A comparative study of inactivation of peach polyphenol oxidase and carrot polyphenol oxidase induced by high‐pressure carbon dioxide

The inactivation of polyphenol oxidase (PPO) in peach juice and PPO in carrot juice was investigated by high‐pressure carbon dioxide (HPCD), and their inactivation kinetics was analysed and compared. The temperature was 35–55 °C, the pressure was 5–15 MPa under HPCD condition. Results showed that HPCD enhanced the inactivation effect of the temperature on the two PPOs. The inactivation kinetics of peach PPO was well fitted to a first‐order kinetic model, of carrot PPO to a fraction‐conversion model as a function of temperatures or pressures. Susceptibility of the rate constant k of peach PPO was not altered and of carrot PPO was lessened to the temperature, but the susceptibility of the rate constant k of peach PPO and carrot PPO to the pressure was not changed when the pressure was >8 or 12 MPa, indicating the presence of a threshold pressure.     

Inactivation of peroxidase and polyphenol oxidase in red beet (Beta vulgaris L.) extract with continuous high pressure carbon dioxide

The inactivation of peroxidase (POD) and polyphenol oxidase (PPO) in red beet extract (RBE) with continuous high pressure carbon dioxide (HPCD) was investigated. HPCD treatment at 7.5 MPa (55 °C, 30 min) resulted in a reduction of their activities by approximately 73% and 93%, respectively. Compared with thermal treatment, continuous HPCD treatment reduced the decimal reduction time (D) of POD and PPO from 555.6 min to 55.9 min and 161.3 min to 32.1 min, respectively. The inactivation process could be described by first-order kinetics (r² > 0.70, p < 0.05); D values declined when temperature increased and continuous HPCD at 7.5 MPa and 55 °C resulted in the highest reaction rate constant (k value; smallest D value). The activation energy of the inactivation was reduced by HPCD treatment from 92.5 kJ/mol to 69.8 kJ/mol and 57.1 kJ/mol to 49.5 kJ/mol for POD and PPO, respectively. Continuous HPCD treatment had little effect on the antioxidant capacities of RBE samples.     

高压CO2处理对香蕉果肉中多酚氧化酶活性的影响

比较了CO2压力、温度和处理时间对香蕉果肉中多酚氧化酶活性的影响,并且采用二次回归正交旋转组合设计优化了高压CO2处理对香蕉果肉中多酚氧化酶的钝化条件.结果表明,影响高压CO2处理钝化香蕉果肉中多酚氧化酶活性的主次因素顺序为温度＞时间＞ CO2压力;高压CO2处理钝化香蕉果肉中多酚氧化酶的最佳条件为温度60℃、CO2压力19MPa、处理时间50min,在此条件下,香蕉果肉中多酚氧化酶的残活力仅为0.9％.     

高压二氧化碳对鲜榨梨汁杀菌效果及动力学研究

本文研究了高压二氧化碳(HPCD)对梨汁中细菌菌落总数的影响,并分析其杀菌动力学。结果表明:随着温度、压强升高以及处理时间延长,梨汁中细菌菌落总数显著降低(p<0.05);在相同温度和处理时间条件下,HPCD处理显著高于热处理的杀菌效果,处理温度对HPCD杀菌具有协同效应;当HPCD处理条件为30MPa、40℃、60min时,灭菌效果最佳,梨汁中细菌菌落总数的残存率降低了2.66个对数;Weibull模型能较好地拟合HPCD处理后梨汁中细菌菌落总数的失活曲线,模型动力学参数比例因子a和形状因子b随压力增加和温度升高呈现逐渐变小的规律性变化。      

高压CO_2对树莓汁品质的影响

研究了高压二氧化碳(High Pressure Carbon Dioxide,HPCD)对树莓汁品质的影响。处理条件为:压强10、20、30MPa,温度35、45、55℃,时间15、30、45、60min。测定其浊度、褐变指数、悬浮稳定性、pH、可溶性固形物含量和色泽。处理后样品褐变指数降低,浊度和悬浮稳定性增加,pH、可溶性固形物含量和色泽没有显著变化。     

Inactivation of polyphenol oxidase from Pacific white shrimp by dense phase carbon dioxide

The inactivation of polyphenol oxidase (PPO) from Pacific white shrimp exposed to dense phase carbon dioxide (DPCD) treatment was investigated. PPO activity showed a dramatic loss at 4–25 MPa and 37 °C. At the lower pressure (4–15 MPa), the experimental data of inactivation followed the first-order reaction kinetic model, the pressure sensitivity (Z_P) of the kinetic parameters was 49.02 MPa and the activation volume (△ V^≠) was − 120.88 cm³/mol. At the higher pressure (20 and 25 MPa), the experimental data of inactivation followed the biexponential kinetic model. The kinetic rate constant k_F and k_S of fast and stable fractions were 2.45 and 0.08 min^{− 1}, respectively. The decimal reduction time D_F and D_S were 0.94 and 29.43 min at 25 MPa and 37 °C, respectively. After DPCD treatment, the loss activity of PPO had no restoration storing for 6 days at 4 °C. The results of SDS-PAGE and activity staining also showed that DPCD treatment had the obvious inhibitory effect on PPO from Pacific white shrimp. The PPO activity in vivo was easier to be inactivated than that in crude PPO extracts under the same DPCD treatment conditions.

