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BACKGROUND Button mushrooms with completely white appearance are popular with consumers. However, button mushrooms are susceptible to infection with Pseudomonas tolaasii (P. tolaasii), which results in browning. This study evaluates the effects of ultraviolet-C (UV-C) treatment on the inactivation of P. tolaasii in vitro and in vivo and on the physiological and chemical changes of button mushrooms during storage for 21 days at 4 °C. RESULTS UV-C doses of 0.5-9.0 kJ m-2 resulted in 3.91-6.26 log CFU mL-1 reduction of P. tolaasii populations in vitro, and UV-C treatment reduced P. tolaasii populations inoculated on mushroom cap surfaces and browning severity. Moreover, P. tolaasii increased polyphenol oxidase (PPO) activity, and decreased phenylalanine ammonia-lyase (PAL) activity, the accumulation of phenolics and contents of brown melanin precursors, including γ-L-glutaminyl-4-hydroxybenzene (GHB), γ-L-glutaminyl-3,4-dihydroxybenzene (GDHB), and tyrosine in button mushrooms. UV-C treatment was found to reduce the negative changes due to P. tolaasii infection. CONCLUSION These results indicated that the application of UV-C treatment inhibited browning, inactivated P. tolaasii and reduced P. tolaasii - associated chemical and enzymatic changes of button mushrooms. This article is protected by copyright. All rights reserved.

The aim of this paper was to study the effect of infrared radiation (IR) on the activity and conformation of polyphenol oxidase (PPO) in Acetes chinensis. In this paper, the specific activity of PPO was increased from 21.2 to 643.4 U/mg by a four-step purification. The results showed that IR treatment had greater effect on the enzyme activity and conformation of PPO than hot air (HA) treatment. After IR treatment at 70°C, the relative enzyme activity of PPO was 9.28%, the surface hydrophobicity index increased by 80.42%, and the content of sulfhydryl group decreased to 96.99% of the control group. The results of circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) showed that the α-helix of PPO treated by IR decreased and the random coil increased. The intrinsic fluorescence intensity of PPO decreased after IR treatment, indicating that the tertiary structure of PPO was destroyed. Scanning electron microscopy (SEM) results showed that the surface microstructure of PPO after IR treatment became clear and compact. In conclusion, IR treatment can completely destroy the secondary structure and tertiary structure of PPO and cause enzyme inactivation. This study provides a treatment for reducing the activity of PPO from A. chinensis during the production and processing. PRACTICAL APPLICATION: This study shows that IR treatment has a better inhibitory effect on the activity of PPO than HA treatment. It provides a better treatment method for inactivating the activity of PPO from Acetes chinensis during the production and processing.

Postharvest melatonin treatments have been reported to improve the quality and storability, especially to inhibit browning in many fruits, but the effect had not been systematically investigated on longan fruit. In this study, the effect of 0.4 mM melatonin (MLT) dipping on the quality and pericarp browning of longan fruits stored at low temperature was investigated. The MLT treatment did not influence the TSS content of longan fruits but lead to increased lightness and h° value while decreased a* value of pericarp. More importantly, the treatment significantly delayed the increase in electrolyte leakage and malonaldehyde accumulation, inhibited the activities of polyphenol oxidase and peroxidase, and thus retarded pericarp browning. In addition, the treatment significantly inhibited the production of O2•− and H2O2 while promoted the accumulation of glutathione, flavonoids, and phenolics at earlier storage stages in longan pericarp. Interestingly, the activities of ascorbate peroxidase (APX) and superoxide dismutase (SOD) were significantly upregulated but activities of catalase were downregulated in the MLT‐treated longan pericarp. MLT treatment effectively enhanced APX and SOD activities, increased flavonoid, phenolics, and glutathione content, protected cytomembrane integrity, inhibited the production of O2•− and H2O2 and browning‐related enzymes, and thus delayed the longan pericarp browning.

BACKGROUND During the thermal processing of fruit, it has been observed for phenolic compounds to either degrade, polymerize, or transfer into macromolecules. In this study, the bound and free phenolic compound composition, content, and phenolic-related enzyme activity of lychee pulp were investigated to determine whether the free phenolic had converted to bound phenolic during heat-pump drying (HPD). RESULTS It was found that after HPD, when compared with the fresh lychee pulp (control), the content of bound phenolics of dried lychee pulp had increased by 62.69%, whereas the content of free phenolics of dried lychee pulp decreased by 22.26%. It was also found that the antioxidant activity of bound phenolics had also increased after drying. With the use of high-performance liquid chromatography-tandem mass spectrometry, it was identified that (+)-gallocatechin, protocatechuic aldehyde, isorhamnetin-3-O-rutoside, 3,4-dihydroxybenzeneacetic acid, and 4-hydroxybenzoic acid were newly generated during HPD, when compared with the control sample. After drying, the contents of gallic acid, catechin, 4-hydroxybenzoic acid, vanillin, syringic acid, and quercetin in bound phenolics had also increased, and polyphenol oxidase and peroxidase still showed enzyme activity, which could be related to the conversion of free phenolics to bound phenolics. CONCLUSION Overall, during the thermal processing of lychee pulp, the free phenolics weres found to be converted into bound phenolics, new substances were generated, and antioxidant activity was increased. Hence, it was concluded that HPD improved the bound phenolics content of lychee pulp, thus providing theoretical support for the lychee processing industry. © 2021 Society of Chemical Industry.

