Characteristics and chemical composition of skins gelatin from cobia (Rachycentron canadum)

Gelatin was obtained from cobia (Rachycentron canadum) skins, which is an important commercial species for marine fish aquaculture, and it was compared with gelatin from croaker (Micropogonias furnieri) skins, using the same extraction methodology (alkaline/acid pre-treatments). Cobia skins gelatin showed values of protein yield, gelatin yield, gel strength, melting point, gelling point and viscosity higher than the values found from croaker skins gelatin. The values of turbidity and Hue angle for cobia and croaker gelatins were 403 and 74 NTU, and 84.8° and 87.3°, respectively. Spectra in the infrared region had the major absorption band in the amide region for both gelatins, but it showed some differences in the spectra. The proline and hydroxyproline contents from cobia skins gelatin (205 residues/1000 residues) was higher than from croaker skins gelatin (188 residues/1000 residues). SDS-PAGE of both gelatins showed a similar molecular weight distribution to that of standard collagen type I. Therefore, cobia skins could be used as a potential marine source of gelatin obtainment for application in diversified industrial fields.     

Improvement of the antioxidant properties of squid skin gelatin films by the addition of hydrolysates from squid gelatin

Gelatin hydrolysates (HG1 and HG2) were obtained from giant squid (Dosidicus gigas) gelatins (G1 and G2) by hydrolysis with Alcalase. Antioxidant properties of both gelatins were highly increased by hydrolysis, especially ABTS radical scavenging capacity, whereas no significant differences were found between HG1 and HG2. The amino acid composition of HG1 and HG2 closely resembled the amino acid composition of the parent proteins, gelatins G1 and G2. Both, HG1 and HG2 were composed by peptides below 30 kDa, although no clear protein bands were observed in HG2. Edible gelatin films with increasing percentages of HG1 (0–10%) were made from G1, giving rise to increasing values of FRAP and ABTS, as well as changes in mechanical properties (decrease puncture force and increase puncture deformation) and water vapour permeability (increase). HG1 gelatin hydrolysate showed lower antioxidant capacity in the gelatin films than in the free form at the same amount added into the filmogenic solution, probably due to interactions with protein matrix.     

Compositions and antioxidant properties of protein hydrolysates from the skins of four carp species

Compositions and antioxidant properties of protein hydrolysates prepared from four carp skins: black carp, grass carp, silver carp and bighead carp, using pepsin, with a degree of hydrolysis (DH) of 6–15%, were investigated. The yield of freeze‐dried hydrolysates was in the range of 54–62 g/100 g (dry skin). The content of protein and ash in four freeze‐dried hydrolysates was 72–81% and 8–17%, respectively. All hydrolysates contained high amount of hydrophobic amino acid residues (389–480 residues/1000 residues). Meanwhile, their antioxidant properties were evaluated by in vitro assays. The results revealed that all hydrolysates possessed potent antioxidant activities and showed dose dependency as the activity increased with sample concentration, capable of scavenging 72–88% of DPPH and 61–69% of hydroxyl radicals, respectively, at the highest tested concentration. The hydrolysates exhibited high reducing power and β‐carotene–linoleic acid oxidation inhibition. Among the four hydrolysates, the hydrolysate derived from bighead carp skin was superior to others in terms of yield, DH and antioxidant activities.     

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 3 mg/ml), DPPH radical scavenging (18–30% at 1 mg/ml), ferric ion reducing power (abs_700nm 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.     

