Effect mechanism of ultrasound pretreatment on fibrillation Kinetics,physicochemical properties and structure characteristics of soy protein isolate nanofibrils

Self-assembly of soy proteins into nanofibrils is gradually considered as an effective method to improve their technical and functional properties. Ultrasound is a non-thermal, non-toxic and environmentally friendly technology that can modulate the formation of protein nanofibrils through controlled structural modification. In this research, the effect of ultrasound pretreatment on soy protein isolate nanofibrils (SPIN) was evaluated by fibrillation kinetics, physicochemical properties and structure characteristics. The results showed that the optimum ultrasound condition (20% amplitude, 15 min, 5 s on-time and 5 s off-time) could increase the formation rate of SPIN by 38.66%. Ultrasound reduced the average particle size of SPIN from 191.90 ± 5.40 nm to 151.83 ± 3.27 nm. Ultrasound could increase the surface hydrophobicity to 1547.67 in the initial stage of nanofibrils formation, and extend the duration of surface hydrophobicity increased, indicating ultrasound could expose more binding sites, creating more beneficial conditions for nanofibrils formation. Ultrasound could change the secondary and tertiary structure of SPIN. The reduction of α-helix content of ultrasound-pretreated soy protein isolate nanofibrils (USPIN) was 12.1% (versus 5.3% for SPIN) and the increase of β-sheet content was 5.9% (versus 3.5% for SPIN) during fibrillation. Ultrasound could accelerate the formation of SPIN by promoting the unfolding of SPI, exposure of hydrophobic groups and formation of β-sheets. Microscopic images revealed that USPIN generated a curlier and looser shape. And ultrasound reduced the zeta potential, free sulfhydryl groups content and viscosity of SPIN. SDS-PAGE results showed that ultrasound could promote the conversion of SPI into low molecular weight peptides, providing building blocks for the nanofibrils formation. The results indicated that ultrasound pretreatment could be a promising technology to accelerate SPIN formation and promote its application in food industry, but further research is needed for the improvement of the functional properties of SPIN.     

Effects of ultrasonic pretreatment of soybean protein isolate on the binding efficiency,structural changes,and bioavailability of a protein-luteolin nanodelivery system

The combination of protein and flavonoids can ameliorate the problems of poor solubility and stability of flavonoids in utilization. In this study, soybean protein isolate pretreated by ultrasonication was selected as the embedding wall material, which was combined with luteolin to form a soybean protein isolate-luteolin nanodelivery system. The complexation effect and structural changes of soybean protein isolate (SPI) and ultrasonic pretreatment (100 W, 200 W, 300 W, 400 W and 500 W) of soybean protein isolate with luteolin (LUT) were compared, as well as the changes in digestion characteristics and antioxidant activity in vitro. The results showed that proper ultrasonic pretreatment increased the encapsulation efficacy, loading amount and solubility to 89.72%, 2.51 μg/mg and 90.56%. Appropriate ultrasonic pretreatment could make the particle size and the absolute value of ζ-potential of SPI-LUT nanodelivery system decrease and increase respectively. The FTIR and fluorescence results show that appropriate ultrasonic pretreatment could reduce α-helix, β-sheet and random coil, increase β-turn, and enhance fluorescence quenching. The thermodynamic evaluation results indicate that the ΔG < 0, ΔH > 0 and ΔS > 0, so the interaction of LUT with the protein was spontaneous and mostly governed by hydrophobic interactions. The XRD results show that the LUT was amorphous and completely wrapped by SPI. The DSC results showed that ultrasonic pretreatment could improve the thermal stability of SPI-LUT nanodelivery system to 112.66 ± 1.69 °C. Digestion and antioxidant analysis showed that appropriate ultrasonic pretreatment increased the LUT release rate and DPPH clearance rate of SPI-LUT nanodelivery system to 89.40 % and 55.63 % respectively. This study is a preliminary source for the construction of an SPI nanodelivery system with ultrasound pretreatment and the deep processing and utilization of fat-soluble active substances.     

