Lipid profile and antioxidant activities of mud crab (Scylla olivacea) extract obtained from muscle and hepatopancreas

ABSTRACT

Mud crab (Scylla olivacea) is a valuable crustacean that has been consumed as nutritious foods for human body maintenance, delicacy tasting and for medicinal purposes. This study aimed to develop a novel mud crab extract processed through lactic acid fermentation. The objective is to compare the nutritional value, antioxidant properties and lipid profiling of mud crab muscles and hepatopancreas extract. Protein content in mud crab muscles extract (MCME) was significantly (p < .05) higher compared to the hepatopancreas. Lipids in MCME were significantly lower (3.36 ± 3.00%) (p < .05) than in hepatopancreas extract (HE) (14.75 ± 2.14%). Both eicosapentaenoic acid and docosahexaenoic acid content in MCME were relatively higher but not significantly (p > .05) different to HE. The DPPH-radical scavenging activity of both extracts was similar (p > .05). However, the ferric reducing antioxidant power in MCME was higher (p < .05) compared to HE. Therefore, MCME has the potential as an alternative natural antioxidant for healthy product.

KEYWORDS:

• Scylla olivacea
• extract
• nutritional value
• EPA
• DHA
• antioxidant activity

Introduction

A ready-to-drink concentrated extract or extract is a liquid product comprising fish, meat, vegetable, cereal or any combination of these. The most popular fish extract marketed is extract of snakehead fish and eel extract. In addition, walit bird nest, chicken and beef extract also have a high market value as ready-to-drink products. Extract may also contain salt, permitted colouring and/or flavouring substance, flavour enhancer, food conditioner and caramel. Extracts are produced with a combination of high temperature, pressure processing and prolonged fermentation time. Thermal processing breaks down the macromolecules into micro- and nanoparticles size and thus improves the bioavailability of biomolecule. Extracts are nutraceutical supplements capable of controlling both cognitive and physical impairments (Suttiwan et al., 2018). Chicken and vegetables are commonly commercialized extracts in the market. Extracts from fish and shellfish, however, also offer high micronutrients, although they impart unpleasant fishy taste and flavour but acceptable for consumer consumption.

Mud crab (Scylla spp.) is a high-value commercial seafood product due to their large size, delicate flavour and high meat yield (Zhao et al., 2015). Mud crab naturally inhabit in mangrove areas and estuaries (Nurdiani & Zeng, 2007). Genetically and morphologically, Scylla consists of four species: S. paramamosain, S. serrata, S. olivacea and S. tranquebarica. Two common species of South China Sea are S. olivacea and S. tranquebarica (Ikhwanuddin et al., 2011). Mud crab offers a nutrient-rich and healthy composition of protein, lipid, vitamins and minerals (Varadharajan, 2014). Mud crab protect themselves against infectious diseases by the innate immune mechanisms in combating the invading of pathogens (Yan et al., 2011). Various studies have documented non-specific innate immune protein commonly found in crabs such as antimicrobial peptide (Brockton et al., 2007; Imjongjirak et al., 2009; K. J. Wang et al., 2007), prophenoloxidase (Ko et al., 2007), anti-lipopolysacchaaride factor (ALF) (Imjongjirak et al., 2007; Li et al., 2008; Yedery & Reddy, 2009), antioxidant enzyme (Liu et al., 2010), superoxide dimutase (Lin et al., 2008), α2-macroglobulin (Vaseeharan et al., 2007) and haemocyanin (Yan et al., 2011). Besides, the immune system of crustacean responds to pollution or abiotic stress including environmental temperature and salinity changes (Paital & Chainy, 2013).

Phanturat et al. (2010) stated that antioxidant properties are beneficial for food preservation and promote human health. Bioactive peptides extracted from aquatic organisms protein by enzymatic hydrolysis potentially consist of antioxidant properties (Thiansilakul et al., 2007). Bioactive peptides are formed by the commercial protease or endogenous muscle enzyme during fermentation processing of fish body parts such as muscle, head, viscera, skin and hepatopancreas. Bioactive peptides generated from a particular protein depend on the primary sequence of the protein substrate and the specificity of the enzymes used to generate such peptides. Mendis et al. (2005) documented that histidine, leucine, tyrosine, methionine and cysteine from molluscs and crustacean proteins are prone to donate the protons to electron-deficient radicals, thus enhancing the radical scavenging activity. Furthermore, Rajapakse et al. (2005) documented two peptides, NADFGLNGLE- GLA and NGLEGLK, isolated from the squid hydrolysate also able to inhibit the free radical-mediated linoleic acid oxidation. Antioxidant activities are commonly measured by using the radical scavenging activity (DPPH) and ferric reducing antioxidant power (FRAP) assays. Senphen et al. (2014) documented that carotenoid produced from the shell of Pacific white shrimp recorded a significantly high DPPH and FRAP activity. Meanwhile, Lekjing et al. (2021) added that Lates calcarifer essence contained approximately 84.43–86.88% DPPH radical scavenging ability.