Bioactive properties of enzymatic hydrolysates from abdominal skin gelatin of yellowfin tuna (Thunnus albacares)

Gelatin (90.6 ± 0.1%) was optimally prepared by response surface methodology from yellowfin tuna (Thunnus albacares, YT) abdominal skin. To investigate bioactive properties of enzymatic hydrolysates from the abdominal skin gelatin (ASG), ASG was hydrolysed with alcalase, protamex, neutrase and flavourzyme as affected by hydrolysis time. Antioxidant, nitrite scavenging and angiotensin‐I converting enzyme (ACE) inhibitory activities of the hydrolysates were determined. Antioxidant activities of the hydrolysates were found through linoleic acid peroxidation inhibitory effects. Alcalase‐derived hydrolysates (AHs) were more effective than others in metal ions chelating, superoxide anion scavenging and hydroxyl radical scavenging activities (P < 0.05). AHs showed significantly stronger nitrite scavenging activities (44.4–60.7%) than others (P < 0.05). Fraction A from AH showed strong ACE inhibitory activity (IC₅₀ of 0.75 mg mL^?1). These results suggest that YT ASG and its enzymatic hydrolysates could be functional food and/or pharmaceutical ingredients with potent antioxidant, anticarcinogenic and antihypertensive benefits.     

Biochemical properties and antioxidant activity of myofibrillar protein hydrolysates obtained from patin (Pangasius sutchi)

Antioxidant activities of myofibrillar protein hydrolysates (MPH) prepared from patin (Pangasius sutchi) using papain and Alcalase^® 2.4 L with different degrees of hydrolysis (DH) were investigated. With a DH of 65.83%, the hydrolysate prepared with papain exhibited the maximum of 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical‐scavenging activity (71.14%) with a reducing power of 0.310. At a concentration of 1 mg mL^?1, the papain‐MPH exhibited a Trolox equivalent antioxidant capacity (TEAC) of 70.50 ± 1.22 μmol g^?1 protein. With a DH of 83.6%, the Alcalase‐MPH had the highest metal‐chelating activity. Low molecular weight peptides showed higher antioxidant activities than high molecular weight peptides. Both papain‐MPH and Alcalase‐MPH contained high amounts of the essential amino acids (48.71% and 48.10%, respectively) with glutamic acid, aspartic acid and lysine as the dominant amino acids. These results suggest that the protein hydrolysates derived from patin may be used as an antioxidative ingredient in both functional food and nutraceutical applications.     

Preparation and antioxidant activity of enzymatic hydrolysates from purple sea urchin (Strongylocentrotus nudus) gonad

Purple sea urchin (Strongylocentrotus nudus) gonad was treated separately with neutral protease, papain, pepsin and trypsin. The resultant hydrolysates were fractionated using a series of ultrafiltration membranes (molecular weight cut-offs of 10, 5, 3 and 1 kDa). Five fractions were prepared from each hydrolysate and the corresponding molecular weight ranges were below 10 kDa, 5-10 kDa, 3-5 kDa, 1-3 kDa and below 1 kDa. The peptide fractions were evaluated for antioxidant activity by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay and reducing power assay. Results indicated that all peptide fractions possessed DPPH radical scavenging capacity and reducing power in a dose-dependent manner. For all four hydrolysates, the below 1 kDa fractions exhibited the highest DPPH radical scavenging capacity. The below 1 kDa fractions prepared with neutral protease, papain and pepsin, and the 1-3 kDa fraction prepared with trypsin showed the highest reducing capacity among corresponding hydrolysates.     

Physicochemical and antioxidant properties of buckwheat (Fagopyrum esculentum Moench) protein hydrolysates

The enzymatic hydrolysis of common buckwheat (Fagopyrum esculentum Moench) protein isolate (BPI) by Alcalase and some physiochemical and antioxidant properties of the resulting hydrolysates were characterised. The hydrolysis resulted in remarkable decrease in the globulins or protein aggregates and concomitant increase in peptide fragments. The surface hydrophobicity of the hydrolysates decreased with increasing degree of hydrolysis (DH) and reached a minimum at DH 15%, but increased at further hydrolysis, whereas their amino acid compositions were unchanged. The polyphenol content of the hydrolysates gradually decreased with DH increasing from 0% to 15%, while it on the contrary increased upon further hydrolysis. The hydrolysates exhibited excellent antioxidant activities, including DPPH radical scavenging ability, reducing power and ability to inhibit linoleic acid peroxidation. The antioxidant activities of these hydrolysates were closely related to their polyphenol contents. The results indicated that polyphenol-rich buckwheat proteins are unique protein materials for the production of the hydrolysates with good nutritional and antioxidant properties.     

