Preparation and evaluation of antioxidant peptide from papain hydrolysate of Sphyrna lewini muscle protein

Oyster-derived dipeptides RI, IR, and VR promote testosterone synthesis by reducing oxidative stress in TM3 cells

Short peptides have gained widespread utilization as functional constituents in the development of functional foods due to their remarkable biological activity. Previous investigations have established the positive influence of oysters on testosterone biosynthesis, although the underlying mechanism remains elusive. This study aims to assess the impact of three dipeptides derived from oysters on the oxidative stress state of TM3 cells induced by AAPH while concurrently examining alterations in cellular testosterone biosynthesis capacity. The investigation encompasses an analysis of reactive oxygen species (ROS) content, antioxidant enzyme activity, apoptotic status, and expression levels of crucial enzymes involved in the testosterone synthesis pathway within TM3 cells, thus evaluating the physiological activity of the three dipeptides. Additionally, molecular docking was employed to investigate the inhibitory activity of the three dipeptides against ACE. The outcomes of this study imply that the oxidative stress state of cells impedes the synthesis of testosterone by inhibiting the expression of essential proteins in the testosterone synthesis pathway. These three dipeptides derived from oysters ameliorate cellular oxidative stress by directly scavenging excess ROS or reducing ROS production rather than enhancing cellular antioxidant capacity through modulation of antioxidant enzyme activity. These findings introduce a novel avenue for developing and utilizing antioxidant peptides derived from food sources.

Biochemical characterization, and anti-inflammatory and antitumor activities of glycoprotein from lamb abomasum

ETHNOPHARMACOLOGICAL RELEVANCE

Lamb abomasum is used as an edible medicinal source in traditional Chinese medicine for the treatment of gastrointestinal disorders. Lamb abomasum sourced biochemical drug Lamb's trip extract and Vitamin B12 capsule used for the clinical treatment of chronic gastritis, gastric ulcer, and reversal of intestinal metaplasia. Therefore, claimed to have prevention of gastric cancer activity.

AIM OF THE STUDY

In this study, we aim to assess whether the glycoprotein has biological activity in the cure of gastric disorder and conduct a structure-activity relationship.

MATERIALS AND METHODS

Glycoproteins' extraction conditions were optimized by the response surface method and purified with DEAE-cellulose and Sephadex G-50 chromatography. Two homogenous glycoproteins' physiochemical structures were studied with electrophoresis, HPLC analysis, peroxide oxidation, and β-elimination, FT-IR, CD, LC-MS/MS, and EDS analysis. The antiinflammation activity of the glycoprotein was determined against COX-2 and LOX-15 enzyme inhibitory ability in vitro, and antitumor activity against HT-29 and HGC-25, and cytotoxicity on L-02 cells was determined in vivo with the MTT method.

RESULTS

The abomasum was abundant in glycoprotein and the extraction yield of glycoprotein was up to 24.6 ± 2.1% under optimized conditions. Two homogeneous glycoproteins SAGP-I and SAGP-II determined to be ribose-conjugated and sulfated glycoproteins with a molecular weight of 15.6 kDa and 6.4 kDa. And according to the structural analysis, SAGP-I was a mucin-type ribose-conjugated glycoprotein with 14 O-glycosylation and one N- glycosylation site. SAGP-I and SAGP-II have remarkable anti-inflammatory activity against COX-2 enzyme with the IC₅₀ of 17.64 ± 1.25 μg/mL and 16.14 ± 1.11 μg/mL, respectively. Meanwhile, the two glycoproteins showed strong antitumor activity against HT-29 with the EC₅₀ of 19.19 ± 1.46 μg/mL and 184.9 ± 5.6 μg/mL, respectively.

CONCLUSION

The Highly purified glycoprotein SAGP-1 and SAGP-II showed anti-inflammatory activity against the COX-2 enzyme, and antitumor activity against HT-29 human colon cancer cells and noun-inhibitory activity against LOX-15 enzyme and HGC-25. Both glycoproteins are ribose conjugated and sulfated whose characters are related to their anti-inflammatory and anti-tumor activity. Such results suggest the possibility of anti-inflammatory and pre-cancer activity. And in some degree explains the pharmacy of abomasum's traditional use in gastric disorder and clinical use of lamb abomasum APIs drugs' in gastric disorders and gastric cancer development. This study provides a preliminary basis for the further study of the per-cancer mechanism of lamb abomasum glycoprotein. And, would be the material basis of the clinical use of Lamb's trip extract and Vitamin B12 capsule.

Eighteen Novel Bioactive Peptides from Monkfish (Lophius litulon) Swim Bladders: Production, Identification, Antioxidant Activity, and Stability

In the study, papain was chosen from five proteases to hydrolyze proteins of monkfish swim bladders for effectively utilizing monkfish (Lophius litulon) processing byproducts, and the hydrolysis conditions of papain were optimized as hydrolysis temperature of 65 °C, pH 7.5, enzyme dose 2.5% and time 5 h using single-factor and orthogonal experiments. Eighteen peptides were purified from the swim bladder hydrolysate of monkfish by ultrafiltration and gel permeation chromatography methods and identified as YDYD, QDYD, AGPAS, GPGPHGPSGP, GPK, HRE, GRW, ARW, GPTE, DDGGK, IGPAS, AKPAT, YPAGP, DPT, FPGPT, GPGPT, GPT and DPAGP, respectively. Among eighteen peptides, GRW and ARW showed significant DPPH· scavenging activities with EC₅₀ values of 1.053 ± 0.003 and 0.773 ± 0.003 mg/mL, respectively; YDYD, QDYD, GRW, ARW and YPAGP revealed significantly HO· scavenging activities with EC₅₀ values of 0.150 ± 0.060, 0.177 ± 0.035, 0.201 ± 0.013, 0.183 ± 0.0016 and 0.190 ± 0.010 mg/mL, respectively; YDYD, QDYD, ARW, DDGGK and YPAGP have significantly O2-· scavenging capability with EC₅₀ values of 0.126 ± 0.0005, 0.112 ± 0.0028, 0.127 ± 0.0002, 0.128 ± 0.0018 and 0.107 ± 0.0002 mg/mL, respectively; and YDYD, QDYD and YPAGP showed strong ABTS⁺· scavenging ability with EC₅₀ values of 3.197 ± 0.036, 2.337 ± 0.016 and 3.839 ± 0.102 mg/mL, respectively. YDYD, ARW and DDGGK displayed the remarkable ability of lipid peroxidation inhibition and Ferric-reducing antioxidant properties. Moreover, YDYD and ARW can protect Plasmid DNA and HepG2 cells against H₂O₂-induced oxidative stress. Furthermore, eighteen isolated peptides had high stability under temperatures ranging from 25-100 °C; YDYD, QDYD, GRW and ARW were more sensitive to alkali treatment, but DDGGK and YPAGP were more sensitive to acid treatment; and YDYD showed strong stability treated with simulated GI digestion. Therefore, the prepared antioxidant peptides, especially YDYD, QDYD, GRW, ARW, DDGGK and YPAGP from monkfish swim bladders could serve as functional components applied in health-promoting products because of their high-antioxidant functions.

