Isolation and identification of antioxidant peptides from enzymatically hydrolyzed rice bran protein

Physicochemical and functional properties of a protein isolate from maca (Lepidium meyenii) and the secondary structure and immunomodulatory activity of its major protein component

Maca protein isolate (MPI) was extracted from maca root, and its physicochemical and functional properties, and the secondary structure and immunomodulatory activity of its major protein component, MMP, were investigated. The MPI lacked essential amino acids compared with soybean protein isolate (SPI) and casein, but was rich in cysteine and proline. The MPI had rich free sulfhydryl (20.6 μmol g-1), and its surface hydrophobicity (H0, 812.4), oil absorption capacity (7.4 g g-1), foaming capacity (100%) and emulsifying activity (58.2 m2 g-1) were higher than that of SPI. However, the thermal stability (Td, 87.4 °C), foaming stability (75%) and emulsifying stability (26.3 min) of the MPI were weaker than that of the SPI. MMP was a pentamer with a molecular weight of 22 kDa and rich in β-sheets. MMP could significantly enhance the phagocytic capacity and promote the NO, TNF-α and IL-6 secretion of RAW 264.7 cells, involving toll-like receptor 4 and complement receptor 3 mainly.

Novel antioxidant peptides obtained by alcalase hydrolysis of Erythrina edulis (pajuro) protein

BACKGROUND

Oxidative reactions are responsible for the changes in quality during food processing and storage. Oxidative stress is also involved in multiple chronic diseases, such as cardiovascular and neurodegenerative disorders, diabetes, cancer, and aging. The consumption of dietary antioxidants has been demonstrated to help to reduce the oxidative damage in both the human body and food systems. In this study, the potential of Erythrina edulis (pajuro) protein as source of antioxidant peptides was evaluated.

RESULTS

Pajuro protein concentrate hydrolyzed by alcalase for 120 min showed potent ABTS^·+ and peroxyl radical scavenging activity with Trolox equivalent antioxidant capacity (TEAC) and oxygen radical absorbance capacity (ORAC) values of 1.37 ± 0.09 µmol TE mg^-1 peptide and 2.83 ± 0.07 µmol TE mg^-1 peptide, respectively. Fractionation of the hydrolyzate to small peptides resulted in increased antioxidant activity. De novo sequencing of most active fractions collected by chromatographic analysis enabled 30 novel peptides to be identified. Of these, ten were synthesized and their radical activity evaluated, demonstrating their relevant contribution to the antioxidant effects observed for pajuro protein hydrolyzate.

CONCLUSIONS

The sequences identified represent an important advance in the molecular characterization of the pajuro protein, demonstrating its potential as a source of antioxidant peptides for food and nutraceutical applications. © 2018 Society of Chemical Industry.

Rice Bran Supplement Containing A Functional Substance, the Novel Peptide Leu-Arg-Ala, has Anti-Hypertensive Effects: A Double-Blind, Randomized, Placebo-Controlled Study

The anti-hypertensive effect of processed rice bran (PRB) was recently reported, for which the novel peptide Leu-Arg-Ala (LRA) was identified as the functional substance. The purpose of this study was to assess the anti-hypertensive effects of a rice bran supplement containing PRB in individuals with high-normal blood pressure (systolic blood pressure (SBP): 130–139 mmHg and/or diastolic blood pressure (DBP): 85–89 mmHg) or grade 1 hypertension (SBP: 140–159 mmHg and/or DBP: 90–99 mmHg). One hundred individuals with high-normal blood pressure or grade 1 hypertension were recruited to participate in this double-blind, randomized, placebo-controlled study. Participants were randomly allocated to the placebo group (n = 50) or the test group (n = 50). Each group took four test tablets (43 μg LRA/day) or four placebo tablets daily. The decrease in blood pressure in the test group compared with the placebo group was the primary outcome. Adverse events were recorded and hematological/urinary parameters measured to determine the safety of the supplement, which was the secondary outcome. In total, 87 participants completed the study. The SBP of the test group at 12 weeks was significantly lower than that of the placebo group (p = 0.0497). No serious adverse events were observed. Daily consumption of a rice bran supplement containing PRB can safely improve mildly elevated blood pressure.

