Glycosylation fish gelatin with gum Arabic: Functional and structural properties

Techno-Functional, Rheological, and Physico-Chemical Properties of Gelatin Capsule By-Product for Future Functional Food Ingredients

The utilization of gelatin capsule waste (GCW) poses a challenge for the industry. This study investigates its potential as a functional food ingredient by evaluating the physico-chemical, rheological, and techno-functional properties of gelatin capsule waste powder (GCWP). To achieve this, the gelatin capsule waste (GCW) was mixed with maltodextrin at varying ratios (1:1, 1:2, 1:3, 1:4, and 1:5) and subjected to spray drying. The findings highlight maltodextrin's crucial role in stabilizing the drying process, reducing stickiness, and enhancing handling and storage properties. All the obtained GCWP samples appeared light white and had a slightly sticky texture. The 1:5 (w/w) GCW-to-maltodextrin ratio produced the highest powder recovery with minimal stickiness, indicating enhanced drying efficiency. Increasing maltodextrin reduced gel strength, texture, and foaming properties while raising the glass transition temperature. The FTIR analysis indicated a decline in protein-protein interactions and increased polysaccharide interactions at higher maltodextrin levels. The rheological analysis demonstrated lower elastic and loss moduli with increased maltodextrin, affecting GCWP's structural behavior. For overall properties, the GCW mixed with maltodextrin at a 1:1 ratio (GCW-1M) is recommended for future applications, particularly for its gelling characteristics. The GCW-1M, being rich in amino acids, demonstrates its potential as a functional food ingredient. However, certain properties, such as gel strength and powder stability (hygroscopicity and stickiness), require further optimization to enhance its industrial applicability as a functional food ingredient.

Molecular interactions and gel network modulation in ionic polysaccharide-gelatin hydrogels for improved texture of skipjack tuna products

The present study investigates the enhancement of skipjack tuna (Katsuwonus pelamis) texture by incorporating ionic polysaccharide-bovine bone gelatin (BBG) hydrogels. Three ionic polysaccharides, namely carboxymethyl chitosan (CMCS), konjac glucomannan (KGM), and oat β-glucan (OBG), were utilized in BBG-based hydrogels. And their effects on the rheological, structural, and protein properties of the composite gels were explored. Results showed that charge density influenced pore size, wall thickness, and cross-linking density in hydrogels. Structural analyses revealed that all polysaccharides promoted ordered rearrangements in protein secondary structure, increasing surface hydrophobicity and β-sheet content, with OBG having the pronounced effect by mediating gelation through enhanced hydrophobic interactions and hydrogen bonding. The incorporation of BBG + OBG-20 % hydrogels significantly enhanced water-holding capacity, and texture while reducing oral processing energy (p < 0.05). These findings provide insights for improving the texture of skipjack tuna products and demonstrate the potential application of polysaccharide-BBG hydrogels in enhancing the quality of fish products.

Fabrication, modification, interaction mechanisms, and applications of fish gelatin: A comprehensive review

Fish gelatin (FG) is an essential natural biopolymer isolated from aquatic sources and has been considered as a feasible substitute for mammalian gelatins. However, its inferior mechanical and gelling properties limit its applications. Consequently, FG has been modified using various methods. This review summarizes the extraction techniques (including traditional acid and alkaline methods, as well as newer technologies such as ultrasonic-assisted and microwave-assisted extraction), modification strategies (mechanical treatments, physical mixing with polysaccharides, utilization of the Hofmeister effect, chemical modifications, etc.), along with their mechanisms of action. Additionally, we discussed the applications of FG and its modified products. Furthermore, this review highlights the safety and prospects for FG and its derivatives. The mechanical properties and biological functions of FGs are enhanced after modification. Thus, modified FG composites exhibit diverse applications in areas such as foaming agents and emulsifiers, food packaging, three-dimensional printing, drug delivery systems and tissue engineering. This paper aims to provide comprehensive information for future research on FG with the intention of broadening its applicability within the industries of food, cosmetics, and pharmaceuticals. Nevertheless, the development of tough gels, aerogels, and stimuli-responsive hydrogels based on FG requires further investigation.

