Purification and structural analysis of membrane-bound polyphenol oxidase from Fuji apple

JrPPO1/2 play distinct roles in regulating walnut fruit browning by different spatiotemporal expression and enzymatic characteristics

Polyphenol oxidase (PPO) activity drives walnut fruit browning, but the roles of its only two-family genes, JrPPO1 and JrPPO2, remain unclear. This study explores the spatiotemporal expression and enzymatic characteristics of JrPPO1 and JrPPO2 in walnut. Treatment with the PPO activator CuSO4 and H2O2 accelerated fruit browning and up-regulated JrPPO1/2 expression, whereas treatment with the PPO inhibitor ascorbic acid delayed browning, down-regulating JrPPO1 and up-regulating JrPPO2 expression. Compared to mJrPPO1, mJrPPO2 can exhibited better enzyme activity at higher temperatures (47 °C) and in more acidic environments (pH 4.25). mJrPPO2 exhibited a higher substrate specificity over mJrPPO1, and the preferred substrates are catechol, chlorogenic acid, and epicatechin. Additionally, mJrPPO2 adapted better to low concentration of oxygen (as low as 1.0% O2) and slightly elevated CO2 levels compared to mJrPPO1. Subcellular localization and spatiotemporal expression patterns showed that JrPPO1 is only expressed in green tissues and located in chloroplasts, while JrPPO2 is also located in chloroplasts, partly associated with membranes, and is expressed in both green and non-green tissues. Silencing JrPPO1/2 with virus-induced gene silencing (VIGS) reduced fruit browning, maintained higher total phenols, and decreased MDA production. Notably, silencing JrPPO1 had a greater impact on browning than JrPPO2, indicating JrPPO1's greater contribution to PPO activity and fruit browning in walnut fruits. Consequently, JrPPO1 can be effectively regulated both at the molecular level and by manipulating environmental conditions, to achieve the objective of controlling fruit browning.

In silico guided pre-treatment of sugarcane juice with natural inhibitors of polyphenol oxidase (PPO) is a new and effective strategy for development of spray-dried formulation

Sugarcane juice is a popular beverage and is also processed to produce sugar. The polyphenol oxidase (PPO) in sugarcane juice causes enzymatic browning and makes the process of sugar production complex and cumbersome. Storage of sugarcane juice is also hampered by the high sugar content and rapid microbial fermentation. The present research assessed the potential of lemon juice (LJ) and ginger extract (GE) as natural inhibitors of PPO. Enzyme kinetics and the mechanism of inhibition of LJ and GE were studied. Primary investigation was carried out using molecular docking approach to assess the inhibitory potential of LJ and GE and to determine the nature of interaction between the enzyme and inhibitors. Extracts were used as inhibitors and studies revealed that both reduced the PPO activity. Subsequently, pure bioactive inhibitors such as ascorbic acid, citric acid, and 6-shogaol present in these natural extracts were used to study the mode of inhibition of PPO. Citric acid decreased PPO activity by lowering pH, while ascorbic acid was found to be a competitive inhibitor of PPO with a Ki of 75.69 µM. The proportion of LJ and GE required in sugarcane juice was optimized on the basis of browning index and sensory acceptance. Further, the sugarcane cane juice after inhibition of PPO under optimized conditions was spray dried and evaluated for reconstitution properties. The product formulated in the present study is a new and effective approach to address quality-compromising issues associated with long-term storage of cane juice.

The PPO family in Nicotiana tabacum is an important regulator to participate in pollination

Polyphenol oxidases (PPOs) are type-3 copper enzymes and are involved in many biological processes. However, the potential functions of PPOs in pollination are not fully understood. In this work, we have screened 13 PPO members in Nicotiana. tabacum (named NtPPO1-13, NtPPOs) to explore their characteristics and functions in pollination. The results show that NtPPOs are closely related to PPOs in Solanaceae and share conserved domains except NtPPO4. Generally, NtPPOs are diversely expressed in different tissues and are distributed in pistil and male gametes. Specifically, NtPPO9 and NtPPO10 are highly expressed in the pistil and mature anther. In addition, the expression levels and enzyme activities of NtPPOs are increased after N. tabacum self-pollination. Knockdown of NtPPOs would affect pollen growth after pollination, and the purines and flavonoid compounds are accumulated in self-pollinated pistil. Altogether, our findings demonstrate that NtPPOs potentially play a role in the pollen tube growth after pollination through purines and flavonoid compounds, and will provide new insights into the role of PPOs in plant reproduction.

