Relating the variation of secondary structure of gelatin at fish oil–water interface to adsorption kinetics, dynamic interfacial tension and emulsion stability

Enzymatically produced acylglycerol and glycerin monostearate additives improved the characteristics of gelatin-stabilized omega-3 emulsions and microcapsules

The impacts of enzymatically produced acylglycerol and glycerin monostearate on the characteristics of gelatin-stabilized omega-3 emulsions and microcapsules were investigated. Tuna oil was enzymatically produced and the resulting acylglycerol was mixed with tuna oil at 12.5% (w/w) to prepare a novel oil phase. This oil phase was stabilized by gelatin to prepare oil-in-water emulsions and subsequent microcapsules via complex coacervation. The tuna oil with glycerin monostearate (GMS) at 1 and 2% (w/w) were used as controls. Results showed that both acylglycerol and GMS significantly reduced the emulsion droplet size and zeta potential, while increasing the viscoelasticity and stability. The diacylglycerol/monoacylglycerol were involved in the oil/water interfacial layer formation by lowering interfacial tension and increasing droplet surface hydrophobicity. Overall, the changed emulsion properties promoted the complex coacervation and contributed to the formation of microcapsules with improved oxidative stability. Therefore, enzymatically produced acylglycerol can develop high-quality stable omega-3 microencapsulated novel food ingredients.

Synergistic effects of phosphorylation modification and protocatechuic acid copolymerization improve the physical and oxidation stability of high internal phase emulsion stabilized by perilla protein isolate

A compact antioxidant interfacial layer was fabricated by combining phosphorylation treatment with protocatechuic acid (PA) copolymerization to enhance the physical and oxidative stability of high internal phase emulsions (HIPEs) prepared using perilla protein isolate (PPI). The covalent binding between PPI and phosphate groups induced conformational changes, facilitating the interaction between PPI and PA. The formed phosphorylated PPI-PA conjugates (LPPI-PA) exhibited a reduced particle size of 196.75 nm, promoting their adsorption at the interface. HIPEs prepared by LPPI-PA conjugates showed higher storage stability due to decreased droplet size, increased interfacial protein adsorption content (90.48%), and the formation of an interconnected network within the system. Additionally, the combination of LPPI and PA anchored PA to the interface, significantly inhibiting lipid oxidation in HIPEs as evidenced by low levels of lipid hydroperoxide (30.33 μmol/g oil) and malondialdehyde (379.34 nmol/g oil). This study holds significant implications for improving the stability of HIPEs.

Effects of maltodextrin and protein hydrolysate extracted from lotus seed peel powder on the fat substitution and lipid oxidation of lotus seed paste

The fat substitution of maltodextrin from lotus seed peel powder (LSP-MD) and the lipid oxidation inhibitory effect of protein hydrolysate (LSP-PH) on lotus seed paste were investigated in this study. The LSP-MD with a dextrose equivalent value of 2.28 showed the smallest specific volume, strongest water-holding capacity and retrogradation. This LSP-MD effectively maintained the sensory quality, hardness and elasticity of low-fat lotus seed paste during storage at 25 °C. For protein hydrolysate, LSP-PH with a hydrolyzation degree of 13.45 % had the strongest DPPH· scavenging capacity and ferric reducing antioxidant power, which was further confirmed by FTIR spectra that enzymatic hydrolysis of LSP protein could facilitate the transformation of β-sheet into β-turn. Following 15 days of storage, supplementation with 0.5 % LSP-PH reduced the peroxide value and acid value of lotus seed paste, suggesting its excellent inhibitory effect on lipid peroxidation via interacting with hydrophobic polyunsaturated fatty acids.

