Mechanical, water vapor barrier and thermal properties of gelatin based edible films

Edible films are thin materials based on a biopolymer. The objectives of this work were to determine the water vapor permeability and the mechanical and thermal properties of edible films based on bovine hide and pigskin gelatins. These films were prepared with 1 g of gelatin/100 ml of water; 15–65 g sorbitol/100 g gelatin; and at natural pH. The samples were conditioned at 58% relative humidity and 22°C for 4 days before testing. The mechanical properties were determined by the puncture test and the water vapor permeability by gravimetric method at 22°C. For DSC analysis, samples were conditioned over silica gel for 3 weeks. Samples (10 mg) were heated at 5°C/min, between −150 and 150°C in a DSC TA 2010. A second scan was run after cell cooling with liquid nitrogen. As expected, the puncture force decreased and the puncture deformation and water vapor permeability increased with the sorbitol content. The origin of gelatin was important only above 25 g sorbitol/100 g gelatin. The DSC traces obtained in the first scan of samples with 15–35 g sorbitol/100 g gelatin, showed a well visible glass transition followed by a sol–gel transition. However, with the increase of sorbitol concentration, the glass transition became broader, typical of the system presenting a phase separation. The model of Couchman and Karazs for ternary system, was used to predict the Tg values as a function of sorbitol concentration.     

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.     

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.     

The effect of sodium chloride on the glass transition of potato and cassava starches at low moisture contents

The effect of NaCl on the glass transition of cassava and potato starches at low water levels (<20% dwb) was investigated. Sodium chloride (up to 6% of the starch dry weight) was mixed thoroughly with cassava and potato starches using a twin-screw extruder. The samples were equilibrated over saturated salt solutions (LiCl, CH₃COOK, MgCl₂, NaBr, CuCl₂ and NaCl) to give a range of moisture contents. The addition of sodium chloride caused a considerable reduction in the DSC measured glass transition temperature for both starches. For example, the T_g of cassava starch without and with 6% NaCl equilibrated at relative humidity of 11% was 166 and 136 °C, respectively. Similar reductions were found for potato starch. Although the starch sorption isotherms are affected by the addition of salt when T_g is plotted against water content as opposed to relative humidity a T_g reduction on salt addition is still observed. The possible reasons for the plasticization of starch by salt are discussed.     

Phase transitions of pigskin gelatin

Edible films are flexible thin materials based on biopolymers. It is therefore necessary to know the physicochemical properties of those macromolecules in order to obtain films with desirable characteristics. Dried gelatin is a partially crystalline polymer that exhibits glass and helix–coil transitions. The knowledge of phase properties is important for the choice of the type and concentration of the plasticizer to be utilized to obtain a flexible and easy-to-handle film. The objective of this work is to determine the phase transitions of pigskin gelatin as a function of moisture content in the hygroscopic domain. Pure gelatin was conditioned over different saturated salt solutions at 25°C to allows samples with various moisture content. After equilibrium was established, the samples and an empty pan, as reference, were heated twice between −100 and 250°C at the rate of 5°C/min, in a DSC (TA 2010) after quench-cooling with liquid nitrogen. Gelatin was placed in a pan with a perforated cover, and maintained at 105°C for 24 h in the DSC cell before thermal analyses, to obtain completely dried samples. The glass transition temperature of these samples was found to be 220.2°C. The DSC traces obtained in the first scan, except those conditioned at 11% relative humidity, showed a glass transition followed by two endothermic peaks due to two sol–gel transitions in the gelatin. The plasticizing effect of moisture on Tg was observed in all the samples conditioned by absorption and in the second scan with the samples conditioned by desorption. This behavior was well represented by the Gordon and Taylor model, with κ=5.26 and R²=0.96. Also, a plasticizing effect of moisture over the sol–gel transitions was observed. The Flory-Huggins model was applied to experimental data with: χ₁=1.94 and R²=0.999, for the first peak Tm, and χ₁=1.90 and R²=0.989, for the second peak.     

