甜菜果胶的醇析工艺研究

乙醇沉淀法是纯化果胶的工业化方法,应用广泛。本文以甜菜果胶为研究对象,考察了醇析p H、乙醇浓度等对甜菜果胶的醇析率、物化特性的影响;通过zeta电位表征甜菜果胶在醇析过程中的分子相互作用,并采用通过高效液相体积排阻色谱(HPSEC)、高效阴离子色谱(HPAEC)和高效液相色谱(HPLC)等技术分析醇析所得甜菜果胶的分子结构。研究结果表明:纯化前后的SBP醇析率均在p H为2.5,体系乙醇浓度为71.25%时达到最大,分别为96.81%和57.23%;SBP的重均分子量范围为145.07~404.27 kg/mol;含有鼠李糖、阿拉伯糖、半乳糖、葡萄糖和木糖等五种中性糖,范围为16.23~17.83%。SBP溶液初始p H与体系乙醇浓度在一定范围内对SBP的水合作用有影响,醇沉所得SBP的结构受到了醇析条件的影响。     

Effects of Pulsed Electric Field Processing on Quality Characteristics and Microbial Inactivation of Soymilk

Effects of pulsed electric fields (PEF) on quality characteristics and microbial inactivation of soymilk were studied with different PEF parameters. PEF did not affect significantly the values of pH, “a” (an indicator of redness ranging from “?a” to “+a”, ?a?=?green, +a?=?red) and electric conductivity. The values of “L” (white if “L”?=?100, black if “L”?=?0) increased slightly, whereas values of viscosity and “b” (an indicator of yellowness ranging from “?b” to “+b”, ?b?=?blue, +b?=?yellow) decreased slightly as PEF time increased from 0 to 547 μs. Cysteine, tyrosine, phenylalanine, and serine reduced with the increase of PEF time. The relative activities of soybean lipoxygenase (SLOX) decreased with PEF time increasing from 0 to 1,036 μs. When PEF time and strength increased, the inactivation of Escherichia coli and Staphylococus aureus increased significantly (p?<?0.05), achieving a maximum of 5.20 and 3.51 log₁₀ cycles reduction at PEF time 547 μs and pulsed electric strength 40 kV/cm, respectively. The inactivation of E. coli, S. aureus, and SLOX as a function PEF time followed Weibull distribution. This study demonstrated that PEF could inactivate efficiently E. coli, S. aureus, and SLOX without affecting the quality characteristics of soymilk. Thus, this technique could be an advantageous alternative to heat treatment for pasteurization of soymilk.     

基于三场耦合的脉冲电场杀菌系统的工作过程仿真

脉冲电场(Pulsed Electric Field,PEF)杀菌是将脉冲电压施加到处理室的两极,产生电场对食品物料进行杀菌的过程,在整个过程中,处理室中的电场强度与温度分布是影响系统杀菌效果以及食品质量的两个关键因素。作者在建立同场处理室的三维模型的基础上,根据电场、流场、温度场理论,建立了脉冲电场杀菌系统三场耦合的数学模型,模拟在脉冲电压V、脉宽τ、频率f、流速υ和温度T等条件下,NaCl溶液的流体特性、温度分布以及处理室中的电场分布,得出了同场处理室几何尺寸与温度和电场分布的关系,为优化处理室结构,改善杀菌效果提供重要依据。     

高压脉冲电场对抗氧化肽荧光特性的影响

以前期研究所得的Gln-Trp-Phe-Met(QWFM,652.78)和Lys-Trp-Phe-Met(KWFM,610.78)抗氧化四肽为研究对象,探究高压脉冲电场技术(pulsed electric field,PEF)对抗氧化肽荧光特性的改变。研究表明,在PEF作用下QWFM和KWFM的荧光强度发生了不同程度的改变,由于两条结构相似的抗氧化四肽中色氨酸前端所连接的氨基酸不同,在相同的PEF处理条件下,QWFM的荧光强度变化更为显著,在电场频率为1 800 Hz和电场强度为15 k V/cm时,其荧光强度变化最显著。通过监测经PEF处理后2 h抗氧化四肽荧光强度的变化,发现抗氧化四肽荧光强度的变化随着时间的延长而逐渐减弱。通过圆二色谱分析和核磁共振波谱技术分析发现维持QWFM中β-折叠的氢键含量有所改变从而导致了β-折叠结构的含量有所减少。这些变化表明PEF技术可能通过改变抗氧化肽的化学结构而改变其荧光特性,为PEF技术应用于抗氧化肽的研究提供了理论基础。     

糖汁超滤传质过程的研究

根据糖汁在超滤过程中的通量变化规律 ,以“凝胶层阻力”理论及“渗透压阻力”理论为基础 ,求出糖汁超滤过程的传质方程式 ,分析造成传质阻力的主要因素 ,并对糖汁在全回流和一次式超滤过程的透过机理进行描述     

