Effects of partial hydrolysis and plasticizer content on the properties of film from cuttlefish (Sepia pharaonis) skin gelatin

Properties of film from cuttlefish (Sepia pharaonis) ventral skin gelatin with different degree of hydrolysis (DH: 0.40, 0.80 and 1.20%) added with glycerol as plasticizer at various levels (10, 15 and 20%, based on protein) were investigated. Films prepared from gelatin with all DH had the lower tensile strength (TS) and elongation at break (EAB) but higher water vapor permeability (WVP), compared with the control film (without hydrolysis) (p < 0.05). At the same glycerol content, both TS and EAB decreased, while WVP increased (p < 0.05) with increasing %DH. At the same DH, TS generally decreased as glycerol content increased (p < 0.05), however glycerol content had no effect on EAB when gelatins with 0.80 and 1.20% DH were used (p > 0.05). DH and glycerol content had no marked impact on color and the difference in color (ΔE^∗) of resulting films. Electrophoretic study revealed that degradation of gelatin and their corresponding films was more pronounced with increased %DH, resulting in the lower mechanical properties of films. Based on FTIR spectra, with the increasing %DH as well as glycerol content, higher amplitudes for amide-A and amide-B peaks were observed, compared with film from gelatin without hydrolysis (control film) due to the increased –NH₂ group caused by hydrolysis and the lower interaction of –NH₂ group in the presence of higher glycerol. Thermo-gravimetric analysis indicated that film prepared from gelatin with 1.20% DH exhibited the higher heat susceptibility and weight loss in the temperature range of 50–600 °C, compared with control film. Thus, both chain length of gelatin and glycerol content directly affected the properties of cuttlefish skin gelatin films.     

Effects of hydrogen peroxide and Fenton’s reagent on the properties of film from cuttlefish (Sepia pharaonis) skin gelatin

Properties of film from cuttlefish (Sepia pharaonis) ventral skin gelatin without and with partial hydrolysis (1.2% degree of hydrolysis), as influenced by H₂O₂ and Fenton’s reagent at different levels, were investigated. Films treated with H₂O₂ (0.01–0.04 M) and Fenton’s reagent [H₂O₂ (0.01–0.04 M) + FeSO₄ (0.001–0.004 M)] had higher tensile strengths (TS) but similar or lower elongations at break (EAB), compared with the control film (p < 0.05). Slight differences in water vapour permeability (WVP) were observed for all films. Films treated with Fenton’s reagent had a lower L^∗-value but higher a^∗-, b^∗- and ΔE^∗-values, while films treated with H₂O₂ had lower b^∗-values (p < 0.05), than had the control film. Cross-linking was pronounced in films treated with H₂O₂ or Fenton’s reagent and was associated with increased heat stability. Films treated with Fenton’s reagent had the lowest solubility in water (p < 0.05). However, fragmentation more likely took place when Fenton’s reagent (at a higher level) was used. Generally, similar results were noticeable between films from gelatin with and without partial hydrolysis. Thus, H₂O₂ and Fenton’s reagent directly affected the properties of film from cuttlefish skin gelatin, regardless of hydrolysis.     

Effect of heat treatment of film-forming solution on the properties of film from cuttlefish (Sepia pharaonis) skin gelatin

Effects of heat treatment at different temperatures (40–90 °C) of film-forming solution (FFS) containing 3% gelatin from cuttlefish (Sepia pharaonis) ventral skin and 25% glycerol (based on protein) on properties and molecular characteristics of resulting films were investigated. The film prepared from FFS heated at 60 and 70 °C showed the highest tensile strength (TS) with the highest melting transition temperature (T_max) (p < 0.05). Nevertheless, film from FFS heated at 90 °C had the highest elongation at break (EAB) with the highest glass transition temperature (T_g) (p < 0.05). With increasing heating temperatures, water vapor permeability (WVP) of films decreased (p < 0.05), but no differences in L*-value and transparency value were observed (p > 0.05). Based on FTIR spectra, the lower formation of hydrogen bonding was found in film prepared from FFS with heat treatment. Electrophoretic study revealed that degradation of gelatin was more pronounced in FFS and resulting film when heat treatment was conducted at temperature above 70 °C. Thus, heat treatment of FFS directly affected the properties of resulting films.     

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.     