The commercialization of mud crabs extract not only benefits human health and controls number of health disorders (Ngo et al., 2011) but also helps the aquaculture industry. The demand for the culture and catch of mud crab for the production of extract has a positive impact on the livelihoods of artisanal fisherman and thus on aquaculture economic growth. The objective of this study is to prepare and determine the nutritional composition and antioxidant activities of S. olivacea muscle and hepatopancreas extract. In addition, fatty acid profiling of both mud crab muscle and hepatopancreas extract was evaluated.

Materials and methods

Lactic acid bacteria isolation and identification

Approximately 10 ± 0.1 g of yoghurt sample was added in 90 ml of De Man, Rogosa and Sharpe (MRS) broth before anaerobically incubating at 30°C for 48 h. A serial dilution was prepared in the range of 10⁻² to 10⁻⁶ with maximum recovery diluent (MRD). An aliquot of 0.1 ml samples were spread on MRS agar uniformly by using L-glass spreader. All samples were anaerobically incubated for 48 h. Gram staining, oxidase and catalase test were done for the presumptive LAB colonies. The LAB isolates were cultured anaerobically on MRS medium at 37°C for 24 h. Pure colonies were identified using VITEK 2 ID Card. The rod-shaped and Gram-positive bacteria were identified using VITEK 2 BCL ID Card. The results were analysed using VITEK 2 Compact System (BioMérieux).

Collection and preparation of the mud crab muscle and hepatopancreas

Mud crabs (Scylla olivacea) ranging in size from 210 to 220 g were collected from locals and immediately brought to the laboratory. The muscles and hepatopancreas of mud crab were freeze dried separately before kept at −20°C. The extract was prepared by mixing the muscles or hepatopancreas, respectively, with deionized water and molasses (fine brown sugar) in the ratio of 9:3:1 (w/v/v). Approximately 1.0 ± 0.1 ml of Lactobacilli sp. isolated from pure culture (bacterial concentration: 1500 × 10⁶ OD: 1.25) was mixed into the extract. All samples were fermented for 2 weeks.

Biochemical analysis

The proximate analysis of mud crab muscles and hepatopancreas extract was conducted according to the AOAC method (2005).

Protein analyses were subjected to three processes: digestion, distillation and titration. Approximately 0.2 ± 0.1 g samples were weighed accurately and labelled as W. The samples were put into 100 ml Kjeldahl digestion tubes, and each sample was prepared in three replicates. Blanks were prepared without samples. Five millilitres of sulphuric acid and the concentrated catalyst were added about half a tablet to all tubes, including the blanks. The tubes were shaken to ensure the samples were wetted with sulphuric acid and continued until all the samples’ digestion solution dissolved and a green/blue clear solution formed. The tubes were refrigerated vertically for 10–20 min.

During the distillation process, 30 ml 4% boric acid and 8 drops of methyl red were mixed into a 250 ml conical flask, turning the solution red. The collector flasks were placed under the condenser end, located below the surface of the receiver. The Kjeldahl distillation apparatus (Buchi, Germany) was activated, and 40 ml distilled water and 30 ml concentrated NaOH (40%) were pumped into the tube containing the refined sample. The solution in the beaker collectors changed the colour from red to green or dark blue. The receiver flask was removed for the titration process. The same distillation process was performed for the blank tube.

During the distillation process, the yield from the distillation process was titrated with 0.1 N HCl in the beaker until the green or dark blue colour changed to red. The endpoint of titration is reached when green or blue colour begins to turn red, but in a proper state, the solution is coloured gray. The volume of HCl used was recorded for titration Q. The step was repeated for the distillate from the blank tube, and the volume of HCl used was recorded as B.

