A novel hybrid sensor array based on the polyphenol oxidase and its nanozymes combined with the machine learning based dual output model to identify tea polyphenols and Chinese teas

A novel sensor array was developed based on the enzyme/nanozyme hybridization for the identification of tea polyphenols (TPs) and Chinese teas. The enzyme/nanozyme with polyphenol oxidase activity can catalyze the reaction between TPs and 4-aminoantipyrine (4-AAP) to produce differences in color, and the sensor array was thus constructed to accurately identify TPs mixed in different species, concentrations, or ratios. In addition, a machine learning based dual output model was further used to effectively predict the classes and concentrations of unknown samples. Therefore, the qualitative and quantitative detection of TPs can be realized continuously and quickly. Furthermore, the sensor array combining the machine learning based dual output model was also utilized for the identification of Chinese teas. The method can distinguish the six teas series in China, and then precisely differentiate the more specific tea varieties. This study provides an efficient and facile strategy for the identification of teas and tea products.

Enzymatic synthesis of Vaccinium blue using vaccinoside as a bifunctional precursor

Since Tang dynasty in China, the fresh leaves of Vaccinium bracteatum (VBL) have been applied as natural pigment to produce black rice. However, detailed information on its biosynthetic mechanism still remained unclear. Following rice dyeing capacity assay, vaccinoside, one of iridoid glycosides, was identified as the key active compound. Increased methodical research demonstrated vaccinoside as a distinct bifunctional precursor, which could be catalyzed by polyphenol oxidase or β-glucosidase independently, followed by reaction with 15 amino acids to give blue pigments (VBPs; λmax 581-590 nm) of different hues. Two synthetic pathways of VBPs were proposed, using multiple techniques such as HPLC, HPSEC, UV-Vis spectrum and colorimeter as analysis tools. Black rice was interpreted to be prepared by cooking, using vaccinoside, intrinsic enzymes from fresh VBL and rice protein in combination. These findings promote the understanding of VBP formation mechanisms and provide an efficient method of producing novel Vaccinium blue pigments.

A sensor array based on a nanozyme with polyphenol oxidase activity for the identification of tea polyphenols and Chinese green tea

Green tea is popular among consumers because of its high nutritional value and unique flavor. There is often a strong correlation among the type of tea, its quality level and the price. Therefore, the rapid identification of tea types and the judgment of tea quality grades are particularly important. In this work, a novel sensor array based on nanozyme with polyphenol oxidase (PPO) activity is proposed for the identification of tea polyphenols (TPs) and Chinese green tea. The absorption spectra changes of the nanozyme and its substrate in the presence of different TPs were first investigated. The feature spectra were scientifically selected using genetic algorithm (GA), and then a sensor array with 15 sensing units (5 wavelengths × 3 time) was constructed. Combined with the support vector machine (SVM) discriminative model, the discriminative rate of this sensor array was 100% for different concentrations of typical TPs in Chinese green tea with a detection limit of 5 μM. In addition, the identification of different concentrations of the same tea polyphenols and mixed tea polyphenols have also been achieved. Based on the above study, we further developed a facile and efficient new method for the category differentiation and adulteration identification of green tea, and the accuracy of this array was 96.88% and 100% for eight types of green teas and different adulteration ratios of Biluochun, respectively. This work has significance for the rapid discrimination of green tea brands and adulteration.

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.

The biotic effects of lignite on humic acid components conversion during chicken manure composting

Targeted regulation of composting to convert organic matter into humic acid (HA) holds significant importance in compost quality. Owing to its low carbon content, chicken manure compost often requires carbon supplements to promote the humification progress. The addition of lignite can increase HA content through biotic pathways, however, its structure was not explored. The Parallel factor analysis revealed that lignite can significantly increase the complexity of highly humified components. The lignite addition improved phenol oxidase activity, particularly laccase, during the thermophilic and cooling phases. The abundance and transformation functions of core bacteria also indicated that lignite addition can influence the activity of microbial transformation of HA components. The structural equation model further confirmed that lignite addition had a direct and indirect impact on enhancing the complexity of HA components through core bacteria and phenol oxidase. Therefore, lignite addition can improve HA structure complexity during composting through biotic pathways.

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.

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.

Inhibition of cinnamic acid and its derivatives on polyphenol oxidase: Effect of inhibitor carboxyl group and system pH

Phenolic acids are promising inhibitors of polyphenol oxidase (PPO), but the effects of carboxyl group and pH on their inhibition effects are still unclear. In this study, methyl cinnamate, cinnamic acid and 4-carboxycinnamic acid were investigated by their inhibitory effects with pH varied from 6.8 to 5.0. Results showed that 4-carboxycinnamic acid had the strongest inhibitory effect on PPO, followed by cinnamic acid and methyl cinnamate. Acidic pH enhanced the inhibitory effects of cinnamic acid and its derivatives on PPO, and the enhancement degree, IC50 and Ki declining degree were followed as 4-carboxycinnamic acid > cinnamic acid > methyl cinnamate. Methyl cinnamate exhibited competitive inhibition on PPO, while cinnamic acid and 4-carboxycinnamic acid exhibited mixed-type inhibition. Inhibitors induced slight changes in the secondary and tertiary structures of PPO, which were enhanced by acidic pH. Molecular docking results showed that 4-carboxycinnamic acid exhibited the strongest binding ability, and the main interaction forces were around carboxyl groups, and acidic pH enhanced the binding effect through more interactions and lower binding energy. This study could provide new insights into industrial application of cinnamic acid and its derivatives for the control of enzymatic browning of fruits and vegetables.

Expression of polyphenol oxidase of Litopenaeus vannamei and its characterization

Polyphenol oxidase (PPO) plays a critical role in decrement of shrimp quality. To obtain active PPO and elucidate its enzymatic properties, PPO from Litopenaeus vannamei (Lv-PPO) was cloned, expressed in E. coli and purified by affinity column chromatography. The Lv-PPO gene was 2076 bp in length encoding 691 amino acids. The recombinant Lv-PPO (rLv-PPO) with a molecular mass of ∼85.0 kDa was successfully expressed and its sequence was verified by LC-MS/MS. rLv-PPO was biologically active with an optimal temperature of 40℃ and an optimal pH of 6.0. Metal ions Cu2+ and Zn2+ altered the activity of rLv-PPO by influencing its secondary and tertiary structures. rLv-PPO showed catalytic activity towards l-Dopa and catechol. A specific polyclonal antibody against rLv-PPO was prepared. Western blot analysis revealed that PPO levels were highest in hemolymph, followed by telson, carapace, and eyestalk. Expression of rLv-PPO will assist future studies on the mechanism in shrimp melanosis.

Identification and stability evaluation of polyphenol oxidase substrates of pineapple fruit

Pineapple as an important tropical fruit in the world is prone to internal browning (IB) caused by the oxidation of phenolic substances. To address the occurrence of IB, endogenous polyphenol oxidase (PPO) substrates were extracted, separated, and purified from pineapple fruit, and then four compounds were obtained and identified as catechin, epicatechin, chlorogenic acid and pyrocatechol. The contents of these substrates increased, reached the maximum value in the middle storage period, decreased gradually, and then maintained a relatively stable level by the end of storage. Meanwhile, pineapple PPO substrates were unstable in structure and susceptible to be degraded under the condition of light, high temperature (>40 °C), alkalinity (pH > 9) or metal ion (Ca2+, Cu2+, Fe2+, Pb2+ and Zn2+). Additionally, the presences of O2 and H2O2 increased the enzymatic oxidation of the pineapple PPO substrates, whereas CO2, N2, Vc (Vitamin C), l-cysteine, Na2SO3 and Na2S2O5 inhibited this oxidation.

