Rational Design, Synthesis, and Computational Investigation of Dihydropyridine [2,3-d] Pyrimidines as Polyphenol Oxidase Inhibitors with Improved Potency.

Polyphenol oxidase (PPO) is an industrially important enzyme associated with browning reactions. In the present study, a set of ten new dihydropyridine [2,3-d] pyrimidines (TD-Hid-1-10) were synthesized and was found to be proven characteristically by 1H NMR, 13C NMR, IR, elemental analysis, and assessed as possible PPO inhibitors. PPO was purified from banana using three-phase partitioning, achieving an 18.65-fold purification and 136.47% activity recovery. Enzyme kinetics revealed that the compounds TD-Hid-6 and TD-Hid-7 are to be the most potent inhibitors, exhibiting mixed-type inhibition profile with IC50 values of 1.14 µM, 5.29 µM respectively against purified PPO enzyme. Electronic structure calculations at the B3LYP/PBE0 level of theories using def-2 SVP, def2-TZVP basis sets with various molecular descriptors characterized the electronic behavior of studied derivatives TD-Hid-1-10. Molecular electrostatic potential (MEP) and reduced density gradient analyses of RDG-NCI provided insights into charge distributions and weak intermolecular interactions. Docking study simulations predicted binding poses within crucial amino acid sequence in the 2y9x enzyme's active site, which is typically similar in sequence to the PPO form is not allowed. Ligands were analysed in terms of binding energies, inhibitor concentrations (mM) and various molecular interactions such as H-bonds, H-carbon, π-carbon, π-sigma, π-sigma, π-π T-shaped, π-π stacked, π-alkyl, Van der Waals and Cu interactions. The lowest binding energy (-7.83 kcal/mol) and the highest inhibitory effect (1.83 mM) were shown by the ligand Td-Hid-6, which forms H-bonds with Met280 and Asn260, exhibits π-sigma interactions with His61 and π-alkyl interactions with Val283. Other ligands also showed different interactions with various amino acids; for example, the Td-Hid-1 ligand formed H-bonds with His244 and showed π-sigma interactions with His244 and Val283.

Impressive promiscuous biomimetic models of ascorbate, amine, and catechol oxidases.

Copper metalloenzymes ascorbate oxidase (AOase), amine oxidase (AmOase), and catechol oxidase (COase) possess copper(II) sites of coordination, which are trimeric, homodimeric, and dimeric, respectively. Two newly mononuclear copper(II) complexes, namely, [Cu(L)(bpy)](ClO4) (1) and [Cu(L)(phen)](ClO4) (2) where HL = Schiff base, have been synthesized. UV-visible, EPR and single-crystal X-ray diffraction examinations were used to validate the geometry in solution and solid state. For complex 1, the metal exhibits a coordination sphere between square pyramidal and trigonal bipyramidal geometry (τ, 0.49). A positive CuII/I redox potential indicates a stable switching between CuII and CuI redox states. Despite the monomeric origin, both homogeneous catalysts (1 or 2) in MeOH were found to favor three distinct chemical transformations, namely, ascorbic acid (H2A) to dehydroascorbic acid (DA), benzylamine (Ph-CH2-NH2) to benzaldehyde (Ph-CHO), and 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) [kcat: AOase, 9.6 (1) or 2.0 × 106 h-1(2); AmOase, 13.4 (1) or 9.4 × 106 h-1 (2); COase, 2.0 (1) or 1.9 × 103 h-1 (2)]. They exhibit higher levels of AOase activity as indicated by their kcat values compared to the AOase enzyme. The kcat values for COase activity in buffer solution [5.93 (1) or 2.95 × 105 h-1 (2)] are one order lower than those of the enzymes. This is because of the labile nature of the coordinated donor, the flexibility of the ligand, the simplicity of the catalyst-substrate interaction, and the positive CuII/I redox potential. Interestingly, more efficient catalysis is promoted by 1 and 2 concerning that of other mono- and dicopper(II) complexes.

Modified Metal-Organic Framework (MOF-818) inspired by natural enzymes for intelligent detection of total antioxidants and bisphenol A in infant beverages.

