Influence of extreme alkaline pH induced unfolding and aggregation on PSE-like chicken protein edible film formation

Antioxidant and antimicrobial PSE-like chicken protein isolate films loaded with oregano essential oil nanoemulsion for pork preservation

The oregano essential oil (OEO) nanoemulsion was prepared, and the effects of different added amounts of OEO nanoemulsion on the mechanical and antibacterial properties of PSE-like chicken protein isolate (PPI) film were investigated. Results revealed that the nanoemulsion containing 12 % Tween 80 and 6 % OEO had the smallest particle size (82.46 nm) and the best stability. Compared to the control group, the film of the PPI/OEO-2.5 % treatment group demonstrated superior mechanical properties. With the increase of the concentration of OEO nanoemulsion, the UV transmittance and water contact angle of the films decreased gradually (more hydrophilic), the opacity and water vapor permeability significantly increased, while the thermal stability, antioxidant properties (DPPH scavenging activity, 17.07 % ∼ 56.00 %), and antibacterial properties were markedly enhanced. The PPI/OEO-2.5 % treated film was applied to the preservation of pork, extending the shelf life by 2-4 days. These findings suggested that PPI had great application potential in bioactive packaging materials.

Formation of molecularly imprinted polymers: Strategies applied for the removal of protein template (review)

The key step in the entire molecularly imprinted polymer (MIP) preparation process is the formation of the complementary cavities in the polymer matrix through the template removal process. The template is removed using chemical treatments, leaving behind selective binding sites for target molecules within the polymer matrix. Other MIP preparation steps include mixing monomers and template molecules in the appropriate solvent(s), monomer-template complex equilibration, and polymerisation of the monomers around the template. However, template removal is the most important among all the preparation steps because the final structure, which can be accepted and recognised as the MIP, is obtained only after the template removal. A thorough analysis of the studies dedicated to MIP applications demonstrates that this MIP preparation step, namely the template removal, is relatively understudied. MIP template removal is especially challenging in the synthesis, where the molecular template is a macromolecule such as a protein. This review aims to provide a deliberate, systematic, and consistent overview of protein removal as the MIP template molecules. The most prevalent template removal methods are outlined for removing protein templates from electrochemically synthesised MIPs, particularly thin layers on electrodes used in electrochemical sensors. Five protein template removal approaches involving chemical treatment are highlighted, which include the utilisation of (i) chaotropic agents, (ii) salt, (iii) acidic cleavage, (iv) alkaline, and finally, (v) proteolytic treatment focusing on studies conducted over the past decade. In addition, we discuss the interactions driving the removal of protein templates in each approach and associated challenges. This review provides insights into MIPs protein template removal strategies while highlighting the prevalent issue of this understudied step of template removal.

Effects of plasma-activated water on structural and functional properties of PSE-like chicken protein isolate

Pale, soft and exudative (PSE)-like chicken meat is rich in high-quality proteins, however, due to the properties of PSE-like meat, the functional characteristics of PSE-like chicken meat protein isolate (PPI) are affected. The present investigation aimed to improve the functional properties of PPI by employing plasma activation water (PAW), with the ultimate goal of enhancing its utility in various applications. The effects of PAW on the structure and function of PPI were evaluated. PAW treatment induced the protein structure to change from random coil to α-helix, which made the protein conformation more stable. PAW caused the hydrophobic residues to be exposed, thereby effectively enhancing their surface hydrophobicity. Dynamic rheology revealed the storage modulus of PPI gradually raised with increasing of PAW activation time. The scanning electron microscopy (SEM) showed that PAW promoted PPI to form a rough surface. When PAW activation time increased to 40 s, the foaming ability of PPI was raised by 77.84%, the emulsifying activity index was increased to 20.94 m2/g, the emulsion stability index was improved by 20.40%, and the in vitro digestibility was increased by 25.15% (P < 0.05). The above results showed PAW could modify the structural properties, and effectively improve the emulsifying and foaming properties of PPI, and increase the in vitro digestibility of PPI.

