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.     

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.     

The use of carbon dioxide at high pressure to control nine stored-product pests

The development of alternative treatments for pest control in food commodities is an increasing demand from the food industry, which should meet consumer demands for the reduced use or elimination of pesticides. The use of carbon dioxide (CO₂) at high pressure is one of the most rapid options for arthropod pest control among current commercial treatments, offering complete control within hours. The present study aimed to establish the efficacy of the technique against different stages of several insect and mite pests that affect stored-food products. Standard food diets containing eggs, larvae, pupae and adults of Oryzaephilus surinamensis, Cryptolestes ferrugineus, Lasioderma serricorne, Sitophilus oryzae, Rhyzopertha dominica, Acanthoscelides obtectus, Ephestia kuehniella, Liposcelis bostrychophila and Tyrophagus putrescentiae were treated with CO₂ for different times at two high pressures, 15 and 20 bar. A high level of control was achieved for most species and development stages when they were treated with CO₂ at 20 bar for 60 min. However, the efficacy at 15 bar was much lower. The eggs of L. bostrychophila and L. serricorne showed the highest tolerance of all species/stages and survived the most extreme conditions tested. The beetle O. surinamensis, the moth E. kuehniella, and the mite T. putrescentiae were easier to kill than the other species tested. Our results confirmed that the use of high-pressure CO₂ offers an effective and fast way to control most stored-product pests that affect food commodities.     

Purification and enzymatic characteristics of a novel polyphenol oxidase from lotus seed (Nelumbo nucifera Gaertn.)

A polyphenol oxidase (PPO) from lotus seed was purified by the procedures including ammonium sulphate precipitation and affinity chromatography. The apparent molecular mass was 38.6 kDa by SDS‐PAGE. Kinetic studies showed that the K_m and V_max values for catechol were 6.04 mm and 416.67 U, respectively. The PPO performed optimal activity in 20 °C and pH 7.0. The enzymatic activity could be mainly maintained up to 50 °C and pH 4.0–7.0. The activity could be inhibited by various inhibitors including thiourea, urea, sodium hydrogen sulphite, EDTA·2Na, SDS, citric acid, guanidine hydrochloride, ascorbic acid, sodium sulphite and sodium thiosulphate. The metal ions Ba²⁺, Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺ and Zn²⁺ could inhibit the activity of PPO, while Cu²⁺ performed obvious enhancement. The enzymatic properties of PPO could probably provide practical application in inhibiting the PPO activity and preventing enzymatic browning in the process of picking, transportation, processing and storage of fresh lotus seeds.     

Comparison of biochemical properties and thermal inactivation of membrane‐bound polyphenol oxidase from three apple cultivars (Malus domestica Borkh)

A comparative study of the properties of membrane‐bound polyphenol oxidase (mPPO) from three apple cultivars, namely Red Fuji (FJ), Granny Smith (GS) and Golden Delicious (GD), was carried out for the first time. Data indicate that mPPOs from three cultivars exhibit significantly different properties. GS mPPO had the strongest affinity to catechol, but FJ mPPO had the highest maximum velocity. Red Fuji (FJ) mPPO had the significantly higher activity than those of GD and GS mPPOs. Red Fuji (FJ) mPPO had the highest activity at pH 8.00, while GD and GS mPPOs at 4.50 and 7.50–8.00, respectively. Red Fuji (FJ) mPPO was more stable than GD and GS mPPOs over the pH range of 5.0–8.5. The optimal temperature for GS mPPO was within 70–75 °C, which is higher than those for mPPOs from FJ and GD. Thermal inactivation of the three mPPOs followed a first‐order kinetic model with different inactivation kinetic parameters.     