Humidity-controlled heat treatment of fresh spinach noodles for color preservation and storage quality improvement

The high sensitivity to color browning during room-temperature storage was a significant factor in limiting the development of fresh spinach noodles (FSN). The practice of humidity-controlled heat treatment (HCHT) at varying temperatures, relative humidity, and time was carried out to limit enzyme activity and improve the quality of FSN. Results showed that HCHT could maximize the color preservation of fresh spinach noodle quality while effectively inactivating polyphenol oxidase and the yeasts, and mold count in FSN during storage was almost undetectable after mild conditions (80 °C). The hardness and chewiness of HCHT noodles were significantly increased, but the free sulfhydryl content was reduced. At 80 °C, 90 %, 5 min, protein structural aggregation was found in the microstructure of HCHT fresh spinach noodles. HCHT also caused partial gelatinization, as evidenced by the decrease in starch gelatinization enthalpy from 5.49 to 4.77 J/g, although the gelatinization degree of FSN was comparatively low.

Enhancing defense against rice blast disease: Unveiling the role of leaf endophytic firmicutes in antifungal antibiosis and induced systemic resistance

Rice remains the primary staple for more than half of the world's population, yet its cultivation faces numerous challenges, including both biotic and abiotic stresses. One significant obstacle is the prevalence of rice blast disease, which substantially diminishes productivity and increases cultivation costs due to frequent fungicide applications. Consequently, the presence of fungicide residues in rice raises concerns about compliance with international maximum residue limits (MRLs). While host resistance has proven effective, it often remains vulnerable to new variants of the Magnaporthe oryzae pathogen. Therefore, there is a critical need to explore innovative management strategies that can complement or enhance existing methods. An unexplored avenue involves harnessing endophytic bacterial communities. To this end, the present study investigates the potential of eleven endophytic Bacillus spp. in suppressing Pyricularia oryzae, promoting plant growth, and eliciting a defense response through phyllobacterization. The results indicate that the secreted metabolome and volatilome of seven tested isolates demonstrate inhibitory effects against P.oryzae, ranging from a minimum of 40% to a maximum of 70%. Bacillus siamensis L34, B. amyloliquefaciens RA37, B. velezensis L12, and B. subtilis B18 produce antifungal antibiotics targeting P.oryzae. Additionally, B. subtilis S4 and B. subtilis S6 emerge as excellent inducers of systemic resistance against blast disease, as evidenced by elevated activity of biochemical defense enzymes such as peroxidase, polyphenol oxidase, and total phenol content. However, a balance between primary metabolic activity (e.g., chlorophyll content, chlorophyll fluorescence, and photosynthetic rate) and defense activity is observed. Furthermore, specific endophytic Bacillus spp. significantly stimulates defense-related genes, including OsPAD4, OsFMO1, and OsEDS1. These findings underscore the multifaceted potential of endophytic Bacillus in managing blast disease through antibiosis and induced systemic resistance. In conclusion, this study highlights the promising role of endophytic Bacillus spp. as a viable option for blast disease management. Their ability to inhibit the pathogen and induce systemic resistance makes them a valuable addition to the existing strategies. However, it is crucial to consider the trade-off between primary metabolic activity and defense response when implementing these bacteria-based approaches.

Helicoverpa zea-Associated Gut Bacteria as Drivers in Shaping Plant Anti-herbivore Defense in Tomato

Insect-associated bacteria can mediate the intersection of insect and plant immunity. In this study, we aimed to evaluate the effects of single isolates or communities of gut-associated bacteria of Helicoverpa zea larvae on herbivore-induced defenses in tomato. We first identified bacterial isolates from the regurgitant of field-collected H. zea larvae by using a culture-dependent method and 16S rRNA gene sequencing. We identified 11 isolates belonging to the families Enterobacteriaceae, Streptococcaceae, Yersiniaceae, Erwiniaceae, and unclassified Enterobacterales. Seven different bacterial isolates, namely Enterobacteriaceae-1, Lactococcus sp., Klebsiella sp. 1, Klebsiella sp. 3, Enterobacterales, Enterobacteriaceae-2, and Pantoea sp., were selected based on their phylogenetic relationships to test their impacts on insect-induced plant defenses. We found that the laboratory population of H. zea larvae inoculated with individual isolates did not induce plant anti-herbivore defenses, whereas larvae inoculated with a bacterial community (combination of the 7 bacterial isolates) triggered increased polyphenol oxidase (PPO) activity in tomato, leading to retarded larval development. Additionally, field-collected H. zea larvae with an unaltered bacterial community in their gut stimulated higher plant defenses than the larvae with a reduced gut microbial community. In summary, our findings highlight the importance of the gut microbial community in mediating interactions between herbivores and their host plants.

Inhibitory mechanism of sodium hexametaphosphate on enzymatic browning in yellow alkaline noodles

The effect and mechanism of sodium hexametaphosphate (SHMP) on polyphenol oxidase (PPO) enzymatic browning in yellow alkaline noodles (YAN) were investigated. The browning degree and PPO activity in YAN or PPO solutions decreased with the SHMP concentrations increased. Variations in pH values (pH 7-8.5) adjusted by HCl or acetic acid slightly affected the PPO activity, but SHMP inhibited PPO activity more pronounced. The inhibition of SHMP on PPO activity was irreversible. SHMP formed coordinate covalent bonds with Cu²⁺ to make PPO inactive. HPLC analysis revealed that SHMP reduced the browning products and led to the color of PPO-catechol systems being lightened. Furthermore, SHMP inhibited browning by hampering the auto-oxidization of intermediate products due to the change in pH value. Besides, the HPLC chromatogram, UV-vis spectrum, and mass spectrometry revealed that SHMP could convert melanin (m/z 248.97, 723.5, and 836.58) to light-colored substances (m/z 137.11).

Effects of high pressure synergistic enzymatic physical state and concentration on the denaturation of polyphenol oxidase

The synergistic effect of the initial state of the enzyme and pressure level on the denaturation of PPO has not been clear yet, but it significantly affects the application of high hydrostatic pressure (HHP) in the enzyme-containing food processing. Solid (S-) and low/high concentration liquid (LL-/HL-) polyphenol oxidase (PPO) was used as the study object, and the microscopic conformation, molecular morphology and macroscopic activity of PPO under HHP treatments (100-400 MPa, 25 °C/30 min) were investigated by spectroscopic techniques. The results show that the initial state has a significant effect on the activity, structure, active force and substrate channel of PPO under pressure. The effec can be ranked as follows: physical state > concentration > pressure, S-PPO > LL-PPO > HL-PPO. High concentration has a weakening effect on the pressure denaturation of the PPO solution. Under high pressure, the α-helix and concentration factors play a crucial role in stabilizing the structure.