Unveiling differential impact of heat and microwave extraction treatments on the structure, functionality, and digestibility of jack bean proteins extracted under varying extraction pH

The poor extractability and digestibility of jack beans restrict their application in food systems. Thermal treatment could be a processing tool to disrupt the compact conformation of the plant matrix and inactivate inherent antinutrients. Therefore, this research investigated the impact of conventional heat-aided (HA-) and microwave-aided (MA-) extraction treatments on the structure, functional properties, and digestibility of jack bean protein concentrate (JBPC) under varying extraction pH. The novelty brought by the present study is establishing the thermal treatment/extraction pH combinations for improving techno-functionalities and digestibility of JBPC. Heat (50 °C for 1 h) and sequential microwave power (400 W, 600 W, and 800 W for 5 min) at three extraction pH (9.0, 10.0, and 11.0) were studied. Upon increasing extraction pH, a significant decrease in the protein content, and β-Sheet structure was observed, in the order of pH 11.0 > 10.0 > 9.0. JBPC extracted using HA treatments displayed the highest contents of surface hydrophobicity (90.02) and sulfhydryl groups. In functional properties, MA-extracted JBPC under 400 W showed significantly improved solubility (93.45 %), emulsifying activity index (45.23 m2/g), and foaming capacity (141.70 %) when compared to other thermal treatments. The degree of hydrolysis result revealed that MA treatment improved the JBPC in vitro digestibility at a low power level of 400 W. These findings suggest that MA extraction treatment can improve the functional and nutritional properties of JBPC regardless of the extraction pH, and thus, expand the potential application in food systems.

Extrusion modification of prolamins from distiller's grains to facilitate the construction of biopolymer films

BACKGROUND

Distiller's grains (DGs), which are rich in natural ingredients such as prolamins, are often used as low-value feed or discarded directly, resulting in great environmental pollution and resource waste. Prolamins from DGs (PDGs) were found to be a potential material for the construction of biopolymer films due to their good film-forming properties. In this study, extrusion processing was conducted to modify the physicochemical and structural properties of PDGs to facilitate the construction of biopolymer films with superior characteristics.

RESULTS

Results indicated that extrusion led to improved solubility (17.91% to 39.95%) and increased disulfide bonds (1.46 to 6.13 μmol g-1) in PDGs. The total and sulfur amino acid contents of extruded PDGs were increased by 13.26% and 38.83%, respectively. New aggregation patterns were formed after extrusion according to the results of scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Extrusion resulted in reduced surface hydrophobicity of PDGs (10 972 to 3632), sufficient evidence for which could be also found from structure analyses of PDGs. Finally, PDGs extruded at 110 °C were found to facilitate the forming of biopolymer films with superior mechanical properties, water resistance and thermal stability.

CONCLUSIONS

Physicochemical and structural properties of PDGs were effectively modified by extrusion processing, and extrusion modification of PDGs could be a great way to facilitate the construction of biopolymer films with superior characteristics. It could provide more possibilities to extend the applications of DGs to alleviate the problems of environmental pollution and resource waste. © 2024 Society of Chemical Industry.

Water extractability of the zinc protoporphyrin IX-myoglobin complex from Parma ham is pH-dependent

The bright red color of Parma ham is mainly derived from zinc protoporphyrin IX (ZnPP), which exists in both water-soluble and insoluble states. Water-soluble ZnPP mainly binds to hemoglobin, however, the presence of water-insoluble ZnPP remains unexplained. Therefore, we aimed to elucidate how ZnPP exists in a water-insoluble state by focusing on its binding substance. Depending on the skeletal muscle, water-insoluble ZnPP comprised 30-50% of total ZnPP. The ZnPP water extractability was positively correlated with muscle pH. Water-insoluble ZnPP was extractable with a high-pH solution and existed as a complex with myoglobin or hemoglobin; nevertheless, myoglobin-binding ZnPP was more abundant. Furthermore, the water solubility of the myoglobin globin moiety at pH 5.5-6.0 was reduced by ZnPP binding. These results suggest that water-insoluble ZnPP mainly exists as a ZnPP-Mb complex, with low solubility attributed to the low pH of the ham.

