Immobilized Microalgae Extracts: Antioxidant Activity, Growth Characteristics, and Bioactive Packaging Applications

The high energy consumption and cost associated with harvesting suspended microalgae limit their large-scale utilization as a sustainable resource. To address this limitation, we immobilized Chlorella sp. in a silk fibroin-reinforced sodium alginate (SA-SF) composite gel, which increased biomass accumulation by 95.1 % and polysaccharide yield by 170 % compared with suspension cultures. The resulting post-separation extract (PSE), obtained after complete removal of the SA-SF matrix, displayed exceptional thermal and oxidative stability, retaining over 80 % DPPH and ABTS⁺ scavenging activity after heat treatment (80 °C, 20 min) and surpassing the performance of ascorbic acid. When incorporated into carboxymethyl cellulose/starch (CMC/SR) films, PSE imparted strong antioxidant function and enhanced moisture-barrier performance. In apple-slice preservation tests, PSE-based films significantly reduced browning and weight loss over 24 h, performing better than commercial plastic packaging. Overall, these results demonstrate that SA-SF immobilization not only boosted microalgal antioxidant production but also enabled the development of high-efficiency bioactive packaging materials for prolonging the freshness of perishable foods.