Purification and characterization of novel isoforms of the polyphenol oxidase from Malus domestica fruit pulp

Polyphenol oxidases (PPOs), belong to the group of oxidoreductases that are copper containing enzymes and are responsible for plant browning. PPOs are extensively distributed in plant kingdom and can oxidize wide range of aromatic compounds of industrial importance. The aim of this study was purification and characterization of PPO isoforms from the fruit pulp of Golden delicious apple. High performance liquid chromatography was used to purify the two novel isoforms of PPO and further their molecular weights (45 and 28 kDa) were determined using sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified isoforms have optimum pH (6.5), optimum temperature (40°C), the Vmax (4.45 μM/min) and Km (74.21 mM) with catechol substrate. The N-terminal microsequences of both PPO isoforms were determined using a pulse liquid protein sequencer and found to be AKITFHG (28 kDa) and APGGG (45 kDa). Polyphenol oxidases are efficiently used in the pharmaceutical, paper and pulp, textiles and food industries. Recently, the PPOs have been used for bioremediation and in the development of biosensors.

Integrated Transcriptome and Metabolome Analysis Revealed the Causal Agent of Primary Bud Necrosis in 'Summer Black' Grape

Primary bud necrosis of grape buds is a physiological disorder that leads to decreased berry yield and has a catastrophic impact on the double cropping system in sub-tropical areas. The pathogenic mechanisms and potential solutions remain unknown. In this study, the progression and irreversibility patterns of primary bud necrosis in 'Summer Black' were examined via staining and transmission electron microscopy observation. Primary bud necrosis was initiated at 60 days after bud break and was characterized by plasmolysis, mitochondrial swelling, and severe damage to other organelles. To reveal the underlying regulatory networks, winter buds were collected during primary bud necrosis progression for integrated transcriptome and metabolome analysis. The accumulation of reactive oxygen species and subsequent signaling cascades disrupted the regulation systems for cellular protein quality. ROS cascade reactions were related to mitochondrial stress that can lead to mitochondrial dysfunction, lipid peroxidation causing damage to membrane structure, and endoplasmic reticulum stress leading to misfolded protein aggregates. All these factors ultimately resulted in primary bud necrosis. Visible tissue browning was associated with the oxidation and decreased levels of flavonoids during primary bud necrosis, while the products of polyunsaturated fatty acids and stilbenes exhibited an increasing trend, leading to a shift in carbon flow from flavonoids to stilbene. Increased ethylene may be closely related to primary bud necrosis, while auxin accelerated cell growth and alleviated necrosis by co-chaperone VvP23-regulated redistribution of auxin in meristem cells. Altogether, this study provides important clues for further study on primary bud necrosis.

Substrate specificity of polyphenol oxidase and its selectivity towards polyphenols: Unlocking the browning mechanism of fresh lotus root (Nelumbo nucifera Gaertn.)

Polyphenol oxidase (PPO) causes the browning of lotus roots (LR), negatively affecting their nutrition and shelf-life. This study aimed to explore the specific selectivity of PPO toward polyphenol substrates, thus unlocking the browning mechanism of fresh LR. Results showed that two highly homologous PPOs were identified in LR and exhibited the highest catalytic activity at 35 ℃ and pH 6.5. Furthermore, the substrate specificity study revealed (-)-epigallocatechin had the lowest Km among the polyphenols identified in LR, while (+)-catechin showed the highest Vmax. The molecular docking further clarified that (-)-epigallocatechin exhibited lower docking energy and formed more hydrogen bonds and Pi-Alkyl interactions with LR PPO than (+)-catechin, while (+)-catechin entered the active cavity of PPO more quickly due to its smaller structure, both of which enhance their affinity to PPO. Thus, (+)-catechin and (-)-epigallocatechin are the most specific substrates responsible for the browning mechanism of fresh LR.

