Mechanical and structural properties of rabbit skin gelatin films

In this article, the characteristics and structure of rabbit skin gelatin (RG) films were measured and compared with porcine skin gelatin (PG) films. The RG film was 8–10 μm thinner than that of PG film. RG films had better resistance to water and lower water solubility than did the PG film with the same gelatin and glycerol ratio due to the difference in their amino acid composition. The two types of gelatin films were almost transparent, which could give food a good appearance quality if these are used as packaging films. Both showed excellent barrier properties against UV light and could prevent the lipid oxidation reaction induced by ultraviolet light in the food system. The RG and PG films showed similar trends in mechanical properties as the change of their components. In general, the rigidity of the RG films was slightly lower than that of the PG films, but the flexibility was more prominent. This was due to intense interaction between gelatin molecules and glycerol molecules in RG films, but the dominant interaction was between the gelatin molecules in the PG films. The surfaces and cross-section microstructures of the RG and PG films were smooth and homogeneous, however for the RG films were more compact compared with the PG films.     

Gelation, oxygen permeability, and mechanical properties of mammalian and fish gelatin films

The objective of this study was to evaluate the gelation, thermal, mechanical, and oxygen permeability properties of different mammalian, warm- and cold-water fish gelatin solutions and films. Mammalian gelatin solutions had the highest gel set temperatures, followed by warm-water fish and then cold-water fish gelatin solutions. These differences were related to concentrations of imino acids present in each gelatin, with mammalian gelatin having the highest and cold-water fish gelatin having the lowest concentrations. Mammalian and warm-water fish gelatin films contained helical structures, whereas cold-water fish gelatin films were amorphous. This was due to the films being dried at room temperature (23 °C), which was below or near the gelation temperatures of mammalian and warm-water fish gelatin solutions and well above the gelation temperature of cold-water fish gelatin solutions. Tensile strength, percent elongation, and puncture deformation were highest in mammalian gelatin films, followed by warm-water fish gelatin film and then by cold-water fish gelatin films. Oxygen permeability values of cold-water fish gelatin films were significantly lower than those for mammalian gelatin films. These differences were most likely due to higher moisture sorption in mammalian gelatin films, leading to higher oxygen diffusivity.     

明胶添加量对兔皮明胶膜特性与结构的影响

从兔皮中提取明胶制备明胶膜,通过测定不同明胶添加量下膜的机械性能、水蒸气透过率、亚基组成和结构,探究明胶添加量对明胶膜特性与结构的影响。结果表明随着明胶添加量的增加,明胶膜体系内网络空间结构变大,从而膜的厚度增加。力学结果显示,明胶添加量为4 g/100 m L（w/v）时,明胶膜抗拉强度最高（p<0.05）;明胶添加量为6 g/100 m L（w/v）时,明胶膜断裂伸长率最低（p<0.05）。水蒸气透过率结果表明随着明胶添加量的增加,水蒸气透过率呈现上升趋势。凝胶电泳结果显示,明胶添加量为4 g/100 m L（w/v）时,低分子量的蛋白组分产生更多交联,形成蛋白质-蛋白质交联的结构,此浓度下明胶膜的抗拉强度最大。FT-IR分析表明:当明胶添加量增加至4 g/100 m L（w/v）时,酰胺A带向高波数移动,说明肽链上的N-H基团并没有与甘油的-OH基团相互反应,而是明胶分子的官能团之间产生更强的相互作用,形成独特的网络结构。同时,酰胺Ⅰ带曲线拟合结果也表明当明胶添加量为4 g/100 m L时,膜内稳定结构较多,明胶分子之间的相互反应达到最大化,明胶膜的稳定性和成膜性能较优。      

Effects of various plasticizers on mechanical and water vapor barrier properties of gelatin films