Antioxidant Peptides From Protein Hydrolysate of Marine Red Algae Eucheuma cottonii: Preparation, Identification, and Cytoprotective Mechanisms on H2O2 Oxidative Damaged HUVECs

To screen, prepare, identify, and evaluate the activities of natural antioxidants for treating chronic diseases caused by oxidative stress. Two algal proteins, namely ZD10 and ZD60, precipitated with 10 and 60% (NH₄)₂SO₄ were extracted from red algae Eucheuma cottonii (E. cottonii) and hydrolyzed using five proteolytic enzymes. The results showed that ZD60 played the most significant role in the enhancement of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH⋅) scavenging activity (25.91 ± 0.24%) among all protein hydrolysates. Subsequently, six antioxidant peptides (EP1-EP6) were isolated from the papain hydrolysate of ZD60 by ultrafiltration and chromatography methods. Their amino acid sequences were identified as Thr-Ala (EP1), Met-Asn (EP2), Tyr-Ser-Lys-Thr (EP3), Tyr-Ala-Val-Thr (EP4), Tyr-Leu-Leu (EP5), and Phe-Tyr-Lys-Ala (EP6) with molecular weights of 190.21, 263.33, 497.55, 452.51, 407.51, and 527.62 Da, respectively. Of which, EP3, EP4, EP5, and EP6 showed strong scavenging activities on DPPH⋅, hydroxyl radical (HO⋅), and superoxide anion radical (O- 2⋅). Moreover, EP4 and EP5 could significantly protect human umbilical vein endothelial cells (HUVECs) from H₂O₂-induced oxidative damage by increasing the levels of antioxidant enzyme systems including superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) to reduce the levels of reactive oxygen species (ROS) (60.51 and 51.74% of model group) and malondialdehyde (MDA) (75.36 and 64.45% of model group). In addition, EP4 and EP5 could effectively inhibit H₂O₂-induced apoptosis by preventing HUVECs from early apoptosis to late apoptosis. These results indicated that the antioxidant peptides derived from E. cottonii, especially EP4 and EP5, could serve as the natural antioxidants applied in pharmaceutical products to treat chronic cardiovascular diseases caused by oxidative damage, such as coronary heart disease, atherosclerosis, etc.

Influence of Commercial Protease and Drying Process on Antioxidant and Physicochemical Properties of Chicken Breast Protein Hydrolysates

Different proteases can be applied to produce certain bioactive peptides. This study focused on the effects of some commercial proteases and drying processes on the physical, chemical, and biological properties of chicken breast hydrolysates (CBH). Chicken breast hydrolyzed with Alcalase® presented a higher degree of hydrolysis (DH) than papain. Moreover, the treatment with Alcalase®, followed by papain (A-P), was more proficient in producing antioxidant activities than a single enzyme treatment. Conditions comprising 0.63% Alcalase® (w/w) at pH 8.0 and 52.5 °C for 3 h, followed by 0.13% papain (w/w) at pH 6.0 and 37 °C for 3 h, resulted in the highest yields of DH and peptide contents. The spray-dried microencapsulated powder improved the physicochemical properties including moisture content, color measurement, solubility, and particle morphology. In summary, the dual enzyme application involving the hydrolysis of Alcalase® and papain, coupled with the spray-drying process, could be used to produced antioxidant CBH.

Tryptophan-tagged peptide from serine threonine-protein kinase of Channa striatus improves antioxidant defence in L6 myotubes and attenuates caspase 3-dependent apoptotic response in zebrafish larvae

This study reports the antioxidant property and molecular mechanism of a tryptophan-tagged peptide derived from a teleost fish Channa striatus of serine threonine-protein kinase (STPK). The peptide was tagged with tryptophan to enhance the antioxidant property of STPK and named as IW13. The antioxidant activity of IW13 peptide was investigated using in vitro methods such as DPPH, ABTS, superoxide anion radical scavenging and hydrogen peroxide scavenging assay. Furthermore, to investigate the toxicity and dose response of IW13 peptide on antioxidant defence in vitro, L6 myotubes were induced with generic oxidative stress due to exposure of hydrogen peroxide (H₂O₂). IW13 peptide exposure was found to be non-cytotoxic to L6 cells in the tested concentration (10, 20, 30, 40 and 50 μM). Also, the pre-treatment of IW13 peptide decreased the lipid peroxidation level and increased glutathione enzyme activity. IW13 peptide treatment upregulated the antioxidant enzyme genes: GPx (glutathione peroxidase), GST (glutathione S transferase) and GCS (glutamine cysteine synthase), in vitro in L6 myotubes and in vivo in zebrafish larvae against the H₂O₂-induced oxidative stress. The results demonstrated that IW13 renders protection against the H₂O₂-induced oxidative stress through a cellular antioxidant defence mechanism by upregulating the gene expression, thus enhancing the antioxidant activity in the cellular or organismal level. The findings exhibited that the tryptophan-tagged IW13 peptide from STPK of C. striatus could be a promising candidate for the treatment of oxidative stress-associated diseases.

