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Piceatannol is a naturally occurring hydroxylated analogue of the stilbene phytoalexin resveratrol that can be found in grape fruit and derived products. Piceatannol has aroused great interest as it has been shown to surpass some human health-beneficial properties of resveratrol including antioxidant activity, several pharmacological activities and also bioavailability. The plant biosynthetic pathway of piceatannol is still poorly understood, which is a bottleneck for the development of both plant defence and bioproduction strategies. Cell cultures of Vitis vinifera cv. Gamay, when elicited with dimethyl-β-cyclodextrin (MBCD) and methyl jasmonate (MeJA), lead to large increases in the accumulation of resveratrol, and after 120 h of elicitation, piceatannol is also detected due to the regiospecific hydroxylation of resveratrol. Therefore, an ortho-hydroxylase must participate in the biosynthesis of piceatannol. Herein, three possible types of resveratrol hydroxylation enzymatic reactions have been tested, specifically, a reaction catalyzed by an NADPH-dependent cytochrome, P450 hydroxylase, a 2-oxoglutarate-dependent dioxygenase and ortho-hydroxylation, similar to polyphenol oxidase (PPO) cresolase activity. Compared with P450 hydoxylase and the dioxygenase activities, PPO displayed the highest specific activity detected either in the crude extract, the particulate or the soluble fraction obtained from cell cultures elicited with MBCD and MeJA for 120 h. The overall yield of PPO activity present in the crude extract (107.42 EU) was distributed mostly in the soluble fraction (66.15 EU) rather than in the particulate fraction (3.71 EU). Thus, partial purification of the soluble fraction by precipitation with ammonium sulphate, dialysis and ion exchange chromatography was carried out. The soluble fraction precipitated with 80% ammonium sulphate and the chromatographic fractions also showed high levels of PPO activity, and the presence of the PPO protein was confirmed by Western blot and LC-MS/MS. In addition, a kinetic characterization of the cresolase activity of partially purified PPO was carried out for the resveratrol substrate, including Vmax and Km parameters. The Km value was 118.35 ± 49.84 µM, and the Vmax value was 2.18 ± 0.46 µmol min−1 mg−1. [ABSTRACT FROM AUTHOR]

This study evaluates the biocontrol efficacy of three bacterial strains (Pseudomonas fluorescens DTPF-3, Bacillus amyloliquefaciens DTBA-11, and Bacillus subtilis DTBS-5) and two fungal strains (Trichoderma harzianum Pusa-5SD and Aspergillus niger An-27) antagonists, along with their combinations at varying doses (5.0, 7.5, and 10.0 g/kg of seeds), against wheat powdery mildew. The most effective dose (10 g/kg seeds) was further analyzed for its impact on induced resistance and plant growth promotion under greenhouse conditions. The study measured defense enzyme activities, biochemical changes, and post-infection plant growth metrics. All tested microbial antagonists at 10 g/kg significantly reduced PM severity, with B. subtilis strain DTBS-5 outperforming others in reducing PM severity and achieving the highest biocontrol efficacy. It was followed by B. amyloliquefaciens strain DTBA-11 and P. fluorescens strain DTPF-3, with the fungal antagonists showing no significant effect. Wheat crops treated with B. subtilis strain DTBS-5 exhibited substantial increases in defense-related enzyme activities and biochemicals, suggesting an induced resistance mechanism. The study found a 45% increase in peroxidase (POD) activity, a 50% increase in catalase (CAT) activity, a 30% increase in phenolic content, and a 25% increase in soluble protein content in the wheat plants treated with microbial antagonists. The study highlights the effectiveness of microbial antagonists, particularly B. subtilis strain DTBS-5, in managing wheat PM through biocontrol, induced resistance, and enhanced plant growth, offering a sustainable alternative to chemical treatments. [ABSTRACT FROM AUTHOR]

This study investigated the changes in the quality-related parameters and physicochemical properties of yam (Dioscorea alata L. var. Dasan) harvested after 260 d. The stem tip, middle, and bottom sections of yams were stored at room temperature (20 °C ± 2 °C) for 16 weeks. Samples were taken every 2 weeks and analyzed to determine the changes in physicochemical properties during storage. α-Amylase and PPO activities were highest in the stem tip section. A positive correlation between enzyme activities and storage time was observed in all groups. polyphenol oxidase (PPO) peaked during week 10 of storage and gradually decreased. No significant correlation was found between α-amylase activity and starch content. Moreover, similar to free sugar content, α-amylase activity reached its maximum value during week 14 of storage. All sections of the yams showed reductions in cooking loss rates with the prolongation of storage and reached their minimum cooking loss during week 10 of storage. During the storage, the middle sections of the yams exhibited the most consistent quality, presenting minimal changes in hardness and color stability and the lowest rate of cooking loss. The quality of yam tubers, particularly in enzymatic browning after slicing, post-cooking hardness, cooking loss, and free sugar content, was affected by fluctuations in α-amylase and PPO activities during storage. Therefore, these factors should be considered when evaluating quality and determining optimal storage and handling procedures. The results of this study may serve as a reference for determining the quality of yams during postharvest storage and are important for companies and researchers seeking to optimize yam storage for maximum yield and profitability.