Extraction and functional properties of gelatin from the skin of cuttlefish (Sepia officinalis) using smooth hound crude acid protease-aided process

The characteristics and functional properties of gelatin from skin cuttlefish (Sepia officinalis) were investigated and compared to those of halal bovine gelatin (HBG). The gelatin extraction efficiency was improved by an acid-swelling process in the presence of smooth hound crude acid protease extract (SHCAP). The yields of gelatins from cuttlefish skin after 48 h with acid and with crude acid protease (15 units/g alkaline-treated skin) were 2.21% and 7.84%, respectively. The gelatin from skin cuttlefish had high protein (91.35%) but low fat (0.28%) contents. Compared to HBG, the cuttlefish-skin gelatin (CSG) has different amino acids composition than halal bovine gelatin. CSG contained slightly low hydroxyproline and proline (180‰) than HBG (219‰), whereas the content of serine was higher (49‰ versus 29‰). The gel strength of the gelatin gel from CSG (181 g) was lower than that of HBG (259 g) (p < 0.05) possibly due to lower hydroxyproline content. Cuttlefish-skin gelatin exhibited a similar emulsifying activity but greater emulsifying and foam stability than the halal bovine gelatin (p < 0.05). Foam formation ability, foam stability and water-holding capacity of CSG were slightly lower than those of the HBG, but fat-binding capacity was higher in the cuttlefish gelatin.     

Yellow discoloration of the liposome system of cuttlefish (Sepia pharaonis) as influenced by lipid oxidation

Lipid oxidation, discoloration, loss of amine groups and pyrrolization of the liposome systems of cuttlefish (Sepia pharaonis) in the presence of FeCl₃ and ascorbic acid were studied. Thiobarbituric acid-reactive substances (TBARS) and the b^∗-value of cuttlefish liposomes increased with a coincidental decrease in amine groups when the incubation temperatures (0, 4, 25, and 37 °C) and incubation times (0–24 h) were increased (p < 0.05). As lipid oxidation and yellow pigment formation in the cuttlefish liposome proceeded, a loss of amine groups and pyrrolization were also detected. The effects of FeCl₃ and ascorbic acid, at different concentrations, on TBARS production, b^∗-value, loss of amine groups and pyrrolization of cuttlefish liposome were also investigated. Both FeCl₃ and ascorbic acid showed prooxidative effects in cuttlefish liposome in a concentration-dependent manner. Sodium chloride (0–2%) reduced TBARS, b^∗-values and pyrrole compounds. These results suggest a positive correlation between lipid oxidation and the development of yellow pigments in cuttlefish phospholipids.     

The effect of antioxidants on the quality changes of cuttlefish (Sepia pharaonis) muscle during frozen storage

The changes in quality of cuttlefish (Sepia pharaonis) treated with 5% NaCl and 0.3% H₂O₂ and soaked with and without different antioxidants during frozen storage at -18 °C for 16 weeks were investigated. Thiobarbituric acid reactive substances (TBARS) in all cuttlefish samples increased when the storage time increased (P<0.05). Ascorbate (ASC) and erythorbate (ERT) showed a prooxidative effect while EDTA and tripolyphosphate (TPP) had no antioxidative effect in frozen cuttlefish. Soaking the cuttlefish in 5% NaCl and 0.3% H₂O₂ for 15 min could improve the color of cuttlefish by increasing the L^*-value and decreasing the a^*-value. ASC, ERT, EDTA and TPP solutions had no impact on the a^*-value and L^*-value of cuttlefish during frozen storage. However, the treated samples, which were soaked in ASC and ERT solutions had an increased b^*-value during frozen storage. Surface hydrophobicity (S₀ANS) of cuttlefish natural actomyosin increased when the frozen storage period increased up to 12 weeks. The increase in disulfide bond content was generally coincidental with the decrease in sulfhydryl content. ASC, ERT, EDTA and TPP had no significant effect on those changes. Protein solubility decreased slightly during prolonged storage. Soaking cuttlefish with 5% NaCl and 0.3% H₂O₂ together with 0.5% TPP could retard the decreases in solubility and increase in thaw drip of frozen cuttlefish. However, ASC, ERT and EDTA showed no impact on the solubility and thaw drip of frozen cuttlefish.     