Structural and physicochemical properties of the different ultrasound frequency modified Qingke protein

There is a burgeoning demand for modified plant-based proteins with desirable physicochemical and functional properties. The cereal Qingke is a promising alternative protein source, but its use has been limited by its imperfect functional characteristics. To investigate the effect of ultrasound treatment on Qingke protein, we applied single- (40 kHz), dual- (28/40 kHz), and tri- (28/40/50 kHz) frequency ultrasound on the isolated protein and measured subsequent physicochemical and structural changes. The results showed that the physicochemical properties of proteins were modified following ultrasound treatment, and many of these changes significantly increased with increasing frequency. Compared with the native Qingke protein (control), the solubility, foaming activity, stability, and water or oil holding capacity of tri-frequency ultrasound modified Qingke protein increased by 43.54%, 20.83%, 20.51%, 28.9%, and 45.2%, respectively. Furthermore, ultrasound treatment altered the secondary and tertiary structures of the protein resulting in more exposed chromophoric groups and inner hydrophobic groups, as well as reduced β-sheets and increasedrandom coils, relative to the control. Rheological and texture characterization indicated that the values of G' and G'', hardness, gumminess, and chewiness decreased after ultrasound treatment. This study could provide a theoretical basis for the application of multi-frequency ultrasonic technology for modification of Qingke protein to expand its potential use as an alternative protein source.

Effect of multiple-frequency ultrasound-assisted transglutaminase dual modification on the structural, functional characteristics and application of Qingke protein

Qingke protein rich in restricted amino acids such as lysine, while the uncoordination of ratio of glutenin and gliadin in Qingke protein has a negative impact on its processing properties. In this study, the effect of multiple-frequency ultrasound combined with transglutaminase treatment on the functional and structural properties of Qingke protein and its application in noodle manufacture were investigated. The results showed that compared with the control, ultrasound-assisted transglutaminase dual modification significantly increased the water and oil holding capacity, apparent viscosity, foaming ability, and emulsifying activity index of Qingke protein, which exhibited a higher storage modulus G' (P < 0.05). Meanwhile, ultrasound combined with transglutaminase treatment enhanced the cross-linking degree of Qingke protein (P < 0.05), as shown by decreased free amino group and free sulfhydryl group contents, and increased disulfide bond content. Moreover, after the ultrasound-assisted transglutaminase dual modification treatment, the fluorescence intensity, the contents of α-helix and random coil in the secondary structure of Qingke protein significantly decreased, while the β-sheet content increased (P < 0.05) compared with control. SDS-PAGE results showed that the bands of Qingke protein treated by ultrasound combined with transglutaminase became unclear. Furthermore, the quality of Qingke noodles made with Qingke powder (140 g/kg dual modified Qingke protein mixed with 860 g/kg extracted Qingke starch) and wheat gluten 60-70 g/kg was similar to that of wheat noodles. In summary, multiple-frequency ultrasound combined with transglutaminase dual modification can significantly improve the physicochemical properties of Qingke protein and the modified Qingke proteins can be used as novel ingredients for Qingke noodles.

Flavor mechanism of micro-nanoparticles and correlation analysis between flavor substances in thermoultrasonic treated fishbone soup

To study the physicochemical properties of micro-nanoparticles (MNPs) in thermoultrasonic treated fishbone soup, it was subjected to ultra-filtration with a 100 kDa ultrafiltration membrane to obtain large MNPs (LMNPs) and small MNPs (SMNPs). LMNPs and SMNPs were treated with force-breakers, and the interactions of the MNPs with five characteristic volatile compounds were investigated. LMNPs covered most proteins (222.66 mg/mL) and fatty acids (363.76 mg/g), while SMNPs was mostly soluble small molecules with taste substances like total free amino acids (85.26 mg/g), organic acids (2.55 mg/mL), and 5'-nucleotides (169.17 mg/100 mL). The stability of LMNPs is significantly higher than raw bone soup, and SMNPs can exist stably in the solution. Correlation analysis between flavor substance content and flavor suggested that the overall flavor profile of halibut bone soup was closely related to the content changes of 72 significant influence variables. The binding of LMNPs to characteristic flavor compounds was largely affected by hydrophobic interactions, hydrogen bonds, and ionic effects. While the binding of SMNPs to characteristic flavor compounds was largely determined by hydrophobic interaction and hydrogen bonding. This study explores the characteristics of MNPs and provides the possibility to clarify the interaction mechanism between MNPs and flavor.

