Characteristic and antioxidant activity of retorted gelatin hydrolysates from cobia (Rachycentron canadum) skin

Alkali-pretreated cobia (Rachycentron canadum) skin was extracted in a retort (121 °C) for 30 min to obtain a retorted skin gelatin hydrolysate (RSGH). The molecular mass distributions and antioxidant activities of cobia RSGH and enzyme-treated RSGHs (ET-RSGHs) derived from bromelain, papain, pancreatin, and trypsin digestion were then characterized. The molecular mass distribution of the RSGH ranged mainly between 20,000 and 700 Da and those of ET-RSGHs ranged between 6500 and 700 Da. The DPPH (α,α-diphenyl-β-picrylhydrazyl) radical scavenging effects (%) of 10 mg/ml of RSGH and 10 mg/ml of the four ET-RSGHs were 55% and 51–61%, respectively. The lipid peroxidation inhibition (%) of RSGH and ET-RSGHs (10 mg/ml) were 58% and 60–71% on the fifth day in a linoleic acid model system, respectively. The 3Kd-ET-RSGHs, obtained by using a series of centrifugal ultrafiltration filters (molecular weight cut-offs of 10, 5, and 3 kDa done sequentially with decreasing pore size), exhibited dramatically improved antioxidant activity, with most of the molecular mass ranging below 700 Da. Compared to 10 mg/ml of the RSGH, 10 mg/ml of 3Kd-ET-RSGHs exhibited 45–65% more scavenging of DPPH radical and 24–38% more inhibition of lipid peroxidation. The peptides with molecular masses below 700 Da in the ET-RSGHs or 3Kd-ET-RSGHs significantly affect the antioxidant properties. These peptides are composed of a small number of amino acids or free amino acids and have the potential to be added as antioxidants in foods.     

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.     

Characteristics of gelatin from the skins of bigeye snapper, Priacanthus tayenus and Priacanthus macracanthus

Gelatins extracted from the skins containing fine scales of two species of bigeye snapper, Priacanthus tayenus (GT) and Priacanthus macracanthus (GM), were characterised. Both gelatins had the protein as the major component with high content of imino acids (proline & hydroxyproline) (186.29–187.42 mg/g). GT and GM contained calcium at levels of 6.53 and 2.92 g/kg, respectively. Both gelatins contained α1 and α2 chains as the predominant components and some degradation peptides. The absorption bands of both gelatins in Fourier transform infrared (FTIR) spectra were mainly situated in the amide band region (amide I and amide II). GT and GM had a relative solubility greater than 90% in the wide pH ranges (1–10). The bloom strength of GM (254.10 g) was higher than that of GT (227.73 g) (P < 0.05), but was slightly lower than that of commercial bovine gelatin (293.22 g) (P < 0.05). Finer gel structure with smaller strands and voids was observed in GM gel, in comparison with that observed in GT counterpart.     

Characteristics and functional properties of gelatin from splendid squid (Loligo formosana) skin as affected by extraction temperatures

Gelatin was extracted from the skin of splendid squid (Loligo formosana) at different temperatures (50, 60, 70 and 80 °C) with extraction yield of 8.8%, 21.8%, 28.2%, and 45.3% (dry weight basis) for G50, G60, G70 and G80, respectively. Gelatin from the skin of splendid squid had a high protein content (∼90%) with low moisture (8.63–11.09%), fat (0.22–0.31%) and ash contents (0.17–0.68%). Gelatin extracted at higher temperature (G80) had a relatively higher free amino group content than gelatin extracted at lower temperatures (G50, G60 and G70) (P < 0.05). All gelatins contained α- and β-chains as the predominant components. Amino acid analysis of gelatin revealed the high proline and hydroxyproline contents for G50 and G60. FTIR spectra of obtained gelatins revealed the significant loss of molecular order of the triple-helix. The gel strength of gelatin extracted at lower temperature (G50) was higher than that of gelatins extracted at higher temperatures including G60, G70 and G80, respectively. The net charge of G50, G60, G70 and G80 became zero at pHs of 6.84, 5.94, 5.49, and 4.86, respectively, as determined by zeta potential titration. Gelatin extracted at higher temperature (G80) had the lower L* value but higher a* and b* values, compared with those extracted at lower temperatures (P < 0.05). Emulsion activity index decreased, whilst emulsion stability index, foam expansion and stability increased as the concentration (1–3%) increased (P < 0.05). Those properties were governed by extraction temperatures of gelatin. Thus gelatin can be successfully extracted from splendid squid skin using the appropriate extraction temperature.     