Antioxidant Activity Evaluation of Oviductus Ranae Protein Hydrolyzed by Different Proteases

As nutrition and a health tonic for both medicine and food, the protein content of Oviductus Ranae is more than 40%, making it an ideal source to produce antioxidant peptides. This work evaluated the effects of six different proteases (pepsin, trypsin, papain, flavourzyme, neutral protease and alcalase) on the antioxidant activity of Oviductus Ranae protein, and analyzed the relationship between the hydrolysis time, the degree of hydrolysis (DH) and the antioxidant activity of the enzymatic hydrolysates. The results showed that the antioxidant activity of Oviductus Ranae protein was significantly improved and the optimal hydrolysis time was maintained between 3-4 h under the action of different proteases. Among them, the protein hydrolysate which was hydrolyzed by pepsin for 180 min had the strongest comprehensive antioxidant activity and was most suitable for the production of antioxidant peptides. At this time, the DH, the DPPH radical scavenging activity, the absorbance value of reducing power determination and the hydroxyl radical scavenging activity corresponding to the enzymatic hydrolysate were 13.32 ± 0.24%, 70.63 ± 1.53%, 0.376 ± 0.009 and 31.96 ± 0.78%, respectively. Correlation analysis showed that there was a significant positive correlation between the hydrolysis time, the DH and the antioxidant activity of the enzymatic hydrolysates, further indicating that the hydrolysates of Oviductus Ranae protein had great antioxidant potential. The traditional anti-aging efficacy of Oviductus Ranae is closely related to the scavenging of reactive oxygen species, and its hydrolysates have better antioxidant capacity, which also provides support for further development of its traditional anti-aging efficacy.

Intracellular ROS scavenging and antioxidant regulation of WL15 from cysteine and glycine-rich protein 2 demonstrated in zebrafish in vivo model

Antioxidant peptides are naturally present in food, especially in fishes, and are considered to contain rich source of various bioactive compounds that are structurally heterogeneous. This study aims to identify and characterize the antioxidant property of the WL15 peptide, derived from Cysteine and glycine-rich protein 2 (CSRP2) identified from the transcriptome of a freshwater food fish, Channa striatus. C. striatus is already studied to contain high levels of amino acids and fatty acids, besides traditionally known for its pharmacological benefits in the Southeast Asian region. In our study, in vitro analysis of WL15 peptide exhibited strong free radical scavenging activity in 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), superoxide anion radical and hydrogen peroxide (H2O2) scavenging assay. Further, to evaluate the cytotoxicity and dose-response, the Human dermal fibroblast (HDF) cells were used. Results showed that the treatment of HDF cells with varying concentrations (10, 20, 30, 40 and 50 μM) of WL15 peptide was not cytotoxic. However, the treatment concentrations showed enhanced antioxidant properties by significantly inhibiting the levels of free radicals. For in vivo assessment, we have used zebrafish larvae for evaluating the developmental toxicity and for determining the antioxidant property of the WL15 peptide. Zebrafish embryos were treated with the WL15 peptide from 4 h of post-fertilization (hpf) to 96 hpf covering the embryo-larval developmental period. At the end of the exposure period, the larvae were exposed to H2O2 (1 mM) for inducing generic oxidative stress. The exposure of WL15 peptide during the embryo-larval period showed no developmental toxicity even in higher concentrations of the peptide. Besides, the WL15 peptide considerably decreased the intracellular reactive oxygen species (ROS) levels induced by H2O2 exposure. WL15 peptide also inhibited the H2O2-induced caspase 3-dependent apoptotic response in zebrafish larvae was observed using the whole-mount immunofluorescence staining. Overall results from our study showed that the pre-treatment of WL15 (50 μM) in the H2O2-exposed zebrafish larvae, attenuated the expression of activated caspase 3 expressions, reduced Malondialdehyde (MDA) levels, and enhanced antioxidant enzymes, including superoxide dismutase (SOD) and catalase (CAT). The gene expression of antioxidant enzymes such as glutathione S-transferase (GST), glutathione peroxide (GPx) and γ-glutamyl cysteine synthetase (GCS) was found to be upregulated. In conclusion, it can be conceived that pre-treatment with WL15 could mitigate H2O2-induced oxidative injury by elevating the activity and expression of antioxidant enzymes, thereby decreasing MDA levels and cellular apoptosis by enhancing the antioxidant response, demonstrated by the in vitro and in vivo experiments.

Peptidases from Maclura Pomifera for Preparation of Food Protein Hydrolysates: Purification by Single-Step Chromatography and Characterization of Pomiferin I

Our objective was to isolate peptidases from the latex of Maclura pomifera fruits and use them to hydrolyze food proteins, as well as to purify and characterize the main peptidase. Two partially purified proteolytic extracts were prepared by ethanol (EE) and acetone (AE) precipitation from an aqueous suspension of exuded fruit latex. EE was used to hydrolyze food proteins with a ratio of 0.19 caseinolytic units (Ucas) per mg of substrate. Different values of hydrolysis degree were observed for hydrolysates of egg white, soy protein isolate, and casein at 180 min (9.3%, 31.1%, and 29.1%, respectively). AE was employed to purify a peptidase which exhibited an isoelectric point (pI) of 8.70 and whose abundance in AE was 28.3%. This enzyme was purified to homogeneity using a single-step procedure by cation-exchange chromatography, achieving an 8.1-fold purification and a yield of 16.7%. The peptidase was named pomiferin I and showed a molecular mass of 63,177.77 Da. Kinetic constants (K_M 0.84 mM, V_max 27.50 uM s^-1, k_cat 72.37 s^-1, and k_cat/K_M 86.15 mM^-1 s^-1) were determined employing N-α-carbobenzoxy-L-alanyl-p-nitrophenyl ester as substrate. Analysis by PMF showed only partial homology of pomiferin I with a serine peptidase from a species of the same family.

