高强度脉冲电场在食品巴氏杀菌中的应用

加热处理是食品工业中为增长货架期、保持食品安全性、减少腐败菌和微生物污染的最常用的一种方法。然而,热处理对产品的风味。滋味和营养价值会产生一些副作用,因而目前非加热处理食品正得到人们的关注。已有的非加热处理保藏技术包括:添加防腐剂以控制微生物生长、辐射处理以抑制微生物、物理离心处理以除去微生物、低温贮藏以减缓微生物生长,或两种以上这些方法结合使用。食品工业中有几种新技术,在替代热处理方面具有一定的潜力。这些方法包括:脉冲电流、振动磁场、流体静压、强光脉冲、辐射、抑菌及杀菌剂。     

高强度脉冲电场应用于食品的巴氏杀菌

由高压脉冲发生器产生的高强度脉冲电来处理液态食品，可以灭治食品中的腐败菌和病原微生物，延长食品的保藏期和维持食品的安全性。这是一种不用加热的巴氏杀菌方法。专家们认为，这种方法是一种有前景的新的食品加工工艺。     

磷脂酶C对大肠杆菌细胞膜通透性的影响

本文在大肠杆菌(E.coli BL21 DE3)中分别克隆表达了产气荚膜梭菌(Clostridium perfringens)和单核细胞增生性李斯特菌(Listeria monocytogenes)来源的磷脂酶C(PLC)基因,并系统研究了内源表达的重组PLC对大肠杆菌BL21(DE3)内外膜通透性的影响。结果表明内源表达的产气荚膜梭菌和单核细胞增生性李斯特菌重组PLC对宿主菌内膜通透性影响较大,但对宿主菌外膜通透性的影响相对较弱。此外,本文对两种不同来源重组表达的磷脂酶C蛋白进行了分离纯化,分析了外源添加重组磷脂酶C对大肠杆菌BL21(DE3)细胞膜通透性的影响。结果表明外源PLC对大肠杆菌外膜通透性影响较大,而对内膜通透性影响相对较小。综上所述,产气荚膜梭菌和单核细胞增生性李斯特菌来源的磷脂酶C可以改善大肠杆菌细胞膜的通透性,为进一步提高大肠杆菌工程菌株蛋白异源表达提供新的思路。     

胡桃醌对大肠杆菌细胞膜的作用研究

通过考察胡桃醌对大肠杆菌细胞膜的作用来研究胡桃醌的抑菌机理。采用3种不同质量浓度的胡桃醌作用于大肠杆菌后,测定培养液中的相对电导率、蛋白质质量浓度和细胞内外K+、Na+含量的变化,并结合透射电镜图来分析胡桃醌对大肠杆菌细胞膜的影响。结果表明:胡桃醌能够改变大肠杆菌细胞膜的渗透性,大量带电离子和蛋白质外漏;菌体细胞内外K+、Na+含量与空白对照组相比变化显著。透射电镜观察,经胡桃醌作用后菌体细胞被破坏,细胞膜变薄,细胞个体之间界限变模糊,内容物流出。并且,随胡桃醌质量浓度的增加和作用时间的延长,对大肠杆菌细胞膜的破坏越显著。显示胡桃醌的抑菌活性与其对大肠杆菌细胞膜的破坏有直接关系。     

高强度脉冲电场对酶活性的影响

高强度脉冲电场技术（High--intensity pulsed electric Fields．HIPEF）是一种迄今为止发现的新的食品加工技术,因为它能阻止一些有害微生物和酶的活动,伴随引起食品温度少量增加。这种加工使获得成分、物理化学特性以及感官品质几乎不发生变化的稳定食品成为可能。     

脉冲强光对大肠杆菌细胞膜损伤及胞内酶活性的影响

通过脉冲强光处理对数生长期大肠杆菌细胞悬液,研究菌体细胞膜通透性及胞内酶活性的变化.结果表明,蛋白质的漏出量及丙二醛的生成量均随大肠杆菌存活率的下降而增加,在处理电压1 500 V、闪照次数32次的条件下,蛋白质漏出量为13.03 μg/mL,丙二醛生成量为2.76 nmol/L,对氯化钠的耐受性明显低于对照组(P＜0.01).此外,胞内酶活性与处理前相比均有所降低,超氧化物歧化酶活性最低降至83.78%,过氧化氢酶活性最低降至76.92%.因此,细菌屏障结构破坏所造成的细胞膜渗透压及通透性改变,可使细菌胞内物质发生改变,甚至导致菌体死亡,羟自由基可能对致死细胞的协同作用有一定的意义.     

