Evaluation of Physicochemical Properties and In-vitro Biological Activities of Subcritical Water Extracts from Codium fragile

다국어 초록 (Multilingual Abstract)

Codium fragile (Cheonggak), a green seaweed widely consumed in Korea, exhibits a broad range of antioxidant and other biological activities. However, conventional ex- traction methods—including hydrothermal treatment, organic solvent extraction, and acid hydrolysis—are often constrained by long processing times and the environmental burden associated with organic solvent use. To overcome these limitations, C. fragile extracts were prepared using subcritical water hydrolysis (SWH; 120–240 °C, 30 min, 3 MPa; solid-to-solvent ratio, 1:20, w/v) and the outcomes were compared with those obtained using a 48 h methanolic extraction. To address these limitations, this study prepared C. fragile extracts using subcritical water hydrolysis (SWH; 120–240 °C, 30 min, 3 MPa, solid-to-solvent ratio 1:20, w/v) and compared the outcomes with those obtained from a 48 h methanol extraction. Proximate composition analysis showed that C. fragile is rich in nutrients, containing high levels of carbohydrates (43.40%) and proteins (17.05%) on a dry weight basis. Extracts produced under different SWH con- ditions were evaluated for extraction yield, color, total sugar content (TSC), total pro- tein content (TPrC), total phenolic content (TPC), and total flavonoid content (TFC). In addition, in vitro antidiabetic activity (α-glucosidase inhibition) and antioxidant ac- tivity (ABTS⁺, DPPH, and FRAP) were assessed. To characterize major constituents, GC-MS and LC-MS/MS analyses were conducted, identifying phenolic compounds such as hydroxytyrosol, caffeic acid, vanillin, eugenol, p-coumaric acid, and piceatan- nol, which were considered to contribute to the high TPC and strong antioxidant activ- ity. Gel permeation chromatography (GPC) revealed a temperature-dependent decrease in average molecular weight, suggesting that low-molecular-weight fractions may play an important role in enhancing antioxidant and antidiabetic activities. Overall, C. frag- ile extracts produced by SWH exhibited superior bioactivity and functionality com- pared with methanol extracts, indicating their potential as a promising eco-friendly nat- ural resource for developing antioxidant ingredients for functional foods and cosmetic applications.

목차 (Table of Contents)

• I. Introduction 1
• II. Materials and methods 5
• 1. Raw materials, chemicals and reagents 5
• 2. Proximate composition analysis 5
• 3. Process of subcritical water extraction 6
• 4. Physicochemical characteristics of CFEs 8
• 4.1. Color 8
• 4.2. pH 8
• 4.3. Maillard reaction products (MRPs) 8
• 4.4. Molecular weight distribution (GPC) 9
• 4.5. Total sugar content(TSC) 9
• 4.6. Reducing sugar content(RS) 10
• 4.7. Total protein content(TPrC) 10
• 4.8. Total penolic content(TPC) 11
• 4.9. Total flavonoid content(TFC) 11
• 4.10. Sulfate content 12
• 4.11. GC-MS analysis of bioactive compounds 13
• 4.11.1. Sample preparation 13
• 4.11.2. GC–MS analysis 13
• 4.12. HPLC-ESI-QTOF-MS/MS 14
• 5. In-vitro biological activities of CFE 15
• 5.1. Anti-diabetic activity 15
• 5.2. Anti-oxidant activity 16
• 5.2.1. ABTS+ radical scavenging activity 16
• 5.2.2. DPPH radical scavenging activity 16
• 5.2.3. Ferric reducing antioxidant power (FRAP) assay 17
• 5.3. Anti-inflammatory activity 17
• 6. Statistical analysis 18
• III. Results and Discussions 19
• 1. Proximate composition analysis 19
• 2. Yield 20
• 3. Physicochemical properties of CFEs 21
• 3.1. Color 21
• 3.2. Maillard reaction products 24
• 3.3. pH 24
• 3.4. Molecular weight distribution 26
• 3.5. Total protein, total sugar, and reducing sugar contents 28
• 3.6. TPC, TFC, and Sulfate content 30
• 3.7. Identification of chemical compounds in CFE by GC–MS 32
• 3.8. Phenolic compound profiling of CFE-240 by UPLC–ESI–QTOF MS/MS 36
• 3.8.1. Phenolic acids 37
• 3.8.2. Flavonoids 39
• 3.8.3. Other polyphenols 42
• 4. Anti-diabetic activity 51
• 5. Anti-oxidant activity 53
• 6. Correlation between the antioxidant activity of C. fragile extracts and their total phenolic and flavonoid contents 56
• 7. Anti-inflammatory activity 58
• IV. Conclusions 59
• References 60
• Abstract(in korea) 70