Chemical composition and characteristics of skin gelatin from grey triggerfish (Balistes capriscus)

Gelatin was extracted from the skin of grey triggerfish (Balistes capriscus) by the acid extraction process with a yield of 5.67 g/100 g skin sample on the basis of wet weight. The chemical composition and functional properties of gelatin were investigated. The gelatin had high protein (89.94 g/100 g) but low fat (0.28 g/100 g) contents. Differences in the amino acid composition between grey triggerfish skin gelatin (GSG) and halal bovine gelatin (HBG) were observed. GSG contained a lower number of imino acids (hydroxyproline and proline) (176 residues per 1000 residues) than HBG (219 residues per 1000 residues), whereas the content of serine was higher (40 versus 29 residues per 1000 residues, respectively). The gel strength of the GSG (168.3 g) was lower than that of HBG (259 g) (p < 0.05) possibly due to lower hydroxyproline content. Grey triggerfish skin gelatin exhibited a slightly lower emulsifying activity and water-holding capacity but greater emulsifying and foam stability, foam formation ability and fat-binding capacity than the halal bovine gelatin (p < 0.05). SDS-PAGE of GSG showed high band intensity for the major protein components, especially, α- and β-components and a similar molecular weight distribution to that of standard calf skin collagen type I.     

Characteristics of gelatin from the skin of unicorn leatherjacket (Aluterus monoceros) as influenced by acid pretreatment and extraction time

Gelatins from the skin of unicorn leatherjacket (Aluterus monoceros) pretreated with different acids (0.2 M acetic acid or 0.2 M phosphoric acid) and extracted with distilled water at 45 °C for various times (4 and 8 h) were characterized. Yields of 5.23–9.18 or 6.12–11.54% (wet weight basis) were obtained for gelatins extracted from the skin pretreated with 0.2 M acetic acid or 0.2 M phosphoric acid, respectively. Extracted gelatins contained α₁ and α₂ chains as the predominant components and some degradation peptides. The absorption bands of gelatins in FTIR spectra were mainly situated in the amide band region (amide I, amide II and amide ???) and showed the significant loss of molecular order of triple helix. Gelatin samples had a relative solubility greater than 90% in the wide pH ranges (1–10). The gel strength of gelatin from skin pretreated with phosphoric acid (GPA) was higher than that of gelatin from skin pretreated with acetic acid (GAA). Both GPA and GAA had the lower gel strength than that of commercial bovine gelatin (P < 0.05). Net charge of GAA and GPA became zero at pHs of 6.64–7.15 and 6.78–7.26, respectively, as determined by zeta potential titration. Emulsifying and foaming properties of GAA and GPA increased with increasing concentrations (1–3%, w/v). Those properties were governed by pretreatments and extraction time. Thus gelatin can be successfully extracted from unicorn leatherjacket skin using the appropriate acid pretreatment and extraction time.     

Characteristics and functional properties of gelatin from zebra blenny (Salaria basilisca) skin

Gelatin was extracted from alkali-pretreated skin of zebra blenny (Salaria basilisca) using commercial pepsin with a yield of 18 g/100 g of skin sample. The polypeptides pattern, gel strength, viscosity, textural parameters and functional properties of the zebra blenny skin gelatin (ZBSG) were investigated. Amino acid analysis revealed that ZBSG contained almost all essential amino acids, with glycine being the most predominant one. ZBSG was identified as a type I gelatin, containing α₁ and α₂-chains as the major constituents. Its gel strength and viscosity were 170.2 g and 5.95 cP, respectively. Fourier transformed infrared spectroscopy (FT-IR) spectra showed helical arrangements in its structure. Its solubility and functional properties were concentration-dependent. While foam expansion (FE) and foam stability (FS) increased with the increase of concentration, emulsifying activity index (EAI) and emulsion stability index (ESI) were noted to decrease. ZBSG also showed strong clarification ability particularly for apple juice, without affecting nutritional value.     