Development of fish gelatin edible films using extrusion and compression molding

Fish gelatin was plasticized with 20% and 25% glycerol (w/w of gelatin) and used to develop edible films by twin-screw extrusion at 110 and 120 °C followed by compression molding at 80 °C. Tensile and moisture barrier properties and glass transition temperature were then measured and compared with solution-cast films. The films extruded at 110 °C and with 25% glycerol had the highest percent elongation at break of 293 ± 27%. The water vapor permeability values of extruded films (the highest value being 2.9 ± 0.2 g mm h⁻¹ cm⁻² Pa⁻¹) were higher than those of solution-cast films while the glass transition temperatures (T_g) of the extruded films were generally lower than those of solution-cast films. Films with 25% glycerol that were extruded at 110 °C had the lowest T_g (2.10 ± 0.31 °C). This investigation showed that extrusion processing followed by compression molding is a feasible method to produce fish gelatin films for commercial applications in a wide range of food products.     

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.     

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.     

Characterization of fish gelatin from surimi processing wastes: Thermal analysis and effect of transglutaminase on gel properties

Fish gelatin extraction from wastes of fish Herring species (Tenualosa ilisha) was carried out by a series of pretreatment with 0.2 M Ca(OH)₂ followed by 0.1 M citric acid and final water extraction at 50 °C for 3 h. The resulting fish gelatin preparation was evaluated for its dynamic viscoelastic properties, gelling and melting temperatures and gel strength. The gelling and melting temperatures of gelatin samples (at 6.67%, w/v) were obtained from differential scanning calorimetry and rheological studies. The melting temperature of extracted fish gelatin (EFG) obtained ranged from 16.2 to 16.7 °C compared to that of commercial fish gelatin gel (CFG), from 23.7 to 25.6 °C and halal bovine gelatin (HBG), from 26.5 to 28.7 °C. On the other hand, gelling temperatures of EFG, CFG and HBG ranged from 5.1 to 5.2 °C, 11.9 to 17.46 °C, and 12.6 to 19.33 °C, respectively. EFG gave gels with a considerably lower G′ values than CFG and HBG. The bloom strength of EFG gels at 6.67% (w/v) was 69.03 g which was much lower than HBG (336.2 g) and CFG (435.9 g). Enzyme transglutaminase was added in the amounts of 0.5, 1.0, 3.0 and 5.0 mg/g gelatin to modify the gel properties of the extracted fish gelatin. The modified EFG gels obtained had higher gel strengths of 101.1 g and 90.56 g with added transglutaminase of 1.0 and 3.0 mg/g, respectively. However with addition of 5.0 mg/g enzyme the gel strength increased only up to 75.06 g. SDS-PAGE of extracted gelatin gel showed protein band intensities for α1-chains and 53 kDa but in gels added with higher concentration of transglutaminase, these protein band intensities seemed to disappear.     

Extraction and characterisation of pepsin-solubilised collagen from the skin of unicorn leatherjacket (Aluterus monocerous)

Pepsin-solubilised collagen (PSC) was extracted from the skin of unicorn leatherjacket (Aluterus monocerous), using 0.5 M acetic acid in the presence of pepsin from albacore tuna, yellowfin tuna or porcine pepsin at a level of 20 units/g of defatted skin. Yields of 8.48 ± 0.3%, 8.40 ± 0.3% and 7.56 ± 0.4% (wet weight basis) were obtained for PSC extracted with the aid of albacore tuna pepsin (APSC), yellowfin tuna pepsin (YPSC) and porcine pepsin (PPSC), respectively. All PSCs were classified as Type I collagen containing two α₁-chains and one α₂-chain with no disulphide bond. The peptide maps of different PSCs hydrolysed by V8 protease and lysyl endopeptidase were different. ATR-FTIR spectra analysis revealed that PSC molecules had the compact triple helical structure stabilised mainly by the hydrogen bond. T_max of all PSCs (31.68–31.98 °C) shifted to lower values (29.33–29.40 °C) when dispersed in 0.05 M acetic acid, indicating the conformational changes in the collagen structure induced by acid. Relative viscosity of 0.03% PSC in 0.1 M acetic acid solution decreased progressively as the temperature increased from 4 to 52 °C, indicating thermal destabilisation or denaturation of PSC molecules. All PSCs were soluble in the pH range of 1–6 and sharply decreased at neutral pH. Decreases in solubility were observed in the presence of NaCl, especially at concentrations above 2% (w/v). Therefore, the skin of unicorn leatherjacket could serve as a potential source of collagen.     

