Improvement in enzymolysis efficiency and changes in conformational attributes of corn gluten meal by dual-frequency slit ultrasonication action

Preparation of housefly (Musca domestica) larvae protein hydrolysates: Influence of dual-sweeping-frequency ultrasound-assisted enzymatic hydrolysis on yield, antioxidative activity, functional and structural attributes

Dual-sweeping-frequency ultrasound (DSFU) was utilized in the preparation of polypeptides from housefly (Musca domestica) larvae protein (HLP). Results indicated that ultrasonication (20 ± 2/28 ± 2 kHz, 42 W/L, 25 min) significantly increased peptide yield and DPPH scavenging capacity by 8.25 % and 14.83 %, respectively. Solubility, foaming and emulsification properties of polypeptides were improved by 19.89 %, 33.33 % and 38.74 % over the control; along with notable reduction in particle size and increase in zeta potential. Tertiary structural changes of the sonicated hydrolysates were illustrated by UV and fluorescence spectra. FTIR showed that ultrasonication increased α-helix, β-turn, and random coil by 38.23 %, 46.35 % and 16.36 %, respectively, but decreased β-sheet by 48.03 %, indicating partial unfolding in HLP hydrolysate conformation and reduction in intermolecular interactions. The research results demonstrated that dual-sweeping-frequency ultrasonication has a great prospect in industry application for the purpose of improving enzymolysis efficiency and product quality for housefly larvae protein hydrolysates production.

Extrusion puffing as a pretreatment method to change the surface structure, physicochemical properties and in vitro protein digestibility of distillers dried grains with solubles

BACKGROUND

Distillers dried grains with solubles (DDGS) are rich in nutrition, and they are potential protein feed raw material. However, the existence of cellulose, hemicellulose and lignin hinders animals' digestion and absorption of DDGS. Making full use of unconventional feed resources such as DDGS can alleviate the shortage of feed resources to a certain extent. This research investigated the effects of twin-screw extrusion on the macromolecular composition, physical and chemical properties, surface structure and in vitro protein digestibility (IVPD) of DDGS.

RESULTS

The findings showed that extrusion puffing significantly increased the protein solubility, bulk density, water holding capacity, and swelling capacity, while significantly decreased hemicellulose and crude protein content, particle size and zeta potential of DDGS. The structure damage of DDGS induced by the extrusion was characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FITR) spectroscopy and X-ray diffraction (XRD) analysis. Interestingly, no random coil was observed in the analysis of the secondary structure, and extrusion promoted the transformation of α-helix and β-turn to β-sheet, which led to significant increases in protein solubility and IVPD of DDGS (P < 0.05). Additionally, correlation analysis revealed that IVPD and PS had a positive relationship.

CONCLUSION

Extrusion puffing was an ideal pretreatment method for DDGS modification to improve in vitro protein digestibility. © 2023 Society of Chemical Industry.

Hexagonal plate ultrasound pretreatment on the correlation between soy protein isolate structure and cholesterol-lowering activity of peptides, and protein's enzymolysis kinetics, thermodynamics

In this study, a hexagonal plate ultrasound (HPU) pretreatment technology was employed to modify soy protein isolate (SPI) and enhance the hypocholesterolemic activity of enzymatic digests from SPI. Results demonstrated that under the condition of ultrasound power density of 40 W/L, the hypocholesterolemic activity of enzymatic digests from HPU-pretreated SPI (HPU-SPI) increased by 88.40 % compared to control group after gastrointestinal digestion. The sulfhydryl content of HPU-SPI increased by a maximum of 45.32 % compared to control group. Fourier transform infrared and scanning electron microscopy revealed that HPU pretreatment partially unfolded the SPI conformation, reduced the intermolecular interactions, and exposed the internal hydrophobic regions. Pearson correlation analysis showed that sulfhydryl groups (r = 0.860), disulfide bonds (r = -0.875) and random coil (r = 0.917) were strongly correlated with the cholesterol-lowering activity of soy protein hydrolysate (SPH), following a simulated gastrointestinal digestion. Finally, the effects of HPU pretreatment on enzymolysis kinetics and thermodynamics of the SPI enzymatic process showed that HPU pretreatment significantly reduced the Mie's constant, activation energy, activation enthalpy, activation entropy and Gibbs free energy. Overall, the study outcome suggested that HPU pretreatment could positively influence the hypocholesterolemic peptide activity, and thus, may be beneficial to the pharmaceutical/food industry.