BACKGROUND: Accurate and quick judgement of the food quality can protect the legitimate rights of consumers. Currently, nanozymes are widely employed in the rapid detection of food due to their stability and economy. The contents of bisphenol A and antioxidant can be used to measure the quality of beverages. However, due to the complexity of the actual samples, it is still challenging to achieve the sensitive detection of both at the same time. The development of nanozyme with high enzyme activity is essential for sensitive detection of targets in complex foods. RESULTS: In this work, a novel nanomaterial (ZrTGA) was synthesized based on thioglycolic acid-modified Metal-Organic Framework (MOF-818). The interaction between Cu-S bonds and increase in the proportion of Cu1+ resulted in ZrTGA exhibiting higher peroxidase-like and polyphenol oxidase-like activities. These enzyme activities were 317 % and 200 % of the original values, respectively. With high enzyme activity can sensitively detect two important indicators of bisphenol A and antioxidants in beverages. The increased enzyme activity of ZrTGA enabled the content of both substances to be detected by smartphone extraction of RGB. Finally, through the output of the ''0″ and ''1″ signals of the logic gates, it is possible to quickly determine the level of the two substances and thus directly assess the quality of the beverages. SIGNIFICANCE: The modification of nanozyme enables the detection of substances at low concentrations based on enhancing dual-enzyme activity. The combination of mobile phone photography and logic gate technology enables the continuous detection of two important indicators in beverages, overcoming the limitations of traditional large-scale instruments. It also provides an alternative strategy for food quality detection.

Fluorescence detection of valence speciation of Cr(III) based on the catechol oxidase mimic enzyme activity of CuSeNP nanozymes.

Copper selenide nanoparticles (CuSeNP) were synthesized using histidine, ethylenediamine, and sodium selenate as precursors by one-step microwave digestion methods. The as-prepared CuSeNPs exhibit excellent catechol oxidase mimic enzyme and catalase (CAT)-like activities. Dopamine (DA) can be oxidized to aminochrome with H2O2 by CuSeNPs, and the intermediate product aminochrome can further react with α-naphthol to yield a highly fluorescent derivative. It was confirmed that Cr(III) could adsorb on the surface of CuSeNPs and inhibit the production of semiquinone radicals in the reaction system, and the catalytic activity of CuSeNPs was inhibited. The detection mechanisms, kinetics, and catalytic properties of CuSeNPs were systematically investigated. As a result, a novel fluorescence method for the assay of Cr(III) was established. The feasibility of CuSeNP nanozyme in detecting speciation Cr(III) in food samples was explored with satisfactory results. It showed the obvious potential for developing effective and dependable fluorescent detection method for protecting food safety.

Insight into the mechanism of high hydrostatic pressure effect on inhibitory efficiency of three natural inhibitors on polyphenol oxidase.

The development of natural inhibitors of polyphenol oxidase (PPO) is crucial in the prevention of enzymatic browning in fresh foods. However, few studies have focused on the effect of subsequent sterilization on their inhibition efficiency. This study investigated the influence and mechanism of high hydrostatic pressure (HHP) on the inhibition of PPO by epigallocatechin gallate (EGCG), cyanidin-3-O-glucoside (C3G), and ferulic acid. Results showed that under the conditions of 550 MPa/30 min, the activity of EGCG-PPO decreased to 55.92%, C3G-PPO decreased to 81.80%, whereas the activity of FA-PPO remained stable. Spectroscopic experiments displayed that HHP intensified the secondary structure transformation and fluorescence quenching of PPO. Molecular dynamics simulations revealed that at 550 MPa, the surface interaction between PPO with EGCG or C3G increased, potentially leading to a reduction in their activity. In contrast, FA-PPO demonstrated conformational stability. This study can provide a reference for the future industrial application of natural inhibitors.

Kiwi (Actinidia deliciosa) juice as a natural inhibitor of the enzymatic activity of sugarcane juice, insights from experimental assessment and molecular docking analysis.

The present work evaluated kiwi juice addition alongside pasteurization (at 85 °C for 5 min) or microwave treatment (for 3 min) on the quality improvement of sugarcane juice. The juice was treated in the presence of kiwi juice (0-8%), and its physicochemical properties and microbial load were compared with raw juice. The study also highlighted the key enzymes causing sugarcane juice discoloration, peroxidase (POD) and polyphenol oxidase (PPO), by quantifying kiwi juice constituents using GC-MS and monitoring their effects by molecular docking. Kiwi addition considerably raised (p < 0.05) acidity, ascorbic acid (54.28%), and phenolic compounds (32%), and decreased the POD and PPO activity of raw cane juice. Pasteurization in the presence of kiwi, rather than microwave treatment, has significantly (p < 0.05) increased the phenolic compounds and reduced POD and PPO activities until barley was detected. Molecular docking revealed that heptacosane, oleic acid, and melezitose are the primary kiwi components responsible for enzyme inactivation.