Biochemical properties of purified polyphenol oxidase from bitter leaf (Vernoniaamygdalina)

Polyphenol oxidase which is responsible for oxidative conversion of phenolic compounds to polymers, has continued to attract the attention of scientists. Here, we report the extraction, purification and biochemical properties of polyphenol oxidase (PPO) from bitter leaf (Vernonia amygdalina). The enzyme was purified and concentrated using a non-conventional approach, aqueous two-phase partitioning (ATPS) and the biochemical properties of the purified enzyme were investigated. Substrate specificity studies revealed that the enzyme predominantly exhibits diphenolase activity. The order of substrate preference was catechol > L-DOPA > caffeic acid > L-tyrosine > resorcinol>2-naphthol > phenol. The optimum pH and temperature obtained for the enzyme using catechol as substrate were 5.5 and 50 °C respectively. The estimated Michaelis constant (K_m) and maximum velocity (V_max) for the purified vaPPO using catechol as substrate were 183 ± 5.0 mM and 2000 ± 15 units/mg protein respectively. The catalytic efficiency (V_max/K_m) of the purified vaPPO was 10.9 ± 0.03 min/mg. Na⁺, K⁺ and Ba²⁺ remarkably activated the enzyme and the level of activation was proportional to the concentration. The vaPPO presented stability in the presence of up to 50 mM of the different metal ions tested. In contrast, Cu²⁺ and NH₄⁺ inhibited the enzyme even 10 mM concentrations. The enzyme was stable in chloroform retaining up to 60% relative activity at 50% (v/v) concentration. There was an increase in the activity (143%) of the enzyme at 30% (v/v) chloroform., revealing that vaPPO could catalyze the substrate more efficiently in 30% (v/v) chloroform. Total loss of enzyme activity was observed at 20% (v/v) concentrations of acetone, ethanol and methanol. In conclusion, the properties of the vaPPO such as its catalysis in the presence of organic solvents, metals and high temperature would be of interest in many biotechnological applications.

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.

Thin film preparation of polyphenol oxidase enzyme (PPO) and investigation of its organic vapor interaction mechanism

This study investigated spin coated thin films of polyphenol oxidase enzyme (PPO) as vapor sensor to detect chloroform, acetone, ethyl acetate, isopropyl alcohol and toluene. Thin film of enzyme was produced onto a bio-composite (gelatine chitosan) first layer via 5000 rpm spin speed. UV-visible spectroscopy and Quartz Crystal Microbalance (QCM) measurements were carried out to analyze the reproducibility of PPO spun film. It was found that the PPO enzyme can be transferred onto a solid substrate as a solid state thin film form. 
The sensor films of PPO enzyme were exposed to various VOCs (chloroform, acetone, ethyl acetate, isopropyl alcohol and toluene) with different fixed concentrations. The sensing responses of PPO thin films versus five vapors were investigated using QCM as the time dependence frequency recording method. The PPO sensor films exhibited high sensitivity and fast responses against all VOCs. But the response rate and magnitude were changed depending on the chemical structure and the molecular size of the analyte vapor. Recorded frequency changes as monitored by QCM technique have been integrated with the Fick's second law of diffusion to determine the diffusion coefficients of analyte vapors. 
The results showed that the interaction characteristics between PPO and the analytes can be considered in terms of two main processes which are surface interaction and diffusion. And it was concluded that the formation of these two processes during the interaction depend on the molecular size and functional group of the analytes. These results showed that enzymes can be integrated into vapor sensor system as active layer and are promising for further sensor studies. &#xD.

Polyphenol oxidases regulate pollen development through modulating flavonoids homeostasis in tobacco

Pollen development is critical in plant reproduction. Polyphenol oxidases (PPOs) genes encode defense-related enzymes, but the role of PPOs in pollen development remains largely unexplored. Here, we characterized NtPPO genes, and then investigated their function in pollen via creating NtPPO9/10 double knockout mutant (cas-1), overexpression 35S::NtPPO10 (cosp) line and RNAi lines against all NtPPOs in Nicotiana tabacum. NtPPOs were abundantly expressed in the anther and pollen (especially NtPPO9/10). The pollen germination, polarity ratio and fruit weights were significantly reduced in the NtPPO-RNAi and cosp lines, while they were normal in cas-1 likely due to compensation by other NtPPO isoforms. Comparisons of metabolites and transcripts between the pollen of WT and NtPPO-RNAi, or cosp showed that decreased enzymatic activity of NtPPOs led to hyper-accumulation of flavonoids. This accumulation might reduce the content of ROS. Ca²⁺ and actin levels also decreased in pollen of the transgenic lines.Thus, the NtPPOs regulate pollen germination through the flavonoid homeostasis and ROS signal pathway. This finding provides novel insights into the native physiological functions of PPOs in pollen during reproduction.

Applications of ultrasonication on food enzyme inactivation- recent review report (2017-2022)

Ultrasound processing has been widely applied in food sector for various applications such as decontamination and structural and functional components modifications in food. Enzymes are proteinaceous in nature and are widely used due to its catalytic activity. To mitigate the undesirable effects caused by the enzymes various technologies have been utilized to inactive the enzymes and improve the enzyme efficiency. Ultrasound is an emerging technology that produces acoustic waves which causes rapid formation and collapse of bubbles. It has the capacity to break the hydrogen bonds and interact with the polypeptide chains due to Vander Waals forces leading to the alteration of the secondary and tertiary structure of the enzymes thereby leading to loss in their biological activity. US effectively inactivates various dairy-related enzymes, including alkaline phosphatase (ALP), lactoperoxidase (LPO), and γ-glutamyl transpeptidase (GGTP) with increased US intensity and time without affecting the natural dairy flavors. The review also demonstrates that inactivation of enzymes presents in fruit and vegetables such as polyphenol oxidase (PPO), polygalacturonase (PG), Pectin methyl esterase (PME), and peroxidase. The presence of the enzymes causes detrimental effects causes off-flavors, off-colors, cloudiness, reduction in viscosity of juices, therefore the formation of high-energy free molecules during sonication affects the catalytic function of enzymes and thereby causing inactivation. Therefore this manuscript elucidates the recent advances made in the inactivation of common, enzymes infruits, vegetables and dairy products by the application of ultrasound and also explains the enzyme inactivation kinetics associated. Further this manuscript also discusses the ultrasound with other combined technologies, mechanisms, and its effects on the enzyme inactivation.

Genes cloning, sequencing and function identification of recombinant polyphenol oxidase isozymes for production of monomeric theaflavins from Camellia sinensis

Theaflavins (TFs) are important quality compounds in black tea with a variety of biological activities. However, direct extraction of TFs from black tea is inefficient and costly. Therefore, we cloned two PPO isozymes from Huangjinya tea, termed HjyPPO1 and HjyPPO3. Both isozymes oxidized corresponding catechin substrates for the formation of four TFs (TF1, TF2A, TF2B, TF3), and the optimal catechol-type catechin to pyrogallol-type catechin oxidation rate of both isozymes was 1:2. In particular, the oxidation efficiency of HjyPPO3 was higher than that of HjyPPO1. The optimum pH and temperature of HjyPPO1 were 6.0 and 35 °C, respectively, while those of HjyPPO3 were 5.5 and 30 °C, respectively. Molecular docking simulation indicated that the unique residue of HjyPPO3 at Phe260 was more positive and formed a π-π stacked structure with His108 to stabilize the active region. In addition, the active catalytic cavity of HjyPPO3 was more conducive for substrate binding by extensive hydrogen bonding.