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.     

大目金枪鱼皮明胶的理化性质及结构分析

以大目金枪鱼皮为原料制备明胶,对所得明胶的凝胶强度、胶凝温度、熔化温度、氨基酸组成、十二烷基硫酸钠-聚丙烯酰氨凝胶电泳（sodium dodecyl sulfate-polyacrylamide gel electrophoresis,SDS-PAGE）、光谱学特性等理化性质及结构特性进行研究,并与猪皮明胶进行比较。结果表明,金枪鱼皮明胶的凝胶强度为403?g,胶凝温度和熔化温度分别为21.5?℃和28.8?℃,略低于猪皮明胶;氨基酸分析结果表明,金枪鱼皮明胶中亚氨基酸质量分数为19.09%,低于猪皮明胶的22.82%,可以解释金枪鱼皮明胶凝胶特性、胶凝温度和熔化温度低于猪皮明胶的原因。SDS-PAGE电泳结果显示,金枪鱼皮明胶的小分子组分质量分数仅为6.67%,说明预处理及热水提胶过程并没有破坏明胶中亚基的完整性。金枪鱼皮明胶的紫外光谱与红外光谱谱图均与猪皮明胶相似,进一步说明实验所制得的产物为高质量明胶。     

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.     

Characterization of salmon gelatin based film on antimicrobial properties of chitosan against E. coli

Salmon gelatin and chitosan are high potential biopolymer to obtain edible films with antimicrobial effect for fresh meat. Therefore, it is important to characterize the structural (glassy or rubbery) state of the gelatin film on antimicrobial properties of chitosan. Extracted salmon (Salmo Salar) gelatin (acid-basic extraction) and low molecular weight chitosan solutions (0; 0.25; 0.5 and 1% w/w) at pH 5.5 were prepared to obtain a final concentration to 7% w/w (gelatin + chitosan). Films were obtained by casting at 5 °C and equilibrated at 33% and 85% of relative humidity (RH) in order to obtain a glassy and rubbery state, respectively. Water content, specific volume and glass transition temperature (Tg) were measured and antimicrobial properties against Escherichia coli (E.c.) (105 ufc/ml) were obtained by agar plate diffusion and kinetic measurements at 37 °C. Chitosan diffusion in agar plate was determined using liquid solutions and films over agar plate. The results showed diminution of Tg (maintaining structural state) as increase chitosan concentration, increasing also specific volume and water content due their high capacity to adsorb water. Although inhibition by chitosan of bacteria growth kinetic was 100%, solutions and films samples could not diffuse in the agar. In conclusion, the chitosan could not diffuse on the films matrix and also in agar plate and therefore in food when is combined with salmon gelatin. The implication of this work have been investigate the use of edible films from marine sources with antimicrobial effects in an effort to growing demand from consumers for safer and better quality foods.     

Oxidative stability of gelatin coated pork at refrigerated storage

As consumers are chiefly concerned with odor and appearance, refrigerated meats have a greater possibility of rejection due to their perishability. A treatment was designed to preserve the quality parameters such as color and oxidation rate. The treatment encompassed coating pork loin samples with aqueous porcine gelatin solutions (175 bloom) at three concentrations (0%, 10% and 20%) and studying its effect on lipid oxidation, protein oxidation, oxidation pre-cursors, color and purge of meat. Vacuum packed Longissimus dorsi muscle was cut into 10 × 5 × 1 cm samples and randomly dipped in one of three solutions. Samples were stored at 4 °C and analyzed for thio-barbituric acid reactive substances, metmyoglobin content, protein carbonyls, heme iron content and color change. There was a significant difference (p < 0.05) for TBARS values, protein carbonyls, heme iron content, total color change, metmyoglobin content with treatments maintaining values more similar to a fresher product when compared to control on days 3, 5 and 7. There was no significant difference (p > 0.05) between 10% and 20% gelatin coating on any of the parameters between storage days.     