A facile and on-site sensing strategy for phenolic compounds based on a novel nanozyme with high polyphenol oxidase-like activity.

Phenolic compounds (PCs) are diverse in nature and undergo complex migration and transformations in the environment, making it challenging to use techniques such as chromatography and other traditional methods to determine the concentration of PCs by separation, individual monitoring and subsequent addition. To address this issue, a facile and on-site strategy was developed to measure the concentration of PCs using a novel nanozyme with polyphenol oxidase-like activity. First, the nanozyme was designed by coordinating the asymmetric ligand nicotinic acid with copper to mimic the structure of mononuclear and trinuclear copper clusters of natural laccases. Subsequently, by introducing 2-mercaptonicotinic acid to regulate the valence state of copper, the composite nanozyme CuNA10S was obtained with significantly enhanced activity. Interestingly, CuNA10S was shown to have a broad substrate spectrum capable of catalyzing common PCs. Building upon the superior performance of this nanozyme, a method was developed to determine the concentration of PCs. To enable rapid on-site sensing, we designed and prepared CuNA10S-based test strips and developed a tailored smartphone sensing platform. Using paper strip sensors combined with a smartphone sensing platform with RGB streamlined the sensing process, facilitating rapid on-site analysis of PCs within a range of 0-100 µM. Our method offers a solution for the quick screening of phenolic wastewater at contaminated sites, allowing sensitive and quick monitoring of PCs without the need for standard samples. This significantly simplifies the monitoring procedure compared to more cumbersome large-scale instrumental methods.

Inactivation of polyphenol oxidase by low intensity DC field: Experiment and mechanism analysis via molecular dynamics simulation and molecular docking.

In this study, inactivation of mushroom polyphenol oxidase (PPO) by low intensity direct current (DC) electric field and its molecular mechanism were investigated. In the experiments under 3 V/cm, 5 V/cm, 7 V/cm and 9 V/cm electric fields, PPOs were all completely inactivated after different exposure times. Under 1 V/cm, a residual activity of 11.88 % remained. The inactivation kinetics confirms to Weibull model. Under 1-7 V/cm, n value closes to a constant about 1.3. The structural analysis of PPO under 3 V/cm and 5 V/cm by fluorescence emission spectroscopy and molecular dynamics (MD) simulation showed that the tertiary structure was slightly changed with increased radius of gyration, higher potential energy and rate of C-alpha fluctuation. After exposure to the electric field, most of the hydrophobic tryptophan (TRP) residues turned to the hydrophilic surface, resulting the fluorescence red-shifted and quenched. Molecular docking indicated that the receptor binding domain of catechol in PPO was changed. PPO under electric field was MD simulated the first time, revealing the changing mechanism of the electric field itself on PPO, a binuclear copper enzyme, which has a metallic center. All these suggest that the low intensity DC electric field would be a promising option for enzymatic browning inhibition or even enzyme activity inactivation.

Optimizing color enhancement in dried Penaeus vannamei through high-humidity hot air impingement cooking: Enzyme inactivation, reduced drying time, and Maillard reaction inhibition.

This study was aimed to evaluate the potential of high-humidity hot air impingement cooking (HHAIC) on Penaeus vannamei, focusing on its drying characteristics, microstructure, water distribution, enzyme activity, astaxanthin content, antioxidant capacity, color, and Maillard reaction. Results demonstrated that a 3 min HHAIC significantly improved the shrimp's color and optimized astaxanthin content with a notable increase in scavenging capacity based on an in-vitro as antioxidation activity evaluation. Compared to the untreated samples, HHAIC could significantly inactivate polyphenol oxidase by 95.76%. Also, it suppressed the Maillard reaction by decreasing 5-hydroxymethylfurfural content and shortened the drying time by 40%. In addition, the low-field nuclear magnetic resonance and microstructure analysis showed alterations in the shrimp muscle fiber structure and water distribution. This study indicated that HHAIC could elevate quality, enhance appearance, and reduce the processing time of dried shrimp, presenting valuable implications for industry progress.

Microbial Biofilm Inhibition Using Magnetic Cross-Linked Polyphenol Oxidase Aggregates.