Comparing the Effect of HPP on the Structure and Stability of Soluble and Membrane-Bound Polyphenol Oxidase from 'Lijiang Snow' Peach: Multispectroscopic and Molecular Dynamics Simulation

Polyphenol oxidase (PPO) easily causes fruits and vegetables to lose their color and nutritional value. As a non-thermal process, high-pressure processing (HPP) showed different inactivation effects on endogenous enzymes. In this work, soluble PPO (sPPO) and membrane-bound PPO (mPPO) from 'Lijiang snow' peaches were purified, and then the effect of high pressure on the conformation of sPPO and mPPO was investigated and compared at the molecular level. The maximum activation of sPPO and mPPO by 11.2% and 4.8% was observed after HPP at 200 MPa, while their activities both gradually decreased at 400 MPa and 600 MPa; in particular, the residual activities of sPPO and mPPO at 600 MPa for 50 min were 41.42% and 72.95%, respectively. The spectroscopic results indicated that the secondary structure of PPOs was little affected by HPP, but HPP led to obvious changes in their tertiary structure. The simulations showed that the decreasing distance between the copper ion and His residue in the copper-binding region of two PPOs at 200 MPa was favorable to catalytic activity, while the increasing distance between copper ions and His residues and the disordered movement of the loop region above 400 MPa were unfavorable. In addition, the structure of sPPO was relatively looser than that of mPPO, and high pressure showed a more significant effect on the conformation of sPPO than that of mPPO. This study clarified the effect of HPP on PPO's structure and the relationship between its structure and activity and provided a basis for the prevention of enzymatic browning.

Purification and comparison of soluble and membrane-bound polyphenol oxidase from potato (Solanum tuberosum) tubers

Enzymatic browning greatly affects the quality of potato products. Polyphenol oxidase (PPO) is the enzyme mainly responsible for potato enzymatic browning. PPO has soluble polyphenol oxidase (sPPO) and membrane-bound polyphenol oxidase (mPPO) forms. In this study, the properties of sPPO and mPPO were investigated in potato tubers. The molecular weight of potato sPPO and mPPO were estimated to be 69 kDa in the form of homodimers in vivo. The mass spectrometry results showed that the purified sPPO and mPPO protein in potato tubers was mainly tr|M1BMR6 (Uniprot). The optimum pH for sPPO and mPPO was 6.5, and the optimum temperatures were 20 and 30 °C, respectively. The Michaelis constant (K_m) and maximum unit enzyme activity (V_max) of sPPO were 6.08 mM and 2161 U/S when catechol was used as the substrate, whereas those of mPPO were 2.95 mM and 2129.53 U/S, respectively. The mPPO had stronger affinity to the substrate catechol than sPPO, whereas pyrogallic acid was stronger affinity for sPPO. Ascorbic acid and sodium sulfite were inhibitors of sPPO and mPPO, respectively. After understanding the different binding states of polyphenol oxidase, different inhibitors and treatment methods can be used to treat the enzyme according to different enzymatic properties, so as to achieve a greater degree of Browning control. These results will provide a theoretical basis for regulating PPO activity to reduce enzymatic browning during potato processing.

Comparison of Inhibitory Effects of Cinnamic Acid, β-Cyclodextrin, L-Cysteine, and Ascorbic Acid on Soluble and Membrane-Bound Polyphenol Oxidase in Peach Fruit

There has been considerable interest in controlling polyphenol oxidase (PPO) activity to prevent enzymatic browning in foods. However, studies on inhibitions of different forms of PPO are very limited. Thus, this study focuses on the effects of cinnamic acid, β-cyclodextrin, L-cysteine, and ascorbic acid on soluble PPO (sPPO) and membrane-bound PPO (mPPO) in peach fruit. The activity of partially purified sPPO was 3.17 times higher than that of mPPO. However, mPPO was shown to be more stable than sPPO in the presence of inhibitors with different concentrations (i.e., 1, 3, 5 mM); activation of mPPO was found by 5 mM L-cysteine. Both sPPO and mPPO inhibitions were PPO substrate-dependent. Ascorbic acid showed the highest inhibitory effect on both sPPO and mPPO with all studied inhibitors and substrates. The inhibition of 1 mM ascorbic acid on sPPO and mPPO reached 95.42 ± 0.07% and 65.60 ± 1.16%, respectively. β-Cyclodextrin had a direct inhibitory effect only on sPPO, while the other three inhibitors had direct effects on both sPPO and mPPO. Cinnamic acid exhibited a non-competitive inhibition on sPPO and mPPO, with L-cysteine showing the same, though on sPPO. The inhibition of studied inhibitors on sPPO and mPPO is highly related to the substrate environment, type, and concentration of inhibitors. This study provides a basis for the further prevention of peach fruit browning from the perspective of different enzyme forms.