Effect of Heat Treatment on Gelatin Properties and the Construction of High Internal Phase Emulsions for 3D Printing

The effect of tilapia skin gelatin properties on the characteristics of high internal phase emulsions (HIPEs) and the quality of 3D printing remains unidentified. In this work, HIPEs were constructed by gelatin with various properties that were obtained by heat treatment. The results indicated that the gelatin undergoes degradation gradually with an increase in heating intensity. The highest values of intrinsic fluorescence intensity, surface hydrophobicity, and emulsification were obtained when the heating time was 5 h. The gel strength and hardness of gelatin hydrogels were negatively correlated with heat treatment temperature. HIPEs constructed by gelatin extracted at 70 °C demonstrated a suitable material for 3D printing. The storage modulus (G') and viscosity of HIPEs exhibited a similar tendency as the gel strength of gelatin. The microstructure of HIPEs revealed that gelatin established a gel network around oil droplets, and the higher G' of HIPEs corresponded to a more compact network structure. This study elucidated the correlation between the structure and properties of gelatin, offering essential insights for the formulation of HIPEs by natural gelatin, which is suitable for applications across several domains.

Fish oil-loaded multicore submillimeter-sized capsules prepared with monoaxial electrospraying, chitosan-tripolyphosphate ionotropic gelation, and Tween blending

In order to load fish oil for potential encapsulation of fat-soluble functional active substances, fish oil-loaded multicore submillimeter-sized capsules were prepared with a combination method of three strategies (monoaxial electrospraying, chitosan-tripolyphosphate ionotropic gelation, and Tween blending). The chitosan-tripolyphosphate/Tween (20, 40, 60, and 80) capsules had smaller and evener fish oil cores than the chitosan-tripolyphosphate capsules, which resulted from that Tween addition induced smaller and evener fish oil droplets in the emulsions. Tween addition decreased the water contents from 56.6 % to 35.0 %-43.4 %, increased the loading capacities from 10.4 % to 12.7 %-17.2 %, and increased encapsulation efficiencies from 97.4 % to 97.8 %-99.1 %. In addition, Tween addition also decreased the highest peroxide values from 417 meq/kg oil to 173-262 meq/kg oil. These properties' changes might result from the structural differences between the chitosan-tripolyphosphate and chitosan-tripolyphosphate/Tween capsules. All the results suggested that the obtained chitosan-tripolyphosphate/Tween capsules are promising carriers for fish oil encapsulation. This work also provided useful knowledge to understand the preparation, structural, and physicochemical properties of the chitosan-tripolyphosphate capsules.

Effects of Maillard reaction of different monosaccharide-modified on some functional properties of fish gelatin

In this work, the effects of Maillard reaction of different monosaccharide-modified fish gelatin were studied. The changes of gel properties, rheology and structure of fish gelatin before and after modification were compared and analyzed, and oil-in-woter emulsions were prepared. The results showed that the five-carbon monosaccharide had stronger modification ability than the six-carbon monosaccharide, which was mainly due to the different steric hindrance of the amino acids in the nuclear layer and the outer layer to the glycosylation reaction. With the progress of the Maillard reaction, the color of fish gelatin gradually became darker. The attachment of sugar chains inhibited the gelation process of fish gelatin, decreased the gelation rate, changed the secondary structure, increased the content of β-turn or α-helix, increased the degree of fluorescence quenching, and enhanced the emulsifying properties and emulsion stability. This study provides useful information for the preparation of different types of monosaccharide-modified proteins and emulsions.

Discrimination and characterization of different ultrafine grinding times on the flavor characteristic of fish gelatin using E-nose, HS-SPME-GC-MS and HS-GC-IMS

Three different methods were used to identify and analyze the flavor of fish gelatin with different ultrafine grinding time (0, 2, 4 and 8 h). The results of electronic nose showed that overall flavor of the samples changed. HS-SPME-GC-MS identified 65 volatile compounds, including 18 aldehydes, 7 ketones, 7 alkanes, 11 alcohols, 8 esters, 7 phenols, and 7 acids. HS-GC-IMS identified 46 volatile compounds, including 21 aldehydes, 5 ketones, 5 alcohols, 6 esters, 7 acids, 1 ether, and 1 amine. The particle size analysis results indicate that the size distribution decreases from 918.97-1167.16 and 1388.81-1780.40 nm to 157.63-177.37 and 285.90-344.55 nm with the increased of grinding time. The SEM analysis results indicate that the change in flavor characteristics of FG is due to the different storage and release abilities of volatile compounds in FG with different particle sizes.