Antioxidant Peptides from Sepia esculenta Hydrolyzate Attenuate Oxidative Stress and Fat Accumulation in Caenorhabditis elegans

The hydrolysate of golden cuttlefish (Sepia esculenta) was prepared by using papain, and then, it was further separated by ultrafiltration, gel filtration chromatography, and reverse-phase high-performance liquid chromatography (RP-HPLC). The peptide components of the active fraction were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and then two novel peptides, SeP2 (DVEDLEAGLAK, 1159.27 Da) and SeP5 (EITSLAPSTM, 1049.22 Da), were obtained and displayed significant alleviation effects on oxidative stress in Caenorhabditis elegans. Studies indicated that S. esculenta antioxidant peptides (SePs) increase superoxide dismutase (SOD) activity but reduce reactive oxygen species (ROS) and malondialdehyde (MDA) levelsin oxidation-damaged nematodes. Using transgenic CF1553 nematodes, the sod-3p::GFP expression in the worms treated with SePs was significantly higher than that of the control nematodes. Real-time PCR also demonstrated that the expression of stress-related genes such as sod-3 is up-regulated by SePs. Furthermore, studies showed that SePs could obviously decrease fat accumulation as well as reduce the elevated ROS and MDA levels in high-fat nematodes. Taken together, these results indicated that SePs are capable of the activation of antioxidant defense and the inhibition of free radicals and lipid peroxidation, play important roles in attenuating oxidative stress and fat accumulation in C. elegans, and might have the potential to be used in nutraceutical and functional foods.

Facile and moderate immobilization of proteases on SPS nanospheres for the active collagen peptides

Although collagen peptides have been proved to possess wide applications in functional foods, cosmetics, medical materials and pharmaceuticals, the production of collagen peptides are deeply affected by proteases and substrate. In this study, the scalable-synthesis sulfonated polystyrene (SPS) nanospheres were utilized as accessible supports for efficient subtilisin immobilization. Detailed characterizations through SEM-EDS, TEM, TGA and FT-IR confirmed the undamaged formation of the SPS-subtilisin. Owing to the moderate hydrophobic effect and electrostatic interaction, the SPS-subtilisin could achieve 397.15 mg/g enzyme loading and 77.3% activity recovery. The tilapia skin collagen, as a resource-rich raw material, was hydrolyzed by the prepared immobilized subtilisin. The antioxidant activity of the attained peptides was verified. With the mass spectrometry and molecular docking analysis of product peptides sequences, representative peptides were synthesized and their anti-oxidation capacity and mechanism were affirmed, which further verified the undiminished catalytic ability of immobilized subtilisin.

Identification and Active Evaluation of Antioxidant Peptides from Protein Hydrolysates of Skipjack Tuna (Katsuwonus pelamis) Head

For the full use of fish by-products to produce antioxidant peptides, skipjack tuna (Katsuwonus pelamis) heads generated during can processing were defatted and hydrolyzed using the in vitro gastrointestinal (GI) digestion (pepsin–trypsin system) method and six antioxidant peptides (P1 to P6) were purified from the head hydrolysate (KPH) using ultrafiltration and serial chromatography methods. Six isolated peptides (P1 to P6) were identified as Val-Glu-Glu (VEE, P1), Trp-Met-Phe-Asp-Trp (WMFDW, P2), Asp-Ala-Gly-Pro-Tyr-Gly-Pro-Ile (DAGPYGPI, P3), Trp-Met-Gly-Pro-Tyr (WMGPY, P4), Glu-Arg-Gly-Pro-Leu-Gly-Pro-His (ERGPLGPH, P5), and Glu-Met- Gly-Pro-Ala (EMGPA, P6), respectively, using a protein sequencer and electrospray ionization-mass spectrometer. Among skipjack tuna head hydrolysates, fractions, and six isolated peptides (P1 to P6), WMFDW (P2), WMGPY (P4), and EMGPA (P6) showed the highest radical scavenging activities on 2,2-diphenyl-1-picrylhydrazyl (DPPH) (EC₅₀ values of 0.31, 0.33, and 0.46 mg/mL for WMFDW, WMGPY, and EMGPA, respectively), hydroxyl (EC₅₀ values of 0.30, 0.43, and 0.52 mg/mL for WMFDW, WMGPY, and EMGPA, respectively), and superoxide anion (EC₅₀ values of 0.56, 0.38, and 0.71 mg/mL for WMFDW, WMGPY, and EMGPA, respectively). Moreover, WMFDW, WMGPY, and EMGPA showed strong capability in reducing power and lipd peroxidation inhibition in the linoleic acid system. In addition, WMFDW, WMGPY, and EMGPA can retain strong antioxidant activity at temperatures lower than 60 °C and pH values ranged from 5 to 9. The results showed that six isolated peptides (P1 to P6) from skipjack tuna heads, especially WMFDW, WMGPY, and EMGPA, might be applied in health care products acting as powerful antioxidant agents.

Four Antioxidant Peptides from Protein Hydrolysate of Red Stingray (Dasyatis akajei) Cartilages: Isolation, Identification, and In Vitro Activity Evaluation

In the work, water-soluble proteins of red stingray (Dasyatis akajei) cartilages were extracted by guanidine hydrochloride and hydrolyzed using trypsin. Subsequently, four antioxidant peptides (RSHP-A, RSHP-B, RSHP-C, and RSHP-D) were isolated from the water-soluble protein hydrolysate while using ultrafiltration and chromatographic techniques, and the amino acid sequences of RSHP-A, RSHP-B, RSHP-C, and RSHP-D were identified as Val-Pro-Arg (VPR), Ile-Glu-Pro-His (IEPH), Leu-Glu-Glu--Glu-Glu (LEEEE), and Ile-Glu-Glu-Glu-Gln (IEEEQ), with molecular weights of 370.46 Da, 494.55 Da, 647.64 Da, and 646.66 Da, respectively. VPR, IEPH, LEEEE, and IEEEQ exhibited good scavenging activities on the DPPH radical (EC50 values of 4.61, 1.90, 3.69, and 4.01 mg/mL, respectively), hydroxyl radical (EC50 values of 0.77, 0.46, 0.70, and 1.30 mg/mL, respectively), superoxide anion radical (EC50 values of 0.08, 0.17, 0.15, and 0.16 mg/mL, respectively), and ABTS cation radical (EC50 values of 0.15, 0.11, 0.19, and 0.18 mg/mL, respectively). Among the four isolated antioxidant peptides, IEPH showed the strongest reducing power and lipid peroxidation inhibition activity, but LEEEE showed the highest Fe2+-chelating ability. The present results suggested that VPR, IEPH, LEEEE, and IEEEQ might have the possibility of being an antioxidant additive that is used in functional food and pharmaceuticals.

