Yields in dry extracts
The results indicated that, the aqueous extract produced the highest yield (6.20%) compared to the methanolic extract (5.10%). Similarly, the color was light orange for the methanolic extract and dark orange for the aqueous extract. This difference can be explained by the amount of total extractable compounds which is inversely proportional to decreasing polarity of the solvent used
(Belhaoues et al., 2020).
Screening
Screening is presented in Table 1, the results revealed the presence of saponosides, mucilages, alkaloids, combined anthraquinones (C-heterosides), polyphenols and flavonoids. However, steroids, triterpenoids, tannins, anthocyanins, combined anthraquinones (O-heterosides), free anthraquinones, leucoanthocyanins and reducing compounds, were not present. Likewise, several scientific studies have shown that sea urchin gonads offer numerous types of components with high medical value. The gonads are rich in bioactive components, such as polyunsaturated fatty acids
(Robinson and Blair, 2008), carotenoids
(Matsuno and Tsushima, 2001), phospholipids
(Shikov et al., 2012), sulfated fucans
(Biermann and Mourao, 2002) and active polysaccharides
(Shikov et al., 2018). The results from this study were more or less comparable to those of
Akerina et al., (2015) which indicated the presence of steroids and triterpenoids. On the other hand,
Sidiqi et al., (2019) reported the absence of alkaloids and phenols on sea urchin
Diedema setosum. These differences in composition may be due to the detection capacity of the chemical test as some tests are unable to detect low amounts
(Artini et al., 2013). Further, it could be due to the different environmental conditions and also due to the different maturity stages of sea urchin gonad, which was used as research material
(Darsono, 1986) as well as the genera and species.
Estimation of carotenoids
The composition of carotenoids is represented in Table 2, the carotenoids contents were 15.84±0.01 µg/g of gonads. Carotenoids are widely distributed, naturally occurring pigments, usually red, orange, or yellow in color
(Matsuno and Hirao, 1989). The carotenoids concentrations are high in the reproductive organs, which suggests their importance in reproduction
(Goodwin, 1984). In our results, the concentrations obtained are more or less variable compared to those reported by
Griffiths and Perrot (1976);
Tsushima and Matsuno (1990);
Lamare and Hoffman (2004), they recorded concentrations between 5 and 1870 µg/g of gonads. This difference could be attributed to the methodology adopted, species used, feeding, environmental conditions as well as gametogenesis.
Borisovets et al., (2002) reported that the pigments of the gonads, were high at spawning or during active gametogenesis. In general, animals do not synthesize carotenoids and those found in bodies of animals are an accumulation of carotenoids from the food
(Griffiths and Perrott, 1976). The work of
McLaughlin and Kelly (2001) indicated that the diet rich in microalgae improves gonad quality.
Estimation of vitamin C and E content
The composition of vitamin C and E is represented in Table 2, a high vitamin E (112.74±0.10 mg/g) was found, compared to vitamin C (61.77±0.71 µg/g). The gonads are a source of vitamins, minerals and other micronutrients, the diet of the sea urchin can influence biochemical composition of the gonads
(Chen et al., 2010). Sea urchin roes are rich in vitamins
(Jinadasa et al., 2016) as the food source comes from different types of algae
(Akerina et al., 2015). Vitamin E is an antioxidant, which serves to neutralize free radicals and prevent lipid oxidation
(Vasanthi et al., 2012). The abundance of vitamin E in sea urchins has already been highlighted in the work of
Salma et al., (2016) of the species
Diadema setosum (23.47 mg/100 g of gonads). Also, the work of
De-Quiros et al., (2001) reported the presence of vitamin C in
Paracentrotus lividus (26.57±1.50 mg/100 g of gonads).
Antioxidant capacity
The results obtained with DPPH and FRAP methods are presented in Table 3, the antioxidant capacity is of the order of IC50 = 02.690±0.37 µg/µg of DPPH by methanolic extract and IC50 = 05.87±0.27 µg/µg of DPPH for the aqueous extract. Methanolic extract is the most active with the lowest EC50, because a low IC50 value represents a high antioxidant activity. The reducing power of the two extracts showed better activity of the methanolic extract compared to the aqueous extract, the methanolic extract showed higher FRAP than ascorbic acid (800±0.98 µM). Data presented no significant difference (p>0.05) between extracts and standards, which indicates a appreciable antioxidant activity. The strong antioxidant activity of the methanolic extract would be due to solvent, which is able to destroy cell wall and causes the components in the cell to disintegrate and dissolve in solvents
(Lapornik et al., 2005). Various results indicated that sea urchins generate has many components that act as antioxidants
(Jazayeri, 2012), the gonads are rich in antioxidants like polyhydoxylated naphthoquinone and echinochrome A (Aminur
Rahman et al., 2014). The antioxidant potential of gonads has already been reported in
Strongylocentrotus droebacheinsis (Mamelona and Peltetier, 2010),
Strongylocentrotus nudus (Shang
et al., 2018),
Tripneustes gratilla (Chen and Hwang, 2014) and
Stomopneustes variolaris (Archana and Babu, 2016). This good antioxidant capacity is the fact that the gonads contain carotenoids and polyphenols which possess potent antioxidant activity
(Archana and Babu, 2016). The consumption of gonads of sea urchin is associated with anti-inflammatory, anti-atherosclerotic and anti-carcinogenic activities
(Mamelona and Peltetier, 2010). Likewise, Extracts from the gonad of sea urchin may act as photoprotectants, mitigating the damaging effects of UV radiation and increasing larval survival rates
(Lamare and Hoffman, 2004).