Trichomes mediate plant-herbivore interactions in two Cucurbitaceae species through pre- and post-ingestive ways

Plant structural defenses such as trichomes exert a significant selection pressure on insect herbivores. However, whether variation in structural defense traits affects common herbivores in related plant species is less understood. Here, we examined the role of trichomes in plant-herbivore interactions in two commonly cultivated members in Cucurbitaceae: bottle gourd (Lagenaria siceraria) and cucumber (Cucumis sativa). In common garden experiments when the two species were grown together, we observed that they differed in their attractiveness to four major herbivore species (Trichoplusia ni, Acalymma vittatum, Diaphania indica, and Anasa tristis) and, consequently, their feeding behavior. We found that L. siceraria consistently harbored less herbivores, and the two lepidopteran herbivores (T. ni and D. indica) were found to take significantly longer time to commence feeding on them, a primary mode of pre-ingestive defense function of trichomes. To tease apart structural and chemical modes of defenses, we first used scanning electron microscopy to identify, quantify, and measure trichome traits including their morphology and density. We found that C. sativa has significantly lower number of trichomes compared to L. siceraria, regardless of trichome type and leaf surface. We then used artificial diet enriched with trichomes as caterpillar food and found that trichomes from these two species differentially affected growth and development of T. ni showing cascading effects of trichomes. Taken together, we show that trichomes, independent of chemical defenses, are an effective pre- and post-ingestive defense strategy against herbivores with negative consequences for their feeding, growth, and development.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10340-023-01611-x.

Purification, characterization and inactivation kinetics of polyphenol oxidase extracted from Cistanche deserticola

PPO was purified from Cistanche deserticola, and its enzymatic characteristics were clarified. It was found that microwave treatment was an efficient way to inactivate PPO. Polyphenol oxidase (PPO) from Cistanche deserticola was obtained and purified through an acetone precipitation and anion exchange column, the enzymatic characteristics and inactivation kinetics of PPO were studied. The specific activity of PPO was 73135.15 ± 6625.7 U/mg after purification, the purification multiple was 48.91 ± 4.43 times, and the recovery was 30.96 ± 0.27%. The molecular weight of the PPO component is about 66 kDa by SDS-PAGE analysis. The optimum substrate of PPO was catechol (V_max = 0.048 U/mL, K_m = 21.70 mM) and the optimum temperature and pH were 30 °C and 7, respectively. When the temperature is above 50 °C, pH < 3 or pH > 10, the enzyme activity can be significantly inhibited. The first-order kinetic fitting shows that microwave inactivation has lesser k values, larger D values and shorter t_1/2. It was found that microwave treatment is considered as an efficient and feasible way to inactive PPO by comparing the Z values and E_a values of the two thermal treatments.

Changes in structural and functional properties of whey protein cross-linked by polyphenol oxidase

The natural whey protein is unstable, to achieve more efficient utilization, the functional properties of whey protein were modified by changing its structure, and enzymatic cross-linking is one of the common methods in dairy products to change the functional characterization. This study was conducted with objective to evaluate the structural and functional of whey protein which was cross-linked by polyphenol oxidase from Agaricus bisporus. Whey protein was cross-linked by polyphenol oxidase, and the polymers and dimers were revealed by SDS-PAGE and LC-MS/MS, the structural alterations of the polymers were analyzed by UV-vis, fluorescence spectroscopy and SEM, and the effects of functional properties of whey protein after cross-linked were also explored. Results showed that dimer and high polymer of β-lactoglobulin were formed, the secondary structure of whey protein was exhibited a significant variation, and the microstructure changed obviously. Moreover, the foaming and antioxidant activity of whey protein was enhanced although the emulsifying was reduced after cross-linked. These findings emphasize the feasible application of enzymatic cross-linking in improving the functional properties of whey protein, and provide a new direction for changing the traditional processing technology of whey protein and developing high-quality products.

Bio-imprinted magnetic cross-linked polyphenol oxidase aggregates for enhanced synthesis of L-dopa, a neurodegenerative therapeutic drug

Bio-imprinted magnetic cross-linked enzyme aggregates (i-m-CLEAs) of polyphenol oxidase (PPO) obtained from potato peels were prepared using amino-functionalized magnetic nanoparticles. Bio-imprinting is being used to improve the catalytic efficiency and conformational stability of enzymes. For bio-imprinting, PPO was incubated with different imprint/template molecules (catechol, 4-methyl catechol and l-3,4-dihydroxy phenylalanine) before cross-linking with glutaraldehyde. CLEAs imprinted with 4-methyl catechol showed maximum activity as compared with non-bio-imprinted magnetic CLEAs (m-CLEAs). They were further characterized by scanning electron microscopy and confocal microscopy. In bio-imprinted m-CLEAs, half-life (t_1/2) of PPO significantly improved (364.74 min) as compared to free PPO (43.58 min) and non-bio-imprinted m-CLEAs (266.54 min). Bio-imprinted m-CLEAs showed excellent thermal and storage stability as well as reusability. The CLEAs preparation were used for the synthesis of l-3,4-dihydroxyphenylalanine (L-dopa, a therapeutic drug to treat neurodegenerative disorder) and a remarkable increase in L-dopa yield (23.5-fold) was obtained as compared to free enzyme. A cost effective and reusable method has been described for the production of L-dopa.

Polyphenol oxidase inhibited by 4-hydroxycinnamic acid and naringenin: Multi-spectroscopic analyses and molecular docking simulation at different pH

It is still unclear how pH affects the inhibitory effects of phenolic acids and flavonoids on polyphenol oxidase (PPO). In this study, 4-hydroxycinnamic acid and naringenin were selected to investigate their interactions with PPO from pH 6.8 to 5.0. Results showed that acidic pH could enhance the inhibitory effect of inhibitors and a greater enhancement effect was observed in 4-hydroxycinnamic acid. Fluorescence emission spectra indicated that 4-hydroxycinnamic acid and naringenin interacted with PPO and quenched its intrinsic fluorescence, which was also enhanced by acidic pH. Circular dichroism suggested that 4-hydroxycinnamic acid and naringenin could reversibly bind to PPO molecules and transform α-helix into β-sheet. Molecular docking results revealed that 4-hydroxycinnamic acid and naringenin interacted with PPO through hydrogen bond and hydrophobic interaction, and more interactions were observed near the carboxyl group. These results indicated that acidic pH could significantly enhance the inhibitory effect of phenolic acid on PPO.

