 80% across most pH levels, indicating extensive peptide release and improved compatibility with aqueous media. The Oil-binding capacity (2.78–3.75 mL/g) was consistent with reported values for marine hydrolysates. Antioxidant and antimicrobial evaluations revealed clear enzyme-dependent patterns, with Bromelain exhibiting the strongest DPPH activity and Alcalase and Flavourzyme showing the most pronounced inhibition of major foodborne pathogens. Additionally, all hydrolysates exhibited measurable ACE-inhibitory activity, with flavourzyme-derived peptides showing the highest inhibitory activity, underscoring their potential relevance for antihypertensive applications. These findings highlight the strategic valorization of A. boyeri through enzymatic hydrolysis, demonstrating its potential as a sustainable, clean-label functional ingredient source.

Gelatin production from fish-processing by-products has gained attention as a sustainable strategy for value-added utilization of aquatic resources. In this study, gelatin was extracted from rainbow trout (Oncorhynchus mykiss) skins and its physicochemical, structural, and functional properties were evaluated in comparison with commercial bovine gelatin. Compared with bovine gelatin (220±3.00 g), trout gelatin displayed a milder gel network characterized by a gel strength of 95.1±5.00 g, a pH of 4.78±0.23, and a water-holding capacity of 13.92±0.73 mL water/g protein, reflecting distinct structural and functional behavior rather than reduced quality. In contrast, the high protein content (95.30±0.41%) indicated considerable compositional purity. Functional analyses revealed distinct interfacial advantages for trout gelatin. Oil-binding capacity was significantly higher (1.17±0.10 mL oil/g protein) than that of bovine gelatin (P