Preparation and functional characterisation of fish skin gelatin and comparison with commercial gelatin

Gelatin was extracted from the skin of farmed giant catfish (GC) and tilapia (TP) at a yield of 19.50% and 23.34% (wet wt). It was high in protein (84–88%) but low in fat (0.09–1.24%) and ash content (0.15–0.17%). The GC exhibited lower emulsifying activity (24–35%), but greater foam ability (98–110%), water holding capacity (477–844%) and fat binding capacity (2541–3314%) than commercial beef skin gelatin (BF) (P < 0.05). GC and TP showed comparable functional properties to BF. SDS‐PAGE patterns of TP gelatin showed high band intensity for the α‐ and β‐components, while the lowest band intensity of the major component was found in the BF. From the study, it can be concluded that the farmed freshwater fish skin GC and TP is a prospective source for producing a significant gelatin yield with desirable functionalities. Because of these, fish skin gelatin could be more effectively and widely used in food industries as a good food ingredient.     

Re-extraction,Recovery, and Characteristics of Skin Gelatin from Farmed Giant Catfish

This study was aimed to investigate the re-extraction process for gelatin recovery from the skin of farmed giant catfish. The first extraction was done by incubating the acid-treated fish skin at 45 °C for 12 h. The remnant was re-extracted at temperatures of 60–90 °C for 1–12 h. The gelatin yield of the first extraction was 10.14%, while the re-extraction at high temperature provided higher recovery (19.5%). Low band intensity of α₁ and α₂ chains of gelatin was observed when it was re-extracted at high temperature for a longer time. The absorption bands of amide I and II from both extracted gelatins were similar. Low-transition temperature with high transition enthalpy of gelatin extracted at 90 °C was observed. The obtained results suggested that the re-extraction process could be applied as a supplemental step for other sources to obtain high recovery with the desired properties.     

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.     

Effects of nisin concentration on properties of gelatin film-forming solutions and their films

The addition of nisin into a gelatin matrix can change properties of the film. The aim of this work was to develop gelatin-based films containing different nisin concentrations in order to study their influence on the film's antimicrobial and physical properties and their rheological properties as a film-forming solution (FFS). The FFS was characterised by rheological assays, and the gelatin-based active films were characterised and assessed by the effects of nisin concentrations on their various properties, including antimicrobial activity. Nisin's concentration affected not only its viscoelastic properties of FFS but also its film solubility in water, film surface roughness and light barrier. The addition of nisin also slightly modified the water contact angle and the mechanical properties of the gelatin films. Finally, the films demonstrated activity against Staphylococcus aureus and Listeria monocytogenes at concentrations above 56 mg of nisin g⁻¹ of gelatin.     

Improved microstructure and properties of the gelatin film produced through prior cross‐linking induced by horseradish peroxidase,glucose oxidase and glucose

The effects of prior enzymatic cross‐linking of bovine gelatin via horseradish peroxidase, glucose oxidase and glucose on microstructure and properties of the target film (cross‐linked gelatin film) were assessed. The cross‐linked gelatin film exhibited similar film thickness and moisture content, lower water solubility and higher opacity than the gelatin film directly prepared with bovine gelatin. The cross‐linked gelatin film also demonstrated improved thermal stability and mechanical properties, characterised by higher melting point and glass transition temperature, enhanced tensile strength and elongation at break and greater storage modulus. Prior gelatin cross‐linking resulted in 30.2% and 68.6% reductions in water vapour and CO₂ permeability of the cross‐linked gelatin film, respectively, but did not affect oil permeability. Furthermore, the cross‐linked gelatin film possessed smaller cross‐sectional voids (diameter 100?360 nm vs. 200?595 nm) than the bovine gelatin film. This study shows that cross‐linking can efficiently improve film microstructure and properties of the gelatin‐like products.     

