Properties of Alaska Pollock Skin Gelatin: A Comparison with Tilapia and Pork Skin Gelatins

ABSTRACT:  The objective of this work was to compare the physiochemical and rheological properties of Alaska pollock skin gelatin (AG) to those obtained for tilapia and pork skin gelatins. Results were also obtained for some mixed gels containing AG and pork skin gelatin, or AG and tilapia gelatin. AG contained about 7% hydroxyproline (Hyp), which was lower than that of tilapia (∼11%) or pork skin gelatin (∼13%). Most of the protein fractions in AG were α chain, β chain, and other oligomers. The gel strength of AG was 98 gram-force at 10 °C, and increased at a greater rate than other gelatins with decreasing temperature. The gel melting point of AG was the lowest with the oil-drop method, while the viscosity of AG was the highest of the samples studied. The rheological properties of gelatins were determined using small amplitude oscillatory shear testing. G' was nearly independent of frequency for most of the gelatin gels, but AG gels showed a slight dependence on G' and a minimum in G". G' was found to be a power law function of concentration for all gelatins used: G'= k × Cⁿ. In rheological measurements, AG also showed the lowest gel melting temperature and sharpest melting region. Increasing gelatin concentration resulted in a higher melting temperature and a broader melting region for all gelatin gels. For both the AG-pork and AG-tilapia mixed gels, the gel melting temperatures decreased and melting regions narrowed as the AG fraction was increased.     

Effects of Concentration,Bloom Degree,and pH on Gelatin Melting and Gelling Temperatures Using Small Amplitude Oscillatory Rheology

Concentration, gel strength (Bloom), and pH effects on both melting and gelling temperatures of gelatin were studied using small amplitude oscillatory rheology. Temperature sweeps were applied to gelatin gel samples for heating and cooling at fixed frequencies. Results showed that melting temperatures were higher than gelling temperatures, and both increased with increasing concentration at pH from 3 to 6 for all gel strength. For constant gelatin concentration and pH, as gel strength increased, melting temperatures decreased, whereas gelling temperatures increased. A mathematical model was obtained which correlates melting and gelling temperatures, respectively, with pH and concentration at fixed Bloom degrees. All gelatin gels showed storage modulus higher (2 to 10 kPa) than loss modulus (50 to 500 Pa).     

Comparison of gelling properties and flow behaviors of microbial transglutaminase (MTGase) and pectin modified fish gelatin

The gelling and structural properties of microbial transglutaminase (MTGase) and pectin modified fish gelatin were compared to investigate their performances on altering fish gelatin properties. Our results showed that within a certain concentration, both MTGase and pectin had positive effects on the gelation point, melting point, gel strength, textural, and swelling properties of fish gelatin. Particularly, low pectin content (0.5%, w/v) could give fish gelatin gels the highest values of gel strength, melting temperature, and hardness. Meantime, flow behavior results showed that both MTGase and pectin could increase fish gelatin viscosity without changing its fluid characteristic, but the latter gave fish gelatin higher viscosity. Both MTGase and pectin could increase the lightness of fish gelatin gels but decreases its transparency. More importantly, fluorescence and UV absorbance spectra, particle size distribution, and confocal microscopy results indicated that MTGase and pectin could change the structure of fish gelatin with the formation of large aggregates. Compared with MTGae modified fish gelatin, pectin could endow fish gelatin had similar gel strength, thermal and textural properties to pig skin gelatin.     

鱼鳞明胶的提胶工艺

根据单因素试验结果,利用正交试验,考察了提胶温度、pH值和时间对鱼鳞明胶品质的影响。并得到提胶条件为:提胶温度为55℃,pH值为6,时间为5h。在该条件下明胶的提取率达到58%,6.67%的明胶溶液在60℃时的黏度为8.16mPa·s,7℃下保温18h后凝胶强度为1 202.65g,约290Bloom,凝胶温度和熔化温度分别为20.8℃,26.9℃,等电点约为pH 7,可达到高品质明胶的要求。     

Improvement of gel strength and melting point of fish gelatin by addition of coenhancers using response surface methodology

