Enzymolysis kinetics,thermodynamics and model of porcine cerebral protein with single-frequency countercurrent and pulsed ultrasound-assisted processing

The present work investigated the enzymolysis kinetics, thermodynamics and model of porcine cerebral protein (PCP) which was pretreated by single-frequency countercurrent and pulsed ultrasound. The kinetic constants for ultrasonic pretreated and traditional enzymolysis have been determined. Results showed that the value of K_M in ultrasonic PCP (UPCP) enzymolysis decreased by 9% over that in the traditional enzymolysis. The values of reaction rate constant (k) for UPCP enzymolysis increased by 207%, 121%, 62%, and 45% at 293, 303, 313 and 323 K, respectively. For the thermodynamic parameters, ultrasound decreased activation energy (E_a), change in enthalpy (ΔH) and entropy (ΔS) by 76%, 82% and 31% in PCP, respectively. However, ultrasound had little change in Gibbs free energy (ΔG) value in the temperature range of 293–323 K. Therefore, a general kinetic equation for the enzymolysis model of UPCP by a simple empirical equation was suggested. The experimental values fits with the enzymolysis kinetic model with a low average relative error (4%) confirmed that the kinetic model was accurate to reflect the enzymolysis process. The positive effect of single-frequency countercurrent and pulsed ultrasound in this study and application of the kinetic model may be useful for the release of bioactive peptides from meat processing by-products.     

Enzymolysis kinetics and structural characteristics of rice protein with energy-gathered ultrasound and ultrasound assisted alkali pretreatments

This research investigated the structural characteristics and enzymolysis kinetics of rice protein which was pretreated by energy-gathered ultrasound and ultrasound assisted alkali. The structural characteristics of rice protein before and after the pretreatment were performed with surface hydrophobicity and Fourier transform infrared (FTIR). There was an increase in the intensity of fluorescence spectrum and changes in functional groups after the pretreatment on rice protein compared with the control (without ultrasound and ultrasound assisted alkali processed), thus significantly enhancing efficiency of the enzymatic hydrolysis. A simplified kinetic equation for the enzymolysis model with the impeded reaction of enzyme was deduced to successfully describe the enzymatic hydrolysis of rice protein by different pretreatments. The initial observed rate constants (K_in,0) as well as ineffective coefficients (k_imp) were proposed and obtained based on the experimental observation. The results showed that the parameter of k_in,0 increased after ultrasound and ultrasound assisted alkali pretreatments, which proved the effects of the pretreatments on the substrate enhancing the enzymolysis process and had relation to the structure changes of the pretreatments on the substrate. Furthermore, the applicability of the simplified model was demonstrated by the enzymatic hydrolysis process for other materials.     

Effects of multi-frequency ultrasound pretreatment under low power density on the enzymolysis and the structure characterization of defatted wheat germ protein

The effects of ultrasonic frequency mode, power density, pretreatment time and other parameters under low power density on the degree of hydrolysis (DH) of defatted wheat germ protein (DWGP) and angiotensin-I-converting enzyme (ACE) inhibitory activity of DWGP hydrolysate were studied in this research. Ultraviolet–visible (UV–Vis) spectra, free sulfhydryl (SH), disulfide bond (SS), surface hydrophobicity and hydrophobic protein content of ultrasound-pretreated protein and hydrophobic amino acid (HAA) content of alcalase-hydrolysate of DWGP were measured under optimized ultrasonic condition. The ultrasonic frequency mode with dual-fixed frequency combination of 28/40 kHz showed higher ACE inhibitory activity of DWGP hydrolysate compared with that of other ultrasound frequency modes and all the ultrasonic frequency combinations involving in 28 kHz showed higher ACE inhibitory activity. Under the dual-fixed frequency ultrasound mode of 28/40 kHz, ultrasonic power density of 60 W/L, pretreatment time of 70 min, temperature of 60°C and substrate concentration of 60 g/L, the ACE inhibitory activity of DWGP hydrolysate was the highest with its value of 74.75% (increased by 62.30% compared to control). However, all the ultrasonic pretreatment did not increase the DH of DWGP significantly (p > 0.05). The changes in UV–Vis spectra, SH and SS groups, surface hydrophobicity and hydrophobic protein content indicated that the structure of DWGP unfolded after ultrasound pretreatment. The HAA content of hydrolysate from the pretreated DWGP increased significantly (p < 0.05). The results proved that ultrasound pretreatment loosed the protein structure and exposed more HAA residues of protein to be attacked easily by alcalase. This resulted in the increase in the HAA content which related to the ACE inhibitory activity.     