高压脉冲电场静态处理室的研制

高压脉冲电场(Pulsed Electric Field,PEF)是一项极具前景的食品非热杀菌技术,其处理关键部件——处理室直接影响杀菌效果。作者设计了电场分布均匀、处理物料容量可调、安全可靠的PEF处理室,应用该PEF处理室对接种大肠杆菌的液蛋进行杀菌,当电场强度为34.2 kV/cm处理时间为400μs时,原样品菌体浓度为106~107cfu/mL,大肠杆菌细菌数量降低了约5.05个对数,从而说明作者设计的静态处理室是可行的,可以进行杀菌钝酶等相关机理研究。     

高压脉冲电场杀菌效果的F值理论研究

有关高压脉冲电场杀菌动力学方面的研究颇多,但至今仍未有一种衡量高压脉冲电场杀菌效果的统一方法。本文参考热力致死时间F值的概念,提出电场强度致死时间F值,在电场强度与微生物致死时间之间建立关系模型。提出高压脉冲电场F值理论,并以F值作为衡量高压脉冲电场杀菌效果的指标。以大肠杆菌O157:H7为目标菌,研究其F值,探究不同电场强度下微生物的致死时间,为衡量不同电场设备杀菌效果提供一定的理论依据。     

Influence of Pulsed Electric Field on Escherichia coli and Saccharomyces cerevisiae

Heat sterilization destroys the color, smell, taste, and nutrients of food. Pulsed electric field can effectively kill microorganisms for many foods at room temperature without compromising sensory and nutritional quality. The effect of pulsed electric field on the sterilization rates of Escherichia coli and Saccharomyces cerevisiae was investigated. The fundamental mechanism of pulsed electric field sterilization on S. cerevisiae was briefly discussed. The inactivation of E. coli and S. cerevisiae increased as the electric field strength and treatment time increased. Pulsed electric field treatments at 35 kV/cm and 90 μs reduced S. cerevisiae and E. coli by 5.30 and 5.15 log numbers, respectively. The inactivation of E. coli and S. cerevisiae was not remarkable at increased conductivity and the same electric field strength. Concaves and holes in S. cerevisiae cell surface, protoplast deletion, overflow of substances from cells, and denatured DNA were observed. These results supported the hypothesis of “membrane perforation” to explain the mechanism underlying pulsed electric field sterilization.     

高压脉冲电场对苹果多酚氧化酶的钝化效果

多酚氧化酶(PPO)促褐变影响苹果鲜果和果汁的品质。探讨高压脉冲电场(PEF)钝化苹果鲜果PPO的可行性。在电压、停留时间、频率、脉冲宽度等单因素试验的基础上,采用响应曲面分析法优化钝酶工艺。结果表明,PEF对红富士多酚氧化酶活性抑制的最佳条件为:电压25 k V,频率530 Hz,停留时间45 s和脉冲宽度8μs,此条件下多酚氧化酶的抑制率达51.86%。鲜榨果汁的色值和褐变指数与PPO的相对活力直接相关。PEF处理能够抑制果汁的酶促褐变,与对照组相比,由最优钝化条件下处理的果块制备的果汁(4 h时)的色值极显著大于对照组(P0.01),总可溶性固形物,pH值没有发生显著改变(P0.05),还原型维生素C呈下降趋势,但下降不显著(P0.05)。     

大豆压榨取油过程基本特性的研究

利用柱塞式压榨试验装置对大豆进行压榨试验,探讨了大豆压榨的出油率与出油压力之间的关系,大豆的冷榨应力-应变关系.     

脉冲电场对食品蛋白质改性作用的研究进展

脉冲电场(PEF)技术是一项很有前景的用于食品加工与贮藏的非热处理技术,与传统热加工相比,它可以最大限度地保持食品品质,如风味和营养价值,而在传统热加工中这些品质往往会遭到破坏。PEF能替代热加工处理技术或与热加工处理技术联用,成为食品加工业极具应用潜力的技术,近年来引起了国内外研究学者的广泛关注。研究显示它会诱导食品蛋白质成分的结构发生变化,从而诱导其功能特性的改变。本文综述了脉冲电场处理食品蛋白质后,破坏了维系蛋白质高级结构的次级键,导致蛋白分子内部疏水基团暴露,改变蛋白质表面疏水性,且局部伸展的蛋白质提高了分子的柔性、溶解度等特性,从而改善在食品蛋白质的功能特性中的应用,以期为脉冲电场在食品中的工业应用提供参考。     