Industrial relevance

There is a growing interest in non-thermal pasteurization methods, which could retain food's freshlike physical, nutritional, and sensory qualities. Pacific white shrimp accounts for 90% of the global aquaculture shrimp production, they are becoming increasingly popular. However, enzymatic browning of shrimp has been of great concern to food scientists and food processors. Dense phase carbon dioxide (DPCD) may be an adequate tool to obtain high quality since PPO activity could not be inactivated totally by high pressure under 400 MPa yet. The present work deals with the inactivation of PPO from Pacific white shrimp exposed to DPCD treatment in order to explore the feasibility of shrimp by DPCD process.     

Effect of carbon dioxide on the inactivation of florida spiny lobster polyphenol oxidase

Florida spiny lobster (Panulirus argus) polyphenol oxidase (PPO) exposed to CO₂ (1 atm) at 33, 38, and 43°C showed a decrease in enzyme activity with increased heating time. Enzyme inactivation by CO₂ was faster for PPO heated at 43 than at 33 or 38°C. Inactivation kinetics revealed PPO was more labile to CO₂ and heat in the range 33–43°C than to heat alone. Kinetic data also revealed that CO₂, in addition to pH changes, was involved in the loss of PPO activity. Studies using get electrophoresis showed no differences in protein patterns and isoelectric point between CO₂-treated and non-treated control. The pH of CO₂-treated PPO stock solution was brought back from 5.4 to 8.0 after 6 weeks of frozen-storage and no enzyme reactivation was observed.     

高压二氧化碳对西瓜汁中过氧化物酶钝化动力学的研究

为了延长西瓜汁的货架期,研究高压二氧化碳处理对西瓜汁中过氧化物酶(peroxidase,POD)的钝化效果。研究以热处理为对照,比较不同高压二氧化碳处理温度和压强对其POD活性残存率的影响。采用二段式模型模拟POD的钝化效果(R2>0.975),证明西瓜汁中POD存在敏感型和稳定型两部分。通过动力学分析考察两种类型POD对温度和压强的敏感性,确认高压二氧化碳处理温度、压力、时间、pH和CO2等因素共同导致了POD活性的降低。高压二氧化碳处理比热处理可以更加有效钝化西瓜汁中POD,有助于延长西瓜汁的货架期。     

高压二氧化碳杀菌机理研究进展

高压二氧化碳（HPCD）技术作为一种新型非热杀菌技术,越来越受到研究者的关注,但目前对其杀菌机理尚未明确。本文分析了目前国内外有关HPCD杀菌机理的研究进展,并分析了HPCD对微生物细胞内几个作用靶点包括细胞壁、细胞膜、细胞质、蛋白质、酶和核质的影响,以期为进一步研究和应用提供理论依据。     

The contribution of high pressure carbon dioxide in the inactivation kinetics and structural alteration of myrosinase

High pressure carbon dioxide (HPCD) has been verified to be an efficient way of inactivating enzyme activity. This work investigates the influence of temperature (T), pressure (P), exposure times (t) on the activity of commercial myrosinase (MYR) submitted to HPCD. Results showed that only 1.00% of MYR activity retained at 22 MPa and 65 °C for 5 min. Moreover, the first‐order reaction kinetic data of MYR inactivation as influenced by pressure of HPCD were analysed. With the pressure rising from 8 to 22 MPa at 55 °C, the inactivation rate constant (k) increased from 0.015 to 0.024 min^?1, while the decimal reduction time (D) decreased from 157.2 to 96.1 min. Additionally, a series of exploratory experiments were conducted to investigate the contribution of the HPCD parameters (T, P and CO₂ dissolution), with analysing circular dichroism spectroscopy and tryptophan fluorescence spectra, illustrate that CO₂ dissolution plays a dominant role in MYR inactivation and structural alteration.     

