Study on the Extraction Technology and Antioxidant Capacity of Rhodymenia intricata Polysaccharides

A red alga named Rhodymenia intricata was explored, and the extraction technology and antioxidant capacity of its polysaccharides were investigated. The crude polysaccharides were extracted using the ultrasound-assisted water extraction method, precipitated by alcohol, and purified using the trichloroacetic acid method. Subsequently, the scavenging rates of polysaccharides on hydroxyl, DPPH, and ABTS free radicals, were determined both prior to and following purification to evaluate their antioxidant activity. Extraction technology was optimized to improve polysaccharide yield, and the optimal parameters were as follows: particle size 100 mesh, material-liquid ratio 1:84 (g/mL), ultrasonic time 30 min, and extraction for 95 min at 80 °C. The maximized extraction rate of crude polysaccharides was 37.78 ± 0.15%. The obtained crude polysaccharides were purified with different concentrations of trichloroacetic acid, and the purification effect was evaluated according to protein removal rate and polysaccharide retention rate, which could reach 62.61 ± 1.82% and 96.10 ± 1.60%, respectively. Infrared spectrum analysis suggested that Rhodymenia intricata polysaccharide might be α-pyranose. The Congo red test illustrated that the polysaccharide contained a triple helix structure. In the antioxidant activity assessment, the scavenging rates of polysaccharide prior to purification for RIP-1 (10 mg/mL) for hydroxyl, DPPH, and ABTS free radicals were observed to achieve maximum values of 94.71 ± 0.13%, 42.80 ± 7.12%, and 76.30 ± 5.20%, respectively. In contrast, the scavenging rates of polysaccharide following purification for RIP-2 (10 mg/mL) for the same free radicals reached maximum values of 94.10 ± 0.27%, 32.37 ± 0.78%, and 98.30 ± 0.34%, respectively. Notably, these scavenging rates exhibited a dose-dependent relationship. These results demonstrated the potential of the extraction method for polysaccharides from Rhodymenia intricata, and for adding value to the by-product for its potential application as an antioxidant in food and pharmaceutical products.