Optimization of antioxidant peptide production from grass carp sarcoplasmic protein using response surface methodology

Prokaryotic Expression, Purification, and Antibacterial Activity of the Hepcidin Peptide of Crescent Sweetlips (Plectorhinchus cinctus)

The hepcidin peptide of crescent sweetlips (Plectorhinchus cinctus) is a cysteine-rich, cationic antimicrobial peptide that plays a crucial role in the innate immune system's defense against invading microbes. The aim of this study was to identify the optimal parameters for prokaryotic expression and purification of this hepcidin peptide and characterize its antibacterial activity. The recombinant hepcidin peptides were expressed in Escherichia coli strain Arctic Express (DE3), with culture and induction conditions optimized using response surface methodology (RSM). The obtained hepcidin peptides were then purified before tag cleavage, and their antibacterial activity was determined. The obtained results revealed that induction temperature had the most significant impact on the production of soluble recombinant peptides. The optimum induction conditions were determined to be an isopropylthio-β-galactoside (IPTG) concentration of 0.21 mmol/L, induction temperature of 18.81 °C, and an induction time of 16.01 h. Subsequently, the recombinant hepcidin peptide was successfully purified using Ni-IDA affinity chromatography followed by SUMO protease cleavage. The obtained hepcidin peptide (without His-SUMO tag) demonstrated strong antimicrobial activity in vitro against V. parahaemolyticus, E. coli, and S. aureus. The results showed prokaryotic (E. coli) expression is a feasible way to produce the hepcidin peptide of crescent sweetlips in a cost-effective way, which has great potential to be used as an antimicrobial agent in aquaculture.

Physical and Oxidative Stability of Emulsions Stabilized with Fractionated Potato Protein Hydrolysates Obtained from Starch Production Side Stream

This work studies the emulsifying and antioxidant properties of potato protein hydrolysates (PPHs) fractions obtained through enzymatic hydrolysis of potato protein using trypsin followed by ultrafiltration. Unfractionated (PPH1) and fractionated (PPH2 as >10 kDa, PPH3 as 10-5 kDa, PPH4 as 5-0.8 kDa, and PPH5 as <0.8 kDa) protein hydrolysates were evaluated. Pendant drop tensiometry and dilatational rheology were applied for determining the ability of PPHs to reduce interfacial tension and affect the viscoelasticity of the interfacial films at the oil-water interface. Peptides >10 kDa showed the highest ability to decrease oil-water interfacial tension. All PPH fractions predominantly provided elastic, weak, and easily stretchable interfaces. PPH2 provided a more rigid interfacial layer than the other hydrolysates. Radical scavenging and metal chelating activities of PPHs were also tested and the highest activities were provided by the unfractionated hydrolysate and the fractions with peptides >5 kDa. Furthermore, the ability of PPHs to form physically and oxidatively stable 5% fish oil-in-water emulsions (pH 7) was investigated during 8-day storage at 20 °C. Our results generally show that the fractions with peptides >5 kDa provided the highest physicochemical stability, followed by the fraction with peptides between 5 and 0.8 kDa. Lastly, promising sensory results with mostly mild attributes were obtained even at protein concentration levels that are higher than needed to obtain functional properties. The more prominent attributes (e.g., bitterness and astringency) were within an acceptable range for PPH3 and PPH4.

Antioxidant and protective effects of a peptide (VTAL) derived from simulated gastrointestinal digestion of protein hydrolysates of Magallana gigas against acetaminophen-induced HepG2 cells

Oxidative stress is an automatic mechanism responsible for the commencement and continuance of liver injury. In this study, an antioxidative peptide Val-Thr-Ala-Leu (VTAL) was purified from simulated gastrointestinal digestion of protein hydrolysates of the triploid oyster Magallana gigas. Significant antioxidant activity was identified, as well as a protective effect against acetaminophen (APAP)-induced human liver cancer (HepG2) cells. The results suggested that the antioxidant activity improved in a dose-dependent manner. The highest cell viability (88.105 ± 3.62%) was observed in 15 mM APAP-induced cells when treated with 25 μg/mL M. gigas peptide [M.g (pep)]. The peptide sequences include hydrophobic amino acids, which could be responsible for its chemoprotective and antioxidant activities. Treatment with M.g (pep) significantly promoted the proliferation of HepG2 cells, thus protecting them against APAP and imbuing them with significant antioxidant capacity. M.g (pep) could be beneficial for treating drug-induced oxidative stress and liver damage. Additionally, M.g (pep) could serve as an alternative to synthetic antioxidant drugs.

Extraction optimization and screening of antioxidant peptides from grass carp meat and synergistic-antagonistic effect

Grass carp (Ctenopharyngodon idellus) is one of the three most cultivated freshwater fish around the world, but it is mainly consumed afresh, so only a small part of them are processed into salted fish or snack food. This research was performed to prepare and screen antioxidant peptides from grass carp muscle to promote its high‐value utilization. The parameters of double‐enzyme two‐step hydrolysis were optimized, the peptides with the highest ABTS.⁺ scavenging ability were enriched and identified by Sephadex G‐25 and LC‐Q‐Orbitrap‐MS/MS. The synergistic–antagonistic effect among identified peptides was also investigated. The optimized conditions were hydrolyzed with protamex (10,000 U/g) at pH 8.0, 50°C for 3 h, followed by hydrolysis with alcalase (6,000 U/g) at pH 9.0, 50 °C for 2 h, and the protein–liquid ratio was 4%. The hydrolysates were further fractionated to obtain five fractions, in which fraction 3 (F3) exhibited the strongest ABTS.⁺ and O2·‐ scavenging ability with the IC₅₀ values of 0.11 and 0.47 mg/ml, respectively. Twelve novel antioxidant peptides were identified, in which VAGW possessed the highest activity (139.77 μmol GSH/g). Significantly synergistic effects were observed on the two and three peptides’ combination among VAGW, APPAMW, LFGY, FYYGK, and LLLYK, while the C‐terminal tryptophan (Trp) played an important role in the synergism. This study found that grass carp muscle hydrolysates can be potential natural antioxidants in functional products. The synergistic effects among peptides may provide a perspective for the combined application of peptides.