Percentage N in sample = ((T-B) × N × 14.007)/w × 100

Percentage of protein in sample = % N × F

where,

T: The volume of HCI used in the titration from distillation sample (ml)

B: The volume of HCI used in the titration from blank distillation (ml)

N: Normality of HCI

W: Weight of the sample (mg)

F: Protein factor; 6.25

Lipid analyses were conducted according to the method outlined by AOAC (2005). Approximately, 2 g of samples labelled as W1 were placed onto filter paper, and both ends were wrapped using fat-free cotton and put into the fatty sheath. The samples were transferred into a lipid flask that was weighed and labelled as W2. The lipid flask was subsequently connected to a Soxhlet tube. The fatty sheath was placed into the extractor chamber of the Soxhlet tube and doused by fat solvent (hexane). After 6 h, the reflux process was completed. The mixture of the extracted fat and fat solvent in the lipid flask was distilled until all the fat solvent evaporated. Any solvent remaining in the extractor chamber at the time of distillation was removed and could not be added back into the flask. The lipid flask was dried in an oven at a temperature of 105°C. The flask was cooled until it reached a weight constant in desiccators and labelled as W3.

% Lipid content = (W_3-W_2)/W_1 × 100%

where,

W1: Sample weight (g)

W2: Weight of the flask without lipid (g)

W3: Weight of the flask containing lipid (g)

Moisture analyses were conducted according to the method outlined by AOAC (2005). The evaporating dish was dried using an oven (Memmert, Germany) at 105°C for about 1 h. The evaporating dish was put into the desiccators for approximately 15 min and weighed. Then, 2 g of the samples (W1) were placed into the evaporating dish. It was dried in the oven at 105°C for 5 h. Once the drying process was complete, the dish was placed into the desiccators. The sample was cooled and weighed again (W2).

% Moisture = (W1 − W2)/W × 100%

where,

W1: Sample weight before drying

W2: Sample weight after drying

Ash analyses were conducted according to the method outlined by AOAC (2005). The ash crucibles were dried in the oven (Memmert, Germany) at 100°C for 1 h. They were cooled in desiccators and weighed accurately and then recorded as W1. Approximately 2 g dried sample was weighed accurately into a crucible ash and recorded as W2. The crucible ashes were placed on the heating plate, and 0.5 ml of concentrated nitric acid was added into it. The temperatures were increased, and the samples were introduced into “ash wet” for 45 min until no white smoke was produced. These processes were done in a fume hood. The crucible ashes were put in a muffle furnace, and the sample was allowed to be ash for 3 h at a temperature of 600°C. The sample was cooled in a desiccator, and the grab sample was weighed accurately and recorded as W3.

% Ash = (W3 − W1)/(W2 − W1) × 100

where:

W1 = weight of ash crucible

W2 = weight of ash crucible + dried sample

W3 = weight of ash crucible + ash

Lipid profiling

Fatty acid methyl ester synthesis

Fatty acid methyl ester (FAME) was prepared using extraction-transesterification method (Sofian et al., 2021). Mud crab extract samples (20 ± 0.1 mg) were mixed with methanol, sulphuric acid and chloroform (17:3:20 v/v/v). All samples were placed in a water bath at 90°C for 30 min before being added with 1 mL distilled water. The lower phase of two layer containing FAME was transferred into a 10 mL bottle before being dried with anhydrous sodium sulphate.

FAME analysis

FAME was analysed using Shimadzu QP 5000 MS and GC-17A equipped with a BPX70 capillary column (0.25 mm diameter and 25 m length). The helium and hydrogen were used as the carrier gas and were regulated at 43.0 kPa column pressure with 1 mL min⁻¹ flow rate. GC initial temperature was set at 70°C before accelerated to 330°C (15°C per min). The temperature was set at 330°C for injection and detector. GC mass spectrum was evaluated to NIST Mass Spectra Library. FAME was identified at time retention correspond to FAME standard (CG18-91).

Antioxidant activity determination

Radical scavenging activity (DPPH)

Radical scavenging activity (DPPH) was analysed according to Binsan et al. (2008). An aliquot of samples was added to 1.5 ml of 0.15 mM 2,2-diphenyl-1-picryl hydrazyl (DPPH) (1:1/v/v). The mixtures were mixed before being left in the dark for 30 min. The solution absorbance was measured at 517 nm using Mini 1240 UV-VIS Spectrophotometer (Shimadzu, Japan). Standard curves were done using 10–60 µM Trolox. DPPH activity was determined as µmol TE g⁻¹ sample.