Characterization of Tenebrio molitor Larvae Protein Preparations Obtained by Different Extraction Approaches

Edible insects have recently attracted research attention due to their nutritional value and low environmental footprint. Tenebrio molitor larva was the first insect species to be classified by European Food Safety Authority (EFSA) as safe for human consumption. However, it is thought that the incorporation of edible insect as an ingredient in a food product would be more appealing to consumers than being visible. The aim of the present study was to determine the physicochemical properties of the larvae meal and protein concentrates. Different methods to extract and recover proteins from defatted (DF) Tenebrio molitor larvae were applied; i.e., alkaline extraction (DF-ASP); isoelectric precipitation after alkaline extraction (DF-AIP); and NaCl treatment (DF-SSP), and the obtained protein fractions were characterized. The DF-ASP exhibited the highest protein extraction/recovery efficiency (>60%), while it was the most effective in decreasing the interfacial tension at the oil/water (o/w) interface. The DF-AIP had the highest protein content (75.1%) and absolute values of ζ-potential and the best ability to retain water (10.54 g/g) and stabilize emulsions at pH 3.0. The DF-SSP protein preparation had the highest oil binding capacity (8.62%) and solubility (~88%) at acidic pHs and the highest emulsifying activity (~86 m2/g). Electrophoresis of the protein preparations revealed proteins with different molecular weights, while the protein secondary structure was dominated by β-structures and α-helix. Protein concentrates with different properties were able to be recovered from Tenebrio molitor larvae, that could affect their interactions with other food ingredients and their behavior during processing or storage. These findings would be valuable guidance for the technological exploitation of larvae protein preparations in the development of food formulations.

Single-Chain Mechanical Properties of Gelatin: A Single-Molecule Study

Gelatin is an important natural biological resource with a wide range of applications in the pharmaceutical, industrial and food industries. We investigated the single-chain behaviors of gelatin by atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS), and found that gelatin exists as long chains by fitting with the M-FJC model. By comparing the single-chain elasticity in a nonpolar organic solvent (nonane) and DI water, it was surprising to find that there was almost no difference in the single-chain elasticity of gelatin in nonane and DI water. Considering the specificity of gelatin solubility and the solvent size effect of nonane molecules, when a single gelatin chain is pulled into loose nonane, dehydration does not occur due to strong binding water interactions. Gelatin chains can only interact with water molecules at high temperatures; therefore, no further interaction of single gelatin chains with water molecules occurred at the experimental temperature. This eventually led to almost no difference in the single-chain F-E curves under the two conditions. It is expected that our study will enable the deep exploration of the interaction between water molecules and gelatin and provide a theoretical basis and experimental foundation for the design of gelatin-based materials with more functionalities.

Improvement of O/W emulsion performance by adjusting the interaction between gelatin and bacterial cellulose nanofibrils

This study was designed to improve the stability of medium internal phase emulsion by adjusting the electrostatic interaction between gelatin (GLT) and TEMPO-oxidized bacterial cellulose nanofibrils (TOBC). The influences of polysaccharide-protein ratio (1:10, 1:5, and 1:2.5) and pH (3.0, 4.7, 7.0, and 11.0) on the emulsion properties were investigated. The droplet size of TOBC/GLT-stabilized emulsion was increased with the TOBC proportion increasing at pH 3.0-11.0. Additionally, emulsion had a larger droplet size at pH 4.7 (the electrical equivalence point pH of mixtures). However, the addition of TOBC significantly improved the emulsion stability. The emulsions prepared with TOBC/GLT mixtures (mixing ratio of 1:2.5) at pH 3.0-7.0 were stable without creaming during the storage. It was because the formation of nanofibrils network impeded the droplet mobility, and the emulsion viscosity and viscoelastic modulus were increased with the addition of TOBC. These findings were meaningful to modulate the physical properties of emulsions.