Abstract: Fish gelatin is a potential alternative to mammalian gelatin. However, poor gel strength and low melting point limit its applications. The study was aimed at improving these properties by adding coenhancers in the range obtained from response surface methodology (RSM) by using Box–Behnken design. Three different coenhancers, MgSO₄, sucrose, and transglutaminase were used as the independent variables for improving the gel strength and melting point of gelatin extracted from Tiger‐toothed croaker (Otolithes ruber). Addition of coenhancers at different combinations resulted gel strength and melting point in the range of 150.5 to 240.5 g and 19.5 to 22.5 °C, respectively. The optimal concentrations of coenhancers for predicted maximum gel strength (242.8 g) obtained by RSM were 0.23 M MgSO₄, 12.60% sucrose (w/v), and 5.92 mg/g transglutaminase and for predicted maximum melting point (22.57 °C), the values were 0.24M MgSO₄, 10.44% sucrose (w/v), and 5.72 mg/g transglutaminase. By addition of coenhancers at these optimal concentrations in verification experiments, the gel strength and melting point were improved from 170 to 240.89 g and 20.3 to 22.7 °C, respectively. These experimental values agreed well with the predicted values demonstrating the fitness of the models. Results from the present study clearly revealed that the addition of coenhancers at a particular combination can improve the gel strength and melting point of fish gelatin to enhance its range of applications. Practical Application: There is a growing interest in the use of fish gelatin as an alternative to mammalian gelatin. However, poor gel strength and low melting point of fish gelatin have limited its commercial applications. The gel strength and melting point of fish gelatin can be increased by incorporation of coenhancers such as magnesium sulphate, sucrose, and transglutaminase. Results of this work help to produce the fish gelatin suitable for wide range of applications in the food industry.     

微波-快速冻融耦合鱼皮明胶理化性质分析

本实验采用微波-快速冻融耦合处理鱼皮获得鱼皮明胶，并通过等电点、透射比、凝冻强度测定以及十二烷基硫酸钠-聚丙烯酰胺凝胶电泳、流变学特性、氨基酸组成和傅里叶变换红外光谱分析对鱼皮明胶的理化性质进行表征。结果表明：与市场上的A型和B型明胶不同，微波-快速冻融耦合鱼皮明胶等电点为7，在450 nm波长处透射比为57.13%，在620 nm波长处透射比为78.07%，凝冻强度为524.40 Bloom g，满足GB 6783—2013《食品安全国家标准 食品添加剂 明胶》要求（在450 nm波长处透射比不低于30%，620 nm波长处透射比不低于50%，凝冻强度不低于50 Bloom g）。与传统酸法鱼皮明胶相比，微波-快速冻融耦合明胶氢键含量更高，三螺旋结构较为完整，亚氨基酸比例相近；但由于高分子亚基比例低，导致凝胶特性总体不及传统明胶。总体而言，微波-快速冻融耦合鱼皮明胶符合国标要求，该方法是明胶绿色清洁制备的良好探索。     

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

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

RHEOLOGICAL PROPERTIES OF MIXED GELS

The rheological properties of carrageenan/gelatin and agar/gelatin mixed gels were investigated by measuring the rupture properties, the texture parameters and the dynamic viscoelasticities. fie melting point, transparency and syneresis of these gels were measured in order to obtain the relationship with the rheological properties. The physical properties of the two mixed gels were slightly different. The agar/gelatin mixed gels generally showed the hindered effect of gelatin. The brittleness of agar gel disappeared on mixing with gelatin. It then became a flexible, cohesive and transparent gel. Carrageenan/gelatin mixed gels showed a decrease in the values of almost all of the mechanical properties when compared with carrageenan gels. However, the rupture properties of the C0.5 mixed gel were much higher than those of simple carrageenan gels.     

Characterizations of fish gelatin films added with gellan and κ-carrageenan

Fish gelatin is known to be inferior to mammalian gelatins. Gellan and κ-carrageenan were added to improve properties of the fish gelatin films. Initially, polysaccharides were added to make fish gelatin gels, and tested for the melting point. Mechanical, barrier, color and microstructure properties, as well as Fourier transform infrared (FTIR) and thermal analysis (DSC) of the modified fish gelatin films were evaluated. The addition of gellan and κ-carrageenan increased the melting point of fish gelatin gels, gellan being more effective. Polysaccharides modified fish gelatin films by increasing tensile strength and barrier against water vapor, but made films slightly darker. Scanning electron microscopy (SEM) microstructure analysis revealed that gellan eliminated cracks present in the film matrix resulting in a more uniform structure. FTIR and DSC analyses showed that both polysaccharides effectively interacted with fish gelatin, and moreover, gellan being more effective. Overall, addition of gellan up to 2 g/100 g of gelatin performed better in enhancing fish gelatin films properties.     