Using RSM for Optimum of Optimum Production of Peptides from Edible Bird’s Nest By-Product and Characterization of Its Antioxidant’s Properties

In this research, the neutrase hydrolysis conditions of edible bird’s nest (EBN) by-products were optimized by response surface methodology (RSM). Antioxidant peptides were then isolated from the EBN by-products by ultrafiltration and chromatography taking the DPPH radical scavenging ability as an indicator. The antioxidant activity of the purified peptides was estimated by radical scavenging ability and sodium nitroprusside (SNP)-induced damage model in PC12 cells. When the enzyme concentration was10 kU/g-hydrolysis temperature was 45 °C, and hydrolysis time was 10.30 h, the degree of hydrolysis (DH) of EBN by-product hydrolysate (EBNH) was the highest. The purified peptide exerted strong scavenging ability with EC₅₀ values of 0.51, 1.31, and 0.65 mg/mL for DDPH, ABTS, and O₂⁻ radicals, respectively. In addition, the purified peptides could significantly reduce the SNP-induced oxidative damage of PC12 cells, and twelve peptides that were rich in leucine (Leu), valine (Val), and lysine (Lys) were identified by LC-MS/MS. These results suggested that EBN by-products have potential as new materials for natural antioxidant peptides.

Experimental and Mathematical Modelling of Factors Influencing Carbon Dioxide Absorption into the Aqueous Solution of Monoethanolamine and 1-Butyl-3-methylimidazolium Dibutylphosphate Using Response Surface Methodology (RSM)

This paper investigated the solubility of carbon dioxide (CO₂) in an aqueous solution of monoethanolamine (MEA) and 1-butyl-3-methylimidazolium dibutylphosphate ((BMIM)(DBP)) ionic liquid (IL) hybrid solvents. Aqueous solutions of MEA-(BMIM)(DBP) hybrid solvents containing different concentrations of (BMIM)(DBP) were prepared to exploit the amine’s reactive nature, combined with the IL’s non-volatile nature for CO₂ absorption. Response surface methodology (RSM) based on central composite design (CCD) was used to design the CO₂ solubility experiments and to investigate the effects of three independent factors on the solubility of CO₂ in the aqueous MEA-(BMIM)(DBP) hybrid solvent. The three independent factors were the concentration of (BMIM)(DBP) (0–20 wt.%), temperature (30 °C–60 °C) and pressure of CO₂ (2–30 bar). The experimental data were fitted to a quadratic model with a coefficient of determination (R²) value of 0.9791. The accuracy of the developed model was confirmed through additional experiments where the experimental values were found to be within the 95% confidence interval. From the RSM-generated model, the optimum conditions for CO₂ absorption in aqueous 30 wt% MEA-(BMIM)(DBP) were 20 wt% of (BMIM)(DBP), a temperature of 41.1 °C and a pressure of 30 bar.

Antioxidant properties of papain mediated protein hydrolysates from fresh water carps (Catla catla, Labeo rohita and Cirrhinus mrigala) and its application on inhibition of lipid oxidation in oil sardine mince during ice storage

Fish protein hydrolysates (FPH) from fresh water carps Catla catla, Labeo rohita and Cirrhinus mrigala were prepared with 5, 10, 15 and 20% degree of hydrolysis (DH) using papain enzyme. FPH were evaluated for antioxidant properties using in vitro assays such as DPPH free radical scavenging activity (at 10 mg/ml), ferric reducing antioxidant power assay (at 20 mg/ml) and linoleic acid peroxidation inhibition activity (at 10 mg/ml). Antioxidant properties of FPH varied with species and DH. The DPPH radical scavenging activity, linoleic acid peroxidation inhibition activity and ferric reducing antioxidant power (as absorbance at 700 nm) of FPH from carps was in the range of 59-92%, 52-85% and 0.388-0.663 respectively. Based on the overall antioxidant activity, FPH from C. catla with 20% DH was added to oil sardine mince at different concentration (0.1, 0.2 and 0.4%) and found to inhibit effectively the formation of peroxides and malonaldehyde in dose dependent manner. FPH from C. catla with 20% DH was fractionated using size exclusion chromatography and had three different peptide fractions with the approximate molecular weight of 6561-2106 Da (fraction 1), 1942-994 Da (fraction 2) and 935-383 Da (fraction 3). The present study showed promising results that the fish protein hydrolysates from fresh water carps muscle proteins can be used as natural antioxidants in food system. Production of fish protein hydrolysates with nutraceutical properties could be the way forward for better utilization and value addition.

