Characterization of polyphenol oxidase from Uapaca kirkiana fruit

Polyphenol oxidase (PPO), the enzyme responsible for the postharvest spoilage of fruits, was extracted and purified from Uapaca kirkiana peel and pulp by ammonium sulfate precipitation and dialysis. Further purification of peel PPO was carried out by gel filtration chromatography. Optimum pH values were 7 and 8 for peel and pulp PPO, respectively. The optimum temperatures for peel and pulp PPO were 45 and 35 °C, respectively. Inhibition studies of the PPO enzyme were performed using citric acid, sodium azide, sodium metabisulfite and thiourea. The most effective inhibitors were sodium azide and citric acid for both peel and pulp PPO. V_max and K_m values were 13.63 units min^?1 and 4.923 mmol L^?1, respectively, for peel PPO and 14.03 units min^?1 and 5.43 mmol L^?1, respectively, for pulp PPO. Three isoenzymes of Uapaca kirkiana PPO were detected by polyacrylamide gel electrophoresis. One of the isoenzymes could be identified as having a molecular weight of 26 625 Da. Copyright © 2005 Society of Chemical Industry     

Polyphenol oxidase activity of two olive (Olea europaea L.) cultivars as an early criterion of Mn toxicity

BACKGROUND: The time course of polyphenol oxidase (PPO) activity in the leaves of two olive cultivars (Picual and FS‐17) irrigated with nutrient solutions differing in Mn concentration (0, 2 and 1280 µmol L^?1) was studied under hydroponic conditions to determine whether PPO activity could be used as an early criterion of Mn status of olive plants, and to elucidate whether genotypic differences exist between the two olive cultivars studied, concerning the effect of Mn concentration on PPO activity. RESULTS: In all the Mn treatments, PPO activity was greater in Picual than in FS‐17. Under excess Mn (1280 µmol L^?1), PPO activity gradually increased with time, starting from day 30 of the experiment in both cultivars, and this increase preceded the appearance of Mn toxicity symptoms. In contrast, in the other two Mn treatments (0 and 2 µmol L^?1) PPO activity increased and afterwards decreased during the experiment, but the trend was not clear. In the 1280 µmol L^?1 treatment, PPO activity linearly increased (R = 0.8836 for Picual and 0.943 for FS‐17) with the increase of Mn concentration in the leaves of both cultivars. In the 1280 µmol L^?1 Mn treatment, PPO activity was negatively related with Fe and Zn concentrations in the leaves, and positively in the 0 and 2 µmol L^?1 Mn treatments with the Ca, Mg and K concentrations. CONCLUSION: From the differential time course of PPO activity in the three Mn treatments (0, 2 and 1280 µmol L^?1), it is concluded that periodic measurements of PPO activity in the leaves of the olive cultivars Picual and FS‐17 can be used for the early detection of Mn toxicity (before the appearance of symptoms). Copyright © 2010 Society of Chemical Industry     

Efficacy of various naturally occurring caffeic acid derivatives in preventing post‐harvest protein losses in forages

BACKGROUND: In red clover, oxidation of endogenous o‐diphenols by polyphenol oxidase (PPO) inhibits post‐harvest proteolyis. This system is transferable to alfalfa by providing PPO (via a transgene) and o‐diphenol PPO substrates (via exogenous application). To exploit the PPO system for protein protection, it would be advantageous to produce PPO substrates in alfalfa, which lacks them. We assessed the extent of PPO‐mediated proteolytic inhibition by phenolic compounds, especially those whose biosynthesis could be engineered into alfalfa. RESULTS: Tested compounds included o‐diphenols (caffeic acid, phaselic acid, chlorogenic acid, clovamide) and monophenols (p‐coumaric acid, p‐coumaroyl‐malic acid). In the presence of PPO, 2 mmol o‐diphenol g^?1 protein reduced 24 h proteolysis 68–87% (P < 0.001) and as little as 0.25 mmol g^?1 protein still decreased 24 h proteolysis 43–60% (P < 0.001). At high concentrations, clovamide inhibited 24 h proteolysis 50% (P < 0.001) in the absence of PPO, likely due to non‐PPO oxidation. Monophenol p‐coumaric acid did not inhibit 24 h proteolyis, although high levels of its malate ester did exhibit PPO‐ and oxygen‐independent inhibition (37%, P < 0.001). CONCLUSIONS: For PPO‐mediated proteolytic inhibition, pathways for both phaselic acid and chlorogenic acid may be good targets for engineering into alfalfa. Clovamide may be useful for inhibiting proteolysis without PPO. Published 2012 by John Wiley & Sons, Ltd.     