Determining the critical relative humidity at which the glassy to rubbery transition occurs in polydextrose using an automatic water vapor sorption instrument

Similar to an increase in temperature at constant moisture content, water vapor sorption by an amorphous glassy material at constant temperature causes the material to transition into the rubbery state. However, comparatively little research has investigated the measurement of the critical relative humidity (RHc) at which the glass transition occurs at constant temperature. Thus, the central objective of this study was to investigate the relationship between the glass transition temperature (Tg), determined using thermal methods, and the RHc obtained using an automatic water vapor sorption instrument. Dynamic dewpoint isotherms were obtained for amorphous polydextrose from 15 to 40 °C. RHc was determined using an optimized 2nd-derivative method; however, 2 simpler RHc determination methods were also tested as a secondary objective. No statistical difference was found between the 3 RHc methods. Differential scanning calorimetry (DSC) Tg values were determined using polydextrose equilibrated from 11.3% to 57.6% RH. Both standard DSC and modulated DSC (MDSC) methods were employed, since some of the polydextrose thermograms exhibited a physical aging peak. Thus, a tertiary objective was to compare Tg values obtained using 3 different methods (DSC first scan, DSC rescan, and MDSC), to determine which method(s) yielded the most accurate Tg values. In general, onset and midpoint DSC first scan and MDSC Tg values were similar, whereas onset and midpoint DSC rescan values were different. State diagrams of RHc and experimental temperature and Tg and %RH were compared. These state diagrams, though obtained via very different methods, showed relatively good agreement, confirming our hypothesis that water vapor sorption isotherms can be used to directly detect the glassy to rubbery transition. Practical Application: The food polymer science (FPS) approach, pioneered by Slade and Levine, is being successfully applied in the food industry for understanding, improving, and developing food processes and products. However, despite its extreme usefulness, the Tg, a key element of the FPS approach, remains a challenging parameter to routinely measure in amorphous food materials, especially complex materials. This research demonstrates that RHc values, obtained at constant temperature using an automatic water vapor sorption instrument, can be used to detect the glassy to rubbery transition and are similar to the Tg values obtained at constant %RH, especially considering the very different approaches of these 2 methods--a transition from surface adsorption to bulk absorption (water vapor sorption) versus a step change in the heat capacity (DSC thermal method).     

Effect of two different lipid sources on glass transition temperatures and tensile properties of corn semolina

The effect of adding corn oil (CO) and corn germ (CG) on the thermal and mechanical properties of corn semolina (CS) was investigated. The lipids concentration employed were 2% and 3% of CO or CG. The thermal transitions were studied in a moisture content range of 3–27% (d.b.), by means of dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) techniques. Wide angle X-ray scattering (WAXS) experiments showed that type-V amylose–lipid complexes were formed with the native lipids within the corn semolina during thermo-moulding and that re-crystallization to a type-A structure, favored by the added lipids, occurred upon storage in high relative humidity (RH) environments. Two thermal events were observed during the first DSC scan and tan δ DMTA curves. The first one appearing at around 55–60 °C was attributed to a possible phase separation or ageing phenomenon taking place during storage of the samples, while the second was ascribed to the glass transition temperature of CS. It was found that addition of both, CO and CG, reduced the moisture content required for these transitions to appear. The expected decrease in the glass transition temperatures with moisture content was well described by the Gordon–Taylor equation. The addition of CO and CG also causes plasticization of CS. Hence, corn germ meal can be used as a lipid source that is more convenient to handle than liquid fats. However, the CS T_g values were independent of the lipids content. Tensile properties of CS and CS-lipid systems were found to be influenced by the moisture content, the physical state of the samples, and their composition.     

