酶解法提取香菇多糖的探讨

用酶解法提取香菇多糖,研究了酶解浓度、酶解时间、温度、pH等因素对多糖提取率的影响。结果表明,酶解法提取香菇多糖的最佳工艺为纤维素酶0.5%,果胶酶0.5%,木瓜蛋白酶1.0%,pH4.5,温度50℃,反应时间为80min,用酶水解后其多糖的提取率可达0.4588%。     

动态瞬时高压作用对膳食纤维酶解速度的影响

 对纤维素酶对动态瞬时高压处理后膳食纤维的酶解速度进行了研究。豆渣膳食纤维（Dietary Fiber,DF）经微射流均质机的瞬时高压作用（Instantaneous High Pressure,IHP）,在不同的压力以及同一压力的不同作用次数下产生不同粒径和密度,它们对应的酶解速度是不同的。纤维素酶水解膳食纤维产生纤维二糖和葡萄糖等还原糖,通过测定水解后还原糖的含量判断不同粒径和密度的膳食纤维的酶解速度。结果表明,在40～90 MPa的压力范围内随压力的增大物料粒径呈显著下降,物料密度随之增大,酶解速度增大,在90 MPa的均质压力下物料粒径达到最小,为202.4 nm;当压力继续增大时,物料因膨化作用,物料粒径呈增大趋势,但其密度开始减小,酶解速度继续增大,在140 MPa的均质压力下物料密度达到最小,为1.027 g/mL,此时酶解后还原糖含量最高,酶解速度最快。压力超过140 MPa后,由于超微颗粒间的团聚,物料的密度和粒径均增大,酶解速度减小。在90 MPa和140 MPa下对分别对物料进行多次的瞬时高压处理,发现随处理次数的增多物料粒径增大,体系密度先减小后增大,酶解速度减小。     

壁载纤维素酶微反应器内传递及转化特性

壁载纤维素酶微反应器能够实现纤维素类生物质水解制备葡萄糖,为后续微生物能源转化提供原料。本文对壁载纤维素酶微反应器内羧甲基纤维素模型化合物的酶解糖化进行了实验与模拟研究,获得了内表面结构对微反应器物质传递及酶解反应的影响规律。模拟结果表明,相较于等边三角形、半圆形等内表面结构,设置高矩形结构对微反应器内葡萄糖生产的促进显著。此外,具有高矩形结构的微反应器单位压降下的出口葡萄糖浓度最高,有利于实际应用。相较于增加表面结构尺寸,减小结构间距具有更好的强化效果。在最适表面结构参数下,对于不同黏度的酶解反应,出口平均葡萄糖浓度的提升率均高于7.0%。     

酶法提取番茄红素

在提取番茄中番茄红素时,添加果胶酶和纤维素酶,筛选出最佳工艺为:果胶酶和纤维素酶的比例为4∶1、添加酶量为0.5%、酶的作用温度为40℃、pH4、浸提时间为4h,按此条件可大大提高番茄红素的提取率。     

云南盘鮈酶水解条件研究

采用动物蛋白水解酶对云南盘鮈进行酶水解,通过正交实验法确定了酶水解条件。结果表明,酶水解的最适条件为:温度50℃,pH7.0,时间3h,加酶量0.5%,固液比1∶2.5。在该条件下盘鮈肉蛋白的水解度为32.85%。氨基酸分析表明,游离氨基酸含量36.47mg/mL,必需氨基酸14.42mg/mL,占39.54%。尤其是亮氨酸、缬氨酸、苏氨酸、赖氨酸含量丰富,为低值鱼深加工研究提供理论依据。     

串联酶解耦合超微粉碎法对蔗渣酶解的促进作用

报道了一种新颖的串联酶解(先酶I后酶II)耦合超微粉碎方法,并系统研究了其对蔗渣酶水解的促进作用. 通过对三种酶解方法(单酶I、单酶II、先酶I后酶II) 的比较发现,串联酶解对蔗渣酶解最为有效. 超微粉碎能破坏蔗渣细胞结构,使纤维素充分暴露出来便于酶解.在串联酶解耦合超微粉碎模式下,蔗渣在反应温度50 oC,pH=4.8,酶I(7.5 FPU/g底物)和酶II(5.0 FPU/g底物),摇床速率1200 r/min条件下反应72 h后,酶水解能得到65%的还原糖浓度,其中葡萄糖选择性为90.1%.     

