Rhizopus rot of peach fruits could be significantly suppressed by Pichia membranefaciens. Polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonium-lyase (PAL) activities induced by inoculation with P. mem...Rhizopus rot of peach fruits could be significantly suppressed by Pichia membranefaciens. Polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonium-lyase (PAL) activities induced by inoculation with P. membrane faciens or R. stolonifer were studied in postharvest peach fruits. The activities of PPO and PAL in peaches increased significantly after being inoculated with P. membrane faciens + R. stolonifer by 24 h, the activities maintained at a high level throughout the experiment. Under the condition of infected with R. stolonifer alone, activity of PPO and PAL could also increased, but the levels were lower than those treated with P. membrane faciens+ R. stolonifer. However, fruits inoculaed with P. membrane-faciens + R. stolonifer or R. stolonifer alone did not stimulated POD activity. The results suggest that the activation of these defense enzymes is involved in the action of P. membrane faciens against R. stolonifer.展开更多
To improve the processing quality of potatoes,phosphate buffer extract(PBE),50%ethanol(E50),and aqueous extract(AE)of tartary buckwheat seedlings were evaluated for their ability to inhibit the enzymatic browning of p...To improve the processing quality of potatoes,phosphate buffer extract(PBE),50%ethanol(E50),and aqueous extract(AE)of tartary buckwheat seedlings were evaluated for their ability to inhibit the enzymatic browning of potatoes.The results suggest that all extracts of tartary buckwheat seedlings exert significant inhibitory effects on the polyphenol oxidase(PPO)activity in potatoes.The relative concentrations required for a 50%reduction in the PPO activity(IC50)were 0.21,0.28 and 0.41 mg mL^-1,for PBE,E50 and AE,respectively.The strongest inhibitory activity was observed for PBE,followed by E50 and AE.Four flavone compounds in the PBE of tartary buckwheat seedlings(i.e.,rutin,kaempferol-3-O-rutinoside,quercetin,and kaempferol)were identified by high-performance liquid chromatography.These compounds were subsequently evaluated for their roles in the inhibition of PPO from potatoes using a model system.The results indicated that rutin exhibited the highest inhibition rate on the PPO of potato.A synergistic inhibitory effect was observed by mixing rutin,kaempferol-3-Orutinoside,quercetin,and proteins.The inhibitory patterns of rutin,kaempferol-3-O-rutinoside,and quercetin on the enzyme were noncompetitive and reversible,with inhibitory constants of 0.12,0.31,and 0.40 mg mL^-1,respectively.Flavonoids from tartary buckwheat seedlings may exhibit a common mechanism with phenolic compounds,involving the blockage of the reaction of oxygen with PPO leading to the inhibition of the enzymes involved in browning.Based on these results,extracts of tartary buckwheat seedlings can be used as potent natural inhibitors.展开更多
In this study an effort has been made to use plant polyphenol oxidases; potato （Solanum tuberosum） and brinjal （Solanum melongena）, for the treatment of various important dyes used in textile and other industries....In this study an effort has been made to use plant polyphenol oxidases; potato （Solanum tuberosum） and brinjal （Solanum melongena）, for the treatment of various important dyes used in textile and other industries. The ammonium sulphate fractionated enzyme preparations were used to treat a number of dyes under various experimental conditions. Majority of the treated dyes were maximally decolorized at pH 3.0. Some of the dyes were quickly decolorized whereas others were marginally decolorized. The initial first hour was sufficient for the maximum decolorization of dyes. The rate of decolorization was quite slow on long treatment of dyes. Enhancement in the dye decolorization was noticed on increasing the concentration of enzymes. The complex mixtures of dyes were treated with both preparations of polyphenol oxidases in the buffers of varying pH values. Potato polyphenol oxidase was significantly more effective in decolorizing the dyes to higher extent as compared to the enzyme obtained from brinjal polyphenol oxidase. Decolorization of dyes and their mixtures, followed by the formation of an insoluble precipitate, which could be easily removed simply by centrifugation.展开更多