Inactivation of Saccharomyces cerevisiae in conference pear with high pressure carbon dioxide and effects on pear quality

This work explores the use of high pressure carbon dioxide (HPCD) for the inactivation of Saccharomyces cerevisiae in fresh-cut conference pears. This fruit was chosen as an example of a ready to eat and minimally processed food. Assays were carried out with continuous CO₂ flow at different pressures (6–30 MPa), temperatures (25–55 °C), and exposure times (10–90 min). Heat treatments at similar temperatures and times were compared to the use of HPCD, wherein it was observed that HPCD was more effective. The total inactivation (5 log₁₀ cycles) of the yeast took place at 55 °C with HPCD while it was necessary to reach 70 °C when only heat was applied. Required pressures and exposure times were relatively low (?6 MPa and on the order of minutes) because of the direct contact between the CO₂ and the pear. The pH and °Brix were not affected by the HPCD treatment; however, the pears lost their texture and became darker due to a decrease in vitamin C and enzymatic browning. Peroxidase activity was only partially reduced. The addition of an antioxidant did not help to prevent darkening. Therefore, HPCD could be a low temperature conservation method that is superior to conventional thermal treatments for the preparation of fruit preserves where a firm texture is not essential.     

Inactivation of microorganisms naturally present in raw bovine milk by high‐pressure carbon dioxide

This study assessed the inactivation of microorganisms naturally present in raw bovine milk by high‐pressure carbon dioxide (HPCD) at 10–30 MPa and 20–50 °C for 20–70 min. The log reduction of microorganisms increased as raw bovine milk was exposed to higher pressures and temperatures and longer treatment times. The maximum reduction of aerobic bacteria (AB) was 4.96‐log at 25 MPa and 50 °C for 70 min. At lower temperatures and treatment times, a complete inactivation of yeasts and moulds (Y&M) and coliform bacteria (CB) was obtained at 25 MPa. Changes in microorganisms naturally present in raw bovine milk during storage were also assessed. There were 1.83‐log survival of AB, 0.65‐log survival of Y&M and a complete inactivation of CB in raw bovine milk when subjected to HPCD at 25 MPa and 40 °C for 50 min. Moreover, the AB, Y&M and the CB in raw bovine milk exhibited insignificant alterations during storage at 4 °C for 15 days, indicating a potential capability of HPCD to extend the shelf life of milk.     

Change of polyphenol oxidase activity, color, and browning degree during storage of cloudy apple juice treated by supercritical carbon dioxide

The effects of supercritical carbon dioxide (SCCO₂) treatment of 8, 15, 22, and 30 MPa for 60 min at 55 °C on polyphenol oxidase (PPO) activity, color, and browning degree in cloudy apple juice during storage at 4 °C for 4-weeks were investigated. The SCCO₂ treatment had significant effects on inactivation of PPO and the least residual activity of PPO was 38.50% at 30 MPa. The restoration of PPO residual activity after SCCO₂ treatment was also observed, which was dependent on the pressure level. A greater reduction of lightness L and a minor increase of redness a of cloudy apple juices after SCCO₂ treatment occurred. Moreover, the total color difference (ΔE), which was significantly less than that of untreated sample, was decreased by enhancing the pressure level. The changes of lightness L and browning degree A during storage were well fitted to a first-order kinetic model. The rate constants of k _L and k _A of samples subjected to SCCO₂ treatment reduced from 4.75×10⁻² to 0.42×10⁻² and 37.19×10⁻² to 8.02×10⁻², respectively, when pressure increased from 0 MPa (untreated sample) to 30 MPa.     

Inactivation of apple (Malus domestica Borkh) polyphenol oxidases by radio frequency combined with pulsed electric field treatment

Radio frequency (RF) preprocessing combined with pulsed electric field (PEF) processing was employed to inactivate polyphenol oxidase (PPO) in apple juice. PPO enzyme levels, loss of total phenolic content (TPC), colours and volatile components in the apple juice were subsequently determined and compared with conventional processing methods (60 °C for 10 min and 70 °C for 10 min). Results indicated that, when the apple tissue was preprocessed using RF for 10 min, the residual activity of PPO decreased to 13.57%; when the squeezed juice was processed by PEF, the residual activity decreased to about 5% at 15–35 kV cm^?1 for 400 μs. RF treatment caused no significant loss in TPC. Compared with the conventionally processed samples, the apple juice that was RF‐treated for 10 min and PEF‐treated at 15 kV cm^?1 for 400 μs increased its lightness and maintained its fresh‐like flavour.