Physico-Chemical Characteristics of pH-Driven Active Film Loading with Curcumin Based on the Egg White Protein and Sodium Alginate Matrices

The low solubility and stability of fat-soluble curcumin in water limit its application in active packaging. This study explored the use of a pH-driven method to investigate the preparation and enhancement of the performance of films loaded with curcumin in a matrix of sodium alginate (Alg) and egg white protein (EWP). In this study, the EWP, Alg, and curcumin primarily bind through hydrogen bonding, electrostatic interactions, and hydrophobic interactions. Compared to EWP films, the films loaded with curcumin through the pH-driven method exhibited enhanced extensibility and water resistance, with an elongation at break (EB) of 103.56 ± 3.13% and a water vapor permeability (WVP) of 1.67 ± 0.03 × 10-10 g·m/m2·Pa·s. The addition of Alg improved the encapsulation efficiency and thermal stability of curcumin, thereby enhancing the antioxidant activity of the film through the addition of 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radicals, which resulted in 106.95 ± 2.61 μg TE/g and 144.44 ± 8.89 μg TE/g, respectively. It is noteworthy that the detrimental effect of Alg on the color responsiveness of films containing curcumin has also been observed. This study provides a potential strategy and consideration for the loading of low water-soluble active substances and the preparation of active packaging.

Application of hydroxypropyl methylcellulose to improve the wettability of chitosan coating and its preservation performance on tangerine fruits

Hydroxypropyl methylcellulose (HPMC) was employed as an intermediate layer to enhance interfacial interaction between chitosan (CS) coating and tangerine fruits, thereby improving the preservation effect. Owing to the low surface tension of tangerine fruit (26.04 mN/m), CS coating solutions showed poor wetting properties on fruit peels (contact angle > 100°). However, by applying a 1.0 % (w/v) HPMC coating on fruits, the contact angle of CS solutions with concentrations of 0.5 %, 1.0 %, and 1.5 % (w/v) decreased to 47.0°, 47.4°, and 48.5°, respectively, whereas the spreading coefficient increased to -16.0 mN/m, -17.6 mN/m and -19.8 mN/m, respectively. Subsequently, the effects of the coatings on fruit quality were investigated. The results demonstrated the promising performance of HPMC-CS two-layer coating in inhibiting fruit respiration, reducing decay rate, and maintaining nutrient content. Notably, HPMC-1.5%CS coating not only reduced the decay rate of tangerine fruit by 45 % and 31 %, in comparison to the uncoated group (CK) and pure CS coating respectively, but also maintained a high content of ascorbic acid. Therefore, this study confirmed that the use of amphiphilic polymers for improving the surface properties of fruits can effectively facilitate the wetting of hydrophilic coatings on fruits, and significantly improve the fresh-keeping performance of edible coatings.

Ternary composite degradable plastics based on Alpinia galanga essential oil Pickering emulsion templates: A potential multifunctional active packaging

To reduce the use of petroleum-based plastics and explore multifunctional plastics, this study was conducted to prepare ternary composite plastics by doping Pickering emulsions containing Alpinia galanga essential oil into a polymer network consisting of poly(vinyl alcohol)-acetylated pullulan polysaccharides. Scanning electron microscopy results showed that although incompatible components were present in the composite plastic, compatibility improved with the addition of pullulan polysaccharides, resulting in smooth surfaces and cross-sections, which was consistent with the observation of continuous dark zones and low relative roughness (Ra = 5.51) in Atomic force microscopy. Further, Fourier transform spectroscopy and X-ray diffraction characterization revealed that the composite plastic disrupted the molecular and crystalline structures of the pure PVA, causing the stretching vibration of -OH and the decrease of relative crystallinity. Moreover, this plastic performed optimally at a PVA to pullulan polysaccharide ratio of 75:25, exhibiting good thermal (13.12 J/g) and mechanical properties, low water absorption (70.71 %) and water vapor transmission (1.80 × 10-3 g/m2 s), as well as excellent degradability. In addition, Alpinia galanga essential oil components in the composite plastic provided favorable antioxidant scavenging of DPPH and ABTS and inhibitory effects against Escherichia coli and Staphylococcus aureus. Chicken meat packaging revealed that the plastic maintained sensory parameters such as pH and color by inhibiting the oxidation of proteins and lipids during shelf-life. The findings provide insights into developing innovative, green, multifunctional packaging and broaden the in-depth application of Alpinia galanga essential oil.

