Modifying the physicochemical properties, solubility and foaming capacity of milk proteins by ultrasound-assisted alkaline pH-shifting treatment

Esterification of dextran by octenyl succinic anhydride (OSA): Physicochemical characterization and functional properties assessment

The chemical modification of biopolymers to enhance their functional properties in the food, cosmetic, and pharmaceutical industries is an area of particular interest today. In this study, different molecular weight dextrans were chemically modified for the first time with octenyl succinic anhydride (OSA). This reaction involves an esterification process wherein the hydroxy groups of dextran are partially substituted by a carbonaceous chain, imparting hydrophobic properties to dextran molecules and, consequently, an amphiphilic nature. To assess and quantify the incorporation of OSA into the dextran structure, reaction products were analysed using NMR and FTIR. Additionally, the thermal properties, the Z-potential and the foaming and emulsifying capacity of both native and modified dextrans were examined. The introduction of OSA groups to dextran molecules, with degrees of substitution between 0.028 and 0.058, increased the zeta potential and the thermal stability of the polymer. Furthermore, the chemical modification of dextran backbone with this radical conferred a hydrophobic nature to the biopolymer, which enhance its foaming and emulsifying capacity. Therefore, these results demonstrate that the incorporation of hydrophobic moieties into dextran polymers improves their functional properties and broadens their potential applications in the industry.

Ultrasound-mediated host-guest self-assembly between different dietary fatty acids and sodium caseinate and their complexes improving the water dispersibility, stability, and bioaccessibility of quercetin

Quercetin (QUE) sufferred from poor processing adaptability and absorbability, hindering its application as a dietary supplement in the food industry. In this study, fatty acids (FAs)-sodium caseinate (NaCas) ligand complexes carriers were fabricated to improve the aqueous dispersibility, storage/thermal stability, and bioaccessibility of QUE using an ultrasound method. The results indicated that all six selected common dietary FAs formed stable hydrophilic complexes with NaCas and the FAs-NaCas complexes achieved an encapsulation efficiency greater than 90 % for QUE. Furthermore, the introduction of FAs enhanced the binding affinity between NaCas and QUE, but did not change the binding mode (static bursting) and types of intermolecular forces (mainly hydrogen bonding). In addition, a distinct improvement was discovered in the storage stability (>2.37-fold), thermal processing stability (>32.54 %), and bioaccessibility (>2.37-fold) of QUE. Therefore, the FAs-NaCas ligand complexes could effectively protect QUE to minimize degradation as fat-soluble polyphenol delivery vehicles.

Effect of different salts on the foaming properties of model protein systems for infant formula

This multiscale study aimed to evaluate the effects of different salts (NaCl, KCl, MgCl2, and CaCl2) on the foaming capacity (FC) and foam stability (FS) of model protein systems (MPS) for infant formula via changes in surface and structural properties. Our results showed that the FC and FS of MPS were increased with the addition of NaCl, KCl, and MgCl2, whereas CaCl2 significantly decreased FC (79.5 ± 10.6%) and increased FS (93.2 ± 2.2%). The surface hydrophobicity was increased and the net charge and surface tension were reduced after the addition of salts. Structural analysis revealed the reduction of intensity of intrinsic fluorescence spectroscopy and UV absorption, and the conversion of α-helix into β-strand, which was attributed to protein agglomeration. Additionally, MgCl2 and CaCl2 exhibited larger size and lower net charge compared with NaCl and KCl, indicating a greater ability to bind to charged amino acids and form larger aggregates. Correlation analysis indicated that FC was positively related to adsorbed protein and β-turn and negatively correlated with particle size. In addition, FS showed a positive correlation with β-strand, apparent viscosity, and zeta potential. However, it exhibited a negative correlation with β-turn, α-helix, and sulfhydryl content. These results provide a theoretical reference for further understanding of the effect of salts on the foaming properties of MPS.

Development of Novel Nanocarriers by Ultrasound and Ethanol-Assisted Soy Protein Isolate: Enhancing the Resistance of Lutein to Environmental Stress

The aim of this work was to investigate the effects of the processing sequence of ultrasound and ethanol on the physicochemical properties of soy protein isolate (SPI), which were further evaluated for the morphology and stability of SPI-lutein coassembled nanoparticles. The results showed that the sequence of ultrasound followed by ethanol treatment was the optimal one. The samples were subjected to ultrasonication followed by subunit disassembly and reassembly induced by 40% (v/v) ethanol, with the resulting molecular unfolding and subsequent aggregation being attributed to intramolecular hydrogen bonds. The recombined nanoparticles had smaller particle size (142.43 ± 2.91 nm) and turbidity (0.16 ± 0.01), and the exposure of more hydrophobic groups (H0 = 6221.00 ± 130.20) induced a shift of SPI structure toward a more ordered direction. The homogeneous and stable particle provided excellent stability for the loading of lutein. The bioaccessibility (from 25.48 ± 2.35 to 65.85 ± 1.78%) and release rate of lutein were modulated in gastrointestinal digestion experiments. Our discoveries provide a new perspective for the development of combined physicochemical modification of proteins as nanocarriers in functional foods.