Tapioca Starch Improves the Quality of Virgatus nemipterus Surimi Gel by Enhancing Molecular Interaction in the Gel System

The gel prepared using Nemipterus virgatus (N. virgatus) surimi alone still has some defects in texture and taste. Complexing with polysaccharides is an efficient strategy to enhance its gel properties. The main objective of this study was to analyze the relationship between the gel quality and molecular interaction of N. virgatus surimi gel after complexing with tapioca starch. The results make clear that the gel strength, hardness, and chewiness of surimi gel were increased by molecular interaction with tapioca starch. At the appropriate addition amount (12%, w/w), the surimi gel had an excellent gel strength (17.48 N), water-holding capacity (WHC) (89.01%), lower cooking loss rate (CLR) (0.95%), and shortened T2 relaxation time. Microstructure analysis indicated that the addition of tapioca starch facilitated even distribution in the gel network structure, resulting in a significant reduction in cavity diameter, with the minimum diameter reduced to 20.33 μm. In addition, tapioca starch enhanced the hydrogen bonding and hydrophobic interaction in the gel system and promoted the transformation of α-helix to β-sheet (p < 0.05). Correlation analysis showed that the increased physicochemical properties of surimi gel were closely related to the enhanced noncovalent interactions. In conclusion, noncovalent complexation with tapioca starch is an efficient strategy to enhance the quality of surimi gel.

3D printable vegan plant-based meat analogue: Fortification with three different mushrooms, investigation of printability, and characterization

In this study, a meat analogue formulation prepared using different protein sources as a printable ink for 3D printers and fortified with three different mushroom cultivars (reishi, Ganoderma lucidum (GL); saffron milk-cap, Lactarius deliciosus (LD); and oyster, Pleurotus ostreatus (PO)). 3D printing performance of the prepared inks was evaluated by factorial design in terms of nozzle height, printing speed, and flow compensation. New methods of maximum layer height and reprintability of plant-based meat analogues were conducted for the first time. Inks were characterized by analyzing rheological properties, microstructure, color characteristics, texture profile, cooking loss, amino acid content, and sensory evaluation. Results showed that the nozzle height and printing speed were found to be most effective on accuracy of prints and smoothness of layers. All inks (C, GL, LD and PO) represented shear-thinning and gel-like viscoelastic behavior (G' > G″) with predominant elasticity (tan δ < 1). Therefore they were suited for 3D printing and possessed supporting the following layers for additive manufacturing as well as meeting the criteria for a stable structure. Meat analogue was printed successfully without perceived defects in all formulations, except the GL was looking linty. LD and PO inks brought the advantage of recycling as a result of their re-printability whereas GL could not. Moreover, mushroom fortification reduced hardness, stiffness, springiness, and chewiness properties of the meat analogues whereas it increased the juiciness with reasonable overall acceptance. Mushroom fortification also enhanced the nutritional value and improved release of umami amino acids. The findings of the study demonstrated that mushrooms could be a functional and nutritious candidate for 3D printable plant-based meat analogues.

Effects of gelatin concentration, adding temperature and mixing rate on texture and quality characteristics of model gels

In this study, the effects of gelatin concentrations (GC) (5.0-10.0 g/100 g), mixing rate (MR) (100-1100 rpm), and gelatin addition temperature (GAT) (55, 60, and 65°C) were investigated on the main textural and various physicochemical properties of model gels (n = 72) prepared using sucrose and glucose syrup (40-42 DE). Considering the p-value of the F-statistic calculated by analysis of variance and the 5% significance level, the production parameters and their interactions had a significant effect on the quality parameters. The influence of the production parameters GC, MR, and GAT, and the interaction of these parameters, GC * MR, GC * GAT, MR * GAT, and GC * MR * GAT of the model gels on the quality characteristic were expressed by converting the Type III SS values into percent values. When all quality characteristics were considered together, MR was the most influential with a score of 58%. PCAmix, a combination of factorial analysis with PCA, was used to visualize the correlations between the production parameters and the quality characteristics of the modeled gels. A great influence was observed between MR and moisture content, color properties, and texture parameters, except springiness. A moderate effect of GC and a minor effect of GAT could be characterized. With the 2D-map of observations, the model gels could be clearly divided into two groups according to the MRs. In accordance with the observations diagram of PCAmix, the similarity dendrogram of AHC also formed two clusters, one cluster for the samples with MR 100 and 200 rpm and one cluster for the samples with MR 500 and 1100 rpm.