Evaluation of sono-physico-chemical and processing effects in the mixed sarcoplasmic protein/soy protein isolate system

Since it may be employed to guide the production of high-quality plant protein as a partial substitute for animal protein using sono-physico-chemical effects, it is important to investigate the mixing of animal and plant protein in ultrasound (UID)-assisted processing systems. A study group of sono-physico-chemical processing with five distinct soy protein isolate (SPI)/ sarcoplasmic protein (SPN) ratios was developed in this work. The results showed that adding additional SPN to the mixed protein can increase its sono-physico-chemical impact, and this effect is greatest when the ratio of SPI to SPN is 1:3. The high SPN group's grafting rate rose from 39.13% to 55.26% in comparison to the high SPI content group. Quercetin (Que) may more readily modify SPN than SPI in the "dual protein" system used in this work, highlighting the critical function of plant protein in controlling the effects of UID-assisted processing in the "dual protein" system. Changes in apparent viscosity and microstructure are the primary parameters that affect the severity of sono-physico-chemical effects in SPI/SPN mixed protein systems, in addition to structural variables.

Conformational Fluctuations and Induced Orientation of a Protein, Its Solvation Shell, and Bulk Water in Weak Non-Unfolding External Electric Fields

Extreme external electric fields have been reported to disrupt the tertiary structure of stably folded proteins; however, the effects of weaker electric fields on many biomolecules, especially net-uncharged proteins, and on the surrounding aqueous environment have been rarely discussed. To explore these effects at the atomic level, here, we have used molecular dynamics simulations to estimate rotational motion and induced structural fluctuations in the model protein ubiquitin and its hydration layer due to applied non-unfolding electrostatic fields. When exposed to weak electric fields of up to 0.2 V nm-1, ubiquitin displayed competition between internal structure-maintaining molecular interactions and the external orienting force, which disrupted the local structure in certain regions of the protein. Moreover, relative to hydration water, bulk water showed a greater tendency to align with the electric field, indicating that the presence of protein caused hydration water to acquire rotational mobility different from that in a pure-water system. The differential influence of the applied electric field on the hydration and bulk water surrounding ubiquitin will be common to almost all (nonmembrane) biomacromolecules. Our findings highlight the importance of local dipoles and their electric polarizability even in net-uncharged biomolecules.

The Nutritional and Functional Properties of Protein Isolates from Defatted Chia Flour Using Different Extraction pH

This study aims to determine the effects of various alkaline pHs on the nutritional and functional properties of protein isolated from defatted chia flour (DCF). The DCF isolated using alkali extraction method at pH 8.5, 10.0, and 12.0 were coded as CPI-8.5, CPI-10.0, and CPI-12.0, respectively. The highest extraction yield and protein recovery yield was demonstrated by CPI-12.0 (19.10 and 59.63%, respectively), with a total protein content of 74.53%, and glutelin showed the highest portion (79.95%). The CPI-12.0 also demonstrated the most elevated essential (36.87%), hydrophobic (33.81%), and aromatic (15.54%) amino acid content among other samples. The DCF exhibited the highest water (23.90 gg-1) and oil (8.23 gg-1) absorption capacity, whereas the CPI-8.5 showed the highest protein solubility (72.31%) at pH 11. DCF demonstrated the highest emulsifying capacity at pH 11 (82.13%), but the highest stability was shown at pH 5 (82.05%). Furthermore, CPI-12.0 at pH 11 shows the highest foaming capacity (83.16%) and stability (83.10%). Despite that, the CPI-10.0 manifested the highest antioxidant capacity (DPPH: 42.48%; ABTS: 66.23%; FRAP: 0.19), as well as ACE-I (35.67%). Overall, the extraction pH had significant effects in producing chia protein isolates (CPI) with improved nutritional and functional qualities.