Characteristics of the gelatin extracted from Channel Catfish (Ictalurus Punctatus) head bones

Three gelatins were prepared from channel catfish head bones by hot water after the head was pretreated with alkali protease, quickly desalted by 0.4 mol/L HCl and soaked in 9 g/L Ca(OH)₂. The extraction conditions of gelatins were 5 °C, pH 4.0, 4 h, 82 °C, pH 2.5, 2 h and 90 °C, pH 3.0, 3 h, respectively. The studies showed there were many differences between these gelatins. The first head bone gelatin contained high content of imino residues and more high molecular weight proportions of β and γ components. Gel strengths of the second and third gelatins were 209 ± 7 g and 117 ± 5 g, lower than that of the first head bone gelatin (282 ± 11 g). Furthermore, the first head bone gelatin achieved the highest gelling and melting points. The first head bone gelatin showed strong ability of clarification when it was used to clarify apple juice. At the same time, the nutritional components of apple juice changed a little except Vitamin C.     

Extraction and properties of gelatin from channel catfish (Ietalurus punetaus) skin

Response surface method was used to determine the optimum operating conditions for extracting the gelatin from channel catfish skin. The optimal conditions for maximum gel strength are 68.8 h for the time of treatment with calcium hydroxide solution, 43.2 °C for the extraction temperature, 5.73 h for the extraction time with hot water. The gelatin from channel catfish skin showed a high gel strength, 276±5 g. Compare to porcine skin gelatin, the gelatin from channel catfish skin has different amino acids composition and a lower thermo-stability.     

Extraction of antioxidant compounds from Jabuticaba (Myrciaria cauliflora) skins: Yield, composition and economical evaluation

Obtaining an extract with high antioxidant activity using environmentally friendly technologies and low-cost raw materials is of great interest. In the present work, a combined extraction process developed by our research group involving ultrasound treatment and agitated solvent extraction was evaluated. This method was compared in terms of yield, composition, and economical feasibility to traditional extraction methods, including ultrasound assisted, agitated bed and soxhlet extraction with ethanol (acidified or not). The proposed method maximizes the extraction of phenolic compounds with acceptable degradation of anthocyanin pigments from an unusual source: Brazilian jabuticaba (Myrciaria cauliflora) skins. The use of ultrasonic irradiation continuously supporting a main extraction process has demonstrated increased performance but implies in high consumption of energy and consequently, money. However, the procedure described in this paper appears to be a viable option because it uses shorter ultrasonic irradiation and results in high antioxidant activity extracts, and the anthocyanin profile corroborates literature data (cyanidin-3-glucoside and delphinidin-3-glucoside).     

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.     

Rheological properties of channel catfish (Ictalurus punctaus) gelatine from fish skins preserved by different methods

Gelatins were extracted from channel catfish skins preserved by different methods using 50 mmol/l acetic acid. Molecular weight distribution, gel strength and viscoelastic properties of gelatin samples were studied. Compared to gelatins from fresh and frozen skins, gelatin from dried channel catfish skin exhibited higher gel strength. This can be explained by the large α-chains content of gelatin from the dried skins. The gelling point and melting point of dried channel catfish skin gelatin solution were similar to those of fresh skin gelatin solution, but distinctly different from those of frozen skin gelatin. After maturation at low temperature, melting points of gelatins increased. But the melting point of frozen skin gelatin was still the highest among the three gelatin samples studied.     

The characteristics of gelatin extracted from sturgeon (Acipenser baeri) skin using various pretreatments

The physicochemical characteristics of gelatin obtained by different pretreatments of sturgeon (Acipenser baeri) skin with alkaline and/or acidic solutions have been studied. Visual appearance, pH, gel strength, viscosity and amino acid profile of the gelatins were evaluated. Pretreatment with alkaline solutions of Ca(OH)₂ and/or acetic acid (HAC) provided gelatin with a favourable colour. Pretreatment with alkali removed noncollagenous proteins effectively, whilst acid induced some loss of collagenous proteins. Gel strength and viscosity of gelatin pretreated with HAC or alkali followed by HAC were as high as gelatin extracted in the presence of protease inhibitors. Amino acid composition had no significant effect on the gelatin characteristics. The total acid concentration for the highest gel strength was inversely proportional to ionisation strength, and the preferred pH for extracting gelatin with the optimum gel strength was approximately 5.0. The results showed that any available protons, regardless of the type or concentration of the acid, inhibit protease activity, which significantly affects the gelatin characteristics.     