Microbial biofilm accumulation poses a serious threat to the environment, presents significant challenges to different industries, and exhibits a large impact on public health. Since there has not been a conclusive answer found despite various efforts, the potential green and economical methods are being focused on, particularly the innovative approaches that employ biochemical agents. In the present study, we propose a bio-nanotechnological method using magnetic cross-linked polyphenol oxidase aggregates (PPO m-CLEA) for inhibition of microbial biofilm including multidrug resistant bacteria. Free PPO solution showed only 55-60% biofilm inhibition, whereas m-CLEA showed 70-75% inhibition, as confirmed through microscopic techniques. The carbohydrate and protein contents in biofilm extracellular polymeric substances (EPSs) were reduced significantly. The m-CLEA demonstrated reusability up to 5 cycles with consistent efficiency in biofilm inhibition. Computational work was also done where molecular docking of PPO with microbial proteins associated with biofilm formation was conducted, resulting in favorable binding scores and inter-residual interactions. Overall, both in vitro and in silico results suggest that PPO interferes with microbial cell attachment and EPS formation, thereby preventing biofilm colonization.

Effect of continuous microwave processing on enzymes and quality attributes of bael beverage.

Bael (Aegle marmelos) beverage was pasteurized using continuous-microwave (MW) and traditional thermal processing and the activity of native enzymes, pulp-hydrolyzing enzymes, bioactive, physicochemical, and sensory properties were analyzed. First-order and linear biphasic models fitted well (R2 ≥ 0.90) for enzyme inactivation and bioactive alteration kinetics, respectively. For the most resistant enzyme, polyphenoloxidase (PPO), the inactivation target of ≥ 90 % was achieved at 90 °C TMW (final temperature under MW) and 95 °C for 5 min (conventional thermal). MW treatment displayed faster enzyme inactivation and better retention of TPC and AOC. MW treatment at 90 °C TMW showed 5.3 min D-value, 90% total carotenoid content, 3.42 crisp sensory score (out of 5), and no or minor change in physicochemical attributes. Thermal and MW treatment caused the loss of 14 and 10 bioactive compounds, respectively. The secondary and tertiary structural modifications of PPO enzyme-protein revealed MW's lethality primarily due to its thermal effects.

Construct Phenylethanoid Glycosides Harnessing Biosynthetic Networks, Protein Engineering and One-Pot Multienzyme Cascades.

Phenylethanoid glycosides (PhGs) exhibit a multitude of structural variations linked to diverse pharmacological activities. Assembling various PhGs via multienzyme cascades represents a concise strategy over traditional synthetic methods. However, the challenge lies in identifying a comprehensive set of catalytic enzymes. This study explores biosynthetic PhG reconstruction from natural precursors, aiming to replicate and amplify their structural diversity. We discovered 12 catalytic enzymes, including four novel 6'-OH glycosyltransferases and three new polyphenol oxidases, revealing the intricate network in PhG biosynthesis. Subsequently, the crystal structure of CmGT3 (2.62 Å) was obtained, guiding the identification of conserved residue 144# as a critical determinant for sugar donor specificity. Engineering this residue in PhG glycosyltransferases (FsGT61, CmGT3, and FsGT6) altered their sugar donor recognition. Finally, a one-pot multienzyme cascade was established, where the combined action of glycosyltransferases and acyltransferases boosted conversion rates by up to 12.6-fold. This cascade facilitated the reconstruction of 26 PhGs with conversion rates ranging from 5-100 %, and 20 additional PhGs detectable by mass spectrometry. PhGs with extra glycosyl and hydroxyl modules demonstrated notable liver cell protection. This work not only provides catalytic tools for PhG biosynthesis, but also serves as a proof-of-concept for cell-free enzymatic construction of diverse natural products.

Chemical kinetics and thermodynamics of PPO activity, colour changes and microbial degradation during blanching of the sugarcane billets.