Preparation and Evaluation of Peptides with Potential Antioxidant Activity by Microwave Assisted Enzymatic Hydrolysis of Collagen from Sea Cucumber Acaudina Molpadioides Obtained from Zhejiang Province in China

The present study was focused on the preparation and characterization of the antioxidant peptides by microwave-assisted enzymatic hydrolysis of collagen from sea cucumber Acaudina molpadioides (ASC-Am) obtained from Zhejiang Province in China. The results exhibited the effects of microwave irradiation on hydrolysis of ASC-Am with different protease. Neutrase was selected from the four common proteases (papain, pepsin, trypsin, and neutrase) based on the highest content and DPPH scavenging activity of hydrolysate Fa (Molecular weight < 1 kDa). The content and 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity of Fa obtained by hydrolysis of neutrase increased by 100% and 109% respectively at a microwave power of 300 W compared with no microwave irradiation. Five subfractions were obtained after performing the gel filtration chromatography, and the Fa.2 exhibited the highest DPPH scavenging activity. The amino acid analysis showed that the contents of Glutamic acid, Alanine, Tyrosine, and Phenylalanine in fraction Fa.2 increased significantly, but an obvious decrease in the content of Glycine was observed compared to Fa. Four peptides (Fa.2-A, Fa.2-B, Fa.2-C, and Fa.2-D) were purified from Fa.2 by high performance liquid chromatography, and Fa.2-C showed the highest DPPH scavenging activity. The sequence of Fa.2-C was identified as Phenylalanine-Leucine- Alanine-Proline with a half elimination ratio (EC₅₀) of 0.385 mg/mL. The antioxidant activity of Fa.2-C was probably attributed to the small molecular sizes and the presence of hydrophobic amino acid residues in its sequence. This report provided a promising method for the preparation of antioxidant peptides from collagen for food and medicinal purposes.

Vasorelaxant and Antihypertensive Effects That Are Dependent on the Endothelial NO System Exhibited by Rice Bran-Derived Tripeptide

We recently identified a novel, potent antihypertensive peptide, Leu-Arg-Ala (LRA; minimum effective dose = 0.25 mg/kg), from rice bran protein. In this study, we found that LRA potently relaxed mesenteric arteries isolated from spontaneously hypertensive rats (SHRs) (EC₅₀ = 0.1 μM). In contrast, the vasorelaxant activity of each amino acid that constitutes the LRA tripeptide was remarkably attenuated. The LRA-induced vasorelaxant activity was inhibited by N(G)-nitro-l-arginine methyl ester (L-NAME; NO synthase [NOS] inhibitor) but not by an antagonist of bradykinin B2 and Mas receptors or by a phosphoinositide 3-kinase inhibitor. The antihypertensive effect induced after the oral administration of LRA was inhibited by L-NAME. LRA also induced the phosphorylation of endothelial NOS in human umbilical vein endothelial cells. Taken together, LRA may exhibit antihypertensive effects via NO-mediated vasorelaxation. LRA is the first example of a NO-dependent vasorelaxant peptide identified from rice bran protein.

The protective effects of Nile tilapia (Oreochromis niloticus) scale collagen hydrolysate against oxidative stress induced by tributyltin in HepG2 cells

Oxidative stress is regarded as one of the most important factors associated with many diseases, such as atherosclerosis, cancer, and diabetes. Various chemicals are released into the environment, causing environmental pollution. Importantly, many of them may cause damage to organisms through oxidative stress. In this work, we investigated the possible protective effects of Nile tilapia (Oreochromis niloticus) scale collagen hydrolysate (TSCH) (molecular weight approximately 4 kDa) against tributyltin (TBT)-induced oxidative stress in vitro. The results showed that pretreatment with TSCH protected against decreases in cell viability and changes in cell morphology in HepG2 cells exposed to TBT. Treatment with TSCH reduced the TBT-induced elevation in malondialdehyde (MDA) levels in HepG2 cells in a dose-dependent manner. Pretreatment with TSCH increased glutathione reductase (GR) and superoxide dismutase (SOD) activity. Moreover, TSCH decreased the expression of the proapoptotic protein Bax, reducing apoptosis. These results suggest that the protective mechanism of TSCH may be associated with its ability to scavenge MDA, increase antioxidant enzyme activity and downregulate the expression of Bax.

