Inactivation of Polyphenoloxidase by Pulsed Light

The effect of pulsed light on the inactivation of polyphenoloxidase (PPO) in model solutions was investigated focusing on the effect of enzyme concentration and total energy dose of the treatment. PPO inactivation increased with the dose of the treatment. Complete enzyme inactivation was achieved by pulsed light doses higher than 8.75 J cm^?2. At low PPO concentrations (4 to 10 U), the enzyme resulted highly inactivated by pulsed light treatment. Further increase in enzyme units determined a progressive decrease in PPO inactivation. The latter was attributed to protein structural modifications including cleavage and unfolding/aggregation phenomena. PPO amounts higher than 10 U probably favoured enzyme conformations that were less prone to intermolecular rearrangements leading to inactivation.     

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.     

Process Parameters Affecting Listeria innocua Inactivation by Pulsed Light

The impact of several processing parameters on the effectiveness of pulsed light (PL) technology was investigated. The distribution of the light on the surface of the PL treatment chamber and the fluence striking on the sample under different treatment conditions were evaluated. Higher pulse fluences were registered when input voltage increased and the distance from the sample to the light source decreased. Distance from the sample to the xenon lamp also played a major role in the light distribution onto the surface of the treatment zone. Whereas quartz shelf placed close to the xenon lamp resulted in a non-uniform distribution of fluence, a homogeneous light distribution was found when increasing the distance to the flash lamp. Moreover, the impact of several PL processing parameters on microbial inactivation was investigated. Neither pulse voltage nor total voltage determined the antimicrobial effectiveness of PL technology in the operating range tested. Reduction in Listeria innocua counts increased with the number of pulses and the pulse fluence, being total fluence reaching the samples the most relevant process factor affecting microbial inactivation by PL. Considering the importance of this processing parameter, an accurate quantification of the fluence striking on the sample will be needed in order to design effective PL treatments.     

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.     

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.     

脉冲放电等离子体杀灭苹果汁中鲁氏接合酵母及对苹果汁品质的影响

应用研制的脉冲放电等离子体杀菌设备,以鲁氏接合酵母（Zygosaccharomyces rouxii,Z.rouxii）为试验菌株,探讨电气参数（脉冲电压、通气量和处理时间）、溶液参数（果汁可溶性固形物）及菌初始浓度对苹果汁中鲁氏接合酵母的杀灭影响,并比较了不同菌株杀灭效果的差异;同时对处理前后苹果汁的基本理化指标、有机酸、多酚及挥发性风味物质含量进行测定,探讨脉冲放电等离子体对苹果汁品质的影响。结果表明：在脉冲电压24 kV、通气量150 mL/min、果汁可溶性固形物12%和果汁pH=3.84时,脉冲放电等离子体能够将初始浓度为1.08×104 CFU/mL的鲁氏接合酵母LB在5 min内杀灭。同时脉冲放电等离子体对苹果汁基本理化指标、有机酸、多酚及挥发性风味物质含量大部分影响均不显著（p<0.05）,能够较大程度保持苹果汁品质,该研究为脉冲放电等离子体在食品杀菌中应用提供了重要依据。     

Pulsed Light Inactivation of Mushroom Polyphenol Oxidase: a Fluorometric and Spectrophotometric Study

Polyphenol oxidase (PPO) is one of the most important food enzymes; it is responsible for the browning of many foods. Pulsed light (PL) is a non-thermal method of food preservation that is able to inactivate PPO. The aim of this work was to gain insight into the mechanism of PPO inactivation by PL. To this, the kinetics of PPO inactivation by PL was measured, together with associated changes in tryptophan fluorescence, KI fluorescence quenching, and turbidity; and results were analyzed by parameter A and phase diagram methods. Enzyme inactivation followed the Weibull model. Tryptophan fluorescence decreased during PL treatment, as well as the parameter A, while Stern-Volmer constants increased and turbidity was constant. The phase diagram showed only two populated states. There was a high correlation between the loss of activity and parameter A. Results indicate that under the experimental conditions, the inactivation of PPO by PL is an all-or-none process where the enzyme progressively unfolds with no evidence of aggregation.     

