Modified barley straw as a potential biosorbent for removal of copper ions from aqueous solution

Barley straw (BS), a very low-cost material, has been utilized as a biosorbent material for the removal of copper (Cu²⁺) ions from aqueous solutions after treatment with citric acid. Barley straw was thermochemically modified with citric acid (CA–BS) for the purpose of improving the Cu²⁺ ion sorption capacity of the straw. Biosorption studies have been carried out to determine the effect of pH, adsorbent concentration, contact time, extent of modification, and adsorbate concentration on the biosorption capacity of Cu²⁺ ions by the esterified straw. The equilibrium sorption capacities of Cu²⁺ were 4.64 mg/g and 31.71 mg/g for BS and CA–BS, respectively. The optimum pH for the removal of Cu²⁺ ions by CA–BS was around pH 7.0 and the removal of Cu²⁺ ions was 88.1%. Langmuir, Freundlich, Scatchard and D–R (Dubinin–Radushkevich) isotherms have been used to characterize the observed biosorption phenomena of Cu²⁺ ions on CA–BS. The carboxyl groups on the surface of the modified barley straw were primarily responsible for the sorption of Cu²⁺ ions.     

Synthesis and Applications of Functional Polymers from Natural Okra Fibers for Removal of Cu(II) Ions from Aqueous Solution

Functional groups (?COOCH₃ and ?NH₂) in natural okra fiber had been introduced by free radical graft polymerization of methyl methacrylate (MMA) and acrylamide (AAm) from their binary solution using ascorbic acid/H₂O₂ as a redox initiator at a temperature of 45°C for 90 min. Factors affecting the grafting of lignocellulosic fiber such as feed molarity and comonomer composition were investigated. The grafted copolymers were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM-EDX), and thermogravimetric analysis (TGA). Functional groups were tested for their potential application in the removal of copper ions from aqueous solutions. Batch experiments were performed to evaluate the adsorption capacity of the maximum grafted cellulosic fibers toward the Cu (II) ions. Pseudo-first-order and pseudo-second-order kinetic models were studied to analyze the Cu²⁺ adsorption process and results showed that the pseudo-second-order model was more suitable than the pseudo-first-order model. Further, Langmuir, Freundlich, and Tempkin models were also applied to describe the adsorption isotherm of Cu²⁺ by different fiber adsorbents. The results indicate that the Langmuir model fitted the adsorption equilibrium data better than other two models. The maximum monolayer capacity q_m calculated using the Langmuir isotherm for raw and MMA+AAm grafted fiber were 4.89 and 33.05 mg/g, respectively.     

Heat-treated wood as chromium adsorption material

Heavy metals adsorption with lignocellulosic materials has been heavily researched in the last years. Since heat activation has been used with good results to increase the adsorption capacity of some materials, heat-treated wood might be a better adsorbent. This hypothesis is the basis of the present study. The adsorption tests were made with powdered pine wood, heat-treated at 190–210?°C. All the heat-treated samples showed a significantly higher adsorption compared to untreated wood. The maximum adsorption was obtained at pH 3 for heat-treated wood at 210?°C. The kinetics of the adsorption process fitted a pseudo-second-order reaction (R² 0.990–0.996). Adsorption fitted well both the Langmuir and the Freundlich model, but the Freundlich model presented higher R² (0.988–0.998). The q_max values estimated by the Langmuir plotting were in the range 15.6–19.4 mg/g and the n values from Freundlich isotherms between 1.87 and 2.39. Heat-treated wood was a better adsorption material than untreated wood for chromium adsorption. This can be a good application for the sawdust produced by the processing of heat-treated wood at primary and secondary wood processing mills or for the recycling of heat-treated wood at the end of product life.     