Structure-informed separation of bioactive peptides

The application of proteomic and peptidomic technologies for food-derived bioactive peptides is an emerging field in food sciences. These technologies include the use of separation tools coupled to a high-resolution spectrometric and bioinformatic tools for prediction, identification, sequencing, and characterization of peptides. To a large extent, one-dimensional separation technologies have been extensively used as a continuous tool under different optimized conditions for the identification and analysis of food peptides. However, most one-dimensional separation technologies are fraught with significant bottlenecks such as insufficient sensitivity and specificity limits for complex samples. To address this limitation, separation systems based on orthogonal, multidimensional principles, which allow for the coupling of more than one analytical separation tool with different operational principles, provide a higher separation power than one-dimensional separation tools. This review describes the structure-informed separation and purification of protein hydrolyzates to obtain peptides with desirable bioactivities. PRACTICAL APPLICATIONS: Application of bioactive peptides in the formulation of functional foods, nutraceuticals, and therapeutic agents have increasingly gained scholarly and industrial attention. The bioactive peptides exist originally in protein sources and are only active after hydrolysis of the parent protein. Currently, several tools can be configured in one-dimensional or multidimensional systems for the separation and purification of protein hydrolyzates. The separations are informed by the structural properties such as the molecular weight, charge, hydrophobicity or hydrophilicity, and the solubility of peptides. This review provides a concise discussion on the commonly used analytical tools, their configurations, advantages and challenges in peptide separation. Emphasis is placed on how the structural properties of peptides assist in the separation and purification processes and the concomitant effect of the separation on peptide bioactivity.

ACE-inhibitory and antioxidant peptides from coconut cake albumin hydrolysates: purification, identification and synthesis

Coconut cake albumin was hydrolysed by sequential digestion with alcalase, flavourzyme, pepsin and trypsin to purify bioactive peptides with ACE-inhibitory and antioxidant activities. Following fractionation with sequential ultrafiltration, Sephadex gel chromatography and RP-HPLC, three novel peptides KAQYPYV, KIIIYN and KILIYG were identified. KAQYPYV, KIIIYN and KILIYG provided an IC₅₀ value of 37.06 μM, 58.72 μM and 53.31 μM on ACE-inhibitory activity, respectively. For hydroxyl radical scavenging activity, KAQYPYV, KIIIYN and KILIYG demonstrated an IC₅₀ value of 70.84 μM, 77.62 μM and 95.23 μM, respectively. All the three peptides exhibited a mixed modality of noncompetitive and uncompetitive inhibition on ACE and KAQYPYV showed good stability against gastrointestinal enzymes digestion. Moreover, these peptides could effectively lower intracellular endothelin-1 content without significant cytotoxicity, and protected vascular endothelial cells from reactive oxygen species mediated damage. Furthermore, KAQYPYV, KIIIYN and KILIYG also demonstrated high ion chelating ability (62.13% ± 4.21%, 64.66% ± 5.51% and 69.82% ± 7.24% at 0.1 mg mL⁻¹, respectively) and considerable superoxide radical scavenging activity (39.30% ± 2.72%, 46.79% ± 1.70% and 51.16% ± 3.23% at 1.0 mg mL⁻¹, respectively). These results indicate that coconut cake albumin is a potential source of bioactive peptides possessing ACE-inhibitory and antioxidant activities.

Three ACE-inhibitory and antioxidant peptides were identified from enzymatic hydrolysates of coconut cake albumin in the current study.

Anti-proliferative Effect of a Novel Anti-oxidative Peptide in Hanwoo Beef on Human Colorectal Carcinoma Cells

The present study aimed to characterise anti-oxidant peptides from water-soluble protein extracts of Hanwoo beef and evaluate their anti-proliferative effect on human colorectal carcinoma cells (HCT116). Antioxidant peptides were purified from the low-molecular-weight fraction (<3 kDa) of Hanwoo beef extract. Antioxidant activity of peptide fractions was determined using the oxygen radical absorbance capacity (ORAC) assay. Purified peptide (P3) displayed higher ORAC activity than the low-molecular-weight fraction (202.66 μM TE/g vs 167.38 μM TE/g of dry matter, respectively) (p<0.05). The peptide sequence of P3 was Cys-Cys-Cys-Cys-Ser-Val-Gln-Lys (888.30 Da). The novel peptide P3, at 250 μg/mL, also significantly inhibited HCT116 cell proliferation up to 25.24% through phosphorylation of ERK, JNK, and p38 kinase (p<0.05). Hence, antioxidant peptide P3 from Hanwoo beef extract can be used as an antioxidative and anti-cancer agent in the functional food industry.