Eggplant is a popular vegetable in Asia; however, it has a short storage life and considerable economic losses have resulted from eggplant browning. Calcium has been reported to play a key role in the postharvest storage of plants. Here, we found that exogenous calcium application could delay eggplant fruit browning and maintain higher storage quality. The increased browning index (BI), relative electrolytic leakage (REL), and water loss were suppressed by calcium treatment during storage. Delayed browning with calcium treatment might result from a higher phenolic level and suppressed the activity of polyphenol oxidase (PPO). Less H2O2 and O2 ‐ but more activated reactive oxygen species (ROS) scavenging enzymes accumulated in calcium‐treated fruits than in H2O‐treated fruits. Moreover, the nonenzymatic antioxidant, ascorbic acid (AsA), was accumulated more in calcium‐treated eggplant fruits. Taken together, our data demonstrated that exogenous calcium application delayed eggplant fruit browning by regulating phenol metabolism and enhancing antioxidant systems., 1. Calcium treatment delayed browning of eggplant fruits during storage.2. Calcium treatment maintained ROS scavenging enzyme activities in eggplant fruits during storage.

Surface browning is a vital phenomenon that adversely reduces the quality of fresh-cut potatoes. Although many anti-browning methods have been explored, it is unclear whether exogenous catalase (CAT) treatment influences the enzymatic browning. Our results showed that 0.05% CAT immersion for 5 min alleviated browning during cold storage (4°C, 8 days), which was accompanied by a higher lightness and lower redness; additionally, lower H2 O2 and O2 ·- contents were found. The activities of CAT, ascorbate peroxidase, and glutathione peroxidase and the scavenging efficiency of 2,2-diphenyl-1-picrylhydrazyl were also increased. Moreover, CAT treatment inhibited the activities of polyphenol oxidase, peroxidase, and phenylalanine ammonia lyase and reduced phenol accumulation. Treatment with 0.1% hydrogen peroxide (H2 O2 ) achieved the opposite results. This is the first report of CAT application reducing fresh-cut potato browning, providing a safe treatment alternative for enzymatic discoloration and preliminarily revealing the underlying mechanism with insight into antioxidant regulation. PRACTICAL APPLICATION: This research is helpful for fresh-cut potato producers because a novel, safe, easy-to-carry out anti-browning solution was proposed. Dipping in 0.05% catalase solution for 5 min revealed color improvement in the quality of fresh-cut potato slices. The mechanism may rely on enhancing antioxidant ability (ascorbate peroxidase, and glutathione peroxidase, and 2,2-diphenyl-1-picrylhydrazyl scavenging), reducing reactive oxygen species (H2 O2 , O2 ·-, malondialdehyde) and controlling enzymatic browning reaction factors (polyphenol oxidase, peroxidase, and phenylalanine ammonia lyase, and phenol accumulation). This method shows promise for better meeting the requirements and demands of consumers for fresh quality products.

BACKGROUND Rice spikelet rot disease (RSRD) is an emerging disease that significantly reduces rice yield and quality. In this study, we evaluated the potential use of the broad-spectrum endophytic fungus Phomopsis liquidambaris B3 as a biocontrol agent against RSRD. We also compared the control effects of different treatments, including chemical fungicides and treatment with multiple strains and single strains in combination or individually, against RSRD. The objective of this study was to find an effective and environmentally friendly control strategy to reduce the occurrence of RSRD and improve the rice yield. RESULTS In pot experiments, the effect of B3 alone was better than that of fungicide or combined measures. The results showed that root colonization by B3 significantly reduced the incidence and disease index of RSRD by 41.0% and 53.8%, respectively. This was related to enhanced superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO) activity, and to significantly upregulated expression levels of OsAOX, OsLOX, OsPAL, and OsPR10 in rice. Moreover, B3 improved the diversity of the bacterial community rather than the fungal community in the rice rhizosphere. It also led to a decrease in Fusarium proliferatum colonization and fumonisin content in the grain. Finally, root development was markedly promoted after B3 inoculation, and the yield improved by 48.60%. The result of field experiments showed that the incidence of RSRD and the fumonisin content were observably reduced in rice receiving B3, by 24.41% and 37.87%, respectively. CONCLUSION The endophytic fungus Phomopsis liquidambaris B3 may become an effective tool to relieve rice spikelet rot disease. © 2020 Society of Chemical Industry.

In this study, the color of the dry fruiting bodies, fresh weight (FW): dry weight (DW) ratio, amino acids, and total phenolics, which are of nutritional or commercial interest, were compared among different drying temperature treatments. The effect of rehydration methods and color protection reagents on the fruiting body color, polyphenol oxidase (PPO) activity, and browning inhibition rate were evaluated. The results showed that drying with hot air at 65℃ was quickest and resulted in a better color without compromising the FW:DW ratio and rehydration ratio of the fruiting bodies. Furthermore, some reactions that occurred under high temperatures increased the content of protein, amino acids, and total phenolics. Soaking after boiling was the most suitable rehydration method, leading to the lowest PPO activity (39.87 ± 1.35 U/g). All of the four analyzed color protection reagents could significantly inhibit the browning of Yu Muer fruiting bodies under room temperature water rehydration conditions, with a citric acid content of 6 g/L showing the best performance. These results provide technical support for the development of the Yu Muer industry and for promoting the commercial processing of Yu Muer fruiting bodies slices.