Impact of Process Parameters on Listeria innocua Inactivation Kinetics by Pulsed Light Technology

The impact of several pulsed light (PL) processing parameters on microbial inactivation was evaluated in buffered water systems using Listeria innocua as test microorganism. Reduction in L. innocua population increased directly with pulse energy, pulse fluence and the number of light pulses, and inversely with the distance between samples and a xenon lamp. Overall, the higher the amount of light received by the target microorganism by both direct and reflected light, the larger the loss of cell counts. Total fluence striking on the samples per area unit was shown to be the most relevant process factor affecting L. innocua inactivation by PL. Microbial population decreased with total fluence, obtaining more than 7 log reductions after 0.4 J?cm^?2. The inactivation kinetics was clearly sigmoidal, showing an initial shoulder in the inactivation curve. No significant reduction (<1 log) in L. innocua counts was induced at fluences lower than 0.04 J?cm^?2. From this threshold total fluence, L. innocua inactivation increased exponentially to the maximum detectable level. Since total fluence is the most relevant process factor affecting microbial inactivation by PL, this parameter must be reported to describe PL processing conditions.     

Inactivation of Escherichia coli O157:H7 on Inoculated Alfalfa Seeds with Pulsed Ultraviolet Light and Response Surface Modeling

: Escherichia coli O157:H7‐inoculated alfalfa seeds with seed layer thicknesses of 1.02 to 6.25 mm were subjected to pulsed UV light for up to 90 s at a 8‐cm distance from the UV strobe. Population reductions higher than 4 log₁₀ colony‐forming units (CFU)/g were achieved. For effect of distance from the UV strobe, seeds with 6.25‐mm layer thickness were treated 3 to 13 cm from the strobe. Reductions at shorter distances, such as 60 s at 5 cm (1.93 log₁₀ CFU/g) and 60 to 90 s at 8 cm (4.89 log₁₀ CFU/g), were significantly higher (P≤ 0.05). Data from the treatments were used to develop empirical models as a function of distance or layer thickness and treatment time for predicting the population of E. coli O157:H7 during pulsed UV‐light treatment. This study demonstrates that pulsed UV light holds promise for eliminating pathogens from alfalfa seeds, and the models developed can be useful predictive tools.     

Inactivation of Oxidative Enzymes by High-Intensity Pulsed Electric Field for Retention of Color in Carrot Juice

The effects of high-intensity pulsed electric fields (HIPEF) on oxidative enzymes and color of fresh carrot juice were studied. A response surface methodology (RSM) was used to evaluate the effect of pulse polarity (mono or bipolar mode), pulse width (from 1 to 7 μs), and pulse frequency (from 50 to 250 Hz) on color and peroxidase (POD) inactivation of carrot juice treated by HIPEF. The total treatment time and the electric field strength were set at 1,000 μs and 35 kV/cm, respectively, at a temperature below 35°C. The physicochemical characteristics of carrot juice were measured. There was a linear relationship between electrical conductivity and temperature of the carrot juice. The results showed that HIPEF-treated carrot juice at 35 kV/cm for 1,000 μs applying 6 μs pulse width at 200 Hz in bipolar mode led to 73.0% inactivation of POD. The color coordinates did not change significantly. Therefore, HIPEF was effective in POD inactivation and carrot juice color preservation.     

The Effect of Ultraviolet Light on Microbial Inactivation and Quality Attributes of Apple Juice

Non-thermal technologies such as UV irradiation can offer advantages for minimal processing of transparent beverages. In this study, reconstituted apple juice was exposed to UV light in a continuous laboratory scale system at energy dosages ranging from 2.66 to 53.10 J/cm² by changing the exposure time. Treated juices were then evaluated for microbial inactivation and selected physical and chemical attributes. Product quality was further assessed by sensory evaluation using a 30-member consumer panel. Microbiological analysis was performed by inoculating apple juice with Escherichia coli K12 and Listeria innocua and microbial numbers were counted pre- and post-processing. UV energy levels did not affect pH, °Brix, or total phenols content, but decreased non-enzymatic browning (p < 0.01) and antioxidant capacity (p < 0.05) compared to unprocessed juice. A colour-lightening effect was noted with increasing energy dose. All UV treatments applied (2.66 J/cm² and above) resulted in a reduction below the detection level (<1 log cfu/ml) for both E. coli and L. innocua in apple juice. Sensory evaluation showed that samples treated with energy dosages up to 10.62 J/cm² were comparable to the control in terms of acceptability, though higher dosages produced adverse effects in terms of flavour and colour. Based on these results, UV treatment with low energy dosages could represent a valid alternative to thermal processing to eliminate pathogenic microorganisms while maintaining quality in reconstituted apple juice.     