Antioxidant properties and protein compositions of porcine haemoglobin hydrolysates

Porcine haemoglobin hydrolysates were prepared through hydrolysis by Alcalase followed by Flavourzyme, and their protein compositions were analyzed using Sephadex G-50 gel filtration chromatography. The antioxidant activities, including reducing power, ferrous ion chelating ability, and DPPH radical scavenging activity, of the hydrolysates were evaluated. The results showed that the hydrolysates of haemoglobin exhibited low reducing powers, but high ferrous ion chelating abilities and DPPH radical scavenging activities. The hydrolysate, obtained through hydrolysis by 2% Alcalase for 4 h and followed by 1% Flavourzyme for 6 h, had the highest ferrous ion chelating ability of 63.54% at a concentration of 5.0 mg/mL. The hydrolysate, obtained through hydrolysis by 2% Alcalase for 4 hrs, had the highest DPPH radical scavenging activity of 41.94% at a concentration of 5.0 mg/mL. According to the results of protein composition analysis, we divided the hydrolysates into three groups, including high molecular weight (MW) group (Group I), medium MW group (Group II), and low MW group (Group III). The reducing power and ferrous ion chelating ability of the hydrolysates were significantly and positively correlated to the relative amount of Group I, and negatively correlated to the relative amount of Group III. This study revealed that the antioxidant activities of porcine haemoglobin hydrolysates were dependent on their protein compositions. The high MW protein fraction (Group I) was responsible for the high reducing power and ferrous ion chelating ability of the hydrolysate.     

Angiotensin-I converting enzyme inhibitory and antioxidant activity of bioactive peptides produced by enzymatic hydrolysis of skin from grass carp (Ctenopharyngodon idella)

Grass carp skin pieces were homogenized in water and hydrolyzed by Alcalase®, collagenase, proteinase K, and/or trypsin at their optimum conditions. Samples were taken at various degrees of hydrolysis and were evaluated for antioxidant, antimicrobial, and angiotensin-converting enzyme inhibitory activities. Alcalase and collagenase completely hydrolyzed the skin with different rates, and released peptides with antioxidant and angiotensin-converting enzyme-inhibitory activity. These activities increased linearly with increasing degrees of hydrolysis. Subsequent incubation of the collagenase hydrolysates with trypsin slightly increased the antioxidant activity. Proteinase K, although only partially hydrolyzing the skin, also catalyzed the release of peptides with antioxidant and angiotensin-converting enzyme-inhibitory activities. These results show that skin by-products from grass carp can be a source of bioactive peptides produced by a one-step reaction. Such hydrolysates may be applied in food products to prolong shelf life and provide beneficial effects on blood pressure.     

The effect of enzymatic hydrolysis time and temperature on the properties of protein hydrolysates from Persian sturgeon (Acipenser persicus) viscera

Protein hydrolysate was prepared from the viscera of Persian sturgeon (Acipenser persicus), a major sturgeon species in the Caspian Sea. Hydrolysis was performed at three different temperatures (35, 45 and 55 °C), pH 8.5, using commercially available Alcalase^® and an enzyme to substrate ratio of 0.1 AU/g viscera protein over a 205 min incubation period. Protein and lipid content of the hydrolysate were 65.82%, and 0.18%, respectively. Protein recovery and degree of hydrolysis ranged from 34.97% to 61.96% and 13.32% to 46.13%, respectively. The highest degree of hydrolysis was observed at 55 °C after 205 min (p < 0.05). The amino acid score of the hydrolysates was similar to that of the FAO/WHO reference protein. It is revealed that Persian sturgeon visceral protein hydrolysate amino acid fulfils adult human requirements. Based on National Research Council guidelines, phenylalanine is the first limiting amino acid in the hydrolysate. However, the hydrolysate has the potential for application as an ingredient in formulated diets.     