Wampee fruit is a popular fruit cultivar in South‐East Asia due to its high levels of nutrients and antioxidants; however, pericarp browning leads to a short storage life with great economic loss during years. The purpose of this work was to determine whether postharvest ethanol fumigation affected pericarp browning development of wampee fruit during 12 days of storage at 8 ± 0.5°C, and if so, how it is related to phenol metabolism and how it affects quality attributes and antioxidant systems during storage. After fruits were fumigated with 100, 300, 500, and 800 μl/L for 5 hr at 22 ± 0.5°C, ethanol significantly reduced the development of pericarp browning by increasing total phenolics (TP) content and decreasing the activity of polyphenol oxidase (PPO), especially in 500 μl/L ethanol treatment. Additionally, ethanol delayed the losses in fruit firmness (FF), soluble solid content (SSC), and titratable acidity (TA), retarded weight loss and accumulation of malondialdehyde (MDA) content and maintained relatively high contents of ascorbic acid (AsA), total flavonoids (TF), and total antioxidant capacity (TAC) and activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). In conclusion, results demonstrated that postharvest ethanol fumigation in wampee fruit has ability to reduce pericarp browning development by regulating phenol metabolism and enhancing antioxidant systems., Ethanol fumigation reduced the development of pericarp browning; ethanol fumigation delayed the losses in firmness, the degradation of TSS, TA, and VC of wampee fruit. Ethanol fumigation maintained high contents of AsA, TF, and TAC and activities of SOD, CAT, POD in wampee fruit.

Walnut (Juglans regia) is economically important for both its wood and nut nutritional value, but it is susceptible to diseases such as walnut bacterial blight, caused by Xanthomonas arboricola pv. juglandis (Xaj). Walnuts contain many phenolic compounds, providing a good model on which to study polyphenol oxidase (PPO). We inoculated the detached walnut fruits of cultivars Ford, Chandler, Franquette, Robert Livermore, and Payne with Xaj and measured the induction of PPO activity in infected sites and adjacent to infected sites. Compared to infected and uninfected sites, PPO activity was induced significantly in areas adjacent to infected sites in all cultivars except Ford. Ford and Franquette, presenting the lowest and highest PPO activity, showed the largest and smallest mean diameter spots in response to Xaj, respectively. Polyacrylamide gel electrophoresis confirmed monophenol oxidase activity of walnut PPO in the assessed tissues. Then, we revealed the antipathogenic potential of walnut PPO through Agrobacterium tumefaciens‐mediated walnut JrPPO1 gene transfer into tobacco (Nicotiana tabacum). Two transformed tobacco lines overexpressing the JrPPO1 gene were regenerated successfully and challenged with Pseudomonas syringae pv. tabaci. Transgenic lines showed significantly higher PPO activity and lower disease severity to the pathogen compared to the control. However, a significant difference in disease severity and PPO activity level was observed between the two transgenic lines. Our results demonstrate a potential defence‐related role of PPO in transgenic tobacco and its induction in areas adjacent to infection sites in walnut cultivars treated with Xaj.

Taking betel nut (Betel catechu L.) kernel as raw materials, to analyze the browning mechanism of betel nut kernel. First, we extract and separate the phenolic substances and polyphenol oxidase (PPO) from the betel nut kernel and then find out how O2 penetrates into the kernel, study the above 3 key factors of enzymatic browning so as to prove the possibility of enzymatic browning, and further study the browning products to clarify the mechanism of browning of betel nut kernel during storage process. The results showed that 11 kinds of phenolic compounds were isolated and identified from the betel nut kernel by liquid chromatography–mass spectrometry, among which chlorogenic acid was the highest, followed by dopamine and L‐epicatechin, and other contents were relatively low. Meanwhile, PPO was also separated from the betel nut kernel by DEAE–Sepharose Fast Flow and Phenyl–Sepharose 6 Fast Flow column chromatography. On this basis, scanning electron microscopy showed that the damage of the betel nut tissue was aggravated with the prolonged storage time, the wax was gradually decomposed, and the stratum corneum of the peel is destroyed in a honeycomb‐shaped; the lignification of the flesh was aggravated, and the interstitial space was increased; and the crack of the kernel membrane was also enlarged. These changes of structure contribute to increase gas exchange within and outside the organization, including the entry of O2. Finally, the oxidation products generated from simulated reaction of chlorogenic acid, dopamine, and epicatechin with purified PPO under aerobic conditions in vitro were compared with the products extracted from naturally brown betel nut, and the same absorption spectra were found. Therefore, it indicates that the browning of betel nut kernel is an enzymatic browning caused by the reaction of phenolic substrates were oxidized by PPO.