Different kinds of plasticizers were chosen to study the effects of plasticizer composition, size and shape on the mechanical properties and water vapor permeability (WVP) of gelatin films in this paper. Firstly, oligosaccharides – sucrose, and some organic acids such as oleic acid, citric acid, tartaric acid, malic acid (MA) were added to gelatin. It was found that only MA could improve the ductility of gelatin film, and the visual appearance of MA modified gelatin film was better. Secondly, polyethylene glycols (PEG) with different molecular weights (300, 400, 600, 800, 1500, 4000, 10?000, 20?000) were used to plasticize gelatin films. This showed that PEG of lower molecular weights exhibited better plasticizing effect for gelatin films, and such films had better visual properties. This shows that mannitol (Man) and sorbitol (Sor) could make gelatin films flexible, whereas Man could crystallize from gelatin film. Following this, the plasticization of ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG) series and ethanolamine (EA), diethanolamine (DEA), triethanolamine (TEA) series was studied. At last, suitable plasticizers (MA, PEG300, sorbitol, EG, DEG, TEG, EA, DEA, TEA) for gelatin were selected to investigate the WVP and water content of these plasticized gelatin films. The mechanical properties of these films were also compared.     

草鱼皮明胶-可得然胶共混体系流变特性及作用机理的研究

为探讨可得然胶与草鱼皮明胶之间的相互作用,以草鱼皮明胶为原料,加入不同浓度的可得然胶,研究鱼皮明胶-可得然胶共混体系的粒径、流变学特性以及FTIR的影响。结果表明,共混体系的粒径随可得然胶浓度的增加而增大,当可得然胶浓度为0.5%时,粒径达到1203.8 nm,约为明胶分子的4倍;动态流变学表明,共混体系具有更高的储能模量G’和损耗模量G″,表现出较优越的黏弹特性,而且在低频率区域,可得然胶浓度对体系的粘性影响较大,在高频率区域对弹性影响较大;红外光谱扫描结果证实可得然胶与明胶发生相互作用。总之,添加可得然胶提高草鱼皮明胶的稳定性,对鱼皮明胶的广泛应用具有一定的价值。      

Physical properties and internal microstructures of films made from catfish skin gelatin and triacetin mixtures

Gelatin from catfish skin was obtained by thermal extraction. Triacetin was added to the gelatin at 0, 50, 100, and 150% of the gelatin content to improve the hydrophobic properties of the resulting films. Tween 80 (10% of triacetin amount) was also added as an emulsifier. Internal microstructures of the films were examined using a transmission X-ray microscope (TXM). Other film properties, such as thickness, mechanical properties, water vapor permeability, water solubility, light transparency, and thermal properties were also evaluated. Possible relationships between the internal microstructures and the film properties were hypothesized. The triacetin distribution changed from homogeneous to heterogeneous with its increased content in the films. The addition of triacetin resulted in decreased tensile strength (TS) and increased percent elongation (%E), water solubility, UV and visible light barrier properties, and protein denaturation temperature of the films. Water vapor permeability of the films increased in some treatments (100% and 150% triacetin) possibly due to the heterogeneous distribution of the triacetin and also the increased Tween 80 amount in the films.     

Rheological properties of gelatin from silver carp skin compared to commercially available gelatins from different sources

Gelatin is used as a functional ingredient in many foods, pharmaceuticals, and cosmetics as a stabilizing, thickening, and gelling agent. The rheological properties of gelatins are important in the potential functionality of gelatin. This study is designed to determine the rheological properties of gelatin extracted from the skins of silver carp (Hypophthalmichthys molitrix Valenciennes 1844). The extracted gelatin is compared with commercially available gelatins from different sources. The results indicate that the stress-strain relationship of gelatin gels remained in the linear region over a broad range of strains and stresses and gave similar elastic moduli at varying frequency, stress, and strain levels. One exception was a commercial high molecular weight fish skin gelatin that gave a lower elastic modulus indicating that its gel strength was low compared to the other gelatin samples studied. Gel strength varied between 220 and 1230 g while viscosity varied between 4.53 and 6.91 cP among the samples. Melting and gelling temperatures varied between 14.2 and 32.3 °C and 3.2 and 25.4 °C, respectively. Texture profile analysis was done at 2 deformation levels, 25% and 75%, and the results correlated well with gel strength. The correlations between hardness, cohesiveness, and gumminess and gel strength were 0.98, 0.82, and 0.99, respectively, at 25% deformation but lower at 75% deformation. The results suggest that rheological measurements might be used to quickly estimate gel strength using less material. In addition, the silver carp skin gelatin seemed to be of equal quality to some of the commercial gelatins.     