Properties and antioxidant activity of fish skin gelatin film incorporated with citrus essential oils

Properties of protein-based film from fish skin gelatin incorporated with different citrus essential oils, including bergamot, kaffir lime, lemon and lime (50% based on protein) in the presence of 20% and 30% glycerol were investigated. Films containing 20% glycerol had higher tensile strength (TS) but lower elongation at break (EAB), compared with those prepared with 30% glycerol, regardless of essential oils incorporated (p < 0.05). Films incorporated with essential oils, especially from lime, at both glycerol levels showed the lower TS but higher EAB than the control films (without incorporated essential oil) (p < 0.05). Water vapour permeability (WVP) of films containing essential oils was lower than that of control films for both glycerol levels (p < 0.05). Films with essential oils had varying ΔE^* (total colour difference), where the highest value was observed in that added with bergamot essential oil (p < 0.05). Higher glycerol content increased EAB and WVP but decreased TS of films. Fourier transforms infrared (FTIR) spectra indicated that films added with essential oils exhibited higher hydrophobicity with higher amplitude at wavenumber of 2874–2926 cm⁻¹ and 1731–1742 cm⁻¹ than control film. Film incorporated with essential oils exhibited slightly lower thermal degradation resistance, compared to the control film. Varying effect of essential oil on thermal degradation temperature and weight loss was noticeable, but all films prepared using 20% glycerol had higher thermal degradation temperature with lower weight loss, compared with those containing 30% glycerol. Films added with all types of essential oils had rough cross-section, compared with control films, irrespective of glycerol levels. However, smooth surface was observed in all film samples. Film incorporated with lemon essential oil showed the highest ABTS radical scavenging activity and ferric reducing antioxidant power (FRAP) (p < 0.05), while the other films had lower activity. Thus, the incorporation of different essential oils and glycerol levels directly affected the properties of gelatin-based film from fish skin.     

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.     

Physico-chemical properties,morphology and antioxidant activity of film from fish skin gelatin incorporated with root essential oils

The influences of three root essential oils (ginger, turmeric and plai) at different levels (25%, 50% and 100%, based on protein content) on properties and antioxidative activity of fish skin gelatin-based film were investigated. Films incorporated with all essential oils showed the lower tensile strength (TS) but higher elongation at break (EAB) with increasing amount of essential oils, compared with the control film (without oil incorporated), regardless of types of essential oil (p < 0.05). Water vapor permeability (WVP) of films containing essential oils decreased as the amount of essential oils increased (p < 0.05). Decreases in L^*-value and increases in b^*-, ΔE^*- and transparency value were observed with increasing amount of essential oils incorporated (p < 0.05). FTIR spectra indicated that films added with essential oils, especially from plai root, exhibited higher hydrophobicity than the control film, as evidenced by higher amplitude at wavenunber of 2877–2922 cm⁻¹ and 1732 cm⁻¹. Lower degradation temperature was obtained in films containing essential oils. Microstructural study revealed that bilayer films could be formed when essential oils at level above 50% were incorporated. Film incorporated with plai and turmeric essential oils showed the higher DPPH and ABTS radical scavenging activity, respectively, (p < 0.05), compared with the control film and ginger essential oil added film. Thus, the incorporation of root essential oils directly affected properties of fish skin gelatin-based film, depending on types and levels incorporated.     

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.     

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.     

Manufacture and characterization of gelatin films derived from beef,pork and fish sources using twin screw extrusion

Gelatin films derived from beef, pork and fish sources were manufactured by twin-screw, co-rotating extrusion. The effect of extrusion processing parameters, namely; screw speed (100–400 rpm) and temperature (90, 90, 90, 90 °C and 90, 120, 90, 90 °C) on the mechanical and barrier properties of gelatin films were studied. Increasing screw speed up to 300 rpm improved (P < 0.05) tensile strength (TS) and reduced (non-significantly) water vapour permeability (WVP) values for all manufactured gelatin films. However, the WVP of various gelatin film types was reduced (P < 0.05) when a screw speed of 400 rpm was employed. Increasing the speed of extrusion promoted (P < 0.05) increased solubility of films in water. Manufacture of films using a higher temperature profile resulted in films possessing higher puncture strengths (PS), increased water barrier properties with higher water solubility.     

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.     

