Title : Comparative evaluation of antioxidant activity and phytochemical content in freeze-dried and shade-dried brown seaweeds from the coastal waters of Oman

Brown seaweeds are a rich source of bioactive phytochemicals, with high antioxidant activity, such as polyphenols, flavonoids, phlorotannins, and condensed tannins. Research seeks to comparatively evaluate the effects of freeze-dried and shade-dried on the phytochemical content and in vitro antioxidant activity of three brown seaweed species, Turbinaria sp. Jolyna furcata, and Nizamuddinia zanardinii were collected from the Omani coast. Extracts were prepared using 80% methanol. Standard colorimetric methods were used to measure total phenolic content (TPC), total flavonoid content (TFC), total phlorotannin content (TPhC), and total tannin content (TCT). ABTS, CUPRAC, and DPPH tests were used to measure antioxidant activity. Freeze-dried samples exhibited significantly higher phytochemical contents and antioxidant activities than shade-dried samples (p < 0.05). While Nizamuddinia zanardinii had the best TCT (0.35 mg CE/g), DPPH (41%), and ABTS (1.21 mg TE/g), Turbinaria sp. recorded the highest TPC (0.91 mg GAE/g), TPhC (1.02 mg PGE/g), and CUPRAC antioxidant capacity (2.03 mg TE/g). Pearson correlation analysis replicates (n = 18) revealed strong positive correlations between TPC and CUPRAC (r = 0.960, p < 0.001), TPhC and CUPRAC (r = 0.960, p < 0.001), and TCT and DPPH activity (r = 0.870, p < 0.001), indicating that phenolic compounds, particularly phlorotannins and condensed tannins, were major contributors to antioxidant activity. These findings demonstrate the freeze drying is the most effective method for preserving for phytochemical and antioxidant potential of Omani seaweeds, highlight their potential as natural bioactive ingredient for nutraceutical, functional food, pharmaceutical, and cosmetic industries.

Keywords: drying methods, phytochemicals, antioxidant activity, phlorotannins, brown seaweed, Oman.

Fatma Al-Abri is a Research Assistant at the Centre of Excellence in Marine Biotechnology, Sultan Qaboos University, Oman. Her research focuses on marine natural products, antioxidant compounds, anti-aging bioactive molecules, functional foods, and marine biotechnology. She has extensive experience in phytochemical analysis, antioxidant evaluation, enzyme inhibition assays, and statistical analysis of natural products. Her current research investigates the effects of processing methods on the bioactive properties of Omani seaweeds and explores their applications in nutraceutical, pharmaceutical, and cosmetic industries.