Inactivation kinetics of polyphenol oxidase using a two-stage method with low pressurized carbon dioxide microbubbles

Inactivation kinetics of polyphenol oxidase (PPO) by a two-stage method which was additionally pressurized at ambient temperature after carbon dioxide microbubbles (MB-CO₂) was mixed with a solution at low temperature and pressure (two-stage MB-CO₂) was analyzed. The PPO inactivation efficiency of the two-stage MB-CO₂ treatment was higher than that of heat treatment. A decrease in the decimal reduction time (D value) and activation energy during PPO inactivation using the two-stage MB-CO₂ treatment was observed as the temperature of the heating coil and the pressure in the mixing vessel increased. The temperature rise required for a 90% reduction in the D value was increased. Furthermore, the pressure rise required for a 90% reduction in the D value and activation volume increased with the temperature of the heating coil. These results showed that PPO inactivation using the two-stage MB-CO₂ treatment could be achieved with less energy than heat treatment.     

Inactivation of polyphenol oxidases in cloudy apple juice exposed to supercritical carbon dioxide

The inactivation of polyphenol oxidase (PPO) in cloudy apple juice exposed to supercritical carbon dioxide (SCCO₂) treatment was investigated. Higher pressure, higher temperature, and longer treatment time caused more inactivation of PPO. The maximum reduction of PPO activity reached more than 60% at 30 MPa and 55 °C for 60 min. The experimental data followed first-order reaction kinetics; the kinetic rate constant k and the decimal reduction time D were closely related to the pressure and temperature of SCCO₂ treatment. Higher pressures or higher temperatures resulted in lower D values (higher k), the D value of PPO was minimized to 145 min treated by the combination of 30 MPa and 55 °C. Activation energy of 18.00 kJ /mol, was significantly reduced by SCCO₂ treatment at 30 MPa, as compared to activation energy of 72.0 kJ/mol for identical treatment at atmospheric pressure. Pressure and temperature sensitivity of kinetic parameters were studied. Z_P at 55 °C was 66.7 MPa and Z_T at 30 MPa was 108 °C.     

Determination of some biochemical properties of polyphenol oxidase from Emir grape (Vitis vinifera L. cv. Emir)

Polyphenol oxidase (PPO) was extracted from Emir grapes grown in Turkey and its characteristics in terms of pH and temperature optima, thermal inactivation, kinetic parameters and potency of some PPO inhibitors were studied. The optimum pH and temperature for grape PPO were found to be 4.2 and 25 °C respectively using catechol as substrate. K_m and V_max values were found to be 25.1 ± 2.72 mmol L⁻¹ and 0.925 ± 0.04 OD₄₁₀ min⁻¹ respectively. Of the inhibitors tested, the most potent was sodium metabisulfite, followed by ascorbic acid. The thermal inactivation curve was biphasic. Activation energy (E_a) and Z values were calculated as 251.4 kJ mol⁻¹ (r² = 0.996) and 8.92 °C (r² = 0.993) respectively. Copyright © 2006 Society of Chemical Industry     

高压二氧化碳保鲜双孢蘑菇的工艺优化

为了优化高压二氧化碳(high pressure carbon dioxide,HPCD)保鲜双孢蘑菇的工艺,在单因素实验基础上,采用响应面法分析HPCD处理压力、处理时间和处理温度对双孢蘑菇硬度和颜色的影响并对其进行优化。结果表明,HPCD保鲜双孢蘑菇的最佳工艺条件为:处理压力0.3 MPa,处理时间3 min,处理温度17℃;与对照相比,该条件HPCD处理后的双孢蘑菇可以更好的保持其硬度和颜色,低温贮藏8 d后的硬度为191.7 N(提高了18.85%),褐变指数(BI)为33.13(降低了16.80%)。因此,HPCD技术可以应用于双孢蘑菇的贮藏保鲜,具有良好的前景。      

High pressure carbon dioxide treatment for fresh-cut carrot slices

The effects of high pressure carbon dioxide (HPCD) treatment on natural microorganisms, indigenous enzyme activity, damage to cell membranes and hardness in fresh-cut carrot slices were investigated. 1.86 log₁₀ cycle reduction for aerobic bacteria (AB) and 1.25 for yeasts and molds (Y&M) were achieved at 5 MPa and 20 °C for 20 min. The residual activity (RA) of peroxidase (POD), polyphenol oxidase (PPO), and pectinmethylesterase (PME) exhibited initially increase and secondly decrease with treatment time and their minimum activity was 75.8%, 90.9% and 52.8% at 5 MPa and 20 C for 15 min, respectively. Membrane damage was evaluated by relative electrolyte leakage (REL) and malondialdehyde (MDA) content. HPCD caused a significant increase of REL in carrot slices and the REL of carrot slices treated at 5 MPa and 20 °C for 15 min was 5.7 times as much as that of the untreated, however, HPCD showed no effect on MDA content. The hardness was well retained after HPCD treatment and the largest loss was 7.9% at 5 MPa and 20 °C for 15 min.