Preparation and functional properties of fish gelatin–chitosan blend edible films

With the goal of improving the physico-chemical performance of fish gelatin-based films, composite films were prepared with increasing concentrations of chitosan (Ch) (100G:0Ch, 80G:20Ch, 70G:30Ch, 60G:40Ch and 0G:100Ch, gelatin:Ch), and some of their main physical and functional properties were characterised. The results indicated that the addition of Ch caused significant increase (p < 0.05) in the tensile strength (TS) and elastic modulus, leading to stronger films as compared with gelatin film, but significantly (p < 0.05) decreased the elongation at break. Ch drastically reduced the water vapour permeability (WVP) and solubility of gelatin films, as this decline for the blend film with a 60:40 ratio has been of about 50% (p < 0.05). The light barrier measurements present low values of transparency at 600 nm of the gelatin–chitosan films, indicating that films are very transparent while they have excellent barrier properties against UV light. The structural properties investigated by FTIR and DSC showed a clear interaction between fish gelatin and Ch, forming a new material with enhanced mechanical properties.     

Role of lignosulphonate in properties of fish gelatin films

A commercial low-gelling fish skin gelatin was used to prepare edible films by casting with glycerol and sorbitol added as plasticizers. In order to improve the extremely low water resistance of gelatin films, composite films were prepared with increasing concentrations (wt/wt) of lignosulphonate (LS) from eucalyptus wood (100:0, 85:15, 80:20, 75:25, 70:30 and 65:35, gelatin:LS). How gelatin film properties were affected by the different types of gelatin and LS was determined by comparing bovine gelatin and three different LS (Ca²⁺, Mg²⁺ and Na⁺) in a mixture ratio of 80:20. Physical properties of films were characterized in terms of tensile strength, elongation at break, water solubility, water vapour permeability and opacity. Dynamic oscillatory tests of film-forming solutions revealed strong LS interference with the cold-renaturation ability of gelatin. LS ratios equal to or higher than the 80:20 blend interfered with intermolecular aggregation of gelatin helices. Supposedly, LS acted as a filler, inducing mostly nonbonding interactions with gelatin, as deduced from Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR) and Differential Scanning Calorimetry (DSC) studies. Lignosulphonate significantly reduced the elongation at break of fish gelatin films, water solubility being drastically reduced with a mixture ratio of 80:20 or higher. The water solubility of bovine gelatin-LS composite films was significantly lower than that for fish gelatin, regardless of the type of LS employed. For potential food packaging applications, the three LS were characterized in terms of cytotoxicity, radical scavenging capacity (DPPH assay) and antimicrobial capacity. The effective antioxidant levels (IC₅₀: 83.4-97.5 μg/mL) were noticeably lower than the cytotoxic ones (IC₅₀: 1480-1745 μg/mL), indicating that these compounds could be used as antioxidants at non-cytotoxic concentrations. No relationship between antioxidant and antimicrobial properties could be observed, the only notable antimicrobial finding being some activity against yeasts.     

Effect of Addition of Halloysite Nanoclay and SiO<Subscript>2</Subscript> Nanoparticles on Barrier and Mechanical Properties of Bovine Gelatin Films

Casting method was used to prepare bovine gelatin based bio-nanocomposite films with halloysite nanoclay and nano-SiO₂ as the reinforcing materials. The composition included gelatin with 20% (w/w) of glycerol (as plasticizer) compounded with halloysite nanoclay and nano-SiO₂ (0%, 2%, 3%, 4%, 5% w/w), respectively. Both types of nanocomposite films showed better mechanical and water solubility than the pristine gelatin films. On comparison with the control, increase in the nanoparticles content resulted in higher tensile strength (9.19 to 13.39 and 12.22 MPa in nanoclay and nano-SiO₂, respectively) and elastic modulus (1.32 to 2.99 and 3.02 MPa% in nanoclay and nano-SiO₂, respectively) with lower elongation at break (80.80 to 55.72 and 40.31% in nanoclay and nano-SiO₂, respectively) and water solubility (85.99 to 69.67 and 69.59% in nanoclay and nano-SiO₂, respectively). Even though a decrease in water vapor permeability was recorded, it was statistically non-significant (1.94 to 1.50 and 1.73 g mm/m² h kPa in nanoclay and nano-SiO₂, respectively). Studies on the heat sealing and peel seal test, conducted to determine the seal strength of the nanocomposite films, revealed lower seal strength compared to control (739.59 to 304.95 and 397.85 N/m in nanoclay and nano-SiO₂, respectively). Between the two nanomaterials used, halloysite nanoclay showed the best results in terms of mechanical properties. The results obtained support the concept of nanocomposite technology and can be employed to improve the barrier and mechanical properties of bovine gelatin films with high potential to be used for food packaging purposes.     

