Polysaccharides

In recent years, the sustained and even increasing interest in the development and application of novel composite materials based on the polysaccharide bacterial cellulose (BC) has been driven by the accumulation of experimental data and the emergence of analytical reviews that narratively summarize these findings. This review presents a comparative and critical analysis of various approaches to the fabrication of BC-based composites. Among them, in situ biosynthesis is highlighted as the most promising strategy. In this approach, different additives are introduced directly into the culture medium of BC-producing microorganisms, enabling the formation of materials with different mechanical and physicochemical properties. Such a method also allows imparting to the composites a range of properties that BC itself does not possess, including antibacterial and enzymatic activity, as well as electrical conductivity. During the so-called “cell weaving” stage, performed by BC-producing microorganisms, diverse substances and microorganisms can be incorporated into the cultivation medium. By varying the concentrations of the introduced compounds, their ratios to the synthesized BC, and by employing different BC-producing strains and substrates, it becomes possible to regulate the characteristics of the resulting composites. Special attention is given to the role of various polysaccharides that are either introduced into the medium during BC biosynthesis or co-synthesized alongside BC within the same environment. Depending on the mode of incorporation of these additional polysaccharides, the resulting materials demonstrate variations in Young’s modulus and tensile strength. Nevertheless, they almost invariably exhibit a decreased degree of BC crystallinity within the composite structure and an enhanced water absorption capacity compared to the pure polymer.

The mechanical, thermal, physicochemical and structural properties of a thermoplastic cassava starch obtained by a twin-screw extrusion process were evaluated, using glycerol and isosorbide as plasticizers at different concentrations (30, 35 and 40% by weight) and storage times (1, 15 and 30 days) under controlled conditions of relative humidity of 47 ± 2% and temperature of 25 ± 2 °C. The results obtained show a decrease in tensile strength and modulus of elasticity and an increase in elongation in the initial measurements, suggesting that, in both cases, a plasticization phenomenon via absorption of humidity predominated in short times, while at prolonged times, a rigidification of the material occurred due to the generation of a retrogradation process. Likewise, a higher tensile strength and lower elongation were found in the materials plasticized with isosorbide. Finally, it was observed that the retrogradation phenomenon was more evident in the thermoplastic starch samples made with glycerol, and that the starches plasticized with isosorbide had lower moisture absorption, higher crystallinity and a predominantly Eh-type crystalline pattern, related to greater stability over time.

The global aquaculture industry faces a number of challenges, including the risk of infection spreading in closed aquatic ecosystems. Since 1942, vaccination has become a mainstream approach in fish cultivation. However, the immune system of cold-blooded organisms differs significantly from that of mammals, which must be taken into account when developing vaccines for aquaculture. Modern technology employs delivery systems for antigens to protect them from degradation in the water and the digestive tract. Packaging the antigen into a biodegradable structure protects the protein or target gene from degradation and enhances antigen delivery to immune cells. The combination of chitosan and alginate is widely used for the development of various types of nano- and microcarriers. New vaccines based on these polysaccharides are more effective, increasing survival rates in some fish species by up to 100% compared to 20% in the control group. However, the correlation between the observed effects and the physicochemical characteristics of the polysaccharides/carriers, and the mechanisms of their action, remains unclear. This review summarizes and analyzes the data on the use of chitosan and alginate in aquaculture vaccines. Particular focus is given to the physicochemical properties and sources of the polysaccharides, and their potential implementation in aquaculture vaccination practices.