连载十一 高强度脉冲电场对蛋白质构成、维生素和风味稳定性的影响

摘自中国轻工业出版社出版的《新型食品加工技术》,Gustavo.V Barbosa-Canovas等著,张憨等译,原书书名《NOVEL FOODPROCESSING TECHNOLOGIES》,CRC Press出版。高强度脉冲电场(HIPEF)对维生素的影响Shama等(1998)发现经33kV/cm的HIPEF处理92μs的橘子汁,可以使维生素含量在4℃下维持8周。HIPEF处理对果汁中维生素的影响是Qiu等(1998)研究得到的。研究表明热巴氏杀菌果汁同HIPEF处理相比,维生素C含量的损失较     

高压脉冲电场对酵母菌和大肠杆菌存活率的影响

本文研究了高压脉冲电场对酿酒酵母和大肠杆菌的致死率的影响，并对脉冲电场的灭菌机理进行了初步探究。结果表明：随着电场强度、脉宽和脉冲个数的增加，微生物的存活率显著下降，在9kV／cm场强下作用1000个脉宽为11μs的脉冲，可得到最优灭菌效果-酵母菌活菌数下降4．5个对数值，大肠杆菌活菌数下降3个对数值。电场作用后死亡酵母菌表面出现凹陷，胞内物质外渗，支持了用以解释高压脉冲电场灭菌机理的“电穿孔”学说。     

液态食品的高强度脉冲电场杀菌技术

回顾了运用高强度脉冲电场对液态食品进行杀菌研究的历史和现状，介绍近期研究成果的特点、杀菌原理及杀菌装置和在不同场强和不同ｐＨ条件下对大肠杆菌进行杀菌的实验效果。展望了该技术潜在的实用价值。     

高压脉冲电场处理时间对啤酒酵母大肠杆菌和青霉的致死动力学研究

以啤酒酵母、大肠杆菌和青霉为研究对象，在一级动力学模型的基础上，研究处理时间对这3种微生物的致死动力学方程，并获得它们的临界处理时间t。和回归系数k2，从而证明三种菌对高压脉冲电场的耐受能力为：青霉〉大肠杆菌〉啤酒酵母。     

高压脉冲电场对酵母和大肠杆菌的杀灭效果

研究了高压脉冲电场的电场强度和脉冲时间对胡萝卜汁中接种的啤酒酵母 (CGM CC 2 60 4)和大肠杆菌 (CGMCC 1 90 )的杀灭效果。结果表明 ,啤酒酵母和大肠杆菌的残活率都随着电场强度的增大和脉冲时间的延长而逐渐下降 ,同轴式电极中 ,在 2 3kV的电压和1 2 42ms的脉冲处理时间下 ,酵母达到最小残活率 -4 113个对数 ;平板电极中 ,在 17kV/cm的电场强度和 0 45ms的脉冲处理时间下 ,大肠杆菌达到最小残活率 -2 3 97个对数。同时发现 ,酵母对电场强度和脉冲时间的敏感程度大于大肠杆菌。     

脉冲电场对荔枝汁中酿酒酵母的杀灭效果

研究不同电场强度和处理时间的脉冲电场(PEF)对荔枝汁中酿酒酵母菌的杀灭效果,并探讨能量输入对酿酒酵母杀灭效果的影响。结果显示：电场强度的增大和处理时间的延长均能增大酿酒酵母的菌数减少指数;对不同生长时期酿酒酵母进行杀菌,表明荔枝汁中处于4 个不同生长时期的酿酒酵母对电场敏感度不同,由强到弱依次为稳定期＞对数期＞衰亡期＞调整期。PEF 对酿酒酵母的灭菌效果随着电场能量输入的增加而增强。     