Effects of slit dual-frequency ultrasound-assisted pulping on the structure, functional properties and antioxidant activity of Lycium barbarum proteins and in situ real-time monitoring process

To improve the protein dissolution rate and the quality of fresh Lycium barbarum pulp (LBP), we optimized the slit dual-frequency ultrasound-assisted pulping process, explored the dissolution kinetics of Lycium barbarum protein (LBPr), and established a near-infrared spectroscopy in situ real-time monitoring model for LBPr dissolution through spectral information analysis and chemometric methods. The results showed that under optimal conditions (dual-frequency 28-33 kHz, 300 W, 31 min, 40 °C, interval ratio 5:2 s/s), ultrasonic treatment not only significantly increased LBPr dissolution rate (increased by 71.48 %, p < 0.05), improved other nutrient contents and color, but also reduced the protein particle size, changed the amino acid composition ratio and protein structure, and increased the surface hydrophobicity, zeta potential, and free sulfhydryl content of protein, as well as the antioxidant activity of LBPr. In addition, ultrasonication significantly improved the functional properties of the protein, including thermal stability, foaming, emulsification and oil absorption capacity. Furthermore, the real-time monitoring model of the dissolution process was able to quantitatively predict the dissolution rate of LBPr with good calibration and prediction performance (Rc = 0.9835, RMSECV = 2.174, Rp = 0.9841, RMSEP = 1.206). These findings indicated that dual-frequency ultrasound has great potential to improve the quality of LBP and may provide a theoretical basis for the establishment of an intelligent control system in the industrialized production of LBP and the functional development of LBPr.

Ultrasound-Assisted Enzymatic Protein Hydrolysis in Food Processing: Mechanism and Parameters

Ultrasound has been widely used as a green and efficient non-thermal processing technique to assist with enzymatic hydrolysis. Compared with traditional enzymatic hydrolysis, ultrasonic-pretreatment-assisted enzymatic hydrolysis can significantly improve the efficiency of enzymatic hydrolysis and enhance the biological activity of substrates. At present, this technology is mainly used for the extraction of bioactive substances and the degradation of biological macromolecules. This review is focused on the mechanism of enzymatic hydrolysis assisted by ultrasonic pretreatment, including the effects of ultrasonic pretreatment on the enzyme structure, substrate structure, enzymatic hydrolysis kinetics, and thermodynamics and the effects of the ultrasonic conditions on the enzymatic hydrolysis results. The development status of ultrasonic devices and the application of ultrasonic-assisted enzymatic hydrolysis in the food industry are briefly described in this study. In the future, more attention should be paid to research on ultrasound-assisted enzymatic hydrolysis devices to promote the expansion of production and improve production efficiency.

Slit dual-frequency ultrasound-assisted pulping of Lycium barbarum fresh fruit to improve the dissolution of polysaccharides and in situ real-time monitoring

