动态高压微射流对猪胰脂肪酶的影响

以猪胰脂肪酶(PPL)为原料,研究动态高压微射流(DHPM)对酶活性和构象的影响.结果显示:DHPM处理对PPL具有钝化作用,处理压力越大,钝化作用越小;4℃下贮存24 h,相对酶活有所回升.通过紫外光谱和圆二色谱分析DHPM对PPL构象的影响,发现经100 MPa DHPM处理后,PPL的紫外吸收强度降低,β-折叠含量减少,但随着处理压力增大,紫外吸收强度和β-折叠含量逐渐增大;4℃放置24 h后,紫外吸收强度和β-折叠含量进一步上升.PPL的相对酶活与紫外吸收强度、β-折叠含量呈一定的正相关.     

动态高压微射流对茎菠萝蛋白酶性质和构象的影响

以茎菠萝蛋白酶为原料,研究动态高压微射流(DHPM)对其活性、稳定性和构象的影响。结果显示：DHPM 对茎菠萝蛋白酶具有钝化作用,但活力并不随着压力的升高而降低。压力为60、80、100、120MPa 时,茎菠萝蛋白酶的相对酶活力分别是94%、93%、98% 及92%。DHPM 不同压力对茎菠萝蛋白酶的最适反应温度的影响不同,但对最适pH 值几乎没有影响。然而经DHPM 60、120MPa 处理后,茎菠萝蛋白酶在pH8.0 的稳定性显著增强。在pH8.0 保温40min 后,60、120MPa 处理的茎菠萝蛋白酶相对酶活力分别为85% 和82%,分别比未经处理的高14% 和11%。可见,DHPM 60、120MPa 处理极大地提高了茎菠萝蛋白酶在pH8.0 时的稳定性。此外,紫外光谱和荧光光谱的结果表明：DHPM 导致茎菠萝蛋白酶部分去折叠,分子中赖氨酸和色氨酸残基所处的微环境发生了变化;红外光谱结果显示：DHPM 处理后茎菠萝蛋白酶二级或三级结构发生了变化。     

动态高压微射流协同糖基化处理对β-乳球蛋白热稳定性和结构的影响

采用动态高压微射流(dynamic high pressure microfluidization,DHPM)协同葡聚糖糖基化处理对β-乳球蛋白(β-lactoglobulin,β-Lg)进行改性,研究其热稳定性和结构的变化。结果表明,β-Lg的峰顶温度为73. 48℃,经DHPM不同压力(40、80、120 MPa)处理后,其热稳定性先下降后上升,但经DHPM协同糖基化处理后,其热稳定性均呈上升趋势。理化分析结果显示,80 MPa DHPM协同糖基化处理的β-Lg具有最低的游离氨基酸含量(2. 20 mg/m L)和最高的褐变程度(A294=1. 092,A420=0. 062),说明DHPM预处理可以促进β-Lg-葡聚糖的糖基化反应,且80 MPa为最佳处理压力。结构分析表明,DHPM处理可明显提高β-Lg的表面疏水性和自由巯基含量,降低其内源荧光强度,使其发生二级结构变化。经DHPM协同糖基化处理后,β-Lg的表面疏水性有所降低,但仍高于天然β-Lg的表面疏水;自由巯基含量呈现先降低后升高趋势,在80 MPa时明显高于天然β-Lg,内源荧光强度随着压力的增加呈先降低后上升的趋势,但均明显低于天然β-Lg的内源荧光强度。因此,DHPM 80 MPa预处理样品具有最高的热稳定性和糖基化程度,且β-Lg的糖基化程度越高,其热稳定性越好。     

动态高压微射流协同糖基化对β-乳球蛋白乳化性和结构的影响

采用动态高压微射流(dynamic high pressure microfluidization,DHPM)协同糖基化处理β-乳球蛋白,研究改性β-乳球蛋白乳化性、乳化稳定性和结构的变化。研究发现DHPM协同糖基化处理过程中β-乳球蛋白结构变化与其乳化性能可能存在关联;DHPM协同糖基化处理能显著提高β-乳球蛋白的乳化性和乳化稳定性。0、40、120 MPa糖基化处理后β-乳球蛋白的乳化活性指数(emulsifying activity index,EAI)分别为136.3、168.1、177.9 m2/g。0 MPa协同糖基化处理后β-乳球蛋白的乳化稳定指数(emulsifying stability index,ESI)为52.3 min;随着压强逐渐增加至40 MPa和120 MPa,协同糖基化处理后ESI值分别升高为56.4 min和59.0 min。通过表征分析β-乳球蛋白结构变化发现:不同压力DHPM协同糖基化处理后,β-乳球蛋白分子质量升高;巯基含量升高;表面疏水性降低;二级结构变化以及氨基酸三维空间构象暴露程度发生变化。这些变化说明β-乳球蛋白与低聚半乳糖发生共价交联时改变了蛋白质结构,造成β-乳球蛋白表面亲水基团的增加,从而导致其乳化性能显著提高。     

