Inactivation Kinetics of Tomato Juice Lipoxygenase by Pulsed Electric Fields

ABSTRACT: Pulsed electric field (PEF) inactivation models for tomato juice lipoxygenase (LOX) were studied. Tomato juice was treated by PEF with the combinations of electric field strength (0, 10, 15, 20, 30, 35 kV/cm), PEF treatment time (20, 30, 50, 60, 70 μs), and PEF treatment temperature (10, 20, 30, 40, 50 °C). The first-order inactivation models, Hulsheger's model, Fermi's model, and the 2nd-order polynomial equation adequately described the LOX inactivation. Calculated D values were 161.0, 112.9, 101.0, and 74.8 μs at 15, 20, 30, and 35 kV/cm, respectively, at 30 °C. The activation energy for the inactivation of LOX by PEF was 35.7 kJ/mol. Applied electric field strength was the primary variable for the inactivation of LOX.     

Effects of Commercial-scale Pulsed Electric Field Processing on Flavor and Color of Tomato Juice

Effects of commercial‐scale pulsed electric field (PEF) processing on the flavor and color of tomato juice during storage at 4 deg;for 112 d were studied. Tomato juice was prepared by hot break at 88°C for 2 min and then thermally processed at 92° for 90 s or PEF processed at 40 kV/cm for 57 μs. The PEF‐processed tomato juice retained more flavor compounds of trans‐2‐hexenal, 2‐isobutylthiazole, cis‐3‐hexanol than thermally processed or unprocessed control tomato juice (P < 0.05). PEF‐processed juice had significantly lower nonenzymatic browning and higher redness than thermally processed or control juice (P < 0.05). Sensory evaluations indicated that the flavor of PEF‐processed juice was preferred to that of thermally processed juice (P < 0.01).     

Effects of Pulsed Electric Fields on Microorganisms in Orange Juice Using Electric field Strengths of 30 and 50 kV/cm

ABSTRACT: Inactivation of 4 microorganisms in orange juice was investigated in a 100 L/h flowing pulsed electric field (PEF) system. Electric field levels of 30 kV/cm and 50 kV/cm were applied, and Leuconostoc mesenteroides, E. coli , and Listeria innocua were inactivated by as much as 5 log cycles at 30 kV/cm and 50 °C. Saccharomyces cerevisiae ascospores were the least susceptible to PEF at all treatment levels, and a maximum of 2.5 log reduction was achieved at 50 kV/cm and 50 °C. Both electric field levels were effective in inactivating microorganisms at temperatures below standard thermal treatment, however, the number of pulses applied was particularly important in inactivation.     

Microbial and Enzymatic Changes in Fruit Juice Induced by High-Intensity Pulsed Electric Fields

High-intensity pulsed electric fields (HIPEF) treatment is a nonthermal technology that has been studied in the last few years as an alternative to heat treatments. It consists of applying pulses of high electric field (kV/cm) during a short time (μsec or msec) at low or moderate temperature.

Because of their properties, fruit juices are appropriate products to be processed by HIPEF. Studies on the effects of HIPEF on microorganisms show that this treatment destroys microorganisms at levels of heat pasteurization with lower destruction of vitamins, flavor compounds, and other micronutrients. The majority of enzymes that are responsible for adverse biological reactions in fruit juices are inactivated by HIPEF. The effects of HIPEF, as for thermal treatments, are mainly described by first-order models. Furthermore, others models are also proposed to fit some effects of HIPEF on the enzymatic activity or microorganisms population. Fewer works are focused on the effects on organoleptic, physical, and chemical properties of fruit juices, but results show that most of the properties remain unchangeable. The changes, if they occurred after a HIPEF treatment, are always less important than those produced by heat.     

脉冲电场和热处理对鲜榨苹果汁贮藏期品质的影响

研究高压脉冲电场处理 (PEF)和热处理对鲜榨苹果汁贮藏期的品质影响。研究发现 ,4℃贮藏 3 0d ,PEF( 2 5kV/cm ,1 0 3 5个脉冲 )和热处理 ( 72℃、1 5s和 90℃、60s)可以降低果汁中微生物数量 ,而且对苹果汁的电导率、Brix和 pH值的影响不显著 (P >0 0 5 )。但是热处理对果汁的浊度有显著影响 (P <0 0 5 ) ,而PEF处理差异不显著 (P >0 0 5 )。PEF处理苹果汁的L值和色值均优于热处理 ,感官评价中风味和色泽比热处理的苹果汁更接近对照的风味和色泽。     

高压脉冲电场对蓝莓汁杀菌效果及品质的影响

研究了高压脉冲电场(PEF)对蓝莓汁的杀菌效果及其对蓝莓汁理化性质的影响。结果显示:随电场强度、处理时间的增大,PEF对蓝莓汁中大肠杆菌的杀灭效果增强。当电场强度为35 kV/cm,处理时间为82μs时,蓝莓汁中大肠杆菌致死率为5.12个对数。电场强度一定时,电导率增大,PEF对大肠杆菌的钝化效果略微下降。PEF对蓝莓汁VC、花青素、总酚、可滴定酸、还原糖、可溶性固形物及色泽等理化性质没有影响。     

