Repurposing fish waste into gelatin as a potential alternative for mammalian sources: A review

Mammalian gelatin is extensively utilized in the food industry because of its physicochemical properties. However, its usage is restricted and essentially prohibited for religious people. Fish gelatin is a promising alternative with no religious and social restrictions. The desirable properties of fish gelatin can be significantly improved by various methods, such as the addition of active compounds, enzymes, and natural crosslinking agents (e.g., plant phenolics and genipin), and nonthermal physical treatments (e.g., ionizing radiation and high pressure). The aim of this study was to explore whether the properties of fish gelatin (gel strength, melting or gelling temperature, odor, viscosity, sensory properties, film-forming ability, etc.) could be improved to make it comparable to mammalian gelatin. The structure and properties of gelatins obtained from mammalian and fish sources are summarized. Moreover, the modification methods used to ameliorate the properties of fish gelatin, including rheological (gelling temperature from 13–19°C to 23–25°C), physicochemical (gel strengths from ∼200 to 250 g), and thermal properties (melting points from ∼25 to 30°C), are comprehensively discussed. The relevant literature reviewed and the technological advancements in the industry can propel the development of fish gelatin as a potential alternative to mammalian gelatin, thereby expanding its competitive market share with increasing utility.     

高效液相色谱-高分辨率质谱联用技术鉴定阿胶块中不同胶类的特征性多肽

为研究阿胶块中不同明胶的来源,本文以4种品牌的阿胶块为原料,向其中分别加入低含量（1 mg/mL）的牛明胶和猪明胶,采用高效液相色谱-质谱联用技术（high-performance liquid chromatography-mass spectrometry,HPLC-MS/MS）分别鉴定阿胶、牛明胶和猪明胶的特征性多肽。结果表明,在4种阿胶块中准确检测出阿胶、牛明胶和猪明胶的共有特征性多肽数量分别为18、3和5个,其中来自α₁链的特征性多肽有10、1和1个,来自α₂链的则有8、2和4个;同时,有羟基化修饰脯氨酸的共有特征性多肽数量分别为15、2和4个,不包含任何修饰基团的特征性多肽对应则有3、1和1个。这些共有的特征性多肽可为HPLC-MS/MS溯源鉴定阿胶块中的明胶源提供依据,对阿胶块产品的质量保障具有一定的参考意义。     

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.     

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.     

Effect of Extraction Temperature on Functional Properties and Antioxidative Activities of Gelatin from Shark Skin

Physico-chemical properties, functional properties, and antioxidative acitivities of gelatin from the skins of brownbanded bamboo shark (BBS; Chiloscyllium punctatum) and blacktip shark (BTS; Carcharhinus limbatus), as affected by extraction temperature, were investigated. ??-Amino acid group content and surface hydrophobicity of both gelatins from both species increased as the extraction temperature increased (P?<?0.05). Both gelatins had a high solubility (more than 80%) in a wide pH range (1?C10). Both gelatins extracted at 60?°C exhibited the highest emulsion activity index (EAI), emulsion stability index (ESI) and foam expansion (FE). The lowest foam stability (FS) was obtained when gelatin was extracted at 75?°C (P?<?0.05). The BBS gelatin had lower EAI, ESI, and FE than did BTS gelatin. Nevertheless, a higher FS was found in the former (P?<?0.05). Antioxidative activities of both gelatins increased with coincidental increase in ??-amino group content as the extraction temperature increased (P?<?0.05). The BTS gelatin generally exhibited the higher antioxidative activities, compared with the BBS gelatin (P?<?0.05). Gelatin extracted at 60?°C showed the highest interfacial properties, while those extracted at higher temperature (75?°C) had enhanced antioxidative activities. Extraction temperature may therefore be regulated to maximize applications.     

酸/碱预处理对美洲鳗鲡（Anguilla rostrata）鱼骨明胶理化性质与凝胶特性的影响

以美洲鳗鲡（Anguilla rostrata）鱼骨为原料,采用酸或碱预处理结合热水浸提制备鱼骨明胶,并通过得率、凝胶强度测定、SDS-PAGE、紫外全波长扫描、红外光谱扫描、动态流变学测定以及扫描电镜等研究鱼骨明胶的理化性质和凝胶特性。结果表明:酸法预处理明胶（AG60）与碱法预处理明胶（BG60）得率分别为13.6%和6.88%,凝胶强度分别为101.95 g和78.74 g。AG60和BG60的羟脯氨酸含量为3.2 g/100 g和2.7 g/100 g。两种明胶均含有β和α₁、α₂链,其中AG60的α₁+α₂含量显著高于BG60。AG60与BG60均具有明胶的特征吸收峰,且无杂蛋白吸收峰。与BG60相比,AG60具有更高的凝胶温度与熔融温度,以及更短的胶凝时间。扫描电镜分析显示,AG60具有更致密、均一的凝胶网络结构。本研究表明,与碱法预处理相比,酸法预处理制备得到的鳗鱼骨明胶具有更高的得率与更好的凝胶特性。     