Impact of Type of Sugar Beet Pectin-Sodium Caseinate Interaction on Emulsion Properties at pH 4.5 and pH 7

Equal parts of sugar beet pectin and sodium caseinate were interacted through electrostatic attraction, enzymatic crosslinking, and the Maillard reaction to prepare three oil-in-water emulsifier systems. Oil-in-water emulsions (10%) were processed via high shear overhead mixing at the natural pH of the emulsifier systems, followed by pH adjustment to pH 4.5 and pH 7. The emulsions were stable against coalescence, except for a slight increase in the mean droplet size for the enzymatic cross-liked emulsion at pH 4.5 over a 14-day storage period. This emulsion also showed the lowest absolute zeta (ζ)-potential value of near 30 mV. The Maillard interaction emulsifier system resulted in larger droplet sizes compared to the other two emulsifier systems. Small deformation oscillatory shear rheology assessment of the emulsion cream phases revealed an impact of the emulsifier system design at pH 4.5.

Investigation of enhanced oxidation stability of microencapsulated enzymatically produced tuna oil concentrates using complex coacervation

Tuna oil was selectively hydrolysed using Thermomyces lanuginosus lipase for 6 h to prepare omega-3 acylglycerol concentrate with the DHA content significantly increased from 24.9% in tuna oil to 36.3% in the acylglycerol concentrate. The acylglycerol concentrate was subsequently encapsulated into the "multi-core" microcapsules using gelatin-sodium hexametaphosphate complex coacervates as the shell material. Rancimat, Oxipres and thermogravimetric analyses all showed that the microencapsulated acylglycerol concentrate had unexpectedly improved oxidation stability, compared to those produced using tuna oil, even though the concentrated oils themselves were significantly less stable than tuna oil. The incorporation of enzymatic tuna oil acylglycerol concentrate also significantly improved the oxidation stability of microencapsulated standard refined unconcentrated tuna oil. A wide range of characteristics including lipid and fatty acid composition, oil-in-water (O/W) emulsion properties, morphology, nanomechanical strength and physicochemical stability of acylglycerol, acylglycerol oil-in-water (O/W) emulsion and final microcapsules were investigated throughout the preparation. The result suggests that high levels of monoacylglycerol (about 35%) and diacylglycerol (about 8.5%) were produced in the acylglycerol. The acylglycerol O/W emulsion exhibited significantly smaller droplet size, lower zeta-potential and higher surface hydrophobicity, which contributed to the formation of the microcapsule with a significantly smoother surface and more compact structure, finally leading to improved oxidative stability compared to those prepared from native tuna oil.

Physical Stability of Oil-In-Water Emulsion Stabilized by Gelatin from Saithe (Pollachius virens) Skin

The objective of the present study was to investigate the physical stability of an oil-in-water (O/W) emulsion stabilized with gelatin from saithe (Pollachius virens) skin obtained with three different extraction protocols compared to two commercial fish skin gelatins. We first investigated the gelatin powder composition, and then produced the O/W emulsions at pH 3 by mechanical dispersion followed by an ultrasonication process. Sodium dodecyl sulfate (SDS) profiles for commercial samples indicated that extensive and unspecific hydrolysis of collagen occurred during the production process, whereas gelatin extracted from saithe fish skin showed typical electrophoresis patterns of type I collagen, with the presence of γ- and β-chains. Emulsions obtained with commercial samples presented high physical stability over 7 days, with particle size of ~200 nm. However, emulsions obtained with saithe fish skin presented particle size between 300 and 450 nm. Slight differences were observed in viscosity, with values between ~1 and ~4 mPa·s. Interfacial tension measurements presented values between 13 and 17 mN·m-1 with three different regimes for all the systems.