Exploiting of Secondary Raw Materials from Fish Processing Industry as a Source of Bioactive Peptide-Rich Protein Hydrolysates

Developing peptide-based drugs are very promising to address many of the lifestyle mediated diseases which are prevalent in a major portion of the global population. As an alternative to synthetic peptide-based drugs, derived peptides from natural sources have gained a greater attention in the last two decades. Aquatic organisms including plants, fish and shellfish are known as a rich reservoir of parent protein molecules which can offer novel sequences of amino acids in peptides, having unique bio-functional properties upon hydrolyzing with proteases from different sources. However, rather than exploiting fish and shellfish stocks which are already under pressure due to overexploitation, the processing discards, regarded as secondary raw material, could be a potential choice for peptide based therapeutic development strategies. In this connection, we have attempted to review the scientific reports in this area of research that deal with some of the well-established bioactive properties, such as antihypertensive, anti-oxidative, anti-coagulative, antibacterial and anticarcinogenic properties, with reference to the type of enzymes, substrate used, degree of particular bio-functionality, mechanism, and wherever possible, the active amino acid sequences in peptides. Many of the studies have been conducted on hydrolysate (crude mixture of peptides) enriched with low molecular bioactive peptides. In vitro and in vivo experiments on the potency of bioactive peptides to modulate the human physiological functions beneficially have demonstrated that these peptides can be used in the prevention and treatment of non-communicable lifestyle mediated diseases. The information synthesized under this review could serve as a point of reference to drive further research on and development of functionally active therapeutic natural peptides. Availability of such scientific information is expected to open up new zones of investigation for adding value to underutilized secondary raw materials, which in turn paves the way for sustainability in fish processing. However, there are significant challenges ahead in exploring the fish waste as a source of bioactive peptides, as it demands more studies on mechanisms and structure–function relationship understanding as well as clearance from regulatory and statutory bodies before reaching the end user in the form of supplement or therapeutics.

The Preparation and Identification of Characteristic Flavour Compounds of Maillard Reaction Products of Protein Hydrolysate from Grass Carp (Ctenopharyngodon idella) Bone

This study aims at preparing the Maillard reaction products of protein hydrolysate from grass carp (Ctenopharyngodon idella) bone and identifying its characteristic flavour compounds. Meanwhile, bioactivities and amino acids composition of hydrolysates and its Maillard reaction products were compared with the thermal degradation reaction as one positive control. Single factor experiment was applied to optimize the enzymolysis parameters of grass carp bone protein using flavourzyme, under which the highest degree of hydrolysis (40.1%) was obtained. According to the response surface methodology, the top predicted value (70.45%) of degree of graft of Maillard reaction was obtained with initial pH of 7.07, temperature of 118.33°C, and time of 1.75 h. Moreover, the results of Maillard reaction products illustrated a significant increase in DPPH radical scavenging activity ( $p<0.05$ ) compared to that of hydrolysate and its thermal degradation products, which was accompanied by the decreased ACE inhibitory activity. Besides, the umami-sweet taste amino acid ratio in free amino acids of Maillard reaction products climbed considerably compared to those of hydrolysate and its thermal degradation products, which proved that Maillard reaction is an effective way to improve the flavour taste of protein hydrolysate. The GC-MS results showed that 37, 40, and 62 kinds of volatile compounds were detected in hydrolysate, thermal degradation products, and Maillard reaction products, respectively. The Maillard reaction products contained more flavour volatile compounds of aldehydes, alcohol, ketone, pyrazine, and other compounds that contribute to pleasant aromas. These results suggested that the grass carp bone protein hydrolysate after Maillard reaction could potentially have a wide range of applications as antioxidant and flavour substances.

Extraction optimization and screening of angiotensin-converting enzyme inhibitory peptides from Channa striatus through bioaffinity ultrafiltration coupled with LC-Orbitrap-MS/MS and molecular docking

Channa striatus is high-protein food with many health functions. This study aimed to prepare, screen and identify the angiotensin-converting enzyme inhibition peptides (ACEIPs) from C. striatus hydrolysates by response surface methodology and bioaffinity ultrafiltration coupled with LC-Orbitrap-MS/MS and molecular docking. The optimal conditions for preparing ACEIPs were hydrolysis temperature 55 °C, hydrolysis time 3 h, pH 9, solid-liquid ratio 1:20 g/mL, and enzyme addition 5%, the ACE inhibition and molecular weight distribution of obtained hydrolysate was 54.35% and 8770-160 Da, respectively. Seven novel ACEIPs were screened through the established high-throughput screening approach, among which, EYFR and LPGPGP showed the strongest ACE inhibition with the IC₅₀ value of 179.2 and 186.3 μM, respectively (P > 0.05). Molecular docking revealed that three and ten hydrogen bonds were formed between ACE and LPGPGP and EYFR, respectively, S1 and S2 were the major active pockets, but the major driving forces varied.

Antioxidant properties of peptides obtained from the split gill mushroom (Schizophyllum commune)

This study sought to assess the ideal conditions under which hydrolysate can be produced from the split gill mushroom proteins through the microbial protease, Alcalase. The research employed a central composite design and response surface methodology. Three specific parameters were varied for the purposes of the experimental process, while a fixed pH value of 8 was used in all cases. The variables were hydrolysis temperature (set as 45 °C, 50 °C, or 55 °C), hydrolysis time (set as 60 min, 120 min, or 180 min), and the ratio of enzyme to substrate (set as 2%, 4%, or 6% w/v). The variables under investigation exert a significant influence upon degree of hydrolysis (DH) in addition to 2,2'-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical-scavenging activity (p < 0.05). Fractionation of the hydrolysate was accomplished using molecular weight (MW) cut-off membranes, while the greatest radical-scavenging capability was observed in the < 0.65 kDa fraction. The MW < 0.65 kDa fraction underwent separation through RP-HPLC in order to create five sub-fractions. Among these, the greatest ABTS radical-scavenging capability was observed in the F₅ sub-fraction, which was therefore chosen to undergo additional examination using quadrupole-time-of-flight-electron spin induction-mass spectrometry-based de novo peptide sequencing. Via this process it was possible to determine five antioxidant peptides. Furthermore, the MW < 0.65 kDa fraction was able to demonstrating cellular antioxidant activity in the context of a human intestinal cancer cell line (HT-29). The extent of this activity was shown to depend upon the concentration levels of the peptide.