Effects of ultrasound on the structural and emulsifying properties and interfacial properties of oxidized soybean protein aggregates

Oxidative attack leads to the oxidative aggregation and structural and functional feature weakening of soybean protein. We aimed to investigate the impact of ultrasonic treatment (UT) with different intensities on the structure, emulsifying features and interfacial features of oxidized soybean protein aggregates (OSPI). The results showed that oxidative treatment could disrupt the native soy protein (SPI) structure by promoting the formation of oxidized aggregates with β1-sheet structures through hydrophobic interactions. These changes led to a decrease in the solubility, emulsification ability and interfacial activity of soybean protein. After low-power ultrasound (100 W, 200 W) treatment, the relative contents of β1-sheets, β2-sheets, random coils, and disulfide bonds of the OSPI increased while the surface hydrophobicity, absolute ζ-potential value and free sulfhydryl content decreased. Moreover, protein aggregates with larger particle sizes and poor solubility were formed. The emulsions prepared using the OSPI showed bridging flocculation and decreased protein adsorption and interfacial tension. After applying medium-power ultrasound (300 W, 400 W, and 500 W) treatments, the OSPI solubility increased and particle size decreased. The α-helix and β-turn contents, surface hydrophobicity and absolute ζ-potential value increased, the structure unfolded, and the disulfide bond content decreased. These changes improved the emulsification activity and emulsion state of the OSPI and increased the protein adsorption capacity and interfacial tension of the emulsion. However, after a high-power ultrasound (600 W) treatment, the OSPI showed a tendency to reaggregate, which had a certain negative effect on the emulsification activity and interfacial activity. The results showed that UT at an appropriate power could depolymerize OSPI and improve the emulsification and interfacial activity of soybean protein.     

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 increased random 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 high-intensity ultrasound on the physicochemical properties,microstructure, and stability of soy protein isolate-pectin emulsion

In this study, an emulsion stabilized by soy protein isolate (SPI)-pectin (PC) complexes was prepared to investigate the effects of high-intensity ultrasound (HIU) treatment (150–600 W) on the physicochemical properties, microstructure, and stability of emulsions. The results found that the emulsion treated at 450 W showed the best emulsion stability index (ESI) (25.18 ± 1.24 min), the lowest particle size (559.82 ± 3.17 nm), the largest ζ-potential absolute value (16.39 ± 0.18 mV), and the highest adsorbed protein content (27.31%). Confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM) revealed that the emulsion aggregation was significantly improved by ultrasound treatment, and the average roughness value (Rq) was the smallest (10.3 nm) at 450 W. Additionally, HIU treatment reduced the interfacial tension and apparent viscosity of the emulsion. Thermal stability was best when the emulsion was treated at 450 W, D₄₃ was minimal (907.95 ± 31.72 nm), and emulsion separation also improved. Consequently, the creaming index (CI) was significantly decreased compared to the untreated sample, indicating that the storage stability of the emulsion was enhanced.     

Improvement of the emulsifying properties of mixed emulsifiers by optimizing ultrasonic-assisted processing

Optimizing ultrasound (ULD)-assisted flavonoid modification is an important component of enhancing its application potential. In this work, diverse flavonoids, such as quercetin (Que), apigenin (Api), and morin (Mor), were used to modify protein in myofibrillar protein (MP)/cellulose nanocrystal (CN) complexes using ULD-assisted method. Compared with the MP/CNs group, the triiodide contents of MP-Que/CNs, MP-Api/CNs, and MP-Mor/CNs increased by 1175.84%, 479.05%, and 2281.50% respectively. The findings revealed that the actual intensity of ULD was drastically reduced by the molecular weight decrease of these flavonoids. For olive oil emulsions prepared with mixed emulsifiers, the low interfacial diffusion rates (0.03 mN·m·s^−1/2) and weak emulsifying activity (8.33 m²/g) of the MP/CN complexes were significantly improved by the flavonoids after ULD-assisted treatment. Notably, the emulsions prepared using MP-Api/CNs contained smaller oil droplets and exhibited better emulsifying properties, compared to emulsions prepared with MP-Mor/CNs or MP-Que/CNs. This study is essential for ULD-assisted treatment since the processing impact may be increased by choosing the most suitable flavonoid.     

Effects of ultrasound pretreatment on functional property,antioxidant activity,and digestibility of soy protein isolate nanofibrils

