Development and characterization of microalgae-based hydrogel with Nannochloropsis oceanica and soy protein isolate:...

Microalgae are a promising source of polysaccharides and proteins, with unsaturated fatty acids, minerals, and antioxidants, which can strengthen the hydrogel's network and deliver bioactive compounds. This study incorporated different concentrations of microalga Nannochloropsis oceanica into soy protein isolate (SPI) hydrogels. SPI-N. oceanica (20 wt%) demonstrated regular and uniformly distributed pores in the structure and an enhanced viscoelasticity behavior, as shown in SEM and rheological analyses. All hydrogel samples demonstrated low water solubility (1.62-3.43%), swelling rate of 1398.7 to 1721.7% after 24 h, and a linear viscoelasticity region (G' values higher than 1000). SPI-N. oceanica (20 wt%) demonstrated the highest antioxidant activity in terms of the total phenolic content, total flavonoid content, ABTS, and DPPH assays. When immersed in a 10 mg/mL gallic acid solution for 72 h, the loading rate increased to 58.85-64.60% and loading amount increased to 220.26-244.62 mg gallic acid/g hydrogel. Then, all hydrogel samples loaded with 5 mg/mL and 10 mg/mL gallic acid exhibited a release amount of 11.73 to 17.73 mg gallic acid/g hydrogel and 42.56-57.86 mg gallic acid/g hydrogel, respectively, after 24 h. The antimicrobial activity of the hydrogel samples was enhanced upon loading with gallic acid against Escherichia coli and Enterococcus faecalis. Overall, the successful integration of N. oceanica into SPI hydrogel demonstrated its potential as a slow-release drug delivery system, thereby expanding the applications of microalgae-based biocarriers in biomedical fields.