Effect of reaction pH on the photodegradation of model melanoidins

The effect was studied of the pH of the amino-carbonyl reaction on the photodegradation of model melanoidins. Nondialyzable model melanoidins were prepared from glucose and lysine with or without initial pH control to 7.0.: 2 mol/l phosphate buffer (buffer-melanoidin) and pH adjustment at the reaction start with NaHCO₃ (NaHCO₃-melanoidin). Melanoidin was also prepared from glucose and the lysine-Cu²⁺complex to investigate the difference of complexes between melanoidin and Cu²⁺ (Cu²⁺-melanoidin). Each melanoidin solution was irradiated with a Xe or tungsten-halogen lamp under dissolved oxygen or by the continuous supply of oxygen in a Cu²⁺/O₂ or ascorbic acid/Cu²⁺/O₂ system. The effects of the concentrations of Cu²⁺ and melanoidin, reaction pH value, and metal ion species on the decolorization rate in the Cu²⁺/O₂ system were investigated. The most effective factor for decolorization was found to be the melanoidin concentration. The decolorization rate was negligible when 14 g/l of Cu²⁺-melanoidin was photodegraded in the ascorbic acid/Cu²⁺/O₂ system under dissolved oxygen, although depolymerization was observed. Photodegradation of NaHCO₃-melanoidins in the Cu²⁺/O₂ system by the continuous supply of oxygen resulted in an increased decolorization rate, decreased molecular mass, production of low-molecular-weight compounds, release of free lysine, and pI change. The buffer- and Cu²⁺-melanoidins did not show changes in chemical characteristics similar to those of the NaHCO₃-melanoidin.     

Adsorption of Cu2+ by Crosslinked Graft Copolymers of Starch

With the use of acrylic acid(AA)as a monomer,humic acid(HA)and starch as raw materials,potassium persulfate(KPS)as initiator,and N,Ndimethylacrylamide(MBA)as a cross-linking agent,AA/HA/Starch graft copolymer was prepared and characterized by SEM and FT-IR.The effects of temperature,adsorption time,adsorbent dosage,pH value and Cu²⁺initial concentration of the solution on the adsorption performance of the crosslinked graft copolymer were also investigated.The results showed that the Cu²⁺adsorption capacity of the AA/HA/Starch graft copolymer increased firstly and then decreased with increasing adsorbent dosage and the initial pH value of Cu²⁺solution.With the increase of Cu²⁺initial concentration and the extension of adsorption time,the adsorption amount of Cu²⁺increased rapidly and then stabilized.And it decreased slightly with the increase of temperature.At pH value of 5.5,temperature of 298 K,adsorbent dosage of 50 mg,adsorption time of 125 min,and 100 mL Cu²⁺solution with Cu²⁺initial concentration of 100 mg/L,the Cu²⁺adsorption capacity of the crosslinked graft copolymer was 238 mg/g.The adsorption of Cu²⁺by the adsorbent followed the pseudo-second-order kinetic equation and Langmuir isothermal adsorption model,and the adsorption was attached to monolayer chemical adsorption.This study proved that AA/HA/Starch graft copolymer could be used as an efficient adsorbent for the removal of harmful and toxic metal cations such as Cu²⁺from industrial wastewater.     

Synthesis of Poly(Methacrylic Acid-)Starch Graft Copolymers Using Mn-IV-Acid System

When starch was treated with KMnO₄ solution, MnO₂ was deposited overall the starch. The amount of MnO₂ deposited relied on the KMnO₄ concentration. Subjecting the MnO₂-containing starch to a solution consisting of monomer (methacrylic acid, MAA) and acid (citric, tartaric, oxalic or sulphuric acid) resulted in formation of poly(MAA)-starch graft copolymer. The magnitude of grafting, expressed as meq. -COOH/100 g starch, was determined by amount of MnO₂ deposited, MAA concentration, temperature and duration of polymerization as well as kind and concentration of the acid. Incorporation of cations such as Fe⁺³, Cu⁺² and Li⁺¹ had a significant effect on grafting. The highest extent and rate of grafting were obtained with citric acid and the least with sulphuric acid; tartaric acid stood in-mid-way position. The magnitude of grafting increased as the acid concentration increased till a certain concentration beyond which grafting levelled off. Similar trend was observed when the magnitude of grafting was related to the amount of MnO₂ deposited. The extent and rate of grafting increased by raising the polymerization temperature from 30° to 50°C then decreased by raising the temperature further from 60° to 70°C. On the other hand, grafting enhanced significantly by addition of Fe⁺³, Cu⁺² or Li⁺¹ and followed the order Fe⁺³ > Cu⁺² > Li⁺¹. A tentative mechanism for grafting of starch with MAA using MnO₂-acid system was elucidated.     