Physical and chemical modification of SPI as a potential means to enhance small peptide contents and antioxidant activity found in hydrolysates

The hydrolytic behaviour of the thermal and chemical modified soy protein isolate (SPI) and the antioxidant activity of the resultant hydrolysates have been evaluated in the present study. Thermal treatment, especially in combination with the addition of sodium sulfite, increased the susceptibility of protein hydrolysis due to the unfolding of proteins and the cleavage of disulfide bonds. Succinylation and acylation resulted in significant decrease in amino acids content than that of phosphorylation due to steric hindrance effect as a result of introduction of longer and bulky side chains. Thermal and chemical modification resulted in a significant increase in small peptide content found in hydrolysates, which in turn enhanced significantly the 2,2-Diphenyl-1-picryhydrazyl (DPPH) radical scavenging activity of the hydrolysates, indicating that modification of proteins before hydrolysis could be an efficient way to enhance the small peptide content with desired antioxidant activity.Industrial relevanceEnzymatic hydrolysis of SPI using selected protease has been intensively studied, however, reports on optimization of the substrate by thermal and chemical modifications before hydrolysis to obtain desired hydrolysates are still limited. In this work, SPI was thermally treated or chemical modified and then hydrolyzed by Alcalase. The results indicated that physical and chemical modification of SPI could change the levels of formaldehyde nitrogen and small peptide nitrogen, and consequently enhanced significantly the DPPH radical scavenging activity of the hydrolysates. This work was helpful to provide a feasible and economic way to enhance the contents of small peptides with desired antioxidant properties.     

Purification and characterisation of a new antioxidant peptide from chickpea (Cicer arietium L.) protein hydrolysates

An antioxidant peptide was purified using consecutive chromatographic methods from chickpea protein hydrolysates (CPH). This peptide was designated as Fra.7. It had a molecular weight of 717.37 Da, and its amino acid sequence was identified as Asn-Arg-Tyr-His-Glu by an ABI 4700 proteomics analyser. This antioxidant peptide was identified for the first time from food-derived protein hydrolysates. The molar ratio of the five amino acids in the sequence was 1:1:1:1:1. This antioxidant peptide efficiently quenched the free radical sources 1,1-diphenyl-2-pycryl-hydrazyl (DPPH), hydroxyl, and superoxide free radicals. The Cu²⁺ and Fe²⁺ chelating activities were 76.92% and 63.08% at the peptide concentration of 50 μg mL⁻¹, respectively. Furthermore, the inhibition of the Fra.7 on lipid peroxidation was greater than that of α-tocopherol. The inhibition ratio of the linoleic acid autooxidation was 88.81% at the eighth day of analysis.     

Textural and biochemical properties of cobia (Rachycentron canadum) sashimi tenderised with the ultrasonic water bath

The present study investigated the tenderisation effects ultrasound processing (UT) on farmed cobia sashimi. Age-treated cobia trunk muscles (AT) were used as the control. The pH, total volatile base nitrogen, trimethylamine nitrogen, thiobarbituric acid reactive substances, ATP catabolism components, K₁ value, and texture were evaluated. The texture of AT sashimi reached the optimal firmness range with 8.53 N at day 7. However, AT samples could not be served raw after day 7 because of their poor freshness indexes, including a TVBN value of 18.53 g/100 g, a TMAN value of 3.25 mg/100 g, and a TBARS value 0.983 MDA mg/100 g. Moreover, the K₁ value of AT sashimi was 20.21% at day 5. UT was employed to efficiently tenderise cobia sashimi with an initial firmness of 9.70-7.82 N after 90 min of treatment. The results of this study indicate that UT accelerates the biochemical reaction rate, as evidenced by the increases in the TVBN, TMAN, and TBARS contents; however, these values were very low. The results of this study could provide basic information for the development of a novel ultrasonic tenderisation technique in raw seafood designed for restaurants and consumers.     