Complex Modification Orders Alleviate the Gelling Weakening Behavior of High Microbial Transglutaminase (MTGase)-Catalyzed Fish Gelatin: Gelling and Structural Analysis

In this paper, the effects of different modification orders of microbial transglutaminase (MTGase) and contents of pectin (0.1-0.5%, w/v) on the gelling and structural properties of fish gelatin (FG) and the modification mechanism were studied. The results showed that the addition of pectin could overcome the phenomenon of high-MTGase-induced lower gelling strength of gelatin gels. At a low pectin content, the modification sequences had non-significant influence on the gelling properties of modified FG, but at a higher pectin content (0.5%, w/v), P0.5%-FG-TG had higher gel strength (751.99 ± 10.9 g) and hardness (14.91 ± 0.33 N) values than those of TG-FG-P0.5% (687.67 ± 20.98 g, 12.18 ± 0.45 N). Rheology analysis showed that the addition of pectin normally improved the gelation points and melting points of FG. The structural results showed that the fluorescence intensity of FG was decreased with the increase in pectin concentration. Fourier transform infrared spectroscopy analysis indicated that the MTGase and pectin complex modifications could influence the secondary structure of FG, but the influenced mechanisms were different. FG was firstly modified by MTGase, and then pectin (P-FG-TG) had the higher gelling and stability properties.

Modified Structural and Functional Properties of Fish Gelatin by Glycosylation with Galacto-Oligosaccharides

This study aimed to investigate the effects of galacto-oligogalactose (GOS) glycosylation on the structural and functional properties of fish gelatin (FG). Results showed that with the increase of glycosylation time, grafting degree and browning increased, and new protein bands with increased molecular weight were observed by SDS-PAGE. Structural analysis showed that glycosylation reduced intrinsic fluorescence intensity and increased surface hydrophobicity of FG. FTIR analysis showed α-helix content decreased while random coil content increased in glycosylated FG. Emulsion activity index and emulsion stability index along with foam activity and foam stability were significantly elevated in GOS-4 and GOS-8, but FG glycosylated longer than 12 h exhibited less pronounced improvement. Glycosylated FG showed lower gel strength than control. The results indicate that moderate glycosylation could be applied to improve interfacial properties of FG.

Comparative investigations of various modification methods on the gelling, rheological properties and mechanism of fish gelatin

In this study, κ-carrageenan(κC) and Transglutaminase (TG) were used to modify fish gelatin (FG). Three types of modified gelatin groups FG-κC, FG-TG and FG-κC-TG were prepared. The results showed that the gel strength and textural properties of FG gels were greatly enhanced by κC modification and κC-TG complex modification, whilst pure TG modification weakened the gelling properties. And the pure 0.1 % κC modified FG had the highest gel strength and hardness, respectively. Rheological behavior showed that the complex modified FG samples had the highest viscosity, gelling points, melting points and G'∞. Fourier infrared spectra and LF-NMR analysis showed that κC and κC-TG modification respectively improved the contents of hydrogen and isopeptide that decreased the water mobility but stabilized the helical structure of gelatin gels. Fluorescence intensity showed that three types of modification decreased fluorescence intensity. While, the formation of aggregates and denser gel networks decreased in vitro digestibility of FG.

Ultrasonic-assisted glycosylation with κ-carrageenan on the functional and structural properties of fish gelatin

BACKGROUND

Fish gelatin (FG) has multifunctional properties similar to mammalian gelatin (MG), and it has been recognized as the optimal alternative to MG. While its poor surface-active and gelling properties significantly limit its application values, glycosylation has been successfully used to increase surface-active properties of FG, but the influence of ultrasonic-associated glycosylation (UAG) on the gelling and structural characteristics of FG is still rarely reported. This article explores UAG (100-200 W, 0.5-1 h) with κ-carrageenan (κC) on the functional properties (emulsifying, gelling and rheological properties) and structural characteristics of FG.