In this study, the slit dual-frequency ultrasound-assisted pulping of fresh Lycium barbarum fruit was optimized to improve the dissolution of polysaccharides. The microscopic mechanism of polysaccharide dissolution was explored through establishing polysaccharides dissolution kinetics model and visualizing the multi-physical fields during ultrasonic process, and an in situ real-time monitoring model was established by the relationship between the chemical value and spectral information collected by near-infrared spectroscopy. The results showed that, under optimal conditions, treatment with ultrasound (28-33 kHz, 250 W, 30 min) not only significantly promoted the dissolution rate of polysaccharides in Lycium barbarum pulp (LBPPs, increased by 43.64 %, p < 0.01), reduced its molecular weight, but also improved the arabinose molar ratio, the uniformity of polysaccharide particles, and the antioxidant activity of LBPPs. Correlation analysis indicated that ultrasonic treatment is closely related to LBPPs content, particle size and scavenging capacity against superoxide anion radicals (ptotal sugar content < 0.01, pparticle size < 0.05 and psuperoxide anion scavenging < 0.05). Moreover, the in situ real-time monitoring model for the pulping process could quantitatively predict LBPPs dissolution rate and its superoxide anion radical scavenging capacity with good calibration and prediction performance (Rc = 0.9841, RMSECV = 0.0873, Rp = 0.9772, RMSEP = 0.0530; Rc = 0.9874, RMSECV = 0.1246, Rp = 0.9868, RMSEP = 0.0665). These results indicated that slit dual-frequency ultrasound has great potential in improving the quality of Lycium barbarum pulp, which may provide theoretical support for the industrial development of intelligent systems for polysaccharides preparation.

Effect of multi-mode sweep frequency ultrasound pretreatment on properties of the zeins and ACE inhibitory peptides activity of the hydrolysates

Effects of sweep frequency ultrasound (SFU) pretreatment of a new multifunctional ultrasonic equipment on hydrolysis characteristics of zeins and angiotensin-converting enzyme (ACE) inhibitory activity of zein hydrolysates were investigated. Degree of hydrolysis of zeins reached the highest of 25.93 % and 25.72 % at 40 kHz and 25/40 kHz, respectively. While 25/40 kHz increased solubility, surface hydrophobicity, particle size uniform of zeins and ACE inhibitory activities of the hydrolysates significantly. Endogenous fluorescence indicated that 25/40 kHz promoted unfolding of protein molecules and exposure of hydrophobic residues, thereby facilitating enzymatic hydrolysis. Circular dichroism spectrum and Fourier transform infrared spectrometer illustrated that 25/40 kHz unfolded protein molecules and decreased α-helical contents remarkably. Gel permeation chromatography showed that more small-molecule active peptides were obtained from hydrolysates at 25/40 kHz. In conclusion, SFU pretreatment at 25/40 kHz with the new equipment before proteolysis is an efficient method to improve ACE inhibitory activity of the hydrolysates.

Insights into Ultrasonication Treatment on the Characteristics of Cereal Proteins: Functionality, Conformational and Physicochemical Characteristics

BACKGROUND

It would be impossible to imagine a country where cereals and their byproducts were not at the peak of foodstuff systems as a source of food, fertilizer, or for fiber and fuel production. Moreover, the production of cereal proteins (CPs) has recently attracted the scientific community's interest due to the increasing demands for physical wellbeing and animal health. However, the nutritional and technological enhancements of CPs are needed to ameliorate their functional and structural properties. Ultrasonic technology is an emerging nonthermal method to change the functionality and conformational characteristics of CPs. Scope and approach: This article briefly discusses the effects of ultrasonication on the characteristics of CPs. The effects of ultrasonication on the solubility, emulsibility, foamability, surface-hydrophobicity, particle-size, conformational-structure, microstructural, enzymatic-hydrolysis, and digestive properties are summarized.

CONCLUSIONS

The results demonstrate that ultrasonication could be used to enhance the characteristics of CPs. Proper ultrasonic treatment could improve functionalities such as solubility, emulsibility, and foamability, and is a good method for altering protein structures (including surface hydrophobicity, sulfhydryl and disulfide bonds, particle size, secondary and tertiary structures, and microstructure). In addition, ultrasonic treatment could effectively promote the enzymolytic efficiency of CPs. Furthermore, the in vitro digestibility was enhanced after suitable sonication treatment. Therefore, ultrasonication technology is a useful method to modify cereal protein functionality and structure for the food industry.