Investigation of optimal conditions for production of antioxidant peptides from duck blood plasma: response surface methodology

Duck blood is rich in protein. It is one of the main by-products in the slaughter industry. The objective of this research was to optimize and establish a method for producing duck plasma antioxidant peptides. The composition of duck plasma powder was analyzed. Protease selection experiment (Alcalase, Protamex, and Flavourzyme) and single-factor experiment were performed, and response surface methodology was used to determine the optimal hydrolysis conditions for duck plasma. Among the proteases, Alcalase hydrolysate exhibited the strongest 1,1-diphenyl-2-picrylhydrazyl scavenging rate. The optimum enzymatic hydrolysis conditions were hydrolysis time of 6 h, temperature of 65.5°C, pH 10.0, and enzyme-to-substrate ratio of 0.3%. The 1,1-diphenyl-2-picrylhydrazyl scavenging rate reached 64.84%, and the ratio of essential amino acids was 38.76%. Briefly, the duck plasma hydrolysate exhibited strong antioxidant properties and reasonable composition of amino acids. Thus, it may be used as a nutritional or functional ingredient in foods or medicines. This research provides a theoretical basis for comprehensive processing and high value utilization of duck plasma.

Optimization of Oyster (Crassostrea talienwhanensis) Protein Hydrolysates Using Response Surface Methodology

Oyster (Crassostrea talienwhanensis) protein was hydrolyzed by trypsin to produce peptides with different response values, and response surface methodology (RSM) was applied to optimize the hydrolysis conditions. The highest degree of hydrolysis (DH) of the oyster peptide (OP) was obtained at an enzyme concentration of 1593.2 U/g, a pH of 8.2, a hydrolysis temperature of 40.1 °C, a hydrolysis time of 6.0 h, and a water/material ratio of 8.2. The greatest hydroxyl-radical-scavenging activity of OP was obtained at an enzyme concentration of 1546.3 U/g, a pH of 9.0, a hydrolysis temperature of 50.2 °C, a hydrolysis time of 5.1 h, and a water/material ratio of 5.6. The largest branched-chain amino acid (BCAA) content of OP was obtained at an enzyme concentration of 1323.8 U/g, a pH of 8.3, a hydrolysis temperature of 41.7 °C, a hydrolysis time of 6.7 h, and a water/material ratio of 4.8. The three experimental values were significantly in agreement with the predicted values within the 95% confidence interval. Furthermore, ultrafiltration and chromatographic methods were used to purify the OP, and 13 peptides that were rich in Lys, Arg, His, and Thr were identified by LC-MS/MS. The results of this study offer different optimum hydrolysis conditions to produce target peptides from oyster protein by using RSM, and this study provide a theoretical basis for the high-value utilization of oyster protein.

Improvement of chicken plasma protein hydrolysate angiotensin I-converting enzyme inhibitory activity by optimizing plastein reaction

Chicken plasma protein hydrolysate (CPPH) was prepared by trypsin with angiotensin I-converting enzyme (ACE) inhibitory activity of 53.5% ± 0.14% and the degree of hydrolysis (DH) of 16.22% ± 0.21% at 1 mg·ml-1; then, five proteases, including pepsin, trypsin, papain, alcalase, and neutrase, were employed to improve ACE inhibitory ability by catalyzing plastein reaction. The results indicated that trypsin-catalyzed plastein reaction showed the highest ACE inhibitory activity. The exogenous amino acids of leucine, histidine, tyrosine, valine, and cysteine were selected to modify the CPPH. The leucine-modified plastein reaction released the highest ACE inhibitory activity. The effects of four reaction parameters on plastein reaction were studied, and the optimal conditions with the purpose of obtaining the most powerful ACE inhibitory peptides from modified products were obtained by response surface methodology (RSM). The maximum ACE inhibition rate of the modified hydrolysate reached 82.07% ± 0.03% prepared at concentration of hydrolysates of 30%, reaction time of 4.9 hr, pH value of 8.0, temperature of 40°C, and E/S ratio of 5,681.62 U·g-1. The results indicated that trypsin-catalyzed plastein reaction increased ACE inhibitory activity of chicken plasma protein hydrolysates by 28.57%.

Purification and identification of antioxidant peptides from duck plasma proteins

The antioxidant peptides extracted from duck plasma hydrolysate (DPH) was investigated. The antioxidant activity of DPH, which was isolated and purified via ultrafiltration, size exclusion chromatography, and reversed-phase high-performance liquid chromatography, was evaluated using its free radical scavenging ability. Nano-liquid chromatography-tandem mass spectrometry was conducted to identify the DPH fractions with the highest antioxidant ability. Seven novel peptides: LDGP, TGVGTK, EVGK, RCLQ, LHDVK, KLGA, and AGGVPAG (400.43, 561.63, 431.48, 260.14, 610.71, 387.47, and 527.57 Da, respectively) were identified and synthesized using a solid-phase peptide produce to evaluate their antioxidant activities. Of these, EVGK exhibited the highest Fe²⁺ chelating ability (16.35%), and RCLQ presented the highest reducing power, 2,2-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt scavenging activity, and 1,1-diphenyl-2-picrylhydrazyl scavenging rate (0.62, 274.83 mM TE/mg, and 95.12%, respectively). Our results indicated that DPH possessed antioxidant capabilities and could be used to obtain antioxidant peptides, thus adding economic value to duck blood.