Physico-chemical and film forming properties of giant squid (Dosidicus gigas) gelatin

Giant squid (Dosidicus gigas) inner and outer tunics were subjected to hydrolysis with pepsin prior to gelatin extraction (G1 gelatin) by a mild-acid procedure. Furthermore, a second gelatin extraction (G2 gelatin) was done using the collagenous residues that remained from the first extraction. Pepsin allows the collagen solubilisation and the extraction yield to increase by yielding extracts high in α-chains. G1 exhibited good gel forming ability but G2 showed poor viscoelastic behaviour and low gel strength, in agreement with the results for the molecular weight distribution, which showed a considerably higher content of low molecular weight components. In spite of these differences, both G1 and G2 showed good filmogenic ability and similar properties were found including the absence of colour, opacity, low water vapour permeability and high puncture deformation. Nevertheless, films made from G1 had a higher puncture force than films made from G2 as a result of the different molecular weight distribution.     

Characterisation of gelatin–fatty acid emulsion films based on blue shark (Prionace glauca) skin gelatin

Incorporation of fatty acids (stearic and oleic) into edible films based on blue shark (Prionace glauca) skin gelatin was investigated to modify properties such as water vapour barrier and flexibility due to their hydrophobicity and plasticizing effect, respectively. Addition of stearic acid from 0% to 100% of protein concentration in the film-forming solution considerably decreased water vapour permeability of gelatin–fatty acid emulsion films compared to addition of oleic acid at the same fatty acid concentration. Increasing concentrations of both fatty acids decreased tensile strength, but increased elongation at break due to their plasticizing effect. At the same concentration, oleic acid gave a greater plasticizing effect than did stearic acid. On the other hand, transparency of the gelatin–stearic acid emulsion film was lower than that of the gelatin–oleic acid emulsion film. Faster stirring speed of homogenisation improved properties of only the gelatin–stearic acid emulsion film.     

Rheological and functional properties of gelatin from the skin of Bigeye snapper (Priacanthus hamrur) fish: Influence of gelatin on the gel-forming ability of fish mince

The rheological and functional properties of gelatin from the skin of bigeye snapper (Priacanthus hamrur) fish were assessed. The protein content of dried gelatin was 94.6% and moisture content was 4.2%. The amino acid profile of gelatin revealed high proportion of glycine and imino acids. The bloom strength of solidified gelatin was 108 g. The average molecular weight of fish skin gelatin was 282 kDa as determined by gel filtration technique. The emulsion capacity (EC) of gelatin at a concentration of 0.05% (w/v) was 1.91 ml oil/mg protein and with increase in concentration, the EC values decreased. The gelling and melting temperatures of gelatin were 10 and 16.8 °C, respectively as obtained by small deformation measurements. The flow behavior of gelatin solution as a function of concentration and temperature revealed non-Newtonian behavior with pseudoplastic phenomenon. The Casson and Herschel–Bulkley models were suitable to study the flow behavior. The yield stress was maximum at 10 °C with the concentration of 30 mg/ml. Thermal gelation behavior of threadfin bream (Nemipterus japonicus) mince in presence of different concentration of gelatin was assessed. Gelatin at a concentration of 0.5% yielded higher storage modulus (G′) value than control. Frequency sweep of heat set gel with gelatin revealed strong network formation.     

Functional properties of gelatin from cuttlefish (Sepia pharaonis) skin as affected by bleaching using hydrogen peroxide

Functional properties of gelatin from dorsal and ventral skin of cuttlefish with and without bleaching by H₂O₂ at different concentrations (2% and 5% (w/v)) for 24 and 48 h were studied. Gelatin from skin bleached with 5% H₂O₂ for 48 h showed the highest yield (49.65% and 72.88% for dorsal and ventral skin, respectively). Bleaching not only improved the colour of gelatin gel by increasing the L^∗-value and decreasing a^∗-value but also enhanced the bloom strength, and the emulsifying and foaming properties of the resulting gelatin. Gelatin from bleached skin contained protein with a molecular weight of 97 kDa and had an increased carbonyl content. Fourier transform infrared spectroscopic study showed higher intermolecular interactions and denaturation of gelatin from bleached skin than that of the control. These results indicated that hydrogen peroxide most likely induced the oxidation of gelatin, resulting in the formation of gelatin cross-links, giving improved functional properties.     