Influence of the Cross‐linking Agent on the Gel Structure of Starch Derivatives

Hydrogels were synthesized through cross‐linking of carboxymethyl starch (CMS; Degree of Substitution DS = 0.45) using polyfunctional carboxylic acids (malic, tartaric, citric, malonic, succinic, glutaric and adipic acid). The syntheses used a cross‐linking agent ratio (ratio of the number of cross‐linking agent molecules to the number of monomer units constituting the polymer) of F_Z = 0.05. After cross‐linking the gels were dried, ground and then hydrogels of a polymer concentration of 4 mass‐% were produced. These CMS‐hydrogels were then rheologically characterized using dynamic oscillatory measurements. From measurements of the plateau region storage modulus G'_P, the network parameters molar mass between two entanglement points M_e (M_e ranging from 9.318 (citric acid) to 281.397 g/mol (tartaric acid)), the cross‐link density ν_e and the distance between two entanglement points ξ were calculated. Using carboxylic acids without other functional groups, a maximum in gel sturdiness is found at a spacer length of two CH₂‐groups. The evaluation of the loss factor tan δ for the CMS‐hydrogels showed that values of tan δ = 0.2 varied only slightly with the frequency ω. Flow curves showed a pseudopIastic flow behavior for all CMS‐hydrogels (the shear viscosity η declining over five decades in the range of the shear rate γ of 10⁻³ to 10³ s⁻¹) The different polyfunctional carboxylic acids have a strong influence on the sturdiness of the synthesized CMS‐hydrogels.     

Optimization of Trace Metals Concentration on Citric Acid Production by Aspergillus niger NRRL 2001

Citric acid is nowadays produced by submerged fermentation of Aspergillus niger. The process yield depends on the composition of the medium, as well as on the microorganism strain. In this work, the effect of Fe⁺³, Zn⁺², and Mn⁺² on citric acid production by A. niger NRRL 2001 is presented. The culture medium composition was glucose (120 g/L) KH₂PO₄ (1.0 g/L); K₂HPO₄ (1.0 g/L), MgSO₄.7H₂O (0.5 g/L), (NH₄)₂SO₄ (3.0 g/L). The ions Fe⁺³, Zn⁺², and Mn⁺² had their concentrations changed according to an experimental design. The experiments were carried out in an orbital shaker at 200 rpm and 30°C. The strain produced an extracellular polysaccharide that was also quantified. The optimum experimental condition was found using 7.0 mg/L of Fe⁺³ and 6.5 mg/L of Zn⁺² in absence of Mn⁺². No oxalic acid formation was observed using this experimental condition. Metal contents were not significant for the production of the polysaccharide. The highest production rate (2.95 g L⁻¹ day⁻¹) was reached after 10 days of fermentation. After this period, the productivity decreased slightly. In 20 days, the citric acid production rate (2.44 g L⁻¹ day⁻¹) was 82% of the highest productivity. The conversion into citric acid increased continuously, yielding 45.8% in 20 days of fermentation.     

Novel Approach of Using Nutraceutic‐Directed Caloric Antioxidant Density and Ion‐Ratio for Evaluating Fruit's Health Quality

Seven kinds of indigenous fruits and five imported fruits were compared for their “health quality.” Methods including the calorific, antioxidant, and ion ratios were carried out. Results indicated the order of content (in mg/100g) was: Ca²⁺, Murcott orange (218.2) > Kiwifruit (200.0) > pineapple (138.5) > Golden kiwi (117.6); Mg²⁺, Pitaya (192.2), banana (88.0), Kiwifruit (63.4), and Golden kiwi (58.4); Zn²⁺, Pitaya (19.53) > pear (10.8) > Kiwifruit (6.09) > Irwin mango (4.58). Cu²⁺, Kiwifruit (0.70) > Red globe grape (0.67) > Golden kiwi (0.65) > Irwin mango (0.42) ≈ Pitaya (0.40). In terms of ion ratio, Pitaya showed Zn²⁺/Cu²⁺ (48.8), Mg²⁺/Ca²⁺ (6.7) and uniquely possessed selenium 0.002 mg/100 g; for pear, Zn²⁺/Cu²⁺ = 37.2, while Kyoho grape, Red globe grape, and Golden kiwi revealed extremely high Fe²⁺/(Co²⁺+Ni²⁺) ratios. On the other hands, Irwin mango and Pitaya astonishingly contained huge amount of inositol, reaching 3523.2 mg/100 g and 1998.7 mg/100 g, respectively. To evaluate the “health quality” of fruits, an overall ranking method by combining (a) the Function‐directed Caloric Antioxidant Density (CAD) and (b) the ion ratio was developed. The finalized ranking of these selected fruits was: Pitaya > cherry > Irwin mango > Murcott orange = pineapple > banana > Golden kiwi > pear > Kiwifruit > Red globe grape > apple > Kyoho grape. Conclusively, this evaluation method is novel, contemporary and scientific, which could more clearly assess the “health quality” of fruits in view of nutritional, calorific, and antioxidant balance.     

