Effects of Pretreatment on Properties of Gelatin from Perch (Lates Niloticus) Skin

Fish gelatins obtained from perch fish skin pretreated with various solutions containing acetic acid, sodium hydroxide (NaOH) and sodium chloride (NaCl) were successfully characterized for their nanostructure pattern using field emission scanning electron microscopy. Each pretreatment transformed collagen to gelatin with fibril, zigzag cracks, straight rods, and cross-linked rods nanostructure patterns. Pretreatment solutions also affect the gel yield, gel strength, amino acid profile, and functional groups in perch gelatin as analyzed by Fourier transform infrared spectroscopy. Samples pretreated with NaCl, NaOH, and acetic acid solution showed the highest gel yield (22.84%) and gel strength (179.84 g). Fourier transform infrared spectra for perch gelatins also revealed weak C–N amide II and III bond stretches as well as weak C=O bond stretch.     

快速鉴别冰鲜和解冻石斑鱼的研究

运用伏安法测定不同频率下冰鲜和解冻石斑鱼的阻抗,当电流频率从1kHz增大到16kHz时,冰鲜和解冻石斑鱼的阻抗均随频率的增大而减小。冰鲜1、3、5、7天石斑鱼的阻抗相对变化值(Q)值分别为40.0%、30.7%、25.0%、21.9%;而在-20℃冷冻2天解冻后第一天的石斑鱼,其Q值为16.2%,在-30℃冷冻2天解冻后第一天的石斑鱼,其Q值为13.4%。对比可知,冰鲜鱼的Q值明显大于解冻鱼,所以,依据Q值>20%或<20,可以区分冰鲜和解冻石斑鱼。     

凝胶淀粉的理化特性研究

用凝胶淀粉中试产品进行理化特性分析:包括粘度测定、热糊与冷糊稳定性;不同pH值、糖、盐存在下淀粉粘度曲线与凝胶强度以及冻融稳定性;颗粒形貌、红外光谱和X-射线分析等。结果表明:本品是一种易分散于冷水,加热易糊化成均匀透明胶体液,其热、冷糊稳定性高;在低或高pH值范围内,用糖或不用糖,不用硬化用盐类均能胶凝。凝胶强度强,尤其耐酸性特好;冻融稳定性增强,保水性亦好;凝胶淀粉与天然淀粉颗粒形貌几乎没有差别,表明交联、水解反应只在淀粉颗粒的表面进行。晶体结构也未发生变化。     

Effect of Epigallocatechin Gallate on the Properties of Gelatin

Epigallocatechin gallate was added to gelatin, and the changes in the gelatin were characterized to determine the effects of epigallocatechin gallate modification. The microstructural changes in the samples were analyzed using Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and scanning electron microscopy. The results indicated that the gel strength and thermal stability of gelatin can be improved by appropriate epigallocatechin gallate addition. The optimal final concentration of epigallocatechin gallate was 1.0 g l^?1 in a gelatin solution (66.7 g l^?1). The concentration was also verified using Fourier transform infrared spectroscopy and X-ray diffraction. Covalent bonds were not observed in the epigallocatechin gallate-gelatin samples. Hydrogen bonds were the main molecular interactions observed in the epigallocatechin gallate-gelatin samples. The color of the epigallocatechin gallate-gelatin hydrogels or xerogels was darker because of the epigallocatechin gallate oxidation.     

An indirect ELISA and a PCR technique for the detection of Grouper ( Epinephelus marginatus ) mislabeling

An indirect enzyme-linked immunosorbent assay (ELISA) and a multiplex polymerase chain reaction (PCR) procedure was applied for the detection of Grouper (Epinephelus marginatus) mislabelling in the fish market. An indirect ELISA (microtiter-plate format) using two monoclonal antibodies (3D12 and 1A4) was assayed and multiplex PCR performed using species-specific primers of the 5S rDNA gene for the rapid authentication of grouper. A total of 70 commercial fish fillet samples, collected from local markets and supermarkets, labelled as grouper were analysed: 12 of the 70 samples were confirmed to be Grouper. The PCR technique permitted the detection of Nile Perch (Lates niloticus) in the commercial fillet samples, which was not possible using ELISA. The results suggest that both ELISA and PCR are specific and reliable tools for the detection of Grouper mislabelling/adulteration and the accurate implementation of traceability for successful regulatory food controls.     

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.     