To study insecticidal mechanism of terpinen-4-ol, a main insecticidal composition in the essential oil of Sabina vulgaris, the 5th instar larvae of Mythimna separta, were investigated with terpinen-4-ol by topical app...To study insecticidal mechanism of terpinen-4-ol, a main insecticidal composition in the essential oil of Sabina vulgaris, the 5th instar larvae of Mythimna separta, were investigated with terpinen-4-ol by topical application. The activities of phosphatase, glutathione S-transferase （GSTs）, cytochrome P450 （P450）, and polyphenol oxidase （PPO） of tested insects were determined in all poisoning stages, including exciting stage, convulsing stage, paralysis stage, and recover stage. The result showed that the activities of both acid phosphatase （ACP） and alkaline phosphatase （AKP） in treated insects were induced by terpinen-4-ol, but ACP was inhibited in paralysis stage. The activities of GSTs were inhibited in exciting stage, convulsing stage, and paralysis stage, but gradually recovered in recover stage. O-demethylase activity of cytochrome P450 was inhibited by terpinen-4-ol, and the inhibition rate in all poisoning stages were 26.27, 46.03, 80.24, and 90.22%, respectively. PPO activities were strongly inhibited by terpinen-4-ol both in vitro and in vivo. In conclusion, the activities of P450, GSTs, and PPO could have relation with toxicity of terpinen-4-ol against larvae of the Mythimna separta, but recover stage of the poisoning insects might be related to GSTs induced. As a new insecticide or synergist, terpinen- 4-ol has a potential value in field of insecticide resistance management.展开更多
[Objective] This study aimed to investigate the enzymatic kinetics of polyphenol oxidase in peel of Nephelium lappaceum to explore the environmental factors affecting its catalytic activity. [ Method ] With N. lappace...[Objective] This study aimed to investigate the enzymatic kinetics of polyphenol oxidase in peel of Nephelium lappaceum to explore the environmental factors affecting its catalytic activity. [ Method ] With N. lappaceum peel as the experimental material and catechol as substrate, effects of temperature, pH, four inhibitors （EDTA, Vc, sodium bisulfite and citric acid） and substrate concentration on the activity of polyphenol oxidase were investigated. [ Result] The optimal temperature for polyphenol oxidase in N. lappaceum peel was 40 %, and the optimal pH was 6.8. EDTA, Vc, sodium bisulfite and citric acid all showed ideal in- hibitory effects on the activity of polyphenol oxidase; specifically, EDTA had the strongest inhibitory effect. [ Conclusion] At low temperature, EDTA, Vc, sodi- um bisulflte and citric acid with certain concentrations can inhibit the catalytic activity of polyphenol oxidase in peel of N. lappaceum, extend the storage and trans- portation time of N. lappaceum fruit, and inhibit the browning. This study provides theoretical basis for the development and utilization of polyphenol oxidase in peel of N. lappaceum.展开更多
[Objectives] To study the polyphenol oxidase (PPO) activity and total phenol content of Docynia indica .[Methods] The tender branches and petioles of the medicinal and edible plant D. indica were used as experimental ...[Objectives] To study the polyphenol oxidase (PPO) activity and total phenol content of Docynia indica .[Methods] The tender branches and petioles of the medicinal and edible plant D. indica were used as experimental materials, and the annual changes of total phenol content and polyphenol oxidase (PPO) activity were analyzed.[Results] pH 7.0 was the optimum value of polyphenol oxidase activity in D. indica plants;the best substrate was catechol with the concentration of 0.15 mol/L;the optimum temperature was 25 ℃.[Conclusions] The total phenol content of D. indica plants was the lowest in April, May and September of each year. The polyphenol oxidase activity of D. indica plants at flowering and fruiting stage was significantly higher than that at pre-flowering stage.展开更多
The browning of fruits can be considered as an enzymatic oxidation which is believed to be one of the main causes of quality loss during post-harvest handling. The enzymes responsible for this are the oxidoreductases;...The browning of fruits can be considered as an enzymatic oxidation which is believed to be one of the main causes of quality loss during post-harvest handling. The enzymes responsible for this are the oxidoreductases;the polyphenol oxidase (PPO) (monophenol, o-diphenol, oxygen oxidoreductase;EC 1.14.18.1) belongs to this group. This enzyme, which is found in the sapodilla plum (Achras sapota), was purified using a phenylsepharose and a SephacrylS-200 columns. The molecular weight of the purified enzyme was estimated to be about 66 kDa by gel filtration and 29 kDa by SDS-PAGE. A single protein band was found using the latter system (SDS-PAGE), which shows that the PPO of the pulp of the sapodilla plum may be composed of two protein subunits with similar molecular weight. The optimum pH was 7.0 and the optimum temperature 60℃. The most effective inhibitors tested were ascorbic acid, sodium metabisulfite and acetic acid.展开更多