RESULTS

The longer time and higher power of ultrasonics accelerated the glycosylation reaction with an increase in glycosylation degree and browning index values. Compared with original FG, FG-κC mixture and bovine gelatin, UAG-modified FG possessed higher emulsification activity index, emulsion stability index, gel strength, hardness and melting temperature values. Among them, gelatin modified by appropriate ultrasonic conditions (200 W, 0.5 h) had the highest emulsifying and gelling properties. Rheological results showed that UAG contributed to the gelation process of gelatin with advanced gelation time and endowed it with high viscosity. Structural analysis indicated that UAG promoted κC to link with FG by the formation of covalent and hydrogen bonds, restricting more bound and immobilized water in the gels, exhibiting higher gelling properties.

CONCLUSION

This work showed that UAG with κC is a promising method to produce high gelling and emulsifying properties of FG that could replace MG. © 2023 Society of Chemical Industry.

Ultrasonic-Assisted Glycosylation with Glucose on the Functional and Structural Properties of Fish Gelatin

The effects of ultrasound-assisted glycosylation (UG) with glucose (GLU) on the emulsifying properties, foaming properties, gelling properties, and structural properties of fish gelatin (FG) were investigated. It was shown that UG with high power and a long duration facilitated the Maillard reaction through the reduction of the free amino acid contents. UG significantly improved the emulsifying ability index and foaming capacity of FG whilst decreasing the gel strength. Rheological analysis showed that UG modification prolonged the gelling time by hindering the triple-helix formation and decreasing the apparent viscosity of the gelatin solution. Structural analysis showed that UG treatment changed the secondary structure of the gelatin molecule by the formation of Millard reaction products (MRPs). Moreover, the UG treatment generally decreased the bound water contents of the gelatin gels with an increase in free water.

Microwave processing technology influences the functional and structural properties of fish gelatin

The objective of this study was to evaluate the effects of microwave processing technology (MPT, 240-800 W, 1 and 4 min) on the functional and structural properties of fish gelatin (FG). It showed that MPT could increase gel strength and texture properties of FG, especially for 240 W. MPT greatly increased emulsifying activity index (EAI) of FG, but decreased its emulsion stability index (ESI). Rheology results showed that MPT increased viscosity of FG, but decreased gelation times. Intrinsic fluorescence and Fourier transform infrared (FTIR) spectroscopy results indicated that MPT could unfold gelatin, contributing to the formation of H-bonds. Scanning electron microscopy (SEM) analysis revealed that low power and short time of MPT-treated gelatin gels had much more dense and less voids. This work provided guidance for the applications of MPT to improve the functional properties of FG, and the results show that MPT-treated FG can replace mammalian gelatin and meet the religious requirement.

The Structural and Functional Differences between Three Species of Fish Scale Gelatin and Pigskin Gelatin

In this paper, gelatin was extracted from the scales of Coregonus peled, Carp and Bighead carp by the acid method, and the structure and functional properties of the obtained scale gelatin and food-grade pigskin gelatin (FG) were compared. The results showed that all gelatins exhibited relatively high protein (86.81-93.61%), and low lipid (0.13-0.39%) and ash (0.37-1.99%) contents. FG had the highest gel strength, probably because of its high proline content (11.96%) and high average molecular weight distribution. Low β-antiparallel was beneficial to the stability of emulsion, which led FG to have the best emulsifying property. The high content of hydrophobic amino acids may be one of the reasons for the superior foaming property of Bighead carp scales gelatin (BCG). The gel strength of Carp scales gelatin (CG) and BCG, the ESI of Coregonus peled scales gelatin (CPG) and the foaming property of BCG indicate that fish gelatin has the potential to be used in food industry as a substitute for pig skin gelatin.