Effect of microfluidization on quality characteristics of sapodilla (Manilkara achras L.) juice

Various oxidative enzymes account for the quality degradation of sapodilla (Manilkara achras L.) juice and need to be inactivated through emerging and continuous green pressure processing technology. In this study, pressurization of sapodilla juice was attempted via microfluidization (MF) at pressure range of 10,000-30,000 pound per square inch (psi) with 1-3 passes or cycles. The impact of microfluidization on the activity of polyphenol oxidase (PPO), peroxidase (POD), color, total soluble solid (TSS), viscosity, serum cloudiness along with particle size, and microbial load of sapodilla juice was assessed. Results showed that microfluidization (MF) decreased the residual PPO activity from 100 to 80.78 % and POD activity from 100 to 40.57%. However, TSS (18.81-19.01 %), viscosity (2.64-2.06 cP), serum cloudiness (2.19-1.22 %) and total color change (3.19-18.54) was also significantly affected. Most of these changes were observed due to particle size (PS) reduction that varied from 65.19 to 8.13 μm. Microfluidized juice revealed color improvement at particular MF pressure and pass due to enzyme inactivation. Moreover, lowest microbial load (2.89 Log CFU/ mL) was found at 30,000 psi/3 pass of MF as compared to control sample (unprocessed juice) (7.57 Log CFU/ mL). Consequently, MF can be potential candidate in processing of juices against spoilage.

Effects of light quality, photoperiod, CO2 concentration, and air temperature on chlorogenic acid and rutin accumulation in young lettuce plants

Environmental stimuli modulate plant metabolite accumulation, facilitating adaptation to stressful conditions. In this study, the effects of blue and red light, photoperiod, CO2 concentration, and air temperature on the chlorogenic acid (CGA) and rutin contents of lettuce (Lactuca sativa L.) were evaluated. Under continuous blue light and a high CO2 concentration (1000 ppm), the CGA level increased. The increased expression of phenylalanine ammonia-lyase (PAL) and activity of its product were correlated with high expression of cinnamate 4-hydroxylase (C4H) and coumarate 3-hydroxylase (C3H). Furthermore, changes in PAL activity altered the CGA content in lettuce exposed to the three environmental factors, blue light, continuous lighting and high CO2 concentration. In addition, the expression levels of genes related to flavonoid biosynthesis increased in accordance with the promotion of CGA accumulation by the environmental factors. Under continuous blue light, 400 ppm CO2 promoted rutin accumulation to a greater degree compared to 1000 ppm CO2, by downregulating DFR expression. Low air temperature induced CGA accumulation in lettuce grown under continuous blue light and 1000 ppm CO2. Therefore, light quality, photoperiod, CO2 concentration, and air temperature exert synergistic effects on the CGA and rutin contents of lettuce by modulating activity in the corresponding biosynthesis pathways.

Enzyme activity and population genetic structure analysis in wheat associated with resistance to Bipolaris sorokiniana-common root rot diseases

Common root rot disease (CRR) caused by Bipolaris sorokiniana (Sacc.) (Pleosporaceae), is an important fungal disease of wheat, Triticum aestivum (Poaceae), causing considerable yield losses globally. Incorporating genetic resistance in cultivated crops is considered the most efficient and sustainable solution to counter root rot diseases. Moreover, resistance to CCR is quantitative in nature, and thus the mechanism is poorly understood. To this aim, we analyzed the activities of defense-related enzymes; peroxidase (POX), superoxide dismutase (SOD), polyphenol oxidase (PPO), catalase (CAT), phenylalanine ammonia-lyase (PAL), β-1,3-glucanase (GLU) and chitinase (CHI), as well as total phenol content (TPC) to CRR on the three known resistant wheat 'Alvand' and 'Bam', 'Mehregan' at different time points (wpi) following CRR pathogen, B. sorokiniana inoculation. Of which, were selected out of 33 wheat cultivars previously screened for resistance to CRR. We also analyzed the genetic variability of the entire germplasm, 33 wheat cultivars using seven simple sequence repeat (SSR) primer pairs. The activity of antioxidant enzymes was increased in the related resistant genotypes. Of which, 'Bam' had the highest increase in PPO, and GLU activities, followed by 'Alvand' in SOD, PAL, and CHI significantly. Whereas, 'Mehregan' showed the highest level of TPC, POX, and CAT activities. In addition, five out of seven used SSR primers produced a total of 20 polymorphic bands, of which the number of alleles in each gene locus varied within 3-7 bands. The polymorphism information content (PIC) value also ranged from 0.44 to 0.81, with the mean of 0.65, Shannon Information Index (I) between 0.29 and 0.63 with an average of 0.47 per locus, and Nei's gene diversity (h) value varied from 0.16 to 0.44 with an average of 0.32. The average number of effective alleles was 1.52, ranging between 1.21 and 1.8. The gene locus Xgwm 140 showed the highest diversity in the population genetic structure, which explains the ability of the primers to resolve the assayed germplasm. Thus, resistance to CRR in wheat was mainly related to the enhancement of antioxidant enzymes, although the specific metabolic pathways require further study. This study presents new insights for understanding resistance mechanisms of the selected wheat cultivars to CRR, thus improving wheat yield in the future.

Formation and nature of non-extractable residues of emerging organic contaminants in humic acids catalyzed by laccase

Formation of non-extractable residues (NERs) is the major fate of most environmental organic contaminants in soil, however, there is no direct evidence yet to support the assumed physical entrapment of NERs (i.e., type I NERs) inside soil humic substances. Here, we used ¹⁴C-radiotracer and silylation techniques to analyze NERs of six emerging and traditional organic contaminants formed in a suspension of humic acids (HA) under catalysis of the oxidative enzyme laccase. Laccase induced formation of both type I and covalently bound NERs (i.e., type II NERs) of bisphenol A, bisphenol F, and tetrabromobisphenol A to a large extent, and of bisphenol S (BPS) and sulfamethoxazole (SMX) to a less extent, while no induction for phenanthrene. The type I NERs were formed supposedly owing to laccase-induced alteration of primary (active groups) and secondary (conformation) structure of humic supramolecules, contributing surprisingly to large extents (23.5%-65.7%) to the total NERs, particularly for BPS and SMX, which both were otherwise not transformed by laccase catalysis. Electron-withdrawing sulfonyl group and bromine substitution significantly decreased amount and kinetics of NER formation, respectively. This study provides the first direct evidence for the formation of type I NERs in humic substances and implies a "Trojan horse" effect of such NERs in the environment.

The unexpected flavone synthase-like activity of polyphenol oxidase in tomato

The biosynthesis of flavones has drawn considerable attention. However, the presence of flavones and their biosynthesis in tomato (Solanum lycopersicum) remain unclear. Here, we confirmed that flavones are present in MicroTom tomato and unexpectedly found that a tomato polyphenol oxidase (SlPPO F) possesses a flavone synthase-like activity and catalyzes the conversion of eriodictyol to luteolin without the need for any cofactor. SlPPO F showed a similar K_m value to that of other polyphenol oxidases, and could be inhibited by ascorbic acid. The flavone synthase-like activity of SlPPO F exhibited strict substrate specificity and only accepted flavanones with two hydroxyl groups (3' and 4') on the B ring as substrates. SlPPO F showed higher catalytic efficiency and better thermostability than type I flavone synthase from Apium graveolens, suggesting its possible application in enzyme engineering. In summary, we identified flavones in tomato and unraveled a polyphenol oxidase exhibiting flavone synthase-like activity.