Polyphenol contents and in vitro antioxidant activities of lyophilised aqueous extract of kiwifruit (Actinidia deliciosa)

The aim of this study was to determine the antioxidant potency and total phenolic and flavonoid contents of kiwifruit (Actinidia deliciosa) in vitro by analysing the radical scavenging activity of lyophilised water extract from kiwifruit (LEK) for 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), 1,1-diphenyl-2-picryl-hydrazyl (DPPH), N,N-dimethyl-p-phenylenediamine (DMPD), and superoxide anion radical (O₂⁻) as well as the total reducing power by FRAP and CUPRAC assays and the metal chelating activities. LEK showed efficient radical scavenging activity with DPPH, ABTS, DMPD, and O₂⁻ radicals; ferric (Fe³⁺) and cupric (Cu²⁺) ion reducing power and metal chelating activities. Moreover, the amounts of phenolic compounds, such as caffeic acid, ferulic acid, syringic acid, ellagic acid, catechol, pyrogallol, p-hydroxy benzoic acid, vanillin, p-coumaric acid, gallic acid, quercetin, ??-tocopherol and ascorbic acid, in LEK were quantified by LC-MS-MS. The results show that pyrogallol (2070.0 mg/kg LEK) is the main phenolic compound responsible for the antioxidant and radical scavenging activities of LEK. Finally, total phenolic and flavonoid contents were determined as gallic acid (GAE) and quercetin equivalents (QE). The GAE and QE values in LEK were 16.67 ± 2.83 ??g GAE/mg and 12.95 ± 0.52 ??g QE/mg, respectively. The results suggest that consumption of kiwifruit (A. deliciosa) can be beneficial effects due to its antioxidant properties.     

Antioxidant activity of predigested protein obtained from a range of farmed edible insects

This study investigated the antioxidant activities of peptides obtained by in vitro gastrointestinal digestion of edible insects. The antioxidant potential of edible insects' hydrolysates was determined as the free radical‐scavenging activity, ion chelating activity and reducing power. The highest antiradical activity against DPPH^˙, whose IC₅₀ value is the lowest, was noted for Amphiacusta annulipes (19.1 μg/mL) and that against ABTS^˙+ was the highest for Zophobas morio (4.6 μg/mL). The peptides obtained from A. annulipes also showed the highest Fe²⁺ chelation ability (58.82%) and reducing power (0.652). The highest ability to chelate Cu²⁺ was noted for Locusta migratoria (86.05%). The locust was characterised by the highest concentration of peptides before digestion and after digestion (3.13 and 5.88 mg/mL, respectively), and the DH was 36.29%.     

Preparation,Characterization and Evaluation of Anionic Starch Derivatives as Flocculants and for Metal Removal

Anionic starch derivatives bearing carboxyl groups were prepared by reacting maize starch and hydrolyzed maize starch with a previously synthesized citric acid adduct (2‐hydroxy‐3‐chloropropylcitric acid) using the dry process. Different factors affecting the preparation, i.e. catalyst concentration, citric acid adduct concentration, duration and temperature have been studied. The modified starch was characterized by IR spectroscopy, X‐ray diffraction analysis and scanning electronic microscopy. The anionic starch derivatives were evaluated as flocculants. Different factors affecting the flocculation efficiency of the prepared flocculants were studied. These factors include effect of dose, acid content, pH of the flocculation medium and molar mass. The anionic starch samples were chelated with different metal cations such as Cu²⁺, Co²⁺, Mg²⁺, and Hg²⁺, in the form of acetates, chlorides and sulfates.     