Optimization of Antioxidant Hydrolysate Produced from Tibetan Egg White with Papain and Its Application in Yak Milk Yogurt

The objective of the present study was to produce antioxidant hydrolysate from Tibetan egg white protein hydrolyzed with papain, and to investigate the effect of added papain egg white hydrolysate (PEWH) on the quality characteristics and amino acid profiles of yak milk yogurt. A response surface methodology (RSM) was utilized to analyze the effects of hydrolysis time (X₁), the ratio of enzymes to substrates, and enzyme dosage (X₃) on the superoxide anion radical (O₂⁻) scavenging activity of hydrolysates. The predicted maximum value of O₂⁻ scavenging activity (89.06%) was obtained an X₁ of 2.51 h, X₂ of 4.13%, and X₃ of 4500 U/g of substrate, almost approaching the experimental value (88.05 ± 1.2%). Furthermore, it was found that the addition of PEWH to yak milk can enhance acidification, sensory score, the number of lactic acid bacteria (LAB), and the amino acid content in yak milk yogurt. The results suggested that PEWH displayed an exceptional potential to be developed as a functional food ingredient that could be applied during the manufacturing process of yak milk yogurt.

Double enzyme hydrolysis for producing antioxidant peptide from egg white: Optimization, evaluation, and potential allergenicity

Egg white is a good source of high-quality proteins in food products and an excellent source of antioxidant active peptides through hydrolysis. The hydrolysis conditions for the preparation of potent antioxidant peptides from egg white with chymotrypsin and pepsin were optimized by the response surface methodology. The antioxidant activity and potential allergenicity of the prepared peptides were evaluated by the oxidative damage model and IgE-binding capability, respectively. After ultrafiltration, the peptide produced using the optimized parameters (preheating time of 3.16 hr, hydrolysis time of 3 hr, a sample/solution ratio of 10%, multiple enzymes ratio (E1/E2) of 1.7:1, and E/S of 0.4%) showed antioxidant activity of was 30.86 μmol AAE/g DW and with low potential for allergenicity. The optimized method is efficient and economical and may be applied to the industrial production of antioxidant peptides to obtain nutraceutical and pharmaceutical agents with low sensitivity. However, further in vivo studies must be conducted. PRACTICAL APPLICATIONS: Egg is consumed as an excellent source of protein. Antioxidant peptides released from egg white is considered to be used in food preservation and human health. Few researches on the optimization of egg peptides were aimed to obtain practical techniques used in the food industry. In this paper, egg white hydrolysis peptide with high antioxidant property and low potential allergenicity was prepared after the optimization of double enzyme hydrolysis. The products could be a natural health care products derived from a dietary source and considered using in additive during food production and health food. And the methods used are economical and energy-saving and could be developed to utilize in the food industry.

Purification, Characterization, and Application for Preparation of Antioxidant Peptides of Extracellular Protease from Pseudoalteromonas sp. H2

The study reported on the isolation of a metalloprotease named EH2 from Pseudoalteromonas sp. H2. EH2 maintained more than 80% activity over a wide pH range of 5–10, and the stability was also nearly independent of pH. Over 65% activity was detected at a wide temperature range of 20–70 °C. The high stability of the protease in the presence of different surfactants and oxidizing agents was also observed. Moreover, we also investigated the antioxidant activities of the hydrolysates generated from porcine and salmon skin collagen by EH2. The results showed that salmon skin collagen hydrolysates demonstrated higher DPPH (1,1-diphenyl-2-picrylhydrazyl) (42.88% ± 1.85) and hydroxyl radical (61.83% ± 3.05) scavenging activity than porcine skin collagen. For oxygen radical absorbance capacity, the hydrolysates from porcine skin collagen had higher efficiency (7.72 ± 0.13 μmol·TE/μmol). Even 1 nM mixed peptides could effectively reduce the levels of intracellular reactive oxygen species. The two types of substrates exerted the best antioxidant activity when hydrolyzed for 3 h. The hydrolysis time and type of substrate exerted important effects on the antioxidant properties of hydrolysates. The hydrolyzed peptides from meat collagens by proteases have good antioxidant activity, which may have implications for the potential application of marine proteases in the biocatalysis industry.

Preparation and Identification of Antioxidative Peptides from Pacific Herring (Clupea pallasii) Protein

The aim of this study was to isolate and purify antioxidative peptides from Pacific herring (Clupea pallasii) protein. Five enzymes (pepsin, trypsin, papain, flavourzyme, and neutrase) were used for protein hydrolysis, and Pacific herring protein hydrolysates (PHPH) were separated by ultrafiltration. The fraction with the molecular weight below 3500 Da exhibited the highest in vitro antioxidant activities and cellular antioxidant activity. The PHPH was isolated and purified by consecutive chromatographic methods including gel filtration chromatography and reverse high-performance liquid chromatography (RP-HPLC). The purified antioxidant peptides were identified as Leu-His-Asp-Glu-Leu-Thr (MW = 726.35 Da) and Lys-Glu-Glu-Lys-Phe-Glu (MW = 808.40 Da), and the IC₅₀ values of cellular antioxidant activity were 1.19 ± 0.05 mg/mL and 1.04 ± 0.06 mg/mL. The results demonstrate that is possible to produce natural antioxidative peptides from Pacific herring protein via enzymatic hydrolysis and purification.