This study evaluates the biocontrol efficacy of three bacterial strains (Pseudomonas fluorescens DTPF-3, Bacillus amyloliquefaciens DTBA-11, and Bacillus subtilis DTBS-5) and two fungal strains (Trichoderma harzianum Pusa-5SD and Aspergillus niger An-27) antagonists, along with their combinations at varying doses (5.0, 7.5, and 10.0 g/kg of seeds), against wheat powdery mildew. The most effective dose (10 g/kg seeds) was further analyzed for its impact on induced resistance and plant growth promotion under greenhouse conditions. The study measured defense enzyme activities, biochemical changes, and post-infection plant growth metrics. All tested microbial antagonists at 10 g/kg significantly reduced PM severity, with B. subtilis strain DTBS-5 outperforming others in reducing PM severity and achieving the highest biocontrol efficacy. It was followed by B. amyloliquefaciens strain DTBA-11 and P. fluorescens strain DTPF-3, with the fungal antagonists showing no significant effect. Wheat crops treated with B. subtilis strain DTBS-5 exhibited substantial increases in defense-related enzyme activities and biochemicals, suggesting an induced resistance mechanism. The study found a 45% increase in peroxidase (POD) activity, a 50% increase in catalase (CAT) activity, a 30% increase in phenolic content, and a 25% increase in soluble protein content in the wheat plants treated with microbial antagonists. The study highlights the effectiveness of microbial antagonists, particularly B. subtilis strain DTBS-5, in managing wheat PM through biocontrol, induced resistance, and enhanced plant growth, offering a sustainable alternative to chemical treatments.

Piceatannol is a naturally occurring hydroxylated analogue of the stilbene phytoalexin resveratrol that can be found in grape fruit and derived products. Piceatannol has aroused great interest as it has been shown to surpass some human health-beneficial properties of resveratrol including antioxidant activity, several pharmacological activities and also bioavailability. The plant biosynthetic pathway of piceatannol is still poorly understood, which is a bottleneck for the development of both plant defence and bioproduction strategies. Cell cultures of Vitis vinifera cv. Gamay, when elicited with dimethyl-β-cyclodextrin (MBCD) and methyl jasmonate (MeJA), lead to large increases in the accumulation of resveratrol, and after 120 h of elicitation, piceatannol is also detected due to the regiospecific hydroxylation of resveratrol. Therefore, an ortho-hydroxylase must participate in the biosynthesis of piceatannol. Herein, three possible types of resveratrol hydroxylation enzymatic reactions have been tested, specifically, a reaction catalyzed by an NADPH-dependent cytochrome, P450 hydroxylase, a 2-oxoglutarate-dependent dioxygenase and ortho-hydroxylation, similar to polyphenol oxidase (PPO) cresolase activity. Compared with P450 hydoxylase and the dioxygenase activities, PPO displayed the highest specific activity detected either in the crude extract, the particulate or the soluble fraction obtained from cell cultures elicited with MBCD and MeJA for 120 h. The overall yield of PPO activity present in the crude extract (107.42 EU) was distributed mostly in the soluble fraction (66.15 EU) rather than in the particulate fraction (3.71 EU). Thus, partial purification of the soluble fraction by precipitation with ammonium sulphate, dialysis and ion exchange chromatography was carried out. The soluble fraction precipitated with 80% ammonium sulphate and the chromatographic fractions also showed high levels of PPO activity, and the presence of the PPO protein was confirmed by Western blot and LC-MS/MS. In addition, a kinetic characterization of the cresolase activity of partially purified PPO was carried out for the resveratrol substrate, including Vmax and Km parameters. The Km value was 118.35 ± 49.84 µM, and the Vmax value was 2.18 ± 0.46 µmol min−1 mg−1.

Litchi (Litchi chinensis Sonn.) is a type of commercially prevalent subtropical and tropical fruit. Since litchi has a highly heterozygous genetic background and a long reproductive cycle, conventional breeding methods (such as hybridization) have limited ability to nurture new litchi cultivars. Here, an efficient and stable Agrobacterium tumefaciens-mediated genetic transformation of embryogenic callus was established in ‘Feizixiao’ litchi. Transgenic materials were verified using polymerase chain reaction (PCR) analysis, β-glucuronidase (GUS) assay, and green fluorescent protein (GFP) assay. To implement the technology of the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/associated protein 9 (CRISPR/Cas9) technology in ‘Feizixiao’ litchi and verify the validity of these transformation systems, the litchi polyphenol oxidase gene (LcPPO, JF926153) was knocked out. Various categories of mutations, covering base insertions, deletions, and substitutions, were found in transgenic materials via sequence analysis. The transformation system achieved high feasibility and efficiency, and the system of CRISPR/Cas9 was successfully employed to edit genes in ‘Feizixiao’ litchi. This work provides an essential foundation for investigating the functions of genes and accelerating litchi genetic improvement.

Rust fungi are devastating plant pathogens, and several Puccinia species have exerting substantial financial impacts on global barley cultivation. Fungicides are used on a large scale as an effective method for combating phytopathogenic fungi. The negative environmental impacts of fungicides are steadily escalating on a daily basis. Consequently, researchers are currently exploring alternative approaches to mitigate the use of fungicides, such as the utilization of plant extracts. This method has proven effective due to its incorporation of natural antifungal substances. Among the nine natural elicitors that were tested, the application of plant extracts on barley seedlings resulted in an increase in the incubation and latent periods of Puccinia hordei. These periods are integral components of partial and induced resistance, effectively mitigating the incidence of barley leaf rust disease by over 70% on mature plants. Similarly, the biochemical analyses demonstrated a notable augmentation in all the tested treatments' overall phenolics and oxidative enzyme activities (peroxidase and polyphenol oxidase). Random amplified polymorphic DNA (SCoT) test serves as a viable approach for assessing the impact of plant extracts and microorganisms on barley plants. The results obtained from this study indicate that the detection of DNA polymorphism through SCoT analysis holds a significant potential powerful tool to evaluate genetic changes compared with untreated plants although some of them tested displayed high similarities at the morphological reaction. [ABSTRACT FROM AUTHOR]

