2.1. Extraction Efficiency of the Various Components
The yields of the bioactive compounds and polysaccharide extraction from the five seaweed collected samples are displayed in
Table 1.
The extraction yields of bioactive compounds from the seaweeds in this study show significant variations and are ranked as follows, in descending order: D. dichotoma (27.07 ± 1.19%), C. laetevirens (12.07 ± 0.44%), U. lactuca (9.55 ± 0.12%), C. officinalis (6.11 ± 0.12%), and S. muticum (5.29 ± 0.44%).
The extraction yield of bioactive compounds from
D. dichotoma was 27.07%. In contrast, the yield from the same species, gathered at the shores near Bahía Bustamante in summer (Chubut Province, Argentina) [
24], amounted to only 3.6% for a methanolic crude extract. Conversely,
D. dichotoma, hand-collected in December along the Kachchh coast in Gujarat, India [
25], showcased a notably higher yield of 37.97% using the same solvent, underscoring the substantial variability in yield within this species. Another Mediterranean harvest of
D. dichotoma, resulting in a 14.22% yield for a methanolic extract, occurred in May 2015 during a scuba dive in Bou Ismail Bay (central Algerian coast) [
26].
Our investigation revealed that
S. muticum contained 5.29% of extracted bioactive compounds. Conversely, various
Sargassum species collected across different regions exhibited significantly variable yields. For example, ethanol absolute extraction of
S. aquifolium, harvested along the Kuwaiti coast, manifested a higher yield of 11.9% [
27]. In contrast, methanolic extraction of
S. oligocystum yielded 7.11% in Malaysia [
28], and methanol (1:10
w/
v) extraction in Manado, Indonesia, resulted in a 4.95% yield [
29], emphasizing the diversity of extraction yields within this genus.
The red seaweed
C. officinalis, collected from our northeastern Algerian coast, exhibited an extraction yield of bioactive compounds of 6.11%, slightly surpassing that of the methanolic extract of
C. officinalis (4.3%) collected in Egypt (Abu Qir Bay) [
30].
The extraction of bioactive compounds from
U. lactuca (9.55%) (
Table 1) diverges from the results obtained for the same genus harvested in similar Mediterranean waters, such as the methanolic extract of
Ulva lactuca (formerly
U. fasciata) (15.0%) in Abu Qir Bay (Egypt) [
30], while the methanolic extract of
U. intestinalis harvested on the central Algerian coast (Bou Ismaïl Bay) demonstrates a comparable yield (10.55%) [
26].
A total of 12.07% of the bioactive compounds in
C. laetevirens were extracted from our northeastern Algerian coastline. This yield contrasts with other results from
Cladophora collections, revealing significant variations in extraction yields.
Cladophora sp. collected from the Kuwaiti coast displayed the highest extraction yield of bioactive compounds (26.5%) for the 50% ethanol extract [
27], while
C. glomerata from Thailand exhibited the lowest yield (3.82%) for the methanolic extract [
31].
In terms of polysaccharide extraction yields (
Table 1),
D. dichotoma produces alginate at a rate of 14.15 ± 0.19%. However, this figure varies significantly depending on the collection location, with a notably higher yield of 18.73% observed on the Indian Gujarat coast [
32], contrasting starkly with a lower yield of 8.8 ± 2.12% when collected on the Sudanese Red Sea coast [
33]. In our current investigation,
S. muticum yielded an alginate content of 17.40 ± 0.95%, quite high compared with
S. muticum (10.23%) sampled in Spain [
34].
Furthermore, our findings indicate that
C. officinalis produces agar-agar at a rate of 8.85 ± 0.29%, contrasting with the significantly higher yield of 36.57 ± 1.06% from
C. officinalis collected on the Egyptian Mediterranean coast [
35].
In our study,
C. officinalis yielded approximately 8.19 ± 0.18% carrageenan. This rate is relatively low compared to
E. elongata (14.2%) collected during the low tide period in March 2015 on the Pamban and Manapdu coasts in India [
36], as well as to the carrageenan extracted from
Corallina officinalis (4.82 ± 1.52%) collected in a rocky shore basin near Skagaströnd (north-west Iceland) in October 2020 [
37].
Ulvan production from
U. lactuca was 2.47 ± 0.10% (
Table 1). This result is slightly lower than other ulvan extraction yields in various studies, such as ulvan from
U. fasciata (6.87 ± 1.21%) found in Abu Quir Bay, Egypt [
38], and from
U. lactuca (4.69 ± 0.76%) collected in Ho-Ping, Keelung, Taiwan [
39].