The role of salt washing of fish skins in chemical and rheological properties of gelatin extracted

Dover sole (Solea vulgaris) skins were washed with different salt solutions previous to gelatin extraction by a mild acid pre-treatment. The effects of NaCl, KCl, MgCl₂, MgSO₄ and no-salt washing on the mineral content, yield of extraction, molecular weight distribution, gel strength, aggregation phenomena and viscoelastic properties of gelatin newly dissolved and after overnight cold maturation were evaluated. Skin washing with NaCl and KCl induced noticeable changes in molecular weight distribution, and consequently in gel strength and rheological properties, especially when compared with unsalted gelatin preparations. However, salts containing Mg²⁺ gave rise to the retaining of this bivalent cation in the resultant gelatin, which is detrimental to the gelatin quality.     

Properties of film from cuttlefish (Sepia pharaonis) skin gelatin incorporated with cinnamon,clove and star anise extracts

Properties of film from cuttlefish (Sepia pharaonis) ventral skin gelatin without and with partial hydrolysis (1.2% degree of hydrolysis) incorporated with 1% ethanolic extract of cinnamon (CME), clove (CLE) and star anise (SAE) were determined. Films with different herb extracts (without and with oxidation) had higher tensile strength (TS) but lower elongation at break (EAB), compared with the control film (without addition of herb extracts) (p < 0.05). Lower water vapor permeability (WVP) and L^∗-value but higher b^∗- and ΔE^∗-values were observed when the extracts were incorporated (p < 0.05). Electrophoretic study revealed that cross-linking was pronounced in films containing different herb extracts. Oxidized extracts yielded films with higher TS and WVP than those without oxidized herb extracts (p < 0.05). Generally, similar properties were noticeable for films from gelatin with and without partial hydrolysis. Nevertheless, higher mechanical properties were obtained for the latter. FTIR spectra indicated that protein–polyphenol interactions were involved in the film. Thermo-gravimetric analysis revealed that films incorporated with SAE or SAE with oxidation (OSAE) exhibited lower heat susceptibility and weight loss in the temperature range of 50–600 °C, compared with control film. Films with SAE and OSAE had smoother surface for gelatin without hydrolysis; however, coarser surface was observed in film from gelatin with partial hydrolysis. Thus, the incorporation of different herb extracts directly affected the properties of film from cuttlefish skin gelatin with and without hydrolysis.     

不同提取方法对东北林蛙皮胶原蛋白理化特性的影响

以东北林蛙皮为原材料,用乙酸和胃蛋白酶两种方法对其中所含的胶原蛋白进行提取,最终得到两种胶原蛋白:酸溶性胶原蛋白（ASC）和酶溶性胶原蛋白（PSC）,并对这两种胶原蛋白的理化性质及功能特性进行比较研究。结果发现,ASC和PSC在234 nm附近都有强吸收峰,符合胶原蛋白的特征;红外光谱发现ASC在3346.0、2952.0、1662.0、1548.0、1242.0 cm^-1有吸收峰,PSC在3322.0、2944.0、1662.0、1551.0、1236.0 cm^-1有吸收峰,证明这两种胶原蛋白都存在酰胺A、酰胺B、酰胺Ⅰ、酰胺Ⅱ、酰胺Ⅲ,内部三螺旋结构都保留完整;氨基酸组成表明ASC和PSC都含有18种氨基酸,包括人体所需的8种必需氨基酸,但是组成略有差异;SDS-PAGE电泳结果显示,这两种胶原蛋白都存在β、α1和α2链,符合Ⅰ型胶原蛋白的结构特征;PSC的变性温度较ASC要高,但是保湿率较低,它们的吸湿率和相对溶解度差异不显著（p>0.05）;以上结果表明不同提取方法对东北林蛙皮胶原蛋白的结构、功能特性有一定影响,但是不影响胶原蛋白的品质。