Rheological and physico‐chemical properties of gelatin extracted from the skin of a few species of freshwater carp

The physico‐chemical and rheological properties of gelatin from the skins of three different freshwater carp species, namely Catla catla, (catla) Cirrhinus mrigala (mrigal) and Labeo rohita (rohu), have been assessed and compared with that of gelatin from porcine skin. The average solids yield from the three species of carp varied in the range of 11.8–14.1%. The amino acid profile showed that the porcine gelatin had a higher proportion of imino acids and glycine than carp skins gelatin. The average molecular weight of carp skins gelatin as determined using a gel filtration technique was 233 kDa, while that of porcine skin gelatin was 282 kDa. The gelling temperature of carp skins gelatin was in the range of 6–15.7 °C, and the melting temperature was 17.9–23.7 °C as determined using a controlled stress rheometer. A higher gelling and melting temperature was observed for porcine skin gelatin.     

白鲢鱼皮明胶的脱脂方法及其脱脂前后理化特性的研究

为了探究白鲢鱼皮是水产明胶的良好来源,得到低脂肪含量的白鲢鱼皮明胶,本实验研究了白鲢鱼皮的基本成分,白鲢鱼皮明胶的脱脂方法,并对其脱脂前后的理化特性进行对比。通过国标等方法对白鲢鱼皮进行基本成分分析,采用热水提取法制备白鲢鱼皮明胶并添加四种不同型号大孔树脂（D101、X-5、XAD1180、AB-8）以静态吸附的方式对明胶溶液进行脱脂处理。结果表明:白鲢鱼皮富含蛋白质、矿物质元素等,可作为水产明胶的良好来源;经D101型树脂在40℃、树脂添加量为10%的条件下处理的明胶溶液,脱脂效果最佳,脱脂率达到78.94%±2.98%;羟脯氨酸含量由6.77%±0.09%上升到7.17%±0.13%;脱脂前后明胶的紫外光谱均在221 nm处出现最大吸收峰;SDS-PAGE电泳图谱均主要由β,α₁,α₂三条肽链组成;红外光谱图的趋势基本相同,均具有胶原的典型官能团;脱脂后明胶的凝胶强度较脱脂前略有降低;脱脂后的明胶粘度较脱脂前有所增大;脱脂后的明胶中Ca、Mg、Zn含量较脱脂前分别增加了75.96%、284.13%和2.68%,但Cu、Fe、Mn含量较脱脂前分别降低了16.67%、48.11%和15.56%。      

鱼皮质量分数对热水浸提明胶的性质及其成膜性能的影响

以罗非鱼皮为原料,考察了热水浸提液中鱼皮质量分数对明胶性质及其成膜性能的影响。结果发现,随着鱼皮质量分数的提高,明胶的黏度和凝胶强度都呈现先上升后下降的趋势。当利用明胶制备成蛋白膜时,膜的机械性能也呈现相同的变化趋势。当热水浸提液中的鱼皮质量分数为10.0%时,提取的明胶其凝胶强度为281g,制备的明胶蛋白膜其抗拉伸强度为60MPa。然而,明胶的氨基酸组成和蛋白组分都没有发现明显的差异。根据差示扫描量热分析和圆二色谱分析的结果,表明利用鱼皮质量分数为10.0%浸提时,提取的明胶其无规则卷曲程度相对较小,结果形成的明胶蛋白膜的热稳定性最高。      

Physical and chemical properties of tuna-skin and bovine-hide gelatin films with added aqueous oregano and rosemary extracts