Investigating the microbial properties of sodium alginate/chitosan edible film containing red beetroot anthocyanin extract for smart packaging in chicken fillet as a pH indicator

The current trend in the production of smart films involves the use of pH-responsive color indicators derived from natural sources. In line with this trend, the aim of this research is to produce edible films from sodium alginate (A) and chitosan (Ch) incorporating red beet anthocyanin (Ac) extract, and to assess the properties of these films and their use as coatings for chicken fillets. The study employed a factorial design to evaluate the effects of treatments C (control), A25%-ch75% (films consisting of 25% sodium alginate and 75% chitosan), and A25%-ch75%-Ac (films consisting of 25% sodium alginate, 75% chitosan, and red beet anthocyanin). The findings indicate that the inclusion of red beet anthocyanin extract did not result in any discernible differences in the FTIR spectra of the film samples. Analysis of the XRD results revealed that the addition of the extract led to a reduction in the crystal structure of the film. Moreover, SEM results demonstrated that the extract caused alterations in the polymer chains and an increase in the porosity of the film matrix. With regard to the chicken fillet samples coated with the film, over time, there was an increase in microbial analysis (total microorganism count and Staphylococcus aureus coagulase-positive) and chemical properties (pH, peroxide, thiobarbituric acid, and nitrogen compounds) for all samples. However, this trend was significantly lower in the samples coated with the Ac extract (P < 0.05). Texture analysis results revealed that the hardness parameter of all samples decreased over the storage period, while the samples containing the Ac extract demonstrated a significant increase in this parameter (P < 0.05). Additionally, the color changes of the pH sensor corresponded to the anthocyanin structure. Based on the results, the smart film composed of sodium alginate/chitosan incorporating red beet anthocyanin extract has the potential to enhance the quality, prolong the shelf life, and decrease the microbial load of chicken fillet when used as a coating. Furthermore, red beet anthocyanin can serve as a suitable indicator for spoilage changes in packaged food products.

Chitosan-pullulan films enriched with Artemisia annua essential oil: Characterization and application in grape preservation

Composite films were prepared using a flow casting method, with chitosan and pullulan as film-forming agents and Artemisia annua essential oil as the UV absorber. The utility of the composite films for preserving grape berries was assessed. The effect of the added Artemisia annua essential oil on the physicochemical properties of the composite film was investigated to determine the optimal amount of essential oil that should be added to the composite film. When the Artemisia annua essential oil content was 0.8 %, the elongation at break of the composite film increased to 71.25 ± 2.87 % and the water vapor transmission rate decreased to 0.378 ± 0.007 g‧mm/(m²‧h‧kpa). The transmittance of the composite film was almost 0 % in the UV region (200-280 nm) and <30 % in the visible light region (380-800 nm), reflecting the UV absorption by the composite film. Additionally, the composite film extended the storage time of the grape berries. Therefore, the composite film containing Artemisia annua essential oil may be a promising fruit packaging material.

Fortification of polysaccharide-based packaging films and coatings with essential oils: A review of their preparation and use in meat preservation

As the demand for botanical food additives and eco-friendly food packaging materials grows, the use of essential oils, edible biodegradable films and coatings are becoming more popular in packaging. In this review, we discussed the recent research trends in the use of natural essential oils, as well as polysaccharide-based coatings and films: from the composition of the substrates to preparing formulations for the production of film-forming technologies. Our review emphasized the functional properties of polysaccharide-based edible films that contain plant essential oils. The interactions between essential oils and other ingredients in edible films and coatings including polysaccharides, lipids, and proteins were discussed along with effects on film physical properties, essential oil release, their active role in meat preservation. We presented the opportunities and challenges related to edible films and coatings including essential oils to increase their industrial value and inform the development of edible biodegradable packaging, bio-based functional materials, and innovative food preservation technologies.