Enhancing the Gelation Behavior of Transglutaminase-Induced Soy Protein Isolate(SPI) through Ultrasound-Assisted Extraction

Gelation, as an important functional property of soy protein isolate (SPI), can be improved by some green technologies in food manufacturing, including ultrasound, ultrahigh pressure and microwave treatments. This work investigated the effect of an alkaline solubilisation step in SPI extraction combined with sonication on protein properties. The TGase-induced gel of the modified SPI was prepared to explore the effect of ultrasound on gel properties, including structures, strength, water-holding capacity and rheological properties. Additionally, the differences between traditional ultrasound modification of SPI and current modification methods were analyzed. The results showed that the ultrasonication-assisted extraction method could result in a significant increase in extraction rate from 24.68% to 42.25%. Moreover, ultrasound-assisted modification of SPI gels induced with transglutaminase (TGase) exhibited significant improvement in mechanical properties, such as texture, water-holding capacity and rheological properties, In particular, SPI extracted at 400 W ultrasound intensity for 180 s showed the best overall performance in terms of gel properties. Our method efficiently uniformizes gel structure, enhancing mechanical properties compared to conventional ultrasound methods, which reduced energy consumption and costs. These findings provide insights into the production of high-gelation SPI in food manufacturing.

Effects of Germination on the Structure, Functional Properties, and In Vitro Digestibility of a Black Bean (Glycine max (L.) Merr.) Protein Isolate

The utilization of black beans as a protein-rich ingredient presents remarkable prospects in the protein food industry. The objective of this study was to assess the impact of germination treatment on the physicochemical, structural, and functional characteristics of a black bean protein isolate. The findings indicate that germination resulted in an increase in both the total and soluble protein contents of black beans, while SDS-PAGE demonstrated an increase in the proportion of 11S and 7S globulin subunits. After germination, the particle size of the black bean protein isolate decreased in the solution, while the absolute value of the zeta potential increased. The above results show that the stability of the solution was improved. The contents of β-sheet and β-turn gradually decreased, while the content of α-helix increased, and the fluorescence spectrum of the black bean protein isolate showed a red shift phenomenon, indicating that the structure of the protein isolate and its polypeptide chain were prolonged, and the foaming property, emulsification property and in vitro digestibility were significantly improved after germination. Therefore, germination not only improves functional properties, but also nutritional content.

Structure and functionality of whey protein, pea protein, and mixed whey and pea proteins treated by pH shift or high-intensity ultrasound

Three modifications (pH shift, ultrasound, combined pH shift and ultrasound) induced alterations in pure whey protein isolate (WPI), pea protein isolate (PPI), and mixed whey and pea protein (WPI-PPI) were investigated. The processing effect was related to the protein type and technique used. Solubility of WPI remained unchanged by various treatments. Particle size was enlarged by pH shift while reduced by ultrasound and combined approach. All methods exposed more surface hydrophobic groups on WPI, while pH shift and joint processing was detrimental to its emulsifying activity. The PPI and mixture exhibited similar responses toward the modifications. Solubility of PPI and the blend enhanced in the sequence of pH shift and ultrasound > ultrasound > pH shift. Individual approach expanded while co-handling diminished the particle diameter. Treatments also caused more disclosure of hydrophobic regions in PPI and WPI-PPI and emulsifying activity was ameliorated in the order of pH shift and ultrasound > ultrasound > pH shift.

DHA-mediated milk protein treated by ultrasound-assisted pH-shifting for enhanced astaxanthin delivery and processed cheese application