The objective of this research was investigated the effect of polyphenol oxidase microwave treatment on phenolic composition, antioxidant activity and microstructure of loquat fruit. Phenolic profile of methanolic ext...The objective of this research was investigated the effect of polyphenol oxidase microwave treatment on phenolic composition, antioxidant activity and microstructure of loquat fruit. Phenolic profile of methanolic extracts prepared from fresh, and microwave-treated samples were analyzed. Antioxidant activity was also evaluated by 2,2’-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS?+) and 1,1-diphenyl-2-picrylhydrazyl (DPPH+) methods. In addition, polyphenol oxidase inactivation was carried out using a response surface methodology to establish the optimal conditions of treatment. The phenolic content of fresh mesocarp was 311 ± 0.60 mg gallic acid equivalents (GAE)/100g dry weight (DW) and that of microwave-treated mesocarp was 1230 ± 0.36 mg GAE/100g DW. Total phenolic content of water/ methanol extract significantly increases after microwave treatment rather than methanolic extract of fresh loquat. Five glycoside phenolics were identified by HPLC-DAD-MS as 3-caffeoylquinic acid, 3-p-coumaroylquinic acid, 5-caffeoylquinic acid and quercetin-3-O-sambubioside. Methanolic extract of microwave-treated mesocarp showed higher antioxidant activity than that of fresh mesocarp. Thus, polyphenol oxidase inactivation by microwave energy preserved the integrity of phenolic compounds as well as antioxidant activity in mesocarp extracts prepared from loquat fruit. It was also noted that phenolics were more abundant in the microwaved samples than in the fresh samples.展开更多
Polyphenol oxidase, a bi-functional enzyme, has been implicated in enzymatic browning of yam and other tubers in a negative way. The objective of this present study was to examine the activity of polyphenol oxidase in...Polyphenol oxidase, a bi-functional enzyme, has been implicated in enzymatic browning of yam and other tubers in a negative way. The objective of this present study was to examine the activity of polyphenol oxidase in Dioscorea rotundata. Var. laasirin and the efficiency of heat and chemical treatments in inhibiting this enzyme. Crude Polyphenol Oxidase （PPO） of Dioscorea rotundata.Var. Laasirin was isolated and the kinetics studied using the lineweaver-burk plot. The activity of the enzyme was evaluated using spectrophotomeric method. Yam PPO catalyzes oxidation of various substrates with catechol being the most readily oxidized substrate. The Michaelis-Menten constant （Km） and maximum reaction velocity （Vmax） for yam PPO were 0.00037 and 0.3125 respectively. Inhibition data showed that the enzyme had least activity （71.70） when blanched at 95℃ for 7 mins with chemical treatment involving a combination of 0.5% Sodium metabisulphite （Food grade） and 0.5% Ascorbic acid （Food grade）. The activity was highest （83.02） when it was blanched at 95 ℃ for 7 rains. This study has shown that it is possible to inhibit polyphenol oxidase activity in white yam using the chemical pretreatments and processing conditions described in this study for possible adoption in the production of packaged frozen yam chips by food industries.展开更多
The objective was to study the effect of alginate coating on polyphenol oxidase (PPO) activity and colour of ‘Starking’ apple cubes during dehydration with hot air. Apple cubes were dehydrated at 20oC, 35oC, or 40oC...The objective was to study the effect of alginate coating on polyphenol oxidase (PPO) activity and colour of ‘Starking’ apple cubes during dehydration with hot air. Apple cubes were dehydrated at 20oC, 35oC, or 40oC, with a parallel airflow. Analysis of PPO activity, colour (L*, a*, b*) and dry matter were performed along the dehydration process at each temperature. All samples presented a peak in relative PPO activity in the beginning of the drying. Exponential models fitted well the experimental data after the peak. Cubes without coating presented lower PPO activity, suggesting lower browning, than coated samples throughout the dehydration process, for all temperatures. Better results for coated samples were obtained with a perpendicular airflow drying at 40oC, after dipping the whole apple in water at 60oC for 10 min. In order to prevent coated samples from browning, drying by perpendicular airflow preceded by a thermal treatment of the whole apple is required.展开更多
[Objectives]This study was conducted to investigate the effects of embedding conditions on activity and catalytic properties of immobilized polyphenol oxidase.[Methods]Polyphenol oxidase was immobilized in a polymer m...[Objectives]This study was conducted to investigate the effects of embedding conditions on activity and catalytic properties of immobilized polyphenol oxidase.[Methods]Polyphenol oxidase was immobilized in a polymer material by the embedding method,and the optimal immobilization conditions were obtained by single factor tests:CaCl_(2) concentration 2.0%,sodium alginate concentration 2.0%,immobilization time 2 h and mass ratio of enzyme to carrier 10 mg/100 g,under which the immobilized enzyme activity was 93.33 U/g.Under the above conditions,the properties of polyphenol oxidase immobilized by sodium alginate(A-PPO)and free polyphenol oxidase were studied.[Results]The thermostability of A-PPO was better than that of the free enzyme,but the pH stability of A-PPO was inhibited.The Michaelis constant K_(m) values of free polyphenol oxidase and A-PPO were 0.37 and 0.48 mmol/L,respectively,and the maximum reaction rate V_(max) values were 0.38 and 0.51 mmol/(L·g),respectively.[Conclusions]This study provides a theoretical basis for the study of the properties of polyphenol oxidase.展开更多