The effect of iron oxide nanoparticle (NP) at four concentrations (0, 30, 60 and 90 ppm) and salinity at three levels (0, 50 and 100 mM) were investigated on rosmarinic acid (RA) production in 5-week-old Moldavian balm (Dracocephalum moldavica L.) plants. Salinity and spraying iron oxide NPs significantly affected tyrosine (Tyr), phenylalanine (Phe) and proline (Pro) amino acids content, Phenylalanine Ammonia-Lyase (PAL), Tyrosine Aminotransferase (TAT) and Rosmarinic Acid Synthase (RAS) genes expression levels, RA content, Polyphenol Oxidase (PPO), PAL and Superoxide Dismutase (SOD) activities, malondialdehyde (MDA) content and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity. PAL, TAT and RAS genes expression rate and content of RA were enhanced in Moldavian balm plants exposed by NaCl + NPs. The results of high performance liquid chromatography (HPLC) revealed that simultaneous application of 50 mM NaCl and 90 ppm NPs increases the RA content in leaf by 81.15% as compared to control plants. The Tyr and Phe contents decreased in Moldavian balm plants exposed to salt stress. Application of NPs had a positive effect on the content of these amino acids. Proline content increased under salinity stress and application of iron NPs induced a significant increase in the Pro content of leaf. The results revealed that PAL, PPO and SOD enzymes activities increased under salinity conditions. The highest activity of PPO and SOD was observed in 100 mM NaCl + 60 ppm NPs treatment. Simultaneous application of 100 mM NaCl + 90 ppm NPs increased the MDA content and DPPH radical scavenging activity compared to control plants. It can be concluded that the application of appropriate levels of NPs moderates the effect of salinity stress in D. moldavica L. and results in an increased amount of RA compared to control plants.

We investigated the effects and possible mechanisms of Bacillus amyloliquefaciens NCPSJ7 against the gray mold caused by Botrytis cinerea in the postharvest Red Globe grapes. The disease incidence, lesion diameter, decay index, and some resistance‐related enzymes were evaluated. The antioxidant capacity of grape treated with 1 × 104 CFU/ml B. cinerea alone and combined with 1 × 107 CFU/ml NCPSJ7 was also determined. The results showed that NCPSJ7 + B. cinerea reduced the disease incidence, lesion diameter, and decay index of postharvest grapes and enhanced the activities of polyphenol oxidase, peroxidase, chitinase, and β‐1,3‐glucanase during different storage periods. Furthermore, the oxidative resistance, demonstrated by an escalating trend in the total phenolic content, DPPH free radical clearance rate, reducing power, and superoxide anion clearance rate after lesion presence, was improved. However, NCPSJ7 showed an inhibitory effect on gray mold, but resulted in the reduced antioxidant capacity in the grapes., Bacillus amyloliquefaciens NCPSJ7 reduced the disease incidence, lesion diameter, and decay index of postharvest Red Globe grapes. About 107 CFU/ml of B. amyloliquefaciens NCPSJ7 is effective in inducing resistance against gray mold in Red Globe grapes.

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.

In order to study the effect of volatile organic compounds (VOCs) produced by Bacillus subtilis CF-3 combined with heat treatment on Monilinia fructicola in peach and Colletotrichum gloeosporioides in litchi fruit, fruits were treated with B. subtilis CF-3 VOCs and hot air alone or in combination. The quality indexes of peach and litchi fruit after treatment and the changes in defense-related enzymes were measured. The results showed that the B. subtilis CF-3 VOCs combined with heat treatment could significantly reduce the rot index of peach and litchi fruit, and effectively maintain firmness and soluble solids content, as well as reduce weight loss of fruits. The combined treatment effectively enhanced the activity of peroxidase (POD), polyphenol oxidase (PPO), catalase (CAT), and superoxide dismutase (SOD) than either treatment alone, and enhanced the resistance of fruit to pathogenic fungi by activating disease-resistant enzymes (phenylalanine ammonia-lyase [PAL], chitinase [CHI], β-1, 3-glucanase [GLU]) activity. In this study, B. subtilis CF-3 VOCs combined with heat treatment maintained the quality and delayed the decline of peach and litchi fruit, providing a theoretical basis for future applications. PRACTICAL APPLICATION: The combination of B. subtilis CF-3 VOCs and heat treatment reduce the extent of M. fructicola and C. gloeosporioides. The combination maintain the quality of peach and litchi better. The combination obviously improve the activity of defense-related enzyme in fruit.

BACKGROUND: Peanut is among the most common of food allergies, and one of its allergens is Ara h 2. A previous study revealed that this allergen was recognized by serum immunoglobulin E (IgE) in over 90% of a peanut‐allergic patient population. Enzymatic cross‐linking is a popular processing method used to tailor food functionality, such as antigenicity. RESULT: The cross‐linking reactions of Ara h 2 were catalyzed by polyphenol oxidase (PPO), and the relevant reaction sites were identified using mass spectrometry and StavroX software. Two pairs of intramolecular cross‐linking peptides and two intermolecular cross‐linking peptides were found. Intramolecular cross‐linking was speculated to occur between ARG¹³¹ (amino acids 116–131) and TYR⁶⁵ (amino acids 63–80) and between TYR⁶⁰ (amino acids 56–62) and ARG⁹² (amino acids 92–102); the intermolecular cross‐linking sites were ARG³¹ with TYR⁸⁴ or TYR⁸⁹ and TYR⁶⁵ or TYR⁷² with ARG⁹² or ARG¹⁰². Three out of four cross‐linking peptides were found in α‐helices, and destruction of this secondary structure resulted in a loose tertiary structure. Although seven linear allergen epitopes were involved in cross‐linking, the IgE binding capacity of protein changed slightly, while its sensitization potential decreased in mouse model. CONCLUSION: Exploring the structural change of Ara h 2 after cross‐linking is beneficial in further understanding the influence of structure on sensitization. This result indicated the future possibility of precision processing on structure of proteins to improve their properties. © 2019 Society of Chemical Industry