Phosphorylation modification on functional and structural properties of fish gelatin: The effects of phosphate contents

The gel, rheological and structural properties of fish gelatin (FG) were investigated through phosphorylation with different ratios of sodium pyrophosphate (TSPP) (FG:TSPP = 40:0, 40:1, 40:2, 40:4, and 40:6). It showed that phosphorylation modification significantly increased gel strength, textural properties, emulsification, and emulsification stability of FG. The surface hydrophobicity and intrinsic fluorescence of phosphorylated FG were also significantly increased. Rheological results revealed that the apparent viscosity, melt/gel points, and gel strength of FG were increased by phosphorylation with TSPP, but shortened the gelation time. Low field nuclear magnetic resonance (LF-NMR) showed that phosphorylation reduced mobility of water in FG. FTIR results indicated that phosphorylation increased the β-sheet/β-turn contents but reduced the random coil contents. This study might provide a new guideline for the exploration of TSPP phosphorylation increased the functional properties of FG.

Effect of carbon numbers and structures of monosaccharides on the glycosylation and emulsion stabilization ability of gelatin

Herein, the effect of saccharide glycosylation by nine monosaccharides on bovine bone gelatin for the stabilization of fish oil-loaded emulsions was explored. The gelatin modification was analyzed and then the emulsifying properties of monosaccharide-modified gelatins were analyzed at pH 9.0 and 3.0. The results demonstrated that glycosylated gelatin structure, droplet stability, creaming stability, and liquid-gel transition time were dependent on monosaccharide carbon numbers, monosaccharide structures, and solution pH. Glycosylation modification of gelatins did not obviously change the emulsion droplet stability at pH 9.0, whereas it increased the emulsion droplet stability at pH 3.0. Glycosylation modification of gelatins did not obviously change the emulsion creaming index values (5.1%-8.4% at pH 9.0 and 25.8%-33.1% at pH 3.0). Three-carbon and four-carbon monosaccharides glycosylation significantly increased emulsion liquid-gel transition times. This work provided useful information to understand the effects of carbon numbers and structures of monosaccharides on the protein modification.

Adding Humic Acids to Gelatin Hydrogels: A Way to Tune Gelation

Exploring the chance to convert biowaste into a valuable resource, this study tests the potential role of humic acids (HA), a class of multifunctional compounds obtained by oxidative decomposition of biomass, as physical agents to improve gelatin's mechanical and thermal properties. To this purpose, gelatin-HA aqueous samples were prepared at increasing HA content. HA/gelatin concentrations changed in the range 2.67-26.67 (wt/wt)%. Multiple techniques were employed to assess the influence of HA content on the gel properties and to unveil the underlying mechanisms. HAs increased gel strength up to a concentration of 13.33 (wt/wt)% and led to a weaker gel at higher concentrations. FT-IR and DSC results proved that HAs can establish noncovalent interactions through H-bonding with gelatin. Coagulation phenomena occur because of HA-gelatin interactions, and at concentrations greater than 13.33 (wt/wt)%, HAs established preferential bonds with water molecules, preventing them from coordinating with gelatin chains. These features were accompanied by a change in the secondary structure of gelatin, which lost the triple helix structure and exhibited an increase in the random coil conformation. Besides, higher HA weight content caused swelling phenomena due to HA water absorption, contributing to a weaker gel. The current findings may be useful to enable a better control of gelatin structures modified with composted biowaste, extending their exploitation for a large set of technological applications.

3D Printing of Shiitake Mushroom Incorporated with Gums as Dysphagia Diet

With the speeding tendency of aging society, the population experienced dysphagia is increasing quickly. Desirable dysphagic diets should be safe, visually appealing and nutritious. 3D printing allows for creation of personalized nutritious foods with regular-like appearance. Shiitake mushroom, rich in protein and bioactive compounds, is suitable for elderly, but its hard texture was not friendly to the elderly with dysphagia. This study investigated the feasibility of production of dysphagic product using shiitake mushroom by 3D printing with various gums addition, including arabic gum (AG), xanthan gum (XG) and k-carrageenan gum (KG) at concentrations of 0.3%, 0.6% and 0.9% (w/w). Data suggested that XG and KG incorporation significantly increased inks’ mechanical strength by decreasing water mobility and promoting the formation of hydrogen bond, enabling 3D printed objects with great self-supporting capacity. The XG containing and KG-0.3% samples were categorized into level 5—minced and moist dysphagia diet within international dysphagia diet standardization initiative (IDDSI) framework. AG addition decreased mechanical strength and viscosity, hardness and self-supporting capacity of 3D printed constructions. AG-0.3% and AG-0.6% samples could not be classified as dysphagia diets based on IDDSI tests. This study provides useful information for dysphagia diet development with appealing appearance by 3D printing.