Polyphenoloxidase from DeChaunac grapes

Polyphenoloxidase (PPO) from red grape cultivar, DeChaunac, grown in New York State was isolated and purified 17-fold by using Phenyl Sepharose CL-4B column. Disc gel electrophoresis revealed near homogeneity of three isoenzyme bands. The molecular weight of this enzyme ranged from 73 000 to 85 000. The temperature and pH optima of the purified enzyme were 20 °C and 6.0, respectively. Kinetic studies showed that the thermal inactivation of the PPO followed first-order kinetics, with the activation energy, Ea = 52.39 Kcal mol^?1. The substrate specificity showed a high degree of PPO activity toward o-diphenolic compounds with the highest affinity toward caffeic acid among substrates studied. The apparent K_m values for caffeic acid and 4-methylcatechol as substrates for the Dechaunac PPO were 16 mmol and 25 mmol, respectively. The most potent inhibitors of the PPO were D.L-dithiothreitol and sodium metasulphite at the concentration level of 0.5 mmol.     

Latent polyphenol oxidase from quince fruit pulp (Cydonia oblonga): purification,activation and some properties

Quince fruit polyphenol oxidase (PPO) was partially purified using a combination of phase partitioning in Triton X‐114 and PEG 8000/phosphate with a final ammonium sulfate fractionation between 30% and 75%, to avoid the deep browning of the enzyme due to the high amount of oxidizing substances present in the quince pulp. The clean and stable enzyme was partially purified in a latent form and could be optimally activated by the presence of 0.5 g dm^?3 sodium dodecyl sulfate (SDS) with an optimum pH of 5.0. In the absence of SDS, the enzyme showed maximum activity at acid pH. The apparent kinetic parameters of the latent enzyme were determined at pH 5.0, the V_m value being 15 times higher in the presence of SDS than in its absence, whereas the K_M was the same in both cases, with a value of 1.2 mmol L^?1. The effect of several inhibitors was studied, tropolone being the most active with a K_i value of 4.7 µmol L^?1. In addition, the effect of cyclodextrins was studied, and the complexation constant (K_c) between 4‐tert‐butylcatechol and cyclodextrins was calculated using an enzymatic method. The value obtained for K_c was 15 310 mol L^?1. Copyright © 2006 Society of Chemical Industry     

Expression,purification and refolding of recombinant Cry1Ab/Ac obtained in Escherichia coli as inclusion bodies

BACKGROUND: The Cry toxins are already a useful alternative or supplement to synthetic chemical pesticide application in commercial agriculture and forest management. RESULTS: The Cry1ab/ac gene from Bacillus thuringiensis was cloned from the genome of genetically modified rice by polymerase chain reaction (PCR). Owing to the large number of Escherichia coli low‐usage codons in the Cry1ab/ac gene, the first 20 codons were optimised by PCR to improve the expression of the Cry1ab/ac gene in E. coli. The Cry1Ab/Ac protein was highly expressed in E. coli as inclusion bodies that could be dissolved in 8 mol L^?1 urea and purified on a His Trap^? FF crude column under denaturing conditions. The purified Cry1Ab/Ac protein was dialysed in refolding buffers to obtain a soluble and biologically active protein. To achieve better biological activity, the His‐tag was digested from the Cry1Ab/Ac protein with enterokinase, and the Cry1Ab/Ac protein was further purified by gel filtration on a fast performance liquid chromatography Superdex 75 HR 10/30 column using an AKTA purifier. The identity of the purified Cry1Ab/Ac protein sequence was confirmed by western blot and matrix‐assisted laser desorption ionisation time‐of‐flight mass spectrometry. The final purified Cry1Ab/Ac protein was 99.2% pure and retained its biological activity, as determined in a growth inhibition assay of Chilo suppressalis. CONCLUSION: The purified Cry1Ab/Ac protein could be used to evaluate the food safety of transgenic plants containing the Cry1ab/ac gene and to produce antibodies for immune‐based methods employed in the detection of genetically modified organisms containing the Cry1ab or Cry1ac gene. It might also serve as a new biological insecticide to reduce the use of broad‐spectrum insecticides. Copyright © 2009 Society of Chemical Industry     