The use of food additives with xanthine oxidase (XO) inhibitory activity offers an alternative approach to hyperuricemic and gout disease treatment, and provides an example of antioxidant nutraceutics. The in vitro an...The use of food additives with xanthine oxidase (XO) inhibitory activity offers an alternative approach to hyperuricemic and gout disease treatment, and provides an example of antioxidant nutraceutics. The in vitro and in silico XO inhibitory activity of polyphenols from Uruguayan Tannat grape pomaces and propolis extracts was evaluated as well as the scavenging capacity of said compounds. When comparing propolis and grape pomace samples, the in vitro studies demonstrated that polyphenols extracted from propolis are more active as free radical scavengers than those from Tannat grape pomace. Both natural products effectively inhibited XO but the capacity of phenols present in GP is higher than the one present in P. The high content of anthocyanins in GP, absent in P, could account for this observation. In silico assays allowed us to determine relevant ligand-receptor interactions between polyphenols, from a database built with previously reported polyphenols from both natural products, and the active site of XO. The in silico results showed that compound (E)-isoprenylcaffeate from propolis was the best potential XO inhibitor displaying hydrophobic aromatic interaction between the conjugated ring of the caffeate moiety and polar interactions between hydroxyl groups from caffeate with the active site polar residues. Among grape pomaces, the Cyanidin-3-O-(6-(E)-p-coumaroyl)-glucoside was the best XO inhibitor;its moiety oxychromenyl being relevant to the docking stabilization. All these results lead us to propose Uruguayan propolis and Tannat grape pomace extracts as food additives as well as phytopharmaceuticals to decrease the uric acid levels in gout disease and to act against oxidative stress.展开更多
Polyphenolic compound in processing apple （Malus domestica Borkh.） varieties and the relationship between polyphenol content and enzymatic browning were studied to provide reference for raw material selection and pr...Polyphenolic compound in processing apple （Malus domestica Borkh.） varieties and the relationship between polyphenol content and enzymatic browning were studied to provide reference for raw material selection and processing method optimization. The content of polyphenol compound in 10 processing apple varieties （4 cider and 6 juice varieties） were analyzed using the Folin-Ciocalteu method and HPLC. The degree of browning and the activities of polyphenol oxidase were also studied. The content and proportion of the polyphenol varied depending on the variety. Bitter varieties globally showed a higher polyphenol concentration than sweet or acid varieties. Proanthocyanidins, chlorogenic acid, （＋）-catechin, （-）-epicatechin were high-concentrated polyphenols in apple fruits. Phloridzin, the unique polyphenol of apple, was abundant in the bitter variety Frequin rouge fruit. Total polyphenols, proanthocyanidins, （＋）-catechin, and phloridzin had higher correlations with browning. The correlation was low between chlorogenic acid and browning. The polyphenolic profiles were correlated with the apple types. Cider apples contained more polyphenol than juice apple varieties. The content of flavan-3-ol has a close relationship with fruit browning.展开更多
Objective Elevation of reactive oxygen species (ROS), especially the level of superoxide is a key event in many forms of cardiovascular diseases. To study the mechanism of tea polyphenols against cardiovascular diseas...Objective Elevation of reactive oxygen species (ROS), especially the level of superoxide is a key event in many forms of cardiovascular diseases. To study the mechanism of tea polyphenols against cardiovascular diseases, we observed the expressions of ROS-related enzymes in endothelial cells. Methods Tea polyphenols were co-incubated with bovine carotid artery endothelial cells (BCAECs) in vitro and intracellular NADPH oxidase subunits p22phox and p67phox, SOD-1, and catalase protein were detected using Western blot method. Results Tea polyphenols of 0.4 ug/mL and 4.0 ug/mL (from either green tea or black tea) down-regulated NADPH oxidase p22phox and p67phox expressions in a dose-negative manner (P<0.05), and up-regulated the expressions of catalase (P<0.05). Conclusions Tea polyphenols regulate the enzymes involved in ROS production and elimination in endothelial cells, and may be beneficial to the prevention of endothelial cell dysfunction and the development of cardiovascular diseases.展开更多
基金the grants fromthe National Natural Science Foundation of China(NNSF-30170663) the Chinese Academy of Sciences.