Diverse enzymatic reactions taking place after the killing of green vanilla beans are involved in the flavor and color development of the cured beans. The effects of high hydrostatic pressure (HHP) at 50–400 MPa/5 min and blanching as vanilla killing methods were evaluated on the total phenolic content (TPC), polyphenoloxidase (PPO), and peroxidase (POD) activity and the color change at different curing cycles of sweating–drying (C0–C20) of vanilla beans. The rate constants describing the above parameters during the curing cycles were also obtained. The TPC increased from C1 to C6 compared with the untreated green beans after which it started to decrease. The 400 MPa samples showed the highest rate of phenolic increase. Immediately after the killing (C0), the highest increase in PPO activity was observed at 50 MPa (46%), whereas for POD it was at 400 MPa (25%). Both enzymes showed the maximum activity at C1, after which the activity started to decrease. As expected, the L* color parameter decreased during the entire curing for all treatments. An inverse relationship between the rate of TPC decrease and enzymatic activity loss was found, but the relationship with L* was unclear. HHP appears to be an alternative vanilla killing method; nevertheless, more studies are needed to establish its clear advantages over blanching. [ABSTRACT FROM AUTHOR]

Copyright of Food Research & Development is the property of Food Research & Development Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study a fast and efficient method for obtain polyphenol oxidase (PPO) from tea leaf, three phase partitioning (TPP) were used to purified PPO and then its enzymatic properties were studied. The results showed that PPO from tea leaf was purified with 15.76-fold enrichment in the specific activity of 210.46 U/mg and 8.04% recovery by TPP purification method for the second time. The strongest affinity substrate was pyrogallol (Km=6.82 mmol/L, Vmax=5.36×10−2 OD/min) for purified tea PPO. The optimum temperature and pH of the enzyme were 45 ℃ and 5.5, respectively. The enzyme had great stability under condition of 25 ℃ and pH4.5~7.0. The most significant inhibitory effect of different compounds on purified tea PPO was ascorbic acid (IC50=2.42±0.18 mmol/L), followed by oxalic acid and EDTA. The inhibitory effect of citric acid was the weakest, while halides had no significant inhibitory effect (P>0.05). This work proves that the TPP method can better retain the tea PPO activity, and easy to operate, time-consuming and low-cost for the purification of tea PPO, which is beneficial to industrial applications.

Enzymatic browning could negatively affect the sensory and nutritional properties of eggplants post-harvest. Polyphenols, polyphenol oxidase (PPO), and reactive oxygen species (ROS) are three material conditions involved in enzymatic browning. This paper seeks to evaluate the effect of fertilization techniques and grafting on the activity of PPO and colorimetric parameters in cultivated eggplants. Fertilization alone significantly increased the PPO activity in all eggplant fleshes (p ≤ 0.05), whereas the grafting technique combined with fertilization decreased the PPO activity in most of the samples significantly (p ≤ 0.05). Moreover, there was a significant positive correlation between the PPO activity and the a* values of the eggplants. The a* values in grafted eggplants were significantly different from each other (p ≤ 0.05), showing that grafting the fertilized eggplants could be effective in controlling the enzymatic browning. The eggplant slices exposed to air for 60 min at room temperature showed a significant increase (p ≤ 0.05) in PPO activity, browning index (BI), total color difference (ΔE), and a*, b*, and c* values. Thus, it is necessary to minimize the exposure time of the slices to air at room temperature, even if combining fertilization techniques with grafting could delay the enzymatic browning in fresh-cut eggplants. [ABSTRACT FROM AUTHOR]

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

Key message: AOS enzymes can be biochemical indicators of abnormal xylogenesis in Karelian birch. The elevation of enzymatic activity correlates with the increase in wood figure intensity. The different biochemical strategies of the antioxidant system (AOS) enzymes (superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO)) are described for the first time for various xylogenesis scenarios in Karelian birch (Betula pendula Roth var. carelica (Mercl.) Hämet-Ahti). Studies have shown that figured wood formation is closely associated with the secondary metabolism processes in this woody plant, as reflected in the elevation of the activity of AOS enzymes. Our results demonstrate that AOS enzymes can be used as biochemical markers of figured wood formation during active cambial growth. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Henan University of Science & Technology, Natural Science is the property of Editorial Office of Journal of Henan University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Enzymatic browning could negatively affect the sensory and nutritional properties of eggplants post-harvest. Polyphenols, polyphenol oxidase (PPO), and reactive oxygen species (ROS) are three material conditions involved in enzymatic browning. This paper seeks to evaluate the effect of fertilization techniques and grafting on the activity of PPO and colorimetric parameters in cultivated eggplants. Fertilization alone significantly increased the PPO activity in all eggplant fleshes (p ≤ 0.05), whereas the grafting technique combined with fertilization decreased the PPO activity in most of the samples significantly (p ≤ 0.05). Moreover, there was a significant positive correlation between the PPO activity and the a* values of the eggplants. The a* values in grafted eggplants were significantly different from each other (p ≤ 0.05), showing that grafting the fertilized eggplants could be effective in controlling the enzymatic browning. The eggplant slices exposed to air for 60 min at room temperature showed a significant increase (p ≤ 0.05) in PPO activity, browning index (BI), total color difference (ΔE), and a*, b*, and c* values. Thus, it is necessary to minimize the exposure time of the slices to air at room temperature, even if combining fertilization techniques with grafting could delay the enzymatic browning in fresh-cut eggplants.