Polyphenol oxidase inactivation and vitamin C degradation kinetics of Fuji apple quarters by high humidity air impingement blanching

In this study, polyphenol oxidase (PPO) and vitamin C were used as the indicators of enzymes and nutrients to evaluate the apple quality during high humidity air impingement blanching (HHAIB) process. The PPO can be completely inactivated within 7 min at 90–120 °C and can retain relatively more vitamin C in the case of PPO fully inactivation. PPO inactivation followed zero‐order kinetics model at 90 and 100 °C, and followed first‐order fraction model at 110 and 120 °C. Activation energy (E_a) of PPO inactivation was between 11.61 and 13.66 kJ mol^?1 by Arrhenius equation. Vitamin C degradation under all processing temperatures was well described by first‐order model and its E_a value was 26.69 kJ mol^?1. Therefore, the HHAIB process was proved to be an effective pretreatment for Fuji apple quarters to inactivate PPO fast and meanwhile to maintain produce quality.     

Development of active plastic crate and evaluation of phytopathogenic and pathogenic food spoilage micro‐organism inhibition

BACKGROUND: The plastic crates used in fruit and vegetable shipping can be vehicles of disease dissemination among production fields, since there is a chance of phytopathogenic micro‐organism adhesion on the crate surfaces when in contact with soil, contaminated produce or handling. The aim of this study was to develop an active plastic crate incorporated with a triclosan‐based antimicrobial agent and to evaluate its efficiency of micro‐organism inhibition. RESULTS: Staphylococcus aureus (a human pathogen), Clavibacter michiganensis ssp. michiganensis and Erwinia carotovora ssp. carotovora (phytopathogens) were the most sensitive micro‐organisms when in contact with samples of plastic crate incorporated with 30 g kg^?1 of antimicrobial agent. They presented diameters of approximately 5.0, 3.5 and 3.5 cm respectively in the halo test. Mean specific growth rates decreased in samples with 30 g kg^?1 of antimicrobial agent, compared with control samples, from 1.13 to 0 h^?1 for S. aureus, from 1.26 to 0.47 h^?1 for Escherichia coli and from 1.75 to 0.18 h^?1 for Listeria monocytogenes. The antimicrobial agent did not influence the mechanical properties of the crates. CONCLUSION: The active plastic crate has great potential to contribute to the safety of horticultural produce by restraining the proliferation of micro‐organisms among production fields. Copyright © 2008 Society of Chemical Industry     

Survival of E. coli O157:H7 during manufacture of dry‐cured Westphalian ham surface‐treated with allyl isothiocyanate or hot mustard powder

BACKGROUND: Escherichia coli O157:H7 can survive commercial manufacture of some uncooked fermented meats. External application of microencapsulated allyl isothiocyanate (AIT) or hot (non‐deheated) yellow mustard powder was used to inactivate the pathogen during dry‐cured Westphalian ham manufacture. RESULTS: Within 45/80 days, E. coli O157:H7 numbers were reduced 5 log₁₀ CFU g^?1 by 400 µg kg^?1 AIT or 60 g kg^?1 mustard powder, but 80 days were required in the untreated control. Mustard powder but not AIT reduced numbers of lactic acid bacteria and staphylococci. Mustard powder or ≥ 300 µg kg^?1 AIT inhibited yeasts and moulds but did not affect ham pH or water activity. CONCLUSION: The commercial Westphalian ham process without AIT or mustard powder treatment was validated capable of reducing E. coli O157:H7 5 log₁₀ CFU g^?1. Surface treatments with ≥ 300 µg kg^?1 microencapsulated AIT or 60 g kg^?1 yellow mustard powder reduced the time required for this reduction by 40–50%. AIT volatility from microcapsules or hot mustard powder during application of these compounds may restrict their use in production facilities. Copyright © 2009 Society of Chemical Industry     

Characterization of Sultaniye grape (Vitis vinifera L. cv. Sultana) polyphenol oxidase

Polyphenol oxidase (PPO) was extracted from Sultaniye 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. Optimum pH and temperature for grape PPO were found to be 3.4 and 30 °C, using catechol as substrate. K_m and V_max values were found to be 44.5 ± 5.47 mm and 0.695 ± 0.0353 OD₄₁₀ min^?1, respectively. Four inhibitors were tested in this study and the most potent inhibitor was sodium metabisulphite, followed by ascorbic acid. From the thermal inactivation studies in the range of 65–80 °C, the half‐life values of the enzyme ranged between 2.6 and 49.5 min. Activation energy (E_a) and Z values were calculated to be 208.5 kJ mol^?1 (r² = 0.9544) and 10.95 °C (r² = 0.9517), respectively.     