动态高压微射流协同糖基化对β-乳球蛋白乳化性和结构的影响

采用动态高压微射流（dynamic high pressure microfluidization,DHPM）协同糖基化处理β-乳球蛋白,研究改性β-乳球蛋白乳化性、乳化稳定性和结构的变化。研究发现DHPM协同糖基化处理过程中β-乳球蛋白结构变化与其乳化性能可能存在关联;DHPM协同糖基化处理能显著提高β-乳球蛋白的乳化性和乳化稳定性。0、40、120 MPa糖基化处理后β-乳球蛋白的乳化活性指数（emulsifying activity index,EAI）分别为136.3、168.1、177.9 m2/g。0 MPa协同糖基化处理后β-乳球蛋白的乳化稳定指数（emulsifying stability index,ESI）为52.3 min;随着压强逐渐增加至40 MPa和120 MPa,协同糖基化处理后ESI值分别升高为56.4 min和59.0 min。通过表征分析β-乳球蛋白结构变化发现：不同压力DHPM协同糖基化处理后,β-乳球蛋白分子质量升高;巯基含量升高;表面疏水性降低;二级结构变化以及氨基酸三维空间构象暴露程度发生变化。这些变化说明β-乳球蛋白与低聚半乳糖发生共价交联时改变了蛋白质结构,造成β-乳球蛋白表面亲水基团的增加,从而导致其乳化性能显著提高。     

动态高压微射流诱导的去折叠胰蛋白酶结构预测

采用差示扫描量热法和圆二色谱分析了动态高压微射流处理前后胰蛋白酶结构的变化,结合前期研究中动态高压微射流诱导的去折叠胰蛋白酶构象的表征,通过PyMOL、3DS Max等软件分别对天然胰蛋白酶和动态高压微射流诱导的去折叠胰蛋白酶的三维空间构象进行模拟和预测,结果表明:与天然胰蛋白酶相比,动态高压微射流处理后胰蛋白酶热焓降低,二级结构构象单元百分含量发生变化.去折叠胰蛋白酶结构更加松散.模拟的胰蛋白酶分子构象示意图更直观地显示了胰蛋白酶的活性中心、二硫键以及二级结构信息,对动态高压微射流诱导的去折叠胰蛋白酶三维结构模型变化做一初探.     

动态高压微射流对杜仲雄花多糖抗氧化能力的影响

文章研究了动态高压微射流(Dynamic high pressure microfluidization,DHPM)对杜仲雄花多糖溶液粒径、结构及抗氧化能力(·OH、ABTS和DPPH自由基清除率)的影响.研究结果表明,DHPM处理后的杜仲雄花多糖溶液平均粒径逐渐减小,从0 MPa的449.5 nm降低到140 MPa...     

动态高压微射流技术超微细化鲢鱼鱼骨

采取动态高压微射流(dynamic high pressure microfluidization,DHPM)不同压力(0～120 MPa)和次数(0～7次)对鲢鱼鱼骨进行处理,以鱼骨粒度分布、微观结构、表面疏水性、游离氨基含量、钙离子溶出量为评价指标,研究了DHPM处理对鲢鱼鱼骨超微细化效果的影响。结果表明,随着DHPM处理压力的增大和次数的增多,鱼骨的粒径明显降低;其表面形貌发生改变,片状结构被破坏形成小颗粒,而后出现凝聚现象; DHPM处理能有效地改变鱼骨表面疏水性和钙离子含量;经DHPM不同压力和次数处理后,鱼骨游离氨基含量均有所降低。这可为DHPM对鱼骨改性利用提供一定的理论参考。     

动态高压微射流对卡拉胶理化性质和结构的影响

为了研究动态高压微射流对卡拉胶理化性质和结构的影响,分别在20, 100, 120, 140和160 MPa下,采用动态高压微射流(DHPM)对卡拉胶进行处理,研究DHPM对溶液中还原糖含量和粒径大小及其分布的影响情况,以及其表观黏度及结构的变化。结果表明,随着压力的增加,还原糖呈现先增加后减少的趋势,粒径尺寸、黏度和分子量均随着压力的增加而减小。傅里叶红外光谱图显示DHPM处理并没有改变糖环的构型,扫描电镜图显示样品经过处理后破坏程度加剧。这些研究为卡拉胶在食品工业中的应用提供了理论依据。     