Thermal treatment alternatives for enzymes inactivation in fruit juices: Recent breakthroughs and advancements

Fruit juices (FJs) are frequently taken owing to their nutritious benefits, appealing flavour, and vibrant colour. The colours of the FJs are critical indicators of the qualitative features that influence the consumer's attention. Although FJs' intrinsic acidity serves as a barrier to bacterial growth, their enzymatic stability remains an issue for their shelf life. Inactivation of enzymes is critical during FJ processing, and selective inactivation is the primary focus of enzyme inactivation. The merchants, on the other hand, want the FJs to stay stable. The most prevalent technique of processing FJ is by conventional heat treatment, which degrades its nutritive value and appearance. The FJ processing industry has undergone a dramatic transformation from thermal treatments to nonthermal treatments (NTTs) during the past two decades to meet the requirements for microbiological and enzymatic stability. The manufacturers want safe and stable FJs, while buyers want high-quality FJs. According to the past investigation, NTTs have the potential to manufacture microbiologically safe and enzymatically stable FJs with low loss of bioactive components. Furthermore, it has been demonstrated that different NTTs combined with or without other NTTs or mild heating as a hurdle technology increase the synergistic effect for microbiological safety and stability of FJs. Concise information about the variables that affect NTTs' action mode has also been addressed. Primary inactivates enzymes by modifying the protein structure and active site conformation. NTTs may increase enzyme activity depending on the nature of the enzyme contained in FJs, the applied pressure, pH, temperature, and treatment period. This is due to the release of membrane-bound enzymes as well as changes in protein structure and active sites that allow substrate interaction. Additionally, the combination of several NTTs as a hurdle technology, as well as temperature and treatment periods, resulted in increased enzyme inactivation in FJs. Therefore, a combination of thermal and non-thermal technologies is suggested to increase the effectiveness of the process as well as preserve the juice quality.

Optimization of enzymatic synthesis of theaflavins from potato polyphenol oxidase

Theaflavin (TF), a chemical component important in measuring the quality of fermented tea, has a strong natural antioxidant effect and many pharmacological functions. Enzymatic oxidation has become a widely used method for preparing TFs at the current research stage. Using plant exogenous polyphenol oxidase (PPO) to enzymatically synthesize TFs can significantly increase yield and purity. In this study, tea polyphenols were used as the reaction substrate to discuss the optimal synthesis conditions of potato PPO enzymatic synthesis of theaflavins and the main products of enzymatic synthesis of TFs. The optimal enzymatic synthesis conditions were as follows: pH of the reaction system was 5.5, reaction time was 150 min, substrate concentration was 6.0 mg/mL, reaction temperature was 20 °C, and the maximum amount of TFs produced was 651.75 μg/mL. At the same time, high-performance liquid chromatography was used to determine the content of theaflavins and catechins in the sample to be tested, and the dynamic changes and correlations of the main catechins and theaflavins in the optimal enzymatic system were analyzed. The results showed that epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG) are all the main substrates synthesis of TFs. The main substrate of TFs and its strongest enzymatic catalytic effect on EGCG make theaflavin-3,3'-digallate (TFDG) the most important synthetic monomer. In this study, theaflavins were synthesized by polyphenol oxidase catalysis, which laid a foundation for industrialization of theaflavins.

Aggregation and conformational change of mushroom (Agaricus bisporus) polyphenol oxidase subjected to atmospheric cold plasma treatment

Atmospheric cold plasma (ACP) is a novel nonthermal technology with potential applications in maintaining and improving food quality. The effect of ACP on the activity and structure of mushroom (Agaricus bisporus) polyphenol oxidase (PPO) was evaluated. Results demonstrated that the dielectric barrier discharge (DBD) based plasma technology could inactivate PPO (up to 69%) at 50 kV with the increased concentrations of H₂O₂ and NO_x. An obvious enhancement of surface hydrophobicity was observed, whereas a gradual reduction of total sulfhydryl content was recorded with the increasing exposure time. Data from circular dichroism, atomic force microscopy, particle size distribution and fluorescence spectra displayed the rearrangement of secondary structure and disruption of the tertiary structure. Red shifts of fluorescence spectra showed positive correlations with the inactivation rate of PPO. Therefore, ACP treatment could be served as an alternative approach to inactivate undesirable enzymes to minimize the loss of food nutrition and quality.

Effects of flat sweep frequency and pulsed ultrasound on the activity, conformation and microstructure of mushroom polyphenol oxidase

The effects of thermal processing (TP) and flat sweep frequency and pulsed ultrasound (FSFPU) treatment with different frequency modes on the activity, conformation and physicochemical properties of mushroom polyphenol oxidase (PPO) were investigated. The results showed that the relative enzymatic activity of PPO gradually decreased with increasing temperature and duration, and thermosonication decreased the PPO activity to a greater extent compared with thermal processing. FSFPU treatment with dual-frequency of 22/40 kHz mode showed the most significant effect. Circular dichroism (CD) showed that the content of α-helix and β-turn dropped, while that of β-sheet and random coil raised after FSFPU treatment. The intensity of endogenous fluorescence decreased, indicating that PPO protein unfolded and the tertiary structure was destroyed. The amount of free sulfhydryl, protein aggregation index, and turbidity all rose. Moreover, FSFPU treatment led to the aggregation of protein from the analysis of atomic force microscope (AFM). Conclusively, FSFPU can be used as an effective method to inhibit the activity of endogenous enzymes in food.

Inhibitory effect of Malaysian coastal plants on banana (Musa acuminata colla "Lakatan"), ginger (Zingiber officinale Roscoe) and sweet potato (Ipomoea batatas) polyphenol oxidase

Undesired browning reaction catalyzed by polyphenol oxidase (PPO) has reduced the nutritional quality and customer acceptance of the products. The inhibitory effects of six coastal plants including Sonneratia alba, Rhizophora apiculata, Syzygium grande, Rhizophora mucronata, Hibiscus tiliaceus and Bruguiera gymnorhiza on PPO in banana, sweet potato and ginger were studied based on oxidation of pyrocatechol. Banana exhibited the highest PPO activity (141,600 U), followed by sweet potato (43,440 U) and ginger (26,880 U). Banana PPO was strongly inhibited by R. apiculata (70.87%) and sweet potato PPO was strongly inhibited by S. alba (82.00%). In general, most banana PPO was the most susceptible to inhibition with all inhibitors having inhibition higher than 60.00% at 0.5 mg/ml and ginger PPO was the least susceptible with all inhibitors showing less than 50.00% inhibition at 0.5 mg/ml. Coastal plant extracts are potentially to be developed as natural inhibitors for preventing enzymatic browning of fruits and vegetables.

The effects of ultrasonication on the phytochemicals, antioxidant, and polyphenol oxidase and peroxidase activities in coffee leaves

In the present study, we investigated the impacts of ultrasonic conditions on the phytochemical profiles, antioxidant activity, and polyphenol oxidase (PPO) and peroxidase (POD) activities in coffee leaves. Ultrasonic frequency, power, and time, pH, and incubation time affected PPO and POD differently, thus resulting in different ABTS scavenging capacity and phenolic content in coffee leaves. Triple-frequency (20/35/50 kHz) ultrasound significantly (P < 0.05) inhibited trigonelline, caffeine, mangiferin, rutin, chlorogenic acids, antioxidant activity, and PPO activity, while the single frequency of 35 kHz increased the phenolics compounds, which was associated with the lowest POD activity. Increasing the incubation time after ultrasonication gradually decreased phenolic compounds and antioxidant activities, however, POD activity followed a temporal pattern of first increase and then decrease. Our results showed that PPO and POD were temporally inactivated after ultrasonication, which leading to the continuous decrease of phenolics in coffee leaves.