Effects of gelatin origin,bovine-hide and tuna-skin,on the properties of compound gelatin–chitosan films

With the purpose to improve the physico-chemical performance of plain gelatin and chitosan films, compound gelatin–chitosan films were prepared. The effect of the gelatin origin (commercial bovine-hide gelatin and laboratory-made tuna-skin gelatin) on the physico-chemical properties of films was studied. The dynamic viscoelastic properties (elastic modulus G′, viscous modulus, G″ and phase angle) of the film-forming solutions upon cooling and subsequent heating revealed that the interactions between gelatin and chitosan were stronger in the blends made with tuna-skin gelatin than in the blends made with bovine-hide gelatin. As a result, the fish gelatin–chitosan films were more water resistant (∼18% water solubility for tuna vs 30% for bovine) and more deformable (∼68% breaking deformation for tuna vs 11% for bovine) than the bovine gelatin–chitosan films. The breaking strength of gelatin–chitosan films, whatever the gelatin origin, was higher than that of plain gelatin films. Bovine gelatin–chitosan films showed a significant lower water vapour permeability (WVP) than the corresponding plain films, whereas tuna gelatin–chitosan ones were only significantly less permeable than plain chitosan film. Complex gelatin–chitosan films behaved at room temperature as rubbery semicrystalline materials. In spite of gelatin–chitosan interactions, all the chitosan-containing films exhibited antimicrobial activity against Staphylococcus aureus, a relevant food poisoning. Mixing gelatin and chitosan may be a means to improve the physico-chemical performance of gelatin and chitosan plain films, especially when using fish gelatin, without altering the antimicrobial properties.     

Characterization of edible film fabricated with channel catfish (Ictalurus punctatus) gelatin extract using selected pretreatment methods

ABSTRACT:  Farm-raised catfish are important to the economy of the southeastern states in the United States, and catfish processing produces about 55% of by-products for inexpensive sale. Therefore, the utilization of catfish by-products is of great interest to the catfish industry. The objectives of this research were to determine the optimum pretreatment method to extract catfish gelatin for edible film application, and to characterize physical, mechanical, and barrier properties of edible films fabricated with catfish skin gelatin. Catfish skins obtained from a local plant were treated with 6 selected pretreatment methods. The main extraction was performed with deionized water at 50 °C after pretreatment. The gelatin yield was calculated and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed to characterize molecular weight (MW) profile. Color, tensile strength (TS), elongation, and water barrier property were determined to characterize the fabricated catfish gelatin films. From the results of gelatin yield, color, SDS-PAGE, as well as mechanical and barrier properties of the film, the pretreatment method with 0.25 M NaOH and 0.09 M acetic acid, followed by extraction at 50 °C for 3 h, was determined as the optimum extraction method. The catfish gelatin exhibited higher MW fractions than commercial mammalian gelatin. The catfish gelatin extracts possessed film-forming properties determined by TS, elongation, and water vapor permeability (WVP) comparable to those of commercial mammalian gelatin. The selected formula for catfish gelatin film was determined as 1% gelatin and 20% glycerol, resulting in greatest TS and lowest WVP.     

Correlations between structural,barrier, thermal and mechanical properties of plasticized gelatin films

The aims of this work were to develop gelatin films using glycerol as plasticizer (0–100% based on protein mass) and to establish relationships between glycerol content and structural, barrier, thermal and mechanical film properties. These correlations were established since WVP exhibited a minimum for films containing 20 g glycerol/100 g gelatin, while flexibility increased from 2.2% to 180.9% and T_g shifted from 137.5 to 21.3 °C, for films without glycerol and plasticized films with 80 g glycerol/100 g gelatin, respectively. Furthermore, a satisfactory fit between T_g experimental data and predicted values by Couchman and Karasz's equation was found, with glycerol ranging from 0 to 60 g/100 g gelatin. T_g values correlated inversely with film moisture content, and both mechanical and thermal properties showed a strong dependence since elastic modulus and T_g followed a similar trend. Films exhibited similar X-ray patterns regardless of the glycerol concentration, showing a displacement in the position of the peak located at around 2θ = 8°, which shifted towards lower 2θ values with glycerol content.The abovementioned correlations between film physical properties and glycerol content, would allow to select the optimum conditions to develop, process and manage gelatin films according to specific requirements.Industrial relevanceThe methodology used in this work is of considerable importance for the film development and could be used in industrial applications. The management of film formulations and the function that each component plays could allow to obtain tailormade films. A series of relationships between film properties based on gelatin was found, as well as between these properties and glycerol content of the films. An inflexion point in the behavior and microstructure of these materials was established due to glycerol concentration. The addition of higher quantities of glycerol than that corresponds to the abovementioned point, would not be recommendable since the properties are not modified and moreover, it is not profitable. These results would allow better management of film formulations and an appropriate selection of plasticizer concentration in accordance with the specific requirements of potential users.     