Inhibitory effect of rice bran extract on polyphenol oxidase of potato and banana

Rice bran was extracted with water and its effects on potato and banana polyphenol oxidase (PPO) were investigated. Rice bran extract (RBE), conc. 0.3 g mL^?1, exhibited PPO inhibition in potato and banana PPO with % inhibition of 69.31% and 47.63%, respectively (P ≤ 0.05). RBE showed a concentration‐dependent inhibition on potato and banana PPO. RBE (conc. 0.3 g mL^?1) inhibited potato PPO higher than ascorbic acid, citric acid, NaCl and EDTA (final conc. 20 mg L^?1); and it also inhibited banana PPO higher than citric acid, NaCl and EDTA (final conc. 20 mg L^?1), respectively. The combination of RBE with citric acid or ascorbic acid appeared to be additive inhibitory effect on banana and potato PPO. Kinetic study of the inhibition on potato and banana PPO by RBE showed that RBE was a mixed‐type inhibitor; however, RBE appeared to be able to act directly on enzyme structure rather than substrate structure.     

Myricetin,an antioxidant flavonol,is a substrate of polyphenol oxidase

The present study demonstrates the antiradical efficiency of myricetin, a flavonol widely distributed in fruits and vegetables, by testing its ability to react with two different free radicals, ABTS^+· and DPPH^·. The polyphenolic nature of myricetin led us to consider the possibility of its oxidation by polyphenol oxidase (PPO). The results reported show that myricetin can be oxidised by PPO extracted and partially purified from broad bean seeds. The reaction was followed by recording spectral changes with time, maximal spectral changes being observed at 372 nm. The presence of two isosbestic points (at 274 and 314 nm) suggested that only one absorbing product was formed. The spectral changes were not observed in the absence of PPO. The oxidation rate varied with the pH, reaching its highest value at pH 5.5. The myricetin oxidation rate increased in the presence of SDS, an activing agent of polyphenol oxidase. Maximal activity was obtained at 1.3 mM SDS. The kinetic parameters were also determined: V _m = 1.35 µM min⁻¹, K _m = 0.3,mM , V _m/ K _m = 4.5 × 10⁻³ min⁻¹. Flavonol oxidation was inhibited by a selective PPO inhibitor such as cinnamic acid (K_I = 1 mM ). The results reported show that myricetin oxidation was strictly dependent on the presence of polyphenol oxidase. © 1999 Society of Chemical Industry     

Atomic force microscopy study of the antimicrobial activity of aqueous garlic versus ampicillin against Escherichia coli and Staphylococcus aureus

BACKGROUND: In this study the effects of ampicillin and aqueous garlic extract on Escherichia coli (ATCC 9637) and Staphylococcus aureus (ATCC 25923) were compared. Atomic force microscopy (AFM) was used to study the possible mechanisms of membrane disruption. RESULTS: Ampicillin disrupted the cell membrane of E. coli, inducing pores and cell leakage. Aqueous garlic extract also induced leakage from the cell membrane in E. coli, but no pores were observed. The trend in Young's modulus for E. coli was E_native ≈ E_age > E_amp. In contrast, S. aureus incubated with low ampicillin (≤50µg mL^?1) and garlic (≤50 mg mL^?1) concentrations showed no significant changes in surface morphology compared with the untreated bacterium. The trend in Young's modulus for S. aureus was E_native ≈ E_age ≈ E_amp. CONCLUSION: The trend E_native ≈ E_age for E. coli and S. aureus supports the hypothesis that the compounds in garlic show intracellular activity. This proof‐of‐concept study of the aqueous crude isolate of garlic points to the feasibility of further AFM investigations to compare the antimicrobial properties of various pure thiosulfinate isolates found in garlic. Copyright © 2009 Society of Chemical Industry     

Isolation and catalytic actions of polyphenoloxidase from sunflower seeds (Helianthus annuus)