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

Coconut pericarp (shell fiber (mesocarp) and shell (endocarp)), the main by-product of coconut production, is often discarded and causing serious environmental pollution. To make better use of coconut pericarp, the extraction process of polyphenols from coconut mesocarp (CM) carefully studied by screening seven solvent systems, optimizing the assisted ultrasonic process by response surface methodology, and comparing the four processes of Ultrasound-Assisted Extraction (UAE), Homogenization-Assisted Extraction (HAE), Homogenization-Ultrasound-Assisted Extraction (HUAE), and Ultrasound-Homogenization-Assisted Extraction (UHAE). The UAE and HAE are considered to be the main methods for efficient extraction of natural active ingredients. The former effectively destroys the cell wall structure and promotes the intermolecular diffusion based on the cavitation, thermal and mechanical effect of ultrasonic, while the latter breaks the material based on strong shear force between the rotor and stator. Their combinations (HUAE and UHAE) enhance the damage to the cell wall of raw materials and improve the extraction efficiency by the synergistic effect. The results showed that using 60% acetone (V : V) as extraction solvent, solid-liquid ratio of 1:5 g mL−1, ultrasonic temperature of 80 ℃, ultrasonic time of 80 min, ultrasonic power of 225 W, and then homogenizing at 10,000 rpm for 10 min, the total flavonoid content of CM reached the maximum value of 551.99 ± 12.69 mg Rutin g−1 dry weight (dw), while the total phenolic content reached the maximum value of 289.48 ± 4.41 mg GAE g−1 dw at 10,000 rpm for 5 min, which may be related to the oxidative degradation of polyphenols caused by the increase of polyphenol oxidase with the extension of homogenization time. This study provides a technical guarantee for the further utilization of phenolic substances in CM.

Abstract Background Plants experience severe physiological stress from heavy metal pollution caused by improper discarding of the industrial wastes. Hexavalent chromium [Cr (VI)] is one of the major heavy metal pollutants in India and is present particularly in some regions where Plantago ovata grows to a great extent. This study was aimed at finding the effects of Cr (VI) on P. ovata and manoeuvres of the plant to combat such heavy metal exposure in vitro. Methods Potassium dichromate was used as a source of Cr (VI) to induce the heavy metal stress. Range of Cr (VI) sublethal doses [0 mM (control), 0.1 mM, 0.3 mM, 0.5 mM, 1 mM, 1.5 mM and1.8 mM] was used to observe its effect on the plant. The seeds of the plant were grown on sucrose-agar media with different concentrations of potassium dichromate, and ten-day old seedlings were then harvested and examined. Results The germination rate reduced below 50% at 1.9 mM Cr (VI) concentration and thus, 0 mM–1.8 mM concentration ranges were found to be suitable for sublethal dose. Morphological changes namely, reduction of the shoot-root length and multiple root development were caused by Cr (VI) in a dose-dependent manner. The plant showed elevated responses against Cr (VI), up to 1.5 mM (10 days treated) in terms of increasing accumulation of secondary metabolites like polyphenols, chlorophyll content (chlorophyll a, b and total chlorophyll), carotenoids and total antioxidant activity. DPPH radical scavenging activity along with malondialdehyde (MDA) content was not significantly elevated with the increase in Cr (VI) concentration indicating that the lipid peroxidation rate within the tissue was low. Phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) gene expressions were upregulated by 1 mM Cr (VI) concentration, which decreased at higher concentrations. The atomic absorption spectroscopy analysis also showed significant accumulation of Cr (VI) in the shoot and root with an increase in the potassium dichromate concentration. Conclusion Cr (VI) reduced the shoot-root length and seed germination in a dose-dependent manner. The plant system tried to combat the Cr (VI) stress by upregulating the stress response genes in the phenylpropanoid pathway along with an increase in polyphenol and antioxidant contents, which were evident from the lowering of lipid peroxidation rate and increase in PAL and PPO gene expressions.

Phenolic compounds, such as catechol, are released into the environment from a variety of industrial sources and they present a serious ecosystem burden. This work examined the possibility of using partially purified apple polyphenol oxidase (PPO) for bioremediation of phenolic contaminants. In order to optimize process conditions, the optimal pH and temperature for PPO activity were determined, while PPO affinity toward various phenols, as well as the effect of some salts and organic solvents which can be found in wastewaters, was used to confirm applicability of PPO in wastewater treatment. It was found that partially purified apple PPO shows maximal activity at pH 6.8 and 25 °C, but exhibits more than 85 % of its maximal activity in pH range from 5 to 8, and more than 90 % of activity in temperature range from 10 to 50 °C. PPO showed high affinity for various diphenols, but lack of affinity toward monophenols. Sodium tetraborate decahydrate moderately inhibited PPO activity, while exposure of PPO to the presence of organic solvents (φ = 5 %) caused 40 % loss in its activity. Catechol oxidation by PPO performed for just 5 min in a batch reactor at optimal process conditions resulted in 25 % conversion. Based on obtained data, it seems that partially purified apple PPO has reasonable potential in wastewater treatment.

This review covers some recent advances in browning prevention in minimally processed potatoes (MPP). Polyphenol oxidase (EC 1.10.3.1, PPO) is one of the main enzymes involved in browning of potatoes. Antibrowning agents are used in combination with other compounds and techniques to reduce browning such as physical treatments with modified atmospheres and cold temperatures in processing and storage. Due to increasing concerns involving toxicity from various traditional food preservatives, this review focuses on studies involving substances that have different mechanisms to control browning. These substances include reducing agents, acidulants, chelating agents, enzyme inhibitors, complexing agents or others, such as Maillard reaction products and natural extracts. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the efficiency of biological applications (Glomas mossa, Trichoderma harzianum, Trichoderma viride and Azotobacter chrococcum) in resisting Damping off and root rot disease. The application of all biological factors has significantly increased the germination percentage of cucumber seeds and decreased the disease severity percentage compared with Pythim aphanidermatum treatment only and a significant increase in the wet weight and dry weight of shoots and root system of the plant. The bacteria A.chrococcom was the most influential in the study, reaching (76.7%, 73.67% 2.067g and 1.600g), respectively. Moreover, the same factors also achieved a significant increase of lignin concentration in leaves. Increase in the concentration of polyphenol oxidase and total protein in the plant reached (15.64 mlg. gm dry weight, 3.110 units. gm. 205.5 micrograms), respectively compared to the control treatment which applied with the fungus Pathogen. [ABSTRACT FROM AUTHOR]