Transglutaminase-induced gelation properties of soy protein isolate and wheat gluten mixtures with high intensity ultrasonic pretreatment

Soy protein isolate (SPI) and wheat gluten (WG) are widely used in commercial food applications in Asia for their nutritional value and functional properties. However, individually each exhibits poor gelation. In this study, we examined the microbial transglutaminase (MTGase)-induced gelation properties of SPI and WG mixtures with high intensity ultrasonic pretreatment. Ultrasonic treatment reduced the particle size of SPI/WG molecules, which led to improvements in surface hydrophobicity (H_o) and free sulfhydryl (SH) group content. However, MTGase crosslinking facilitated the formation of disulfide bonds, markedly decreasing the content of free SH groups. Ultrasonic treatment improved the gel strength, water holding capacity, and storage modulus and resulted in denser and more homogeneous networks of MTGase-induced SPI/WG gels. In addition, ultrasonic treatment changed the secondary structure of the gel samples as determined by Fourier transform infrared spectroscopic analysis, with a reduction in α-helices and β-turns and an increase in β-sheets and random coils. Thus, ultrasound is useful in facilitating the gelation properties of MTGase-induced SPI/WG gels and might expand their utilization in the food protein gelation industry.     

超声波处理对脱脂麦胚分离蛋白结构的变化研究

应用傅里叶红外光谱(FTIR)、荧光光谱研究超声处理对脱脂麦胚分离蛋白(DWGP)结构的变化,建立DWGP高效酶解与其结构变化之间的关系.研究发现,超声处理均可提高DWGP的酶解效果,特别是经超声功率600 W、时间10 min处理后,酶解液抑制活性与对照组相比提高了23.96%.通过荧光光谱发现,超声作用改变DWGP溶液荧光强度,适当超声处理可使蛋白分子伸展、生色基团外露,有助于蛋白酶解后获得活性更高的抑制肽.采用对FTIR谱酰胺I带进行曲线拟合的方法,定量分析了不同超声功率、时间对DWGP二级结构的影响,发现超声作用使β-折叠相对含量下降而β-转角含量增加,这可能是DWGP酶解后获得高效抑制肽的主要原因.     

Synergism between ultrasonic pretreatment and white rot fungal enzymes on biodegradation of wheat chaff

Lignocellulosic biomass samples (wheat chaff) were pretreated by ultrasound (US) (40 kHz/0.5 W cm⁻²/10 min and 400 kHz/0.5 W cm⁻²/10 min applied sequentially) prior to digestion by enzyme extracts obtained from fermentation of the biomass with white rot fungi (Phanerochaete chrysosporium or Trametes sp.). The accessibility of the cellulosic components in wheat chaff was increased, as demonstrated by the increased concentration of sugars produced by exposure to the ultrasound treatment prior to enzyme addition. Pretreatment with ultrasound increased the concentration of lignin degradation products (guaiacol and syringol) obtained from wheat chaff after enzyme addition. In vitro digestibility of wheat chaff was also enhanced by the ultrasonics pretreatment in combination with treatment with enzyme extracts. Degradation was enhanced with the use of a mixture of the enzyme extracts compared to that for a single enzyme extract.     