Chemical inhibition of polyphenol oxidase and cut surface browning of fresh-cut apples

Fresh-cut apples, which offer consumers health benefits and convenience, have become popular in recent years. One of the main challenges for processing fresh-cut apples is rapid development of cut surface browning, immediately after fruits are cut. Browning, a physiological response that impacts organoleptic properties and deters consumer purchase of fresh-cut fresh produce, is mainly a result of enzymatic reaction of phenolic compounds with oxygen catalyzed by polyphenol oxidase (PPO), a decapper enzyme. Many antibrowning agents have been developed and evaluated to inhibit PPO activities by using reducing agents (antioxidants), chelating agents, acidulants, etc. The present manuscript reviews the diverse characteristics of PPO (such as optimum pH and temperature, and molecular weight) in apples reported in the literature and the enzyme's latency, multiplicity and copper states in the active site. It also summarizes the latest development in the investigation and formulations of antibrowning compounds, and discusses future research needs. This review should stimulate further research to discover more effective, low cost, and natural antibrowning compounds to meet the demand of consumers as well as the food industry for clean label and long shelf-life of fresh-cut apples.

Identification of polyphenol oxidases in potato tuber (Solanum tuberosum) and purification and characterization of the major polyphenol oxidases

Potato is widely consumed across the globe. Understanding and inhibiting the oxidation caused by polyphenol oxidase (PPO) could improve shelf life and increase the nutritional and economic value of potato proteins. This study aimed to identify and quantify all expressed PPOs in potato tuber (Solanum tuberosum) and to purify and characterize the major PPOs responsible for oxidase activity. Four different PPOs were expressed in potato tuber, with 2 PPOs constituting the majority. These 2 PPOs were copurified and characterized. Both potato juice and the purified PPOs had an optimum pH of 5 and were stable over a broad pH range (6-11). The optimum temperature and stability varied, with potato juice having an optimum at 30 °C and showing a gradual decline in oxidase activity with increasing incubation temperature, while the purified PPOs had an optimum temperature and were stable up to 40 °C. Reducing agents effectively inhibited oxidase activity, while chelators did not.

Thermal Inactivation Kinetics of Kudzu (Pueraria lobata) Polyphenol Oxidase and the Influence of Food Constituents

The thermal inactivation kinetics of kudzu (Pueraria lobata) polyphenol oxidase (PPO) were investigated in model and food systems. PPO in kudzu tissue (tPPO) showed a higher thermostability than that of PPO in crude extract (cPPO) and purification fractions (pPPO). The PPO inactivation rate constant (k) increased with an increase in temperature, and tPPO showed the lowest k value, followed by that of cPPO and pPPO at the same temperature, indicating that PPO in the food system was more resistant to thermal treatment. Food constituents (pectin, starch, sucrose, and bovine serum albumin) in the food system decreased the activity of PPO but increased the thermostability of PPO, among which pectin exhibited the strongest protective effect against thermal inactivation, and the influence of sucrose was much slighter than that of other macromolecules. Fluorescence emission spectra indicated that pPPO exhibited stronger interactions with pectin than sucrose, and pPPO with pectin showed a more stable conformation under thermal treatment.

Immobilization of Crude Polyphenol Oxidase Extracts from Apples on Polypyrrole as a Membrane for Phenol Removal

This research aims to make a polypyrrole (PPy) membrane and crude extract of polyphenol oxidase (PPO) as a membrane of mPPy/PPO apple extracts. The membrane of PPy/PPO-apple extract has been synthesized by the electrodeposition method. The electrolyte composition consists of a mixture of 0.10-0.20 M pyrrole (Py) and 50-100% PPO apple extract, which is stable using 50 mM of phosphate buffer solution at pH 6.80-7.00 and room temperature. The electrodeposition process is used 400 mesh steel gauze anode ST-304 and carbon plate cathode. Electrodeposition is carried out at potential = 5.00-6.00 V; current = 0.02-0.25 A; the distance from both electrodes = 1.00-2.00 cm for 300-500 seconds. The results from the deposition of PPy/PPO apple extract of the anode are a membrane of mPPy/PPO-apple extract, with total enzyme activity (U) = (957,1441, 2287 and 1754) using 2.00-5.00 mM phenol as a substrate which is measured based on the UV-visible spectrophotometric method. PPy and mPPy/PPO-apple extracts were characterized by SEM and SEM-EDS. The membrane of mPPy/PPO-apple extract can be used to remove phenol in industrial wastewater samples is 50-65% with a filtration capacity of 500 mL for 2 hours.