Characterisation of the bioactive properties and microstructure of chickpea protein-based oil in water emulsions

Legumes, such as chickpea, represent a good source of high quality proteins for which there is an increasing global consumer demand. A chickpea protein concentrate (CP) was generated by isoelectric precipitation. Protein determination, electrophoretic and gel permeation chromatographic analysis revealed that the order of CP solubility was pH 7.5 > 2.5 > 5.0. Sunflower oil in water (O/W) emulsions were generated with the CP at pH 2.5, 5.0 and 7.5. Microstructural evaluation of the emulsions using laser light-scattering particle size analysis, optical microscopy and rheological analysis showed that smaller droplet size (3.1 ± 0.2 and 1.1 ± 0.1 μm) and the highest elastic moduli (876.0 ± 3.2 and 563.5 ± 6.5 Pa) were obtained in those emulsions generated with CP at pH 2.5 and 7.5. The ferric reducing (FRAP) and oxygen radical absorbance capacity (ORAC) values of the CP emulsions ranged from 194.5 ± 19.2 to 242.4 ± 8.4 μmol Trolox Eq·g^-1 CP for FRAP at pH 2.5 and 5.0, respectively, and from 313.2 ± 2.6 to 369.0 ± 1.6 μmol Trolox eq·g^-1 CP for ORAC at pH 5.0 and 2.5, respectively. The enzyme inhibitory activity of the emulsions was generally low irrespective of the pH value (c.a. 3 and 30% inhibition for dipeptidyl peptidase IV (DPP-IV) and angiotensin converting enzyme (ACE) activity, respectively). Simulated gastrointestinal digestion (SGID) of the emulsions significantly decreased their FRAP whereas it increased their ORAC values as well as their ACE and DPP-IV inhibitory activities irrespective of the pH value of the CP. These results demonstrate the potential application of reduced fat CP-stabilized emulsions for the provision of antioxidant and enzyme inhibitory activities.

Antioxidant hydrolyzed peptides from Manchurian walnut (Juglans mandshurica Maxim.) attenuate scopolamine-induced memory impairment in mice

BACKGROUND

Walnut protein, which is obtained as a by-product of oil expression, has not been used efficiently. Although walnuts are beneficial for cognitive functioning, the potential of their protein composition in strengthening learning and memory functions remains unknown. In this study, the inhibition of memory impairment by the Manchurian walnut hydrolyzed peptide (MWHP) was evaluated.

RESULTS

Small-molecular-weight MWHP (<3 kDa) achieved the optimal antioxidative activity. Therefore, MWHP (<3 kDa) was subjected to the following mice trials to evaluate its attenuation effect on memory impairment. In the Morris water maze test, MWHP shortened the total path for searching the platform, reduced the escape latency, and increased the dwelling distance and time in the coverage zone. MWHP also prolonged the latency and diminished errors in the passive avoidance response tests. These behavioral tests demonstrated that MWHP could inhibit scopolamine-induced memory impairment. MWHP improved memory by reducing oxidative stress, inhibiting apoptosis, regulating neurotransmitter functions, maintaining hippocampal CA3 pyramidal neurons, and increasing calmodulin-dependent protein kinase II levels in brain tissues.

CONCLUSION

Experimental results proved that MWHP exhibits potential in improving memory and should be used to develop novel functional food. © 2018 Society of Chemical Industry.

Isolation and identification of peptides from simulated gastrointestinal digestion of preserved egg white and their anti-inflammatory activity in TNF-α-induced Caco-2 cells