Preparation, Identification, and Activity Evaluation of Eight Antioxidant Peptides from Protein Hydrolysate of Hairtail (Trichiurus japonicas) Muscle

In this report, protein of hairtail (Trichiurus japonicas) muscle was separately hydrolyzed using five kinds of proteases (alcalase, trypsin, neutrase, pepsin, and papain), and the papain- and alcalase-hydrolysates showed higher 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH•) and hydroxyl radical (HO•) scavenging activity than other three protease hydrolysates. Therefore, the protein hydrolysate of hairtail muscle (HTP) was prepared using binary-enzymes hydrolysis process (papain + alcalase). Subsequently, eight antioxidant peptides were purified from HTP using membrane ultrafiltration and chromatography technology, and their amino acid sequences were identified as Gln-Asn-Asp-Glu-Arg (TJP1), Lys-Ser (TJP2), Lys-Ala (TJP3), Ala-Lys-Gly (TJP4), Thr-Lys-Ala (TJP5), Val-Lys (TJP6), Met-Lys (TJP7), and Ile-Tyr-Gly (TJP8) with molecular weights of 660.3, 233.0, 217.1, 274.1, 318.0, 245.1, 277.0, and 351.0 Da, respectively. TJP3, TJP4, and TJP8 exhibited strong scavenging activities on DPPH• (EC₅₀ 0.902, 0.626, and 0.663 mg/mL, respectively), HO• (EC₅₀ 1.740, 2.378, and 2.498 mg/mL, respectively), superoxide anion radical (EC₅₀ 2.082, 2.538, and 1.355 mg/mL, respectively), and 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical (EC₅₀ 1.652, 0.831, and 0.586 mg/mL, respectively). Moreover, TJP3, TJP4, and TJP8 showed higher reducing power and inhibiting ability on lipid peroxidation in a linoleic acid model system. These results suggested that eight isolated peptides (TJP1 to TJP8), especially TJP3, TJP4, and TJP8 might serve as potential antioxidants applied in the pharmaceutical and health food industries.

Isolation and identification of an antioxidant collagen peptide from skipjack tuna (Katsuwonus pelamis) bone

To date, many researchers have developed active components that are derived from seafood processing for the purposes of healthcare. Here, an antioxidant collagen peptide was obtained from skipjack tuna (Katsuwonus pelamis) bone by using a combination of trypsin and chymotrypsin as the catalyst. The amino acid sequence of the peptide was identified as Ser–Ser–Gly–Pro–Pro–Val–Pro–Gly–Pro–Met–Gly–Pro–Met–Gly–Pro–Arg (SSGPPVPGPMGPMGPR) by liquid chromatography-electrospray ionization quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF-MS) analysis. We found that the as-prepared collagen peptide can efficiently scavenge DPPH radical (IC₅₀ 3.149 mM), superoxide anion radical (IC₅₀ 3.803 mM) and ABTS radical (IC₅₀ 9.489 mM). In addition, it has been found that the methionine (Met) residue in the collagen peptide could provide a precise active site during the scavenging of DPPH radicals by Fourier transform infrared spectroscopy (FTIR) analysis and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry analysis. These results suggest that the peptide can find wide uses in the food, cosmetic and pharmaceutical industries.

A novel antioxidant peptide was isolated from skipjack tuna bone collagen.

Angiotensin-I-Converting Enzyme Inhibitory Activity and Antioxidant Properties of Cryptides Derived from Natural Actomyosin of Catla catla Using Papain

Natural actomyosin (NAM) from the freshwater fish Catla catla was extracted and hydrolyzed using papain enzyme at different enzyme-to-substrate ratios (0.5%, 1.0%, 2.0%, 5.0%, and 10%) to obtain the cryptides with different degrees of hydrolysis (DH). Derived cryptides were evaluated for bioactive properties such as angiotensin-I-converting enzyme (ACE) inhibitory activity and antioxidant properties. The pattern of hydrolysis of NAM as a function of time revealed that major protein components such as myosin and actin were hydrolyzed within 10 min of hydrolysis. The cryptides obtained with the DH of 29.4% had significantly higher ACE inhibitory activity and linoleic acid peroxidation inhibitory activity (P<0.05). A higher DPPH free radical-scavenging activity and ferric-reducing power were exhibited by the NAM cryptide mixture obtained with the DH of 17.38 and 26.2%, respectively. The natural actomyosin could be a potential precursor to produce the cryptides with therapeutical and antioxidant properties.

Valorisation of tuna processing waste biomass: isolation, purification and characterisation of four novel antioxidant peptides from tuna by-product hydrolysate

Tuna protein hydrolysate (TPH) was prepared by hydrolysis with Prolyve BS and fractionated by membranes process. The antioxidant activities of recovered peptide fractions were evaluated. Four novel antioxidant peptides that were isolated from nanofiltration retentate exhibited the highest antioxidant activity, using gel chromatography and reversed phase high-performance liquid chromatography. The amino acid sequences of isolated peptides were identified as Tyr-Glu-Asn-Gly-Gly (P2), Glu-Gly-Tyr-Pro-Trp-Asn (P4), Tyr-Ile-Val-Tyr-Pro-Gly (P7) and Trp-Gly-Asp-Ala-Gly-Gly-Tyr-Tyr (P8) with molecular weights of 538.46, 764.75, 710.78 and 887.85 Da, respectively. P2, P4, P7 and P8 exhibited good scavenging activities on hydroxyl radical (IC₅₀ 0.41, 0.327, 0.17 and 0.042 mg/ml), DPPH radical (IC₅₀ 0.666, 0.326, 0.451 and 0.377 mg/ml) and superoxide radical (IC₅₀ 0.536, 0.307, 0.357 and 0.115 mg/ml). P7 was effective against lipid peroxidation in the model system. The isolated peptides might be useful used as natural food additive in food industry and formulation of nutritional products.