文摘Rhizopus rot of peach fruits could be significantly suppressed by Pichia membranefaciens. Polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonium-lyase (PAL) activities induced by inoculation with P. membrane faciens or R. stolonifer were studied in postharvest peach fruits. The activities of PPO and PAL in peaches increased significantly after being inoculated with P. membrane faciens + R. stolonifer by 24 h, the activities maintained at a high level throughout the experiment. Under the condition of infected with R. stolonifer alone, activity of PPO and PAL could also increased, but the levels were lower than those treated with P. membrane faciens+ R. stolonifer. However, fruits inoculaed with P. membrane-faciens + R. stolonifer or R. stolonifer alone did not stimulated POD activity. The results suggest that the activation of these defense enzymes is involved in the action of P. membrane faciens against R. stolonifer.
基金Food Processing Institute of the Guizhou Academy of Agricultural Sciences, Potato Engineering Research Center of Guizhou Province, China for the financial supportsupported by the PhD Programs Foundation of Guizhou Province ([2017]1180)+1 种基金the Youth Fund from Guizhou Academy of Agricultural Science, China ([2017]026)the Scientific and Technical Support Programs of Guizhou Province, China ([2017]2543)
文摘To improve the processing quality of potatoes,phosphate buffer extract(PBE),50%ethanol(E50),and aqueous extract(AE)of tartary buckwheat seedlings were evaluated for their ability to inhibit the enzymatic browning of potatoes.The results suggest that all extracts of tartary buckwheat seedlings exert significant inhibitory effects on the polyphenol oxidase(PPO)activity in potatoes.The relative concentrations required for a 50%reduction in the PPO activity(IC50)were 0.21,0.28 and 0.41 mg mL^-1,for PBE,E50 and AE,respectively.The strongest inhibitory activity was observed for PBE,followed by E50 and AE.Four flavone compounds in the PBE of tartary buckwheat seedlings(i.e.,rutin,kaempferol-3-O-rutinoside,quercetin,and kaempferol)were identified by high-performance liquid chromatography.These compounds were subsequently evaluated for their roles in the inhibition of PPO from potatoes using a model system.The results indicated that rutin exhibited the highest inhibition rate on the PPO of potato.A synergistic inhibitory effect was observed by mixing rutin,kaempferol-3-Orutinoside,quercetin,and proteins.The inhibitory patterns of rutin,kaempferol-3-O-rutinoside,and quercetin on the enzyme were noncompetitive and reversible,with inhibitory constants of 0.12,0.31,and 0.40 mg mL^-1,respectively.Flavonoids from tartary buckwheat seedlings may exhibit a common mechanism with phenolic compounds,involving the blockage of the reaction of oxygen with PPO leading to the inhibition of the enzymes involved in browning.Based on these results,extracts of tartary buckwheat seedlings can be used as potent natural inhibitors.
文摘In this study an effort has been made to use plant polyphenol oxidases; potato （Solanum tuberosum） and brinjal （Solanum melongena）, for the treatment of various important dyes used in textile and other industries. The ammonium sulphate fractionated enzyme preparations were used to treat a number of dyes under various experimental conditions. Majority of the treated dyes were maximally decolorized at pH 3.0. Some of the dyes were quickly decolorized whereas others were marginally decolorized. The initial first hour was sufficient for the maximum decolorization of dyes. The rate of decolorization was quite slow on long treatment of dyes. Enhancement in the dye decolorization was noticed on increasing the concentration of enzymes. The complex mixtures of dyes were treated with both preparations of polyphenol oxidases in the buffers of varying pH values. Potato polyphenol oxidase was significantly more effective in decolorizing the dyes to higher extent as compared to the enzyme obtained from brinjal polyphenol oxidase. Decolorization of dyes and their mixtures, followed by the formation of an insoluble precipitate, which could be easily removed simply by centrifugation.
