Determination of kinetic properties of polyphenol oxidase from Thymus (Thymus longicaulis subsp. chaubardii var. chaubardii)

Comparison of soil quality assessment methods for different vegetation eco-restoration techniques at engineering disturbed areas

Scientific assessment of soil quality is the foundation of sustainable vegetation eco-restoration in engineering disturbed areas. This study aimed to find a qualitative and comprehensive method for assessing soil quality after vegetation eco-restoration in engineering disturbed areas. Sixteen soil indicators were used at six vegetation eco-restoration sites as the potential soil indicators. A minimum data set (MDS) and revised minimum data set (RMDS) were determined by principal component analysis. Six soil quality indices (SQIs) of varying scoring functions based on different data sets were employed in this study. Significant positive correlations were observed among all six SQIs, indicating that the effects of different vegetation eco-restoration measures on soil quality could be quantified by all six SQIs. The SQI values of the vegetation concrete eco-restoration slope (VC), frame beam filling soil slope (FB), thick layer base material spraying slope (TB), and external-soil spray seeding slope (SS) were all significantly higher than the SQI value of the abandoned slag slope (AS). It is noteworthy that the SQIs of the VC and TB sites were also significantly higher than the SQI of the natural forest (NF) site. These results indicate that the application of artificial remediation measures can significantly improve the soil quality of the disturbed area at the Xiangjiaba hydropower station. The results of this study also indicate that the SQI-NLRM method is a practical and accurate quantitative tool for soil quality assessment and is recommended for evaluating soil quality under various vegetation eco-restoration techniques in disturbance areas at the Xiangjiaba hydropower station and in other areas with similar habitat characteristics.

Biodegradation of phenol-contaminated soil and plant growth promotion by Myroides xuanwuensis H13

Physicochemical methods for remediating phenol-contaminated soils are costly and inefficient, making biodegradation an environmentally friendly alternative approach. This study aims to screen for potential phenol-degrading bacteria and to verify the removal capacities of a selected strain in a bioaugmentation experiment at the greenhouse level using Brassica chinensis L. (Chinese cabbage) as the model plant and phenol-contaminated soil. In parallel, pot experiments were conducted using a collaborative approach based on this model system. We found that Myroides xuanwuensis strain H13 showed a high degradation capability, with a 97.67% efficiency in degrading 100 mg/L phenol. Under shaking flask conditions, H13 facilitated the solubilization of tricalcium phosphate and potassium feldspar powder. Pot experiments suggested a phenol removal percentage of 89.22% and enhanced availability of soil phosphorus and potassium for plants with H13 inoculation. In this case, the abundance of soil microbes and the activity of soil enzymes significantly increased as well. Furthermore, both photosynthesis and the antioxidant system in Chinese cabbage were enhanced following H13 inoculation, resulting in its increased yield and quality. Partial least squares path modeling revealed that H13 can primarily affect plant root growth, with a secondary impact on photosynthesis. These findings highlight the potential of biodegradation from phenol-degrading bacteria as a promising strategy for efficient phenol removal from soil while promoting plant growth and health.IMPORTANCEThis study is significant for environmental remediation and agriculture by its exploration of a more environmentally friendly and cost-effective bio-strategy in treating phenol-contaminated soil. These findings have essential implications for environmental remediation efforts and sustainable agriculture. By utilizing the biodegradation capabilities of Myroides xuanwuensis strain H13, it is possible to remove phenol contaminants from the soil efficiently, reducing their negative effects. Furthermore, the enhanced growth and health of the Chinese cabbage plants indicate the potential of this approach to promote sustainable crop production.

Purification and characterization of catechol oxidase from Posof Badele apple (Malus domestica L): in vitro and in silico studies

In the current study, polyphenol oxidase (PPO), responsible for enzymatic browning in fruits, was purified from Posof Badele apple (PB) (Malus domestica L.) in two steps as acetone precipitation and affinity chromatography. After purification, the purity of PBPPO was checked by using SDS-PAGE. It was figured out that PBPPO had maximum activity at pH 6.0 and 10 °C and it was stable at pH 5.5 and temperatures of 0–30 °C. Besides, it was determined that Al3+ and Cu2+ metal ions activated the enzyme and the PBPPO was strongly inhibited by ascorbic acid with a Ki constant of 1.67 ± 0.35 µM. Inhibitor-enzyme interactions were examined by molecular docking studies and it was revealed that ascorbic acid had the lowest docking score of −6.54 kcal/mol. We wanted to draw attention to the PB apple, which is red inside as well as outside and very rich in terms of nutrient content.