Whey protein isolate (WPI)-based nanodelivery systems have recently attracted an increasing amount of attention. Despite this, research focusing on milk protein concentrate (MPC) and micellar casein (MCC) as carriers loaded in hydrophobic compounds is lacking. This study investigated the mediated effect of docosahexaenoic acid (DHA) in 3 different milk proteins for the embedding of astaxanthin (ASTA) after ultrasound-assisted pH-shifting treatment. We then evaluated the application of milk protein carriers in cheese processing by comparing MPC, MCC, and WPI. The particle size, polydispersity index, and zeta potential results of the milk protein-DHA complex suggested that the addition of 0.36 μmol/mL DHA optimized the delivery of milk protein to ASTA. All 3 DHA-mediated milk proteins induced an improvement in encapsulation efficiency and antioxidant properties of ASTA. Furthermore, the DHA-mediated MPC and MCC played a stronger role in improving the bioaccessibility, thermal and storage stability of ASTA than those without DHA. Tests conducted to examine the application in cheese production indicated that MCC carrier had a positive effect on the texture of cheeses. However, the delivery effect was dependent on the milk protein variety, in which MCC exhibited the best protection ability of ASTA, followed by MPC and WPI. The simulated digestion and storage stability results of cheese further confirmed that the protein encapsulation mediated by DHA was more conducive to ASTA absorption. These findings suggested that the DHA-mediated milk protein complexes studied here may be suitable hydrophilic delivery carriers for the hydrophobic nutrient ASTA, potentially playing different roles in regulating the storage stability and bioaccessibility.

Comparative study of interfacial properties and thermal behaviour of milk fat globules and membrane prepared from ultrasonicated bovine milk

Milk fat globules or milk fat globule membranes (MFGs/MFGM) have been added to the infant formula to fortify the phospholipids and narrow the nutritional gap from breast milk. The main aim of this study was to profile the interfacial and thermal properties of MFGs/MFGM prepared from ultrasonicated bovine milk. Bovine milk was sonicated at ultrasonic intensities of 20 kHz and 40 kHz independently or synchronously with the duration time of 0 min (control), 5 min, 10 min, and 15 min (work/rest cycles = 5 s: 3 s). Ultrasonic treatments at 20 kHz/ 5 min and 20 + 40 kHz/ 5 min improved the volume density (%) of smaller particles (1-10 µm) while significantly decreasing the surface hydrophobicity (H0) (p < 0.05). 40 kHz/5 min samples showed significantly higher ζ- potential than the other samples (p < 0.05), which might be because more negative charges were detected. In comparison with control samples, ultrasonic treatments decreased the interfacial tension (π) between the air and MFGs/MFGM liquid phase. 20 kHz ultra-sonicated treatments decreased the diffusion rate (k diff) of MFGs/MFGM interfacial compositions significantly as the duration prolonged from 5 min to 15 min (p < 0.05) but did not affect the adsorption or penetration rate (k a) (p > 0.05). X-ray diffraction (XRD) results showed that α-crystal peaks only existed in control and ultrasonicated 5 min samples but disappeared in all 15 min samples. According to the different scanning calorimetry (DSC), one or two new exothermic events (in the range of 17.29 - 18.81 ℃ and 22.14 - 25.21 ℃) appeared after ultrasonic treatments, which, however, were not found in control samples. Ultrasonic treatments resulted in the low-melting fractions (LMF) (TM1) peaks undetectable in MFGs/MFGM samples in which only peaks of medium-melting fractions (MMF) (TM2) and high-melting fractions (HMF) (TM3) were detected. Compared with the control, both enthalpies of crystallisation (ΔHC) and melting (ΔHM) decreased in ultrasonicated samples. In conclusion, ultrasonic treatment affects the interfacial and thermal properties of MFGs/MFGM.

Comparison of milk protein concentrate, micellar casein, and whey protein isolate in loading astaxanthin after the treatment of ultrasound-assisted pH shifting

Milk proteins can be used as encapsulation walls to increase the bioavailability of active compounds because they can bind hydrophobic, hydrophilic, and charged compounds. The objective of this study was to investigate the effects of astaxanthin (ASTA) encapsulation and the functional properties of milk protein and ASTA nanocomposites by an ultrasound-assisted pH-shifting treatment of different milk proteins, including milk protein concentrate (MPC), micellar casein (MCC), and whey protein isolate (WPI). The ultrasound-assisted pH-shifting treatment of milk protein helped to improve the encapsulation rate of ASTA. Therein, MCC showed great improvement of encapsulating ASTA after co-treatment with the raised encapsulated rate of 5.11%, followed by WPI and MPC. Furthermore, the nanocomposites of ASTA with milk protein exhibit improved bioavailability, antioxidant capacity, and storage stability. By comparison, MCC-encapsulated ASTA has the best storage stability, followed by MPC, and WPI-encapsulated ASTA has the least stability over a 28-d storage period. The results of intrinsic fluorescence and surface hydrophobicity showed that milk protein underwent fluorescence quenching after binding to ASTA, which was due to the hydrophobic sites of the protein being occupied by ASTA. In general, the nanocomposites of milk protein and ASTA fabricated by using an ultrasound-assisted pH-shifting treatment have the potential to be better nano-delivery systems for ASTA in functional foods, especially MCC, which showed excellent performance in encapsulation after treatment technique.

