The phase behavior of aqueous mixtures of fish gelatin (FG) and sodium alginate (SA) and complex coacervation phenomena depending on pH, ionic strength, and cation type (Na⁺, Ca²⁺) were studied by turbidimetric acid titration, UV spectrophotometry, dynamic light scattering, transmission electron microscopy and scanning electron microscopy for different mass ratios of sodium alginate and gelatin (Z = 0.01–1.00). The boundary pH values determining the formation and dissociation of SA-FG complexes were measured, and we found that the formation of soluble SA-FG complexes occurs in the transition from neutral (pH_c) to acidic (pH_φ1) conditions. Insoluble complexes formed below pH_φ1 separate into distinct phases, and the phenomenon of complex coacervation is thus observed. Formation of the highest number of insoluble SA-FG complexes, based on the value of the absorption maximum, is observed at рH_opt and results from strong electrostatic interactions. Then, visible aggregation occurs, and dissociation of the complexes is observed when the next boundary, pH_φ2, is reached. As Z increases in the range of SA-FG mass ratios from 0.01 to 1.00, the boundary values of рН_c, рH_φ1, рH_opt, and рH_φ2 become more acidic, shifting from 7.0 to 4.6, from 6.8 to 4.3, from 6.6 to 2.8, and from 6.0 to 2.7, respectively. An increase in ionic strength leads to suppression of the electrostatic interaction between the FG and SA molecules, and no complex coacervation is observed at NaCl and CaCl₂ concentrations of 50 to 200 mM.

Hydrogels based on gelatin–chitosan mixtures have great potential for practical application in the development of new materials in food technology and biomedicine. This study examines the effect of chitosan on the gelling properties, rheological, and structural characteristics of fish gelatin type A hydrogels in the acidic pH range of 3.2–3.9. It was shown that an increase in the chitosan-to-gelatin mass ratio up to 0.15 resulted in a growth in the hydrogel thermal stability and an increase in the elastic modulus, hardness, and yield stress. The structural strength of the fish gelatin–chitosan hydrogel increased due to the strengthening of the binding zones in the fish gelatin gel network in the presence of chitosan. According to scanning electron microscopy, the supramolecular microstructure of the gels demonstrated a significant compaction upon the addition of chitosan to fish gelatin. UV and IR spectroscopy data, as well as changes in zeta potential, showed the formation of supramolecular complexes of fish gelatin with chitosan as a result of hydrophobic interactions between biomacromolecules and the establishment of hydrogen bonds; in this case, electrostatic interactions between macromolecules of fish gelatin and chitosan are practically absent in the acidic pH region. The ability to form supramolecular complexes of different compositions at different mass ratios of polysaccharide-to-fish gelatin makes it possible to obtain hydrogels with high gelling properties, strength, elasticity, and thermal stability comparable to hydrogels of mammalian gelatin.

The objective of the study was to obtain protein ingredients from mussel shell valves and to examine their potential application in the production of dry sauce with regard to the impact on organoleptic and physicochemical parameters, and rheological properties. The organic component of the shells, designated as conchix, is primarily composed of proteinaceous substances with low solubility in water (14.86% at pH 7), as well as in diluted solutions of acids (13.56% at pH 3 and 13.06% at pH 5) and alkalis (16.51% at pH 9 and 28.48% at pH 11). The enzymatic treatment of conchix with pancreatin resulted in the production of a hydrolysate with a high content of readily available protein substances (53.19%) and a degree of hydrolysis of 17.54%. Four product samples with varying proportions of hydrolysate added (1–3% of hydrolysate, 2–6%, 3–9%, and 4–12%) and a control sample were prepared to investigate the impact of hydrolysate dosage on sauce characteristics. Dry sauces with hydrolysate supplementation had higher protein concentrations (17.97%, 18.21%, 18.71%, and 19.01% in samples 1, 2, 3, and 4, respectively) than the control sample (17.60%). An organoleptic evaluation was conducted to ascertain the impact of the hydrolysate on the appearance, color, taste and aftertaste, odor and consistency of the prepared sauces. Sample 4 scored lowest, while sample 1 scored highest. The recommended dosage of hydrolysate in the sauce formulation is between 3 and 9%. The hydrolysate had no significant impact on the rheological characteristics of sauces. The obtained results indicate the possibility of processing shellfish shells into a valuable protein ingredient applicable in the technology of dry sauces.

This study examines the possibility of plastic deformation in low-modulus gels and yielding liquids. The model systems were a gelatin-sodium alginate hydrogel and the same gel filled with nanoscale zinc oxide particles. The experiments involved short- and long-term observations of deformation development under a prescribed shear stress, followed by stress removal and monitoring of deformation recovery. The initial hydrogel is a typical soft-matter system with an elastic modulus of 63 Pa. At low stresses, residual deformations were observed in addition to elastic deformations; these residual deformations reached up to approximately one half of the total deformation. They appeared instantaneously, depended on the applied stress, and did not change during long-term observation. This behavior is characteristic of plastic deformation. The incorporation of 5% dispersed ZnO nanoparticles converted the gel into a yielding liquid. This transition is attributed to partial disruption of the physical network, as evidenced by a sharp decrease in the elastic modulus to 18 Pa and by comparison of the FTIR spectra of the unfilled gel and the nanoparticle-modified gel. The yield stress of the yielding liquid was 7 Pa. However, at stresses below this value, while the material remained in a gel-like state, steady-state flow with a very high viscosity, at the order of 10⁵–10⁶ Pa s, was detected. After the yield point was exceeded, steady-state flow with a much lower viscosity, at the order of 3 Pa s, occurred, as is characteristic of conventional liquids containing a solid filler. Nevertheless, a small fraction of plastic deformation was still observed. Thus, the experimental results show that physical gels can behave as elastic-plastic media and that yielding liquids may flow below the yield point with very high viscosity. All existing models of the mechanical behavior of gels represent various combinations of viscous and elastic elements, to which, for yielding liquids, a slider is added that begins to slide after overcoming static friction. This element models the yield point. However, no model includes plasticity as an independent mechanical phenomenon. The phenomenon of plasticity should therefore be taken into account when developing rheological models of yielding liquids.

Экстракция и характеристика альгината натрия из бурых водорослей Fucus vesiculosus

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.