Chemical compositions and characterisation of skin gelatin from farmed giant catfish (Pangasianodon gigas)

Gelatin was extracted from the skin of farmed giant catfish (Pangasianodon gigas) with a yield of 20.1 g/100 g skin sample on the basis of wet weight. The chemical composition and properties of gelatin were characterised. The gelatin had high protein (89.1 g/100 g) but low fat (0.75 g/100 g) content and contained a high number of imino acids (proline and hydroxyproline) (211 residues per 1000 residues). Giant catfish skin gelatin had a slightly different amino acid composition than calf skin gelatin. The bloom strength of the gelatin gel from giant catfish skin gelatin (153 g) was greater than that of calf skin gelatin (135 g) (P < 0.05). Viscosity, foam capacity and foam stability of gelatin from giant catfish skins were in general greater than those of the gelatin from calf skin tested. SDS-PAGE of giant catfish skin gelatin showed a high band intensity for the major protein components, especially, α-, β- and γ-components and was similar to that of standard calf skin collagen type I.     

Evaluation of antioxidant activity of muscle and skin protein hydrolysates from giant kingfish,Caranx ignobilis (Forsskål, 1775)

To assess the antioxidant properties of fish protein hydrolysate from giant kingfish Caranx ignobilis (Forsskål, 1775), muscle and skin were obtained using various proteases (papain, pepsin, trypsin and α‐chymotrypsin), respectively. Antioxidant activities of the resulting hydrolysates were evaluated using 2, 2‐diphenyl‐1‐picrylhydrazyl radical scavenging activity, reducing power and metal chelating activity. Among the hydrolysates, peptic of muscle (37 ± 1.0; 0.290 ± 0.012; 63.30 ± 0.57) and tryptic of skin (36.2 ± 1.0; 0.190 ± 0.110; 63 ± 0.57) hydrolysates, which had the highest free radical scavenging activity, was subjected to purification using Sephadex G‐25. The fractionated hydrolysates were superior to the original hydrolysates in the antioxidative activity tested. The active fractions (MF2 and SF2) effectively inhibited lipid peroxidation in linoleic acid emulsion system, and the activity was compared with α‐tocopherol. The amino acid profile of MF2 and SF2 showed a high level of essential amino acids, and the most abundant amino acids were in the order His (12.01% and 7.08%), Phe (7.05% and 6.18%) and Lys (6.76% and 4.74%). Conclusively, C. ignobilis muscle and skin hydrolysates could be a promising rich source of natural antioxidants.     

Angiotensin I-converting enzyme inhibitory activity of low-molecular-weight peptides from Atlantic salmon (Salmo salar L.) skin

Collagen extracted from Atlantic salmon (Salmo salar L.) skin (which is normally discarded in the process of manufacture) was hydrolyzed with Alcalase and papain, and treated by multistage separation. The salmon skin collagen peptides (SSCP) obtained had high protein content (91.20 ± 1.03%) and low molecular weights, 90.79% of which were less than 1000 Da. SSCP was then separated by reversed-phase high performance liquid chromatography. Eleven major fractions were collected and their angiotensin I-converting enzyme (ACE) inhibitory activity was assayed. Fractions 5 and 7 displaying higher ACE inhibitory activity were subjected to mass spectrometer to identify the ACE inhibitory peptides. A total of eleven peptide sequences were identified, and two dipeptides, Ala-Pro and Val-Arg, were selected for further ACE inhibitory activity analysis. The ACE inhibitory activities of Ala-Pro (IC₅₀ = 0.060 ± 0.001 mg/ml) and Val-Arg (IC₅₀ = 0.332 ± 0.005 mg/ml) were found to be approximately 20- and 4-fold higher than that of SSCP (1.165 ± 0.087 mg/ml), respectively.     