高压脉冲电场对果胶杆菌的杀菌效果及其致死动力学研究

为明确高压脉冲电场（High plused electric fields,HPEF）对果胶杆菌的最优杀菌参数并对其潜在机制进行初步探索,本研究首先通过测定高压脉冲电场不同处理条件下果胶杆菌的存活率,明确影响杀菌效果的主要因素;然后研究不同电场强度和脉冲占空比对果胶杆菌生长曲线、细胞膜脂肪酸含量变化、细胞膜渗透率以及核酸和蛋白质泄漏量的影响,以及果胶杆菌在不同生长期对高压脉冲电场敏感度的差异。结果表明:电场强度和脉冲占空比是影响高压脉冲电场杀灭果胶杆菌的主要因素。当电场强度为28 kV/cm,脉冲占空比为36.5%时,抑菌作用最强,果胶杆菌活菌对数减少值达1.60;在高压脉冲电场作用下,果胶杆菌延滞期延长,生长受到抑制,同时细胞膜结构被破坏,渗透性增大,胞内核酸和蛋白质发生严重泄漏。此外,不同生长期的果胶杆菌对高压脉冲电场敏感度不同,其中对数生长期最为敏感。最后,建立了果胶杆菌活菌对数减少值lnS与电场强度和脉冲占空比的动力学方程（y=?0.1067x+0.1166和y=?0.0895x+0.3249）。该方程符合一级动力学模型,较好地反映了高压脉冲电场处理后果胶杆菌生长的关系,为选择合适的处理条件提供了理论依据。本研究确定了高压脉冲电场杀灭果胶杆菌的最佳参数,为进一步实现高压脉冲电场杀菌保鲜在采后和鲜切行业的产业化应用奠定了基础。     

Influence of Pulsed Electric Field and Thermal Treatments on the Quality of Blueberry Juice

Fresh blueberries were selected as trial materials. Two blueberry juice samples were sterilized using pulsed electric field and thermal treatments respectively. Their qualities were analyzed and compared by evaluating the microorganisms in the samples. The changes in the quality of fresh blueberry juice samples during storage were also assessed. The results showed that the inactivation of Escherichia coli increased as electric field strength and treatment time increased. Pulsed electric field treatments at 35 kV/cm and 82 μs reduced E. coli by 5.12 logarithms. Pulsed electric field had less effect on juice quality, but after heat treatment, the vitamin C of blueberry juice sample was reduced by 14.78%, whereas its anthocyanin content was reduced by 3.64%. After sterilization, no significant change was observed in the relative reducing sugar, total acid, phenol contents, and Brix value. The vitamin C and anthocyanins contents of the fresh blueberry juice samples treated with pulsed electric field were higher than those treated with heat sterilization.     

脉冲电场对木薯醋酸酯淀粉制备及其性质的影响

以木薯淀粉为原料,以乙酸酐为酯化剂,在不同脉冲电场强度(0 k V/cm、2k V/cm、3 k V/cm、4 k V/cm、5 k V/cm、6 k V/cm、7 k V/cm)、不同有效处理时间(0 ms、3 ms、6 ms、9 ms、12 ms、15 ms)和不同酸酐添加量(4%、6%、8%、10%、12%)下湿法制备醋酸酯淀粉,对乙酰基及取代度进行测定,得出经过脉冲电场处理,木薯醋酸酯淀粉乙酰基含量和取代度都有所提高。乙酸酐添加量为6%,电场强度为4 Kv/cm,有效处理时间为9 ms,样品取代度由0.084提高至0.110,说明脉冲电场处理可以促进酯化反应的进行,提高了酯化反应效率。此外还研究了木薯醋酸酯淀粉糊透明度、溶解度及膨润力、冻融稳定性和淀粉糊黏度性质,并通过红外光谱对产品进行结构表征。结果表明:经过脉冲电场处理,木薯淀粉颗粒均引入了乙酰基团,并提高醋酸淀粉的糊透明度、溶解度和膨润力,提高淀粉糊峰值黏度,而淀粉糊稳定性基本保持不变。     

高压脉冲电场对辣根过氧化物酶活性及构象的影响效果

本实验旨在研究高压脉冲电场(PEF)对辣根过氧化物酶(HRP)的活性及酶构象的影响效果。结果显示:HRP的活性随电场强度的增强和脉冲处理数的增加而降低。在25kV/cm、207个脉冲和22kV/cm、1214个脉冲的时候,HRP的活性分别降低了14.3%和33.2%。PEF处理后的酶液在4℃下贮藏24h和48h后,HRP的活性呈缓慢下降。圆二色谱和荧光光谱分析表明PEF处理后HRP的蛋白构象发生了改变。PEF和热处理后HRP蛋白二级结构的平均摩尔椭圆率都发生了变化,α-螺旋含量分别下降了29.3%和57.7%。荧光光谱分析表明HRP蛋白的荧光强度在PEF处理后也发生了改变。     