Precise control of aggregation morphology: Effective strategy to tune the properties of ovotransferrin particles

Different aggregation morphologies of ovotransferrin (OVT) aggregates were successfully obtained through precise control, and the effects on structural, physical, liquid-liquid and gas-liquid interfacial characteristics as well as mechanisms were explored for the first time. It was observed that the surface hydrophobicity of OVT fibrils was higher than OVT spheres due to the acid-heat treatment. The exploration of liquid-liquid interface behaviors indicated that OVT fibrils possessed higher adsorption capacity at the interface, revealing the higher surface activity at the oil-water interface. During adsorption process, fibrils exhibited higher diffusion rate, while spheres were easier to penetrate and rearrange at the interface. The interfacial film composed of fibrils possessed more elastic solid-like behaviors owing to the higher surface activity of individual fibrous aggregates and rapid fibril-fibril interactions. The analysis of gas-liquid interface characteristics presented that OVT spheres possessed lower interfacial tension and higher interfacial viscoelasticity, and showed significantly higher FC and FS values in comparation to fibrils. These findings will facilitate the reader's understanding of the relationship between protein aggregate structure and properties, and lay a foundation for broadening the application of OVT and even other proteins.

Modification of whey protein isolate by ultrasound-assisted pH shift for complexation with carboxymethylcellulose: Structure and interfacial properties

The application of whey protein isolate (WPI) is limited because of its compact spherical structure. In this study, ultrasound-assisted pH shift was employed to modify WPI for complexation with carboxymethylcellulose (CMC). The foaming and emulsifying properties of WPI/CMC complexes were investigated. The results demonstrate that the pretreatment of ultrasound-assisted pH 12 shift increased the content of free sulfhydryl groups from 16.5 μmol/g to 34.7 μmol/g and enhanced protein hydrophobicity from 311.4 to 370.6 (p < 0.05). Compared to the complexes formed by untreated WPI and CMC, the complexes pretreated with ultrasound-assisted pH 12 shift had a smaller size of 293.4 nm and a more uniform distribution. Furthermore, WPI/CMC complexes pretreated by ultrasound-assisted pH 12 shift exhibited higher emulsifying activity and emulsion stability index, which were increased by 8.9 % and 42.6 % respectively, in comparison with the control group (p < 0.05). A positive correlation was found between the surface hydrophobicity of WPI and emulsifying activity of WPI/CMC complexes. Ultrasound-assisted pH 2 shift improved the foaming capacity of complexes by 28.3 % over the control (p < 0.05). All the results indicate that the interfacial properties of WPI/CMC complexes can be improved significantly by the combination of pH shift and ultrasound.

Optimization of ultrasound-assisted cellulase degradation method on the extraction of mulberry leaf protein and its effect on the functional characteristics

The mulberry leaf protein extracted by ultrasound-assisted cellulase degradation (UACD) method was optimized with the protein dissolution amount (PDA) as the index. The Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy of extracted mulberry leaf protein were measured. The functional characteristics of protein extracted by the UACD method were evaluated. Results showed that the extraction condition was optimized and adjusted to the following parameters: pH value of 7.20, ultrasound temperature of 35.00 °C, enzyme dosage of 4.20% and ultrasound time of 10.00 min. Under these optimized conditions, the experimental verification value of PDA was 13.87 mg/mL, which was approaching to the predicted value of 13.54 mg/mL. The analysis results of FTIR showed that after extraction by the UACD method, the mulberry leaf protein with the vibrational peak of ester carbonyl (C = O) absorption peak (1734.66 cm-1) disappeared. The α-helix content of protein extracted by the UACD decreased by 8.13%, and the β-turn and random coil content of protein increased by 20.22% and 18.79%, respectively, compared to that of the blank. The microstructure of mulberry leaf protein showed that the UACD method could break the dense structure of protein raw materials, reduce the average size of proteins and increase the specific surface area and roughness of proteins. According to the results of functional characteristics, the mulberry leaf protein extracted by the UACD method presented the highest enzymolysis properties and solubility, which was beneficial for the application in the food industry. In conclusion, the UACD method was a very effective way to extract protein from mulberry leaf.