The impact of functional solutions (water infusions of radish sprouts, wheat bran (WBE), basil leaves (BLE) and lentil protein hydrolysate) on enzymatic browning of shredded iceberg lettuce was studied. BLE and WBE, limiting enzymatic browning in the highest degree, were tested during cold storage. The best inhibitors of PPO activity in lettuce stored for 8 days were 10% WBE (a decrease by 97%). POD activity was substantially decreased by ascorbic acid (by 75%) and 1% BLE (by 83%). POD and PPO inhibition was reflected in a decrease in enzymatic browning, that is 91% and 88% reduction was found in 8‐day stored lettuce treated with 1% BLE and 1% WBE, respectively. In the case of POD, mixed inhibition was recorded for BLE and WBE, while these solutions acted as competitive inhibitors of PPO activity. The enzymatic browning of shredded iceberg lettuce during cold storage may be effectively suppressed by natural extracts.

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.

This study was conducted to examine the effects of microwave cold plasma (CP) treatment on inactivation of polyphenol oxidase (PPO) of potato. The PPO activity and treatment variables were fit to first-order kinetics, the Weibull model, and the second-order model. The optimum CP-generation power and treatment time for inactivating PPO in the PPO extract were found to be 900 W and 40 min, respectively, which resulted in the highest inactivation of PPO (49.5%). PPO activity after CP treatment of potato slices decreased from 72.4% to 59.0% as the sample surface-to-volume ratio increased from 7.1 to 9.0. CP treatment delayed the browning of potato slices. Microwave CP treatment effectively inactivated PPO in potatoes, demonstrating the potential of CP treatment for controlling PPO activity in foods. PRACTICAL APPLICATION: This study demonstrated that microwave CP treatment, a nonthermal food processing technology, inactivates PPO activity in potatoes. The results showed that the inactivation effect of CP treatment on PPO corresponded to the surface-to-volume ratio of potato slices. Furthermore, this study proposed an enzyme inactivation model that is suitable for predicting the inactivation of PPO activity and confirmed that CP treatment delayed browning in potatoes.

This study evaluated the influence of Lactobacillus plantarum 299v on the consumer quality of legume sprouts. The probiotic‐rich sprouts were produced by soaking the seeds in probiotic water suspension and further sprouting at 25 °C for 4 days. The enrichment of the sprouts with L. plantarum 299v only slightly affected the sensory quality ‐ the overall acceptability of the probiotic‐rich sprouts was usually higher. The probiotic‐rich sprouts exhibited increased activity of polyphenol oxidase (the highest activity in the mung bean preparations ‐ 73.97 U mg⁻¹ of protein). The peroxidase activity was not altered. The probiotic enrichment increased the phenolic content by 25%, 31% and 23% in the soybean, adzuki and mung bean preparations; however, it was not reflected in the antioxidant activities. The changes in the activity of enzymes involved in mobilisation of stored material (starch and proteins) and the increased content of phenolics only slightly modified the bioavailability of nutrients.

Drought and salinity stress highly affect the plant growth and production around the world. Secondary metabolites play a main role in adaptation to the environment and in overcoming stress conditions. In order to investigate the effect of drought and salinity, alone or in combination, on secondary metabolism-related enzyme activities, plant hormones and yield parameters, a greenhouse pot experiment was conducted using two cotton genotypes Zhongmian 23 (salt tolerant) and Zhongmian 41 (salt sensitive). Results showed that single and combined drought and salinity stresses caused remarkable decrease in plant height, bolls and lint yield in the order as follows: D + S > salinity > drought, and Zhongmian 41 > Zhongmian 23. Lower H2 O2 and superoxide but higher proline content and secondary metabolism-related enzyme activities were observed in Zhongmian 23 under drought and salinity, both alone and combined, compared with control in Zhongmian 41. Our findings suggest that controlling reactive oxygen species (ROS) levels and increasing activities of secondary metabolism-related enzymes in Zhongmian 23 might be an effective mechanism to reduce the negative effects of drought and salinity stress. However, cinnamyl alcohol dehydrogenase (CAD), and shikimate dehydrogenase (SKDH) activities were markedly decreased in Zhongmian 41 under salinity stress alone as compared with control. Meanwhile, Zhongmian 23 had higher expression levels of genes related to secondary metabolism (c.f. phenylalanine ammonia-lyase, PAL; polyphenol oxidase, PPO and CAD) under the three stresses compared to Zhongmian 41. The content of flavonoids and phenols were significantly enhanced under drought and D + S, with higher accumulation in Zhongmian 23. Phenols content in Zhongmian 23 remained unchanged under salinity as relative to control, but were significantly reduced in Zhongmian 41. In addition, callose content, chitinase activities and abscisic acid (ABA) and Indole-3-acetic acid (IAA) were more induced in Zhongmian 23 under drought, salinity and D + S, than in Zhongmian 41. Our results suggest that high tolerance to D + S stress in Zhongmian 23 is closely related to elevated callose, chitinase, flavonoids and phenols contents and higher secondary metabolism-related enzyme activities and their transcript levels.