Effects of Pulsed Electric Fields on the Activities of Microorganisms and Pectin Methyl Esterase in Orange Juice

Orange juice was treated with pulsed electric fields (PEF) in a pilot‐plant system to optimize PEF‐processing conditions for maximum microbial inactivation and to investigate the effects of PEF on pectin methyl esterase (PME) activity. Electric‐field strengths of 20,25,30, and 35 kV/cm and total treatment times of 39, 49, and 59 μs were used. Higher electric‐field strengths and longer total treatment times were more effective to inactivate microorganisms and PME (p < 0.05). PEF treatment of orange juice at 35 kV/cm for 59 μs caused 7–log reductions in total aerobic plate count and yeast and mold counts. About 90% of PME activity was inactivated by PEF treatment at 35 kV/cm for 59 μs. PEF‐treated orange juice at 35 kV/cm for 59 ms did not allow growth of microorganisms and recovery of PME at 4, 22, and 37 °C for 112 d.     

Inactivation of Pectin Methyl Esterase in Orange Juice by Pulsed Electric Fields

ABSTRACT: Pulsed electric fields (PEF) treatments were applied to nonpasteurized orange juice using a bench top PEF system to study effects of PEF on the activity of pectin methyl esterase (PME). Effects of electric strength on PME activity at a constant water bath temperature were studied using electric field strengths up to 35 kV/cm at 30 °C. Increase of electric field strength caused a significant inactivation of PME with increase in orange juice temperature ( p < 0.05). A thermal inactivation study showed that heating of orange juice at the same temperature as orange juice during PEF treatment was not effective as PEF treatment in inactivating PME. Effects of electric field strength at different water bath temperatures were studied using electric field strengths up to 25 kV/cm and water bath temperatures of 10–50 °C. Higher electric field strengths at higher water bath temperature were the more effective to inactivate PME. A combination of PEF treatment at 25 kV/cm and a water bath temperature of 50 °C caused 90% inactivation of PME.     

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。     

高压脉冲电场对百合混汁灭菌的研究

研究了高压脉冲电场(PEF)对百合混汁的灭菌效果。操作过程中电场强度和处理时间是影响其灭菌效果的主要参数,随着电场强度的增大和处理时间的延长,灭菌效果越来越好。当电场强度达到30 kV/cm时,灭菌效果非常显著,处理时间为400μs时菌落总数已降低了4个对数值。经PEF处理后,百合混汁的理化指标没有明显的变化,可以保持其原有品质。     

Kinetics of Peroxidase Inactivation in Carrot Juice Treated with Pulsed Electric Fields

Peroxidase activity accounts for quality losses in many plant‐based foods. The paper provides insight into the inactivation kinetics of peroxidase (POD) in carrot juice treated with pulsed electric fields (PEF). Juice samples were subjected to electric field intensities of 20 to 35 kV/cm for 300 to 2000 μs. Up to 93% of the initial activity was inactivated after treating at 35 kV/cm for 1500 μs. POD activity inactivation correlated well with the increase in energy density input. A first‐order fractional conversion model best fitted the experimental results. Other kinetic approaches such as the Fermi's model can be used to estimate residual POD activity values in treated juices as a function of electric field strength. Practical Application : Pulsed electric fields (PEF) are a processing technology that can be used for the pasteurization of liquid food products. Peroxidase activity inhibition is required in carrot juices to prevent undesirable quality losses, such as discoloration, flavor changes, and loss of nutrients. The most significant processing parameters ruling POD inactivation in PEF‐treated carrot juice are identified and mathematical modeling of experimental data is conducted.     

Volatile compounds and changes in flavour‐related enzymes during cold storage of high‐intensity pulsed electric field‐ and heat‐processed tomato juices

BACKGROUND: The effects of high‐intensity pulsed electric field (HIPEF) processing (35 kV cm^?1 for 1500 µs, using 4 µs bipolar pulses at 100 Hz) on the production of volatile compounds and flavour‐related enzymes in tomato juice were investigated and compared with those of thermal processing (90 °C for 30 or 60 s). RESULTS: Tomato juice treated by HIPEF showed lower residual lipoxygenase (LOX) activity (70.2%) than juice heated at 90 °C for 60 s (80.1%) or 30 s (93.2%). In contrast, hydroperoxide lyase (HPL) was almost completely inactivated when the juice was subjected to 90 °C for 60 s, whereas roughly 50% of the control tomato juice was depleted after HIPEF treatment or thermal processing at 90 °C for 30 s. A slight decrease was observed in the initial LOX activity of treated and untreated samples during storage, whereas initial HPL activity was strongly affected over time. CONCLUSION: HIPEF‐treated juice exhibited higher levels of compounds contributing to tomato aroma than untreated and heat‐treated juices throughout storage. Thus HIPEF processing can preserve flavour quality and stability of tomato juice compared with conventional thermal treatments. Copyright © 2010 Society of Chemical Industry     