Effects of ultrasound-assisted high temperature-pressure treatment on the structure and allergenicity of tropomyosin from clam (Mactra veneriformis)

Tropomyosin (TM) is the major allergen in clams. This study aimed to evaluate the effects of ultrasound-assisted high temperature-pressure treatment on the structure and allergenicity of TM from clams. The results showed that the combined treatment significantly affected the structure of TM-converting the α-helix to β-sheet and random coil, and decreasing the sulfhydryl group content, surface hydrophobicity, and particle size. These structural changes caused the unfolding of the protein, disrupting and modifying the allergenic epitopes. The significant reduction in the allergenicity of TM was approximately 68.1% when treated with combined processing (P < 0.05). Notably, an increase in the content of the relevant amino acids and a smaller particle size accelerated the penetration of the enzyme into the protein matrix, resulting in strengthening the gastrointestinal digestibility of TM. These results prove that ultrasound-assisted high temperature-pressure treatment has great potential in reducing allergenicity, benefiting the development of hypoallergenic clam products.

Characteristics of enzymolysis of silkworm pupa protein after tri-frequency ultrasonic pretreatment: kinetics, thermodynamics, structure and antioxidant changes

As a by-product of the sericulture industry, the utilization rate of silkworm pupa resources is currently not high. Proteins are converted into bioactive peptides through enzymatic hydrolysis. Not only can it solve the utilization problem, but it also creates more valuable nutritional additives. Silkworm pupa protein (SPP) was pretreated with tri-frequency ultrasonic (22/28/40 kHz). Effects of ultrasonic pretreatment on enzymolysis kinetics, enzymolysis thermodynamics, hydrolysate structure as well as hydrolysate antioxidant of SPP were investigated. Ultrasonic pretreatment significantly increased the hydrolysis efficiency, showing a 6.369% decrease in k _m and a 16.746% increase in k _A after ultrasonic action (p < 0.05). The SPP enzymolysis reaction followed a second-order rate kinetics model. Evaluation of enzymolysis thermodynamics revealed that Ultrasonic pretreatment markedly enhanced the SPP enzymolysis, leading to a 21.943% decrease in E _a. Besides, Ultrasonic pretreatment significantly increased SPP hydrolysate's surface hydrophobicity, thermal stability, crystallinity, and antioxidant activities (DPPH radical scavenging activity, Fe²⁺ chelation ability, and reducing power). This study indicated that tri-frequency ultrasonic pretreatment could be an efficient approach to enhancing the enzymolysis and improving the functional properties of SPP. Therefore, tri-frequency ultrasound technology can be applied industrially to enhance enzyme reaction process.

Effects of ultrasonic-assisted pH shift treatment on physicochemical properties of electrospinning nanofibers made from rapeseed protein isolates

Electrospinning nanofibers (NFs) made from natural proteins have drawn increasing attention recently. Rapeseed meal is a by-product that rich in protein but not fully utilized due to poor properties. Therefore, modification of rapeseed protein isolates (RPI) is necessary to expand applications. In this study, pH shift alone or ultrasonic-assisted pH shift treatment was adopted, the solubility of RPI, along with the conductivity and viscosity of the electrospinning solution were detected. Moreover, the microstructure and functional characteristics of the electrospinning NFs, as well as the antibacterial activity of clove essential oil loaded-NFs were investigated. The tested parameters were remarkably improved after different treatments compared with the control, and synergistic effects were observed, especially under alkaline conditions. Hence, pH_12.5 + US showed the maximum value of solubility, conductivity, and viscosity, which was more than 7-fold, 3-fold, and almost 1-fold higher than the control respectively. Additionally, SEM and AFM images showed a finer and smoother surface of NFs after treatments, and the finest diameter of 216.7 nm was obtained after pH_12.5 + US treatment in comparison with 450.0 nm in control. FTIR spectroscopy of NFs demonstrated spatial structure changes of RPI, and improved thermal stability and mechanical strength of NFs were achieved after different treatments. Furthermore, an inhibition zone with a diameter of 22.8 mm was observed from the composite NFs. This study indicated the effectiveness of ultrasonic-assisted pH shift treatment on the physicochemical properties improvement and functional enhancement of NFs made from RPI, as well as the potential antibacterial application of the composite NFs in the future.

Effect of Corn Starch Granules on Stabilizing the Foam Structure of Ultrasonically Modified Whey Isolate Protein

In this study, the mechanism of ultrasound combined with corn starch granules (CSG) treatment improved the foam properties of whey protein isolates (WPI) and was systematically investigated. The results showed that ultrasound combined with corn starch granules treatment increased foam capacity and stability by 15.38% and 41.40%, respectively. Compared with the control group, corn starch granules enhanced the surface charge (52.38%) and system turbidity (51.43%), which certainly provided the necessary conditions for the improvement of foam stabilization stability. In addition, corn starch granules as microgel particles increased the mechanical properties of the interfacial protein film, thus delaying the instability of foam. This research would provide new insights into the design of new protein-based foam foods in the future food industry.