Structural Characteristics of Tilapia (Oreochromis mossambicus) Bone Gelatin: Effects of Different Liming Methods

Fish bone is a good source of gelatin. In this study, gelatins were prepared from tilapia bone after the bone was pretreated with alkali protease, desalted immediately by 0.6 mol L^?1 HCl, and hydrolyzed by papain or limed by Ca(OH)₂. Gelatins extracted from papain-treated tilapia bone exhibited space structures similar to those of alkali-treated tilapia bone. Despite this similarity, many differences were observed between these gelatin samples. Compared with alkali-treated gelatin, papain-treated gelatins showed higher values for imino residue content, molecular weight proportion, bloom strength, and viscosity. The bloom strengths of the second and third papain-treated gelatins were 163 and 94 bloom, respectively, which were lower than the bloom strength of the first papain-treated gelatin (189 bloom). The viscosities of the three papain-treated gelatin samples were 4.18, 2.81, and 0.51 mPa.s^?1. The first papain-treated gelatin achieved the highest gelling (16 °C) and melting points (23.9 °C). The yields of the first (5.40%) and second (6.71%) papain-treated gelatins were higher than those of the alkali-treated gelatins (3.33 and 5.76%, respectively). However, the yield of the third papain-treated gelatin (2.27%) was lower than that of the third alkali-treated gelatin (5.42%). More importantly, papain hydrolysis can prevent destruction by Ca(OH)₂ in the bone structure and effectively reduce the denaturation temperature of tilapia bone collagen. Moreover, papain hydrolysis can dramatically reduce the time required for liming (0.8% of traditional liming process spent). Papain hydrolysis is a clean production method that can replace traditional liming.     

Extraction and Physicochemical Characterization of Greater Lizardfish (Saurida tumbil) Skin and Bone Gelatin

ABSTRACT:  Type A gelatins were extracted from skins and bones of lizardfish and analyzed to determine their functional and chemical properties. Lizardfish skin gelatin had ash content of 2.2 ± 0.3% while bone gelatin had ash content of 12.2 ± 0.2%. Gel strength was 159.1 ± 14 and 135 ± 7.9 g, respectively, for skin and bone gelatins compared to 224.3 ± 7.7 g for porcine gelatin. Gelatin from skin exhibited higher viscosity and lower setting time than bone. Skin gelatin had higher imino acid content than bone gelatin. The total imino acid content was 21.71% and 19.83% for skin and bone, respectively. Both skin and bone gelatins contained more α chains than β and γ components. Both bone and skin gelatins also contained low molecular weight (< α) peptides. The differences in functional properties between the skin and bone gelatins appeared to be related to differences in amino acid composition and molecular weight distribution of the gelatins.     

Properties of Gelatin Film from Horse Mackerel (Trachurus japonicus) Scale

Optimal conditions for extracting gelatin and preparing gelatin film from horse mackerel scale, such as extraction temperature and time, as well as the protein concentration of film‐forming solutions were investigated. Yields of extracted gelatin at 70 °C, 80 °C, and 90 °C for 15 min to 3 h were 1.08% to 3.45%, depending on the extraction conditions. Among the various extraction times and temperatures, the film from gelatin extracted at 70 °C for 1 h showed the highest tensile strength and elongation at break. Horse mackerel scale gelatin film showed the greatly low water vapor permeability (WVP) compared with mammalian or fish gelatin films, maybe due to its containing a slightly higher level of hydrophobic amino acids (total 653 residues per 1000 residues) than that of mammalian, cold‐water fish and warm‐water fish gelatins. Gelatin films from different preparation conditions showed excellent UV barrier properties at wavelength of 200 nm, although the films were transparent at visible wavelength. As a consequence, it can be suggested that gelatin film from horse mackerel scale extracted at 70 °C for 1 h can be applied to food packaging material due to its lowest WVP value and excellent UV barrier properties.     

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.     

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.     

Extraction of Gelatin from Megrim (Lepidorhombus boscii) Skins with Several Organic Acids

ABSTRACT: Light-colored, dry collagen was obtained and, after dissolving in warm water, turned into soluble gelatin. The type of acid used influenced the gelatin viscoelastic and gelling properties. Acetic- and propionic-acid extracts produced the gelatins with the highest elastic modulus, viscous modulus, melting temperature, and gel strength, especially when skins were previously treated with dilute NaOH. After such treatment, lactic acid was also shown to be suitable for collagen or gelatin extraction. The lowest degree of turbidity was achieved by using citric acid, whereas propionic acid led to the most turbid gelatin. No improvements of rheological properties were observed when acid concentration for extraction was increased above 0.05 M.     