Edible films produced with gelatin and casein cross-linked with transglutaminase

In this study, transglutaminase was used to produce cross-linked casein, gelatin and casein–gelatin blend (100:0, 75:25, 50:50, 25:75 and 0:100) edible films. Cross-linking was investigated by SDS–PAGE. Mechanical and water vapor barrier properties of the films were characterized using ASTM procedures, and the film morphology was evaluated using scanning electron microscopy. The casein–gelatin film showed significant greater elongation values (P < 0.05) with or without transglutaminase treatment, as compared to films made from gelatin or casein alone. Mixtures of casein and gelatin produced a synergistic effect only observed in the film elongation, while no improvement was detected for tensile strength and water vapor barrier properties, except for the casein:gelatin (75:25) formulation with transglutaminase, which showed the lowest water vapor permeability value (5.06 ± 0.31 g mm/m² d kPa). Enzymatic cross-linking also induced a substantial increase in the high molecular weight protein components in the film forming solutions.     

Effects of essential oil on the water binding capacity,physico-mechanical properties,antioxidant and antibacterial activity of gelatin films

Gelatin films were prepared from gelatin solutions (10% w/v) containing Zataria multiflora essential oil (ZMO, 2, 4, 6 and 8% w/w of gelatin). Scanning electron microscopy observations indicate that ZMO droplets were well dispersed in the film matrix. Water solubility, water swelling, water uptake, water vapor permeability, tensile strength, elongation at break and Young's modulus for gelatin films were 27 ± 0.8%, 391 ± 11%, 135 ± 5%, 0.22 ± 0.014 g mm/m² kPa h, 4.4 ± 0.4 MPa, 125 ± 7% and 8.8 ± 0.4 MPa, respectively. Incorporation of ZMO into gelatin films caused a significant decrease in swelling and water uptake and increase in solubility and water vapor permeability, a significant decrease in tensile strength, increase in elongation at break, decrease in Young's modulus of the films, dose-dependently. Gelatin/ZMO showed UV–visible light absorbance/transmission ranging from 280 to 480 nm with maximum absorbance at 420 nm. Gelatin films exhibited very low antioxidant activity while, gelatin/ZMO films exhibited excellent antioxidant properties. The gelatin/ZMO films also exhibited excellent antibacterial properties against both Gram-positive and Gram-negative bacteria. Our results suggested that the gelatin/ZMO films could be used as an active film due to its excellent antioxidant and antimicrobial properties for food packaging applications.     

Structural Relaxation of Salmon Gelatin Films in the Glassy State

Mechanical relaxation of glassy carbohydrates has been reported extensively in the literature; however, little work is available on protein-based systems. This study deals with the structural relaxation of salmon (Salmo salar) gelatin in the glassy state. Skin gelatin was obtained by an acid–alkaline extraction method. Molecular weight (M _w) was determined by capillary viscometry. Films prepared by casting (7% w/v) were equilibrated to a moisture content of ~18.4% (db). The glass transition temperature (T _g) and enthalpic relaxation were determined by differential scanning calorimetry (DSC). Mechanical properties were assessed using a texture analyzer at constant temperature and moisture content. DSC showed a T _g ~34°C, and the selected storage temperature (T _a ) was 29°C (T _g − T _a = 5°C). The films were aged for 0, 4, 8, 16, and 40 h. Viscometry produced values of M _w ~90.2 kDa. The stress relaxation was modeled by the Kohlrausch–Wlliams–Watts (KWW) equation, reporting an increase in relaxation time (τ ₀) as the ageing time increased (τ ₀ ~6.41E + 03 s for 0 h; τ ₀ ~9.01E + 05 s for 40 h). β parameter was smaller for the aged films, indicating a spread of relaxation times. The derivative of KWW equation (dφ/dt) indicated a more rapid relaxation in a fresh sample compared with aged films. DSC showed an excess in enthalpy (ΔH) on the aged samples due to the non-equilibrium state of the matrix. ΔH increased with ageing time with values of ΔH ~2.42 J/g for the films aged for 40 h. This work demonstrated molecular relaxation process of gelatin in the glassy state, which must be taken into account if this material is used as a structure forming matrix.     