基金supported by the National Natural Science Foundation of China(30600404)the Key Technologies R&D Program of China during the 10th Five-Year Plan Period(2004BA516A04).
文摘To study insecticidal mechanism of terpinen-4-ol, a main insecticidal composition in the essential oil of Sabina vulgaris, the 5th instar larvae of Mythimna separta, were investigated with terpinen-4-ol by topical application. The activities of phosphatase, glutathione S-transferase （GSTs）, cytochrome P450 （P450）, and polyphenol oxidase （PPO） of tested insects were determined in all poisoning stages, including exciting stage, convulsing stage, paralysis stage, and recover stage. The result showed that the activities of both acid phosphatase （ACP） and alkaline phosphatase （AKP） in treated insects were induced by terpinen-4-ol, but ACP was inhibited in paralysis stage. The activities of GSTs were inhibited in exciting stage, convulsing stage, and paralysis stage, but gradually recovered in recover stage. O-demethylase activity of cytochrome P450 was inhibited by terpinen-4-ol, and the inhibition rate in all poisoning stages were 26.27, 46.03, 80.24, and 90.22%, respectively. PPO activities were strongly inhibited by terpinen-4-ol both in vitro and in vivo. In conclusion, the activities of P450, GSTs, and PPO could have relation with toxicity of terpinen-4-ol against larvae of the Mythimna separta, but recover stage of the poisoning insects might be related to GSTs induced. As a new insecticide or synergist, terpinen- 4-ol has a potential value in field of insecticide resistance management.
基金Supported by Leading Academic Discipline Project of Botany in Guizhou Province ([2011] No.275)College-level Planning Project of Kaili University(Z0804)+1 种基金Leading Academic Discipline Project of Botany from Kaili University (KZD2008002)Construction Project for Basic Course Teaching Team of Biological Science from Kaili University (JXTD201003)
文摘[Objective] This study aimed to investigate the enzymatic kinetics of polyphenol oxidase in peel of Nephelium lappaceum to explore the environmental factors affecting its catalytic activity. [ Method ] With N. lappaceum peel as the experimental material and catechol as substrate, effects of temperature, pH, four inhibitors （EDTA, Vc, sodium bisulfite and citric acid） and substrate concentration on the activity of polyphenol oxidase were investigated. [ Result] The optimal temperature for polyphenol oxidase in N. lappaceum peel was 40 %, and the optimal pH was 6.8. EDTA, Vc, sodium bisulfite and citric acid all showed ideal in- hibitory effects on the activity of polyphenol oxidase; specifically, EDTA had the strongest inhibitory effect. [ Conclusion] At low temperature, EDTA, Vc, sodi- um bisulflte and citric acid with certain concentrations can inhibit the catalytic activity of polyphenol oxidase in peel of N. lappaceum, extend the storage and trans- portation time of N. lappaceum fruit, and inhibit the browning. This study provides theoretical basis for the development and utilization of polyphenol oxidase in peel of N. lappaceum.
基金Supported by Science and Technology Program of Sichuan Province(2018NZ0091)Special Project of Sichuan Provincial Public-Interest Scientific Institution Basal Research FundOpen Fund for Key Laboratory of Coarse Cereal Processing,Ministry of Agriculture and Rural Affairs(2018CC12)
文摘[Objectives] To study the polyphenol oxidase (PPO) activity and total phenol content of Docynia indica .[Methods] The tender branches and petioles of the medicinal and edible plant D. indica were used as experimental materials, and the annual changes of total phenol content and polyphenol oxidase (PPO) activity were analyzed.[Results] pH 7.0 was the optimum value of polyphenol oxidase activity in D. indica plants;the best substrate was catechol with the concentration of 0.15 mol/L;the optimum temperature was 25 ℃.[Conclusions] The total phenol content of D. indica plants was the lowest in April, May and September of each year. The polyphenol oxidase activity of D. indica plants at flowering and fruiting stage was significantly higher than that at pre-flowering stage.