Pulsed Electric Field-Assisted Alcalase Treatment Reduces the Allergenicity and Eliminates the Antigenic Epitopes of Ovomucoid

Physically assisted chemical modifications can effectively reduce the allergenicity of ovomucoid (OVM). However, only a few studies have used pulsed electric field (PEF)-assisted alcalase hydrolysis to reduce the allergenicity of OVM. Herein, we investigated the effect of PEF-assisted alcalase treatment on the spatial conformation, allergenicity, and antigenic epitopes of OVM based on multispectroscopic analyses, bioinformatics, and mass spectrometry. The results showed that PEF-assisted alcalase treatment promoted the hydrolysis of OVM; moreover, the α-helix content and surface hydrophobicity of OVM significantly decreased, which disordered its spatial conformation and weakened its intermolecular interactions. Additionally, enzyme-linked immunosorbent assay (ELISA) results showed that the PEF-assisted alcalase treatment significantly reduced the binding levels of IgE and IgG1, which were 47.66 and 36.41%, respectively. Finally, eight epitopes of OVM were obtained by immunoinformatic tools. Nano-high performance liquid chromatography coupled to tandem mass spectrometry (nano-HPLC MS/MS) results showed that the hydrolysate of OVM and alcalase (HOVM) had nine more peptide-containing epitopes than the hydrolysate of PEF-treated OVM and PEF-treated alcalase (HOVM-PP'), indicating that PEF could promote the elimination of linear epitopes in OVM, thereby reducing OVM allergenicity.

Effect of ultrasonic pretreatment on the rheology and structure of grass pea (Lathyrus sativus L.) protein emulsion gels induced by transglutaminase

In this study, emulsion gels were prepared by sonicated grass pea protein isolates (GPPI) at different ultrasonic amplitudes (25, 50 and 75 %) and times (5, 10 and 20 min). Formation of emulsion gels was induced by transglutaminase. Enzymatic gelation of emulsions stabilized by sonicated GPPI occurred in two stages. A relatively fast stage led to the formation of a weak gel which was followed by a slow stage that strongly reinforced the gel structure. Emulsion gels fabricated by sonicated GPPIs showed a homogeneous and uniform droplet distribution with higher elastic modulus compared to the native protein. A stiffer emulsion gel with a higher G' was formed after the protein was treated at 75 % amplitude for 10 min. After sonication of GPPI, the water holding capacity (WHC) of emulsion gels increased in accordance with the mechanical properties. Higher intermolecular cross-linking within the gel network increased the thermal stability of emulsion gels fabricated by sonicated GPPI. Although sonicated-GPPI emulsion gels clearly displayed homogenous microstructure in comparison to that made with native GPPI, the microstructures of these gels were nearly identical for all sonication amplitudes and times.

Interaction mechanism between cereal phenolic acids and gluten protein: protein structural changes and binding mode

BACKGROUND

Phenolic acids are antioxidant nutrients in cereals and affect the quality of wheat products and the properties of gluten protein. Gallic acid (GA), caffeic acid (CA), syringic acid (SA), and p-coumaric acid (p-CA) were selected to study the interaction mechanism between cereal phenolic acids and gluten protein.

RESULTS

The results showed that adding GA significantly (P < 0.05) decreased the content of free sulfhydryl in gluten proteins by 70-87.26% compared with the control group. The aggregates' behavior of gluten protein induced by adding the phenolic acids would produce oversized particles (>5000 nm). Adding the selected phenolic acids changed the hydrogen-bond linkage of protein secondary structure. Zeta potential values of gluten protein increased significantly (P < 0.05) by 14.41%, 26.49%, 30.77%, and 57.93% for CA, p-CA, GA, and SA respectively added at 0.03 g kg^-1 . Moreover, the gluten protein surface hydrophobicity increased when the phenolic acids were added at 0.03 g kg^-1 , displaying the effect of the phenolic acid on the hydrophobic interaction of protein. Molecular docking results showed that the selected phenolic acids could interact with glutenin and gliadin using hydrogen-bond formation, and SA had the strongest binding with glutenin and gliadin.