In our current study,
C. laetevirens had an ulvan extraction yield of 2.78 ± 0.07%, slightly lower than the ulvan extraction yield of
C. aerea collected in Yantai, China, at 5.65% [
40].
Based on these findings and comparisons, it is clear that the spatial and temporal variability in the bioactive compound’s composition of the collected seaweed is primarily caused by local environmental factors such as nutrient availability, suspended particles, and, thus, light availability, which affect substantially the chemical composition of seaweed biomass.
The water’s residence time may also impact the seaweed composition, which determines the likelihood that nutrients will be converted into new biomass [
41]. This study demonstrated spatial synchronicity in seaweed fractions where seasonal differentiation was typically possible, independent of the sampling site. According to Breuer et al. [
42], the bioactive compounds of the different seaweed groups (environmental and structural parameters) were most influenced by climate, nutrients, flow, and light regime. There is currently no consensus on the variables that control the composition of bioactive compounds in seaweed communities. Therefore, the additional information in this study is useful for understanding ecosystem functioning as well as the ecological assessment and modeling of seaweed. It is necessary to conduct additional research, particularly in other ecoregions, to confirm the results of this study and draw broader conclusions about the five seaweed communities under study. Future studies should concentrate on how environmental influences affect the seaweed communities being further investigated and understood. Local site-specific factors affect the composition of seaweed bioactive compounds, especially short-term temporal dynamics, despite being constrained by primary agents. Therefore, various scales of environmental and structural parameters should be included in investigations.
2.3. Seaweed’s Elementary Analysis Using X-ray
By performing a fundamental analysis, X-ray fluorescence spectroscopy is a vital tool that enables us to delve deeper into the variations between seaweed species and their constituent elements. The values for individual elements that have the same letter indices (e.g., “a”) indicate that there are no statistically significant differences between them. However, subsequent letter indices (a, b, c, d, e) determine groups in descending order. According to the study’s findings, the nutritional makeup of the five seaweed species under investigation differs significantly. For their use in various fields, these variations in nutritional profiles have significant ramifications. In particular, potassium (K), magnesium (Mg), sulfur (S), and calcium (Ca) are crucial for the development of algae (
Table 2). For the content of Rb, Cu, As, and Mn, no significant differences between seaweed species were observed (
Table 2).
The highest magnesium (Mg) level is found in
D. dichotoma (3.96 ± 0.34%), followed by
S. muticum (2.20 ± 0.386%). These results align with those attained for
D. dichotoma (17.17 mg.g
−1) and
Sargassum odontocarpum (formerly
S. coriifolium) (15.45 mg·g
−1) collected on the Caribbean Sea island of St. Martin [
47]. Magnesium is necessary for the production of chlorophyll and other metabolic processes, which may be advantageous for use in agriculture and nutrition [
48].
Dictyota dichotoma (4.93 ± 0.013%) has a significantly higher sulfur (S) content than
S. muticum (2.82 ± 0.011%). However, the latter contains more sulfur than the
Sargassum (0.82 ± 0.22%) collected in Barbados [
49]. Additionally,
D. dichotoma has a silicon (Si) level that is much lower (0.959 ± 0.017%) than that of
S. muticum (4.100 ± 031%). Silicon’s potential role in cell structure and resistance to environmental stress makes it potentially useful for agricultural and pharmaceutical applications [
50].
When compared to
C. officinalis (0.861%) collected in Holbeck, North Yorkshire, UK, the calcium (Ca) content of the same species in this study is relatively high, reaching 36.48 ± 0.035% [
51]. This seaweed also includes aluminum (Al) (2.39 ± 0.056%) and silicon (Si) (3.06 ± 0.031%), but neither phosphorus nor zinc are found. It also has low contents of potassium (K) (0.455 ± 0.004%), iron (Fe) (0.379 ± 0.009%), sulfur (S) (1.03 ± 0.008%), and manganese (Mn) (0.015 ± 0.003%).
The results of an elemental analysis of green seaweed show that the elements in those organisms differ significantly. Many metabolic processes, including seaweed growth, depend heavily on potassium. Ulva lactuca (3.32 ± 0.010%) and C. laetevirens (2.31 ± 0.007%) have equivalent concentrations of potassium (K). In addition, C. laetevirens has significantly higher magnesium (Mg) (6.26 ± 0.269%) and sulfur (S) (13.65 ± 0.022%) contents than those of U. lactuca (1.61 ± 0.361% and 6.62 ± 0.016%, respectively, for Mg and S).
