Marine macroalgae are important renewable marine resources that have attracted considerable scientific attention because of their nutritional value and diverse bioactive compounds with applications in food, pharmaceuticals, cosmetics, agriculture, and biotechnology (Holdt & Kraan, 2011). Seaweeds are generally classified into three major groups based on pigmentation: Chlorophyta (green algae), Phaeophyta (brown algae), and Rhodophyta (red algae). Among these groups, green algae have gained increasing attention due to their abundance of biologically active metabolites, including phenolic compounds, flavonoids, polysaccharides, alkaloids, and terpenoids, which exhibit antioxidant, antimicrobial, anti-inflammatory, antiviral, and anticancer properties (Khalid et al., 2018).

Enteromorpha intestinalis, currently accepted taxonomically as Ulva intestinalis, belongs to the family Ulvaceae and is widely distributed in coastal and estuarine ecosystems worldwide, including the Red Sea. This species is characterized by rapid growth, ecological adaptability, and high nutritional value. Previous studies have demonstrated that U. intestinalis is rich in carbohydrates, proteins, dietary fiber, essential amino acids, vitamins, minerals, and several secondary metabolites that contribute to its biological activities (Ortiz et al., 2006; Holdt & Kraan, 2011; Talukder et al.,  2020).

The increasing demand for natural antioxidants and environmentally friendly antimicrobial agents has stimulated interest in marine algae as alternative sources of bioactive compounds. Oxidative stress caused by excessive production of reactive oxygen species has been associated with the development of numerous chronic diseases, including cardiovascular disorders, diabetes, neurodegenerative diseases, and cancer. Natural antioxidants obtained from marine organisms have therefore become an important area of pharmaceutical and nutraceutical research (Cornish & Garbary, 2010). Likewise, numerous investigations have demonstrated that seaweed extracts possess inhibitory activity against several pathogenic microorganisms, highlighting their potential as natural antimicrobial agents for pharmaceutical and food preservation applications (Cox et al., 2010; Nifa et al., 2026).

Marine algae are also recognized as excellent sources of essential minerals, including calcium, potassium, magnesium, sodium, iron, zinc, manganese, and phosphorus. Their mineral composition is influenced by environmental conditions, geographical location, seasonal variation, and seawater chemistry (Circun-cisão et al., 2018; Ratul et al., 2025). Therefore, comprehensive physicochemical characterization is necessary to determine their nutritional quality and industrial potential. The Red Sea represents one of the world's most distinctive marine ecosystems because of its high biodiversity and unique environmental characteristics. Despite the ecological importance of Red Sea macroalgae, limited information is available regarding the physicochemical composition, phytochemical constituents, and biological activities of U. intestinalis from this region. Comprehensive evaluation of this species is essential to support its sustainable utilization as a natural source of valuable bioactive compounds. Therefore, the present study aimed to investigate the physicochemical characteristics, phytochemical profile, mineral composition, antioxidant activity, and antimicrobial potential of Enteromorpha (Ulva) intestinalis collected from the Red Sea. The findings provide valuable scientific evidence supporting its potential application in food, pharmaceutical, and nutraceutical industries.

Study Area and Sample Collection

Fresh samples of Enteromorpha (Ulva) intestinalis were collected from the coastal region of the Red Sea. Healthy algal thalli were manually harvested from the intertidal zone during low tide. The collected samples were transported to the laboratory in sterile polyethylene bags and washed thoroughly with seawater followed by distilled water to remove sand particles, epiphytes, salts, and other impurities. The cleaned samples were shade-dried at room temperature until a constant weight was achieved, pulverized using a laboratory grinder, and stored in airtight containers for subsequent analyses (AOAC, 2019).

Preparation of Algal Extracts

The dried algal powder was extracted following the procedure described in the original experimental protocol. The crude extracts were filtered and concentrated under reduced pressure using a rotary evaporator before storage at 4°C until further phytochemical and biological analyses were performed.

Physicochemical Analysis

Proximate composition, including moisture, ash, crude protein, crude lipid, crude fiber, and carbohydrate contents, was determined according to the standard methods of the Association of Official Analytical Chemists (AOAC, 2019). All measurements were performed in triplicate, and the results were expressed as mean ± standard deviation.

Phytochemical Screening

Qualitative phytochemical screening was carried out using standard analytical procedures to detect the presence of alkaloids, flavonoids, tannins, phenolic compounds, saponins, glycosides, steroids, and terpenoids as previously described by (Harborne, 1998; Sofowora, 2008).

GC–MS Analysis

Gas chromatography–mass spectrometry (GC–MS) analysis was performed to identify volatile and semi-volatile bioactive constituents present in the algal extracts. The detected compounds were identified by comparing their mass spectra with those available in the National Institute of Standards and Technology (NIST) spectral database (NIST, 2023).

Mineral Analysis

The mineral composition of the algal samples was determined using inductively coupled plasma–optical emission spectrometry (ICP–OES). Acid digestion of dried samples was carried out prior to instrumental analysis following standard analytical procedures for elemental determination (AOAC, 2019).

Determination of Antioxidant Activity

The antioxidant activity of the algal extracts was evaluated using the DPPH free radical scavenging assay following the method described by Brand-Williams et al. (1995). The percentage inhibition was calculated at different extract concentrations, and antioxidant activity was compared with a standard antioxidant.