Polyphenol oxidase (PPO) enzyme is a metalloenzyme containing a copper and catalyzes the conversion of phenolic compounds to quinones and assists the polymerization of their products. It causes browning reactions in fruit and vegetables due to oxidation during handling and storage processes. This enzymatic browning reaction is the one of the biggest problem in the food processing industries during processing and storage of vegetables and fruits. Lately, researchers are very interested in developing new PPO inhibitors to slow the enzymatic browning. Natural anti-brown compounds commonly used for the PPO enzyme are honey, aliphatic alcohols, ascorbic acid and cysteine. In addition to these substances, some metals can affect enzyme activities positively or negatively. For example, iron, copper and zinc are essential metals for plant life, but some heavy metals such as mercury, lead, etc. can adversely affect enzymes in the plant defense system. In this work, the effects of some metals, anti-browning compounds and their complexes were examined on the PPO enzyme from princess tree (Paulownia tomentosa) leaf The results demonstrated that glutathione (GSH) was more powerful anti-browning compound than the others. Ni(II) and Mn(II) increased princess tree PPO activity. But, Pb(II) was the efficient PPO inhibitor. Na(I), Cu(II) and Fe(II) had no considerable effect on the PPO enzyme activity. Additionally, the effects of metal and anti-browning compound mixtures on the PPO enzyme were examined. Our results showed that metal-L-Cys, metal-Ascorbic acid and metal-GSH complexes had inhibitory effects but metal-EDT A complex did not have a significant effect on princess tree PPO enzyme activity. [ABSTRACT FROM AUTHOR]

BACKGROUND: Polyphenol oxidase (PPO) is considered a problem in the food industry because it starts browning reactions during fruit and vegetable processing. Ultrasonic treatment is a technology used to inactivate the enzyme; however, the mechanism behind PPO inactivation is still unclear. For this reason, the inactivation, aggregation, and structural changes in PPO from quince juice subjected to ultrasonic treatments were investigated. Different intensities and times of ultrasonic treatment were used. Changes in the activity, aggregation, conformation, and structure of PPO were investigated through different structural analyses. RESULTS: Compared to untreated juice, the PPO activity in treated juice was reduced to 35% at a high ultrasonic intensity of 400 W for 20 min. The structure of PPO determined from particle size distribution (PSD) analysis showed that ultrasound treatment caused initial dissociation and subsequent aggregation leading to structural modification. The spectra of circular dichroism (CD) analysis of ultrasonic treated PPO protein showed a significant loss of α‐helix, and reorganization of secondary structure. Fluorescence analysis showed a significant increase in fluorescence intensity of PPO after ultrasound treatment with evident blue shift, revealing disruption in the tertiary structure. CONCLUSION: In summary, ultrasonic treatment triggered protein aggregation, distortion of tertiary structure, and loss of α‐helix conformation of secondary structure causing inactivation of the PPO enzyme. Hence, ultrasound processing at high intensity and duration could cause the inactivation of the PPO enzyme by inducing aggregation and structural modifications. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Summary: Plant microRNAs (miRNAs) regulate vital cellular processes, including responses to extreme temperatures with which reactive oxygen species (ROS) are often closely associated.In the present study, it was found that aberrant temperatures caused extensive changes in abundance to numerous miRNAs in banana fruit, especially the copper (Cu)‐associated miRNAs. Among them, miR528 was significantly downregulated under cold stress and it was found to target genes encoding polyphenol oxidase (PPO), different from those identified in rice and maize. Expression of PPO genes was upregulated by > 100‐fold in cold conditions, leading to ROS surge and subsequent peel browning of banana fruit.Extensive comparative genomic analyses revealed that the monocot‐specific miR528 can potentially target a large collection of genes encoding Cu‐containing proteins. Most of them are actively involved in cellular ROS metabolism, including not only ROS generating oxidases, but also ROS scavenging enzymes.It also was demonstrated that miR528 has evolved a distinct preference of target genes in different monocots, with its target site varying in position among/within gene families, implying a highly dynamic process of target gene diversification. Its broad capacity to target genes encoding Cu‐containing protein implicates miR528 as a key regulator for modulating the cellular ROS homeostasis in monocots. [ABSTRACT FROM AUTHOR]

Banana fruit is usually harvested unripe and the peel browning is a quality challenge during the post-ripening or senescence with or without exogenous ethylene's ripening acceleration. Browning can occur during logistics, sales, or domestic storage and largely reduces the economic value and consumer liking. 5-azacytidine (5-azaC) is a DNA methylation inhibitor, which has been recently found important in regulating fruit ripening and quality shaping, but its role remains unknown considering banana browning. Currently, we put bananas in the 10 mmol/L solution of 5-azaC for vacuum infiltration (15 min) and then continuous immersion (30 min), and stored them under controlled-release ethylene for 9 days. This treatment effectively retard peel browning. In the final sampling, there were 9.3 times as many bananas in the control group with severe 20–40% browning as there were in the 5-azaC-treated group. Further analysis demonstrated that the polyphenol oxidase (PPO) activity and programmed cell death (PCD) process were inhibited by 5-azaC with its methylation-inhibiting effects, which also somehow modulated the ethylene sensitivity of peel cells to alleviate senescence-related browning. This study is expected to offer valuable insights into banana anti-browning strategy development. • 5-azacytidine as a DNA demethylator was found to mitigate banana peel browning. • It delayed postharvest banana ripening and alleviate peel spotting development. • This alleviation involved changes in antioxidant capacity and PPO activities. • PCD process and endogenous ethylene sensitivity changes were also included. [ABSTRACT FROM AUTHOR]