Indigenous proteases in the skin of unicorn leatherjacket (Alutherus monoceros) and their influence on characteristic and functional properties of gelatin

Indigenous proteases in the skin of unicorn leatherjacket (Alutherus monoceros) were characterised using autolytic study. Maximised autolysis was found at pH 7 and 50 °C. Autolysis was markedly inhibited by 0.04 mM soybean trypsin inhibitor (SBTI), suggesting that heat activated serine protease was predominant in the skin. The impact of indigenous proteases on the properties of gelatin extracted from unicorn leatherjacket skin was investigated. Gelatin was extracted from unicorn leatherjacket skin using distilled water at 50 °C for 12 h in the presence and absence of 0.04 mM SBTI. In the presence of SBTI, the degradation was markedly inhibited, but a lower gelatin extraction yield was obtained (P < 0.05). Extracted gelatins contained α₁ and α₂ chains as the predominant components with some degradation peptides. FTIR spectra indicated a greater loss of molecular order of the triple helix and a higher degradation was found in gelatin extracted in the absence of 0.04 mM SBTI. The net charge of gelatin samples extracted with and without 0.04 mM SBTI became zero at pHs of 8.45 and 7.31, respectively, as determined by ζ-potential titration. Higher gel strength (320.68 ± 3.02 g) was obtained in gelatin extracted with SBTI, compared with that of gelatin extracted without SBTI (288.63 ± 1.44 g). High emulsifying activity index but lower emulsifying stability index was observed in the former. Therefore, heat-activated serine protease was involved in the degradation of gelatin molecules, thereby affecting the yield, proteinaceous components and properties of gelatin from unicorn leatherjacket skin.     

Physical, mechanical, and barrier properties of carp and mammalian skin gelatin films

Films of 0.11 to 0.13 mm thickness were prepared using gelatins from the skins of cultured freshwater carp species and mammalian gelatins viz., porcine and bovine skin gelatin. A comparative study was made on the physical, mechanical, and barrier properties of these films. The amino acid composition, gel strength, clarity, and gel setting point of the gelatins were also determined. Carp skin gelatins had a lower imino acid content (19.16% to 20.86%) than mammalian skin gelatins (22.91% to 23.7%). Grass carp gelatin had gel strength of 230.2 B that is comparable to the reported value for bovine skin gelatin (227.2 B). The bloom values of rohu and common carp skin gelatins were 188.6 B and 181.3 B, respectively, which were significantly lower than mammalian gelatins. Mammalian gels have significantly higher (P < 0.05) setting temperatures (23.7 to 24.2 °C) than carp skin gelatins. Tensile strength (TS) was lowest for films from common carp and rohu skin gelatin (490 and 497 kg/cm(2), respectively) and highest for porcine skin gelatin film. The degree of transparency (L*) was significantly higher for films from grass carp, bovine hide, and pork skin gelatin films. Carp skin gelatin films had significantly lower water vapor permeability (WVP) and oxygen permeability (OP) than mammalian skin gelatin films, which indicated that carp skin gelatin based films have superior barrier properties than mammalian skin gelatin films.     

Mass spectrometric detection of marker peptides in tryptic digests of gelatin: A new method to differentiate between bovine and porcine gelatin

Gelatin is a mixture of polypeptides obtained by hydrolysis of collagen primarily from bovine and porcine skin and bones. The similarity between different gelatins makes it difficult to trace their species origin. In this work, a new method for differentiation between bovine and porcine gelatin was developed based on detection and identification of marker peptides in digested gelatins. Sequence alignment analysis indicates that bovine and porcine Type I collagen contain differential sequences. The gelatins were digested by trypsin, and the resulting peptides were analyzed by high performance liquid chromatography/tandem mass spectrometry (HPLC–MS/MS). The marker peptides specific for bovine and porcine were successfully detected in the digested bovine and porcine gelatin, respectively. Comparative analysis indicated that more marker peptides could be detected in gelatin with a higher mean molecular weight. It was found that proline hydroxylation was a key factor affecting the peptide identification. For peptides such as GPPGSAGSPGK and GPPGSAGAPGK detected in digested bovine and porcine gelatin, respectively, the sequence should be verified manually since the mass shift caused by proline hydroxylation can be confused with the mass difference between Ser and Ala residues. The results indicate that detection of marker peptides in the digested gelatin sample using HPLC–MS/MS is an effective method to differentiate between bovine and porcine gelatin.