Antimicrobial Activity

The antimicrobial activity of the algal extracts was evaluated against selected pathogenic microorganisms using the agar well diffusion method following the Clinical and Laboratory Standards Institute (CLSI, 2021) guidelines. Antimicrobial activity was expressed as the diameter of inhibition zones (mm).

Statistical Analysis

All experiments were performed in triplicate, and the results were expressed as mean ± standard deviation (SD). Statistical analyses were conducted using appropriate statistical software, and differences among groups were considered statistically significant at p < .05.

Extractable matters content

Upon successive extraction of the E. Intestinalis, with petroleum ether and ethanol, the yield was found to be (0.812%) and (4.36%) for the solvents, respectively.

Table 1: Phytochemical screening E. Intestinalis ethanolic extract.

Phytochemical screening of E. intestinalis from the Red Sea, Eastern Sudan, was consistent with findings from India, confirming flavonoids, alkaloids, steroids, saponins, and phenols. The results also agree with previous studies reporting tannins, glycosides, and cardiac glycosides (Shankhadarwar S. D., 2015).

GC-MS analysis of pet. ether extract

The gas chromatogram of pet. ether extract of E. Intestinalis showed detection of 15 compounds (Fig. 1). Their identification based on their mass spectra. The identified compounds with their percentages are shown in Table 2.

Fig. 1: The gas chromatogram of pet. ether extract.

The petroleum ether extract was mainly composed of phytol (29.16%), palmitic acid methyl ester (25.45%), and fucosterol (18.42%). Phytol has reported antioxidant, anti-inflammatory, antiallergic, and immunostimulant activities.  

Fucosterol exhibits antioxidant and hepatoprotective effects. Other detected compounds included stearic acid (2.35%), linoleic acid (2.20%), palmitoleic acid (0.95%), behenic acid (0.65%), arachidic acid (0.39%), and heptadecane isomers (7.54%).

Table 2: Petroleum ether extracts composition of E. Intestinalis.

 Linoleic acid is also known for anti-inflammatory and skin-moisturizing properties (Santos et al., 2013).

Proximate analysis

Proximate analysis of E. Intestinalis is shown in Table 3.

Table 3: Proximate Composition of E. Intestinalis.

The nutritional composition of E. intestinalis from the Red Sea, Sudan, was comparable to samples from Southern Thailand and Mexico in protein and ash content, but had lower crude fiber. Previous studies reported protein (14.6–19.5%), lipid (2.1–8.7%), ash (25.9–28.6%), soluble fiber (25.3–39.6%), insoluble fiber (21.8–33.5%), and total dietary fiber (51.3–62.2%) on a dry-weight basis.

Mineral content

Detection of minerals content of E. Intestinalis by (ICPES) revealed the presence of macroelements like K, Na, and S Table 4.

Table 4: Elemental composition of E. Intestinalis.

E. intestinalis contained the macroelements K, Na, and S, as well as the trace element Si. This agrees with Benjama and Masniyom (2011), who reported that U. intestinalis is rich in Mg, K, Cl, Na, and Ca.

Antimicrobial activity screening

The crude alcoholic extract of E. Intestinalis was investigated to evaluate its antibacterial activity against two strains of Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) and two strains of Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and one fungal strain (Candida albicans)using cup-plate method. Evaluation of the activity of the extract against the different strains is recorded in Table 5 and illustrated in Fig. 3. 

Table 5: Antimicrobial activity of E. Intestinalis ethanolic extract.

The antibacterial activity ((NCCLS, 1990):

• <9mm zone is considered as inactive
• 9-12mm is considered as partially active
• 13-18mm is considered as active
• >18mm is considered as very active

E. intestinalis showed considerable antimicrobial activity against both Gram-positive and Gram-negative bacteria and pronounced activity against C. albicans. This activity may be attributed to phenolics, flavonoids, tannins, saponins, and fatty acids. Phenolic compounds can disrupt microbial membranes and cellular proteins, while saponins also contribute to antimicrobial effects. Fatty acids may inhibit microorganisms by disrupting cell membranes, interfering with cellular energy production, and inhibiting intracellular processes (Desbois & Smith, 2010; Akter et al., 2025). The antimicrobial activity of polyunsaturated fatty acids has also been demonstrated against bacteria (Kankaanpää et al., 2001).

Fig. 2: Antimicrobial activity screening of E. intestinalis.

Antioxidant activity screening

The antioxidant activity of E. Intestinalis ethanolic extract was investigated using DPPH radical scavenging assay Table 6.

Table 6: Antioxidant activity of E. Intestinalis ethanolic extract.

The ethanolic extract of E. intestinalis showed moderate reducing and free-radical scavenging activities. These effects may be attributed to its phenolic compounds, fucosterol, and phytol, which are known for their antioxidant properties

Enteromorpha (Ulva) intestinalis collected from the Red Sea possesses significant phytochemical, nutritional, and biological properties. It contains valuable bioactive compounds, essential minerals, and nutritional components that contribute to its antimicrobial and antioxidant activities. These findings indicate that the species has promising potential for use as a natural source of pharmaceutical, nutraceutical, and functional food ingredients. Further investigations on the isolation, characterization, and pharmacological evaluation of its active constituents are recommended.

Not applicable, as this study did not involve human participants or experimental animals.

The data generated and analyzed during this study are available from the corresponding author upon reasonable request.

The author gratefully acknowledges the Department of Pharmaceutical Analysis and Quality Control, University of Medical Science and Technology. Special appreciation is extended to the research supervisor for continuous guidance throughout the study.

The author declares no conflicts interests.