Identification and synthesis of multifunctional peptides from wheat germ hydrolysate fractions obtained by proteinase K digestion

Wheat germ protein hydrolysate (WGPH) was obtained by proteinase K digestion, in order to produce bioactive antioxidant and antihypertensive peptides. Response surface methodology (RSM) was used to optimize hydrolysis conditions (enzyme-to-substrate ratio, time, and temperature) for antioxidant activity of hydrolysates. The crude WGPH produced in this way significantly inhibited angiotensin-I converting enzyme (ACE) in a concentration-dependent manner. It was next fractionated by reversed-phase semi-preparative High Performance Liquid Chromatography (HPLC) into 12 fractions that were examined for antioxidant and antihypertensive activities. Fractions with antioxidant and ACE-inhibitory activities were then submitted to further analysis by nano-LC-ESI-MS-MS. Among the various peptides identified, MDATALHYENQK (IC₅₀ : 293.3 ± 6.5 µg/ml) and SGGSYADELVSTAK (IC₅₀ : 265.5 ± 8.3 µg/ml) displayed antioxidant activity and VALTGDNGHSDHVVHF (IC₅₀ : 189.3 ± 4.05 µg/ml), VDSLLTAAK (IC₅₀ : 159.7 ± 0.33 µg/ml), MDATALHYENQK (IC₅₀ : 303.6 ± 2.47 µg/ml), IGGIGTVPVGR (IC₅₀ : 125.7 ± 2.3 µg/ml) and SGGSYADELVSTAK (IC₅₀ : 128.2 ± 1.17 µg/ml) showed good ACE-inhibitory activity. PRACTICAL APPLICATIONS: Wheat milling industries produce massive amounts of wheat germ as by-product that can be converted into valuable compounds. The present research indicates that proteinase K is useful to hydrolyze wheat germ proteins in a search for bioactive peptides with antioxidant and ACE-inhibitory properties. The identified peptides can be regarded as functional food additives, or nutraceuticals to improve human health.

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.

Preparation and Characterization of Antioxidant Peptides from Carrot Seed Protein

Carrot is a very popular vegetable and used for culinary and cosmetic purposes. Carrot seeds can be used for treatment of hangovers and stimulating menstruation. In the present study, the carrot seed protein (CSP) extracted from carrot seed (Daucus carota L.) was hydrolysed by four proteases (papain, trypsin, neutrase, and alcalase). Alcalase hydrolysate exhibited the strongest DPPH radical-scavenging activity (DRSA). The optimum hydrolysis condition for the antioxidant peptide production from CSP was obtained using response surface methodology (RSM). The optimum condition was as follows: hydrolysis time of 3.50 h, substrate concentration of 52.8 g/L, and protease dosage of 419.36 U/g, under which DRSA of 82.46% at 2 mg/mL was obtained. The carrot seed protein hydrolysates (CSPHs) were separated using size exclusion chromatography in order to obtain peptides with stronger antioxidant activity. The hydrolysates were fractionated into four peaks, and fractions F3 and F4 with smaller molecular weight showed stronger antioxidant activity. These findings indicated that the success of RSM in optimizing the hydrolysis conditions and the further work in separation of antioxidant peptides in CSPH is feasible. The CSPH exhibites good antioxidant properties and can be used as useful ingredient in foods.

Response Surface Optimisation for the Production of Antioxidant Hydrolysates from Stone Fish Protein Using Bromelain

Protein hydrolysates produced from different food sources exhibit therapeutic potential and can be used in the management of chronic diseases. This study was targeted to optimise the conditions for the hydrolysis of stone fish protein to produce antioxidant hydrolysates using central composite design (CCD) by response surface methodology (RSM). The stone fish protein was hydrolysed under the optimum predicted conditions defined by pH (6.5), temperature (54°C), E/S ratio (1.5%), and hydrolysis time (360 min). The hydrolysates were then evaluated for 2,2-diphenyl-1-picrylhydrazyl radical (DPPH^•) scavenging activity and ferrous ion- (Fe²⁺-) chelating activity. Results validation showed no significant difference between the experimental values of DPPH^• scavenging activity (48.94%) and Fe²⁺-chelating activity (25.12%) obtained at 54.62% degree of hydrolysis (DH) compared to their corresponding predicted values of 49.79% and 24.08% at 53.08% DH, respectively. The hydrolysates demonstrated non-Newtonian behavior (n < 1) with stronger shear-thinning effect and higher viscosities at increasing concentration. Thus, RSM can be considered as a promising strategy to optimise the production of stone fish protein hydrolysates containing antioxidant peptides. It is hoped that this finding will enhance the potential of stone fish protein hydrolysates (SHs) as therapeutic bioactive ingredient in functional foods development.