Effect of multi-frequency power ultrasound (MFPU) treatment on enzyme hydrolysis of casein

Effect of multi-frequency power ultrasound (MFPU) pretreatments on the degree of hydrolysis (DH) and mechanism of casein during alcalase enzymolysis was investigated. Results showed that MFPU pretreatment in tri-frequency 20/40/60 kHz mode significantly (p < 0.05) improved the DH value of casein. Variation of intrinsic fluorescence spectrum indicated the unfolding and degradation of casein occurred after MFPU pretreatment. Fourier transform infrared spectra showed that α-helix and β-sheet content of MFPU pretreated casein decreased, while β-turn and random coil content increased. Surface topography and nanostructures of caseins were found modified after MFPU pretreatments by the analysis of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM analysis also indicated that the enzymolysis residues of casein pretreated by MFPU were smaller than untreated samples. In conclusion, the MFPU can be used as an efficient pretreatment method to promote the enzymolysis of casein.

Performance of oil-in-water emulsions stabilized by different types of surface-active components

The emulsion stability depends on the physicochemical properties of the dispersed phase and their interaction with the continuous phase. Surface-active compounds (SAC) are added in emulsions to reduce the interfacial tension (IT) between these phases and keep the oil droplets stabilized. Moreover, small amounts of SAC can occupy intermolecular voids in the dried matrix, reducing the oxidation. However, the formulation must reflect a trade-off between protection and emulsion stabilization. Therefore, this work aimed to identify the minimum concentration of SAC (modified starch-MS, gelatin-GE, and whey protein isolate-WPI) ranging from 0.48 to 6 % (w/w) to form and stabilize droplets of an unsaturated triglyceride (fish oil-FO) or a volatile oil (orange essential oil-OEO). GE did not change the IT (6.7 mN/m) and stabilized the emulsions only through an increase of the viscosity (∼42 mPas for FO-emulsions and ∼97 mPas for OEO-emulsions), presenting high droplet size (∼10 μm) and low surface charge (∼1.5 mV). WPI reduced the IT to a limit value (4.5 mN/m at 1.2 % w/w for OEO and 5.3 mN/m at 2.4 % w/w for FO), whereas MS reduce constantly the IT with the increase of the concentration for both oils (∼4.2 mN/m at 6 % w/w). Both WPI and MS-emulsions presented similar droplet size (∼2.0 μm), but WPI presented higher surface charge of WPI-emulsions (-45 mV) than MS-emulsions (-30 mV). This study allowed to gain a consistent understanding of structure-property relationships on the use of SAC in emulsions.

Investigating the Mechanism for the Enhanced Oxidation Stability of Microencapsulated Omega-3 Concentrates

Enzymatically concentrated anchovy oil (concentrate) is known to be much less stable than unconcentrated anchovy oil. However, we previously showed that concentrate surprisingly forms more stable microcapsules, when produced by complex coacervation, than does unconcentrated anchovy oil. Here we investigate the mechanism of this unexpected stability. We also investigate whether or not incorporation of concentrate can be used as an additive to improve the stability of unconcentrated anchovy oil microcapsules. Results showed that microcap stability increased as the amount of added concentrate increased. Decreased emulsion droplet size, lower positively charged zeta potential, and higher surface hydrophobicity were observed in the oil/water (O/W) emulsion, with the incorporation of concentrate in the oil phase, compared with the unconcentrated anchovy oil O/W emulsion. Both the decreased zeta potential and the increased hydrophobicity of concentrate in the mixed oil phase may improve droplet agglomeration, leading to enhanced oxidative stability of the concentrate-containing microcapsules. Decreased repulsive forces between droplets result in a more compact structure, thicker outer shell, and smoother surface, resulting in enhanced oxidation stability of the concentrate-containing microcapsules.