Seasonal differences in the properties of gelatins extracted from skin of silver carp (Hypophthalmichthys molitrix)

The gelatins were extracted from skins of silver carp (Hypophthalmichthys molitrix) caught in winter and summer, respectively. The physicochemical (molecular weight distribution and melting point) and rheological characteristics (viscosity property), as well as functional properties (emulsifying capacity and stability) of the gelatin from winter silver carp skin were compared with those of the summer equivalent. The results showed the properties of the summer gelatin were superior to those of the winter one, showing higher viscosity, emulsion stability, melting point and lower concentration for gelling. The summer gelatin has slightly denser strands of the gel microstructure which was observed by scanning electron microscopy (SEM). Different properties of gelatins from skin of silver carp may be attributed to the big discrepancy of the environmental temperature in the two seasons.     

阿胶制品中典型明胶特征性多肽的鉴定

为了研究不同类型阿胶制品中典型明胶的来源,本文选取9种市面上常见的阿胶制品（阿胶糕、阿胶口服液和阿胶颗粒各3种）为研究对象,分别添加质量分数为1%的牛明胶和猪明胶,采用高效液相色谱-高分辨率质谱联用技术（high-performance liquid chromatography-mass spectrometry,HPLC-MS/MS）鉴定这9种阿胶制品中典型明胶的特征性多肽。结果表明,不同数量的典型明胶特征性多肽被检出于9种阿胶制品。进一步分析发现,所有阿胶制品共有的阿胶、牛明胶、猪明胶的特征性多肽分别为25、3、14条,其中,未经修饰的特征性多肽依次为7、2、3条。在上述共有特征性多肽中,源自α1链的分别有22、2、5条,源自α2链的分别为3、1、9条。这些共有特征性多肽可作为HPLC-MS/MS鉴定复杂体系中明胶源的依据,对不同阿胶制品中明胶来源的鉴定具有指导意义。     

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.     

Dehydration of Pollock Skin Prior to Gelatin Production

ABSTRACT: Alaska pollock (Theragra chalcogramma) is the U.S.A.'s largest commercial fishery, with an annual catch of over 1 million tons. During pollock processing, the skins are discarded or made into fish meal, despite their value for gelatin production. The absence of gelatin-processing facilities in Alaska necessitates drying of the skins before transport to decrease the moisture content, but conventional hot-air drying is expensive. This study evaluated a less energy-intensive technology, the use of desiccants for reducing water weight in pollock skins prior to shipment. To ensure that the functional properties of gelatin obtained from dried pollock skins were not affected during desiccation, gelatins were prepared from each skin-drying treatment and compared with gelatin extracted from air-dried pollock skins. None of the desiccation treatments decreased the gel strength of pollock skin gelatin, nor were there major differences in gelling temperature or viscosity among the gelatin solutions. This suggests that pollock skins can be economically stabilized for transport to a gelatin-processing facility through the use of regenerable desiccants that are already common in the food industry. Practical Application: Pollock skins destined for gelatin production can be stabilized using chemical desiccants prior to shipment. The dehydration process does not harm the functional properties of gelatin, such as gel strength, gelling temperature, and viscosity. This research suggests that fish skins can be economically stabilized for transport to a gelatin-processing facility through the use of regenerable desiccants that are already common in the food industry.     

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     

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.     

Physicochemical Properties of Mammalian Gelatin in Relation to Membrane Process Requirement

In any of the membrane process application, understanding of the characteristics of the feed solution is essential in order to achieve desired level of separation performance. In this study, in an effort to substitute evaporation with membrane processes partially, experiments were carried out to investigate the physicochemical properties of gelatins, namely, molecular weight distribution, pH, viscosity, isoelectric point, and gel strength, which are, of foremost, important parameters in the characterization of gelatin. Two different mammalian gelatins, i.e. from bovine (type B) and porcine (type A) sources, were used in this study. The pH was significantly varied for all gelatins in the vicinity of 4.75–5.51 (±0.01). Experimental result revealed that both sources of mammalian gelatin contained components of different molecular weights with wide distribution ranging from 10 to 400 kDa. Analysis of the molecular weight distribution result also showed strong correlation between average molecular weight and gel strength of gelatin. The isoelectric points of gelatins from bovine were 4.60 ± 0.08 to 5.25 ± 0.43 and porcine gelatins were in the range of 7–9.3, which agreed well with the results obtained from other researchers. The high bloom strength mammalian gelatins were also significantly more viscous and thus, had a higher melting point.     

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.