Enzymolysis kinetics and activities of ACE inhibitory peptides from wheat germ protein prepared with SFP ultrasound-assisted processing

There is a great demand for developing efficient enzymolysis methods in order to increase the enzymolysis efficiencies and activities of angiotensin converting enzyme (ACE) inhibitory peptides from wheat germ protein. The enzymolysis kinetics, ACE inhibitory activity of peptide and conversion rate of protein were studied using sweep frequency and pulsed (SFP) ultrasound-assisted enzymolysis and the results were compared with traditional enzymolysis. The studied factors were enzymolysis time and substrate concentration. By considering the activity of ACE inhibitory peptide and operation cost, the recommended conditions of SFP ultrasound-assisted enzymolysis were enzymolysis time of 120 min and substrate concentration of 24.0 g/L, which gave high conversion rates of protein (60.7%) and ACE inhibitory activity of peptide (65.9%). Compared to traditional enzymolysis, SFP ultrasound-assisted enzymolysis significantly increased the initial reaction rate (V) by 60.0% at substrate concentration of 24.0 g/L, increased the apparent breakdown rate constant (k(A)) by 66.7%, decreased the apparent constant (K(M)) by 6.9%, and raised the conversion rate of protein by 35.5% and ACE inhibitory activity of peptides by 35.6% under the recommended conditions. It has been concluded that SFP ultrasound can remarkably raise the enzymolysis efficiency and activity of ACE inhibitory peptides from wheat germ protein.     

Effects of multi-frequency power ultrasound on the enzymolysis of corn gluten meal: Kinetics and thermodynamics study

The effects of multi-frequency power ultrasound (MPU) pretreatment on the kinetics and thermodynamics of corn gluten meal (CGM) were investigated in this research. The apparent constant (K_M), apparent break-down rate constant (k_A), reaction rate constants (k), energy of activation (E_a), enthalpy of activation (ΔH), entropy of activation (ΔS) and Gibbs free energy of activation (ΔG) were determined by means of the Michaelis–Menten equation, first-order kinetics model, Arrhenius equation and transition state theory, respectively. The results showed that MPU pretreatment can accelerate the enzymolysis of CGM under different enzymolysis conditions, viz. substrate concentration, enzyme concentration, pH, and temperature. Kinetics analysis revealed that MPU pretreatment decreased the K_M value by 26.1% and increased the k_A value by 7.3%, indicating ultrasound pretreatment increased the affinity between enzyme and substrate. In addition, the values of k for ultrasound pretreatment were increased by 84.8%, 41.9%, 28.9%, and 18.8% at the temperature of 293, 303, 313 and 323 K, respectively. For the thermodynamic parameters, ultrasound decreased E_a, ΔH and ΔS by 23.0%, 24.3% and 25.3%, respectively, but ultrasound had little change in ΔG value in the temperature range of 293–323 K. In conclusion, MPU pretreatment could remarkably enhance the enzymolysis of CGM, and this method can be applied to protein proteolysis industry to produce peptides.     

Effect of ultrasonic pretreatment on kinetics of gelatin hydrolysis by collagenase and its mechanism

Gelatin is a mixture of soluble proteins prepared by partial hydrolysis of native collagen. Gelatin can be enzymatically hydrolyzed to produce bioactive hydrolysates. However, the preparation of gelatin peptide with expected activity is usually a time-consuming process. The production efficiency of gelatin hydrolysates needs to be improved. In present work, effect of ultrasonic pretreatment on kinetic parameters of gelatin hydrolysis by collagenase was investigated based on an established kinetic model. With ultrasonic pretreatment, reaction rate constant and enzyme inactivation constant were increased by 27.5% and 27.8%, respectively. Meanwhile, hydrolysis activation energy and enzyme inactivation energy were reduced by 36.3% and 43.0%, respectively. In order to explore its possible mechanism, influence of sonication on structural properties of gelatin was determined using atomic force microscopy, particle size analyzer, fluorescence spectroscopy, protein solubility test and Fourier transform infrared spectroscopy. Moreover, hydrogen peroxide was used as a positive control for potential sonochemical effect. It was found that reduction of gelatin particle size was mainly caused by physical effect of ultrasound. Increased solubility and variation in β-sheet and random coil elements of gelatin were due to sonochemical effect. Both physical and chemical effects of sonication contributed to the change in α-helix and β-turn structures. The current results suggest that ultrasound can be potentially applied to stimulate the production efficiency of gelatin peptides, mainly due to its effects on modification of protein structures.     