Purification and Identification of Antioxidant Peptides from Protein Hydrolysate of Scalloped Hammerhead (Sphyrna lewini) Cartilage

The aim of this study was to purify and identify peptides with antioxidant properties from protein hydrolysate of scalloped hammerhead (Sphyrna lewini) cartilage. Cartilaginous proteins of the scalloped hammerhead were extracted by guanidine hydrochloride, and three antioxidant peptides, named enzymolysis peptide of scalloped hammerhead cartilage A (SCPE-A), SCPE-B and SCPE-C, were subsequently isolated from the hydrolysate of the cartilaginous proteins using ultrafiltration and chromatography. The amino acid sequences of SCPE-A, SCPE-B and SCPE-C were identified as Gly-Pro-Glu (GPE), Gly-Ala-Arg-Gly-Pro-Gln (GARGPQ), and Gly-Phe-Thr-Gly-Pro-Pro-Gly-Phe-Asn-Gly (GFTGPPGFNG), with molecular weights of 301.30 Da, 584.64 Da and 950.03 Da, respectively. As per in vitro activity testing, SCPE-A, SCPE-B and SCPE-C exhibited strong scavenging activities on 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH•) (half elimination ratio (EC₅₀) 2.43, 2.66 and 1.99 mg/mL), hydroxyl radicals (HO•) (EC₅₀ 0.28, 0.21 and 0.15 mg/mL), 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radicals (ABTS⁺•) (EC₅₀ 0.24, 0.18 and 0.29 mg/mL), and superoxide anion radicals ( O 2 - •) (EC₅₀ 0.10, 0.14 and 0.11 mg/mL). In addition, SCPE-A showed inhibition activity similar to butylated hydroxytoluene (BHT) in lipid peroxidation in a linoleic acid model system. The amino acid residues of Gly, Pro and Phe could positively influence the antioxidant activities of GPE, GARGPQ and GFTGPPGFNG. These results suggested that GPE, GARGPQ and GFTGPPGFNG might serve as potential antioxidants and be used as food additives and functional foods.

Preparation of Antioxidant Peptides from Salmon Byproducts with Bacterial Extracellular Proteases

Bacterial extracellular proteases from six strains of marine bacteria and seven strains of terrestrial bacteria were prepared through fermentation. Proteases were analyzed through substrate immersing zymography and used to hydrolyze the collagen and muscle proteins from a salmon skin byproduct, respectively. Collagen could be degraded much more easily than muscle protein, but it commonly showed weaker antioxidant capability. The hydrolysate of muscle proteins was prepared with crude enzymes from Pseudoalteromonas sp. SQN1 displayed the strongest activity of antioxidant in DPPH and hydroxyl radical scavenging assays (74.06% ± 1.14% and 69.71% ± 1.97%), but did not perform well in Fe²⁺ chelating assay. The antioxidant fractions were purified through ultrafiltration, cation exchange chromatography, and size exclusion chromatography gradually, and the final purified fraction U2-S2-I displayed strong activity of antioxidant in DPPH, hydroxyl radical scavenging assays (IC₅₀ = 0.263 ± 0.018 mg/mL and 0.512 ± 0.055 mg/mL), and oxygen radical absorption capability assay (1.960 ± 0.381 mmol·TE/g). The final purified fraction U2-S2-I possessed the capability to protect plasmid DNA against the damage of hydroxyl radical and its effect was similar to that of the original hydrolysis product. It indicated that U2-S2-I might be the major active fraction of the hydrolysate. This study proved that bacterial extracellular proteases could be utilized in hydrolysis of a salmon byproduct. Compared with collagen, muscle proteins was an ideal material used as an enzymatic substrate to prepare antioxidant peptides.

Protein Hydrolysates and Biopeptides: Production, Biological Activities, and Applications in Foods and Health Benefits. A Review

In recent years, a great deal of interest has been expressed regarding the production, characterization, and applications of protein hydrolysates and food-derived biopeptides due to their numerous beneficial health effects. In this regard, research is mainly focused on investigating the therapeutic potential of these natural compounds. Based on their amino acids composition, sequences, hydrophobicity, and length, peptides released from food proteins, beyond their nutritional properties, can exhibit various biological activities including antihypertensive, antioxidative, antithrombotic, hypoglycemic, hypocholesterolemic, and antibacterial activities among others. Protein hydrolysates are essentially produced by enzymatic hydrolysis of whole protein sources by appropriate proteolytic enzymes under controlled conditions, followed by posthydrolysis processing to isolate desired and potent bioactive peptides from a complex mixture of active and inactive peptides. Therefore, because of their human health potential and safety profiles, protein hydrolysates and biopeptides may be used as ingredients in functional foods and pharmaceuticals to improve human health and prevent diseases. In this review, we have focused on the major variables influencing the enzymatic process of protein hydrolysates production. The biological properties of protein hydrolysates will be described as well as their applications in foods and health benefits.

Effect of pulsed electric field (PEF) on structures and antioxidant activity of soybean source peptides-SHCMN

Recently, high-intensity pulsed electric field (PEF) has successfully used in improvement of antioxidant activity. Ser-His-Cys-Met-Asn (SHCMN) obtained from soybean protein was chosen to investigate the phenomenon of antioxidant activity improvement. Effects of PEF treatment on antioxidant activity of SHCMN were evaluated by DPPH radical inhibition. Nuclear magnetic resonance (NMR), mid-infrared (MIR), circular dichroism (CD) were used to analyze structures of SHCMN. Two-factor-at-a-time results show that DPPH radical inhibition of SHCMN is significantly (P<0.05) increased to 94.35±0.03% at conditions of electric field intensity of 5kV/cm, pulse frequency of 2400Hz, and retention time of 2h. In addition, MIR and NMR spectra show that the basic structure of peptides SHCMN is stable by PEF treatment. But the secondary structures (α-helix, β-turn, and random coil) can be affected and zeta potential of PEF-treated SHCNM was reduced to 0.59±0.03mV. The antioxidant activity improvement of SHCMN might result from the changes of secondary structures and zeta potential.