CONCLUSION

The results demonstrated that the selected phenolic acids could interact with gluten protein via covalent cross-linking as well as by hydrogen bonding, thereby changing the structure of the gluten protein. This exploration is expected to provide theoretical support for the development and utilization of whole-grain foods. © 2022 Society of Chemical Industry.

Extraction of phenolics and anthocyanins from purple eggplant peels by multi-frequency ultrasound: Effects of different extraction factors and optimization using uniform design

In this work, multi-frequency ultrasound (working modes for the single-, dual- and tri-frequency in simultaneous ways) was applied to extract bioactive compounds from purple eggplant peels. The single-factor experiments were performed by varying six independent variables. A six-level-five-factor uniform design (UD) was further employed to evaluate the interaction effects between different factors. It was found that extraction temperature and extraction time significantly affected the total phenolic content (TPC), whereas the total monomeric anthocyanins (TMA) was mainly influenced by ethanol concentration, extraction temperature and solid-liquid ratio. Based on partial least-squares (PLS) regression analysis, the optimal conditions for TPC extraction were: 53.6 % ethanol concentration, 0.336 mm particle size, 44.5 °C extraction temperature, 35.2 min extraction time, 1:43 g/mL solid-liquid ratio, and similar optimal conditions were also obtained for TMA. Furthermore, the TPC and TMA extraction were investigated by ultrasound in different frequencies and power levels. Compared with single-frequency (40 kHz) and dual-frequency ultrasound (25 + 40 kHz), the extraction yield of TPC and TMA with tri-frequency ultrasound (25 + 40 + 70 kHz) increased by 23.65 % and 18.76 % respectively, which suggested the use of multi-frequency ultrasound, especially tri-frequency ultrasound, is an efficient strategy to improve the TPC and TMA extracts in purple eggplant peels.

Effects of dual-frequency slit ultrasound on the enzymolysis of high-concentration hydrolyzed feather meal: Biological activities and structural characteristics of hydrolysates

Ultrasound-assisted enzymolysis has been applied to improve conventional enzymolysis, while there are rare reports on the application of ultrasound to high-concentration feather protein enzymolysis. Therefore, the feasibility of dual-frequency slit ultrasound (DFSU) for enzymolysis of high-concentration hydrolyzed feather meal (HFM), as well as the biological activities and structural characteristics of hydrolysates were investigated. The single-factor test was used to optimize the ultrasonic processing parameters: substrate concentration, frequency mode, intermittent ratio, power density, and time. The results showed that protein recovery rate and conversion rate increased by 6.08% and 18.63% under the optimal conditions (200 g/L, 28/80 kHz, 5:2 s/s, 600 W/L, and 3 h) compared with conventional enzymolysis, respectively. The macromolecular proteins in hydrolysates were converted into micromolecular peptides (< 500 Da) when treated by DFSU, and antioxidant activity and angiotensin-I-converting enzyme (ACE) inhibitory activity of hydrolysates were increased. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images illustrated the microstructure changes of feather protein particles in the ultrasound-assisted enzymatic hydrolysates of HFM (UEH), including more porous, smaller, and more uniform. Additionally, the conformation of protein molecules was significantly affected (P < 0.05), including the increase in free sulfhydryl (SH), the decrease in disulfide bond (SS) and surface hydrophobicity (H₀). Fourier transform infrared (FTIR) spectra analysis further showed that the secondary structure of feather proteins was modified with a reduction in α-helix, β-turn, and β-sheet, while an increase in random coil content was observed. These results indicated that DFSU could be a promising method to enhance high-concentration HFM for preparing peptide-rich hydrolysates with high antioxidant activity and ACE inhibitory activity.