Influence of Pulsed Electric Field Protocols on the Reversible Permeabilization of Rucola Leaves

Reversible electropermeabilization of plant tissues with heterogeneous structure represents a technological challenge as the response of the different structures within the same specimen to the application of electric field may differ due to different cell sizes, extracellular space configurations, and electrical properties. The influence of five different pulsed electric field protocols with different pulse polarity, number of pulses (25, 50, 75, 100, 250, and 500), and intervals between pulses (no intervals and 1- and 2-ms intervals) on the reversible permeabilization of rucola (Eruca sativa) leaves was investigated. The electric field intensity was 600 V/cm. Electrical resistance of the bulk tissue was measured before and after electroporation, and propidium iodide was used to analyze the electroporation at the surface of the leaf. Leaf viability was assessed from survival in storage, and cell viability was investigated with fluorescein diacetate. Results indicate that the viability of the leaves could not be predicted by measurements of electrical resistance or permeabilization levels of the leaf surface. Higher survival rate was demonstrated when applying bipolar pulses compared with monopolar pulses, but the latter proved to be more effective than bipolar pulses for permeabilizing the surface of the leaves. Longer intervals between bipolar pulses resulted in increased viability preservation, while the number of electroporated cells on the leaf surface was comparable for all tested protocols.     

电场处理对大米淀粉理化性质的影响

利用脉冲电场对大米淀粉进行预处理,研究不同电场强度和不同有效处理时间对淀粉颗粒结构特征和理化性质的影响。通过扫描电镜(SEM)发现,淀粉颗粒表面受电场影响遭到破坏。傅里叶变换红外光谱(FTIR)和X射线衍射(XRD)表征结果表明脉冲电场处理大米淀粉不会引入新的官能团,在本实验条件下也不会改变淀粉的晶型结构,是一种物理改性的处理手段。经脉冲电场处理后,大米淀粉糊的透明度由6.2%提高到32.4%,冻融析水率由58.31%降低到22.53%,此外凝沉性和冻融稳定性均有所改善。     

高压脉冲电场技术对液体食品品质的影响研究进展

高压脉冲电场技术是国际上最为先进的食品非热加工技术之一,具有效率高、处理温度低、对食品的色泽,风味和营养成分保存效果好、能耗低等一系列优点。文章介绍高压脉冲电场技术的杀菌机理,影响其杀菌效果的主要因素,对液体食品品质的影响以及对高压脉冲电场技术应用前景的展望。     

Effects of Pulsed Electric Field on Yield Extraction and Quality of Olive Oil

The effect of the application of pulsed electric field (PEF) treatments of different intensities (0–2 kV/cm) on Arbequina olive paste in reference to olive oil extraction at different malaxation times (0, 15, and 30 min) and temperatures (15 and 26 °C) was investigated. The extraction yield improved by 54 % when the olive paste was treated with PEF (2 kV/cm) without malaxation. When the olive paste was malaxated at 26 °C, the application of a PEF treatment did not increase the extraction yield as compared with the control. However, at 15 °C, a PEF treatment of 2 kV/cm improved the extraction yield by 14.1 %, which corresponded with an enhancement of 1.7 kg of oil per 100 kg of olive fruits. The application of a PEF treatment could permit reduction of the malaxation temperature from 26 to 15 °C without impairing the extraction yield. Parameters legally established (acidity, peroxide value, K_232, and K₂₇₀) to measure the level of quality of the virgin olive oil were not affected by the PEF treatments. A sensory analysis revealed that the application of a PEF treatment did not generate any bad flavor or taste in the oil.     

A Comparison of the Effects of Pulsed Electric Field and Thermal Treatments on Grape Juice

The work was aimed at comparing the effect of pulsed electric field (PEF) and thermal technologies on physical, chemical, microbiological, and nutritional properties of freshly squeezed grape juice of different varieties when they are applied using continuous flow systems. It has been evidenced that grape variety is a factor to be taken into account when comparing the processing effects of PEF and heat treatments. Nevertheless, results of general and specific microbial populations were not affected by it and followed a very similar trend with each processing treatment. Soluble solids, pH, acidity, and the electrical conductivity of grape juice were not affected by PEF processing. On average, PEF treatment reduced the radical scavenging activity a 9% in front of the 13% of the heat treatment whereas both treatments halved the protein content. Data of vitamin C, total polyphenol, cinnamic acid, free catechin and non-flavonoid content were not enough to show differences between both treatments. However, all these nutritionally related properties share the same behaviour, PEF processing yielded milder values than heat processed samples. Information comparing PEF and thermal processes on food products help to clarify the advantages and disadvantages of each technology even though the disparity in development and use of each one.