Ferric reducing antioxidant power

Ferric reducing antioxidant power (FRAP) was evaluated according to Benzie and Strain (1996). A stock solution containing 300 mM acetate buffer (pH 3.6) and 10 mM 2,4,6-tripyridyl-s-triazine (TPTZ) in 40 mM HCl and 20 mM FeCl₃.6${\mathrm{H}}_2$O was prepared. FRAP solution containing 25 ml of acetate buffer, 2.5 ml of TPTZ solution and 2.5 ml of FeCl₃.6${\mathrm{H}}_2$O solution was prepared before being incubated at 37°C for 30 min. Approximately 150 µl samples were added into 2850 µl of FRAP solution before left in dark for 30 min. The ferrous tripyridyltriazine complex (coloured product) was measured at 593 nm using Mini 1240 UV-VIS Spectrophotometer (Shimadzu, Japan). Standard curve were done using 50 to 600 µM Trolox. FRAP activity was determined as µmol TE g⁻¹ samples.

Statistical analysis

Data were statistically analysed using analysis of variance (IBM SPSS Statistics Software Version 20). The significant differences among the different treatments were determined using Post Hoc Test at 0.05 probability level. All data were shown as mean ± standard deviation of triplicate experiment.

Results and discussion

Nutritional values of mud crab muscles and hepatopancreas extract

The protein content in mud crab muscles extract was significantly higher (p < .05) compared to hepatopancreas extract or among others nutritional properties (Table 1). Meanwhile, lipid content in hepatopancreas extract presented a significant (p < .05) greater amount compared to muscle extract. The moisture content in muscle extract showed a significant (p < .05) higher value compared in hepatopancreas extract. Meanwhile ash content was found significantly higher (p < .05) in hepatopancreas extract compared to muscle extract.

Table 1. Nutritional values of mud crab (Scylla olivacea).

Nutritional values	Mud crab muscles extract (%)	Mud crab hepatopancreas extract (%)
Protein	46.02 ± 3.67^a	26.79 ± 3.51^b
Lipid	3.36 ± 3.00^a	14.72 ± 6.14^b
Moisture	12.19 ± 0.35^a	7.57 ± 0.43^b
Ash	12.30 ± 0.21^a	15.56 ± 0.49^b

Different superscript indicates significant difference (p < .05) between treatments.

Previous study by Sarower et al. (2013) documented that protein content found in S. serrata female and male (regardless to the body part) is in the range between 14.44 ± 1.41 and 24.54 ± 1.32%. Meanwhile, Paul et al. (2015) recorded 11.60 and 19.92% of protein content in S. serrata male and female, respectively. Another study by Sreelakshmi et al. (2016) stated that the protein content in S. transquebarica was approximately 15.63% and 17.63% in male and female, respectively. Yusof et al. (2019) reported that protein content in S. olivacea was recorded at 17.28% in male muscle compared to 13.30% in female muscle. Recently, F. Wang et al. (2021) documented that the protein content in female S. paramamosain muscle collected from various sampling location in China was in the range of 15.1 ± 0.2 to 17.9 ± 0.09%. Cui et al (2017, 2013) stated that the proximate composition varies and may be affected by the size, maturity, sampling season and location, and the availability of the foods.

The lipid content of S. serrata muscle was found lower (1.77 ± 0.44 to 2.62 ± 0.12%) (Sarower et al., 2013) compared to the current study (3.36 ± 3.00%). A similar trend has also been documented by various researchers in regard to the lipid content of S. serrata muscles: 0.38–0.78% (Zafar et al., 2004) and 0.53–1.54% (Sreelakshmi et al., 2016). In addition, Sreelakshmi et al. (2016) recorded that the lipid content of S. transquebanca was in the range of 0.65% to 1.37%. F. Wang et al. (2021) documented that the lipid content in muscles of S. paramamosain was in the range of 0.665 ± 0.09 to 0.825 ± 0.035% regardless of sampling locations. Interestingly, only few researchers have contributed to a study regarding the nutritional quality of hepatopancreas of mud crab, S. olivacea. A recent study documented that protein content in hepatopancreas of mud crab collected at various location of China Sea was recorded at 10.6 ± 0.3 to 11.6 ± 0.4% (F. Wang et al., 2021). Moreover, the lipid content was found at approximately 13.9 ± 0.6 to 20.5 ± 0.8% in hepatopancreas of S. paramamosain. In addition, Zhao et al. (2015) documented that lipid value in hepatopancreas (24.36%) of mud crab, S. paramamosain, was higher than in muscles (5.17%).