复合酶水解云南白鱼制备生物活性肽类物质

研究了复合蛋白酶对云南土著白鱼水解的工艺条件。考察了酶用量、温度、pH值、反应时间、底物浓度、复合酶比例等因素对白鱼水解的影响。确定了最佳酶解条件为:复合酶用量(木瓜蛋白酶+风味蛋白酶1∶1)16000U/g,底物浓度30%,温度55℃,pH值7.5,时间4h。在此条件下,水解度达34.12%,氮回收率90.05%。该结果为云南白鱼生产功能食品提供科学依据。     

高压处理对酪蛋白酶解产物抗氧化活性的影响

研究了高压处理条件和处理对象对胰蛋白酶水解酪蛋白特性及产物抗氧化活性的影响。以水解度、DPPH自由基、超氧阴离子自由基、羟基自由基和还原力为测定指标,研究了高压处理胰蛋白酶、酪蛋白、酪蛋白+胰蛋白酶后的酶解特性和产物的抗氧化活性。结果表明:在水解度方面,高压对酪蛋白的处理效果比胰蛋白酶好,在200MPa的压力下保压20min时,酪蛋白的水解度提高了31.14%,但是高压对酪蛋白+胰蛋白酶的处理效果不佳;经100MPa保压15min或50MPa保压5min处理后胰蛋白酶的酶解产物对DPPH自由基和超氧阴离子自由基有较强的清除能力,而经150MPa保压10min处理的酪蛋白以及经150MPa保压15min处理的酪蛋白+胰蛋白酶的酶解产物在羟基自由基的清除能力和还原力方面表现更好,并且酶解产物的抗氧化活性与水解程度不成正相关。     

黄芩素的酶解提取工艺及其抑制弹性蛋白酶活性研究

利用正交试验对中药黄芩中提取黄芩素酶解工艺进行了初步探讨,确定最佳酶解工艺条件：温度为40℃、pH6.0、时间12h时,黄芩素含量最高;利用酶活力法对黄芩素体外抑制弹性蛋白酶活性进行了研究,发现黄芩素对弹性蛋白酶具有明显的抑制作用,抑制率达92.98%。     

溶胶-凝胶法制备均相掺钛干凝胶

以溶胶-凝胶法制备掺钛干凝胶,采用冰乙酸控制钛酸四丁酯水解,结合钛源与硅源独立预水解技术制备前体掺钛溶胶和凝胶。考察了溶剂量、抑制剂量和掺钛量对溶胶稳定性和均匀性的影响,以及老化、干燥条件和掺钛量对凝胶均匀性的影响,并优化了工艺参数。结果表明,冰乙酸能够有效地控制钛源水解并改善溶胶均匀性,结合钛源和硅源独立预水解技术,能够可控地制备出掺钛溶胶。在乙醇与醇盐物质的量比为5、冰乙酸与钛酸四丁酯物质的量比为6、钛硅原子数比为2%~20%的条件下可以得到均匀、稳定的溶胶。钛硅原子数比低于10%的溶胶在100℃老化24h,100℃开放条件下干燥24h能够形成均匀的干凝胶。钛硅原子数比高于10%的凝胶在干燥过程中析出氯化钠,得不到均匀的凝胶。     

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.     

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.     

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.     