Exposure to Air Accelerates the Gelation of Gelatin: Steady and Dynamic Shear Rheological Characterization to See the Effect of Air on the Strength of Gelatin Gel

In the current study, the effect of air exposure to the gelatin solution on improvement of gel structure was investigated in terms of the steady and dynamic shear rheological properties. Prepared gelation solution (5% w/v) was covered to prevent air incorporation and it was subjected to 5 h gelatin and rheological analyses were carried out for the comparison of non-covered ones. It was observed that the preventing of air into the gelatin solution affected the rheological parameters. Apparent viscosity and complex viscosity values of samples increased during gelation and these values were measured to be tremendously high (1.894 and 8.346 Pa s, respectively) in non-covered gelatin solution while they were 0.474 and 1.611 Pa s in covered samples after 5 h gelation, respectively. Similarly, storage modulus (G′) of samples increased with the increase in gelation time and it was recorded to be 52.203 Pa in gelatin solution exposed to air while it was 9.848 Pa in gelatin solution covered to prevent air incorporation. These results showed importance of air in gelatin solution to the food industry using gelatin in food formulation for the structure of processed foods.     

草鱼鱼鳞明胶的提胶工艺及特性研究

探讨草鱼鱼鳞明胶的提胶条件及其特性。采用正交试验研究pH值、温度和时间对鱼鳞明胶品质的影响,利用物性仪、高效液相色谱仪和红外光谱仪等对制备的明胶特性进行分析研究。得到最佳提胶条件:提胶液pH值为6、提胶温度为55℃和时间为6h。得到的明胶提取率为35.56%,黏度为6.04mPa·s,凝胶强度为478.58g,等电点为pH值7.6,亚氨基酸(脯氨酸和羟脯氨酸)含量达21.6%。所得鱼鳞明胶结构稳定,为较高品质的明胶。     

磺胺甲噁唑和磺胺嘧啶在青石斑鱼组织中的分布及代谢规律

通过一次性投喂各含有200 mg/kg磺胺甲噁唑（sulfamethoxazole,SMZ）和磺胺嘧啶（sulfadiazine,SDZ）的饲料,研究两种药物在青石斑鱼中各组织分布与消除规律。采用超高效液相色谱-串联质谱检测青石斑鱼各组织中SMZ和SDZ的含量,并用内标法定量。结果表明,SMZ在青石斑鱼各组织中的最大含量：肝脏、背肌、血浆、肾脏和鳃依次为827.97μg/kg、776.70μg/kg、610.29μg/L、432.14μg/kg和345.18μg/kg。SDZ在青石斑鱼各组织中的最大含量：肝脏、背肌、鳃、血浆和肾脏依次为895.30μg/kg、660.55μg/kg、431.88μg/kg、419.56μg/L和310.67μg/kg。SMZ在青石斑鱼各组织中的半衰期：肾脏、鳃、背肌、血浆和肝脏半衰期依次为26.65、21.00、20.38、18.73h和16.90h。SDZ在青石斑鱼各组织中的半衰期：肾脏、血浆、鳃、背肌和肝脏依次为31.50、27.72、24.75、21.66h和18.24h。SMZ和SDZ在青石斑鱼肝脏中半衰期最短,代谢速度最快;在肾脏中半衰期最长,代谢速度最慢。在水温（25±2）℃条件下,SMZ和SDZ各200mg/kg的剂量同时单次投喂青石斑鱼,建议休药期不低于3d。SMZ和SDZ代谢规律研究为磺胺类药物在水产品中的合理使用提供了参考。     

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.     

Physicochemical and Rheological Properties of White-Cheek Shark (Carcharhinus dussumieri) Skin Gelatin

Physicochemical and rheological properties of white-cheek shark (Carcharhinus dussumieri) skin gelatin were determined as a function of either an alkaline-acid or an acid pretreatment. With alkaline-acid pretreatment, the purity of white-cheek shark skin gelatin was increased, with a significantly lower extraction yield, a higher retention of high molecular weight components, and greater preservation of the triple helical structure. Moreover, gelatin from alkaline-acid treated skins showed denser spherical structure, significantly (p < 0.05) different textural properties, better thermostability (T_g = 21°C, T_m = 27.5°C), higher values of both G′ and G″, higher gel strength (330 g), more imino acids (20.3%), and lighter colored gels compared with acid treated white-cheek shark skin gelatin.     

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

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

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.     

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.     