苹果POD酶学性质及动态高压微射流对POD的影响

富士苹果榨汁提取POD酶液,以愈创木酚为底物研究POD的酶学性质.结果表明:富士苹果POD的米氏常数为129.09 mmol/L,最大反应速度为476.19 U/main,最适温度40℃,最适pH为5.0.采用动态高压微射流对富士苹果POD酶液进行处理,POD酶活发生钝化;增大处理压力、处理次数及提高进料温度均可降低POD活性.室温条件172.4 MPa处理1次和3次,富士苹果POD活性分别降低23.62%和42.14%;50℃、172.4 MPa 理1次,POD活性降低37.25%.     

交联酶聚集体法制备单宁酶及固定化酶性质研究

交联酶聚集体法(cross-linked enzyme aggregates,CLEAs)是一种新型的无载体酶固定化方法。使用该法固定化黑曲霉产单宁酶,制备无载体固定化单宁酶(Cross-linkedenzyme aggregates-tannase,CLEAs-TA),并对其制备条件、结构特征、酶学性质进行分析。结果表明,最优制备条件为单宁酶游离粗酶液在冰水浴中经80%的硫酸铵沉淀30min后,以1.5%戊二醛水溶液进行酶聚集体交联反应,可获得较高活性、较高稳定性的交联酶聚集体,酶活回收率达47.33%,对酯键水解作用的最适温度、最适pH值分别为50℃、4.5,与游离酶相比,表现更高的pH及温度稳定性,重复使用6次后,活力剩余32.86%,其良好的操作稳定性有利于没食子酸丙酯高效转化为没食子酸及广泛应用于水解茶饮料中单宁的反应。     

Thermal and high-pressure stability of purified polygalacturonase and pectinmethylesterase from four different tomato processing varieties

Polygalacturonase (PG) and pectinmethylesterase (PME) were extracted and purified from four tomato varieties (Galeón, Malpica, Perfectpeel and Soto) used in the processing industry. The processing stability (thermal and high pressure) of PG and PME from the four varieties was analyzed, and they all showed the same behavior. PG was present in two isoforms, PG1 (inactivated at 90 °C, 5 min) and PG2 (inactivated at 65 °C, 5 min). In contrast, PG1s and PG2s showed the same pressure stability, both can be inactivated at room temperature in the pressure range of 300–500 MPa. On the other hand, purified PMEs could be thermally inactivated (5 min, 70 °C) but 50% of its activity remained after high-pressure treatment (850 MPa, 15 min, 25 °C). High pressure processing can thus be used for selective inactivation of PG in tomato processing (while keeping PME intact). This fact could open prospectives for improving texture/rheology of processed tomato based products; however further research in the texture/rheology area is needed.     

Thermal and High-Pressure Stability of Pectinmethylesterase, Polygalacturonase, β-Galactosidase and α-Arabinofuranosidase in a Tomato Matrix: Towards the Creation of Specific Endogenous Enzyme Populations Through Processing

The thermal and pressure stability of tomato pectinmethylesterase (PME), polygalacturonase (PG), β-galactosidase (β-Gal), and α-arabinofuranosidase (α-Af) were investigated in situ. Enzyme inactivation by thermal and high-pressure processing (respectively 5 min at 25–95 °C at 0.1 MPa and 10 min at 0.1–800 MPa at 20 °C) was monitored by measuring the residual activity in crude enzyme extracts of treated tomato purée samples. PME was completely inactivated after a 5-min treatment at 75 °C. Only 30 % of the pressure stable PME was inactivated after a treatment at 800 MPa (20 °C, 10 min). A 5-min treatment at 95 °C and a treatment at 550 MPa (20 °C, 10 min) caused complete PG inactivation. β-Gal and α-Af activities were already reduced significantly by thermal treatments at 42.5–52.5 °C and 45–60 °C, respectively. These enzymes were, however, rather pressure resistant: treatments at respectively 700 and 600 MPa were necessary to reduce the activity below 10 % of the initial value. Assuming that first-order, fractional conversion or biphasic inactivation models could be applied to the respective enzyme inactivation data, inactivation rate constants and their temperature or pressure dependence for the different enzymes were determined. Based on differences in process stability of the enzymes, possibilities for the creation of specific “enzyme populations” in tomato purée by selective enzyme inactivation were identified. For industrially relevant process conditions, the enzyme inactivation data obtained for tomato purée were shown to be transferable to intact tomato tissue.     