Rheological and sensory properties of fish gelatin gels as influenced by agar from Gracilaria tenuistipitata

Agar extracted from Gracilaria tenuistipitata and commercial agars were incorporated into fish gelatin at various levels (0, 5, 10, 15 and 20% gelatin substitution). G. tenuistipitata agar (GA) had lower failure stress (~16 kPa) than commercial agar (CA) (~20 kPa). However, the former showed higher failure strain (~30%) with lower melting temperature (65.9 °C). The critical linear stress and failure stress of agar/gelatin mixed gels increased with increasing agar levels (P < 0.05). At 15 and 20% of agar used, the mixed gels containing CA exhibited higher failure stress than those with added GA (P < 0.05). Two melting points of agar/gelatin mixed gels were observed, corresponding to the melting temperatures of gelatin and agar gels. Nevertheless, the incorporation of agar lowered the likeness score of gelatin gel. Thus, both GA and CA had the impact on rheological property and the selected sensory characteristics of fish gelatin, depending on the level of substitution.     

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.     

鱼鳞明胶与哺乳动物明胶性质的比较

研究了酶法制备的草鱼鱼鳞明胶的理化性质,并将其与哺乳动物明胶的性质作了比较。研究发现,草鱼鱼鳞明胶中富含甘氨酸、脯氨酸、羟脯氨酸和丙氨酸,而亚氨基酸、总疏水性氨基酸的含量以及平均疏水性值要小于哺乳动物明胶;分子质量分布主要以α组分和β组分为主,占明胶分子总量的88%;胶凝温度和熔化温度分别为20.8℃和26.9℃,低于哺乳动物明胶;特性黏度约为0.73;表面疏水性指数为259.59,有较好的乳化性和起泡性。此外发现,明胶的高凝胶强度和胶凝速度主要取决于明胶(α+β)组分的含量,而明胶胶凝和熔化温度则主要取决于亚氨基酸的含量,不同来源明胶的特性黏度η仅与其α组分(α1+α2)的含量存在线性相关。     

Effect of microbial transglutaminase on the functional properties of megrim (Lepidorhombus boscii) skin gelatin

This paper examines the effect of a microbial transglutaminase (TGase) on the gelling and viscoelastic properties of a gelatin from megrim (Lepidorhombus boscii) skins. Although TGase extended the setting time of fish gelatin, it was found that melting temperature, gel strength and viscosity in solution at 60 °C were considerably increased by the covalent cross‐linking action of the enzyme, as observed by SDS‐PAGE and SEM. Increasing concentrations of TGase increased the elasticity and cohesiveness of gelatin gels but reduced gel strength and hardness. Partial inactivation of the enzyme was achieved thermally without negatively affecting the properties of the gelatin; whether or not gelatin is thermoreversible depends essentially on the degree of enzyme inactivation. © 2001 Society of Chemical Industry     

肉冻粉的研究

分别以肉冻粉、琼脂、明胶为材料,加热溶解、冷却凝胶成胶冻。进行黏度、凝胶强度、凝胶水析率、凝胶黏着力、凝胶凝固点及熔点测定等试验,以对比几种凝胶的性能。结果表明,以肉冻粉生产的凝胶比琼脂、明胶生产的凝胶有着更为优良的性能。     

提取pH对鳙鱼鱼鳞明胶功能性质的影响

研究了制备过程中pH值(3.0~7.0)对鳙鱼鱼鳞明胶组成、得率和功能性质(凝胶强度、胶融温度和浊度)的影响,并对鱼鳞明胶的分子量分布进行了探究。结果表明,pH值在3.0~7.0时均能得到高品质的鱼鳞明胶(高蛋白质含量、低灰分含量)。随着pH值的增加,鳙鱼鱼鳞明胶得率逐渐降低,浊度逐渐增加,凝胶强度和胶融温度先增加后减小。此外,鳙鱼鱼鳞明胶的凝胶强度与分子量分布具有一定的相关性。上述研究结果可为特定用途的鱼明胶制备提供技术支撑。     