高压脉冲电场对橙汁大肠杆菌和理化性质的影响效果

高压脉冲电场(pulsedelectricfield)技术是目前研究人员关注的非热加工技术之一。本文研究了高压脉冲电场技术对橙汁中E.coli和理化性质的影响效果。研究表明,高压脉冲电场对橙汁确实有杀菌钝酶的效果。当电场强度为12kV/cm、脉冲时间为1200个脉冲时,橙汁中E.coli的数量减少了1.73个对数;10kV/cm、400个脉冲时过氧化物酶(POD)活性下降了60%。对于橙汁理化性质总酸、0Brix、pH、浊度和色差等指标的影响不大。     

Inactivation of Escherichia coli O157:H7 and Salmonella enteritidis in Liquid Egg White Using Pulsed Electric Field

ABSTRACT: The effects of temperature and pulsed electric field (PEF) intensity on inactivation of pathogens such as Escherichia coli O157:H7 and Salmonella enteritidis in egg white was investigated. Liquid egg white inoculated with 10⁸ colony-forming units (CFU)/mL of each pathogen was treated with up to 60 pulses (each of 2 JAS width) at electric field intensities of 20 and 30 kV/cm. The processing temperatures were 10°C, 20°C, and 30°C. After treatment, uninjured and total viable cells were enumerated in selective and nonselective agars, respectively. Maximum inactivations of 3.7 and 2.9 log units were obtained for S. enteritidis and E. coli O157:H7, respectively, while injured cells accounted for 0.5 and 0.9 logs for E. coli O157:H7 and S. enteritidis , respectively. For both bacteria, increasing treatment temperature tended to increase the inactivation rate. There was synergy between electric field intensity and processing temperature. The inactivation rate constant k _T values for E. coli O157:H7 on both selective and nonselective agars were 8.2 × 10^-3 and 6.6 × 10^-3/μS, whereas the values for S. enteritidis were 16.2 × 10^-3 and 12.6 × 10^-3/μS, respectively. The results suggest that E. coli O157:H7 was more resistant to heat-PEF treatment compared with S. enteritidis.     

Ultraviolet and Pulsed Electric Field Treatments Have Additive Effect on Inactivation of E. coli in Apple Juice

ABSTRACT: Apple juice inoculated with Escherichia coli ATCC 23472 was processed continuously using either ultraviolet (UV), high‐voltage pulsed electric field (PEF), or a combination of the PEF and UV treatment systems. Apple juice was pumped through either of the systems at 3 flow rates (8, 14, and 20 mL/min). E. coli was reduced by 3.46 log CFU/mL when exposed in a 50 cm length of UV treatment chamber at 8 mL/min (2.94 s treatment time with a product temperature increase of 13 °C). E. coli inactivation of 4.87 log CFU/mL was achieved with a peak electric field strength of 60 kV/cm and 11.3 pulses (average pulse width of 3.5 μs, product temperature increased to 52 °C). E. coli reductions resulting from a combination treatment of UV and PEF applied sequentially were evaluated. A maximum E. coli reduction of 5.35 log CFU/mL was achieved using PEF (electrical field strength of 60 kV/cm, specific energy of 162 J/mL, and 11.3 pulses) and UV treatments (length of 50 cm, treatment time of 2.94 s, and flow rate of 8 mL/min). An additive effect was observed for the combination treatments (PEF and UV), regardless of the order of treatment (P > 0.05). E. coli reductions of 5.35 and 5.30 log CFU/mL with PEF treatment (electrical field strength of 60 kV/cm, specific energy of 162 J/mL, and 11.3 pulses) followed by UV (length of 30 cm, treatment time of 1.8 s, and flow rate of 8 mL/min) and UV treatment followed by PEF (same treatment conditions), respectively. No synergistic effect was observed.     

