Enzymatic Browning

Mesquita, Vera Lúcia Valente; Queiroz, Christiane

doi:10.1016/b978-0-08-091809-9.00010-8

Cited by 24 publications

(16 citation statements)

References 217 publications

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“…Regardless of the type of PPO enzyme activity assay (polarimetric, spectrophotometric) or the substrate (monophenol, o-diphenol), PPO-silenced lines displayed essentially no activity, indicating that measured activity in wild-type protein extracts could be attributed to JrPPO1. Catecholase activity was measured by monitoring the rate of oxygen consumption using a Clark oxygen electrode (polarimetric assay), and calculated kinetic parameters using native o-diphenols as substrates (Table I) were comparable to previously reported values in other plant species (Mesquita and Queiroz, 2013). Unlike many plant PPOs, JrPPO1 also displays tyrosinase activity and was capable of oxidizing all tested native monophenols.…”

Section: Discussionmentioning

confidence: 60%

“…These enzymes are broadly distributed among animals, fungi, and plants, though many plant PPOs appear to lack tyrosinase activity (Steffens et al, 1994). The study of PPOs in plants has focused primarily on their role in the process of postharvest browning, whereby cut or damaged plant tissues turn brown due to the polymerization of PPOgenerated quinones, generating phytomelanins (Mesquita and Queiroz, 2013). Classically, PPOs and their potential phenolic substrates have been considered to be physically separated from one another in intact plant cells, with most PPOs targeted to the chloroplasts, while phenolic compounds accumulate primarily in the vacuole and cell wall (Vaughn et al, 1988;Steffens et al, 1994).…”

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confidence: 99%

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Novel Roles for the Polyphenol Oxidase Enzyme in Secondary Metabolism and the Regulation of Cell Death in Walnut

et al. 2014

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The enzyme polyphenol oxidase (PPO) catalyzes the oxidation of phenolic compounds into highly reactive quinones. Polymerization of PPO-derived quinones causes the postharvest browning of cut or bruised fruit, but the native physiological functions of PPOs in undamaged, intact plant cells are not well understood. Walnut (Juglans regia) produces a rich array of phenolic compounds and possesses a single PPO enzyme, rendering it an ideal model to study PPO. We generated a series of PPO-silenced transgenic walnut lines that display less than 5% of wild-type PPO activity. Strikingly, the PPO-silenced plants developed spontaneous necrotic lesions on their leaves in the absence of pathogen challenge (i.e. a lesion mimic phenotype). To gain a clearer perspective on the potential functions of PPO and its possible connection to cell death, we compared the leaf transcriptomes and metabolomes of wild-type and PPO-silenced plants. Silencing of PPO caused major alterations in the metabolism of phenolic compounds and their derivatives (e.g. coumaric acid and catechin) and in the expression of phenylpropanoid pathway genes. Several observed metabolic changes point to a direct role for PPO in the metabolism of tyrosine and in the biosynthesis of the hydroxycoumarin esculetin in vivo. In addition, PPOsilenced plants displayed massive (9-fold) increases in the tyrosine-derived metabolite tyramine, whose exogenous application elicits cell death in walnut and several other plant species. Overall, these results suggest that PPO plays a novel and fundamental role in secondary metabolism and acts as an indirect regulator of cell death in walnut.

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Section: Discussionmentioning

confidence: 60%

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confidence: 99%

Novel Roles for the Polyphenol Oxidase Enzyme in Secondary Metabolism and the Regulation of Cell Death in Walnut

et al. 2014

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“…Enzymatic browning occurred as a result of the oxidation by polyphenoloxidase (PPO) of phenolic compounds to quinones, in the presence of oxygen, and their eventual polymerisation to darkcoloured pigments (Daas & Hambaba, 2016). The reaction started when the tissue was damaged and the plastids rupture released the enzyme, which came in contact with phenolic compounds released by rupture of the vacuole (Mesquita & Queiroz, 2013). To inhibit enzymatic browning, heat treatment and the addition of antibrowning agents are usually applied, but there were other technologies used as alternatives to thermal processing for PPO inactivation.…”

Section: Changes In Optical Propertiesmentioning

confidence: 99%

Osmodehydration assisted by ohmic heating/pulse vacuum in apples (cv. Fuji): retention of polyphenols during refrigerated storage