Hybridising plasma functionalized water and ultrasound pretreatment for enzymatic protein hydrolysis of Larimichthys polyactis: Parametric screening and optimization

Hybridising plasma functionalized water and ultrasound pretreatment for the enzymatic hydrolysis (HPUEH) of Larimichthys polyactis was evaluated by adopting Plackett-Burman design for parametric screening of six key variables, and Box-Behnken design for optimizing three most significant variables including plasma generating voltage (P_V), ultrasound treatment time (U_T), and enzyme concentration (E_C). The models developed for predicting the degree of hydrolysis (DoH), protein recovery (PVY), and soluble protein content (SPC) were sufficiently fitted to the experimental data (R² ≥ 0.966) with non-significant lack of fit and used for determining the optimum conditions as P_V of 70 V, U_T of 15 min, and E_C of 1.787%, with predictive values of 27.74%, 85.62%, and 3.28 mg/mL for DoH, PVY, and SPC, respectively. HPUEH presented hydrolysates with smaller peptide sizes and molecular weights, enhanced DoH, PVY, SPC, amino acids and antioxidant activity, but reduced emulsifying and foaming properties when compared with conventional enzymatic hydrolysis.

Functional and bioactive properties of Larimichthys polyactis protein hydrolysates as influenced by plasma functionalized water-ultrasound hybrid treatments and enzyme types

The effects of plasma functionalized water (PFW) and its combination with ultrasound (UPFW) on the functional and bioactive properties of small yellow croaker protein hydrolysates (SYPHs) produced from three enzymes were investigated. Fluorescence and UV-Vis spectroscopy indicated that SYPHs tended to unfold with increasing intensity and shift in wavelengths to more flexible conformations under PFW and UPFW treatments. Particle size distribution and microstructure analysis revealed that treatments could disrupt aggregation of protein molecules to increase the roughness, specific surface area, and decrease the particle size of peptides during hydrolysis. The partially denatured structure of SYPHs induced by treatments increased the susceptibility of the fish proteins to exogenous enzymes, thereby accelerating the hydrolytic process to yield peptides with improved solubility, decreased emulsifying and foaming properties, and improved enzyme-specific antioxidant properties. The results revealed that the functionality of SYPHs was influenced by the treatment method and the enzyme type employed.

Recent advances in modified food proteins by high intensity ultrasound for enhancing functionality: Potential mechanisms, combination with other methods, equipment innovations and future directions

High intensity ultrasound (HIU) is an efficient and green technology that has recently received enormous research attention for modification of food proteins. However, there are still several knowledge gaps in the possible mechanisms, synergistic effects of HIU with other strategies and improvement of HIU equipment that contribute to its application in the food industry. This review focuses on the recent research progress on the effects and potential mechanisms of HIU on the structure (including secondary and tertiary structure) and functionality (including solubility, emulsibility, foamability, and gelability) of proteins. Furthermore, the combination methods and innovations of HIU equipment for proteins modification in recent years are also detailed. Meanwhile, the possible future trends of food proteins modification by HIU are also considered and proposed.

Application of multi-frequency power ultrasound in selected food processing using large-scale reactors: A review

Ultrasound as an eco-friendly green technology has been widely studied in food processing. Nevertheless, there is a lack of publications regarding the application of ultrasound in food processing using large-scale reactors. In this paper, the mechanisms and the devices of multi-frequency power ultrasound (MFPU) are described. Moreover, the MFPU applied in enzymolysis of protein, and washing of fruits and vegetables are reviewed. The application of MFPU can improve the enzymolysis of protein through modification on enzyme, modification on substrate materials, and facilitation of the enzymatic hydrolysis process. The ultrasound treatment can enhance the removal of microorganisms, and pesticides on the surface of fruits and vegetables. Furthermore, the reactors of ultrasound-assisted enzymolysis of protein, and washing of fruits and vegetables on the industrial scale are also detailed. This review paper also considers future trends, limitations, drawbacks, and developments of ultrasound application in enzymolysis and washing.