Antioxidant and ACE Inhibitory Bioactive Peptides Purified from Egg Yolk Proteins

Protein by-products from the extraction of lecithin from egg yolk can be converted into value-added products, such as bioactive hydrolysates and peptides that have potential health enhancing antioxidant, and antihypertensive properties. In this study, the antioxidant and angiotensin converting enzyme (ACE) inhibitory activities of peptides isolated and purified from egg yolk protein were investigated. Defatted egg yolk was hydrolyzed using pepsin and pancreatin and sequentially fractionated by ultrafiltration, followed by gel filtration to produce egg yolk gel filtration fractions (EYGF). Of these, two fractions, EYGF-23 and EYGF-33, effectively inhibited the peroxides and thiobarbituric acid reactive substance (TBARS) in an oxidizing linoleic acid model system. The antioxidant mechanism involved superoxide anion and hydroxyl radicals scavenging and ferrous chelation. The presence of hydrophobic amino acids such as tyrosine (Y) and tryptophan (W), in sequences identified by LC-MS as WYGPD (EYGF-23) and KLSDW (EYGF-33), contributed to the antioxidant activity and were not significantly different from the synthetic BHA antioxidant. A third fraction (EYGF-56) was also purified from egg yolk protein by gel filtration and exhibited high ACE inhibitory activity (69%) and IC₅₀ value (3.35 mg/mL). The SDNRNQGY peptide (10 mg/mL) had ACE inhibitory activity, which was not significantly different from that of the positive control captopril (0.5 mg/mL). In addition, YPSPV in (EYGF-33) (10 mg/mL) had higher ACE inhibitory activity compared with captopril. These findings indicated a substantial potential for producing valuable peptides with antioxidant and ACE inhibitory activity from egg yolk.

Optimization of ultrasound-assisted-extraction of porcine placenta water-soluble proteins and evaluation of the antioxidant activity

Porcine placenta is commonly used in Chinese as a traditional medicine. It has been reported by a number of researchers that the porcine placenta contains many compounds which have good health benefits. Response surface methodology (RSM) was applied to optimize the parameters of ultrasound power, ultrasound treat time, and extraction temperature on the extraction yield of porcine placenta water-soluble proteins (PPWP). The results indicated that, under optimum conditions of ultrasound power 257 w, extraction temperature at 49 °C for 7 min, the extraction yield of PPWP was 32.7 %, which was significantly higher than that of the conventional extraction method (CEM) of 15.0 %. The experimental data were fitted to a second-order polynomial equation using multiple regression analysis and the estimated model showed a high capacity of predicting the dependent variables. Although not significantly, the antioxidant activity of PPWP from ultrasound-assist-extraction (UAE) were higher than those from CEM, indicated that UAE had a positive effect or at least no negative effect on the bioactivity of PPWP.

Influence of Amino Acid Compositions and Peptide Profiles on Antioxidant Capacities of Two Protein Hydrolysates from Skipjack Tuna (Katsuwonus pelamis) Dark Muscle

Influence of amino acid compositions and peptide profiles on antioxidant capacities of two protein hydrolysates from skipjack tuna (Katsuwonus pelamis) dark muscle was investigated. Dark muscles from skipjack tuna were hydrolyzed using five separate proteases, including pepsin, trypsin, Neutrase, papain and Alcalase. Two hydrolysates, ATH and NTH, prepared using Alcalase and Neutrase, respectively, showed the strongest antioxidant capacities and were further fractionated using ultrafiltration and gel filtration chromatography. Two fractions, Fr.A3 and Fr.B2, isolated from ATH and NTH, respectively, showed strong radical scavenging activities toward 2,2-diphenyl-1-picrylhydrazyl radicals (EC₅₀ 1.08% ± 0.08% and 0.98% ± 0.07%), hydroxyl radicals (EC₅₀ 0.22% ± 0.03% and 0.48% ± 0.05%), and superoxide anion radicals (EC₅₀ 1.31% ± 0.11% and 1.56% ± 1.03%) and effectively inhibited lipid peroxidation. Eighteen peptides from Fr.A3 and 13 peptides from Fr.B2 were isolated by reversed-phase high performance liquid chromatography, and their amino acid sequences were determined. The elevated antioxidant activity of Fr.A3 might be due to its high content of hydrophobic and aromatic amino acid residues (181.1 and 469.9 residues/1000 residues, respectively), small molecular sizes (3–6 peptides), low molecular weights (524.78 kDa), and amino acid sequences (antioxidant score 6.11). This study confirmed that a smaller molecular size, the presence of hydrophobic and aromatic amino acid residues, and the amino acid sequences were the key factors that determined the antioxidant activities of the proteins, hydrolysates and peptides. The results also demonstrated that the derived hydrolysates and fractions from skipjack tuna (K. pelamis) dark muscles could prevent oxidative reactions and might be useful for food preservation and medicinal purposes.