Nanofibrils, an effective method to modulate the functional properties of proteins, can be promoted by ultrasound pretreatment. This study investigated the effect of ultrasound pretreatment on the structure, functional property, antioxidant activity and digestibility of soy protein isolate (SPI) nanofibrils. The results showed that high amplitude ultrasound had a significant effect on structure of SPI nanofibrils. SPI nanofibrils pretreated by 80% amplitude ultrasound showed a blueshift of the amide II band in Fourier transform infrared spectroscopy (FTIR), resulted in more tryptophan residues being buried and increased the crystallinity. Low amplitude ultrasound (20%) pretreatment significantly improved the solubility, emulsifying activity index (EAI) and water absorption capacity (WAC) of SPI nanofibrils, but 80% amplitude ultrasound pretreatment of SPI nanofibrils reduced emulsifying stability index (ESI). High amplitude ultrasound (60% and 80%) pretreatment of SPI nanofibrils improved the foaming capacity and foaming stability and decreased denaturation temperature. DPPH radical scavenging activity of SPI nanofibrils were significantly improved by ultrasound pretreatment. 20% amplitude ultrasound pretreatment improved DPPH, ABTS radical scavenging activity and ferric reducing antioxidant power of SPI nanofibrils. The digestion rate of 80% amplitude ultrasound-pretreated nanofibrils were consistently higher, and SPI nanofibrils pretreated by ultrasound were more fragmented and shorter after simulating gastrointestinal digestion. This study would expand the application of food-grade protein nanofibrils in the food industry.     

Effect of high-intensity ultrasound on the structural,rheological, emulsifying and gelling properties of insoluble potato protein isolates

The denaturation and lower solubility of commercial potato proteins generally limited their industrial application. Effects of high-intensity ultrasound (HIU) (200, 400, and 600 W) and treatment time (10, 20, and 30 min) on the physicochemical and functional properties of insoluble potato protein isolates (ISPP) were investigated. The results revealed that HIU treatment induced the unfolding and breakdown of macromolecular aggregates of ISPP, resulting in the exposure of hydrophobic and R–SH groups, and reduction of the particle size. These active groups contributed to the formation of a dense and uniform gel network of ISPP gel and insoluble potato proteins/egg white protein (ISPP/EWP) hybrid gel. Furthermore, the increase of solubility and surface hydrophobicity and the decrease of particle size improved the emulsifying property of ISPP. However, excessive HIU treatment reduced the emulsification and gelling properties of the ISPP. Meanwhile, HIU treatment changes the secondary structure of ISPP. It could be speculated that the formation of a stable secondary structure of ISPP initiated by cavitation and shearing effect might play a dominant role on gel strengthens and firmness. Meanwhile, the decrease in relative content of β-turn had a positive effect on the formation of small particle to improve emulsifying property of ISPP.     

Ultrasound-assisted limited enzymatic hydrolysis of high concentrated soy protein isolate: Alterations on the functional properties and its relation with hydrophobicity and molecular weight

The effects of power ultrasound (US) pretreatment on the preparation of soy protein isolate hydrolysate (SPIH) prepared at the same degree of hydrolysis (DH) of 12 % were measured. Cylindrical power ultrasound was modified into mono-frequency (20, 28, 35, 40, 50 kHz) ultrasonic cup coupled with an agitator to make it applicable for high density SPI (soy protein isolate) solutions (14 %, w/v). A comparative study of the alterations of the hydrolysates molecular weight, hydrophobics, antioxidants and functional properties change as well as their relation were explored. The results showed that under the same DH, ultrasound pretreatment decelerated the degradation of protein molecular mass and the decrease rate of the degradation lessened with the increase of ultrasonic frequency. Meanwhile, the pretreatments improved the hydrophobics and antioxidants properties of SPIH. Both surface hydrophobicity (H₀) and relative hydrophobicity (RH) of the pretreated groups increased with the decrease of ultrasonic frequency. Lowest frequency (20 kHz) ultrasound pretreatment had the most improved emulsifying properties and water holding capacities, although decrease in the viscosity and solubility were found. Most of these alterations were correspondence toward the change in hydrophobics properties and molecular mass. In conclusion, the frequency selection of ultrasound pretreatment is essential for the alteration of SPIH functional qualities prepared at the same DH.     

Influence of high-intensity ultrasound on physicochemical and functional properties of a guamuchil Pithecellobium dulce (Roxb.) seed protein isolate

