In the present study, fucoidan was extracted from Nizamuddinia zanardinii samples using nine different green extraction techniques in addition to the conventional hot water extraction method (HW). Antioxidant (chemical and cellular assays) and emulsifying activities as well as optical properties of the different extracted fucoidans were investigated. The chemical composition and molecular weight of the fucoidans were also discussed. The results showed that fucoidan extracted using microwaves and a combination of ultrasound and microwaves (UM) exhibited the highest DPPH scavenging activity (72%) and reducing power (0.37–0.39 Abs). Moreover, all extracted fucoidans showed good cytoprotective effects on H₂O₂-induced damage and inhibition of reactive oxygen species formation in HepG₂ cells, and the fucoidan extracted by UM exhibited the highest activity (59.51–69.06%). Additionally, the fucoidans isolated by green techniques showed higher emulsification capacity than those isolated by HW method. Based on the obtained results, the method UM can be recommended for the extraction of fucoidans from N. zanardinii samples.

Novelty impact statement

Fucoidan is a sulfated polysaccharide extracted from brown seaweeds with various bioactivities. In recent years, industry prefer the greener and faster methods to obtain bioactive compounds. In this regard, further studies are needed to determine the bioactivity of compounds extracted by environmentally friendly methods. In the present study, impact of different green extraction methods on the antioxidant and emulsifying activity of fucoidans from N. zanardinii were investigated for the first time. The results confirmed that fucoidans extracted by green methods has antioxidant activity in both chemical and cellular models and also exhibits emulsifying activity. On this basis, the extracted fucoidans can be used for the development of dietary supplements for humans and can also be incorporated into food formulation for the production of functional foods.