Ultrasound, infrared and its assisted technology, a promising tool in physical food processing: A review of recent developments

Traditional food processing techniques can no longer meet the ever increasing demand for high quality food across the globe due to its low process efficiency, high energy consumption and low product yield. This review article is focused on the mechanism and application of Infrared (IR) and ultrasound (US) technologies in physical processing of food. We herein present the individual use of IR and US (both mono-frequency and multi-frequency levels) as well as IR and US supported with other thermal and non-thermal technologies to improve their food processing performance. IR and US are recent thermal and non-thermal technologies which have now been successfully used in food industries to solve the demerits of conventional processing technologies. These environmentally-friendly technologies are characterized by low energy consumption, reduced processing time, high mass-transfer rates, better nutrient retention, better product quality, less mechanical damage and improved shelf life. This work could be, with no doubt, useful to the scientific world and food industries by providing insights on recent advances in the use of US and IR technology, which can be applied to improve food processing technologies for better quality and safer products.

Proteolysis efficiency and structural traits of corn gluten meal: Impact of different frequency modes of a low-power density ultrasound

The influence of varying frequency modes of a low-power density ultrasound (LPDU) on the enzymolysis efficacy and structural property of corn gluten meal (CGM) was investigated. Sonication pretreatment (of CGM) with sequential and simultaneous duple-frequency modes enhanced notably the relative enzymolysis efficiency, compared to other LPDU frequency modes. With a sequential duple-frequency of 20/40 kHz showing the most significant effect, the maximum value of enzymolysis efficiency and protein dissolution rate were 15.99% and 61.69%, respectively. Changes in the surface hydrophobicity, secondary structure and microstructure revealed alterations of conformation of CGM by ultrasound-induced effect. Furthermore, the molecular weight distribution CGM hydrolysates primarily distributed in 200-500 Da following ultrasonication. Sonication efficaciously enhanced the susceptibility of CGM to alcalase proteolysis. Thus, the use of various LPDU frequency modes in pretreating target proteins (CGM) may be considered as a practical approach to improve protein-enzyme reactions (proteolysis).

Simulation Study on the Influence of Multifrequency Ultrasound on Transient Cavitation Threshold in Different Media

Through the introduction of multifrequency ultrasound technology, remarkable results have been achieved in tissue ablation and other aspects. By using the nonlinear dynamic equation of spherical bubble, the effects of the combination mode of multifrequency ultrasound, the peak negative pressure and its duration, the phase angle difference, and the polytropic index on the transient cavitation threshold in four different media of water, blood, brain, and liver are simulated and analyzed. The simulation results show that under the same frequency difference and initial bubble radius, the transient cavitation threshold of the high-frequency, triple-frequency combination is higher than that of the low-frequency, triple-frequency combination. When the lowest frequency of triple frequencies is the same, the larger the frequency difference, the higher the transient cavitation threshold. When the initial bubble radius is small, the frequency difference has little effect on the transient cavitation threshold of the triple-frequency combination. With the increase of initial bubble radius, the influence of frequency difference on the transient cavitation threshold of the higher frequency combination of triple frequency is more obvious than that of the lower frequency combination of triple frequency. When the duration of peak negative pressure or peak negative pressure of the multifrequency combined ultrasound is longer than that of the single-frequency ultrasound, the transient cavitation threshold of the multifrequency combined ultrasound is lower than that of the single-frequency ultrasound; on the contrary, the transient cavitation threshold of the multifrequency combined ultrasound is higher than that of the single-frequency ultrasound. When the phase angle difference of multifrequency excitation is zero, the corresponding transient cavitation threshold is the lowest, while the change of the polytropic index has almost no effect on the transient cavitation threshold for the multifrequency combination. The research results can provide a reference for multifrequency ultrasound to reduce the transient cavitation threshold, which is of great significance for the practical application of cavitation.