Preparation and characterisation of chicken skin gelatin as an alternative to mammalian gelatin

The aims of this study were to report for the first time, the extraction and physico-chemical properties of chicken skin gelatin compared to bovine gelatin. Extracted chicken skin gelatin 6.67% (w/v) had a higher bloom value (355 ± 1.48 g) than bovine gelatin (259 ± 0.71 g). The dynamic viscoelastic profile of chicken gelatin exhibited higher viscous and elastic modulus values compared to bovine gelatin for a range of concentrations and frequencies. Thermal properties studied by differential scanning calorimetry (DSC) showed that the melting temperature of 6.67%, chicken skin gelatin was significantly greater (p < 0.05) than that of bovine gelatin, indicating lower stability of bovine gelatin compared to chicken skin gelatin. Results obtained in this study showed that Gly (33.70%), Pro (13.42%), H.Pro (12.13%) and Ala (10.08%) were the most dominant amino acids in chicken skin gelatin which contributed to the higher gel strength and stability. Raman spectra of chicken skin and bovine gelatin were similar and displayed typical protein spectra. Chicken gelatin showed strong hydrogen bonding compared to bovine gelatin as the tyrosine doublet ratio (I₈₅₅/I₈₃₀) of chicken gelatin was significantly lower than that of bovine gelatin. Significantly, the alpha helix and β-sheet type structures were higher for chicken skin gelatin compared with bovine gelatin. The average molecular weight of chicken gelatin was 285,000 Da. These findings, obtained for the first time for chicken skin gelatin, show that it has high potential for application as an alternative to commercial gelatin.     

Physical and functional characterization of active fish gelatin films incorporated with lignin

In order to provide gelatin films with antioxidant capacity, two sulphur-free water-insoluble lignin powders (L₁₀₀₀ and L₂₄₀₀) were blended with a commercial fish-skin gelatin from warm water species at a rate of 85% gelatin: 15% lignin (w/w) (G–L₁₀₀₀ and G–L₂₄₀₀), using a mixture of glycerol and sorbitol as plasticizers. The water soluble fractions of G–L₁₀₀₀ and G–L₂₄₀₀ films were 39.38 ± 1.73% and 46.52 ± 1.66% respectively, rendering radical scavenging capacity (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid, ABTS assay)) of 27.82 ± 2.19 and 15.31 ± 0.88 mg vitamin C equivalents/g film, and ferric ion reducing ability (FRAP assay) of 258.97 ± 8.83 and 180.20 ± 5.71 μmol Fe²⁺ equivalents/g film, respectively. Dynamic oscillatory test on film-forming solutions and Attenuated Total Reflectance (ATR)-FTIR spectroscopy study on films revealed strong lignin-induced protein conformational changes, producing a noticeable plasticizing effect on composite films, as deduced from the study of mechanical (traction and puncture tests) and thermal properties (Differential Scanning Calorimetry, DSC). The gelatin films lose their typical transparent and colourless appearance by blending with lignin; however, the resulting composite films gained in light barrier properties, which could be of interest in certain food applications for preventing ultraviolet-induced lipid oxidation. Lignin proved to be an efficient antioxidant at non-cytotoxic concentrations, however, no remarkable antimicrobial capacity was found.     

Gelatins from three cultured freshwater fish skins obtained by liming process

The physico-chemical properties of gelatins from the skins of Red tilapia (Oreochromis nilotica), Walking catfish (Clarias batrachus) and Striped catfish (Pangasius sutchi fowler) obtained through a liming process for 14 days were evaluated. All the gelatins had very mild to undetectable fishy odour and had acceptable colour attributes, which were light yellowish to whitish. The highest gelatin yield (dry basis) was obtained from red tilapia (39.97%) skin and the bloom strength exceeded 300 g. The pH values of the gelatins were in the vicinity of 5.0. The viscosity (cp) was highest in striped catfish, followed by red tilapia and walking catfish. Their melting points were in the vicinity of 26 ± 1 °C. Turbidity was lowest in the red tilapia gelatin. Glycine, proline and alanine were the three highest amino acids found in all the gelatins obtained.     