Evaluation of processing qualities of tomato juice induced by thermal and pressure processing

Effects of processing conditions including hot-break processing (92 °C for 2 min), cold-break processing (60 °C for 2 min) and hydrostatic pressure treatments (100-500 MPa) at different temperatures (4, 25 and 50 °C) for 10 min on quality aspects of tomato juice were investigated. Both hot- and cold-break processing induced significant changes in color, viscosity and radical-scavenging capacity of tomato juice compared with control (fresh tomato juice); moreover, hot-break processing induced a specific range of reduction of pectin methylesterase (PME) and polygalacturonase (PG) activities. Pressure treatments at and below 200 MPa at 4 and 25 °C maintained the color, extractable total carotenoids and lycopene, and radical-scavenging capacity; further, those at 500 MPa at 4 and 25 °C improved all the quality attributes the most except inactivation of PME in this study. The residual activity of PME showed the lowest after treating by 200 MPa at 25 °C; however, the PME activity was enhanced by treatments at 300-500 MPa and various temperatures. The residual activity of PG decreased gradually to 72% with pressure elevated from 100 to 400 MPa at 4 and 25 °C, further, that declined quickly to 10% after 500 MPa treatments. This research clearly shows that it is possible to selectively produce good tomato juice products by high pressure processing at ambient temperature.     

Stimulation of polygalacturonase production in an immobilized system by <Emphasis Type="Italic">Aspergillus</Emphasis> sp.: effect of pectin and glucose

The synthesis of polygalacturonases (PG) is known to be influenced by Aspergillus growth conditions, namely, environmental factors and pectin content in the cultivation medium containing a mixed carbon source. Optimal conditions were attained at a temperature of 30 °C and an initial pH of 4.5. PG activity (3.29 and 2.48 U/mL) was determined after a two-day culture of Aspergillus sp. HC1 and Aspergillus sp. CC1, respectively, in a basic medium containing 2% citrus pectin as the sole carbon source. The addition of glucose (2% w/v) to the basic medium led to a 2-fold increase in PG production. However, enzyme synthesis was repressed when a higher concentration of glucose was used in the medium containing the mixed carbon source. Spores from the two fungi were immobilized in a 3% Ca–alginate system and the mechanical strength of the gel beads allowed the use of this process system 6-fold longer (288 h) than the free culture. In the Aspergillus sp. CC1 immobilized system, PG production increased nearly 10-fold in the medium with 2% glucose added (5.95 U/mL) in comparison to the medium without sugar (0.55 U/mL). The results demonstrate that a different response in activity was produced by free and entrapped spore systems. PG production remained approximately constant throughout the six 48 h cycles in the medium containing citrus pectin (2% w/v) as the sole carbon source.     

Fluorescent labeling study of plasminogen concentration and location in simulated bovine milk systems

A fluorescent labeling method was developed to study plasminogen (PG) concentration and location in simulated bovine milk. Activity and stability of PG labeled with Alexa Fluor 594 (PG-594) were comparable to those of native PG. The fluorescent signal of PG-594 exhibited pH, temperature, and storage stability, and remained stable throughout typical sample treatments (stirring, heating, and ultracentrifugation). These characteristics indicate broad applicability of the fluorescent labeling technique for milk protease characterization. In an example application, PG-594 was added to simulated milk samples to study effects of heat and β-lactoglobulin (β-LG) on the distribution of PG. Before heating, about one-third of the PG-594 remained soluble in the whey fraction (supernatant) whereas the rest became associated with the casein micelle. Addition of β-LG to the system slightly shifted PG-594 distribution toward the whey fraction. Heat-induced PG-594 binding to micelles in whey-protein-free systems was evidenced by a decrease of PG-594 from 31 to 15% in the whey fraction accompanied by an increase of PG-594 from 69 to 85% in casein micelle fractions. When β-LG was present during heating, more than 95% of PG-594 became associated with the micelle. A comparison with the distribution pattern of PG-derived activities revealed that heat-induced PG binding to micelles accompanies heat-induced PG inactivation in the micelle fraction. Incubation of the casein micelles with the reducing agent β-mercaptoethanol revealed that disulfide bonds formed between PG and casein or between PG and casein-bound β-LG are the mechanisms for heat-induced PG binding to casein micelles. Western blotting and zymography results correlated well with fluorescent labeling studies and activity studies, respectively. Theoretically important findings are: 1) when heated, serum PG is capable of covalently binding to micellar casein or complexing with β-LG in whey and then coadhering to micelles, and 2) PG that associated with micellar casein through lysine binding sites before heating is capable of developing heat-induced disulfide bonds with casein. The overall results are PG covalently binding to micelles and inactivation thereafter. Our results suggest that, instead of thermal denaturation through irreversible unfolding, covalent bond formation between PG and other milk proteins is the mechanism of PG inhibition during thermal processing.     