脉冲电场技术应用于果蔬汁杀菌的研究进展

脉冲电场作为一种非热加工技术能保持果蔬汁的安全性、稳定性和新鲜度,同时具有处理时间短、温度低、能耗少等优势,是目前食品加工领域的研究热点,亦是最具应用潜力的技术之一。本文综述脉冲电场技术对果蔬汁的杀菌机理、影响因素、处理效果及与其他技术联合应用等方面,并进一步展望了脉冲电场在果蔬汁加工领域的应用前景。     

脉冲电场技术通过氧化应激途径诱导营养物质合成和杀灭微生物的研究进展

脉冲电场（Pulsed Electric Field，PEF）技术是一种新兴非热食品加工技术，由于PEF对食品质量损伤小且能杀灭食品中有害微生物所以被广泛应用。PEF通过氧化应激途径激活植物类食品的营养物质合成途径，诱导营养物质合成、提高食品质量，然而关于这一领域的研究较少。PEF发生了氧化应激反应造成了营养物质合成与积累，植物类食品受到PEF刺激后产生大量活性氧（Reactive Oxygen Species，ROS），ROS会激活代谢物合成途径最终合成蛋白、多酚、硫代葡萄糖苷和胡萝卜素等物质；ROS聚集在微生物的细胞膜上会造成蛋白表达异常，损害脂质层和脱氧核糖核酸（Deoxyribonucleic Acid，DNA），最终导致微生物失活。     

高压脉冲电场对大肠杆菌胞内蛋白的影响

通过聚丙烯酰胺凝胶电泳和傅里叶变换红外光谱研究了高压脉冲电场(PEF)处理对大肠杆菌(E.coli)胞内蛋白的影响,并应用去卷积和曲线拟合等数学方法和圆二(CD)色谱进一步分析PEF处理前后蛋白二级结构中α-螺旋、β-转角、β-折叠和无规卷曲相对含量的变化。结果表明,经过PEF(30 kV/cm,400μs)处理后,在分离胶的顶端出现了蛋白质的聚集。蛋白二级结构中β-折叠相当含量从45.40%降至21.50%,β-转角相对含量从23.8%降至8.81%,而无规卷曲结构从0.13%升至36.95%,α-螺旋结构没有明显的变化。     

Inactivation of Escherichia coli in a Tropical Fruit Smoothie by a Combination of Heat and Pulsed Electric Fields

ABSTRACT: Moderate heat in combination with pulsed electric fields (PEF) was investigated as a potential alternative to thermal pasteurization of a tropical fruit smoothie based on pineapple, banana, and coconut milk, inoculated with Escherichia coli K12. The smoothie was heated from 25 °C to either 45 or 55 °C over 60 s and subsequently cooled to 10 °C. PEF was applied at electric field strengths of 24 and 34 kV/cm with specific energy inputs of 350, 500, and 650 kJ/L. Both processing technologies were combined using heat (45 or 55 °C) and the most effective set of PEF conditions. Bacterial inactivation was estimated on standard and NaCl‐supplemented tryptone soy agar (TSA) to enumerate sublethally injured cells. By increasing the temperature from 45 to 55 °C, a higher reduction in E. coli numbers (1 compared with 1.7 log₁₀ colony forming units {CFU} per milliliter, P < 0.05) was achieved. Similarly, as the field strength was increased during stand‐alone PEF treatment from 24 to 34 kV/cm, a greater number of E. coli cells were inactivated (2.8 compared with 4.2 log₁₀ CFU/mL, P < 0.05). An increase in heating temperature from 45 to 55 °C during a combined heat/PEF hurdle approach induced a higher inactivation (5.1 compared with 6.9 log₁₀ CFU/mL, respectively {P < 0.05}) with the latter value comparable to the bacterial reduction of 6.3 log₁₀ CFU/mL (P≥ 0.05) achieved by thermal pasteurization (72 °C, 15 s). A reversed hurdle processing sequence did not affect bacterial inactivation (P≥ 0.05). No differences were observed (P≥ 0.05) between the bacterial counts estimated on nonselective and selective TSA, suggesting that sublethal cell injury did not occur during single PEF treatments or combined heat/PEF treatments.