Effect of Thermal Processing on the Conformational and Digestive Properties of Myosin

Heat treatment affects the structural properties of meat proteins, which in turn leads to changes in their sensitivity to digestive enzymes, further affecting the nutritional value of meat and meat products. The mechanism of changes in the structure and digestive properties of myosin under different heating conditions were studied. An increase in heating temperature led to the exposure of internal groups to a polar environment, but to a decrease in the sturdy α-helix structure of myosin (p < 0.05). The results of tryptophan fluorescence verified that the tertiary structure of the protein seemed to be unfolded at 70 °C. Higher protein denaturation after overheating, as proven by the sulfhydryl contents and turbidity, caused irregular aggregate generation. The excessive heating mode of treatment at 100 °C for 30 min caused myosin to exhibit a lower degree of pepsin digestion, which increased the Michaelis constant (Km value) of pepsin during the digestion, but induced the production of new peptides with longer peptide sequences. This study elucidates the effects of cooking temperature on the conformation of myosin and the change in digestibility of pepsin treatment during heating.

Development of edible films by incorporating nanocrystalline cellulose and anthocyanins into modified myofibrillar proteins

In this study, a myofibrillar protein (MP) system was used to investigate the film properties changes by adjusting the intensity of the interaction of proteins with other food components. The structure and rheological properties of several film-forming solutions were then determined. Furthermore, the structure of these composite films was examined using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The smooth and uniform surface acquired by scanning electron microscopy (SEM) substantiated the increased compatibility and continuity observed for films with greater food component interaction. In addition, the MP-based edible films with stronger food component interactions (the MP-Myr/ANT/NCC group) displayed superior mechanical (tensile strength: 6.68 MPa, elongation at break: 94.43%), water vapor barrier (10.01 × 10^-9 g m^-1 s^-1 Pa^-1), and ammonia sensitivity (total color difference: 17.00) capabilities compared to those of the other groups (the MP/ANT/NCC, MP-Lut/ANT/NCC, and MP-Que/ANT/NCC groups).

pH-shifting alters textural, thermal, and microstructural properties of mung bean starch-flaxseed protein composite gels

The objective of this study was to investigate the effect of pH-shifting on the textural and microstructural properties of mung bean starch (MBS)-flaxseed protein (FP) composite gels. Results showed that different pH-shifting treatments caused changes in hydrogen bond interactions and secondary structures in composite gels, leading to the formation of loose or compact gel networks. The pH 2-shifting modified protein and starch molecules with shorter chains tended to form smaller intermolecular aggregates, resulting in the formation of a looser gel network. For pH 12-shifting treatment, conformational change of FP caused the unfolding of protein and the exposure of more hydrophobic groups, which enhanced the hydrogen bond and hydrophobic interactions between polymers, contributing to the formation of a compact gel network. Furthermore, pH 12-shifting improved the water-holding capacity (WHC), storage modulus, and strength of gels, while pH 2-treated gels exhibited lower WHC, hardness, and gumminess due to the degradation of MBS and denaturation of FP caused by extreme acid condition. These findings suggest that pH-shifting can alter the gel properties of bi-polymeric starch-protein composite systems by affecting the secondary structures of proteins and the hydrogen bonding between the polymers, and provide a promising way for a wide application of FP in soft gel-type food production.

