Characterization of antioxidative peptide purified from black eelpout (Lycodes diapterus) hydrolysate
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Abstract
The functional peptides from protein hydrolysates of various fishery sources have been identified such as antioxidant activity. The main intention of this study was purification and characterization of antioxidative peptide from black eelpout muscle. The antioxidative peptides were purified from black eelpout (Lycodes diapterus) muscle using different proteases. Antioxidant activity of black eelpout hydrolysates was evaluated using DPPH radical scavenging activity. Among six hydrolysates, the pepsin hydrolysate had the highest antioxidant activity compared to the other hydrolysates. Therefore, it was further purified and a peptide with seven amino acid residues of DLVKVEA (784 Da) was identified by amino acid sequence analysis. The EC50 value for scavenging DPPH radicals by purified peptide was 688.77 μM. Additionally, the purified peptide exhibited protective effect against DNA damage induces by oxidation in mouse macrophages (RAW 264.7 cells). The results of this study suggest that black eelpout muscle protein hydrolysate could potentially contribute to development of bioactive peptides in basic research.
Keywords
Antioxidant DPPH radical scavenging Peptide Hydrolysates Pepsin Black eelpout muscleAbbreviations
- ANOVA
Analysis of variance
- BHA
Butylated hydroxyanisole
- BHT
Butylated hydroxytoluene
- CAT
Catalase
- DAD
Diode array detector
- DNA
Deoxyribonucleic acid
- DPPH
2,2-Diphenyl-1-picryl-hydrazyl-hydrate
- ESI-MS
Electrospray ionization mass spectrometry
- GR
Glutathione reductase
- GSH-Px
Glutathione peroxidase
- H2O2
Hydrogen peroxide
- O2−
Superoxide anion
- •OH
Hydroxyl radical
- Q-TOF
Quadrupole time-of-flight
- ROS
Reactive oxygen species
- RP-HPLC
Reverse-phase high performance liquid chromatography
- SEM
Scanning electron microscope
- SOD
Superoxide dismutase
- SPSS
Statistical package for the social sciences
- TBHQ
Tbutylhydroquinone
- TFA
Trifluoroacetic acid
Background
Free radicals are highly reactive species with their single and unbalanced electrons. The oxidation by free radicals in the body may cause many chronic diseases such as cardiovascular diseases, diabetes, cancer, and neurodegenerative disorders (Dong et al. 2008). Fatty acids and lipids oxidation induced by free radicals deteriorate the food quality (Liceaga-Gesualdo and Li-Chan 1999).
Reactive oxygen species (ROS) (O2− (superoxide anion), •OH (hydroxyl radical), and H2O2 (hydrogen peroxide)) are metabolic by-products of normal aerobic metabolism (Castro and Freeman 2001). Nevertheless, the body is supported with several antioxidant defense systems where they can scavenge and transform ROS or free radicals into harmless species (Yeung et al. 2002). The antioxidant defense system includes catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and glutathione reductase (GR). Enzymatic and non-enzymatic antioxidants team up to scavenge and eradicate the oxidative stress (McCord 1993). Steady-state maintenance of ROS/antioxidant ratio is vital for avoiding oxidative stress (Somani and Rybak 1996). Synthetic antioxidants (butylated hydroxyanisole (BHA), tbutylhydroquinone (TBHQ), butylated hydroxytoluene (BHT), and propyl gallate) have been widely used as food preservatives as they delay the discoloration and deterioration caused by oxidation (Wanita and Lorenz 1996). So, the use of these synthetic antioxidants has been limited in some countries due to their potential health hazard (Becker 1993).
Recently, enzymatic hydrolysis with proteases has garnered much attention. Protein hydrolysates or peptides affect health-related functions such as antioxidant function (Clemente 2000). Therefore, various antioxidant peptides have been isolated from marine organisms through enzymatic hydrolysis, including abalone muscle (Haliotis discus hannai Ino) and scallop (Patinopecten yessoensis) (Zhou et al. 2012), threadfin bream surimi (Wiriyaphan et al. 2012), croaker (Otolithes ruber) muscle (Nazeer et al. 2012), sand eel (Lee et al. 2011a, 2011b), sardinelle (Sardinella aurita) (Bougatef et al. 2010), tuna liver (Je et al. 2009), marine rotifer (Byun et al. 2009), and algae protein waste (Sheih et al. 2009).
Enzymatic hydrolysates exhibited several advantages when incorporated into foods, by improving water-binding ability, solubility of protein, emulsifying stability, heat stability of myofibrillar protein, and the nutritional quality of foods. Thus, enzymatic hydrolysis has become an appreciated tool for modifying the applicability of proteins (Korhonen et al. 1998). Normally, bioactive peptides remain inactive within the parent protein molecule until they are released by hydrolysis. Most of bioactive peptides are composed with 2–20 amino acids. Amino acids arrangement of the peptides plays a critical role in its bioactivity (Himaya et al. 2012).