Polyphenolic profile,antioxidant properties and antimicrobial activity of grape skin extracts of 14 Vitis vinifera varieties grown in Dalmatia (Croatia)

The aim of the present study was to determine polyphenolic composition, related antioxidative and antimicrobial properties of grape skin extracts from 14 grape varieties (seven white and seven red grape) grown in Dalmatia (Croatia). The content of total phenols, flavonoids, catechins, flavanols and individual polyphenols ((+)-catechin, (−)-epicatechin, epicatechin gallate, procyanidin B1 and procyanidin B2, quercetin glucoside, resveratrol monomers, piceid and astringin) was variety dependent. Antioxidant properties were determined as DPPH radical-scavenging ability (IC₅₀), ferric reducing/antioxidant power (FRAP), Fe²⁺-chelating activity (IC₅₀), and using β-carotene bleaching assay. The high antioxidant capacity of all extracts, both red and white, has been observed and related to the relative amounts of polyphenolic compounds with good antioxidant properties. The antimicrobial activity was screened by broth microdilution test using Gram-positive (Staphylococcus aureus, Bacillus cereus) and Gram-negative bacteria (Escherichia coli O157:H7, Salmonella Infantis, Campylobacter coli). It was confirmed against all tested organisms. Minimum inhibitory concentrations (MICs), were found in the range 0.014–0.59 mg of gallic acid equivalents (GAE)/ml, with lower MICs of white cultivars, especially against Campylobacter and Salmonella.     

Enzymatic hydrolysis of hemp (Cannabis sativa L.) protein isolate by various proteases and antioxidant properties of the resulting hydrolysates

Enzymatic hydrolysis of hemp protein isolate (HPI) by six proteases (alcalase, flavourzyme, neutrase, protamex, pepsin and trypsin) and antioxidant activities of the resulting hydrolysates, obtained for 2 and 4 h were investigated. The yield of trichloroacetic acid (TCA)-soluble peptides (Y_sp), protein composition and surface hydrophobicity (H_o) of the hydrolysates were evaluated. The results showed that the hydrolysates exhibited varying DPPH radical scavenging (with lowest IC₅₀, ∼2.3 mg/mL) and Fe²⁺⁺ chelating (with lowest IC₅₀ of 1.6–1.7 mg/mL) abilities and reducing power (with highest absorbance at 700 nm of 0.31–0.35), depending on their Y_sp and H_o values. The DPPH radical scavenging and Fe²⁺⁺ chelating abilities of the hydrolysates were positively correlated with their Y_sp or H_o values. The results suggest that enzymatic hydrolysis can be used as an effective technique to produce high value-added products of hemp proteins.     

Autolysis-assisted production of fish protein hydrolysates with antioxidant properties from Pacific hake (Merluccius productus)

Fish protein hydrolysates (FPH) with antioxidative properties were prepared using Pacific hake fish with high endogenous proteolytic activity from Kudoa paniformis parasitic infection. Infection level of ∼10⁷K. paniformis spores/g fish mince or higher yielded FPH with high antioxidant potential by autolysis and/or Validase^® BNP or Flavourzyme^® 500L. Autolyzing fish mince containing 30 × 10⁶ spores/g for 1 h at 52 °C and pH 5.50 produced FPH (named E-1h) with Trolox equivalent antioxidant capacity (TEAC) in the 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) radical assay of 262 ± 2 μmol/g and oxygen radical absorbing capacity (ORAC) of 225 ± 17 μmol Trolox equivalents/g freeze-dried sample. E-1h FPH also exhibited a marked concentration-dependent scavenging activity on 1,1-diphenyl-2-picrylhydrazyl radical. Antioxidant activity of E-1h FPH was higher (p < 0.05) than BHA and α-tocopherol in a linoleic acid peroxidation system over prolonged storage (∼162 h). Antioxidative FPH from Pacific hake may be useful ingredients in food and nutraceutical applications.