The properties of edible, gelatin-based films with added oregano or rosemary extract (two different concentrations) were studied. Gelatins from different sources (bovine-hides and tuna-skins) were employed with a view to elucidating how inherent gelatin characteristics may affect interaction of the gelatin with the polyphenols in the added extract and hence the properties of the resulting films. The bovine-hide gelatin reacted only slightly with the polyphenols in the extracts as shown by the electrophoretic profile and analysis of the dynamic viscoelastic properties, and consequently the attributes (mechanical properties, water solubility, water vapour permeability) of the films were practically unchanged compared with the film made without any added plant extract. The tuna-skin gelatin did evidence some interactions with the polyphenols in both the oregano and the rosemary extracts, especially for the more concentrated of the two extracts tested, thereby altering the attributes of the corresponding films, namely, a higher glass transition temperature, decreased deformability, and, in particular, increased water solubility. Opacity increased irrespective of gelatin origin and plant extract type and 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.     

pH和双醛淀粉对罗非鱼鱼皮明胶膜性质的影响

考察了pH和双醛淀粉（DAS）对鱼皮明胶膜的机械性能和耐水性能的影响。结果表明,随着pH的升高,明胶膜的抗拉伸强度（TS）呈现先增加后降低的趋势,pH7时达到最大值（23.78MPa）,而膜的固形物溶解率（MS）和蛋白溶解率（PS）逐渐下降。当明胶膜添加了DAS后,膜的TS显著增大（p<0.05）,而MS和PS都显著下降（p<0.05）。另一方面,在pH7下,添加1.5%的DAS可有效提高膜的机械性能和耐水性能。SDS-PAGE分析结果表明,在成膜过程中pH对明胶蛋白组分没有产生明显的影响,DAS与明胶蛋白之间发生了交联反应。      

Effects of nanorod-rich ZnO on rheological,sorption isotherm,and physicochemical properties of bovine gelatin films

The effects of nanorod-rich zinc oxide (ZnO–nr) on the flow properties of bovine gelatin solution and on the sorption isotherm, antimicrobial, and physchochemical properties of gelatin films were investigated. ZnO–nr was incorporated into gelatin solutions at different concentrations (0.01, 0.02, 0.03, and 0.05 g/g dried gelatin). The introduction of low ZnO–nr concentrations (0.05 g/g dried gelatin) to gelatin solutions significantly increased the viscosity of the solution from 9 to 11.9 mPa s and decreased the permeability of the films to water vapor from 8.9 × 10⁻¹¹ to 1.78 × 10⁻¹¹ (g m⁻¹ s⁻¹ Pa⁻¹). Solubility in water decreased from 30% to 20%, and monolayer water content of the films decreased from 0.13 to 0.10 (g water/g dried solid), whereas their contact angle increased from 45° to 85° with increasing ZnO–nr concentration from 0 to 0.05 g/g dried gelatin. The ZnO–nr gelatin films had very low UV transmittance and were able to absorb more than 50% of the near-infrared spectra. These films showed excellent antimicrobial activity against Staphylococcus aureus. These properties suggest that ZnO–nr can be potentially used as fillers in gelatin-based films for active packaging materials in the pharmaceutical and food packaging industries.     

Comparison of the properties of multi-composite fish gelatin films with that of mammalian gelatin films

Four types of films viz. gelatin, gelatin–MMT, gelatin–chitosan and gelatin–MMT–chitosan prepared from redsnapper and grouper bone gelatin were compared with the mammalian gelatin films, for their mechanical and barrier properties. Grouper gelatin films had higher tensile strength (TS) and Young’s modulus (YM), but lower elongation at break (EAB) than redsnapper films. Incorporation of MMT and chitosan improved the TS (p < 0.05) of the films. Water solubilities were lower (p < 0.05) in films incorporated with chitosan compared to simple gelatin film. Protein solubilities were lower in gelatin–MMT films, irrespective of the type of solvent used. The water vapour transmission rates (WVTR) of fish and mammalian gelatin films were similar, but addition of MMT had reduced WVTR (p < 0.05). SEM micrographs depicted smoother surface for gelatin–MMT and gelatin–MMT–chitosan films. Thus, composite fish gelatin films made with MMT and chitosan could be the good natural biodegradable films due to their better mechanical and barrier properties.     