Browning is prevalent in tissue cultures of Paeonia lactiflora Pall. (herbaceous peony), and severely affects and restricts the growth and differentiation of the explants. In this study, dipping excised explants in a sodium chloride (NaCl) solution as a pretreatment, adding polyvinyl pyrrolidone (PVP) to the culture medium, storing planted explants at 4 °C for 24 h, and transferring planted explants to a new medium after 24 h were considered as browning-suppression methods in tissue cultures of herbaceous peony ‘Festival Maxima’. The treated petal explants were cultured in a culture room with a 16-hour photoperiod, 25 °C temperature, and 80% relative humidity in darkness for 4 to 8 weeks. The results demonstrated that dipping excised explants in a 0.5 g·L−1 NaCl solution, adding 0.5 g·L−1 PVP to the medium, storing planted explants at 4 °C for 24 h, and transferring planted explants to the same fresh medium after 24 h could effectively inhibit browning. Adding PVP to the medium led to the greatest browning suppression percentage of 95%. Storing planted explants at 4 °C for 24 h reduced the effectiveness of other treatments in suppressing browning. After 8 weeks, dipping excised explants in a NaCl solution resulted in the highest callus induction percentage of 75%, while storing explants at 4 °C for 24 h suppressed callus formation. It was observed in all treatments that decreases in browning was accompanied with higher levels of phenols and lower activities of phenylalanine ammonia-lyase (PAL) and polyphenoloxidase (PPO). Overall, the results suggest that dipping in a NaCl solution was effective in alleviating the browning issues of herbaceous peony tissue cultures, and had positive synergistic effects with PVP on browning suppression and callus induction.

Polyphenol oxidase (PPO) in plants plays an important role in browning reactions and may affect the quality of sweet melon products. In this study, a browning-related protein (BRP) with PPO activity was partially purified from oriental sweet melon (Cucumis melo var. makuwa Makino) by salt precipitation and column chromatography. The BRP possessed a high degree of identity with several chitinase proteins, particularly defense-related proteins, by MS identification. Pyrogallol was determined as the most appropriate substrate for BRP (Km = 0.04278 M). BRP exhibited extreme resistance under alkaline and high temperature conditions when pyrogallol was used as substrate. Polyacrylamide gel electrophoresis (PAGE) analysis indicated that BRP was a homo-dimer of two subunits and had a molecular weight of 37 kDa. Structural analysis indicated that the α-helix was the dominant conformation of BRP. The active site of the protein might be buried deeply in the protein, and BRP might be monodispersed in an aqueous system.

Copyright of Shipin Kexue/ Food Science is the property of Food Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Mass propagation of date palm through indirect somatic embryogenesis or organogenesis has attracted the interest of commercial producers. But, this technique still faces some problems that hindered the production of date palm plantlets in vitro. Tissue browning is one of the serious problems that reduce callus growth and shoot regeneration. So the objective of the present study is to investigate the effect of cold pretreatment on callus growth, shoot regeneration, and polyphenol oxidase (PPO) activity during the callus culture. Results showed that a high survival rate of callus cultures (100%) were obtained when cultures were incubated in low temperature (cold treatment) for 45 and 75 days. On the other hand, total amount on phenolic compounds was also reduced to 0.47 and 0.53 mg GAE/g after same period of incubation (45 and 75 days respectively) at low temperature. In additional, our results showed that the highest frequency of shoot formation (66.67 and 73.34, %) and the highest shoot numbers (7.8 and 8.6 shoots/100 mg) were obtained from callus treated with low temperature for 45 and 75 days, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Shipin Kexue/ Food Science is the property of Food Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study compared the effects of high pressure processing (HPP), treatments (pasteurization, ascorbic acid, and steviosides), storage time (1 day, 15 days, 30 days, and 45 days at 4 °C) on the polyphenol oxidase (PPO) activity, color, and sensory analysis of pulp from pawpaw fruit. HPP significantly decreased but did not completely inhibit PPO activity compared to the processed samples. HPP did not affect significantly any of the twelve sensory attributes. PPO activity and all color measurements were affected significantly by refrigerated storage. PPO activity declined after day 1 of refrigerated storage and remained unchanged thereafter. The untreated samples exhibited a significant change in all color values to varying degrees during the 45 day storage period, but this effect during storage was not observed in the samples that were pasteurized or treated with stevia or ascorbic acid. There was no difference between the PPO activity of the untreated pulp and the pulp treated with steviosides and pasteurization, however, the pawpaw pulp to which steviosides were added were perceived to be about 60% sweeter and 50% more bitter. HPP is a promising technology for shelf life extension of fresh-packaged pawpaw pulp. [ABSTRACT FROM AUTHOR]

Polyphenol oxidase (PPO) plays a key role in tea processing, converting catechins into theaflavines. Two PPOs were isolated and purified from tea ( Camellia sinensis ) leaves. PPO1 and PPO2 exhibited molecular weights of 85 KDa and 42 KDa, respectively. PPO activities were evaluated at different temperatures and pH values to determine thermal stability as well as the optimal temperature and pH. Moreover, PPO1 and PPO2 were allowed to react with catechol, epigallocatechin (EGC), epigallocatechin gallate (EGCG), l -tyrosine, guaiacol, and pyrogallic acid as enzyme substrates. PPO isozymes were more active with the triphenolic substrate, and PPO2 demonstrated no activity toward guaiacol. PPO1 activity only resulted in the synthesis of simple theaflavin (TF), while PPO2 was able to synthesize four types of theaflavins, particularly theaflavin-3-3'-gallate (TFDG). These data provide insights into the optimum manufacturing conditions for the enzymatic synthesis of theaflavins. [ABSTRACT FROM AUTHOR]