Rheological properties and interactions of fish gelatin-κ-carrageenan polyelectrolyte hydrogels: The effects of salt

This study mainly explored the effects of low-concentration salts (0.1, 0.5 mM NaCl and Na₂ SO₄ ) on the gel, rheological and structural properties of fish gelatin (FG)-κ-carrageenan (κC) polyelectrolyte hydrogels. The results showed that κC could increase the gel strength, hardness, and chewiness of the FG-κC polyelectrolyte hydrogels, while the addition of salts had a negative effect. The rheological behaviors showed that the addition of salts reduced the apparent viscosity, gel, and melting points of the FG-κC polyelectrolyte hydrogels. Compared with NaCl, Na₂ SO₄ -treated FG-κC had lower gel strength, hardness, viscosity, gelation, and melting points, while the addition of salts increased the fluorescence intensity by unfolding FG molecules. The secondary structure analysis results showed that the addition of NaCl and Na₂ SO₄ decreased α-helix and β-sheet contents of FG-κC by destroying the hydrogen bond of FG-κC.

Reversibility of the gel, rheological, and structural properties of alcohol pretreated fish gelatin: Effect of alcohol types

The reversibility of gel property of alcohol (methanol, ethanol)-pretreated fish gelatin (FG) were investigated through removing alcohol solutions by freeze drying. Results showed that the gel strength and the hardness of FG could be retained (1%, 40%) or even improved (1% methanol) using low or high concentration alcohol solutions, while decreased in medium concentration alcohol solutions. Compared with untreated FG, rheology results showed that, all alcohol solutions pretreated FG had lower apparent viscosity, while higher alcohol solutions pretreated ones decreased the gel and melt points and shorten the gelation time. Sodium dodecyl-sulfate polyacrylamide gel electrophoresis showed that methanol pretreated FG had the higher α contents than those of ethanol pretreated. Circular dichroism spectra results indicated that β-sheet could be decreased after removing ethanol solutions, whereas the β-sheet increased after removing the methanol solutions. Moreover, low field nuclear magnetic resonance relaxation test showed that pretreated FG had lower transverse relaxation times of internal water (T₂₁ and T₂₂ ) compared to that of the untreated FG. Overall, FG still retains higher gel properties after removing the low or high alcohol concentrations.

Silver carp scale gelatins for the stabilization of fish oil-loaded emulsions

Herein, three types of silver carp scale gelatins were extracted, and their molecular weight distribution, structural properties, functional properties and emulsifying properties were investigated and discussed. Acetic acid-extracted gelatin (AAG), hot water-extracted gelatin (HWG), and pepsin enzyme-extracted gelatin (PEG) showed similar and four clear bands in sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern, whereas they showed different β chain amounts and β-sheet percentages. The water-holding capacity values (g/g of gelatin) were: AAG (16.8 ± 1.1) > HWG (14.0 ± 0.7) ≈ PEG (13.5 ± 1.6). The fat-binding capacity values (g/g of gelatin) were: AAG (11.8 ± 0.3) > HWG (9.5 ± 1.3) > PEG (5.3 ± 0.4). Emulsion droplet sizes and creaming index values decreased with the increase of gelatin concentrations for all the fish oil-loaded emulsions stabilized by three types of gelatins. Compared with PEG, AAG and HWG show similar and higher emulsion stability at high gelatin concentration (10 mg/mL). The stabilization mechanism of fish oil-loaded silver carp scale gelatin-stabilized emulsions involved an "extraction method-protein molecular weight distribution-protein molecular structure-molecular interaction-emulsibility-droplet structure-emulsion stability" route. This work would be beneficial for the research on the relationship of structure and function of gelatin and to the comprehensive utilization of aquatic products.