In this study, the influence of ultrasound on the physicochemical and functional properties of guamuchil seed protein isolate (GSPI) was investigated. The GSPI was prepared by alkaline extraction and isoelectric precipitation method followed by treating with ethanol (95%), from defatted guamuchil seed flour. GSPI suspensions (10%) were sonicated with a probe (20 kHz) at 3 power levels (200 W, 400 W, 600 W) for 15 and 30 min, in addition, to control treatment without ultrasound. Moisture content, water activity, bulk and compact densities and the L*, a* and b* color parameters of the GSPI decreased due to the ultrasound. Glutelin (61.1%) was the main protein fraction in GSPI. Results through Fourier transform infrared and fluorescence spectroscopy showed that ultrasound modified the secondary and tertiary protein structures of GSPI, which increased the surface hydrophobicity, molecular flexibility and in vitro digestibility of GSPI proteins by up to 114.8%, 57.3% and 12.5%, respectively. In addition, maximum reductions of 11.9% in particle size and 55.2% in turbidity of GSPI suspensions, as well as larger and more porous aggregates in GSPI lyophilized powders were observed by ultrasound impact. These structural and physicochemical changes had an improvement of up to 115.5% in solubility, 39.8% in oil absorption capacity, while the increases for emulsifying, foaming, gelling, flow and cohesion properties of GSPI were 87.4%, 74.2%, 40.0%, 44.4%, and 8.9%, respectively. The amelioration of the functional properties of GSPI by ultrasound could represent an alternative for its possible use as a food ingredient in industry.     

Improving the gel properties of salted egg white/cooked soybean protein isolate composite gels by ultrasound treatment: Study on the gelling properties and structure

In this study, the effects of ultrasound treatment on the texture, physicochemical properties and protein structure of composite gels prepared by salted egg white (SEW) and cooked soybean protein isolate (CSPI) at different ratios were investigated. With the increased SEW addition, the ζ-potential absolute values, soluble protein content, surface hydrophobicity and swelling ratio of composite gels showed overall declining trends (P < 0.05), while the free sulfhydryl (SH) contents and hardness of exhibited overall increasing trends (P < 0.05). Microstructural results revealed that composite gels exhibited denser structure with the increased SEW addition. After ultrasound treatment, the particle size of composite protein solutions significantly decreased (P < 0.05), and the free SH contents of ultrasound-treated composite gels were lower than that of untreated composite gels. Moreover, ultrasound treatment enhanced the hardness of composite gels, and promoted the conversion of free water into non-flowable water. However, when ultrasonic power exceeded 150 W, the hardness of composite gels could not be further enhanced. FTIR results indicated that ultrasound treatment facilitated the composite protein aggregates to form a more stable gel structure. The improvement of ultrasound treatment on the properties of composite gels was mainly by promoting the dissociation of protein aggregates, and the dissociated protein particles further interacted to form denser aggregates through disulfide bond, thus facilitating the crosslinking and reaggregation of protein aggregates to form denser gel structure. Overall, ultrasound treatment is an effective approach to improve the properties of SEW-CSPI composite gels, which can improve the potential utilization of SEW and SPI in food processing.     

Dual-frequency multi-angle ultrasonic processing technology and its real-time monitoring on physicochemical properties of raw soymilk and soybean protein

To improve the soybean protein content (SPC), flavor and quality of soymilk, the effects of dual-frequency ultrasound at different angles (40 + 20 kHz 0°, 40 + 20 kHz 30°, 40 + 20 kHz 45°) on physicochemical properties and soybean protein (SP) structure of raw soymilk were mainly studied and compared with the conventional single-frequency (40 kHz, 20 kHz) ultrasound. Furthermore, the intensity of the ultrasonic field in real-time was monitored via the oscilloscope and spectrum analyzer. The results showed that 40 + 20 kHz 45° treatment significantly increased SPC. The ultrasonic field intensity of 40 + 20 kHz 0° treatment was the largest (8.727 × 10⁴ W/m²) and its distribution was the most uniform. The emulsifying stability of SP reached the peak value (233.80 min), and SP also had the largest particle size and excellent thermal stability. The protein solubility of 40 + 20 kHz 30° treatment attained peak value of 87.09%. 20 kHz treatment significantly affected the flavor of okara. The whiteness and brightness of raw soymilk treated with 40 kHz were the highest and the system was stable. Hence, the action mode of ultrasonic technology can be deeply explored and the feasibility for improving the quality of soymilk can be achieved.     

Ultrasound combined with slightly acidic electrolyzed water thawing of mutton: Effects on physicochemical properties,oxidation and structure of myofibrillar protein

The effects of air thawing (AT), water immersion thawing (WT), microwave thawing (MT) and ultrasound combined with slightly acidic electrolyzed water thawing (UST) on the myofibrillar protein (MP) properties (surface hydrophobicity, solubility, turbidity, particle size and zeta potential), protein oxidation (carbonyl content and sulfhydryl content) and structure (primary, secondary and tertiary) of frozen mutton were investigated in comparison with fresh mutton (FM). The solubility and turbidity results showed that the MP properties were significantly improved in the UST treatment. UST treatment could effectively reduce the MP aggregation and enhance the stability, which was similar to the FM. In addition, UST treatment could effectively inhibit protein oxidation during thawing as well. The primary structure of MP was not damaged by the thawing methods. UST treatment could reduce the damage to MP secondary and tertiary structure during the thawing process compared to other thawing methods. Overall, the UST treatment had a positive influence in maintaining the MP properties by inhibiting protein oxidation and protecting protein structure.     