The composition of
C. laetevirens is quite similar to that of
C. glomerata collected in Iran [
52]. Calcium and potassium were also detected in
U. lactuca harvested on the island of Qheshm (in the Persian Gulf) in southern Iran [
53]. Calcium is essential for dental and bone health, as well as for various physiological processes. The variations in the fundamental composition of the multiple seaweeds provide numerous options for different applications. Each type of seaweed has distinct uses depending on the specific elements present, so to fully exploit their potential, it is essential to understand their composition. Many industries, including human food, agriculture, medical testing, and other areas of interest, can see these advantages.
2.4. Seaweed-Based Analysis by UPLC-ESI-MS/MS
Brown seaweeds, such as
D. dichotoma and
S. muticum, were very rich in polyphenols and vitamins, as shown for the methanolic extract, with chrysin accounting for the majority, at 52.52% and 53.60% for
D. dichotoma and
S. muticum, respectively. Chrysin has also been detected in
D. cervicorni in Saudi Arabia’s Red Sea [
54]. Vanillin levels are similar for both algae, varying between 13 and 14%. Vanillin is a compound quantified in
Sargassum wightii harvested in India [
55].
A low flavonoid concentration was noticed: kaempferol, which accounts for 3.55% of D.
dichotoma and esculin for 4.26% of
S. muticum. If not identical, the ethyl acetate and n-butanol fractions have remarkably similar compositions. Flavonoids are available in trace form, with the compound with the highest content being kaempferol for all fractions of
D. dichotoma and Hespertin for the ethyl acetate and n-butanol fractions of
S. muticum, the latter also making up a variety of Moroccan brown seaweed [
56].
The red seaweed C. officinalis is famous for having gallic and chlorogenic acids in it. However, this study found no gallic acid, and the ethyl acetate and n-butanol fractions only contained trace amounts of chlorogenic acid. Additionally, as polyphenols, the methanolic fraction includes ascorbic acid (17.92%) and vanillin. (13.72%). Flavonoids and esculin are only present in trace amounts (3.59%). In both fractions, benzoic acids were present at 47–56%.
There are differences in the composition of the green seaweed,
U. lactuca, which was the subject of this study. Hespertin, which makes up 3.93% of the methanolic fraction of
C. laetevirens, is a polyphenol. The last 9% comprises naringenin, quercetin, rutin, cinnamic acid, caffeic acid, and 4-hydroxy-coumaric acid. This bioactive composition is quite similar to that obtained from
C. glomerata, where rutin, quercetin, and kaempferol harvested in Thailand could be detected [
57]. On the other hand, the methanolic fraction of
U. lactuca corresponds better to that of the brown and red seaweed studied. Vanillin makes up 39.32% of its composition, making it a predominant polyphenol. The results of Kumar et al. for
Ulva rigida [
55] and esculin as a coumarin at 9.51% are equivalent to those of this study. The amounts of benzoic acid and hesperine in the ethyl acetate and n-butanol fractions of the two seaweeds are still comparable, ranging from benzoic acid (16–19%) to hespertin (3–4%). The results are consistent with those found in samples of
U. fasciata collected in the Mediterranean [
58] and
C. glomerata collected in Poland [
59]. The following figure (
Figure 2) displays the chemical structures of the major bioactive compounds identified in the methanolic extracts of the brown algae
D. dichotoma and
S. muticum, the red algae
C. officinalis, the green algae
U. lactuca, and
C. laetevirens. The overall data for the analysis are provided in the
Supplementary Materials in Tables S1–S5 and Figures S1–S5. These findings suggest that, with a few minor exceptions, the composition of the studied seaweed is mainly comparable. This suggests that their growth environment, including their shared geographic location, environmental conditions, and interactions with other organisms, impacts them [
60,
61].
2.8. Correlation between Antioxidant Assays
In this study, we examined the antioxidant activity, total flavonoid content (TFC), and total phenolic content (TPC) of the five seaweeds.
The mean values of antioxidant activity for the DPPH, ABTS, and reducing power tests are 413.01, 203.65, and 198.46, respectively. The median for each of these tests indicates variation in antioxidant activity among the samples.
The standard deviation for each test shows that the data deviate from the mean, suggesting significant variability in antioxidant activity among the tested samples. Kurtosis and skewness suggest the shape of the data distribution, with higher values for the ABTS and phenanthroline tests potentially indicating a more concentrated but asymmetric distribution.