Improving the enzymolysis efficiency of potato protein by simultaneous dual-frequency energy-gathered ultrasound pretreatment: Thermodynamics and kinetics

The thermodynamics and kinetics of traditional and simultaneous dual frequency energy-gathered ultrasound (SDFU) assisted enzymolysis of potato protein were investigated to get the knowledge of the mechanisms on the SDFU’s promoting efficiency during enzymolysis. The concentration of potato protein hydrolysate and parameters of thermodynamic and kinetic during traditional and SDFU assisted enzymolysis were determined. The results showed that potato protein hydrolysate concentration of SDFU assisted enzymolysis was higher than traditional enzymolysis at the hydrolysis time of 60 min (p < 0.05) whereas not significantly different at 120 min (p > 0.05). In some cases, SDFU assisted enzymolysis took less hydrolysis time than traditional enzymolysis when the similar conversion rates of potato protein were obtained. The thermodynamic papameters including the energy of activation (E_a), enthalpy of activation (△H), entropy of activation (△S) were reduced by ultrasound pretreatment while Gibbs free energy of activation (△G) increased little (1.6%). Also, kinetic papameters including Michaelis constant (K_M) and catalytic rate constant (k_cat) decreased by ultrasound pretreatment. On the contrary, reaction rate constants (k) of SDFU assisted enzymolysis were higher than that of traditional enzymolysis (p < 0.05). It was indicated that the efficiency of SDFU assisted enzymolysis was higher than traditional enzymolysis in a limited time. The higher efficiency of SDFU assisted enzymolysis was related with the decrease of E_a and K_M by lowering the energy barrier between ground and active state and increasing affinity between substrate and enzyme.     

Pretreatment of defatted wheat germ proteins (by-products of flour mill industry) using ultrasonic horn and bath reactors: Effect on structure and preparation of ACE-inhibitory peptides

The ultrasonic horn and bath reactors were compared based on production of angiotensin-converting-enzyme (ACE) inhibitory peptides from defatted wheat germ proteins (DWGP). The DWGP was sonicated before hydrolysis by Alcalase. Degree of hydrolysis, ACE-inhibitory activity, surface hydrophobicity, fluorescence intensity, free sulfhydryl (SH), and disulfide bond (SS) were determined. The highest ACE-inhibitory activity of DWGP hydrolysate was obtained at power intensity of 191.1 W/cm² for 10 min in the ultrasonic horn reactor. The fixed frequency of 33 kHz and the sweep frequency of 40 ± 2 kHz resulted in the maximum ACE-inhibitory activity. The combined irradiation of dual fixed frequency (24/68 kHz) produced significant increase in ACE-inhibitory activity compared with single frequency (33 kHz). The ultrasonic probe resulted in significant higher ACE-inhibitory activity compared with ultrasonic bath operating at single or dual fixed and sweep frequencies. The changes in conformation of the DWGP due to sonication were confirmed by the changes in fluorescence intensity, surface hydrophobicity, SH_f and SS contents and they were found in conformity with the ACE-inhibitory activity in case of the ultrasonic horn reactor but not in bath reactor.     

利用小麦叶片SPAD值预测成熟期籽粒蛋白质含量的研究

研究和建立在收获前对小麦籽粒品质快速无损预测的技术,本文利用31个小麦品种材料,对五个不同时期所测小麦顶一叶至顶四叶的SPAD值进行分析,获得SPAD值随取样时期及叶位的变化规律;利用近红外光谱测定蛋白质含量的方法获得材料的籽粒蛋白质含量,建立叶片SPAD值与成熟期籽粒蛋白质含量的相关关系。发现顶一叶SPAD递减速率与籽粒蛋白质含量之间呈现明显的负相关,直线拟合方程为y=-3.210 9x+14.286,相关系数r=-0.849 0。经显著性分析推断顶一叶SPAD值的递减速率与籽粒蛋白质含量存在着十分显著的直线相关关系。因此可以利用顶一叶SPAD值的递减速率来对籽粒蛋白质含量进行预测,以减轻品质育种工作量,指导育种实践。     