Simulated gastrointestinal digestion of preserved egg white (SGD-PEW) exerts anti-inflammatory effects on Caco-2 cells and a mouse model of DSS-induced colitis. Here, we aimed to separate peptides derived from SGD-PEW and evaluate their anti-inflammatory effects using an in vitro inflammatory model. Six peptides were isolated and identified. DEDTQAMPFR (DR-10), DEDTQAMPF (DF-9), MLGATSL (ML-7) and MSYSAGF (MF-7) significantly inhibited IL-8 secretion and markedly decreased gene expression, including TNF-α, IL-8, IL-6, IL-1β and IL-12 and promoted IL-10 gene expression in Caco-2 cells. DR-10, DF-9, ML-7 and MF-7 significantly inhibited the phosphorylation of JNK. In the meantime, DR-10 and DF-9 significantly reduced the phosphorylation of IκB and p38. These results indicated that ML-7 and MF-7 exerted their anti-inflammatory activity through the MAPK signaling pathway in TNF-α-induced Caco-2 cells. Whereas, DR-10 and DF-9 inhibited the NF-κB and MAPK signaling pathways. The results suggested that DR-10, DF-9, ML-7 and MF-7 derived from SGD-PEW may be a new type of prophylactic food for the treatment of inflammation.

Isolation and Identification of Tyrosinase-Inhibitory and Copper-Chelating Peptides from Hydrolyzed Rice-Bran-Derived Albumin

Rice-bran albumin (RBAlb), which shows higher tyrosinase-inhibitory activity than other protein fractions, was hydrolyzed with papain to improve the bioactivity. The obtained RBAlb hydrolysate (RBAlbH) was separated into 11 peptide fractions by RP-HPLC. Tyrosinase inhibition and copper chelation activities decreased with increasing retention times of the peptide fractions. RBAlbH fraction 1, which exhibited the greatest activity, contained 13 peptides whose sequences were determined by using LC-MS/MS. Most of the peptide sequences contained features of previously reported tyrosinase-inhibitory and metal-chelating peptides, especially peptide SSEYYGGEGSSSEQGYYGEG. RBAlbH fraction 1 showed more effective tyrosinase inhibition (IC50 = 1.31 mg/mL) than citric acid (IC50 = 9.38 mg/mL), but it was less effective than ascorbic acid (IC50 = 0.03 mg/mL, P ≤ 0.05). It showed copper-chelating activity (IC50 = 0.62 mg/mL) stronger than that of EDTA (IC50 = 1.06 mg/mL, P ≤ 0.05). These results suggest that RBAlbH has potential as a natural tyrosinase inhibitor and copper chelator for application in the food and cosmetic industries.

Optimization of the enzymatic hydrolysis of rice protein by different enzymes using the response surface methodology

The optimization of the enzymatic hydrolysis of rice protein was determined using an experimental design tool. The semi-purified protease of Bacillus licheniformis LBA 46 and commercial protease Alcalase 2.4 L were used to produce rice hydrolysates using pH values ranging from 6 to 10 and enzyme concentrations varying from 50 to 150 U/mL. The optimized conditions were validated, and using the chosen conditions (pH 10 and 100 U/mL of protease), it was possible to confirm that the model was predictive for oxygen radical absorbance capacity (ORAC) and ferric reducing antioxidant power (FRAP) responses. The experimental values for the ORAC and FRAP responses were 940 and 18.78 TE µmol/g for the rice protein hydrolysates prepared with LBA protease and 1001.94 and 19.31 TE µmol/g for the rice protein hydrolysates prepared with Alcalase 2.4 L. After optimization of the enzymatic hydrolysis conditions, the antioxidant activity values increased when compared to the values for the intact rice protein: 324.97 TE µmol/g (ORAC) and 6.14 TE µmol/g (FRAP). It was also observed that the LBA protease had an action similar to the commercial protease, showing its potential for application in protein hydrolysis.

Assessment of antioxidant properties of membrane ultrafiltration peptides from mungbean meal protein hydrolysates

BACKGROUND

Bioactive peptides can prevent damage associated with oxidative stress in humans when consumed regularly. Recently, peptides have attracted immense interest because of their beneficial functional properties, safety and little or no side effects when used at high concentration. Most antioxidant peptides are small in size, less than 1 kDa, and contains a high proportion of hydrophobic amino acid. Particularly, tyrosine, leucine, alanine, isoleucine, valine, lysine, phenyalanine, cysteine, methionine and histidine in peptide chain exhibited high antioxidant activity. Mungbean meal protein (MMP) is highly abundant in hydrophobic amino acids. It indicated that MMP might be a good source of antioxidants. Therefore, the objectives were to optimize the conditions used to generate mungbean meal protein hydrolysate (MMPH) with antioxidant activity from bromelain and to investigate the antioxidant activities of different molecular weight (MW) peptide fraction.