Hydrolysis conditions for antioxidant peptides derived from enzymatic hydrolysates of sandfish (Arctoscopus japonicus)

Sandfish (Arctoscopus japonicus) meat and roe were used as natural materials for the preparation of antioxidant peptides using enzymatic hydrolysis. Meat and roe were hydrolyzed using Alcalase 2.4 L and Collupulin MG, respectively. Optimal hydrolysis conditions were determined through the effects of pH, temperature, enzyme concentration, and hydrolysis time on the radical scavenging activity of 1,1-diphenyl-2-picrylhydrazyl (DPPH). The optimal hydrolysis conditions for meat hydrolysate (MHA) obtained via Alcalase 2.4 L treatment were a pH of 6.0, temperature of 70 °C, enzyme concentration of 5% (w/w), and a hydrolysis time of 3 h. The optimal hydrolysis conditions for roe hydrolysate (RHC) obtained via Collupulin MG treatment were pH 9.0, 60 °C temperature, 5% (w/w) enzyme concentration, and 1 h hydrolysis time. Under the optimal conditions, the DPPH radical scavenging activities of MHA and RHC were 60.04 and 79.65%, respectively. These results provide fundamental data for the production of antioxidant peptides derived from sandfish hydrolysates.

Protein hydrolysates of salted duck egg white improve the quality of Jinga Shrimp (Metapenaeus affinis)

The influence of protein hydrolysates of salt duck egg white (PHSDEW) hydrolysed by acid protease on the quality of Jinga Shrimp (Metapenaeus affinis) was analysed. Shrimp immersed in 5% PHSDEW with degree of hydrolysis (DH 3%) had the highest values of cooking yield, water retention, moisture and texture with the lowest cooking loss when compared to which immersed in 0.4% NaCl, 3.5% mixed phosphates and other PHSDEW with different DH (1%, 2% and 5%) (P < 0.05). This treatment made muscle fibres retain the most appropriate compact and regular microstructure and improved the thermal stability of shrimp protein as well (P < 0.05). SDS‐PAGE protein patterns revealed shrimp protein would dissolve out during immersion, while only could PHSDEW infiltrate into shrimp muscle. It suggested PHSDEW would be developed as a new type of water retention agent replaced phosphate used in shrimp or other seafoods, which will decrease the waste of salt duck egg white.

Optimization of ultrasonic-assisted enzymatic hydrolysis conditions for the production of antioxidant hydrolysates from porcine liver by using response surface methodology

Objective

The objective of this study was to optimize ultrasonic-assisted enzymatic hydrolysis conditions, including enzyme-to-substrate (E/S) ratio, pH, and temperature, for producing porcine liver hydrolysates (PLHs) with the highest 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity by using response surface methodology (RSM).

Methods

The study used RSM to determine the combination of hydrolysis parameters that maximized the antioxidant activity of our PLHs. Temperature (40°C, 54°C, and 68°C), pH (8.5, 9.5, and 10.5), and E/S ratio (0.1%, 2.1%, and 4.1%) were selected as the independent variables and analyzed according to the preliminary experiment results, whereas DPPH free radical scavenging activity was selected as the dependent variable.

Results

Analysis of variance showed that E/S ratio, pH, and temperature significantly affected the hydrolysis process (p<0.01). The optimal conditions for producing PLHs with the highest scavenging activity were as follows: E/S ratio, 1.4% (v/w); temperature, 55.5°C; and initial pH, 10.15. Under these conditions, the degree of hydrolysis, DPPH free radical scavenging activity, ferrous ion chelating ability, and reducing power of PLHs were 24.12%, 79%, 98.18%, and 0.601 absorbance unit, respectively. The molecular weight of most PLHs produced under these optimal conditions was less than 5,400 Da and contained 45.7% hydrophobic amino acids.

Conclusion

Ultrasonic-assisted enzymatic hydrolysis can be applied to obtain favorable antioxidant hydrolysates from porcine liver with potential applications in food products for preventing lipid oxidation.

Optimization of the Extraction and Stability of Antioxidative Peptides from Mackerel (Pneumatophorus japonicus) Protein

This study optimizes the preparation conditions for mackerel protein hydrolysate (MPH) by response surface methodology (RSM) and investigates the stability of the antioxidant activity of MPHs (<2.5 kDa). The optimal conditions were as follows: enzyme concentration of 1726.85 U/g, pH of 7.00, temperature of 39.55°C, time of 5.5 h, and water/material ratio of 25 : 1, and the maximum DPPH scavenging activity was 79.14%. The MPHs indicated significant cellular antioxidant activity at low concentrations. Furthermore, the temperature and freeze-thaw cycles had little effect on the antioxidative stability while pH had significant effect on the antioxidative stability. In addition, the MPHs were sensitive to the metal ions, such as Fe2+, Fe3+, Zn2+, and Cu2+. Notably, when the concentrations of Fe2+ and Fe3+ were 5 mM, the DPPH scavenging activities were only 1.1% and 0.6%, respectively; furthermore, Cu2+ at a 5 mM concentration could completely inhibit the DPPH scavenging activity of MPHs. In contrast, K+ and Mg2+ had no notable effect on the antioxidant activity of MPHs. These results may provide a scientific basis for the processing and application of MPHs.

Identification of antioxidant peptides of Jinhua ham generated in the products and through the simulated gastrointestinal digestion system

BACKGROUND

The objective of this study was to purify and identify antioxidant peptides present in the extract of Chinese dry-cured Jinhua ham. Jinhua ham extracts were separated into five fractions (A-E) by size-exclusion chromatography. Each fraction was subjected to a simulated gastrointestinal (GI) digestion system and fractions showing strong antioxidant activities were collected and subjected to liquid chromatography combined with tandem mass spectrometry (LC/MS/MS) for further purification and identification.