Industrial relevance

Fresh-cut carrot slices are one of the most widely used products in prepared salads, and it required strict treatment conditions to protect its quality, especially to prevent microbial spoilage and enzymatic discoloration. HPCD is one promising novel non-thermal technique without compromising the flavor, taste and nutrition aspect of food. This study analyzed the effectiveness of HPCD as a method of preserving fresh-cut carrot slices, including inactivating natural microorganisms and enzymes which are crucial to quality control. Available data provided in this study will benefit the fresh-cut fruits and vegetables industry.     

Characterization of polyphenol oxidase and peroxidase from peach mesocarp (Prunus persica L. cv. Babygold)

The two enzymes involved in enzymatic browning reactions—polyphenol oxidase (PPO) and peroxidase (POD)—were extracted from peach fruit mesocarp. PPO was mainly located in the membrane fraction and was in its latent state. However, POD activity was found in the soluble fraction. The kinetic characterization of PPO and POD was carried out with a natural substrate (chlorogenic acid) and with a non‐physiological substrate. Under native isoelectric focusing (IEF), several PPO isoenzymes were present in the pH range 5.4–5.8. A partially denaturing sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS‐PAGE) showed the presence of two active bands with apparent molecular masses of 49 and 50 kDa. A totally denaturing SDS‐PAGE indicated the presence of a single polypeptide with a molecular mass of 60 kDa, as revealed by western blot. POD was also analyzed by IEF, showing the presence of two strongly basic isoenzymes, which were resolved by cationic native PAGE into two different bands. Copyright © 2007 Society of Chemical Industry     

高压CO2对水酶法乳状液破乳影响的研究

研究高压CO2破乳过程中的各种因素对破乳效果的影响,并采用透射电镜来观察乳状液破乳前后油脂和蛋白的变化情况。在单因素基础上通过响应面优化得到最佳破乳条件:高压CO2压力为13.96MPa,温度155.64℃,处理时间21.46 s,浓度0.53 g/cm3,破乳率最优值(94.88±0.30)%。并且通过透射电镜观察发现,破乳前乳状液中大部分油脂被蛋白牢牢包裹,然而破乳后乳状液中包裹油脂的蛋白被破坏,油脂释放并结合在一起。     

In situ inactivation of polyphenol oxidase in mamey fruit (Pouteria sapota) by microwave treatment

Polyphenol oxidase (PPO) is the enzyme responsible for quality loss in most fruits and vegetables. Quality loss is mainly because of oxidative chemical reactions which generate the darkening of tissues. Mamey fruit (Pouteria sapota) after harvesting suffers a rapid quality decay trough activation of PPO. However, PPO may be inactivated in situ by chemical or thermal treatment. In food processing, microwave treatment (MT) has been used recently as an alternative for PPO inactivation. In this study, it was observed that mamey fruit pulp subjected to a gently MT resulted in a higher PPO activity as the generated heat induced in situ the increase in PPO activity. In contrast, PPO was completely inactivated after long MT by using a high microwave power. Temperature in mamey pulp after MT reached a maximum of 79 °C; although PPO was active up to 60 °C. PPO was completely inactivated when conventional blanching treatment was performed but required a higher temperature (92 °C/300 s). The optimum energy intensity (E(opt)) for PPO inactivation by MT was 0.51 kJ/g or 937 W/165 s. Under this condition, the remaining PPO activity was inversely proportional to energy intensity (E). Interestingly, MT resulted in a negligible damage in microstructure of mamey pulp, although blanching treatment resulted in large damaging effects on tissue organization and shape. Therefore, MT is proposed as an effective way to completely inactivate PPO without causing any significant damage to fruit tissues and shape; as preservation of color, flavor, and taste would be favored.     

Mathematical modeling of Saccharomyces cerevisiae inactivation under high‐pressure carbon dioxide

High‐pressure carbon dioxide inactivation curves of Saccharomyces cerevisiae at different temperatures were analysed using the modified Gompertz model. Comparable λ and μ values were obtained under pressure treatment as function of temperature. The phase of disappearance (λ) and the inactivation rate (μ) of S. cerevisiae were inversely related. Higher μ values were obtained at 50°C than at 40, 30, and 20°C under 10.0 MPa CO₂ pressure. Increased pressure and temperature had significant effects on the survival of S. cerevisiae. Arrhenius, linear and square‐root models were used to analyse the temperature dependence of the inactivation rate constant. For the Arrhenius model the activation energy (E_μ) was 56.49 kJ/mol at 10.0 MPa, and 55.70, 53.83, and 52.20 kJ/mol at 7.5, 5.0, and 2.5 MPa, respectively. Results of this study enable the prediction of yeast inactivation exposed to different CO₂ pressures and temperatures.