The protein and lipid content are not significantly different in regards to the species of mud crab and their sexes. Interestingly, there is a significant difference of nutritional quality value in body parts of mud crab. The present study results agree with the literature report where the protein content was found greater in muscles compared to the hepatopancreas. Furthermore, the lipid content were greater in hepatopancreas than in muscles of mud crab. Protein content in crab has a high biological value with its growth promoting capacity (Rekha et al., 2014). W. Wang et al. (2014) reported that crustaceans stored lipid at large amount in hepatopancreas for their energy expenditure such as moulting, reproduction or starvation. Bodin et al. (2007) added that hepatopancreas also serves as lipid storage reserves. Lipid is significantly used as a source of energy and essential fatty acids (Sheen & Wu, 1999). Moreover, for human consumption, low level of lipid content in extract is necessary because humans only need small amount of lipid in their nutrition. Therefore, mud crab muscles extract is good for human consumption compared to hepatopancreas extract due to high protein content and low lipid content.

Fatty acid profiling in mud crab muscle and hepatopancreas extract

Saturated fatty acid (SFA) in mud crab hepatopancreas extract recorded a significantly (p < .05) greater amount than muscles extract (Table 2). A similar trend was found in regard to the monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA). The eicosapentaenoic acid (EPA) (20:5n3) in muscle extract was relatively higher but not significantly (p > .05) different to EPA in hepatopancreas extract. Similarly, the docosahexaenoic acid (DHA) (22:6) in muscles extract recorded a higher amount compared to the DHA of hepatopancreas extract but was not significantly (p < .05) different. Total omega 3 fatty acids (∑ɷ3) of both samples was not significantly (p > .05) different from each other. Meanwhile, total omega 6 fatty acid (∑ɷ6) was significantly (p < .05) greater in hepatopancreas extract than ∑ɷ6 in muscles extract.

Table 2. Fatty acid profiling in muscles and hepatopancreas of mud crab (Scylla olivacea) extracts.

Carbon name	Molecular formula	Mud crab muscles extract	Mud crab hepatopancreas extract
Methyl decanoate	C 10:0	4.00 ± 2.55^a	3.32 ± 1.18^a
Methyl laurate	C 12:0	3.48 ± 1.38^a	1.14 ± 0.19^b
Methyl tridecanoate	C 13:0	2.91 ± 0.43^a	15.18 ± 2.55^b
Methyl tetradecanoate	C 14:0	2.59 ± 1.06^a	5.55 ± 0.90^b
Methyl pentadecanoate	C 15:0	15.98 ± 1.75^a	108.50 ± 16.78^b
Methyl palmitate	C 16:0	10.25 ± 4.22^a	19.21 ± 3.17^b
Methyl heptadecanoate	C 17:0	22.01 ± 9.31^a	5.62 ± 0.60^b
Methyl arachidate	C 20:0	10.82 ± 0.64^a	2.34 ± 1.96^b
Methyl heneicosanoate	C 21:0	0.65 ± 0.26^a	4.71 ± 0.21^b
Methyl docosanoate	C 22:0	10.51 ± 1.63^a	4.08 ± 0.96^b
Methyl tricosanoate	C 23:0	1.42 ± 0.68^a	5.16 ± 0.42^b
SFA		84.62 ± 23.9^a	174.82 ± 28.91^b
Myristoleic acid methyl ester	C 14:1	4.72 ± 2.87^a	13.53 ± 2.30^b
Cis-10-pentadecenoic acid methyl ester	C 15:1	3.66 ± 0.91^a	12.45 ± 2.17^b
Methyl palmitoleate	C 16:1	0.51 ± 0.26^a	27.97 ± 4.29^b
Cis-10-heptadecenoic acid methyl ester	C 17:1	2.13 ± 1.35^a	4.00 ± 1.30^a
Trans-9-elaidic acid methyl ester	C 18:1n9t	1.48 ± 0.44^a	136.76 ± 19.4^b
Cis-9-oleic acid methyl ester	C 18:1n9c	8.31 ± 4.98^a	0.00 ± 0^b
Methyl cis-11-eicosenoate	C 20:1	7.08 ± 1.35^a	3.15 ± 0.31^b
Methyl erucate	C 22:1n9	14.29 ± 2.79^a	3.44 ± 0.18^b
Methyl nervonate	C 24:1	1.74 ± 1.35^a	2.89 ± 1.48^a
MUFA		43.91 ± 16.29^a	204.20 ± 3.15^b
Linolelaidic acid methyl ester	C 18:2n6t	3.24 ± 2.39^a	12.68 ± 6.50^a
Methyl linoleate	C 18:2n6	3.53 ± 2.16^a	16.70 ± 3.09^b
Gamma-linolenic acid methyl ester	C 18:3n6	8.81 ± 4.11^a	26.66 ± 2.63^b
Cis-11,14-eicosadienoic acid methyl ester	C 20:2	21.82 ± 7.34^a	27.89 ± 21.0^a
Cis-8,11,14-eicosatrienoic acid methyl ester	C 20:3n3	1.21 ± 1.16^a	4.31 ± 1.96^a
Methyl cis-5,8,11,14-eicosatetraenoic	C 20:4	3.39 ± 1.19^a	5.46 ± 1.55^a
Cis-13–16-docosadienoic acid methyl ester	C 22:2	5.25 ± 0.06^a	5.05 ± 2.29^a
Methyl cis-5,8,11,14,17-eicosapentaenoate	C 20:5n3	2.21 ± 1.20 ^a	1.72 ± 0.57^a
All cis-4,7,10,13,16,19-docosahexaenoate	C 22:6	10.39 ± 3.11^a	5.55 ± 0.62^a
PUFA		59.85 ± 2.27^a	106.02 ± 40.2^b
EPA	C 20:5n3	2.21 ± 1.20^a	1.72 ± 0.57^a
DHA	C 22:6	10.39 ± 3.1^a	5.55 ± 0.62^a
∑ɷ3		3.42 ± 3.42^a	6.03 ± 2.31^a
∑ɷ6		15.58 ± 3.90^a	56.04 ± 11.8^b