Background: Zinc (Zn) fertilization has been reported to improve the quality and storability of many fruits, but the mechanism had not been systematically studied. In this study, the effect of preharvest 0.2% zinc sulfate (ZnSO4 ) spray on the storability of longan fruits was investigated.; Results: The preharvest ZnSO4 spray did not significantly influence the quality but increased the Zn content in longan pericarp by 12.5-fold. More importantly, the treatment significantly reduced the rotting rate, pericarp browning, and aril breakdown of longan fruits stored at room temperature and low temperature. Physiological and biochemical results indicated that the treatment resulted in higher water retention capacity and inhibited the degradation of cellulose, pectin, flavonoid, and phenolics of longan pericarp at the late stages of storage. Consistent with these results, the activity of cellulase, polygalacturonase, polyphenol oxidase, and lipoxygenase was significantly inhibited in the ZnSO4 -treated longan pericarp at the late stages of storage.; Conclusion: Higher Zn content in the ZnSO4 -treated longan pericarp might help to enhance the resistance against microbial infection, inhibit the hydrolysis of cell wall components, and thus effectively protected the cell wall components, maintained the cellular compartmentation, and prevented the phenolics and flavonoid from degradation by browning-related enzymes. © 2018 Society of Chemical Industry.; © 2018 Society of Chemical Industry.

Background and objectives: Durum wheat (Triticum turgidum L. ssp. durum) may have advantages over bread wheat in making various styles of noodles due to low polyphenol oxidase (PPO) and high yellow pigment. However, the very hard kernel texture of durum wheat may pose a hindrance to its expanded utilization. The development of soft kernel durum wheat prompted this research into comparing the color of white salted, alkaline, and egg noodle sheets over time and three levels of hydration for one durum and 10 hexaploid wheat varieties. Findings: All noodle sheets darkened over time and “varieties” was a major source of variation. PPO activity was a poor predictor of noodle sheet brightness (L*) at 48 hr for all three styles of noodle. The soft durum variety “Soft Svevo” exhibited about average brightness but tended to have low discoloration (ΔL*) over time. The range in the green‐red axis, a*, was small, and all noodle sheets exhibited a small positive increase with most values near the neutral gray value. All noodle sheets were yellow, with Soft Svevo being markedly more yellow in all three formulations. The alkaline pH increased average yellowness by three units overall, but in Soft Svevo, not at all. In some varieties, a decrease in yellow color occurred from 6 to 48 hr. Conclusions: The low PPO activity of Soft Svevo did not predict an advantage in white salted, alkaline, and egg noodle sheet brightness over the “best” hexaploid wheat varieties. The reason was not resolved but may be related to marked differences in protein content of the flours. Significance and novelty: Soft kernel durum wheat exhibited some advantages over hexaploid wheat, particularly in low discoloration (ΔL*) and high yellow color. In no way was soft durum found to be inferior to hexaploid wheat.

Zoospores of the oomycete Saprolegnia ferax release adhesive material from K-bodies at the onset of attachment to substrates. To understand more fully how K-bodies function in adhesion, enzyme activity was investigated cytochemically in secondary zoospores. Presence of catalase, a marker enzyme for microbodies, was explored in the diaminobenzidine (DAB) reaction. Although pH 9.2 DAB-staining characteristic of catalase activity was detected in the granular matrix regions of K-bodies, reaction controls indicated that the reaction was due to oxidative enzyme activity other than catalase. Because polyphenol oxidase (PPO) is another metal-containing enzyme capable of oxidizing DAB, activity of this enzyme was tested with a more specific substrate, dihydroxyphenylalanine (DOPA). In the DOPA procedure, reaction product was exclusively localized within K-bodies, indicating the presence of PPO. Results with three methods of reaction controls (elimination of substrate, addition of a PPO enzyme inhibitor, and heat-inactivation of enzymes) all supported the presence of PPO in K-bodies. This study highlights potential roles for K-body PPO in stabilization of adhesion bodies by: cross-linking matrix phenolic proteins or glycoproteins as K-bodies discharge adhesives onto substrates, or polymerizing phenolics protective against microbial attacks of the adhesion pad.