Enzymolysis reaction kinetics and thermodynamics of defatted wheat germ protein with ultrasonic pretreatment

This research explores the mechanism of ultrasonic pretreatment on enzymolysis of defatted wheat germ protein (DWGP). The enzymolysis reaction kinetics and thermodynamics were studied after ultrasonic pretreatments using a probe-type sonicator and an ultrasonic cleaning bath, and the results were compared with traditional enzymolysis. The results showed that both the traditional and ultrasonic pretreated enzymolysis fit well to first-order kinetics. Both the temperature and ultrasound had a positive effect on the enzymolysis of DWGP, with temperature playing a dominant role. Under the optimized conditions of DWGP concentration of 1% (w/v), Alcalase concentration of 2000 U/g, time of 10 min and temperature of 50 °C, both the probe and cleaning bath ultrasonic pretreated enzymolysis showed high polypeptide concentrations (231.019 and 231.320 μg/mL) and low energy requirements. In comparison with traditional enzymolysis, these methods significantly increased the reaction rate constant (k) by 166.7% and 144.4%, 92.9% and 85.7%, 28.0% and 28.0%, 16.1% and 12.9% at 20, 30, 40 and 50 °C, and decreased the activation energy (E_a), enthalpy of activation (ΔH), Gibbs free energy of activation (ΔG) and entropy of activation (ΔS) by 68.6% and 62.4%, 74.1% and 67.5%, 34.3% and 31.2%, 1.4% and 1.3%. It can be concluded that ultrasonic pretreatment of DWGP can remarkably improve the enzymolysis efficiency and consequently leads to the production of higher polypeptide yield.     

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.     

Effect of multi-frequency power ultrasound (MFPU) treatment on enzyme hydrolysis of casein

Effect of multi-frequency power ultrasound (MFPU) pretreatments on the degree of hydrolysis (DH) and mechanism of casein during alcalase enzymolysis was investigated. Results showed that MFPU pretreatment in tri-frequency 20/40/60 kHz mode significantly (p < 0.05) improved the DH value of casein. Variation of intrinsic fluorescence spectrum indicated the unfolding and degradation of casein occurred after MFPU pretreatment. Fourier transform infrared spectra showed that α-helix and β-sheet content of MFPU pretreated casein decreased, while β-turn and random coil content increased. Surface topography and nanostructures of caseins were found modified after MFPU pretreatments by the analysis of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM analysis also indicated that the enzymolysis residues of casein pretreated by MFPU were smaller than untreated samples. In conclusion, the MFPU can be used as an efficient pretreatment method to promote the enzymolysis of casein.     

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.     

Localized enzymolysis and sonochemically modified sunflower protein: Physical,functional and structure attributes

Impacts of localized enzymolysis and sonication on physical, techno-functional, and structure attributes of sunflower meal protein (SMP) and its hydrolysate (SMPH) were studied. SMP was subjected to enzymolysis (using alcalase) to prepare SMPH with various degrees of hydrolysis (6–24% DH). Enzymolysis decreased colour lightness, turbidity, and particle size of unsonicated and sonicated SMP, while it increased the absolute values of zeta potential (P < 0.05). Sonication improved oil absorption capacity and dispersibility over unsonicated samples. Contrarily, sonicated preparations showed a decrease in water holding capacity. Intrinsic fluorescence and FTIR spectral analyses suggested that SMPH had more movable/flexible secondary structures than SMP. Moreover, the changes in sulfhydryl clusters and disulfide linkages following sonication demonstrated limited unfolding of SMP and SMPH structure and decrease in intermolecular interactions. SDS-PAGE profile exhibited significant reduction in molecular weight (MW) of sonicated SMP, whereas did not display differences between unsonicated and sonicated SMPH. From further MW analysis, SMPH was categorized with high proportion of small-sized peptides ≤ 3 kDa fractions, which increased from 78.64 to 93.01% (control) and from 82.3 to 93.88% (sonication) with enzymolysis (6–24DH). Localized enzymolysis and sonication can be utilised to modify the physical and conformational attributes of SMP and SMPH, which could enhance their functionalities and broaden the utilisation area in food industry.