In the last few decades, biotechnological applications of phenoloxidase enzymes have become an area of significant interest. In this study, sunflower seeds, seedlings and defatted mill cake were investigated as possible plant source of polyphenoloxidase (PPO). Noticeable variation of chlorogenic acid concentration in each raw material has undoubtedly proven that only sunflower seedlings have significant amounts of active PPO. The activity of the enzymes was assessed by measuring the molar decrease of caffeic acid. Isolated protein powders from each raw material confirmed the presence of PPO only in the seedlings. Catalytic action of the PPO of seedlings was compared to that of the commercial laccase from Trametes versicolor. Sunflower PPO was selectively active on caffeic and chlorogenic acids, less active on ferulic acid and not active on mono-phenols and gallic acid. Conversely, laccase was highly active on all the assessed phenols. PPO activity was good in a large range of pH (4–8), whilst it was approximately halved in solutions containing 35% ethyl alcohol (v/v), 500 mg L⁻¹ citric acid and finally 200 mg L⁻¹ sulphur dioxide. In conclusion, sunflower seedlings can be considered a potential and interesting plant source of PPO. Sunflower PPO could be used to oxidise selectively o-diphenols, for example in alcoholic and nonalcoholic beverages.     

Polyphenol oxidase activity in grass and its effect on plant‐mediated lipolysis and proteolysis of Dactylis glomerata (cocksfoot) in a simulated rumen environment

Little is known about the level or activity of polyphenol oxidase (PPO) in grasses and its potential impact on proteolysis and lipolysis. Six grass species were initially screened for PPO activity (740.6, 291.9, 213.6, 119.0, 16.3 and 6.5 U g^?1 fresh weight (FW) for cocksfoot, hybrid ryegrass, Italian ryegrass, perennial ryegrass, timothy and tall fescue respectively). Cocksfoot, which expressed the highest activity, was then used to determine the effect of PPO on plant‐mediated proteolysis and lipolysis in a simulated rumen environment. Sourced cocksfoot was macerated and incubated in an antibiotic‐containing anaerobic medium with or without ascorbate to deactivate PPO in the dark at 39 °C over five time points. At each time point (0, 1, 2, 6 and 24 h), six replicate samples were destructively harvested; three of the replicates were used for lipid analysis and the other three for protein, free amino acid and bound phenol determination. Characterisation of the herbage showed PPO activities of 649.6 and 0 U g^?1 FW, which were reflected in the extent of phenol (derived from quinones) binding to protein after 24 h of incubation, namely 65.1 and 29.6 mg bound phenol g^?1 protein (P < 0.001) for cocksfoot and cocksfoot + ascorbate respectively. Proteolysis, measured as free amino acids released into the incubation buffer, was significantly reduced (P < 0.001) with increasing PPO activity, with values after the 24 h incubation of 0.03 and 0.07 mmol L^?1 g^?1 FW for cocksfoot and cocksfoot + ascorbate respectively. Lipolysis, measured as the proportional decline in the membrane lipid polar fraction, was likewise reduced (P < 0.001) with increasing PPO activity, with values after the 24 h incubation of 0.43 and 0.65 for cocksfoot and cocksfoot + ascorbate respectively. Changes that occurred in protein and the lipid fractions (polar fraction, monoacylglycerol + diacylglycerol, triacylglycerol and free fatty acids) during the incubations are also reported and discussed. These results support the selection of forages high in PPO activity to reduce protein and lipid losses in silo and potentially in the rumen. Copyright © 2006 Society of Chemical Industry     

Edible film incorporated with chitosan and Artemisia annua oil nanoliposomes for inactivation of Escherichia coli O157:H7 on cherry tomato

As a natural antibacterial agent, Artemisia annua oil (AAO) exhibited significant antibacterial effect on Escherichia coli O157:H7. However, AAO was volatile and not suitable for surface coatings of fresh produce. Therefore, the edible agar films containing chitosan and AAO liposomes were engineered to overcome the defect. Chitosan was added in the film to enhance the antibacterial activity. Finally, the results showed the mean size of AAO liposomes was about 191.8 nm with a polydispersity index (PDI) of 0.463. The absolute zeta potential value was greater than 30 mV, and the loading efficiency (LE) of 5.0 mg mL^?1 AAO liposome was 67.45%. As a proof of concept, the antibacterial activity of the films against E. coli O157:H7 on cherry tomatoes was evaluated. The results indicated that the incorporation of AAO liposomes as a natural antibacterial agent possessed bacteriostatic effect, which had potential for using the developed film as an active packaging.     