The range of values for each test is significant, indicating large variability in antioxidant activity among the samples. The coefficients of variation are high, confirming substantial variability in the data for each of the tests. The descriptive statistics presented in the
supplementary file (Tables S6 and S7) provide a detailed analysis of total phenolic and flavonoid content, as well as the various antioxidant activity tests.
Table 6 presents the results regarding the antioxidant activity, total flavonoid content (TFC), and total phenolic content (TPC) in various samples.
Table 7 shows Pearson’s simple correlation coefficients between different antioxidant assays, including DPPH, ABTS, reducing power, phenanthroline, and SNP.
The DPPH and ABTS show a slight positive correlation (0.18), suggesting that there is some, although limited, similarity in the results of the two tests.
Power reduction has a moderate positive correlation with DPPH (0.36) and a small positive correlation with ABTS (0.30), indicating some commonalities between these tests.
Phenanthroline test results have a small positive correlation with both DPPH (0.23) and ABTS (0.60), suggesting that these tests measure different aspects of antioxidant activity.
The SNP shows a slight positive correlation with DPPH (0.39) and potency reduction (0.38), suggesting some similarity in the results of these assays but little association with other antioxidant assays. Overall, the table suggests that different antioxidant tests may have some common characteristics but also measure different aspects of antioxidant activity.
Table 8 presents Pearson’s simple correlation coefficients, illustrating the relationships between antioxidant activity and bioactive compounds.
DPPH, being compared to itself, naturally shows a perfect positive correlation (1.00).
There is a negligible negative correlation (−0.05) observed between DPPH and ABTS, suggesting a slight inverse relationship between these two antioxidant assays.
A modest positive correlation (0.14) is found between DPPH and reducing power, indicating a tendency for samples with higher DPPH activity to also exhibit higher reducing power.
Phenanthroline displays a weak positive correlation with DPPH (0.02), a moderate positive correlation with ABTS (0.52), and a moderate positive correlation with reducing power (0.45). This suggests that samples with higher levels of phenanthroline tend to have higher antioxidant activity in these assays.
SNP demonstrates a weak positive correlation with DPPH (0.22) but a weak negative correlation with ABTS (−0.12), suggesting a slightly different relationship between SNP and the two antioxidant assays.
Total flavonoid content (TFC) exhibits a strong negative correlation with DPPH (−0.70), implying that samples with higher levels of flavonoids tend to have lower DPPH activity, indicating a potentially inhibitory effect of flavonoids on DPPH radical scavenging.
Total phenolic content (TPC) shows a moderate negative correlation with DPPH (−0.43) and a moderate positive correlation with phenanthroline (0.57), suggesting some degree of association between TPC and these antioxidant assays.
In summary, the correlations between antioxidant activity and bioactive compounds vary in strength and direction, indicating complex relationships between these variables.
2.9. Antibacterial Activity
The study revealed an increase in antimicrobial activity as the concentration of extract increased, indicating a possible correlation between concentration and effectiveness. Antimicrobial activity results for the different species are summarized in
Table 9.
The results are also significantly influenced by the type of bacteria used in the test. When tested against
E. coli,
D. dichotoma displayed marginally higher antibacterial activity than other algae at doses of 1000 g·mL
−1 and 500 g·mL
−1. Although, to a lesser extent,
D. dichotoma also demonstrated above-average performance against
S. aureus. These results are consistent with those of the same species studied by Imran et al. [
46]. The performance of
S. muticum consistently remained stable when tested against E. coli at all concentrations. However, it appears less effective against
S. aureus than
D. dichotoma, particularly at lower concentrations. The results are superior to those found for
S. fusiforme and
S. oligocystum collected along the Zhejiang coast in China [
76] and Cagayan, Philippines [
77], respectively.
As the concentration diminished,
C. officinalis’ antimicrobial activity toward
E. coli decreased. Its performance against
S. aureus was comparable to that of
S. muticum, albeit somewhat lower at lower concentrations. These results are similar to those of
C. elongata collected in Mostaganem, Algeria [
78].
U. lactuca’s antimicrobial properties towards
E. coli are moderate but diminish with decreasing concentrations. When tested against
S. aureus, it appears slightly less potent than
D. dichotoma at all concentrations.
U. lactuca collected in Algeria showed perfect activity (23.2 ± 0.46 mm) against
E. coli and (13.8 ± 0.23 mm) against
S. aureus [
78]. In lower concentrations,
C. laetevirens’ antimicrobial activity toward
E. coli diminishes. As opposed to the other types of seaweed, it appears to be less effective against
S. aureus when tested, especially at lower concentrations. However,
C. glomerata collected in Iran showed weaker antimicrobial activity than
S. aureus [
79].