The black eelpout, Lycodes diapterus, is distributed in the Northwest Pacific/North of central East Sea of Korea and the Sea of Okhotsk and inhabits sand and mud bottoms in deep water of 150–200 m depth. Black eelpout is a traditional food that is rich in protein, essential amino acids, omega-3 polyunsaturated fatty acids, and vitamins. In the present study, we investigated the 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical scavenging activity of enzymatically prepared black eelpout muscle protein hydrolysate to isolate a potent antioxidant peptide. And the protective effect of the purified peptide against deoxyribonucleic acid (DNA) oxidation induced by the hydroxyl radical was verified further.
Materials and methods
Materials
Fresh samples of black eelpout (Lycodes diapterus) were obtained from East Sea Fisheries Research Institute, Gangneung, South Korea. The bones and viscera were removed from the black eelpout. Then the separated muscle was stored at − 80 °C until use. Several commercial enzymes, such as α-chymotrypsin, papain, pepsin, and trypsin, were obtained from Sigma Chemical Co. (St. Louis, MO). Alcalase and Neutrase enzymes were obtained from Novo Co. (Novo Nordisk, Bagsvaerd, Denmark). DPPH was obtained from Wako Chemical Co. All other reagents used in this study were reagent grade chemicals.
Analysis of proximate compositions
Crude protein content of black eelpout was determined by the Kjeldahl method (Auto Kjeldahl system, Buchi B-324/435/412, Switzerland). Ether extraction method was used to determine the crude lipid content. Moisture content was determined by oven drying at 105 °C for 24 h. Ash content was determined by a muffler furnace at 550 °C for 4 h (Association of Official Analytical Chemist (AOAC) 2000). Amino acids were analyzed using an automatic analyzer (Hitachi Model 835-50, Japan) with a C18 column (5 μm, 4.6 × 250 mm, Watchers, MA). The reaction was carried out at 38 °C, with the detection wavelength at 254 nm and a flow rate of 1.0 mL/min. All analyses were carried out in triplicate.
Preparation of black eelpout muscle hydrolysates
Optimal conditions for enzymatic hydrolysis of various enzymes
Enzyme | Buffer | pH | Temperature (°C) |
---|---|---|---|
Alcalase | 50 mM Na2HPO4-NaH2PO4 | 7.0 | 50 |
α-Chymotrypsin | 50 mM Na2HPO4-NaH2PO4 | 7.0 | 37 |
Neutrase | 50 mM Na2HPO4-NaH2PO4 | 7.0 | 50 |
Papain | 50 mM Na2HPO4-NaH2PO4 | 7.0 | 37 |
Pepsin | 20 mM HCl | 2.0 | 37 |
Trypsin | 50 mM Na2HPO4-NaH2PO4 | 7.0 | 37 |
Determination of DPPH radical scavenging activity
Purification and identification of antioxidant peptides
The black eelpout muscle hydrolysate was dissolved in distilled water and loaded onto a Sephadex G-25 gel filtration column (2.5 × 70 cm) which had been previously equilibrated with distilled water. The column was then eluted with distilled water at a flow rate of 1.5 mL/min (fraction volume 7.5 mL) and separated fractions were monitored at 215 nm, collected at a volume of 7.5 mL, and measured for DPPH radical scavenging activity. Highest active fraction was injected into a preparative reverse-phase high performance liquid chromatography (RP-HPLC) column (Grom-Sil 120 ODS-5ST, ø 10 × 250 mm, 5 μm, Grom™, Germany) and was separated using linear gradient of acetonitrile (0–20% v/v) containing 0.1% trifluoroacetic acid (TFA) on an RP-HPLC system (Agilent Technologies, USA). Elution peaks were monitored at 280 nm on diode array detector (DAD). The purified fractions from preparative column were monitored at 280 nm and purified by RP-HPLC on a C18 analytical column (ø 4.6 × 250 mm, 5 μm, Waters, Milford, MA, USA) using an acetonitrile gradient of 5–30% (v/v) at a flow rate of 0.5 mL/min for 40 min. Finally, the fraction with the highest DPPH radical scavenging activity was collected and lyophilized followed by the amino acid sequence identification.
Determination of molecular weight and amino acid sequence
Molecular weight and amino acid sequence of purified peptide from black eelpout muscle protein were determined by quadrupole time-of-flight (Q-TOF) mass spectrometry (Micromass, Altrincham, UK) coupled with electrospray ionization (ESI) source. The purified peptide dissolved in methanol/water (1:1, v/v) was infused into the ESI source and the molecular mass was determined by doubly charged (M+ 2H)2+ state in the mass spectrum. Following molecular mass determination, the peptide was automatically selected for fragmentation and sequence information was obtained by tandem MS analysis.
Protective potential by the hydroxyl radical-induced DNA damage
To assess the protective effects of the hydrolysate against DNA damage caused by hydroxyl radicals, the reaction was induced by placing the following reagents in an Eppendorf tube: 5 μL of genomic DNA (RAW 264.7 cell line), 2 mM FeSO4, and various concentrations of the purified peptide from black eelpout hydrolysate. The mixture was then incubated at 37 °C for 30 min, followed by the addition of 4 μL of 10 mM H2O2 (Dávalos et al. 2004). Finally, the mixture was subjected to 1.0% agarose gel electrophoresis and DNA bands were stained with ethidium bromide.