Nonthermal Inactivation of Soy (Glycine Max Sp.) Lipoxygenase by Pulsed Ultraviolet Light

This study investigated pulsed ultraviolet (PUV) illumination at different distances from the PUV source on soybean lipoxygenase (LOX) (0.4 mg/mL in 0.01 M Tris‐HCl buffer, pH 9) activity. Samples (5 mL) were illuminated for 1, 2, 4, 8, and 16 s at 3 distances 6, 8.5, and 11 cm from the PUV lamp's quartz window. The temperature of 33.5 ± 1.8°C was observed for the highest treatment time of 16 s at the shortest distance of 6 cm, and resulted in a 3.5 log reduction (99.95%) in initial LOX activity. Illumination time and distance from the lamp significantly (P ≤ 0.05) affected LOX inactivation. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) was performed on treated LOX samples and further protein profile for treated LOX filtrate (≤10 kDa), was analyzed by reverse phase high‐performance liquid chromatography (RP‐HPLC). The protein profile analysis revealed that LOX protein degradation was influenced significantly (P ≤ 0.05) by PUV illumination time.     

脉冲强光对枯草芽孢杆菌NG-2灭活机理

采用脉冲强光对枯草芽孢杆菌NG-2及芽孢进行灭活并研究其机理。在脉冲强光辐照枯草芽孢杆菌NG-2菌体及其芽孢后,利用扫描电子显微镜和透射电子显微镜观察形态特征变化,利用紫外分光光度法测定细胞内物质含量,利用荧光光谱法检测细胞内Ca~(2+)浓度和非特异性酯酶活力。结果表明,辐照距离为5 cm,闪照频率为5次/s,辐照15 s时,脉冲强光对NG-2菌体及其芽孢灭活率超过50%;辐照40 s时,脉冲强光对NG-2菌体及其芽孢灭活率超过99.98%。辐照枯草芽孢杆菌及芽孢后菌体结构损伤,芽孢壁破裂,细胞内核酸、蛋白质、Ca~(2+)和2,6-吡啶二羧酸含量显著减少,非特异性酯酶活力降低,研究结果为脉冲强光对枯草芽孢杆菌及芽孢灭活机理提供理论依据。     

Growth and Inactivation of Microorganisms Isolated from Ultrapasteurized Egg

Microorganisms which survived and grew at 4° or 10°C in ultrapasteurized, aseptically packaged liquid whole egg were isolated and identified. Growth at 4° and 10°C, and inactivation from 50 to 70°C, of selected isolates were evaluated in ultrapasteurized egg. Bacillus circulans and a Pseuriomonas species grew well at 4°C. with generation times of 1.0 and 0.3 days, respectively. Enterococcus fuecalis and B. circulans were the most heat resistant isolates studied. Because B. circulans grew at 4°C and was relatively heat resistant it would be a useful test organism for many applications while E. faecalis would be useful since it was heat resistant and would grow rapidly when the storage temperature is less than ideal.     

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.     

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。     

The Impact of Thermosonication and Pulsed Electric Fields on Staphylococcus aureus Inactivation and Selected Quality Parameters in Orange Juice

The effect of thermosonication (TS) and pulsed electric fields (PEF) on inactivation of Staphylococcus aureus (SST 2.4) and selected quality aspects in orange juice was investigated. Conventional pasteurization (HTST, 94 °C for 26 s) was used as a control. TS (10 min at 55 °C) applied in combination with PEF (40 kV/cm for 150 μs) resulted in a comparable inactivation of S. aureus to that achieved by conventional HTST. TS/PEF did not affect the pH, conductivity, or °Brix and had a milder impact on the juice color than thermal treatment. Furthermore, the non-enzymatic browning index was significantly affected by HTST (P < 0.05) but not by TS and PEF. Ascorbic acid retention was almost complete after TS and PEF (96.0%), but it was substantially lower (P < 0.05) after HTST (80.5%). Residual activity of pectin methyl esterase (PME) decreased as PEF field strength and treatment time increased; however, applying TS and PEF in combination left a greater residual PME activity than HTST (12.9 vs 5.0%, respectively).