文摘The browning of fruits can be considered as an enzymatic oxidation which is believed to be one of the main causes of quality loss during post-harvest handling. The enzymes responsible for this are the oxidoreductases;the polyphenol oxidase (PPO) (monophenol, o-diphenol, oxygen oxidoreductase;EC 1.14.18.1) belongs to this group. This enzyme, which is found in the sapodilla plum (Achras sapota), was purified using a phenylsepharose and a SephacrylS-200 columns. The molecular weight of the purified enzyme was estimated to be about 66 kDa by gel filtration and 29 kDa by SDS-PAGE. A single protein band was found using the latter system (SDS-PAGE), which shows that the PPO of the pulp of the sapodilla plum may be composed of two protein subunits with similar molecular weight. The optimum pH was 7.0 and the optimum temperature 60℃. The most effective inhibitors tested were ascorbic acid, sodium metabisulfite and acetic acid.
文摘The objective of this research was investigated the effect of polyphenol oxidase microwave treatment on phenolic composition, antioxidant activity and microstructure of loquat fruit. Phenolic profile of methanolic extracts prepared from fresh, and microwave-treated samples were analyzed. Antioxidant activity was also evaluated by 2,2’-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS?+) and 1,1-diphenyl-2-picrylhydrazyl (DPPH+) methods. In addition, polyphenol oxidase inactivation was carried out using a response surface methodology to establish the optimal conditions of treatment. The phenolic content of fresh mesocarp was 311 ± 0.60 mg gallic acid equivalents (GAE)/100g dry weight (DW) and that of microwave-treated mesocarp was 1230 ± 0.36 mg GAE/100g DW. Total phenolic content of water/ methanol extract significantly increases after microwave treatment rather than methanolic extract of fresh loquat. Five glycoside phenolics were identified by HPLC-DAD-MS as 3-caffeoylquinic acid, 3-p-coumaroylquinic acid, 5-caffeoylquinic acid and quercetin-3-O-sambubioside. Methanolic extract of microwave-treated mesocarp showed higher antioxidant activity than that of fresh mesocarp. Thus, polyphenol oxidase inactivation by microwave energy preserved the integrity of phenolic compounds as well as antioxidant activity in mesocarp extracts prepared from loquat fruit. It was also noted that phenolics were more abundant in the microwaved samples than in the fresh samples.
文摘Polyphenol oxidase, a bi-functional enzyme, has been implicated in enzymatic browning of yam and other tubers in a negative way. The objective of this present study was to examine the activity of polyphenol oxidase in Dioscorea rotundata. Var. laasirin and the efficiency of heat and chemical treatments in inhibiting this enzyme. Crude Polyphenol Oxidase （PPO） of Dioscorea rotundata.Var. Laasirin was isolated and the kinetics studied using the lineweaver-burk plot. The activity of the enzyme was evaluated using spectrophotomeric method. Yam PPO catalyzes oxidation of various substrates with catechol being the most readily oxidized substrate. The Michaelis-Menten constant （Km） and maximum reaction velocity （Vmax） for yam PPO were 0.00037 and 0.3125 respectively. Inhibition data showed that the enzyme had least activity （71.70） when blanched at 95℃ for 7 mins with chemical treatment involving a combination of 0.5% Sodium metabisulphite （Food grade） and 0.5% Ascorbic acid （Food grade）. The activity was highest （83.02） when it was blanched at 95 ℃ for 7 rains. This study has shown that it is possible to inhibit polyphenol oxidase activity in white yam using the chemical pretreatments and processing conditions described in this study for possible adoption in the production of packaged frozen yam chips by food industries.
文摘The objective was to study the effect of alginate coating on polyphenol oxidase (PPO) activity and colour of ‘Starking’ apple cubes during dehydration with hot air. Apple cubes were dehydrated at 20oC, 35oC, or 40oC, with a parallel airflow. Analysis of PPO activity, colour (L*, a*, b*) and dry matter were performed along the dehydration process at each temperature. All samples presented a peak in relative PPO activity in the beginning of the drying. Exponential models fitted well the experimental data after the peak. Cubes without coating presented lower PPO activity, suggesting lower browning, than coated samples throughout the dehydration process, for all temperatures. Better results for coated samples were obtained with a perpendicular airflow drying at 40oC, after dipping the whole apple in water at 60oC for 10 min. In order to prevent coated samples from browning, drying by perpendicular airflow preceded by a thermal treatment of the whole apple is required.
基金Supported by Undergraduate Innovation and Enterpreneurship Training Program(202110514002)Huanggang Normal University High-level Cultivation Project(202108504).