Total phenolic and flavonoids content
The results obtained are represented in Table 3, the total polyphenol contents of extracts were 2.22±0.21 and 3.43± 0.09 mg/g for aqueous and methanolic extracts, respectively. The flavonoid contents of extracts were 0.95±0.07 mg/g for aqueous extract, while the corresponding content for the methanolic extract was 1.70±0.04 mg/g. In our results, there were higher amounts of polyphenols and flavonoids in methanol extract than in aqueous extracts. The data presented no significant difference (p>0.05) between extracts. However, this finding does not resolve the difference both in terms of quantity and quality of bioactive molecules. Methanol showed a little bit better characteristic as a solvent for the extraction polyphenols and flavonoids than water. The polyphenols are a class of low molecular weight secondary metabolites. The polyphenolic compounds are also found in sea urchin gonads, they are considered important as bioactive dietary compounds with putative health benefits, as they are able to terminate free radicals and chelate metal ions, which are capable of catalyzing formation of ROS
(Mamelona and Peltetier, 2010).
Antibacterial activity
The results obtained are represented in Table 4, the DMSO at 2% is adequate and does not exhibit any impact on the normal process of growth of the reference strains. The bacterial resistance could be very critical, the gentamicin (10 µg) tested as a positive control has indicated inhibition zones between 17.5±01.37 and 25.66±01.21 mm. The methanolic extract showed considerable antibacterial activity at 200 mg against
Klebsiella pneumoniae (28.33±0.52 mm),
Escherichia coli (21.46±0.75 mm),
Staphylococcus aureus (19.6±0.59 mm) and
Enterococcus faecalis (18.33±0.57 mm). No zone of inhibition was observed for the species
Pseudomonas aeruginosa. The data presented significant difference (p<0.05) between the different bacterial strains and concentrations. According to
Tiwari et al., (2014), the gram-negative bacteria showed less sensitivity and this may be due to their extra-lipopolysaccharide and protein cell wall that provides a permeability barrier to the antibacterial activity. However, this result was not observed in our study since the extract had an almost similar effect on the gram negative than gram positive. These results suggests that the presence of bioactive molecules have a broad-spectrum antibacterial activity
(Belhaoues et al., 2017). The results of our study differs research reported by
Bragadeeswaran et al., (2013); Lisa Ah Shee Tee et al. (2017);
Sidiqi et al., (2019) and
El-Sayed et al. (2020) where more or less significant zones of inhibition were found. This difference could be caused by several reasons including, the extract concentration
(Ariyanti et al., 2012), the size and gender of gonads. As well, the genus and species of sea urchin and maturity. The gonads of
Sphaerechinus granularis used in this study is in a mature phase, however some sea urchins were in the pre-mature phase. According to
Darsono (1986), the gonadal maturity can not only be determined by size. Likewise, the solvent used for the extraction plays an important role. The methanol was able to extract components derived from alkaloids, phenols and carotenoids. The saponin compounds have potential as antibacterial because they are polyphenol compounds that can inhibit bacteria by damaging the permeability of bacteria cell membranes
(Sikkema et al., 1995). The biological function of saponins which are related to the system of self-defense against marine fungi, predators and parasites
(Pranoto et al., 2012). Likewise, the flavonoids are one of the polar phenol compoundshave high antibacterial activity
(Darsana et al., 2012). It should be noted, however, that the attribution of the antibacterial activity of a complex mixture to a single compound is subjective
(Belhaoues et al., 2020). Because the possible synergistic effect of the phenolics compounds with one another
(Lopes-Lutz et al., 2008). Also, no antibacterial effect was found for the species
Pseudomonas aeruginosa, it is unlikely that this is due to the low concentration of bioactive molecules and ability to develop resistance against multiple classes of antimicrobials which is alarming and concern
(Sekhri et al., 2021). The aqueous extract did not indicate antibacterial activity.
Minimum inhibitory and bactericidal concentration
The results obtained are represented in Table 5, for the methanolic extract, the lowest MIC was observed for the species
Klebsiella pneumonia (50 mg/ml). Values between 60 and 90 mg have been observed for
Escherichia coli,
Staphylococcus aureus and
Enterococus faecalis species. For MBC, it is around 400 mg/ml for
Staphylococcus aureus and
Enterococus faecalis and 100 mg/ml for
Escherichia coli and
Klebsiella pneumonia. Concerning the aqueous extract, the MIC and MBC could not be obtained, due to the turbidity of the extract and the range of concentrations chosen which could be lower than the MIC. For the
Pseudomonas aeruginosa species, the MIC is over 500 mg/ml. This species is a danger to public health because of its rapid growth, plasticity of its genome and is naturally resistant to several antibiotic families
(Benhalima, 2016).The comparison of the MBC/MIC ratio with the intrinsic values of the bioactive molecules proposed by
Marmonier (1990), allowed us to indicate that the methanolic extract has a bactericidal effect against
Escherichia coli and
Klebsiella pneumonia and bacteriostatic against
Staphylococcus aureus and
Enterococcus faecalis. Unfortunately, it was impossible to compare the results obtained, because very little work on the MBC/MIC ratio of sea urchins has been carried out.