Juglans regia 'Yuanfeng' is an elite walnut cultivar in China. Juglans cathayensis, a close relative species of Juglans regia originated from China, possesses some superior traits such as strong disease resistance and high fruit number per branch. So far, transcriptomes of either J. regia or J. cathayensis have not been studied and made available to public yet. In the present study, the transcriptomes of J. regia and J. cathayensis leaves were profiled using Illumina HiSeq 2000 platform. A total of 41,914 unigenes were obtained from the combined clean reads of J. regia and J. cathayensis with an average length of 1363 bp and 2529 differentially expressed genes (DEGs) were detected. Gene annotation analyses revealed that 38,483 unigenes (91.81%) were annotated in at least one of the five databases such as Gene Ontology (GO), etc. Meanwhile, the Ca, Mg, Fe, Zn, K and protein contents in the leaves of J. regia and J. cathayensis were compared and significant differences between J. regia and J. cathayensis in terms of the Ca, Mg, Fe and protein contents were discovered. In addition, DEGs associated with the Ca, Mg and Fe content variations between J. regia and J. cathayensis were investigated. Our comparative transcriptomes' analysis between J. regia and J. cathayensis could provide a useful resource for genetic characterization and improvements of J. regia. [ABSTRACT FROM AUTHOR]

BACKGROUND Polyphenol oxidase ( PPO) mainly contributes to the browning reaction of fruits and vegetables and causes serious damage to the quality of sweet melon products. However, traditional methods to inactivate browning may induce more unexpected risks than ultrasonic processing. Meanwhile, there are no reports on the effect of ultrasound on PPO directly purified from sweet melon. RESULTS The PPO in the original juice was less inactivated than the purified form when treated with ultrasound. As for purified PPO, superior to thermal treatment, less heat was needed to inactivate the PPO with ultrasonic treatment. At intensity lower than 200 W, ultrasound did not significantly affect the structure and activity of PPO ( P > 0.05), and latent PPO was activated. At intensity higher than 200 W, ultrasound inactivated PPO, induced aggregation and dissociation of PPO particles and significantly decreased the α-helix structure content. CONCLUSION Low-frequency high-intensity ultrasound caused an inactivation effect and conformational changes of purified PPO from oriental sweet melons. Changes in the PPO structure induced by ultrasound eventually inactivated the enzyme. Ultrasound may be a potential method to inactivate PPO in oriental sweet melons. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Background: Although borage ( Borago officinalis L.) is a valuable medicinal plant, no information is available on the responses of this plant to salinity. For this reason, it is necessary to determine responses of this plant to salinity . Objective: Since germination and early growth stage is one of the most critical phases of plant life under salinity condition this experiment was conducted to determine some responses of borage to salinity at the seedling stage. Methods: This experiment was laid out in a completely randomized design with three replications and four salinity treatments, including distilled water (EC=0.0dS m-1) and three saline water conditions with EC of 5.0, 10.0 and 15.0 dSm-1. Results: With increasing EC , the content of free proline, soluble carbohydrates and proteins were increased. Moreover, the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and polyphenol oxidase (PPO) enzymes were significantly increased. Although seedlings dry weight and emergence percentage were declined with increasing EC, the seedlings had markedly growth/survival under salinity conditions. Conclusion: The survival and little reduction in emergence under salinity conditions (12.5%) indicated that borage was a salt tolerant species at the early growth stage. This tolerant is certainly due to the enhancement of antioxidant enzymes activities and compatible solutes content. Keywords: Antioxidant enzymes , Borago officinalis L., Osmotic adjustment, Salinity, Seedling stage.

p-Cresol is an environmental pollutant due to its vast use, toxicity and persistence, nevertheless, its degradation in an enzyme is unclear. In this study, we used Pleurotus sp. isolate VLECK02 polyphenol oxidase (PPO) for the determination of p-cresol degradation. On the basis of UV, FT-IR and chromatographic (HPLC and GC-MS) analysis, 4-methylcatechol was identified as the main metabolite of p-cresol catabolism. In addition, batch and semi-continuous degradation of p-cresol (10 and 20 mM) were studied and compared by free and immobilized PPO in different matrices like sodium alginate (SA), sodium alginate-polyvinyl alcohol (SA-PVA) and sodium alginate-polyvinyl alcohol-silver nanoparticles (SA-PVA-AgNPs). The experimental data showed that an enzyme (PPO) immobilized in SA-PVA-AgNPs was completely degraded p-cresol at initial concentrations of 10 and 20 mM within 30 h. These results suggest that the enzyme immobilized in SA-PVA-AgNPs has achieved higher degradation rates at a given time than free PPO and PPO immobilized in SA-PVA and SA. The SA-PVA-AgNPs and SA-PVA immobilized enzyme could be reused for more than 12 and 8 cycles, respectively, without losing any degradation capacity. Moreover, the immobilized PPO showed higher tolerance to various temperatures and pH than free PPO. Hence, immobilized PPO could be useful for the bioremediation of environment contaminated with phenolic compounds like p-cresol. [ABSTRACT FROM AUTHOR]