Different superscript indicates significant difference (p < .05) between treatments.

F. Wang et al. (2021) documented that SFA in hepatopancreas of mud crab, S. paramamosain, was in the range of 42.1 ± 0.3 to 57.1 ± 0.5%, higher than in muscles that were recorded at 28.1 ± 0.7 to 41.8 ± 1.4%. A similar trend was found in regard to the MUFA value. Interestingly, a similar trend was recorded in the current study, including the PUFA value. However, F. Wang et al. (2021) added that PUFA value was found to be higher in mud crab muscle than in hepatopancreas. Similarly, EPA and DHA content were also recorded higher in muscles than in hepatopancreas. The current results of EPA and DHA value agree with the findings of F. Wang et al. (2021). Therefore, muscle extract offers a significant valuable EPA and DHA content in the products. The supplemental dietary intake of EPA and DHA is essential due to the synthesis of linoleic acid (LA, C18:2) and alpha-linoleic acid (ALA, C18:3) from palmitic acid (PA, C16:0) and oleic acid (OLA, C16:1) (Lupette & Benning, 2020) and the pathway to synthesise EPA and DHA from LA or ALA is very low and inefficient in humans. The American Heart Association recommends the EPA and DHA daily dietary intake to be approximately 4 g per day (Siscovick et al., 2017; Skulas-Ray et al., 2019), which leads to a market demand for these fatty acids as daily supplements.

EPA and DHA have potential health benefits. Various researchers (Dyall, 2015; Grasso et al., 2014; Perica & Delaš, 2011) documented that n-3 PUFAs play an important role in brain metabolisms and neuronal processes that associate with depressive symptoms. Song et al. (2016) added the antidepressive effects is benefits to influence the monoamine neurotransmission, neurogenesis and inflammatory responses. Serhan et al. (2008) stated that the EPA and DHA are able to potent lipid mediators and thus benefits to prevent or treat several diseases. Interestingly, EPA and DHA also significantly benefit as anti-cancer and anti-inflammation agents (Mason & Jacob, 2015; Mason et al., 2016). Elagizi et al. (2021) added that the combination of EPA and DHA notably reduces cardiovascular disease risk. In addition, study by Yokoi-Shimizu et al. (2012) documented that EPA and DHA are believed to modulate melatonin production that is crucial for sleep regulation. Dietary intake of EPA and DHA can also treat and prevent anxiety and depression among adults and thus enhance nervous and mental health (Appleton et al., 2015; Kiecolt-Glaser et al., 2011). EPA and DHA also benefit in counteracting the adverse effects of muscle atrophy and hasten neuromuscular adaptation (Jeromson et al., 2015; Ochi & Tsuchiya, 2018) that play an important role in preventing the pathological calcification in cancer tissue. Sharma and Mandal (2020) added that EPA and DHA are able to prevent bone decay and augment bone mineralization and thus enhance bone quality. Furthermore, various researchers have stated that the consumption of EPA and DHA reduces colon and breast cancer risks (Augimeri & Bonofiglio, 2023; Fabian et al., 2015).