文摘[Objectives]This study was conducted to investigate the effects of embedding conditions on activity and catalytic properties of immobilized polyphenol oxidase.[Methods]Polyphenol oxidase was immobilized in a polymer material by the embedding method,and the optimal immobilization conditions were obtained by single factor tests:CaCl_(2) concentration 2.0%,sodium alginate concentration 2.0%,immobilization time 2 h and mass ratio of enzyme to carrier 10 mg/100 g,under which the immobilized enzyme activity was 93.33 U/g.Under the above conditions,the properties of polyphenol oxidase immobilized by sodium alginate(A-PPO)and free polyphenol oxidase were studied.[Results]The thermostability of A-PPO was better than that of the free enzyme,but the pH stability of A-PPO was inhibited.The Michaelis constant K_(m) values of free polyphenol oxidase and A-PPO were 0.37 and 0.48 mmol/L,respectively,and the maximum reaction rate V_(max) values were 0.38 and 0.51 mmol/(L·g),respectively.[Conclusions]This study provides a theoretical basis for the study of the properties of polyphenol oxidase.
文摘The use of food additives with xanthine oxidase (XO) inhibitory activity offers an alternative approach to hyperuricemic and gout disease treatment, and provides an example of antioxidant nutraceutics. The in vitro and in silico XO inhibitory activity of polyphenols from Uruguayan Tannat grape pomaces and propolis extracts was evaluated as well as the scavenging capacity of said compounds. When comparing propolis and grape pomace samples, the in vitro studies demonstrated that polyphenols extracted from propolis are more active as free radical scavengers than those from Tannat grape pomace. Both natural products effectively inhibited XO but the capacity of phenols present in GP is higher than the one present in P. The high content of anthocyanins in GP, absent in P, could account for this observation. In silico assays allowed us to determine relevant ligand-receptor interactions between polyphenols, from a database built with previously reported polyphenols from both natural products, and the active site of XO. The in silico results showed that compound (E)-isoprenylcaffeate from propolis was the best potential XO inhibitor displaying hydrophobic aromatic interaction between the conjugated ring of the caffeate moiety and polar interactions between hydroxyl groups from caffeate with the active site polar residues. Among grape pomaces, the Cyanidin-3-O-(6-(E)-p-coumaroyl)-glucoside was the best XO inhibitor;its moiety oxychromenyl being relevant to the docking stabilization. All these results lead us to propose Uruguayan propolis and Tannat grape pomace extracts as food additives as well as phytopharmaceuticals to decrease the uric acid levels in gout disease and to act against oxidative stress.
文摘Polyphenolic compound in processing apple （Malus domestica Borkh.） varieties and the relationship between polyphenol content and enzymatic browning were studied to provide reference for raw material selection and processing method optimization. The content of polyphenol compound in 10 processing apple varieties （4 cider and 6 juice varieties） were analyzed using the Folin-Ciocalteu method and HPLC. The degree of browning and the activities of polyphenol oxidase were also studied. The content and proportion of the polyphenol varied depending on the variety. Bitter varieties globally showed a higher polyphenol concentration than sweet or acid varieties. Proanthocyanidins, chlorogenic acid, （＋）-catechin, （-）-epicatechin were high-concentrated polyphenols in apple fruits. Phloridzin, the unique polyphenol of apple, was abundant in the bitter variety Frequin rouge fruit. Total polyphenols, proanthocyanidins, （＋）-catechin, and phloridzin had higher correlations with browning. The correlation was low between chlorogenic acid and browning. The polyphenolic profiles were correlated with the apple types. Cider apples contained more polyphenol than juice apple varieties. The content of flavan-3-ol has a close relationship with fruit browning.
基金This study was supported in part by the Japan-China Sasakawa Medical Fellowship.
文摘Objective Elevation of reactive oxygen species (ROS), especially the level of superoxide is a key event in many forms of cardiovascular diseases. To study the mechanism of tea polyphenols against cardiovascular diseases, we observed the expressions of ROS-related enzymes in endothelial cells. Methods Tea polyphenols were co-incubated with bovine carotid artery endothelial cells (BCAECs) in vitro and intracellular NADPH oxidase subunits p22phox and p67phox, SOD-1, and catalase protein were detected using Western blot method. Results Tea polyphenols of 0.4 ug/mL and 4.0 ug/mL (from either green tea or black tea) down-regulated NADPH oxidase p22phox and p67phox expressions in a dose-negative manner (P<0.05), and up-regulated the expressions of catalase (P<0.05). Conclusions Tea polyphenols regulate the enzymes involved in ROS production and elimination in endothelial cells, and may be beneficial to the prevention of endothelial cell dysfunction and the development of cardiovascular diseases.