Enzymatic transformation products of phloretin as potent anti-adipogenic compounds

Enzymatic structure modification of the representative chalcone phloretin (1) with polyphenol oxidase from Agaricus bisporus origin produced two new biphenyl-type phloreoxin (2) and phloreoxinone (3), and a previously undescribed (2R)-5,7,3",5"-tetrahydroxyflavanone (4). The structure of these new oxidized products 2‒4 elucidated by interpreting the spectroscopic data (NMR and FABMS) containing the absolute stereochemistry established by analysis of the circular dichroism (CD) spectrum. Compared to the original phloretin, the new products (2) and (3) showed highly improved anti-adipogenic potencies both toward pancreatic lipase and accumulation of 3T3-L1 cells. Aslo, phloreoxin (2) effectively inhibited the expression of C/EBPβ, PPARγ, and aP2 at the mRNA level in the 3T3 adipocytes. Thus, phloreoxin (2), containing a biphenyl moiety catalyzed by A. bisporus polyphenol oxidase, have the potential to influence the anti-adipogenic capacity.

Genetic diversity and biochemical analysis of Capsicum annuum (Bell pepper) in response to root and basal rot disease, Phytophthora capsici

This study analyzed the genetic variability and biochemical characteristics of edible and ornamental accessions of pepper, Capsicum annuum, in response to root and basal rot disease (RCR), caused by Phytophthora capsici, using resistance screening and genetic variability via Inter Simple Sequence Repeat marker (ISSR), bio-mass parameters, and enzymatic activity of Peroxidase or peroxide reductases (POX), Superoxide dismutase (SOD), Polyphenol oxidase (PPOs), Catalase (CAT), Phenylalanine ammonia-lyase (PAL), β-1,3-glucanase and phenolic content. The resistance in C. annuum '37ChilPPaleo', '19OrnP-PBI' and '23CherryPOrsh' and susceptibility in '2BP-PBI', '24BP-301' and '26BPRStarlet' accessions were confirmed. Nineteen out of 21 ISSR primers generated 185 polymorphic bands with a mean percentage band of 98.5 %, and an average number of bands of 9.9 per primer. Biomass parameters were significantly higher in resistant genotypes than the susceptible ones and non-inoculated controls. All the seven candidate enzymes were highly up-regulated in the resistant C. annuum accessions '19OrnP-PBI', '37ChillP-Paleo' and '23CherryP-Orsh' inoculated with P. capsici The mean level of enzyme activity varied from 1.5 to 5.6-fold higher in the resistant C. annuum, of which SOD was increased by 5.6 fold, followed by PAL 4.40 and PPO 3.75 fold in comparison to susceptible and non-inoculated controls. Overall, there was no significant correlation between resistance and genetic variability, and also between genetic variability and enzyme activity levels. However, there was a highly significant correlation between the resistance, bio-mass parameters and enzyme activity levels.

Regulation of secondary antioxidants and carbohydrates by gamma-aminobutyric acid under salinity-alkalinity stress in rice (Oryza sativa L.)

Gamma-aminobutyric acid (GABA) is known to improve tolerance against abiotic stresses but less studied for salinity-alkalinity stress (SAS). In the present study, GABA regulation of secondary antioxidants and carbohydrates was studied in rice in the presence and absence of SAS. About 1.5 mM GABA, 200 mM SAS, GABA + SAS were applied to 5-day old seedlings, and thereafter measurements were done in shoots and roots at 24, 48, 72 h in rice cultivars CSR 43 (tolerant) and Pusa 44 (susceptible). SAS was applied in molar ratio of 1:9:9:1 of NaCl:Na₂SO₄:NaHCO₃:Na₂CO₃. Peroxidases (POX), polyphenol oxidases (PPO), lignin, flavonoids and phenolics from secondary metabolism and invertases, hexoses, sucrose and starch from carbohydrate metabolism were studied. Pusa 44 increased soluble POX, lignin, flavonoids in shoots but deficient in roots during stress period but improved under GABA + SAS. CSR 43 increased soluble POX, lignin, flavonoids in roots consistently throughout the stress period and also improved under GABA + SAS. Early increase in cell wall POX/PPO under SAS was seen in CSR 43 only, while Pusa 44 improved this under GABA + SAS. During stress period, CSR 43 showed an increasing trend of cell wall invertase activity, sucrose, sucrose-to-hexose ratio and starch in roots but Pusa 44 showed poor such response but Pusa 44 improved starch, sucrose, sucrose-to-hexose ratio by significant amount in both shoots and roots under GABA + SAS. The overall study indicated GABA as an important regulator of secondary and carbohydrate metabolisms. Besides improving secondary antioxidants, GABA under stress may improve cellular reserves like starch and protective sugars like sucrose.

In situ phytoremediation of polycyclic aromatic hydrocarbon-contaminated agricultural greenhouse soil using celery

Although celery has been established as an effective plant in the remediation of organic pollutant-contaminated soil, few studies have investigated the associated biological processes in rhizosphere and the effect of celery on agricultural field remediation in situ. In this study, a polycyclic aromatic hydrocarbon (PAH)-contaminated agricultural greenhouse was used as the experimental site, and three celery species (Apium graveolens L., Oenanthe javanica (Blume) DC., Libanotis seseloides (Fisch. & C.A. Mey. ex Turcz.) Turcz.) were applied for in situ remediation. After 90 days, the PAH dissipation rate of the L. seseloides treatment was highest (50.21%), and most of the PAHs were limited to its roots (translocation factor 0.516). This suggested that L. seseloides is a potential species for phytoremediation coupled with agro-production. The culturable microbial population and invertase activity results strongly supported that O. javanica is suitable for the establishment of exogenous bacteria-celery co-remediation techniques. Pearson's correlation analysis showed that the polyphenol oxidase (PPO) activity was highly significantly positively correlated with the PAH dissipation rate (r = 0.984, P < 0.01), and we suggest that PPO can be used as a microecological index during PAH remediation.

Process optimization of polyphenol oxidase immobilization: Isotherm, kinetic, thermodynamic and removal of phenolic compounds

Chitosan/montmorillonite (CTS/MMT) and chitosan‑gold nanoparticles/montmorillonite (CTS-Au/MMT) composites were prepared, characterized through Fourier transformed infrared (FT-IR), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM), and utilized as support for immobilization of polyphenol oxidase (PPO). PPO was immobilized on CTS/MMT (IPPO) and CTS-Au/MMT (IPPO-Au) by physical adsorption, respectively. In order to achieve simultaneous maximization of immobilization efficiency and enzyme activity, the immobilization process parameters were optimized by Taguchi-Grey relational analysis (TGRA) approach. Under the optimal immobilization condition, the immobilization efficiency and enzyme activity reached at 50.16% and 1.46 × 10⁴ U/mg for IPPO, and 63.35% and 3.01 × 10⁴ U/mg for IPPO-Au, respectively. The isotherm, kinetic and thermodynamics of PPO adsorption were investigated in detail. The adsorption process was better explained by Toth isotherm and Fractal-like pseudo second order model, respectively. Intra-particle diffusion and film diffusion were involved in the adsorption process and intra-particle diffusion was not the only rate-controlling step. The adsorption of PPO was exothermic, physical and spontaneous at the investigated temperature range. The immobilized PPO were used to oxidize phenolic compounds. All investigated phenolic compounds showed the higher conversion as catalyzed by IPPO-Au. For both IPPO and IPPO-Au, the conversion of substituted phenols was higher than that of phenol.