Application of three-phase partitioning to the purification and characterization of polyphenol oxidase from antioxidant rosemary (Rosmarinus officinalis L.)

Polyphenol oxidase (PPO) has been purified from the rosemary plant (Rosmarinus officinalis L.) through three-phase partitioning (TPP) and has been biochemically characterized. The optimized TPP consisted of 50% (w/v) ammonium sulfate and equal volumes of crude extract and tert-butanol prepared at pH 6.5 and room temperature. Using this system, PPO was purified 14-fold, with 230% recovery of activity from the middle phase. The partitioned enzyme had a molecular mass of 53 kDa. The highest enzyme activity was detected at 30 °C and pH 7.0 against catechol. In substrate specificity tests, the enzyme displayed activity towards catechol, 4-methylcatechol, caffeic acid, hydroquinone, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), pyrogallol, syringaldezine, and 3,4-dihydroxy-L-phenylalanine but no activity towards L-tyrosine. The enzyme was inhibited by the common PPO inhibitors; salicylhydroxamic acid (SHAM), cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone (PVP), and the organic solvent dimethyl sulfoxide (DMSO). Enzyme activity increased in the presence of the organic solvents acetone, ethanol, and methanol.

Purification, kinetic parameters, and isoforms of polyphenol oxidase from "Xushu 22" sweet potato skin

We purified and compared the polyphenol oxidase (PPO) isoenzymes present in "Xushu 22," a sweet potato. A membrane-bound form (mPPO) and two soluble forms (sPPO1 and sPPO2) were identified and purified using ammonium sulphate precipitation, ion exchange chromatography, gel filtration chromatography, and mass spectrometer. The three PPO isoforms were characterized enzymatically. The specific activity of mPPO was significantly higher than that of the two sPPO isoforms, being 24.55- and 13.89-fold higher than sPPO1 and sPPO2. The preferred substrates for mPPO and the two sPPOs were catechol and chlorogenic acid, respectively. They can be efficiently and safely applied to phenolic wastewater treatment after being immobilized. Both mPPO and the two sPPOs were rapidly inactivated under acid or base conditions and were unstable at 65°C. The most effective inhibitors of mPPO, sPPO1, and sPPO2 were glutathione, ascorbic acid, and L-cysteine, respectively. PRACTICAL APPLICATIONS: According to incomplete statistics, about 5% of sweet potatoes in china are wasted due to enzymatic browning every year. PPO was regarded as a key molecule contributing to enzymatic browning in fruits and vegetables during ripening, processing, and storage and responsible for economic and industrial loss. It's great importance to characterize the PPO from "Xushu 22" sweet potato and provide data on its inactivation. The three PPO isoforms were purified and identified by chromatography and mass spectrometer. This study will provide useful informations to have a better command of PPO from "Xushu 22" sweet potato and give ideals to solve the browning of sweet potato.

Polyphenol oxidase-based electrochemical biosensors: A review

The detection of phenolic compounds is relevant not only for their possible benefits to human health but also for their role as chemical pollutants, including as endocrine disruptors. The required monitoring of such compounds on-site or in field analysis can be performed with electrochemical biosensors made with polyphenol oxidases (PPO). In this review, we describe biosensors containing the oxidases tyrosinase and laccase, in addition to crude extracts and tissues from plants as enzyme sources. From the survey in the literature, we found that significant advances to obtain sensitive, robust biosensors arise from the synergy reached with a diversity of nanomaterials employed in the matrix. These nanomaterials are mostly metallic nanoparticles and carbon nanostructures, which offer a suitable environment to preserve the activity of the enzymes and enhance electron transport. Besides presenting a summary of contributions to electrochemical biosensors containing PPOs in the last five years, we discuss the trends and challenges to take these biosensors to the market, especially for biomedical applications.

Characterization of membrane-bound polyphenol oxidase from Granny Smith apple (Malus × domestica Borkh.)