BACKGROUND: Sugarcane juice, which has a short shelf life, is a popular thirst-quenching and rejuvenating beverage worldwide. The limited shelf life is a result of changes in polyphenol oxidase (PPO) activity, total plate count (TPC) and color attributes (L*, a* and b*-values). We hypothesized that chemical kinetics and thermodynamics of blanched sugarcane cane juice causing alterations in PPO, TPC, and L, a* and b*-values will address the challenges of sugarcane juice preservation. RESULTS: Sugarcane billets were blanched at variable time-temperature combinations in the range 0-20 min and 70-90 °C. Reaction rates increased with increasing temperature; PPO activity, TPC and colour followed first-order kinetics. PPO activity had an activation energy (Ea) of 81 kJ mol-1. The half life (t½) dropped from 16.5 to 3.47 min and decimal reduction time (D-values) dropped from 54.83 to 11.52 min. Thus reactions were temperature-sensitive. Thermodynamic studies indicated an endothermic (positive enthalpy values, ΔH > 0; 78.10 kJ mol-1) and reversible process (negative entropy values ΔS < 0; -0.044 kJmol-1 K-1). Michaeli-Menten constant (Km) and maximum velocity (Vmax) of PPO activity were determined by adding variable lemon juice concentrations in sugarcane juice. As the Km values increased (from 5.53 to 15.81 mm) and Vmax values decreased (from 666.67 to 384.61 UmL-1), a Lineweaver-Burk plot suggested decreased PPO affinity of sugarcane juice. CONCLUSION: The results of the present study indicate that studies on chemical kinetics and thermodynamics (PPO, TPC and L, a* and b*-values) of blanched sugarcane cane juice shall mitigate challenges of sugarcane juice preservation. © 2024 Society of Chemical Industry.

Rapid and Green Fabrication of Nanozyme with Geminal CuN3O Configuration for Efficient Catecholase-Mimicking.

Fabrication of nanozyme with catecholase-like catalytic activity faces the great challenge of merging outstanding activity with low cost as well as simple, rapid, and low-energy-consumed production, restricting its industrial applications. Herein, an inexpensive yet robust nanozyme (i.e., DT-Cu) via simple one-step coordination between diaminotriazole (DT) and CuSO4 within 1 h in water at room temperature is constructed. The asymmetric dicopper site with CuN3O configuration for each copper as well as Cu─O bond length of ≈1.83 Å and Cu···Cu distance of ≈3.5 Å in DT-Cu resemble those in catechol oxidase (CO), which ensure its prominent intrinsic activity, outperforming most CO-mimicking nanozymes and artificial homogeneous catalysts. The use of inexpensive DT/CuSO4 in this one-pot strategy endows DT-Cu with only ≈20% cost of natural CO per activity unit. During catalysis, O2 experienced a 4e-dominated reduction process accompanied by the formation of 1O2 and H2O2 intermediates and the product of H2O. Benefiting from the low cost as well as the distinctive structure and superior intrinsic activity, DT-Cu presents potential applications ranging from biocatalysis to analytical detection of biomolecules such as epinephrine and beyond.

Research progress on the functions and biosynthesis of theaflavins.

Theaflavins are beneficial to human health due to various bioactivities. Biosynthesis of theaflavins using polyphenol oxidase (PPO) is advantageous due to cost effectiveness and environmental friendliness. In this review, studies on the mechanism of theaflavins formation, the procedures to screen and prepare PPOs, optimization of reaction systems and immobilization of PPOs were described. The challenges associated with the mass biosynthesis of theaflavins, such as poor enzyme activity, undesirable subproducts and inclusion bodies of recombinant PPOs were presented. Further strategies to solve these challenges and improve theaflavins production, including enzyme engineering, immobilization enzyme technology, water-immiscible solvent-water biphasic systems and recombinant enzyme technology, were proposed.

Polyphenol oxidase mediates (-)-epigallocatechin gallate to inhibit endogenous cathepsin activity in Apostichopus japonicus.

Apostichopus japonicus (A. japonicus) has rich nutritional value and is an important economic crop. Due to its rich endogenous enzyme system, fresh A. japonicus is prone to autolysis during market circulation and storage, resulting in economic losses. In order to alleviate this phenomenon, we investigated the effect of polyphenol oxidase (PPO) mediated (-)-epigallocatechin gallate (EGCG) on the activity and structure of endogenous cathepsin series protein (CEP) from A. japonicus. Research on cathepsin activity showed that PPO mediated EGCG could significantly reduce enzyme activity, resulting in a decrease in enzymatic reaction rate. SDS-PAGE and scanning electron microscopy results showed that PPO mediates EGCG could induce CEP aggregation to form protein aggregates. Various spectral results indicated that EGCG caused changes in the structure of CEP. Meanwhile, the conjugates formed by PPO mediated EGCG had lower thermal stability. In conclusion, PPO mediated EGCG was an effective method to inhibit the endogenous enzyme activity.