Kinetics and thermodynamics of Pb(II) adsorption onto modified spent grain from aqueous solutions

Spent grain, a main by-product of the brewing industry, is available in large quantities, but its main application has been limited to animal feeding. Nevertheless, in this study, spent grain modified with 1 M NaCl solution as a novel adsorbent has been used for the adsorption of Pb(II) in aqueous solutions. Isotherms, kinetics and thermodynamics of Pb(II) adsorption onto modified spent grain were studied. The equilibrium data were well fitted with Langmuir, Freundlich and Dubinin-Radushkevick (D-R) isotherm models. The kinetics of Pb(II) adsorption followed pseudo-second-order model, using the rate constants of pseudo-second-order model, the activation energy (E_a) of Pb(II) adsorption was determined as 12.33 kJ mol⁻¹ according to the Arrhenius equation. Various thermodynamic parameters such as ΔG^ads, ΔH^ads and ΔS^ads were also calculated. Thermodynamic results indicate that Pb(II) adsorption onto modified spent grain is a spontaneous and endothermic process. Therefore, it can be concluded that modified spent grain as a new effective adsorbent has potential for Pb(II) removal from aqueous solutions.     

Effects of ultrasound pretreatment with different frequencies and working modes on the enzymolysis and the structure characterization of rice protein

The effects of ultrasound pretreatment with different frequencies and working modes, including mono-frequency ultrasound (MFU), dual-frequency ultrasound (DFU) and tri-frequency ultrasound (TFU), on the degree of hydrolysis (DH) of rice protein (RP) and angiotensin-I-converting enzyme (ACE) inhibitory activity of RP hydrolysate were investigated. Ultraviolet–visible (UV) spectroscopy, fourier transform infrared (FTIR) spectroscopy, surface hydrophobicity and scanning electron microscopy (SEM) of RP pretreated with ultrasound were measured. The results showed that ultrasound pretreatment did not increase DH of RP significantly (p > 0.05). However, all the ultrasound pretreatment increased the ACE inhibitory activity of RP hydrolysate significantly (p < 0.05). The MFU of 20 kHz showed higher ACE inhibitory activity compared to that of other MFU. The ACE inhibitory activity of sequential DFU was higher than that of simultaneous with the same frequency combination. Sequential TFU of 20/35/50 kHz produced the highest increase in ACE inhibitory activity in contrast with other ultrasound frequencies and working modes. All the results under ultrasound pretreatment showed that ultrasound frequencies and working modes were of great effect on the ACE inhibitory activity of RP. The changes in UV–Vis spectra and surface hydrophobicity indicated the unfolding of protein and exposure of hydrophobic groups by ultrasound. The FTIR analysis showed that all the ultrasound pretreatment with different frequencies and working modes decreased α-helix, β-turn content and increased β-sheet, random coil content of RP. The SEM results indicated that ultrasound pretreatment resulted in the deformation of RP. In conclusion, the frequency selection of ultrasound pretreatment of RP is essential for the preparation of ACE inhibitory peptide.     

Experimental and numerical investigation of the effect of ultrasound on the growth kinetics of zeolite A

Ultrasound is a promising technology for the improvement of zeolite production, due to its beneficial effects on mass transfer and nucleation. However, a broad understanding of the sonication parameters that influence the growth of zeolites most is still lacking. In the present work, zeolite A was synthesized and the kinetic model of Gualtieri was used to obtain information about the crystallization parameters. The effect of the sonication power and duration on the relative crystallinity and particle size distribution were investigated using a Langevin-type transducer operating at 40 kHz. The experimental data shows that ultrasound has a significant effect on the nucleation and growth. With that, a reduction of up to 40 % of the initial synthesis time can be achieved. Additionally, a narrower particle size distribution is achieved when ultrasound is used during the zeolite A synthesis.     