Background: In the present study, we investigated the role of ornithine decarboxylase (ODC) in the methyl jasmonate (MeJA)-regulated postharvest quality maintenance of Agaricus bisporus (J. E. Kange) Imbach button mushrooms by pretreating mushrooms with a specific irreversible inhibitor called α-difluoromethylornithine (DFMO) before exposure to MeJA vapor.; Results: Mushrooms were treated with 0 or 100 µmol L-1 MeJA or a combination of 120 µmol L-1 DFMO and 100 µmol L-1 MeJA, respectively, before storage at 4 °C for 21 days. Treatment with MeJA alone induced the increase in ODC activity whereas this effect was greatly suppressed by pretreatment with DFMO. α-Difluoromethylornithine strongly attenuated the effect of MeJA on decreasing cap opening, slowing the decline rate of soluble protein and total sugar, and accumulating total phenolics and flavonoids. α-Difluoromethylornithine pretreatment also counteracted the ability of MeJA to inhibit polyphenol oxidase and lipoxygenase activities, and malondialdehyde production, and to stimulate superoxide dismutase and catalase activities. It also largely downregulated MeJA-induced accumulation of free putrescine (Put).; Conclusion: These results reveal that ODC is involved in MeJA-regulated postharvest quality retention of button mushrooms, and this involvement is likely to be associated with Put levels. © 2018 Society of Chemical Industry.; © 2018 Society of Chemical Industry.

BACKGROUND The objective of the present work was to study the effect of high-power ultrasound (HPU) on the microflora, enzymes and some quality attributes of a strawberry drink and to provide a theoretical basis for strawberry drink processing conducive to the development of more nutritious and healthier strawberry drinks. RESULTS Fresh strawberry drink was subjected to HPU treatment at 20 kHz (242, 605 and 968 W cm-2 ) for 2, 4, 6, 8 and 10 min in an ice bath. Results showed that polyphenol oxidase (PPO), pectin methyl esterase (PME) and β-glucosidase activities were decreased by 44.90, 89.11 and 84.71% respectively at 968 W cm-2 for 10 min. Lower L*, a* and b* values and higher browning degree (BD) were observed in HPU-treated samples, resulting in a significant increase in ΔE value (P

One of the main problems in the button mushroom industry is the rapid deterioration of fruit bodies after harvest. Today, nanotechnology has become a more reliable technique to improve the quality of products in food packaging. In the present study, the effectiveness of chitosan nanoparticles containing Citrus aurantium essential oil on postharvest quality of white button mushroom was examined and compared to essential oil fumigation and control treatments.; Results: Based on high-resolution transmission electron microscopy and dynamic light scattering, nanoparticles exhibited a spherical shape of 20-60 nm diameter. The results revealed that the application of chitosan nanoparticles loaded with C. aurantium oil significantly decelerated the rate of color change, weight loss and firmness compared to fumigation with essential oil and control treatments. Treatment of fruit bodies with chitosan nanoparticles loaded with C. aurantium oil promoted the accumulation of phenolic compounds and ascorbic acid, and resulted in increases in catalase and superoxide dismutase and a decrease in polyphenol oxidase activities, as the highest antioxidant capacity was observed after 15 days of cold storage.; Conclusion: This present research demonstrates that gradual release of C. aurantium essential oil from chitosan nanoparticles could be an effective and practical method for extending the shelf life of white button mushroom up to 15 days without significant decrease in antioxidant capacity. © 2018 Society of Chemical Industry.; © 2018 Society of Chemical Industry.

The effect of hydrogen sulfide (H2 S) on the inhibition of the surface whitening of fresh-cut carrots was investigated. Whitening index; H2 O2 and malondialdehyde (MDA) contents; activities of catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD); and antioxidant capacities were evaluated.; Results: H2 S treatment significantly inhibited the surface whitening of fresh-cut carrots (P

Lectins known to possess an additional enzymatic function are called leczymes. Previous studies reported a unique polyphenol oxidase (PPO) activity in DLL-II—a leczyme from Dolichos lablab. DLL-II shares a high sequence and structural homology with DBL—another leczyme from Dolichos biflorus. Incidentally, DBL possesses lipoxygenase activity, but not the PPO activity. Legume lectins usually possess two metal-binding sites A and B. Although these sites are conserved in both DBL and DLL-II, site A in DLL-II is occupied by Mn2+ and site B by Ca2+. In contrast, DLL-II binds Cu2+ and Ca2+ at sites A and B, respectively. Here, investigating the structural basis of PPO activity in DLL-II, we find that the PPO activity is only dependent on Cu2+, but not Ca2+; and the lectin activity requires only Ca2+. Further, our analysis suggests that an alternative mechanism of PPO reaction may be operative in DLL-II, which involves a mononuclear Cu2+ metal center; this is in contrast to the bi-nuclear Cu2+ metal center commonly observed in all PPOs. Importantly, structural and computational approaches employed here, we hypothesize possible PPO binding sites and the corresponding migration channels for accessing the active site.

Radio frequency (RF) preprocessing combined with pulsed electric field (PEF) processing was employed to inactivate polyphenol oxidase (PPO) in apple juice. PPO enzyme levels, loss of total phenolic content (TPC), colours and volatile components in the apple juice were subsequently determined and compared with conventional processing methods (60 °C for 10 min and 70 °C for 10 min). Results indicated that, when the apple tissue was preprocessed using RF for 10 min, the residual activity of PPO decreased to 13.57%; when the squeezed juice was processed by PEF, the residual activity decreased to about 5% at 15–35 kV cm⁻¹ for 400 μs. RF treatment caused no significant loss in TPC. Compared with the conventionally processed samples, the apple juice that was RF‐treated for 10 min and PEF‐treated at 15 kV cm⁻¹ for 400 μs increased its lightness and maintained its fresh‐like flavour.