The Effect of Glycosylated Soy Protein Isolate on the Stability of Lutein and Their Interaction Characteristics

Lutein is a natural fat-soluble carotenoid with various physiological functions. However, its poor water solubility and stability restrict its application in functional foods. The present study sought to analyze the stability and interaction mechanism of the complex glycosylated soy protein isolate (SPI) prepared using SPI and inulin-type fructans and lutein. The results showed that glycosylation reduced the fluorescence intensity and surface hydrophobicity of SPI but improved the emulsification process and solubility. Fluorescence intensity and ultraviolet–visible (UV–Vis) absorption spectroscopy results showed that the fluorescence quenching of the glycosylated soybean protein isolate by lutein was static. Through thermodynamic parameter analysis, it was found that lutein and glycosylated SPI were bound spontaneously through hydrophobic interaction, and the binding stoichiometry was 1:1. The X-ray diffraction analysis results showed that lutein existed in the glycosylated soybean protein isolate in an amorphous form. The Fourier transform infrared spectroscopy analysis results revealed that lutein had no effect on the secondary structure of glycosylated soy protein isolate. Meanwhile, the combination of lutein and glycosylated SPI improved the water solubility of lutein and the stability of light and heat.

Preparation of a superhydrophilic SiO2 nanoparticles coated chitosan-sodium phytate film by a simple ethanol soaking process

The development of environmentally friendly and transparent superhydrophilic food packaging materials is essential in our daily lives. The objective of this study was to develop a simple method of preparing a superhydrophilic, transparent, and biodegradable composite film. The composite film was obtained by soaking a chitosan-sodium phytate film in an ethanol solution of SiO₂ nanoparticles. The results showed that when the chitosan-sodium phytate film was coated with SiO₂ nanoparticles that were dissolved in 75% ethanol, its water contact angle (WCA) was reduced from 100° to 3°, and the film surface was changed from a hydrophobic to a superhydrophilic. Furthermore, the oxygen transmission rate (OTR) was significantly reduced, and the mechanical properties of the film were improved. The method is easy to carry out and can be used for the potential production of superhydrophilic materials.

Ultrasonication promotes extraction of antioxidant peptides from oxhide gelatin by modifying collagen molecule structure

This study primarily explored the internal mechanism underlying the ultrasonication-induced release of antioxidant peptides. An oxhide gelatin solution was treated ultrasonically (power = 200, 300, and 400 W), followed by enzymatic hydrolysis and structural and morphological analysis. The results showed that ultrasonication increased not only the degree of hydrolysis (DH) and protein recovery rate of the oxhide gelatin but also the ABTS radical scavenging, DPPH radical scavenging, ferrous chelating, and ferric reducing activities of its hydrolysate. The oxhide gelatin hydrolysate treated with 300-W ultrasonication had the maximum antioxidant activities. Ultrasonication inhibited hydrogen bond formation, reduced the crosslinking between collagen molecules, transformed part of the folded structure into a helical structure, and lowered the thermal stability of collagen molecules. The micromorphological analysis revealed that ultrasonication caused the gelatin surface to become loose and develop cracks, and as the power of the ultrasonication increased, the repetition interval distance (dÅ) also increased. Moreover, ultrasonication improved the solubilization, surface hydrophobicity, and interface characteristics and increased the content of basic and aromatic amino acids in the hydrolysate. In conclusion, ultrasonication modifies the protein structure, which increases the enzyme's accessibility to the peptide bonds and further enhances antioxidant peptide release. These findings provide new insights into the application of ultrasonication in the release of antioxidant peptides.

Development and Characterization of Fenugreek Protein-Based Edible Film

The present investigation studied the physicochemical, mechanical, structural, thermal, and morphological attributes of a novel edible film formed from fenugreek protein concentrate. Films were produced at different pH-9, 10, 11, and 12-and the effect of the pH on the films was studied. As the pH increased, tensile strength increased while water vapor absorption decreased, which is interrelated to the surface morphological properties; as the pH increased, the surface became smoother and compact without any cavities. The films produced were darker in color. Fenugreek protein films exhibited good thermal stability. Fourier transform infrared spectroscopy (FTIR) revealed the presence of strong bonding for the films made at alkaline pH. X-ray diffraction analysis (XRD) indicated the major structure of the film was amorphous. The study demonstrated that the fenugreek protein concentrate film has influential characteristics and can be used as an edible packaging film.