Affinity gel synthesis from the p-aminobenzoic acid derivative 4-amino-2-methylbenzoic acid and purification of polyphenol oxidase from various plant sources.

The polyphenol oxidase (PPO) enzyme, which causes enzymatic browning, has been repeatedly purified from fruit and vegetables by affinity chromatography. In the present research, Sepharose 4B-l-tyrosine-4-amino-2-methylbenzoic acid, a novel affinity gel for the purification of the PPO enzyme with high efficiency, was synthesized. Additionally, Sepharose 4B-l-tyrosine-p-aminobenzoic acid affinity gel, known in the literature, was also synthesized, and 9.02, 16.57, and 28.13 purification folds were obtained for the PPO enzymes of potato, mushroom, and eggplant by the reference gel. The PPO enzymes of potato, mushroom, and eggplant were purified 41.17, 64.47, and 56.78-fold from the new 4-amino-2-methylbenzoic acid gel. Following their isolation from the new affinity column, the assessment of PPO enzyme purity involved the utilization of SDS-PAGE. According to the results from SDS-PAGE and native PAGE, the molecular weight of each enzyme was 50 kDa. Then, the inhibition effects of naringin, morin hydrate, esculin hydrate, homovanillic acid, vanillic acid, phloridzin dihydrate, and p-coumaric acid phenolic compounds on purified potato, mushroom, and eggplant PPO enzyme were investigated. Among the tested phenolic compounds, morin hydrate was determined to be the most potent inhibitor on the potato (Ki: 0.07 ± 0.03 µM), mushroom (Ki: 0.7 ± 0.3 µM), and eggplant (Ki: 4.8 ± 1.2 µM) PPO enzymes. The studies found that the weakest inhibitor was homovanillic acid for the potato (Ki: 1112 ± 324 µM), mushroom (Ki: 567 ± 81 µM), and eggplant (Ki: 2016.7 ± 805.6 µM) PPO enzymes. Kinetic assays indicated that morin hydrate was a remarkable inhibitor on PPO.

A nanozyme with switchable enzyme-like activity for the logic gates detection of thymol and hydrogen peroxide in honey.

A new nanozyme (CuGaa) with switchable enzyme-like activity of peroxidase and polyphenol oxidase was successfully prepared based on guanidinoacetic acid and copper. The two enzyme-like activities can be easily switched by changing temperature or adding MnCl2. At 4 °C, polyphenol oxidase-like activity decreased to nearly 1%, and the material is mainly characterized by peroxidase-like activity at this point. However, at 60 °C in the presence of 20 mM MnCl2, the peroxidase-like activity decreased to nearly 10%, and the polyphenol oxidase-like activity of the materials increased to 140%. Based on the switchable enzyme-like activity of CuGaa, detection methods for thymol and hydrogen peroxide were developed. In addition, a rapid combination strategy was further established combined with logic gate technology for the facile identification of complex contamination in honey, which provided new ideas for low-cost and rapid honey identification.

Purification and Biochemical Characterization of Polyphenol Oxidase Extracted from Wheat Bran (Wan grano).

Currently, little is known about the characteristics of polyphenol oxidase from wheat bran, which is closely linked to the browning of wheat product. The wheat PPO was purified by ammonium sulfate precipitation, DEAE-Sepharose ion-exchange column, and Superdex G-75 chromatography column. Purified wheat PPO activity was 11.05-fold higher, its specific activity was 1365.12 U/mg, and its yield was 8.46%. SDS-PAGE showed that the molecular weight of wheat PPO was approximately 21 kDa. Its optimal pH and temperature were 6.5 and 35 °C for catechol as substrate, respectively. Twelve phenolic substrates from wheat and green tea were used for analyzing the substrate specificity. Wheat PPO showed the highest affinity to catechol due to its maximum Vmax (517.55 U·mL-1·min-1) and low Km (6.36 mM) values. Docking analysis revealed strong affinities between catechol, gallic acid, EGCG, and EC with binding energies of -5.28 kcal/mol, -4.65 kcal/mol, -4.21 kcal/mol, and -5.62 kcal/mol, respectively, for PPO. Sodium sulfite, ascorbic acid, and sodium bisulfite dramatically inhibited wheat PPO activity. Cu2+ and Ca2+ at 10 mM were considered potent activators and inhibitors for wheat PPO, respectively. This report provides a theoretical basis for controlling the enzymatic browning of wheat products fortified with green tea.

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.