رسائل ماجيستير
English
2023
Characterization extracts and agar extracted from the Omani seaweed Gracilaria debilis
Ahmed Al-Alawi , Mostafa Waly, Thuraya Humaid Musoud Al-Moqbaliyah , Zaher Al-Attabi
كلية العلوم الزراعية والبحرية-جامعة السلطان قابوس · عمان
The Sultanate of Oman’s coastline is abundant in many natural raw materials, such as seaweed plants. Red seaweeds are rich in a variety of nutrients, including lipids, minerals, vitamins, polyphenols, and carbohydrates. These substances have a range of applications in the food industry as well as in pharmaceutical, nutraceutical, and cosmetic products. A significant amount of agar was found to be present in Gracilaria debilis, a species belonging to the Rhodophyta group (red seaweed).
This study aimed to determine the proximate composition of Gracilaria debilis, extract its organic solvent-soluble compounds, investigate its polyphenol contents (TPC, TFC, and TTC), and extract agar to study its functional, biological, and chemical properties. The non-water-soluble compounds were extracted using three different organic solvents sequentially: ethyl acetate, acetone, and methanol. Agar was extracted using hot water (90°C for 2 hours). High-Performance Liquid Chromatography (HPLC) was performed to study the monosaccharide composition and profile of the agar. The structural characteristics of the organic solvent extracts and agar were analyzed using Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance (FTIR-ATR).
The findings of this study showed that ash (69.78 ± 1.98%) was the most abundant component in G. debilis, followed by carbohydrates (20.63 ± 2.00%) and protein (8.09 ± 0.03%), while the lipid content was the lowest (1.45 ± 0.03%). The main essential minerals found in the sample were Na, K, Ca, P, and Fe, with potassium detected at the highest concentration (48.72 ± 0.67 mg/g).
The methanolic extract exhibited the highest polyphenol contents among the three fractions (TPC: 154.2 ± 4.58 mg/g, TFC: 30.14 ± 0.20 mg/g, and TTC: 409.35 ± 2.91 mg/g). Methanol extracts also showed the highest antioxidant capacity with hydrogen peroxide (38 ± 0.40 U/ml), compared to ethyl acetate (33.6 ± 0.69 U/ml) and acetone (30.66 ± 1.61 U/ml) extracts. The total yield of agar was 21.4 ± 0.812%.
The extracted agar exhibited high antioxidant capacity at a concentration of 0.9%, and gel strength (120.1 ± 5.3 g/cm²) at a KCl concentration of 2.0%. Polysaccharides in the agar mainly consisted of galactose (65.75 ± 1.61%) and glucose (18.80 ± 2.49%), with small amounts of mannose, glucuronic acid, galacturonic acid, xylose, fucose, and arabinose.
Additionally, structural characteristics demonstrated the presence of ester sulfate (1380–1355 cm⁻¹), galactose 4-sulfate (850–845 cm⁻¹), and galactose 6-sulfate (820 cm⁻¹) structures in the agar extract. The sulfate content was found to be 12.13 ± 0.73%.
In conclusion, significant amounts of polyphenols were found in the organic solvent extracts from G. debilis. Moreover, the agar composition displayed excellent functional, biological, and chemical properties, making it suitable for use in the food industry as a thickening, gelling, stabilizing, and antioxidant agent. Future research could focus on protein extraction from G. debilis and investigate its biological, chemical, and functional characteristics.