Active packaging of ground beef patties by edible zein films incorporated with partially purified lysozyme and Na2EDTA

In this study, antimicrobial activity of zein films incorporated with partially purified lysozyme and disodium ethylenediaminetetraacetic acid (Na₂EDTA) has been tested on selected pathogenic bacteria and refrigerated ground beef patties. The developed films containing 700 μg cm^?2 lysozyme and 300 μg cm^?2 Na₂EDTA showed antimicrobial activity on Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella typhimurium. The application of lysozyme and Na₂EDTA incorporated zein films on beef patties significantly decreased total viable counts (TVC) and total coliform counts after 5 days of storage compared to those of control patties (P < 0.05). Zein films incorporated with lysozyme and Na₂EDTA or Na₂EDTA alone significantly slowed down the oxidative changes in patties during storage (P < 0.05). Redness indices of patties coated with zein films were significantly lower than those of uncoated control patties during storage (P < 0.05). This study demonstrated the potential usage of zein films containing lysozyme and Na₂EDTA for active packaging of refrigerated meat products.     

Heat Inactivation Kinetics of Apple Polyphenoloxidase and Activation of its Latent Form

Heat inactivation kinetics of crude polyphenoloxidase (PPO) from six apple cultivars (Golden Delicious, Starking Delicious, Granny Smith; Gloster, Starcrimson and Amasya) were studied at three temperatures (68°, 73° and 78°C). PPO activity initially increased and then decreased with heat, following a first order kinetic model. Increase in activity indicated presence of latent PPO. Regression coefficients for the linear portions of inactivation curves were computed to determine inactivation parameters. Reaction data at 78°C revealed that PPO in Amasya was the least and Starking Delicious the most heat-stable. Rate constants for heat inactivation at 78°C ranged from 15.99–28.27. 10^?2 min^?1. Activation energies varied between 54.7–77.2 kcal. mol^?1 with z values of 7.1–10.0C°.PPO in apples was generally more heat-stable than PPO in most fruits.     

Survival of Escherichia coli O157:H7 in the processing and post-processing stages of acidophilus yogurt

In this study the survival of Escherichia coli O157:H7 in the production process of acidophilus yogurt was examined and compared with traditional yogurt. Milk was inoculated with different doses of E. coli O157:H7 (10², 10⁴ and 10⁶ CFU mL^?1) and two kinds of yogurt were produced. Samples were taken for pH measurements and bacterial enumeration at 0, 3, 24, 48, and 72 h after inoculation. Escherichia coli O157:H7 was analysed by using a Most Probable Number technique and yogurt starter culture and Lactobacillus  acidophilus were counted by using classical culture methods. Elimination times of E. coli O157:H7 were determined for 10² CFU mL^?1 as 3 h, and for 10⁴ and 10⁶ CFU mL^?1 as 48 h in acidophilus yogurt. Elimination times in traditional yogurt were 48 h for 10² and 10⁴ CFU mL^?1 and 72 h for 10⁶ CFU mL^?1E. coli O157:H7. In conclusion, the elimination time of E. coli O157:H7 in acidophilus yogurt was shorter than in traditional yogurt during the processing and post‐processing stages.     

Inactivation of polyphenol oxidase from frozen red raspberry (Rubus idaeus L.) by high pressure carbon dioxide treatment

The effect of high pressure carbon dioxide (HPCD) treatment on polyphenol oxidase (PPO) from frozen red raspberry (Rubus idaeus L.) was evaluated. Moreover, the inactivation kinetics of its PPO was simulated by first‐order reaction theory. The minimum of PPO residual rate was 36.6% under 30 MPa and 55 °C for 60 min by HPCD treatment, while that was 66.8% at 55 °C for 60 min by thermal treatment. Moreover, the decimal reduction time of PPO decreased rapidly after HPCD treatment, compared to that of the thermal treatment. The thermal treatment at 55 °C takes a similar time to reach 10% PPO residual rate with HPCD treatment under 30 MPa at 35 °C. One reason for the results was that activation energy of PPO reduced from 98.9 to 14.6 kJ mol^?1 after HPCD treatment. Therefore, HPCD treatment showed stronger capacity to inactivate PPO from frozen red raspberry than the thermal treatment at same temperature.