RESULTS

Using MS/MS analysis, 33 peptides were identified in these fractions. Several key peptides were selected for synthesis and their antioxidant activity determined. The peptide showing strongest DPPH radical scavenging activity was GKFNV, which showed 92.7% antioxidant activity at a concentration of 1 mg mL(-1); the peptide LPGGGHGDL showed the highest hydroxyl radical scavenging activity; and LPGGGT and HA showed strong inhibition activity against erythrocyte hemolysis (about 45%) before digestion. On the other hand, KEER may contribute to Fe(2+) chelating ability in fraction C after GI digestion.

CONCLUSION

Jinhua dry-cured ham seems to be a potential source of antioxidant peptides generated in the products and in GI digestion.

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.

Ultrasound-assisted extraction of antioxidants in Misai Kucing (Orthosiphon stamineus)

Ultrasound-assisted extraction (UAE) with ethanol was used to extract the compounds responsible for the antioxidant activities of Misai Kucing (Orthosiphon stamineus). Response surface methodology (RSM) was used to optimize four independent variables: ethanol concentration (%), amplitude (%), duty cycle (W/s) and extraction time (min). Antioxidant compounds were determined by total phenolic content and total flavonoid content to be 1.4 g gallic acid equivalent/100 g DW and 45 g catechin equivalent/100 g DW, respectively. Antioxidant activities were evaluated using the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS^•+) radical scavenging capacity assay and the 2,2-diphenyl-1-picrylhydrazyl (DPPH•) radical scavenging capacity assay to be 1,961.3 and 2,423.3 µmol Trolox Equivalent Antioxidant Capacity (TEAC)/100 g DW, respectively. Based on the optimal conditions, experimental values were reported to be close to the predicted value by RSM modeling (p > 0.05), indicating the suitability of UAE for extracting the antioxidants of Misai Kucing. Rosmarinic acid, kaempferol-rutinoside and sinesetine were identified by high performance liquid chromatography-mass spectrometry.

Optimization of hydrolysis conditions, isolation, and identification of neuroprotective peptides derived from seahorse Hippocampus trimaculatus

Hippocampus trimaculatus is one of the most heavily traded seahorse species for traditional medicine purposes in many countries. In the present study, we showed neuroprotective effects of peptide derived from H. trimaculatus against amyloid-β42 (Aβ42) toxicity which are central to the pathogenesis of Alzheimer's diseases (AD). Firstly, H. trimaculatus was separately hydrolyzed by four different enzymes and tested for their protective effect on Aβ42-induced neurotoxicity in differentiated PC12 cells. Pronase E hydrolysate exerted highest protection with cell viability value of 88.33 ± 3.33 %. Furthermore, we used response surface methodology to optimize pronase E hydrolysis conditions and found that temperature at 36.69 °C with the hydrolysis time 20.01 h, enzyme to substrate (E/S) ratio of 2.02 % and pH 7.34 were the most optimum conditions. Following several purification steps, H. trimaculatus-derived neuroprotective peptides (HTP-1) sequence was identified as Gly-Thr-Glu-Asp-Glu-Leu-Asp-Lys (906.4 Da). HTP-1 protected PC12 cells from Aβ42-induced neuronal death with the cell viability value of 85.52 ± 2.22 % and up-regulated pro-survival gene (Bcl-2) expressions. These results suggest that HTP-1 has the potential to be used in treatment of neurodegenerative diseases, particularly AD. Identification, characterization, and synthesis of bioactive components derived from H. trimaculatus have the potential to replace or at least complement the use of seahorse as traditional medicine, which further may become an approach to minimize seahorse exploitation in traditional medicine.

Antibacterial Activity of Brewer's Spent Grains Peptides to Staphylococcus aureus

Antibacterial ability of brewer's spent grains peptides was detected which were hydrolyzed in different hydrolysis time with four proteases. The results showed: Flavourzyme hydrolyze in 180 min has better antibacterial ability to Staphylococcus aureus. The hydrolyzate was separated with polyamide column chromatography, ion exchange column chromatography, respectively. Peptides were tested of antibacterial ability, and better antibacterial ability were collected. Molecular weight is about 1877.67 which is measured with gel column chromatography. The minimal inhibitory concentration to Staphylococcus aureus was 2%.

The role of molecular size in antioxidant activity of peptide fractions from Pacific hake (Merluccius productus) hydrolysates

The antioxidative properties of Pacific hake hydrolysates and their peptidic fractions varying in molecular size were assessed. Hydrolysates produced by different proteases (Alcalase, bromelain, Flavourzyme, Protamex, Protease A"Amano"2, Protease N"Amano"K, Protin SD NY10, Umamizyme-K, Validase BNP-L, Validase FPexo) generally possessed good metal ion chelating (33-73% at 3mg/ml), DPPH radical scavenging (18-30% at 1mg/ml), ferric ion reducing power (abs700nm 0.36-0.86 at 3 mg/ml) and ABTS radical scavenging (47-85% at 0.067 mg/ml) activity, as well as a good capability to suppress lipid peroxidation in a linoleic acid model system. Peptide size (<1.4 kDa) was important for ABTS radical scavenging activity, whereas specific peptide composition (which depended on the particular protease used) was the governing factor for effective lipid peroxidation. Validase BNP-L was the most promising enzyme for producing Pacific hake hydrolysates with good antioxidative activity in various assays and similar effectiveness as the synthetic antioxidant BHT to inhibit lipid peroxidation.