Identification and characterization of the proteins in broth of stewed traditional Chinese yellow-feathered chickens

Soups and broths are popular in the world due to their nutrition and flavor, and flavor compounds tend to be bound by the proteins in the soups and broth, influencing the flavor perception. Thus, identification of the major proteins in meat-based broth may present a basis for understanding protein adsorption of flavor compounds. The present study aimed to identify the major proteins in traditional Chinese chicken broth and to describe the structural changes of proteins during stewing (1, 2, or 3 h). As stewing time increased, protein content in the broth significantly increased. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) indicated that the macro-molecule proteins (>10 kDa) in the broth were mainly gelatin and actin and that the micro-molecule proteins fractions (<10 kDa) increased substantially. The gelatin had an ordered structure even after 3 h of stewing, as seen by circular dichroism (CD) spectroscopy. The presence of reactive sulfhydryl groups increased remarkably with stewing time. The surface hydrophobicity of the proteins significantly increased within 2 h then deceased slightly after 3 h. The intermolecular crosslinks, as indicated by dispersion index, increased remarkably, consistent with the result of atomic force microscopy (AFM), which together suggested that protein aggregation increased during stewing. These findings suggested that gelatin was the structural protein in the broth system and that intermolecular crosslinks functioned to maintain the broth system.

Egg Albumen as a Fast and Strong Medical Adhesive Glue

Sutures penetrate tissues to close wounds. This process leads to inflammatory responses, prolongs healing time, and increases operation complexity. It becomes even worse when sutures are applied to stress-sensitive and fragile tissues. By bonding tissues via forming covalent bonds, some medical adhesives are not convenient to be used by surgeons and have side effects to the tissues. Here egg albumen adhesive (EAA) is reported with ultrahigh adhesive strength to bond various types of materials and can be easily used without any chemical and physical modifications. Compared with several commercial medical glues, EAA exhibits stronger adhesive property on porcine skin, glass, polydimethylsiloxane. The EAA also shows exceptional underwater adhesive strength. Finally, wound closure using EAA on poly(caprolactone) nanofibrous sheet and general sutures is investigated and compared in a rat wound model. EAA also does not show strong long-term inflammatory response, suggesting that EAA has potential as a medical glue, considering its abundant source, simple fabrication process, inherent nontoxicity, and low cost.

On the importance of Bloom number of gelatin to the development of biodegradable in situ gelling copolymers for intracameral drug delivery

To overcome the drawbacks associated with conventional antiglaucoma eye drops, this work demonstrated the feasibility of an effective alternative strategy to administer pilocarpine directly via intracameral injections of drug-containing biodegradable in situ gelling GN copolymers composed of gelatin and poly(N-isopropylacrylamide). Specifically, this study aims to understand the importance of Bloom number of gelatin, a physicochemical parameter, to the development of GN carriers for intracameral drug delivery in glaucoma therapy. Our results showed that both imino acid and triple-helix contents increased with increasing Bloom index from 75-100 to 300. The drug encapsulation efficiency in response to temperature-triggered phase transition in GN copolymers was affected by the Bloom index of gelatin. In addition, the differences in protein secondary structure significantly influenced the degradation rates of GN carriers, which were highly correlated with drug release profiles. The increase in released pilocarpine concentration led to a high intracellular calcium level in rabbit ciliary smooth muscle cell cultures, indicating a beneficial pharmacological response to a drug. Irrespective of Bloom number of gelatin, all carrier materials exhibited excellent in vitro and in vivo biocompatibility with corneal endothelium. In a glaucomatous rabbit model, intracameral injections of pilocarpine-containing GN synthesized from gelatins with various Bloom numbers had different abilities to improve ocular hypertension and induce pupillary constriction, indicating distinct antiglaucoma efficacies due to in vivo drug release. It is concluded that the effects on pharmacological treatment using GN carriers for intracameral pilocarpine administration demonstrate a strong dependence on the Bloom number of gelatin.