Moreno

Zúñiga

Dorvil

et al. 2017

Int J of Food Sci Tech

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Summary Apples are a widely consumed fruit and have a high polyphenol content. The aim of this study was to analyse the combined effects of osmotic dehydration (OD) and ohmic heating (OH) with a pulsed vacuum (PV) on polyphenol retention during the stored refrigeration of apple cubes. Treatments were performed using a 65°Brix sucrose solution at 30, 40 or 50 °C for 120 min, and then, samples were stored for 28 days at 5 °C. OH provides an electric field of 13 V cm−1, and a pulsed vacuum was applied for 5 min at the beginning of the process. The results indicated that a lower temperature process (30–40 °C) resulted in the retention of more polyphenol compounds after treatment than a higher temperature process (50 °C). Nevertheless, during refrigerated storage, we observed that 50 °C preserved these compounds better due to polyphenol oxidase inactivation. PVOD/OH treatment at 50 °C was determined to be the best retention of polyphenols from the fresh apple for dehydrating apples.

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“…In spite of their well-defined role in ultraviolet protection in animals, the physiological role of PPOs in plants has remained unclear and most studies have focused on the postharvest browning reactions observed in cut fruits and vegetables (Arpita et al, 2010;Walker, 1995). Roles of PPO have been demonstrated in biosynthetic processes (Mesquita and Queiroz, 2013;Mueller et al, 1997;Steiner et al, 1999;Strack et al, 2003), defense against herbivores Constabel, 2004a, 2004b), fungal pathogenicity, fungal defense reaction (Jacobson, 2000;Soler-Rivas et al, 2000), and resistance of plant to stress, wounding, pathogenesis, and stressrelated hormones such as methyl jasmonate (MeJA) and salicylic acid (Li and Steffens, 2002;Raj et al, 2006;Thaler et al, 1999;Thipyapong et al, 2004). Until now, no clear report of how PPO might affect pathogens has been presented, but several mechanisms for the effect of PPO on pathogens have been suggested, including the toxicity to pathogens of quinones generated by PPO, cross-linking of quinones with phenolic compounds, and proteins that might result in the formation of physical barriers to pathogens attack (Li and Steffens, 2002).…”

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confidence: 99%

Induction of Polyphenol Oxidase in Walnut and Its Relationship to the Pathogenic Response to Bacterial Blight

Khodadadi

Tohidfar

Mohayeji

et al. 2016

J. Amer. Soc. Hort. Sci.

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Plants respond to pathogens with both active and passive defense mechanisms. These defense responses include the induction of defense or defense-related genes such as polyphenol oxidase (PPO) and pathogenesis-related (PR) proteins. The role of PPO in the interaction between bacterial blight [Xanthomonas arboricola pv. juglandis (Xaj)] and walnut (Juglans regia) was studied. JrPPO-1 and P14a genes were identified in two walnut cultivars, Chandler and Serr, using standard polymerase chain reaction (PCR) to understand their inducible ability in response to Xaj. ‘Serr’ and ‘Chandler’ were inoculated with Xaj strain 417. PPO activity in leaves was assayed at 0, 24, 72, 96, 120, and 144 hours after inoculation. Results showed a steady increase in activity commencing within 24 hours of inoculation. Increase in PPO activity was close to 2-fold greater in ‘Chandler’ than in ‘Serr’ at all time points examined. Real-time PCR analysis showed differences between cultivars in PPO gene expression. The JrPPO-1 gene was highly expressed in both cultivars 24 hours after inoculation but expression in ‘Serr’ was much greater than in ‘Chandler’. Significant expression of P14a gene was observed in both cultivars within 24 hours. Expression in ‘Serr’ was strong and maximized with a significant increase at 96 hours. Expression in ‘Chandler’ was far weaker than ‘Serr’ at 24 hours and did not increase further. Our results imply that the walnut–bacterial blight interaction induces the expression of JrPPO-1 and P14a as well as the activity of PPO.

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Enzymatic Browning

Cited by 24 publications

References 217 publications

Novel Roles for the Polyphenol Oxidase Enzyme in Secondary Metabolism and the Regulation of Cell Death in Walnut

Novel Roles for the Polyphenol Oxidase Enzyme in Secondary Metabolism and the Regulation of Cell Death in Walnut

Osmodehydration assisted by ohmic heating/pulse vacuum in apples (cv. Fuji): retention of polyphenols during refrigerated storage

Induction of Polyphenol Oxidase in Walnut and Its Relationship to the Pathogenic Response to Bacterial Blight

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