METHODS

Response Surface Methodology (RSM) was used for screening of the optimal conditions to produce MMPH. After that MMPH was fractionated using ultrafiltration membranes with different MW distributions. Crude-MMPH and four fractions were investigated for five antioxidant activities: 2,2,1-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl, superoxide, ferric reducing antioxidant power (FRAP) and metal ion chelation activity.

RESULTS

The optimal condition to produce the MMPH was 15% (w/w) of bromelain and hydrolysis time for 12 h which showed the greatest DPPH and ABTS radical scavenging activity. After mungbean protein from optimal condition was separated based on different molecular weight, the DPPH radical scavenging activity was the highest for the F4 (less than 1 kDa) peptide fraction. Metal ion chelating activity was generally weak, except for the F4 that had a value of 43.94% at a protein concentration of 5 mg/mL. The F4 also exhibited high hydroxyl and superoxide activities (54 and 65.1%), but moderate activity for ferric reducing antioxidant power (0.102 mmole Fe2+/g protein) compared to other peptide fractions and crude-MMPH. Molecular weight and amino acid were the main factors that determined the antioxidant activities of these peptide fractions. Results indicated that F4 had strong antioxidant potentials.

DISCUSSION

The lowest MW fraction (less than 1 kDa) contributed to the highest DPPH, superoxide, hydroxyl and metal chelation activity because influence of low MW and high content of hydrophobic amino acid in peptide chain. Results from this study indicated that MMPH peptides donate protons to free radicals because they had significantly high DPPH value compared to superoxide, hydroxyl and FRAP, which reactions were electron donation. Moreover, MMPH peptides had the ability to inhibit transition metal ions because of highly abundant glutamic acid and aspartic acid in peptide chain.

Isolation and characterisation of antioxidative peptides from bromelain-hydrolysed brown rice protein by proteomic technique

In this study, proteins from Thai brown rice (Khao Dawk Mali 105) were separated into albumin (2.18 %), globulin (3.98 %), glutelin (84.23 %), and prolamin (9.61 %) fractions, and were hydrolysed with various bromelain concentrations and hydrolysis times. Liquid chromatography-electrospray ionization/mass spectrometry (LC-ESI-MS/MS) was conducted to assess the composition, molecular weight (MW) distribution, and sequence of the resulting peptides, and showed that most peptides have a MW below 2000 Da (60-70 %). Glutelin fraction hydrolysates exhibited the highest 2,2'-azino-bis 3-ethylbenzthiazoline-6-sulfonic (ABTS•+) radical-scavenging (0.69 ± 0.04 µM trolox) and copper chelating (4.12 ± 0.01 mg ethylenediaminetetraacetic acid; EDTA) activities, which was further fractionated into six fractions using reversed-phase high-performance liquid chromatography. The fourth fraction showed the highest ABTS•+ scavenging (1.08 ± 0.03 mM trolox) and copper chelating (5.00 ± 0.02 mg EDTA) activity. LC-MS/MS analysis revealed that the peptides with MW less than 1500 Da and hydrophobic or aromatic N-terminal residues, such as SPFWNINAHS, MPVDVIANAYR, VVYFDQTQAQA, and VEVGGGARAP, possibly contributed to the highest antioxidant activity in fourth fraction.

Purification and structural characterization of a novel antioxidant and antibacterial protein from Arca inflata

A novel protein (J2-C4) with antioxidant and antibacterial activities was purified from the edible portion of Arca inflata. The purity of J2-C4 was measured to be 97.62% by RP-HPLC analysis, and the molecular weight was 20,537.0 Da by ESI-MS/MS. The isoelectric point of J2-C4 was determined to be 5.18 by IEF-PAGE. Secondary structure analysis of J2-C4 showed that it contained 34.9% α-helix, 15.0% β-sheet, 16.3% β-turn and 34.0% random coil by CD spectroscopy. The complete amino acid sequence of J2-C4 was identified by gel electrophoresis and LC-MS/MS together with transcriptome database analysis. Based on the alignment with NCBI BLAST database, J2-C4 showed 71% homology with a sarcoplasmic calcium-binding protein isolated from Crassostrea virginica. Therefore, J2-C4 was proposed to be a new sarcoplasmic calcium-binding protein-like protein in A. inflata. In vitro antioxidant assays showed that J2-C4 exhibited favorable scavenging activities on ABTS⁺ (EC₅₀ 145.80 μg/mL) and DPPH (EC₅₀ 455.62 μg/mL). J2-C4 exhibited antibacterial activities against Pseudomonas aeruginosa (MIC: 375 μg/mL), Escherichia coli (MIC: 187.5 μg/mL) and Methicillin resistant Staphylococcus aureus (MIC: 750 μg/mL). The results showed that J2-C4 might be developed as a potential food additive agent.