This study evaluated the effects of grinding at atmospheric pressure (control), under vacuum (∼2.67 kPa), or with modified atmosphere (N2and CO2) on the browning, antioxidant activity, phenolics, and oxidative enzyme activity of apples as a function of time. The control group was affected most, showing distinct browning and losing most of the antioxidant activity and concentrations of the main phenolic compounds. The modified atmosphere groups retained color, antioxidant activity, and phenolic compounds better than the control group. Least changes were obtained with vacuum grinding, particularly in terms of preventing enzymatic browning and oxidation of antioxidants apples. At 12 h after grinding, vacuum‐ground apples retained total phenolic contents 5.32, 1.54, and 1.49 times higher than control, nitrogen gas, and carbon dioxide gas‐ground samples, respectively. The oxidative enzyme activity, including that of polyphenol oxidase and peroxidase, decreased in the control and modified atmosphere group, but they were maintained in the samples ground under the vacuum. In this study, we found that grinding with modified atmosphere or vacuum conditions could effectively prevent browning as well as loss of phenolic compounds and antioxidant activity of ground apples. These results can help scientists and engineers build better grinding systems for retaining nutrient and quality factors of ground apples. In addition, these results may be useful to other fruit and vegetable industries that wish to retain fresh‐like quality and nutritional value during grinding and storage.

Rapid wound healing would be critical for successful long-term storage of fruits and vegetables. However, there was no direct evidence for the requirement and efficiency of oxygen in the fruit wound-healing process. This study was conducted to investigate the role of oxygen in wound-induced suberization by analyzing melanin, suberin polyphenolics (SPPs) and related enzymes in half-cut kiwifruits exposed to 100%, 50%, 21% and 0% oxygen.; Results: By 3 days after wounding, the wound surface of kiwifruit in high (50 and 100%) oxygen appeared as a continuous layer of melanin and SPPs underneath, which effectively prevent excessive water vapor loss from the fruit halves. In contrast, melanin and SPPs deposition in the wound surface in 0% oxygen was significantly reduced, with high water vapor loss. Rapid decrease of soluble phenolic acids (caffeic, p-coumaric, ferulic acids) was coupled with the increase of bound ferulic acid (coniferyl diacetate) especially in high oxygen by 9 days after wounding. Meanwhile, high oxygen enhanced peroxidase, catalase, phenylalanine ammonia-lyase, and polyphenol oxidase activities.; Conclusion: Oxygen is required for wound-induced melanin and SPPs formation, and high oxygen is effective in promoting wound suberization in postharvest kiwifruit. © 2017 Society of Chemical Industry.; © 2017 Society of Chemical Industry.

Changes in polyphenols have important effects on the quality (especially color) and health benefits of dried apricots. SO2 concentration, storage and the activities of polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) were factors which had significant effects on polyphenols. Polyphenol profile and activities of PPO and PAL in sulfured dried apricots (SDAs, 0, 451, 832, 2112 and 3241 mg SO2 kg-1 ) were monitored during storage at 4, 20 and 30 °C for 379 days for the first time.; Results: Even the lowest SO2 concentration (451 mg kg-1 ) was sufficient to inactivate PPO during the entire storage period. However, while SO2 led to the increase in PAL activity of the samples (r = 0.767) before storage, PAL activities of SDAs decreased during storage. After 90 days of storage, PAL activity was determined in only non-sulfured dried apricots (NSDAs) and dried apricots containing 451 mg SO2 kg-1 . Although the major polyphenol in NSDAs was epicatechin (611.4 mg kg-1 ), that in SDAs was chlorogenic acid (455-1508 mg kg-1 ), followed by epicatechin (0-426.8 mg kg-1 ), rutin (148.9-477.3 mg kg-1 ), ferulic acid (23.3-55.3 mg kg-1 ) and gallic acid (2.4-43.6 mg kg-1 ). After storage at 30 °C for 379 days, the major polyphenol in SDAs was gallic acid (706-2324 mg kg-1 ). However, the major polyphenol in NSDAs did not change after storage. The highest total polyphenol content was detected in SDAs containing 2112 mg SO2 kg-1 and stored at 30 °C.; Conclusion: To produce dried apricots having high polyphenol content, ∼2000 mg SO2 kg-1 should be used. Low storage temperature (

A comparative study of the properties of membrane‐bound polyphenol oxidase (mPPO) from three apple cultivars, namely Red Fuji (FJ), Granny Smith (GS) and Golden Delicious (GD), was carried out for the first time. Data indicate that mPPOs from three cultivars exhibit significantly different properties. GS mPPO had the strongest affinity to catechol, but FJ mPPO had the highest maximum velocity. Red Fuji (FJ) mPPO had the significantly higher activity than those of GD and GS mPPOs. Red Fuji (FJ) mPPO had the highest activity at pH 8.00, while GD and GS mPPOs at 4.50 and 7.50–8.00, respectively. Red Fuji (FJ) mPPO was more stable than GD and GS mPPOs over the pH range of 5.0–8.5. The optimal temperature for GS mPPO was within 70–75 °C, which is higher than those for mPPOs from FJ and GD. Thermal inactivation of the three mPPOs followed a first‐order kinetic model with different inactivation kinetic parameters.