Two novel antioxidant nonapeptides from protein hydrolysate of skate (Raja porosa) muscle

In the current study, the preparation conditions of neutrase hydrolysate (SMH) from skate (Raja porosa) muscle protein were optimized using orthogonal L9(3)4 tests, and R values indicated that pH was the most important factor affecting HO· scavenging activity of SMH. Under the optimum conditions of pH 7.0, enzymolysis temperature 60 °C, enzyme/substrate ratio (E/S) 2%, and enzymolysis time 5 h, EC50 of SMH on HO· was 2.14 ± 0.17 mg/mL. Using ultrafiltration, gel filtration chromatography, and RP-HPLC, two novel antioxidant nonapeptides (SP-A and SP-B) were isolated from SMH and their amino acid sequences were found to be APPTAYAQS (SP-A) and NWDMEKIWD (SP-B) with calculated molecular masses of 904.98 Da and 1236.38 Da, respectively. Both showed strong antioxidant activities. SP-A and SP-B exhibited good scavenging activities on HO· (EC50 0.390 and 0.176 mg/mL), DPPH· (EC50 0.614 and 0.289 mg/mL), and O2-· (EC50 0.215 and 0.132 mg/mL) in a dose-dependent manner. SP-B was also effective against lipid peroxidation in the model system. The aromatic (2Trp), acidic (2Asp and Glu), and basic (Lys) amino acid residues within the sequences of SP-B might account for its pronounced antioxidant activity. The results of this study suggested that protein hydrolysate and peptides from skate muscle might be effective as food additives for retarding lipid peroxidation occurring in foodstuffs.

Preparation and Characterization of Antioxidant Peptides from Fermented Goat Placenta

The goat placenta was fermented by Bacillus subtilis and the optimal fermentation parameters of strongest antioxidant capacity of peptides were obtained using response surface methodology (RSM). The effects of fermentation time, initial pH value and glucose content on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity of the goat peptides were well fitted to a quadric equation with high determination coefficients. According to the data analysis of design expert, the strongest DPPH radical scavenging capacity value was obtained with the following conditions: content of glucose was 2.23%, initial pH value was 7.00 and fermentation time was 32.15 h. The DPPH radical scavenging capacity commonly referring antioxidant activity showed a concentration dependency and increased with increasing peptide concentration. The effects of temperature and pH were assessed to determine the stability of antioxidant peptides prepared from goat placenta. Antioxidant peptides showed good stabilities when temperature was lower than 70℃. However, the antioxidant peptides lost antioxidant activities rapidly under alkaline and excessive acid condition. Ultrafiltration technique was performed to separate fermentation broth with different Mw (molecular weight). It was found that peptides in the range of < 3 KDa mainly accounted for the antioxidant activities.

Peptides from cowpea present antioxidant activity, inhibit cholesterol synthesis and its solubilisation into micelles

In previous studies, it was reported that the protein isolated from the cowpea interferes favourably in lipid metabolism, and reduces cholesterol synthesis. The present study investigated the role of cowpea peptide fractions in the micellar solubilisation of cholesterol, in the 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) activity, and in the in vitro antioxidant capacity, considering the effects of thermal processing. The protein was isolated from the raw and cooked beans and digested to simulate human digestion. The peptides from the protein isolate of raw bean with molecular mass lower than 3kDa reduced 89% of the HMGCR enzymatic reaction velocity. The cooked cowpeas were more effective in inhibiting the micellar solubility of cholesterol than the raw ones but not the antioxidant activity. This is the first report that cowpea peptides inhibit cholesterol homeostasis in vitro in two distinct routes, and act as an antioxidant.

Isolation and identification of antioxidative peptides from frog (Hylarana guentheri) protein hydrolysate by consecutive chromatography and electrospray ionization mass spectrometry

Frog (Hylarana guentheri) proteins were hydrolyzed by papain and Flavourzyme to obtain antioxidative peptides. The antioxidant activities of the frog protein hydrolysates (FPHs) were measured, including 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (IC50=9.94±0.13 mg/mL), reducing power (0.39±0.01 at 5.0 mg/mL), and oxygen radical absorbance capacity (ORAC) value (789.15±75.10 μmol Trolox equivalents/g). The hydrolysates were purified by ultrafiltration, ion exchange chromatography, gel filtration chromatography, and reverse-phase high-performance liquid chromatography (RP-HPLC). Through analysis of ESI-MS/MS, two dipeptides were identified as Leu/Ile-Lys (259.1607 Da) and Phe-Lys (293.1446 Da), respectively.

Influence of enzymatic hydrolysis and enzyme type on the nutritional and antioxidant properties of pumpkin meal hydrolysates

Nutritional and antioxidant properties of pumpkin meal and their hydrolysates prepared by hydrolysis with alcalase, flavourzyme, protamex or neutrase were evaluated. The hydrolysis process significantly increased protein content from 67.07% to 92.22%. All the essential amino acids met the Food and Agriculture Organization of United Nations/World Health Organization (WHO/FAO) suggested requirements for children and adults. The amino acid score (AAS) of meal was increased from 65.59 to 73.00 except for flavourzyme (62.97) and protamex (62.50). The Biological Value (BV) was increased from 53.18 to 83.44 except for protamex (40.97). However hydrolysis decreased the Essential Amino Acid/Total Amino Acid ratio (EAA/TAA) from 32.98% to 29.43%. Protein Efficiency Ratio (PER) was comparable to that of good quality protein (1.5) except for flavourzyme hydrolysate which had PER1 = 0.92, PER2 = 1.03, PER3 = 0.38. The in vitro protein digestibility (IVPD) increased from 71.32% to 77.96%. Antioxidant activity increased in a dose-dependent manner. At 10 mg mL(-1), the hydrolysates had increased 1,1-diphenyl-2-picrylhydrazy (DPPH) radical scavenging activities from 21.89% to 85.27%, the reducing power increased from Abs(700nm) 0.21 to 0.48. Metal (Iron) chelating ability was improved from 30.50% to 80.03% at 1 mg mL(-1). Hydrolysates also showed better capabilities to suppress or delay lipid peroxidation in a linoleic acid model system. Different proteases lead to different Degrees of Hydrolysis (DH), molecular weight (MW) distribution, amino acid composition and sequence, which influenced the nutritional properties and antioxidant activities of the hydrolysates. Alcalase was the most promising protease in production of pumpkin protein hydrolysates with improved nutritional quality, while flavourzyme was best in production of hydrolysates with improved antioxidative activity among various assays. These results showed that hydrolysates from by-products of pumpkin oil-processing might serve as alternative sources of dietary proteins with good nutritional quality, and protection against oxidative damage.