Effect of pulsed ultrasound on the physicochemical characteristics and emulsifying properties of squid (Dosidicus gigas) mantle proteins

Food technologists are always looking to improve the functional properties of proteins. In this sense, in last years ultrasound has been used to improve some functional properties. For this reason, and considering that jumbo squid is an important fishery in northwest Mexico, the purpose of this research was to determine the effect of pulsed ultrasound on the physicochemical characteristics and emulsifying properties of squid (Dosidicus gigas) mantle proteins. Pulsed ultrasound (20 kHz, 20, and 40% amplitude) was applied for 30, 60, and 90 s to a protein extract prepared from giant squid mantle causing an increase (p < 0.05) in surface hydrophobicity (S_o) from 108.4 ± 1.4 to 239.1 ± 2.4 after application of pulsed ultrasound at 40% of amplitude for 90 s. The electrophoretic profile and the total and reactive sulfhydryl contents were not affected (p ⩾ 0.05) by the ultrasound treatment. The emulsifying ability of the protein solution was improved (p < 0.05), whereas the Emulsifier Activity Index (EAI) varied from123.67 ± 5.52 m²/g for the control and increased up to 217.7 ± 3.8 m²/g after application of the ultrasound. The Stability Emulsifier Index (EEI) was improved at 40% of amplitude by 60 and 90 s. The results suggested that pulsed ultrasound used as pretreatment induced conformational changes in giant squid proteins, which improved the interfacial association between protein-oil phases, thus contributing to the improvement of their emulsifient properties.     

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 ultrasound on the structural characteristics and oxidative stability of walnut oil oleogel coated with soy protein isolate-phosphatidylserine

In this study, the three-dimensional network system formed by rice bran wax (RBW) was used as the internal structure, and the external structure formed by soybean protein isolate (SPI) and phosphatidylserine (PS) was added on the basis of the internal structure to prepare walnut oil oleogel (SPI-PS-WOG). Ultrasonic treatment was applied to the mixed solution to make SPI-PS-WOG, on the basis, the effects of ultrasonic treatment on SPI-PS-WOG were investigated. The results showed that both β and β’ crystalline forms were present in all SPI-PS-WOG samples. When the ultrasonic power was 450 W, the first weight loss peak in the thermogravimetric (TGA) curve appeared at 326 °C, which was shifted to the right compared to the peak that occurred when the ultrasonic power was 0 W, indicating that the thermal stability of the SPI-PS-WOG was improved by the ultrasonic treatment. Moreover, when the ultrasonic power was 450 W, the oil holding capacity (OHC) reached 95.3 %, which was the best compared with other groups. Both confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) showed that the ultrasonic treatment of appropriate power succeeded in making the SPI-PS-WOG samples more evenly dispersed in the internal structure and denser in the external structure. In terms of oxidative stability, it was found that the peroxide value of SPI-PS-WOG remained at 9.8 mmol/kg oil for 50 days under 450 W ultrasonic power treatment, which was significantly improved compared with liquid walnut oil (WO). These results provide a new idea for the preparation of oleogels, and also lay a theoretical foundation for the application of ultrasonic treatment in oleogels.     

Influence of ultrasound-assisted ionic liquid pretreatments on the functional properties of soy protein hydrolysates

In this work, the effect of dual-frequency ultrasound-assisted ionic liquids (ILs) pretreatment on the functional properties of soy protein isolate (SPI) hydrolysates was investigated. The degree of hydrolysis (DH) of SPI pretreated by ultrasound and [BMIM][PF₆] increased by 12.53% as compared to control (P < 0.05). More peptides with low molecular weight were obtained, providing support for the changes in DH. The trichloroacetic acid-nitrogen soluble index presented an increase, suggesting a better protein hydrolysate property. The increase in the calcium-binding activity showed the ultrasound-assisted ILs pretreatment could potentially improve bone health. The foaming capacity and stability of SPI hydrolysates pretreated by ultrasound-assisted [BMIM][PF₆] always increased remarkably as compared to ultrasound-assisted [BDMIM][Cl] pretreatment. However, the synergistic effect of ultrasound-assisted [BMIM][PF₆] on the emulsifying activity and antioxidant activities (DPPH and hydroxyl radical scavenging activity) was not as ideal as ultrasound-assisted [BDMIM][Cl] pretreatment, which may be affected by the structure of peptide. In conclusion, these results indicated the combination of dual-frequency ultrasound and ionic liquids would be a promising method to improve the functional properties of SPI hydrolysates and broaden the application scope of compound modification in proteolysis industry.     