Isolation and characterization of melanin from Osmanthus fragrans’ seeds

Melanin derived from Osmanthus fragrans’ seeds was isolated from O. fragrans’ seeds by alkaline extraction, acid hydrolysis, and repeated precipitation with a yield of 0.34 g/100 g (wet weight basis). Physical and chemical properties of the melanin revealed that the melanin derived directly from O. fragrans’ seeds were similar to typical melanin. The melanin was stable under ultraviolet light or room-light, stable in the range of 25-100 °C, relatively stable in alkaline solution, reducer and salt, but was bleached by strong oxidants (KMnO₄, K₂Cr₂O₇ and NaOCl). The metal-ion of Ca²⁺, Cu²⁺, Fe³⁺ and Zn²⁺ had the function of color increase or color preservation to the melanin. Although Mg²⁺, Al³⁺ and Na⁺ reduce pigment color, it was not obvious. Amino acid and organic acid did not affect the melanin, while sugar, starch, and glucose affected it slightly.     

Characterization of a β-Glucosidase from an Edible Mushroom,Lycoperdon Pyriforme

A β-glucosidase from Lycoperdon pyriforme, a wild edible mushroom, was characterized biochemically. The enzyme showed a maximum activity at pH 4.0 and 50°C when p-nitrophenyl-β-D-glucoside was used as a substrate. K_m and V_max values were calculated as 0.81 mM and 1.62 U/mg protein, respectively. The enzyme activity was conserved about 85% over a broad range of pH (3.0–9.0) at 4°C after 24 h incubation. The activity was fully retained after 60 min incubation at 20–40°C. Na⁺, Li⁺, Mg²⁺, Mn²⁺, Zn²⁺, Co²⁺, Ca²⁺, and Cu²⁺ did not affect the enzyme activity and 0.25% sodium dodecylsulfate inhibited the enzyme activity approximately 76%. Ethylenediamine tetra-acetic acid, phenylmethanesulfonylfluoride, and dithiothreitol showed no or a little negative effect on the enzyme activity. The resistance of the enzyme to some metal ions, chemicals, and ethanol along with the pH stability, can make it attractive for future applications in industry.     

Evaluation of Catechin and its Derivatives as Antioxidant: Recovery of Growth Arrest of Escherichia coli under Oxidative Conditions

Effects of (+)-catechin, (-)-epigallocatechin gallate and gallic acid on the growth of Escherichia coli K-12 under oxidative conditions were examined. (+)-Catechin did not protect the bacterial growth which was inhibited by H₂O₂, lipid hydroperoxide, paraquat, Cu²⁺, H₂O₂+Cu²⁺ and lipid hydroperoxide+Cu²⁺. Both (-)-epigallocatechin gallate and gallic acid could restore the growth inhibition of E coli K-12 under the same conditions. Radical scavenging activity of (-)-epigallocatechin gallate, which is one of the most abundant components in Japanese green tea (Camellia sinensis L), is likely to be dependent upon the gallic acid group of the compound.     

Development of caramel colour with improved colour stability and reduced 4-methylimidazole

ABSTRACT

This study investigated the effect of chemical substances, such as Mg²⁺ (as magnesium sulphate), Zn²⁺ (as zinc sulphate), Fe²⁺ (as iron sulphate), ascorbic acid, and citric acid, on the formation of 4-methylimidazole (4-MI) and colour stability of caramel colour. The 4-MI concentration in the caramel colour without chemical substances was 963.10 μg/g, and this decreased the most (67.7%) with the addition of 0.1 molar ratio of citric acid. Colour stability was evaluated by measuring the total colour change (ΔE) after storage, and heating in pH 2, 4, and 7 solutions and 50% solution in ethyl alcohol. Among the chemical substances added to reduce 4-MI in the caramel colour, Mg²⁺ (0.1 molar ratio) and ascorbic acid improved the colour stability more than the others.     

Xylitol bioproduction from wheat straw: hemicellulose hydrolysis and hydrolyzate fermentation

A 2² central composite design with five center points was performed to estimate the effects of temperature (120, 130 and 140 °C) and acid loading (100, 150 and 200 mg g^?1) on the yield of monomeric xylose recovery from wheat straw hemicellulose (Y_S/RM). Under the best hydrolysis condition (140 °C and 200 mg g^?1), a Y_S/RM of 0.26 g g^?1 was achieved. After vacuum concentration and detoxification by pH alteration and active charcoal adsorption, the hydrolyzate was used as source of xylose for xylitol bioproduction in a stirred tank reactor. A xylitol production of 30.8 g L^?1 was achieved after 54 h^?1 of fermentation, resulting in a productivity (Q_P) of 0.57 g L^?1 h^?1 and bioconversion yield (Y_P/S) of 0.88 g g^?1. The maximum specific rates of xylose consumption and xylitol production were 0.19 and 0.15 g g^?1 h^?1, respectively. Copyright © 2006 Society of Chemical Industry     