氯化钠添加量对鱼皮明胶凝胶性能和结构的影响

以罗非鱼鱼皮为原料制备鱼皮明胶,通过单轴压缩实验、差示扫描量热实验(DSC)和红外光谱法(FT-IR)探讨了不同氯化钠添加量(0、0.5%、1.0%、1.5%、2.0%、3.0%,w/v)对不同浓度鱼胶凝胶样品(2%、4%、6.67%,w/v)的真实应力、杨氏模量、热焓值和结构的影响。结果表明,随着鱼胶浓度增加其真实应力和杨氏模量显著增加,表明鱼胶的凝胶强度和硬度显著增加,添加氯化钠后,鱼胶体系的凝胶强度和硬度随氯化钠添加量的增加呈现显著下降趋势,当氯化钠添加量达到3%时,鱼胶凝胶强度和硬度的值最小。差式扫描量热量热分析结果表明,随着氯化钠浓度的增加,热焓值下降,鱼胶的凝胶网络交联程度变弱。傅里叶变换红外光谱分析结果表明,随着氯化钠添加量增加,酰胺Ⅰ带吸收峰逐渐向低波数方向移动,氢键形成受到抑制,鱼胶凝胶强度降降低。研究表明氯化钠的存在破坏了鱼胶凝胶样品的空间结构,降低了鱼胶的凝胶性能。     

Rheological Properties of Fish Gelatins

ABSTRACT: The rheological properties of fish gelatins (cod, megrim, tuna, and tilapia) and conventional gelatin (bovine and porcine) were compared. The different fish gelatins had from low to high viscosity values. They also had from low to high gel strength values. However, they had lower melting and gelling temperatures than gels from conventional gelatins. Cold-water fish gelatins were more different from conventional gelatins than warm water fish gelatins reflecting the different amino acid composition, as cold-water fish gelatins are low in imino acids. Binary blends of cod and other fish or conventional gelatins seemed to be completely compatible.     

加热方式和加热时间对鱼类明胶理化性质的影响

为探究加热方式和加热时间对鱼类明胶理化性质的影响,对加热明胶溶液的蛋白组成、粘度、流变性质和热稳定性,以及明胶凝胶的强度、质构（texture profile analysis,TPA）参数和微观结构进行分析和比较。结果显示,鱼类明胶溶液的粘度、流变性质及热稳定性随加热时间的增加而明显降低,但间歇加热明胶中这些性质的变化幅度均低于连续加热明胶。连续加热明胶至48 h时电泳图谱中β条带消失,96 h时α₁和α₂亚基明显降解,而当间歇加热明胶至96 h时β条带才消失。鱼类明胶形成的凝胶其强度和TPA参数随热处理时间的延长逐渐减小,但间歇加热明胶的凝胶形成能力优于连续加热明胶。扫描电子显微镜结果显示,连续加热的凝胶表面光滑平整,而间歇加热凝胶的结构更加粗糙且多孔隙。研究结果表明,间歇加热及加热时间小于12 h有利于减少明胶热降解。     

Gelling Properties of Fish/Pork Mince Mixtures

The gel properties of silver carp/pork mince mixtures were investigated as well as the protein structural changes and interactions during gelling using rheology, SEM, and FT‐Raman spectroscopy. The breaking force values for gels containing 0% to 40% pork was significantly lower (P < 0.05) compared with gels containing 50% to 100% pork. Gels containing 70% to 100% pork had significantly higher (P < 0.05) breaking force values compared with gels containing 50% to 60% pork. Deformation values were more mixed. Dynamic rheological data suggested that mixing fish and pork at 3:7 could strengthen the gel network. The addition of 40% pork or above, significantly decreased (P < 0.05) the water retention of the gels compared with the 100% fish gels. The dimensional ordering of gels was also reduced by addition of pork. The reduced ordering was one of the reasons for the low water retention for fish/pork mixed gels. Raman spectral analysis confirmed that mixing fish and pork in 7:3 and 3:7 ratios could promote hydrophobic interactions such as bringing tyrosine residues into the intermolecular interface. The interactions in the 3:7 fish/pork mixed gels were favorable for forming a stronger gel. However, the interactions in the 7:3 fish/pork mixed gels were adverse. The water retention of gels was related to both molecular interactions and secondary structures of protein as well as the microstructure of the gels.