Influence of milk fat globule membrane and milk protein concentrate treated by ultrasound on the structural and emulsifying stability of mimicking human fat emulsions

The primary objective of the present study was to investigate the effectiveness of ultrasonic treatment time on the particle size, molecular weight, microstructure and solubility of milk fat globule membrane (rich in phospholipid, MPL) and milk protein concentrate (MPC). The mimicking human fat emulsions were prepared using modified proteins and compound vegetable oil and the structural, emulsifying properties and encapsulation efficiency of emulsions were evaluated. After ultrasonic treatment, the cavitation caused particle size decreased and structure change of both MPL and MPC, resulting in the enhancement of protein solubility. While, there was no significant change in molecular weight. Modified proteins by ultrasonic may cause a reduction in particle size and an improvement in emulsifying stability and encapsulation efficiency of emulsions. The optimal ultrasonic time to improve functional properties of MPL emulsion and MPC emulsion were 3 min and 6 min, respectively. The emulsifying stability of MPL emulsion was superior to MPC emulsion, which indicated that MPL is more suitable as membrane material to simulate human fat. Therefore, the obtained results can provide basis for quality control of infant formula.     

Effects of ultrasound-assisted enzyme hydrolysis on the microstructure and physicochemical properties of okara fibers

This work focuses on the effects of different ultrasound power densities on the microstructural changes and physicochemical properties of okara fibers, which are composed of carbohydrate-based polymers. Okara suspensions were treated with ultrasound at different power densities (0, 1, 2, 3, 4, and 5 W/mL) for 30 min, after which the ultrasound-treated okara were hydrolyzed by trypsin to obtain okara fibers. The ultrasound treatment of the okara fibers induced structural disorganization and changes, evidenced mainly in their morphological characteristics and their relative crystallinity degrees. Increasing the ultrasound power broke the okara fibers into flaky and stacked structures. When the ultrasound power density reached 4 W/mL, the parenchyma became compact and the hourglass structure fractured. The mean particle size of the okara fiber was reduced from 82.24 µm to 53.96 µm, and the homogeneity was enhanced significantly. The relative crystallinity of the okara fibers was reduced from 55.14% to 36.47%. The okara fiber surface charge decreased when the ultrasound power was increased. However, after ultrasound treatment at 4 W/mL (800 W), the okara fiber suspension exhibited the highest viscosity value and a higher swelling capacity, water-holding capacity, and oil-holding capacity. Therefore, the results indicated that the selection of processing conditions for okara fibers is critical and that okara fiber modification using a high ultrasound treatment might improve their use in potential applications.     

Ultrasound driven conformational and physicochemical changes of soy protein hydrolysates

The effect of ultrasound on the conformational and physicochemical properties of soy protein isolate hydrolysates (SPHs) was investigated. SPHs were prepared at hydrolysis times of 20 min, 60 min, and 180 min, then treated with ultrasound for 10 min, 20 min, and 30 min at a frequency of 20 kHz and output powers of 150 W and 450 W. The structural properties and antioxidant capacities of the aqueous layer of SPHs (ASPHs) after sonication were evaluated by Fourier-transform infrared spectroscopy (FTIR), intrinsic fluorescence, DPPH radical scavenging activity assays, and microscopy observations. Results obtained showed that ultrasound treatment significantly disrupted the peptide aggregates formed during protein hydrolysis. The protein solubility was significantly increased after sonication (by up to 18.33%), as did the percentage of proteins with MW < 1 kDa in ASPHs. The antioxidant capacity of ASPHs also increased, as measured by DPPH assay. FTIR analysis of ASPHs indicated that the protein secondary structures were different, with an increase in β-sheet and a decrease in α-helix and β-turn. Furthermore, the changes in fluorescence spectra of ASPHs showed the transition of protein tertiary structure with a greater exposure of Trp residues in the side chains. Scanning electron microscope (SEM) and atomic force microscope (AFM) observations of the morphological structure of ASPHs further confirmed the significant effect of sonication on disrupting peptide aggregates. In conclusion, ultrasound can be used as an efficient treatment to promote the solubility of protein hydrolysates.