Enzymatic browning is a major factor limiting the shelf life of minimally processed yam slices. The effect of ascorbic acid and calcium chloride (AACCl) dip and UV-C treatment on the browning index (BI), browning related enzymes (i.e. polyphenol oxidase, PPO; peroxidase, POD; phenylalanine ammonia lyase, PAL) and total phenolic content of yam slices during a 10 days storage period at 4 ± 1 °C was investigated. Results showed that untreated yam slices had significantly (p < 0.05) higher BI, PPO and POD activities throughout the storage period. In the case of PAL activity, yam slices treated with only UV-C at 13.68 KJ m −2 exhibited significantly high (p < 0.05) PAL activity throughout the storage period as compared to other treatments. In addition, untreated yam slices had the lowest total phenolic content during the storage period. Yam slices treated with the AACCl dip and a UV-C dosage of 6.84 KJ m −2 were found to be the best as they showed significantly low (p < 0.05) BI, PPO, POD and PAL activities throughout the storage period. In addition, this treatment also maintained a high but insignificant (p> 0.05) total phenolic content throughout the storage period. In summary, AACCl dip plus a UV-C dosage of 6.84 KJ m −2 could be useful in preventing browning of minimally processed yam slices under storage at 4 ± 1 °C. [ABSTRACT FROM AUTHOR]

Browning of fresh-cut romaine lettuce was inhibited in modified atmosphere (MA) packaging with low O 2 and moderate CO 2 concentrations during storage. This study explains the control mechanisms of MA causing differences in phenolic substrates and oxidative enzymes related to browning of two cultivars of romaine lettuce. Modified atmosphere decreased PAL and PPO activities and prevented cut edge browning. In MA, the process from latent to fully active PPO decreased particularly in the cultivar more susceptible to browning. The content of vitamin C was maintained or even increased in MA while decreased markedly in air. Caffeic acid derivatives increased through the storage in air whereas in MA this trend was towards a decrease in these phenolics. Chlorogenic acid was the only caffeic acid derivative that showed the same trend as PAL activity with an increase at d2 after cutting and a progressive decrease after that due to browning development and transformation to isochlorogenic acid. By the analysis of the lettuce midribs, it was possible to correlate the control of browning by MA with the suppressing action on oxidative enzymes and the slowing down of the synthesis and accumulation of caffeic acid derivatives. The browning process seems to correlate better with the biosynthesis of caffeoyl quinic derivatives, rather than with that of caffeoyl tartaric derivatives, that are always the main phenolics present in romaine lettuce midribs. A deeper study of the different behaviour of both groups of caffeic acid derivatives is guaranteed. [ABSTRACT FROM AUTHOR]

A new approach to improve the yield and quality of agricultural crops is the use of plant growth regulators. Brassinosteroids, as a class of plant growth regulators, have been shown to affect different physiological traits of plants. The effect of 24-epibrassinolide (EBL) on some photosynthesis-related physiological traits and stress-related enzyme activity was investigated. Strawberry ( Fragaria × ananassa cv. Sabrosa) seedlings grown in a hydroponic medium were sprayed with 1 and 4 µM EBL and evaluated for different physiological attributes. EBL at the 1 µM level significantly enhanced leaf photosynthetic pigments, gas exchange and net photosynthesis rate, and soluble sugar and starch content but decreased stomatal resistance and intercellular CO content. At the 4 µM level, EBL had no effects on photosynthesis-related activities. EBL, in a concentration dependent manner, enhanced the activity of phenylalanine ammonia-lyase, polyphenol oxidase, and peroxidase. Interestingly, the results showed that EBL, at low concentrations, acts as a growth-promoting and relatively stress-mediating agent and strongly enhances stress resistance at higher doses. [ABSTRACT FROM AUTHOR]

The objectives of this work were to study the ultrasound- and ultraviolet light-induced inactivation kinetics of polyphenol oxidase extracted from different sources in a model system. The polyphenol oxidase crude extract was obtained from bananas, apples, quince, eggplants, plums, dill, and cultured mushrooms, which exhibited high enzyme activity. The polyphenol oxidase crude extract was treated with ultrasound and ultraviolet light at 40°C temperature for 40 min. The study showed that the polyphenol oxidase enzyme was inactivated between 12 and 100% during ultrasound only treatment; between 4 and 29% during ultraviolet light only treatment; and between 80 and 100% during simultaneous ultrasound and ultraviolet light treatment. Based on the measurements, an exponential decay model for determining polyphenol oxidase inactivation kinetics was developed. The model provides high determination coefficients (R2): 0.968–0.999 with ultrasound only treatment, 0.881–0.990 with ultraviolet only treatment, and 0.975–1.000 with simultaneous ultrasound and ultraviolet treatment. The polyphenol oxidase kinetics evaluation showed that different treatments provided different inactivation times, orD-values. TheD-values were 7.0–656.1 min for ultrasound only treatment (DUS), 251–1887 min for ultraviolet only treatment (DUV), and 3.3–59.4 min for combined ultrasound and ultraviolet treatment (DUS+UV). [ABSTRACT FROM AUTHOR]

In this work, potato slices were exposed to different doses of UV-C irradiation (i.e. 2.28, 6.84, 11.41, and 13.68 kJ m) with or without pretreatment [i.e. ascorbic acid and calcium chloride (AACCl) dip] and stored at 4 ± 1 °C. Changes in enzymatic activities of polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia lyase (PAL), as well as total phenolic content (TPC) were investigated after 0, 3, 7 and 10 days of storage. Results showed that untreated and UV-C treated potato slices at 13.68 kJ m dosage level showed significantly higher PPO, POD and PAL activities. Conversely, untreated potato slices showed the lowest TPC during storage period. Potato slices subjected to AACCl dip plus UV-C at 6.84 kJ m produced lower PPO, POD and PAL activities, as well as maintained a high TPC during storage. [ABSTRACT FROM AUTHOR]