Antioxidant activities of mud crab

DPPH radical scavenging activity of both samples was reported around 0.21–0.23 µmol TE g⁻¹ (p > .05) (Table 3). However, FRAP values (18.03 ± 0.00 μmol TE g⁻¹) in muscles extract were significantly (p < .05) higher compared to hepatopancreas extract (16.53 ± 0.04 μmol TE g⁻¹).

Table 3. DPPH and FRAP values of mud crab (Scylla olivacea).

	Mud crab muscles extract	Mud crab hepatopancreas extract
DPPH (μmolTEg^−1)	0.23 ± 0.00^a	0.21 ± 0.07^a
FRAP (μmolTEg^−1)	18.03 ± 0.00^c	16.53 ± 0.04^b

Different superscript indicates significant difference (p < .05) between treatments.

Values are given as mean ± SD from triplicate determinations.

A study by Yusof et al. (2019) stated that the DPPH radical scavenging of muscle of male mud crab, S. olivacea, was approximately 38.80% compared to the DPPH found in female muscle (35.80%) but not significantly (p > .05) different from each other. A previous study by Sujeetha et al. (2015) found that the DPPH value in S. serrata muscle was recorded at 49%. However, the current study showed a lower DPPH value of only 0.21 ± 0.07 to 0.23 ± 0.00% in mud crab regardless to the body parts. Emphasising on other antioxidant properties in mud crab, the FRAP value showed a significantly (p < .05) higher amount in the muscle extract compared to hepatopancreas extract. This finding suggests that a high ferric reducing ability illustrates the presence of natural antioxidants in muscle extract. Furthermore, Paital and Chainy (2010) stated that the presence of natural antioxidants in muscles of mud crab benefits them by acting as protective agents against free radicals. Limam et al. (2011) stated that the presence of natural antioxidants effectively inhibits peroxide during linoleic acid peroxidation, thus leading to the inhibition of lipid peroxidation.

Conclusion

S. olivacea muscle extracts contain high protein content, EPA and DHA values compared to hepatopancreas extract. Both extracts showed promising antioxidant activities, while muscle essence was higher in FRAP compared to hepatopancreas essence. Hence, the nutritionally dense and antioxidant capacity of muscle extract could lower oxidation. Therefore, mud crab muscle extract offers a nutritive ready-to-drink product and an alternative natural antioxidant healthy product.

Author contributions

Nurul Ulfah Karim: Conceptualization; Supervision; Validation; Writing-review & editing, Project administration. Nurul Syazwamimi Mohd Noor: Investigation; Formal analysis; Writing-original draft. Muhammad Fathi Sofian: Investigation; Formal analysis; Writing-original draft. Marina Hassan: Conceptualization, Validation, Resources. Mhd Ikhwanuddin Conceptualization, Validation, Resources Nilesh Prakash Nirmal: Conceptualization; Supervision; Validation; Writing-review & editing.

Acknowledgements

All the authors acknowledge the Ministry of Higher Education, Malaysia under the Higher Institution Centre of Excellence, Institute of Tropical Aquaculture and Fisheries, Universiti Malaysia Terengganu, Kuala Nerus Terengganu Malaysia for providing the samples resources, laboratory equipment and hatchery facilities.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was funded by The Ministry of Higher Education Malaysia (MOHE) under the Higher Institution Centre of Excellence (HICoE), Institute of Tropical Aquaculture and Fisheries (AKUATROP), Universiti Malaysia Terengganu, Kuala Nerus Terengganu Malaysia Programme (Vot No 56054) and the APC was supported by the Research Management Office, Universiti Malaysia Terengganu, Kuala Nerus Terengganu Malaysia.