Effect of ultrasonic power on properties of edible composite films based on rice protein hydrolysates and chitosan

Rice protein hydrolysates (RPH) are incapable of film formation by self-crosslinking due to low molecular mass. Hence, we used chitosan (CS) as a modifier and developed rice protein hydrolysates/chitosan (RPH/CS) edible composite films by means of ultrasound. Results showed that ultrasound treatment decreased the particle size and the viscosity of film-forming solutions. The value of elongation at break of composite films was increased by 125% at 400 W compared with untreated film. The peroxide value of soybean oil was significantly reduced from 16.99 ± 0.78 meq/kg to 2.23 ± 0.09 meq/kg with the increase of ultrasonic power. Ultrasound treatment was efficient in keeping smooth on surface, and the films at ultrasound treatment of 200 W had better compatibility. Moreover, hydrogen bonds and covalent interactions were probably the main forces between RPH and CS and contributed to film formation under ultrasound treatment, which supported by analyses of Fourier transform infrared spectroscopy and X-ray diffraction. These results suggested that ultrasound was an effective method to improve the properties of edible composite films.     

Effect of ultrasonic pretreatment on eliminating cyanogenic glycosides and hydrogen cyanide in cassava

Traditional soaking method takes days to remove cassava cyanide. Ten minutes of ultrasonic pretreatment (UPT) was found to be a new effective method to eliminate both cyanogenic glycosides and hydrogen cyanide in cassava. Here, the parameters of UPT were optimized and the underlying mechanisms were investigated. 40.36% and 24.95% of hydrogen cyanide and cyanogenic glycosides in cassava juice were eliminated under 10 min of UPT (45℃, 81 W). UPT before boiling enhanced the total cyanide elimination to 41.94%. The degradation patterns of hydrogen cyanide and cyanogenic glycosides were different. Ultrasound directly eliminated hydrogen cyanide and indirectly degraded cyanogenic glycosides through promoting enzymatic hydrolysis. The β-glucosidase activity was increased by 17.99% induced by ultrasound. This was supported by the movement of hydrophobic residual and the rearrangement of the secondary structure of the molecular as found in fluorescence, CD, FTIR, DSC and TG analysis. This study revealed that UPT acted as a fast and simple technical way in improving cassava safety.     

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 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.     

Effects and mechanism of ultrasound pretreatment of protein on the Maillard reaction of protein-hydrolysate from grass carp (Ctenopharyngodon idella)

The effects of two types (energy-divergent/gathered) of ultrasound pretreatment of protein on the Maillard reaction of protein-hydrolysate from grass carp (Ctenopharyngodon idella) were studied. The test and analysis of Fourier transform infrared spectroscopy, surface hydrophobicity and atomic force microscopy of protein, peptide concentration, molecular weight distribution and free amino acid content of protein-hydrolysate were performed to reveal the mechanism. Also, the sensory characteristics of Maillard reaction products were evaluated. Results showed that Maillard reaction products presented higher absorbance value at 294 and 420 nm after pretreated by two types of ultrasound compared to that of control. The grafting degree value of products pretreated by energy-divergent ultrasound increased by 13.87%. Both of these two types of ultrasound pretreatment showed higher (p < 0.05) value of grafting degree compared to that of positive control (thermal denaturation). The random coil content and surface hydrophobicity of protein improved significantly (p < 0.05), and the depth distribution of protein molecules narrowed down after pretreated by ultrasound, especially energy-divergent type ultrasound. The change of protein structure increased small molecular peptide/amino acid content in protein-hydrolysate, so that it promoted the Maillard reaction process of protein-hydrolysate and glucose. The mouthfulness and overall acceptance of Maillard reaction products increased after pretreated by two types of ultrasound. Results indicated that ultrasound, especially energy-divergent type ultrasound pretreatment of protein was an effective method to promote Maillard reaction evolution of protein-hydrolysate from grass carp protein and improved the flavor of Maillard reaction products.