Properties and antimicrobial activity of edible films incorporated with kiam wood (Cotyleobium lanceotatum) extract

The antimicrobial properties of wood extracts are well known; however their application to edible films is limited. In this study, the minimum bactericidal concentration (MBC) of kiam wood extract was established as 300 mg/L at which bacterial growth was completely inhibited. The antimicrobial properties of hydroxypropyl methylcellulose (HPMC) films containing 1-5 fold of MBC of kiam wood extract were tested against Escherichia coli O175:H7, Staphylococcus aureus and Listeria monocytogenes. The edible films containing kiam wood extract exhibited more effective impact on the growth reduction of L. monocytogenes than S. aureus and E. coli (p < 0.05). The use of kiam wood extract at 1 and 2 fold of MBC incorporated into edible HPMC films did not exhibit any antimicrobial activity. However, the inhibitory effect of edible HPMC films containing kiam wood extract was observed at 3, 4 and 5 fold of MBC. The greatest zone of inhibition was observed at 5 fold of MBC incorporated in edible HPMC films. Tensile strength and elongation at break significantly decreased with the incorporation of kiam wood extract, whereas water vapor permeability and film solubility increased. The color of edible films became darker and more reddish-yellowish as well as having a lower transparency as the level of kiam wood extract was increased. Kiam wood extract incorporated in edible film provided the films with a rougher surface than pure edible film. Our results pointed out that the incorporation of kiam wood extract as a natural antibacterial agent has potential for use in extending the shelf life of food products.     

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.     

Seasonal changes of fatty acids of cuttlefish Sepia officinalis L. (Mollusca: Cephalopoda) in the north eastern Mediterranean sea

The total lipids and seasonal variations in the fatty acids of the mantle of cuttlefish (Sepia officinalis) captured in the north eastern Mediterranean were investigated and the mantle was found to be a good source of polyunsaturated fatty acids (ω3 PUFAs, in particular). In all seasons, the major fatty acids in the cuttlefish mantle were observed to be palmitic acid (16:0), stearic acid (18:0), eicosapentaenoic acid (EPA, 20:5ω3) and docosahexaenoic acid (DHA, 22:6ω3). A comparison of the saturated fatty acid (29.5–36.8%), monounsaturated fatty acids (7.81–9.84%) and polyunsaturated fatty acids (43.7–49.6%) of the cuttlefish mantle revealed that polyunsaturated fatty acids (PUFA) constituted the highest proportion. The levels of DHA in the cuttlefish mantle in autumn, winter, spring and summer were 27.6%, 28.5%, 29.5% and 23.9%, while those of EPA were 16.8%, 15.4%, 14.7% and 13.9%, respectively.     

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.     

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.     

Assessment of European cuttlefish (Sepia officinalis, L.) nutritional value and freshness under ice storage using a developed Quality Index Method (QIM) and biochemical methods

The aim of this study was to determine the nutritional value of adult commercial cuttlefish, to develop a Quality Index Method (QIM) scheme, and to evaluate the application of some biochemical methods commonly used for freshness assessment of fish under ice storage. Additionally, shelf-life was to be determined based on both QIM and suitable biochemical methods. The nutritional value of the cuttlefish mantle in the first 24 h and after 13 days was determined. Captured cuttlefish was composed (g/100 g) by 16.60 ± 0.10 g protein, 0.09 ± 0.01 g fat, 79.55 ± 0.14 g moisture and 1.39 ± 0.03 g of ash. After 13 days of ice storage, cuttlefish was composed (g/100 g) of 11.90 ± 0.28 g protein, 0.17 ± 0.09 g fat, 87.04 ± 0.13 g moisture and 0.52 ± 0.01 g of ash. Differences (p < 0.001) were found in protein, ash and moisture but not in fat (p > 0.05). These results seem to indicate that there is impregnation of the iced water into the mantle tissue promoting protein leaching with the melting ice. TVB-N and TMA-N displayed a similar increasing tendency, peaking beyond EEC regulations proposed maximum between the 9th and 10th days. The developed QIM scheme for cuttlefish was composed of 29 demerit points, divided into 4 attributes and 13 parameters. The calculated quality index (QI) evolved linearly with storage time in ice (QI = 2.68 × days in ice − 0.61, R² = 0.9866). Storage time could be estimated with an accuracy of ± 1 day, if five cuttlefish from each sample were included in the QIM assessment. The shelf-life was determined as 8 ± 1 days by both type of methods (QIM and biochemical). However, the suitability of some biochemical methods to assess freshness need to be more thoroughly researched.