Cationic peptides from peptic hydrolysates of rice endosperm protein exhibit antimicrobial, LPS-neutralizing, and angiogenic activities

In this study, we hydrolyzed rice endosperm protein (REP) with pepsin and generated 20 fractions containing multifunctional cationic peptides with varying isoelectric point (pI) values using ampholyte-free isoelectric focusing (autofocusing). Subsequently, we determined antimicrobial activities of each fraction against the pathogens Prophyromonas gingivalis, Propionibacterium acnes, Streptocossus mutans, and Candida albicans. Fractions 18, 19, and 20 had pI values greater than 12 and exhibited antimicrobial activity against P. gingivalis, P. acnes, and C. albicans, but not against S. mutans. In further experiments, we purified and identified cationic peptides from fractions 18, 19, and 20 using reversed-phase high-performance liquid chromatography and matrix-assisted laser/desorption ionization-time-of-flight mass spectroscopy. We also chemically synthesized five identified peptides (RSVSKSR, RRVIEPR, ERFQPMFRRPG, RVRQNIDNPNRADTYNPRAG, and VVRRVIEPRGLL) with pI values greater than 10.5 and evaluated antimicrobial, lipopolysaccharide (LPS)-neutralizing, and angiogenic activities. Among these synthetic peptides, only VVRRVIEPRGLL exhibited antimicrobial activity against P. gingivalis, with an IC₅₀ value of 87μM. However, all five cationic peptides exhibited LPS-neutralizing and angiogenic activities with little or no hemolytic activity against mammalian red blood cells at functional concentrations. These present data show dual or multiple functions of the five identified cationic peptides with little or no hemolytic activity. Therefore, fractions containing cationic peptides from REP hydrolysates have the potential to be used as dietary supplements and functional ingredients in food products.

Fractionation and antioxidant properties of rice bran protein hydrolysates stimulated by in vitro gastrointestinal digestion

Rice bran was used as a starting material to prepare protein concentrate through enzyme-assisted extraction. The hydrolysis of protein concentrate under in vitro gastrointestinal digestion (pepsin-trypsin system) greatly improved the antioxidant properties. Rice bran protein hydrolysate was further fractionated by membrane ultrafiltration (UF, F1: molecular weight (MW) <3kDa, F2: MW 3-5kDa, and F3: MW 5-10kDa). Peptides with smaller MW possessed higher antioxidant activities (P<0.05). UF showed a great efficacy to selectively separate the metal-chelating peptides. Tyrosine and phenylalanine had positive correlations with their DPPH & ABTS radicals scavenging activities and ferric reducing antioxidant power (r>0.831). A major peptide fragment was detected at m/z 1088 by a MALDI-TOF mass spectrometry. There is high potential that antioxidative peptides from rice bran might also be produced in the gastrointestinal tract of the human body.

Rice bran constituents: immunomodulatory and therapeutic activities

Rice bran, one of the most abundant and valuable byproducts produced during the rice milling process, is of steadily growing interest in recent years due to its potential health benefits. Evidence is rapidly accumulating for the beneficial effects of nutraceuticals. However, the potential benefits of rice bran are found in several of its bioactive ingredients including oils, polysaccharides, proteins, and micronutrients. In addition, a significant advantage of rice bran is that it contains more than 100 antioxidants and several categories of bioactive phytonutrients, such as polyphenols, phytosterols, tocotrienols, γ-oryzanol, B vitamins, minerals, and trace minerals. As an immunomodulator, rice bran has beneficial constituents such as polysaccharides, proteins, and oils. Numerous studies also reported that potent antioxidants in rice bran included immune system enhancing compounds, such as phytosterols, polysaccharides, minerals and trace minerals including magnesium, selenium, zinc, vitamin E, omega-3 fatty acids and several other phytonutrients. We believe that this review will be a valuable resource for more studies on rice barn as a dietary source.