The potential impact of Octopus cyanea extracts to improve eggplant resistance against Fusarium-wilt disease: in vivo and in vitro studies

The novelty of the present research is conducting a new method in the systemic resistance of plant diseases by using distinct marine extracts. The ability of two octopus extracts to reduce the wilt disease caused by Fusarium oxysporum was observed. The applied methods are soaked roots (SR) and foliar shoots (FS). The antioxidant enzyme activities, percent disease index (PDI), and growth parameters were measured. In vitro antifungal potential of the octopus extracts against F. oxysporum was examined. The obtained result shows that SR extracts reduced PDI. Additionally, all the tested treatments promoted the growth and photosynthetic pigments of the infected plants. SR (in ethanolic extracts) was the most prominent inducer which offered a high advancement in the total soluble protein contents. Also, SR (in methanolic extracts) was the most suitable inducer which provided a very necessary development not only in the total phenol but also in the peroxidase (POD) and polyphenol oxidase (PPO) activities. GC-MS investigation of the octopus extracts exhibited that the compounds which possess antifungal activity were furoscrobiculin B and/or eugenol. They demonstrated a notable antifungal potential against F. oxysporum with a maximum activity of 38.5 and 12.7 mm ZOI after the treatment with the ethanolic and methanolic extract, respectively. FTIR results illustrated the functional group of the compound responsible for the antifungal activity. Additionally, an atomic absorption result reveals that there are traces of metals detected such as Pb, Ag, Cu, Zn, and Mg. The antifungal activity was decreased as the concentrations were reduced. Accordingly, the present extracts may be used as the vital agents in the agricultural field to restrain the plant pathogenic fungi, especially F. oxysporum from a proliferation.

Polyphenol oxidase genes as integral part of the evolutionary history of domesticated tetraploid wheat

Studying and understanding the genetic basis of polyphenol oxidases (PPO)-related traits plays a crucial role in genetic improvement of crops. A tetraploid wheat collection (T. turgidum ssp., TWC) was analyzed using the 90K wheat SNP iSelect assay and phenotyped for PPO activity. A total of 21,347 polymorphic SNPs were used to perform genome-wide association analysis (GWA) in TWC and durum wheat sub-groups, detecting 23 and 85 marker-trait associations (MTA). In addition, candidate genes responsible for PPO activity were predicted. Based on the 23 MTAs detected in TWC, two haplotypes associated with low and high PPO activity were identified. Four SNPs were developed and validated providing one reliable marker (IWB75732) for marker assisted selection. The 23 MTAs were used to evaluate the genetic divergence (F_ST > 0.25) between the T. turgidum subspecies, providing new information important for understanding the domestication process of Triticum turgidum ssp. and in particular of ssp. carthlicum.

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.

Effect of pH on pulsed light inactivation of polyphenol oxidase

The inactivation of diverse food enzymes by pulsed light (PL) has been described before, including the inactivation of polyphenol oxidase (PPO) (at pH 6.5). Since the pH affects the conformation of enzymes, it may influence the inactivation of enzymes by PL. The aim of this work was to evaluate the effect of pH on the kinetics of the PL-inactivation and associated structural changes of a case enzyme. To this, PPO was treated by PL at different pHs (4.0-6.5) and its inactivation kinetics and changes in its structure were evaluated by spectrophotometric and spectrofluorometric methods. The inactivation proceeded faster at low pH and was highly correlated with the decrease in peak intrinsic fluorescence intensity. Phase diagrams and parameter A evolution indicated the absence of intermediate unfolded states during the course of the inactivation. No protein aggregation was detected by turbidimetry. Results indicate that although a low pH favors the PL-inactivation of PPO, the mechanism of inactivation is pH-independent. Beyond the specific outcome for PPO, the results are evidence of a general pH-independence in the mechanism of enzyme inactivation by PL in the pH range 4.0-6.5 and acidification can be a strategy to decrease treatment times during PL processing.

Lam) and its affinity towards acylated anthocyanins and caffeoylquinic acid derivatives

Biochemical characterization of polyphenol oxidase (PPO) present in purple sweet potato (PSP) is a key step in developing efficient methodologies to control oxidative damage caused by this enzyme to the valuable components of PSP, such as caffeoylquinic acid derivatives and acylated anthocyanins. Thus, this work focused on the assessment of the effects of pH, temperature, and chemical agents on the PPO activity as well as characterization of the PPO substrate specificity towards major phenolic compounds found in PSP. The optimum conditions of enzyme activity were pH 7 and a temperature range of 20-30 °C at which phenolic substrates were oxidized with 72.5-99.8% yield. Zn²⁺ ions remarkably reduced PPO activity while Cu²⁺ ions improved enzyme performance. The highest substrate preference was shown for 3,4,5-tri-caffeoylquinic and 3,5-di-caffeoylquinic acid, followed by 5-caffeoylquinic and caffeic acid, 3,4- and 4,5-di-caffeoylquinic acids, peonidin-3-caffeoyl-p-hydroxybenzoyl-sophoroside-5-glucoside. The highest Km values were found for 4,5-feruloyl-caffeoylquinic acid and catechol.

Halophytes as a potential source of melanosis-inhibiting compounds. Mechanism of inhibition of a characterized polyphenol extract of purslane (Portulaca oleracea)

The market value of crustaceans depreciates during storage due to the appearance of melanosis caused by polyphenol oxidases. Sulfite derivatives are used as melanosis-inhibiting agents, but their unhealthy effects make it preferable to replace them with natural preservatives. In this work, a crude enzymatic extract from whiteleg shrimp (Penaeus vannamei) was characterized and used to test the diphenol oxidase-inhibiting activity of polyphenol extracts of five underutilized halophyte plants, namely crystalline ice plant, seaside arrowgrass, purslane, sea fennel, and seashore aster. The extracts inhibited diphenol oxidase activity more efficiently than sodium sulfite. The purslane extract was rich in isoorientins, isovitexin, and apigenin, and showed the highest inhibiting effect, being this classified as mixed or non-competitive. Hydroxyl groups in the phenyl B ring could be responsible for the inhibitory activity of the extract. The polyphenol extracts tested in this work could be promising melanosis-inhibiting agents of interest for seafood industries.

Anti-polyphenol oxidase properties of total flavonoids from young loquat fruits: inhibitory activity and mechanism

This study investigated anti-polyphenol oxidase activity and mechanism of purified total flavonoids (PTF) from young loquat fruits. PTF remarkably inhibited the activity of polyphenol oxidase (PPO) with an IC₅₀ value of 21.03 ± 2.37 μg/mL. Based on enzyme kinetics, PTF was found to be a potent, mixed-type, and reversible inhibitor of PPO. The fluorescence intensity of PPO was quenched by PTF through forming a PTF-PPO complex in a static procedure. Therefore, this study authenticated PTF as an efficient PPO inhibitor, which would contribute to their utilization in food industry.