Trace the difference driven by unfolding-refolding pathway of myofibrillar protein: Emphasizing the changes on structural and emulsion properties

The effective strategy of pH-shifting to improve the emulsifying properties of myofibrillar proteins (MPs) extracted from pale, soft and exudative (PSE)-like chicken was investigated. To determine the mechanism of improvement, changes on structural and physicochemical properties were clarified by tracing the difference driven by unfolding-refolding process. According to the results of tryptophan fluorescence intensity and circular dichroism spectroscopy, it is found that unfolding-refolding process markedly changed MPs secondary and tertiary structure. The atomic force microscopy images showed MPs appeared to have fibrous-like appearance at pH 7.0, however, exhibited as spherical shape after pH-shifting. Both emulsifying activity index and emulsifying stability index increased after pH-shifting. These results systematically illustrated the changes on structural and emulsion properties of MPs during unfolding-refolding process. It proved that the strategy pH 11.0-7.0 could more effectively promote MPs emulsifying properties, whose mechanism was simultaneously the transformation in MPs structure and potentially formation of highly-soluble particle.

Protective coating of strawberries with cellulose nanofibers

Since shelf life of perishable foods is short, a compelling challenge is to prolong the freshness of foods with a cost-effective strategy. A perishable fruit, the strawberry, is chosen as a model perishable food and an edible film coating is applied to it using carboxymethylated cellulose nanofibers (CM-CNFs) stabilized by cationic salts. A transparent and impermeable CM-CNF film is formed at the strawberry surface using a dip coating process. The formation of the film is dependent on the electrostatic interaction between anionic CM-CNF and salt cations. Physical properties of the film are characterized and the effectiveness of edible film coating on the freshness of perishable fruit is evaluated by the measurement of weight loss, CO₂ release, firmness, total solid sugar and acidity. Cellulose nanofiber is a promising cost-effective material appropriate for use as an edible coating that contributes to the long-term storage and prolonged freshness of foods.

Preparation and characterization of clove essential oil loaded nanoemulsion and pickering emulsion activated pullulan-gelatin based edible film

The clove essential oil (CEO) loaded nano and pickering emulsions prepared with Tween 80 and whey protein isolate/inulin mixture, respectively were incorporated into pullulan-gelatin film base fluid at three levels (0.2%, 0.4%, and 0.6%). The droplet sizes of NE and PE loaded with CEO were 15.93 nm and 266.9 nm, respectively. The PDI of CEOs with stable NE and PE were 0.262 and 0.259, respectively. Our results showed the improved compatibility between pullulan-gelatin and essential oil-loaded nanocarriers. The active film composed of PE carrier had the structural characteristics of high density, low water content, and low permeability, thus exhibiting excellent mechanical properties, water barrier properties, and appreciable antioxidant activities. Compared with NE, it was found that the CEO-loaded PE showed slow-release profile in the film sample. The prepared active film containing PE possessed a great potential to be used as effective and natural alternatives for active food packaging.

Applications of asymmetrical flow field-flow fractionation for separation and characterization of polysaccharides: A review

Polysaccharides are the most abundant natural biopolymers on the earth and are widely used in food, medicine, materials, cosmetics, and other fields. The physicochemical properties of polysaccharides such as particle size and molecular weight often affect their practical applications. In recent years, asymmetrical flow field-flow fractionation (AF4) has been widely used in the separation and characterization of polysaccharides because it has no stationary phases or packing materials, which reduces the risk of shear degradation of polysaccharides. In this review, the principle of AF4 was introduced briefly. The operation conditions of AF4 for the analysis of polysaccharides were discussed. The applications of AF4 for the separation and characterization of polysaccharides from different sources (plants, animals, and microorganisms) over the last decade were critically reviewed.