Physico-mechanical and antimicrobial properties of gelatin film from the skin of unicorn leatherjacket incorporated with essential oils

Gelatin films incorporated with bergamot (BO) and lemongrass oil (LO) at various concentrations as glycerol substitute were prepared and characterised. Incorporation of BO and LO at 5–25% (w/w protein) resulted in the decreases in both tensile strength (TS) and elongation at break (EAB) of the films. Water vapour permeability (WVP) were decreased in LO incorporated films, while it was increased in film added with BO at level higher than 5% (P < 0.05). Film solubility and transparency values decreased, and the films had the lowered light transmission in the visible range when BO and LO were incorporated. Films incorporated with LO showed inhibitory effect in a concentration dependent manner against Escherichia coli, Listeria monocytogenes, Staphylococcus aureus and Salmonella typhimurium, but BO added film inhibited only L. monocytogenes and S. aureus. Films containing both BO and LO did not inhibit Pseudomonas aeruginosa. Significant change of molecular organisation and higher intermolecular interactions among gelatin molecules were found in the film structure as determined by FTIR. Thermo-gravimetric analysis (TGA) demonstrated that films added with BO and LO exhibited enhanced heat stability with higher degradation temperature, compared with control film. Scanning electron microscopic (SEM) images revealed the presence of micro-pores in the essential oil incorporated films, which contributed to physical properties of the resulting films. Thus, gelatin films incorporated with BO and LO can be used as active packaging, but the properties could be modified, depending on essential oil added.     

Molecular and structural characteristics of cod gelatin films modified with EDC and TGase

Cod gelatin films before and after cross-linking of gelatin with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) or transglutaminase (TGase) have been characterized by Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC) analysis. For comparison, a film prepared from unmodified pig gelatin has been also analysed. The difference spectra showed that cod gelatin during the film formation involved first of all water-to-amide hydrogen bonds, and the film from pig gelatin contained water-to-amide, amide-to-amide and water-to-water hydrogen bonds. A higher number of hydrogen bonds in the structure of the film from pig gelatin contributed to much better recovering of the helical structure in this film than in the film from cod gelatin, as the peaks at about 1663 cm^?1 in the amide I band and at about 1537 cm^?1 in the amide II band in the second-derivative spectra revealed. The recovered helical structure, in turn, resulted in a significantly higher melting enthalpy value in the case of the film from the pig gelatin. After modification of cod gelatin with EDC or TGase, the inter-chain cross-linkages formed in the films led to the conformation of gelatin with no indications of helical ordering. An increase of melting temperature of gelatin films by 7 °C on EDC and by 10 °C on the TGase modifications was related to the formation of covalent cross-links, and a decrease of glass temperature by 28 °C and 7 °C on EDC and TGase cross-linking, respectively, demonstrated the plasticizing effect of water.     

Development of a chicken feather protein film containing clove oil and its application in smoked salmon packaging

Chicken feathers, a by-product of the poultry industry, were utilized as a film base material after extraction of chicken feather protein (CFP). Composite films of CFP and gelatin were prepared, and their mechanical properties were investigated. The tensile strength and elongation at break of the CFP/gelatin composite film significantly (p < 0.05) increased as the gelatin content in the film increased. As a cross-linking agent, 0.5% cinnamaldehyde further improved the film's mechanical properties. Incorporation of clove oil into the composite film resulted in strong inhibition zones against Escherichia coli O157:H7 and Listeria monocytogenes compared with the film without clove oil. Packaging smoked salmon with the composite film containing 1.5% clove oil resulted in a decrease in the populations of E. coli O157:H7 and L. monocytogenes by 1.41 and 1.34 log CFU/g, respectively, compared with the control during storage at 4 °C for 12 days. Furthermore, the peroxide value and thiobarbituric acid reactive substances value decreased by 28 and 36%, respectively, in the smoked salmon packaged with the composite film containing 1.5% clove oil compared with the control during storage. These results suggest that a CFP/gelatin composite film with 1.5% clove oil can be used as an active packaging material for smoked salmon.