高压脉冲电场对乳铁蛋白抑菌性能的影响

研究了高压脉冲电场(PEF)对乳铁蛋白(LF)的抑菌性能的影响。结果表明,LF质量浓度、电场强度、脉冲频率、脉冲数的增加,有利于LF抑菌能力的增强,而温度的升高会使之减弱。电场强度为35 kV/cm时,LF的抑菌能力达到最大值。LF的质量浓度越高,对电场强度的变化越敏感。当脉冲个数达到744时,LF的相对抑菌能力提高了34%。处理温度为15～55℃时,PEF处理的LF的相对抑菌性能增长了5%左右。当温度升高至65℃时,LF的相对抑菌能力下降显著,降低了约22%。     

氢过氧化物裂解酶的筛选及纯化

研究了不同植物原料中氢过氧化物裂解酶的含量,并最后筛选出苋菜作为提取原料。利用高速离心、表面活性剂溶解、硫酸铵分级沉淀、羟基磷灰石柱层析和离子交换色谱对苋菜氢过氧化物裂解酶进行纯化至电泳纯。结果表明,纯化的苋菜氢过氧化物裂解酶分子量约为55ku,对于13-亚麻酸氢过氧化物的活力高于13-亚油酸氢过氧化物,最适pH6.0,最适温度为25℃,在常温下酶能保持较高水平的活力。     

Plasmin Inactivation with Pulsed Electric Fields

Plasmin (fibrinolysin E.C.3.4.21.7), an indigenous enzyme in bovine milk, added to simulated milk ultrafiltrate (SMUF) at 100 μg/mL (pH 6.11 and ionic strength 0.056 M) was treated at 10°C and 15°C with pulsed electric fields (HVPEF) of 15, 30 and 45 kV/cm and number of pulses 10, 20, 30, 40 and 50. The plasmin activity measured using a commercial assay, was reduced 90% after 50 pulses at both 30 and 45 kV/cm and at a processing temperature of 15°C. Similar inactivation was obtained when plasmin (100 μg/mL) in SMUF was heated at 40°C for 15 min. Inactivation of the enzyme depended on the number of pulses applied during treatment, intensity of the applied field, and processing temperature.     

高压脉冲电场对绿茶饮料杀菌的研究

研究了高压脉冲电场对中性的绿茶饮料的杀菌效果，结果表明，当电场强度达到40kV／cm，处理时间达到120μs时，绿茶饮料中接种的大肠杆菌数量可降低5个对数级以上。此条件下生产的绿茶饮料样品，其茶多酚含量及色泽都无明显变化。     

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。     

高压脉冲电场对大豆分离蛋白结构特征的影响

本文研究了高压脉冲电场对大豆分离蛋白结构特征的影响。结果表明：在其它脉冲条件一定时，脉冲处理时间在0-288us范围，大豆分离蛋白的分子量、粒径及二级结构改变较小或几乎没有改变。当脉冲处理时间大于432us时，由于蛋白质分子变性、亚基的解离以及通过非共价键相互作用重新聚集，大豆分离蛋白的分子量、粒径发生了变化，形成了大分子的聚集体，但二级结构变化较小。     

Effects of Pulsed Electric Fields on the Activity of Enzymes in Aqueous Solution

ABSTRACT: A group of selected enzymes were subjected to continuous pulsed electric field (PEF) treatments to evaluate the inactivation effect of PEF. For a treatment time of 126 μs, 51.7% and 83.8% of pepsin was inactivated at 37.0 kV/cm and 41.8 kV/cm, respectively. Enzyme activity of polyphenol oxidase decreased 38.2% when treated at 33.6 kV/cm for 126 μs. Enzyme activity decreased 18.1% and 4.0% for peroxidase treated at 34.9 kV/cm and chymotrypsin treated at 34.2 kV/cm, respectively. No significant change in lysozyme activity was observed after PEF from 0 to 38 kV/cm for 126 μs. Both PEF and the induced heat contributed to the observed inactivation effect, depending on the properties of enzymes and test conditions.     

Commercial-Scale Pulsed Electric Field Processing of Orange Juice

Effects of commercial‐scale pulsed electric field (PEF) processing on the microbial stability, ascorbic acid, flavor compounds, color, Brix, pH, and sensory properties of orange juice were studied and compared with those of thermal processing. Freshly squeezed orange juice was thermally processed at 90 °C for 90 s or processed by PEF at 40 kV/cm for 97 ms. Both thermally processed and PEF‐processed juices showed microbial shelf life at 4 °C for 196 d. PEF‐processed juice retained more ascorbic acid, flavor, and color than thermally processed juice (P<0.05). Sensory evaluation of texture, flavor, and overall acceptability were ranked highest for control juice, followed by PEF‐processed juice and then by thermally processed juice (P<0.01).