Characteristics and functional properties of gelatin from seabass skin as influenced by defatting

Gelatins from nondefatted and defatted seabass skins were characterised and evaluated for their functional properties in comparison with commercial fish skin gelatin. All gelatins contained α₁‐ and α₂‐chains as the predominant components and showed a high imino acid content (199–201 residues/1000 residues). All gelatins had a relative solubility greater than 90% in the wide pH ranges (1–10). Foaming properties of all gelatins increased with increasing concentrations (1–3%, w/v). Gelatin from defatted skin had higher foam expansion and stability than that extracted from nondefatted skin. Emulsion containing gelatin from defatted skin had smaller oil droplet size (d₃₂, d₄₃), compared with that having gelatin from nondefatted skin (P < 0.05). After 10 days of storage at room temperature (28–30 °C), emulsion stabilised by gelatin from defatted skin showed the higher stability as indicated by the lower increases in d₃₂ and d₄₃, and lower flocculation factor and coalescence index. Coincidentally, emulsion stabilised by gelatin from defatted skin had higher zeta potential than that containing gelatin from nondefatted skin. Thus, defatting of seabass skin directly affected characteristics and functional properties of resulting gelatin.     

Evaluation of tilapia skin gelatin as a mammalian gelatin replacer in acid milk gels and low-fat stirred yogurt

Tilapia skin gelatin (TSG) was studied in a 3-stage process (cooling, annealing, and heating) for pure gelatin gels and in a 4-stage process (acidification, cooling, annealing, and heating) for acid milk gels and cultured yogurt. The aim was to evaluate the use of TSG as a replacement for mammalian gelatin in yogurt. In pure TSG gels, stronger gels with higher melting temperatures were formed with increasing TSG concentrations. Compared with bovine gelatin (BG), which gelled at a concentration of 2.5%, TSG gels had lower gelling (14.1°C) and melting (24°C) temperatures but comparable storage moduli during annealing. In acid milk gels, addition of TSG increased the firmness of the gels with increasing concentration. Gelling and melting points of TSG in milk gels were observed at sufficient concentrations during cooling and heating. Strands and sheets were observed in the electron micrographs of milk gels with 1% TSG and a very dense structure was observed with 2.5% TSG. Yogurt with 0.4% TSG had similar viscosity, consistency, pseudoplasticity, and thixotropy as yogurt containing 0.4% BG; no difference was perceived by sensory panelists according to a triangle test. Addition of 0.4% TSG completely prevented whey separation from the acid milk gel and yogurt. The results suggest that TSG could be a suitable replacement for mammalian gelatin in low-fat stirred yogurt.     

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

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

Effect of clay content, homogenization RPM, pH, and ultrasonication on mechanical and barrier properties of fish gelatin/montmorillonite nanocomposite films

The effect of clay content, homogenization RPM, and pH on the mechanical and barrier properties of fish gelatin/nanoclay composite films was investigated. The addition of 5% nanoclay (w/w) increased the tensile strength from 30.31 ± 2.37 MPa to 40.71 ± 3.30 MPa. The 9 g clay/100 g gelatin film exhibited the largest improvements in oxygen and water barrier properties. Oxygen permeability decreased from 402.8 × 10⁻⁶ ± 0.7 × 10⁻⁶ g m/m² day atm to 114.4 × 10⁻⁶ ± 16.2 × 10⁻⁶ g m/m² day atm and the water vapor permeability decreased from 31.2 × 10⁻³ ± 1.6 × 10⁻³ ng m/m² s Pa to 8.1 × 10⁻³ ± 0.1 × 10⁻³ ng m/m² s Pa. The XRD and TEM observation suggested that the ultrasonication treatment (30 min at 40% output) resulted in exfoliation of the silicates.