Study on the properties of gelatins from skin of carp (Cyprinus carpio) caught in winter and summer season

The objective of this work was to compare the physiochemical (molecular weight distribution and amino acid composition) and rheological (viscosity property, gel strength and melting point) properties of gelatins from skins of carp caught in winter to those obtained for the summer equivalents. Gelatins from winter and summer fish skins were extracted at 60, 70 and 80 °C. SDS-PAGE patterns for gelatins extracted under the same conditions showed that the degradation of gelatins from winter fish skins were more severe than that of the summer ones. The imino acid contents of the winter and summer gelatins extracted at 60 °C were very similar, showing 190 and 188 residues/1000 residues, respectively. The gelatins from summer fish presented higher melting points and gel strengths, as well as better viscosity properties than the winter equivalents (P < 0.05). The differences in the rheological properties between winter and summer gelatins may be explained by different thermostability of interstitial collagen molecules (from which gelatins were derived) in the two seasons.     

兔皮明胶提取工艺优化

以兔皮为原料,研究稀盐酸短时诱导兔皮制备明胶的工艺。以明胶提取率和凝胶强度为评价指标,对兔皮明胶制备工艺中的盐酸质量分数、盐酸处理时间、提胶pH值、提胶温度4 个因素进行了优化,在此基础上通过正交试验确定最佳工艺为盐酸质量分数1%、盐酸处理时间10 min、提胶温度65 ℃、提胶pH 4。在此工艺条件下明胶提取率高达（86.85±1.71）%,凝胶强度为（481.43±16.89）g。明胶基本性质符合GB 6783-2013《食品添加剂：明胶》要求。     

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.     

鱼皮明胶的超高压辅助提取工艺

为建立鱼皮明胶清洁生产工艺,对超高压辅助提取鱼皮明胶进行系统研究,考察超高压处理压力、超高压作用时间、提取温度、提取时间对凝胶强度和提取率的影响。结果表明,较优提取工艺为处理压力300MPa、超高压时间10min、提取温度50～60℃、提取时间4h,在此条件下明胶凝胶强度可达274g,得率可达75.03%,溶解温度和凝胶温度分别为23.6℃和16.4℃。     

斑点叉尾鮰鱼皮明胶的制备

目的以斑点叉尾鮰鱼皮为原料,采用酸碱法制备鱼皮明胶;方法选用NaOH溶液和H2SO4溶液进行明胶的提取,通过单因素试验和正交试验,确定斑点叉尾鮰鱼皮明胶最佳制备工艺;结果NaOH质量分数为0.3%,H2SO4质量分数为0.4%,处理时间均为120 min,提取温度45℃,提取时间6 h,此时,所得明胶的凝胶强度和黏度分别为672.2 g和9.46 mPa·s,明胶提取率为65.21%.     

Optimization of Gelatin Extraction from Silver Carp Skin

ABSTRACT:  Fish skins are a by-product of the fish processing industry that can be successfully processed into gelatin. This study was designed to optimize the extraction process to obtain the highest yield, gel strength, and viscosity for gelatin production from silver carp skin. A fractional factorial design (2 levels, resolution III, 2^9-5) was chosen to screen 9 parameters to determine the most significant ones. Those found to be significant were optimized to determine the maximum value for 3 dependent variables mentioned above. The hydroxyproline content and hydroxyproline/protein ratio of the skin were 1.7% and 6.5%, respectively. The protein content of the skin was 26%. The hydroxyproline content of the gelatin for the sample giving the highest hydroxyproline/protein ratio was 10.9%. This sample was arbitrarily called pure gelatin and the purity of the remaining samples was between 71.8% and 97%. The highest protein and gelatin recovery was 78.1% and 98.8% of the total available, respectively. The latter, gelatin recovery, is proposed to be used instead of protein yield. Four variables were determined as significant in screening and these variables were studied by a central composite rotatable design (4-factor and 5-level with 6 central points) to model the system and response surface methodology was used for optimization. The optimum extraction conditions were 50 °C for the extraction temperature, 0.1 N HCl for the acid concentration, 45 min for the acid pretreatment time, and finally 4 : 1 (v/w) for the water/skin ratio. The predicted responses for these extraction conditions were 630 g gel strength, 6.3 cP viscosity, and 80.8% gelatin recovery. The data suggest that silver carp skin gelatin is similar to those of fish gelatins currently being exploited commercially.