Analysis of tryptophan oxidation by fluorescence spectroscopy: Effect of metal-catalyzed oxidation and selected phenolic compounds

The suitability of using fluorescence spectroscopy to assess tryptophan (TRYP) depletion by quantifying the loss of natural TRYP fluorescence during metal-catalyzed oxidation (MCO) was assessed. To analyze the effect of the oxidation conditions, N-acetyl-l-tryptophanamide (NATA) solutions were oxidized in the presence of Cu²⁺ and Fe²⁺ (40 and 80 μM), with and without 0.8 mM H₂O₂. Also, the effect of selected phenolic compounds (PhC), namely, catechin, genistein, quercetin, rutin, gallic acid and chlorogenic acid (0.08, 0.8 and 8.0 μM), on TRYP MCO was studied. Oxidation systems catalyzed by Fe²⁺ had a major oxidative potential as a result of a higher amount of free radicals formed through the Fenton reaction. PhC could exert both antioxidant and pro-oxidant effects depending on their concentration, chemical structure of the PhC and the oxidation system. In general, all PhC acted as pro-oxidant agents at the highest dose. The major pro-oxidant effect was displayed by gallic and chlorogenic acid in the presence of Fe²⁺, Cu²⁺ or Cu²⁺/H₂O₂. Quercetin, rutin and gallic acid showed antioxidant effect against TRYP oxidation at low concentrations in Fe²⁺/H₂O₂ systems. Plausible mechanisms for the antioxidant and pro-oxidant effects of PhC on TRYP oxidation are discussed in the present article. The antioxidant efficiency of PhC or PhC-rich extracts must be studied before being used as functional food ingredients.     

Characterization of purified xylanase from finger millet (<Emphasis Type="Italic">Eleusine coracana-</Emphasis>Indaf 15) malt

Xylanase (E.C. 3.2.1.8) was purified to apparent homogeneity from 96 h finger millet (Eleusine coracana, Indaf-15) malt by a three step purification procedure via ammonium sulphate fractionation, DEAE-cellulose ion exchange and Sephadex G-75 gel permeation chromatographies with a recovery of 4.0% and fold purification of 60. Xylanase, having a molecular weight of 29 ± 2 kDa was found to be monomeric on SDS-PAGE. pH optimum of the enzyme was found to be in the range of 5.0–5.5. The activation energy was 25 kJmol⁻¹. Xylanase showed maximum stability at 35 °C in a pH range of 5.0–6.0. K _m and V _max of purified xylanase were found to be 0.2% and 4.5 μmol min⁻¹, respectively. Metal ions such as Ca²⁺, Mg²⁺, Mn²⁺, Cu²⁺, Fe²⁺, Ag²⁺ and Ni²⁺ enhanced xylanase activity at 5 mM concentration. p-chloromercuribenzoate, citric, oxalic and boric acids inhibited the enzyme in concentration dependent manner. The mode of action of xylanase was found to be “endo” as determined by the analysis of products liberated from larchwood xylan by ESI-MS and H¹NMR. In vitro studies using Bifidobacterium and Lactobacillus sp. confirmed the prebiotic activity of the xylo-oligosaccharides.     

Purification and enzymatic characteristics of a novel polyphenol oxidase from lotus seed (Nelumbo nucifera Gaertn.)

A polyphenol oxidase (PPO) from lotus seed was purified by the procedures including ammonium sulphate precipitation and affinity chromatography. The apparent molecular mass was 38.6 kDa by SDS‐PAGE. Kinetic studies showed that the K_m and V_max values for catechol were 6.04 mm and 416.67 U, respectively. The PPO performed optimal activity in 20 °C and pH 7.0. The enzymatic activity could be mainly maintained up to 50 °C and pH 4.0–7.0. The activity could be inhibited by various inhibitors including thiourea, urea, sodium hydrogen sulphite, EDTA·2Na, SDS, citric acid, guanidine hydrochloride, ascorbic acid, sodium sulphite and sodium thiosulphate. The metal ions Ba²⁺, Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺ and Zn²⁺ could inhibit the activity of PPO, while Cu²⁺ performed obvious enhancement. The enzymatic properties of PPO could probably provide practical application in inhibiting the PPO activity and preventing enzymatic browning in the process of picking, transportation, processing and storage of fresh lotus seeds.