Membrane-bound polyphenol oxidase (mPPO) from the Granny Smith apple was purified and characterized. The enzyme was purified by a factor of 20.53 with a recovery of 1.8%. The molecular weight of purified mPPO was determined to be 65 kDa by electrophoresis and nano-electrospray ionization mass spectrometry. mPPO exhibited its highest activity at a temperature of 35 °C and a pH of 7.0 and can be regarded as a diphenol oxidase. A low concentration of SDS (≤0.5 mM) enhanced the enzymatic activity, whereas mPPO was activated at high concentration EDTA (≥2 mM). The thermal transition temperature of mPPO was 76.98 °C. The circular dichroism spectrum showed that mPPO contains high α-helix content, the fluorescence spectroscopy indicated that the tryptophan residues of mPPO are partially buried. The particle size of mPPO was 5-10 nm with a complete structure. The structural characterization of mPPO provided better insights into the regions responsible for its activity.

Enzymatic, Phyto-, and Physicochemical Evaluation of Apple Juice under High-Pressure Carbon Dioxide and Thermal Processing

In this study, the changes in enzyme activities, total polyphenols, phenolic profile, and physicochemical properties from thermally (25–75 °C) and high-pressure carbon dioxide (HP-CO₂) (25–65 °C/20 MPa)-treated apple juice were investigated. The HP-CO₂ exhibited complete inactivation of polyphenol oxidase (PPO) at 65 °C, whereas PPO was still active at 75 °C under thermal processing (TP). Similarly, the relative activity of peroxidase (POD) significantly decreased by 71% at 65 °C under HP-CO₂ processing, whereas TP was less effective. HP-CO₂ and TP treatments at 65 °C reduced the browning degree (BD) value to 0.47 and 0.89, respectively. Thus, HP-CO₂ inhibits the browning reactions caused by PPO and POD enzymes at each operating temperature. The concentration of epicatechin and catechin increased significantly with increasing temperature above 45 °C in TP-treated juices. HP-CO₂ treatment increased the same phenolic compounds at 35 °C and 9 MPa, whereas high-temperature and -pressure conditions caused insignificant changes in concentration of epicatechin and catechin. Changes in others phenolic compounds were insignificant under TP and HP-CO₂ treatment. Overall, HP-CO₂ is a promising technology to get high-quality juices with lower enzyme activity.

Antimicrobial mechanism of reaction products of Morus notabilis (mulberry) polyphenol oxidases and chlorogenic acid

Herein, five polyphenol oxidases (PPOs) obtained from Morus notabilis (Mn) were characterized. Chlorogenic acid was the most readily oxidized substrate by these MnPPOs, and the products derived from the oxidation of chlorogenic acid by MnPPOs were tested for antimicrobial activity. The results showed that products of the five MnPPOs exhibited good inhibitory effects against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Sclerotinia sclerotiorum, and Botrytis cinerea. Because the products of MnPPO1 exhibited the strongest antimicrobial activity, the antimicrobial mechanism of these products was explored. The results showed that the products of MnPPO1 increased cell membrane permeability and chitinase and β-1,3-glucanase activities.

Inactivation, Aggregation and Conformational Changes of Polyphenol Oxidase from Quince (Cydonia oblonga Miller) Juice Subjected to Thermal and High-Pressure Carbon Dioxide Treatment

Polyphenol oxidase (PPO) causes the browning reaction in fruits and vegetables and deteriorates the quality. Thermal treatment for enzyme inactivation may result in defects as opposed to high pressure CO₂ (HPCD) processing. In this study, the changes in activity, dissociation, aggregation and conformation of purified PPO from thermal and HPCD treated juice were investigated. HPCD exhibited inactivation of PPO at 55–65 °C whereas thermal processing alone at the same temperature resulted in PPO still showing activity. Under thermal treatment at 25 and 65 °C, the browning degree was higher (0.39 and 0.24) than for HPCD-treated juice (0.23 and 0.12). Fluorescence and circular dichroism spectral results indicated that HPCD induced large decreases in intensities, revealing a rearrangement of the secondary structure and destruction of the native configuration of the PPO molecule. The particle size distribution (PSD) pattern revealed structural modification leading to initial dissociation and subsequent aggregation of PPO after HPCD treatment. Polyacrylamide gel electrophoresis (PAGE) analysis exhibited that molecular size of protein was 40 kDa. In conclusion, the HPCD method was found to be more effective than thermal treatment to inactivate PPO. Structural modifications provided better insights into the phenomena of activation and inactivation of PPO.