Bioactive Peptides

The increased consumer awareness of the health promoting effects of functional foods and nutraceuticals is the driving force of the functional food and nutraceutical market. Bioactive peptides are known for their high tissue affinity, specificity and efficiency in promoting health. For this reason, the search for food-derived bioactive peptides has increased exponentially. Over the years, many potential bioactive peptides from food have been documented; yet, obstacles such as the need to establish optimal conditions for industrial scale production and the absence of well-designed clinical trials to provide robust evidence for proving health claims continue to exist. Other important factors such as the possibility of allergenicity, cytotoxicity and the stability of the peptides during gastrointestinal digestion would need to be addressed. This review discusses our current knowledge on the health effects of food-derived bioactive peptides, their processing methods and challenges in their development.

Fractionation and identification of novel antioxidant peptides from buffalo and bovine casein hydrolysates

Buffalo and bovine caseins were hydrolysed by alcalase and trypsin to produce novel antioxidant peptides. The casein hydrolysates were purified using ultrafiltration (UF) and further characterized by RP-HPLC. The fractions produced higher antioxidant activities were identified for their peptides using LC MS/MS. All UF-VI (MW<1kDa) fractions showed higher antioxidant activity. Hydrolysate produced by alcalase for buffalo casein (UF-VI with 54.84-fold purification) showed higher antioxidant activity than that obtained by trypsin. Trypsin hydrolysate contained high amount of hydrophobic amino acids while alcalase hydrolysate consisted mainly of Ser, Arg, Ala and Leu. The antioxidant peptides identified by LC MS/MS were RELEE, MEDNKQ and TVA, EQL in buffalo casein hydrolysates produced by trypsin and alcalase, respectively. Mechanism and reaction pathways of selected antioxidant peptides with ABTS were proposed. Conclusively, buffalo casein provided antioxidant peptides similar to bovine, suggesting that buffalo casein is a novel source of antioxidant.

Characterization and production of multifunctional cationic peptides derived from rice proteins

Food proteins have been identified as a source of bioactive peptides. These peptides are inactive within the sequence of the parent protein and must be released during gastrointestinal digestion, fermentation, or food processing. Of bioactive peptides, multifunctional cationic peptides are more useful than other peptides that have specific activity in promotion of health and/or the treatment of diseases. We have identified and characterized cationic peptides from rice enzymes and proteins that possess multiple functions, including antimicrobial, endotoxin-neutralizing, arginine gingipain-inhibitory, and/or angiogenic activities. In particular, we have elucidated the contribution of cationic amino acids (arginine and lysine) in the peptides to their bioactivities. Further, we have discussed the critical parameters, particularly proteinase preparations and fractionation or purification, in the enzymatic hydrolysis process for producing bioactive peptides from food proteins. Using an ampholyte-free isoelectric focusing (autofocusing) technique as a tool for fractionation, we successfully prepared fractions containing cationic peptides with multiple functions.

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.

Peptide Fractions Obtained from Rice By-Products by Means of an Environment-Friendly Process Show In Vitro Health-Related Bioactivities

Recently, the isolation of new health-related bioactive molecules derived from agro-food industrial by-products by means of environment-friendly extraction processes has become of particular interest. In the present study, a protein by-product from the rice starch industry was hydrolysed with five commercial proteolytic enzymes, avoiding the use of solvents or chemicals. The digestion processes were optimised, and the digestates were separated in fractions with four different molecular weight ranges by using a cross-flow membrane filtration technique. Total hydrolysates and fractions were tested in vitro for a wide range of biological activities. For the first time rice-derived peptides were assayed for anti-tyrosinase, anti-inflammatory, cytotoxicity and irritation capacities. Antioxidant and anti-hypertensive activities were also evaluated. Protamex, Alcalase and Neutrase treatments produced peptide fractions with valuable bioactivities without resulting cytotoxic or irritant. Highest levels of bioactivity were detected in Protamex-derived samples, followed by samples treated with Alcalase. Based on the present results, a future direct exploitation of isolated peptide fractions in the nutraceutical, functional food and cosmetic industrial fields may be foreseen.

Identification of two novel antioxidant peptides from edible bird's nest (Aerodramus fuciphagus) protein hydrolysates

Two novel antioxidant pentapeptides were isolated from EBN hydrolysates with a protective effect against H₂O₂-induced oxidative damage in cancer cell lines.