浓香大豆油的开发及其氧化稳定性的研究

建立一种新型浓香大豆油(ASO)的生产方法。采用超临界萃取技术对焙烤后的大豆进行提取。通过感官评定对大豆焙烤工艺进行评估：在温度170℃条件下烘烤30min 时,焙烤出的大豆具有浓郁的香味。ASO 的萃取率随着大豆粉粒度的增加而提高,大豆粉的粒度为40～60 目时最佳。采用正交试验设计法对ASO 的萃取参数进行研究：萃取率随着温度的升高,先增大后减小,最佳萃取温度为50℃;萃取率随着压力的增大,先增大后减小,最佳萃取压力为25MPa;萃取率随着时间延长逐渐趋于最大值,确定萃取时间为2.5h。通过对氧化诱导期(IP 值)和抗氧化保护系数(Pf 值)的分析,探讨ASO 的氧化稳定性：ASO 和市售大豆油的IP 值分别为8.93、9.47,其他植物油均大于16;向ASO 中添加0.04% 的BHT、PG 分别能使其IP 值从8.93 提高到12.08、18.55,Pf 值分别达到1.353 和2.077,PG 对ASO 的抗氧化效果要明显优于BHT;在ASO 中单独添加0.01% 柠檬酸能使其Pf 值达到2.25,显示较强的抗氧化能力,复合添加0.01% 柠檬酸和0.04% PG 使其Pf 值达到4.14,显示很强的抗氧化能力。     

超高压催陈对丹阳封缸酒中游离氨基酸的影响

利用氨基酸全自动分析仪对经过超高压处理的封缸酒中的游离氨基酸进行检测分析,共检测出17种游离氨基酸。结果表明,超高压处理对封缸酒中氨基酸种类没有影响,在400MPa下催陈15min,游离氨基酸总量增加了4.03%,达到了最大增加量;其中酪氨酸显著增加22.03%。当催陈时间为15min,压力分别为500、600MPa时,氨基酸总量分别减少了1.53%、1.18%。鲜味、酸味氨基酸所占百分比基本不变;苦味、涩味氨基酸在400MPa下催陈15min,其含量分别增加了13.98%、3.95%。感官评价表明400MPa处理15min后的封缸酒酒体更丰富醇厚,更易让人接受。      

The effects of microfluidization on the physical,microbial, chemical,and coagulation properties of milk

This work examines the use of mild heat treatments in conjunction with 2-pass microfluidization to generate cheese milk for potential use in soft cheeses, such as Queso Fresco. Raw, thermized, and high temperature, short time pasteurized milk samples, standardized to the 3% (wt/wt) fat content used in cheesemaking, were processed at 4 inlet temperature and pressure conditions: 42°C/75 MPa, 42°C/125 MPa, 54°C/125 MPa, and 54°C/170 MPa. Processing-induced changes in the physical, chemical, and microbial properties resulting from the intense pressure, shear, and cavitation that milk experiences as it is microfluidized were compared with nonmicrofluidized controls. A pressure-dependent increase in exit temperature was observed for all microfluidized samples, with inactivation of alkaline phosphatase in raw and thermized samples at 125 and 170 MPa. Microfluidization of all samples under the 4 inlet temperature and processing pressure conditions resulted in a stable emulsion of fat droplets ranging from 0.390 to 0.501 μm, compared with 7.921 (control) and 4.127 (homogenized control) μm. Confocal imaging showed coalescence of scattered fat agglomerates 1 to 3 μm in size during the first 24 h. We found no changes in fat, lactose, ash content or pH, indicating the major components of milk remained unaffected by microfluidization. However, the apparent protein content was reduced from 3.1 to 2.2%, likely a result of near infrared spectroscopy improperly identifying the micellar fragments embedded into the fat droplets. Microbiology results indicated a decrease in mesophilic aerobic and psychrophilic milk microflora with increasing temperature and pressure, suggesting that microfluidization may eliminate bacteria. The viscosities of milk samples were similar but tended to be higher after treatment at 54°C and 125 or 170 MPa. These samples exhibited the longest coagulation times and the weakest gel firmness, indicating that formation of the casein matrix, a critical step in the production of cheese, was affected. Low temperature and pressure (42°C/75 MPa) exhibited similar coagulation properties to controls. The results suggest that microfluidization at lower pressures may be used to manufacture high-moisture cheese with altered texture whereas higher pressures may result in novel dairy ingredients.