Statistical analysis
Data were analyzed for statistical significance using analysis of variance (ANOVA) followed by Dunnett’s multiple comparison test with statistical package for the social sciences (SPSS) software (version 14). All values obtained from three different experiments were expressed as the mean value ± standard deviation (SD).
Results and discussion
Proximate composition of black eelpout muscle
Proximate compositions of black eelpout muscle
Components | Content (%) |
---|---|
Moisture | 20.81 |
Protein | 64.02 |
Lipid | 8.63 |
Ash | 4.09 |
Carbohydrate | 2.46 |
Amino acid contents of black eelpout muscle
Amino acids | Contents (%) |
---|---|
Tau | 0.78 |
Asp | 6.08 |
Thr | 4.07 |
Ser | 3.93 |
Glu | 2.21 |
Gly | 20.82 |
Ala | 17.13 |
Val | 3.61 |
Cys | 0.34 |
Met | 1.96 |
Ile | 2.43 |
Leu | 6.24 |
Try | 1.71 |
Phe | 2.33 |
Lys | 8.10 |
His | 1.80 |
Arg | 5.13 |
Total | 100.00 |
Antioxidant activity of black eelpout muscle hydrolysates
Yields of various hydrolysates from black eelpout muscle
Hydrolysates | Yields (%) |
---|---|
Alcalase | 66.85 |
α-Chymotrypsin | 51.30 |
Neutrase | 39.47 |
Papain | 68.28 |
Pepsin | 66.14 |
Trypsin | 58.76 |
EC50 values for DPPH radical scavenging activity of black eelpout muscle hydrolysates. Statistical significance was determined by ANOVA
Purification of antioxidant peptide
Steps for the purification of DPPH radical scavenging activity peptide from black eelpout muscle hydrolysate. I Sephadex G-25 Gel filtration chromatogram of hydrolysates. Gel filtration chromatogram of hydrolysates prepared with black eelpout muscle. Separation was performed with 1.5 mL/min and collected at a fraction volume of 7.5 mL. The fractions isolated by Sephadex G-25 Gel column were separated (A–D) and DPPH radical scavenging activity was determined as upper panel. II, III Reverse phase-HPLC chromatograms of the potent DPPH radical scavenging activity fractions from the previous steps. The lower panels of each pair show the chromatography results of separated fractions while the top panels of each pair represent the DPPH radical scavenging activity of separated fractions in terms of their EC50 values expressed in mg/mL (I) or μg/mL (II, III). Statistical significance was determined by ANOVA
Purification of antioxidant peptide from black eelpout muscle hydrolysate by pepsin treatment
Purification step | EC50 value (μg/mL) | Purification folda |
---|---|---|
Pepsin hydrolysate | 830.01 ± 0.05 | 1.00 |
Sephadex gel filtration (B) | 650.32 ± 0.14 | 1.28 |
RP−HPLC (F1) | 87.45 ± 0.05 | 9.49 |
Purified peptide (F1–1) | 56.12 ± 0.01 | 16.24 |
Characterization of purified antioxidant peptide
Identification of molecular mass and amino acid sequence of the purified peptides from black eelpout muscle hydrolysate by HPLC. MS/MS experiments were performed on a Q-TOF tandem mass spectrometer equipped with a nano-ESI source
Prevention of oxidation-induced DNA damage by a black eelpout peptide
Protective effect on oxidation-induced DNA damage of purified peptide from black eelpout at various concentrations. Blank: untreated sample and H2O2, FeSO4. Control: distilled water instead of sample. Sample: Treated sample, H2O2, and FeSO4. (+, treatment; −, not treatment)
Conclusion
In this study, black eelpout muscle protein was hydrolyzed using enzymatic hydrolysis with various enzymes. The antioxidant activity of the different enzyme hydrolysates was determined and compared. Pepsin hydrolysate showed the highest antioxidant activity and thus it was further purified using chromatography. A seven-amino acid residue peptide with antioxidant activity was identified from the pepsin hydrolysate of black eelpout muscle. Collectively, the results of this study suggest that black eelpout muscle protein hydrolysate could potentially contribute to development of bioactive peptides in basic research.
Notes
Acknowledgements
This research was supported by a grant from Marine Bioprocess Research Center of the Marine Biotechnology Program funded by the Ministry of Land, Transport and Maritime, Republic of Korea.
Authors’ contributions
HGB and LJK conceived and designed the study and helped to draft the manuscript and revised the manuscript. LJK performed the experiments, analyzed the data, and drafted the manuscript. All authors read and approved the final manuscript.
Funding
The design of the study; collection, analysis, and interpretation of the data; and writing of the manuscript were funded by a grant from Marine Bioprocess Research Center of the Marine Biotechnology Program funded by the Ministry of Land.
Ethics approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
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