Tyrosinase inhibitory mechanism and the anti-browning properties of piceid and its ester

Different mechanisms for inhibiting tyrosinase can be exploited to avoid quality losses caused by the enzymatic browning of fruits and vegetables. Piceid (PI) and piceid 6″-O- azelaic acid ester (PIA) are oxidized by tyrosinase; however, their oxidation products may have inhibitory effects on tyrosinase. This notion is because l-DOPA oxidation was inhibited after the pre-incubation of PI/PIA with tyrosinase, however, l-DOPA oxidation was not affected if this pre-incubation was not performed. Circular dichroism analysis indicated a conformational change in the secondary structure of tyrosinase after pre-incubation. Further, molecular docking and enzyme reaction kinetics assays were employed to reveal the mechanism underlying the effects of PI/PIA on tyrosinase in the absence of pre-incubation with tyrosinase. PI/PIA had anti-browning effects in the potato models. The increased rate of A₄₂₀ in PI/PIA groups at 24 h were 281% and 279%, which were approximately 2.4- and 2.5-fold lower than that of control (668%).

Purification and characterization of avocado (Persea americana) polyphenol oxidase by affinity chromatography

Polyphenol oxidase (PPO) enzyme was purified from avocado (Persea americana) by ammonium sulfate precipitation 0-80%, dialysis and affinity chromatography. Characterization studies were performed with catechol (0.10 M, pH: 7.2, 37 °C), 4-methyl catechol (0.10 M, pH: 6.0, 37 °C), pyrogallol (0.02 M, pH: 8.5, 5 °C), chlorogenic acid (0.20 M, pH: 6.8, 10 °C) and caffeic acid (0.20 M, pH: 8.5, 10 °C), respectively. V_max and K_M values were determined for catechol (15789.96 U*mL^-1*min^-1, 10 mM), 4-methyl catechol (6768.40 U*mL^-1*min^-1, 2 mM), pyrogallol (6802.72 U*mL^-1*min^-1, 4 mM), chlorogenic acid (1377.97 U*mL^-1*min^-1, 14.29 mM) and caffeic acid (2567.24 U*mL^-1*min^-1, 5 mM). PPO was purified as 147.73-fold and 154.00-fold by Sepharose 4B-L-Tyrosine-p-aminobenzoic acid and Sepharose-6B-L-Tyrosine-p-aminobenzoic acid, respectively. 4B isolated PPO gave two bands at 35 and 50 kDa in SDS-PAGE while visible and slightly visible bands at 50-70 kDa and 100 kDa in Native-PAGE. 6B isolated PPO gave bands as distinctively at 50 kDa and unclearly at around 35 kDa in SDS-PAGE while visible and slightly visible bands at 50-70 and 100 kDa in Native-PAGE. The synthesis of original 6B-affinity gel and no any study found in literature on affinity purification of avocado PPO show importance of our study.

Establishment of a Model for Evaluating Shelf Life of Pseudosciaena crocea in Simulated Logistics and Storage

ABSTRACT

Cold chain logistics is a common way of fresh-keeping transportation at present, but in the actual transportation and storage process, temperature control is often not accurate, which leads to shortened shelf life. We evaluated the changes in the quality of yellow croaker (Pseudosciaena crocea) at different temperatures during transportation. Specimens of P. crocea were immersed in slurry ice for 20 min and stored at 22, 4, or -1°C for 4 days. During this period, the development of rancidity of P. crocea was measured by sensory (odor, skin, color, and flesh appearance) and biochemical (total number of colonies, total volatile basic nitrogen, and K value) analyses. A combination of sensory and biochemical parameters and the Arrhenius equation were used to predict the shelf life of P. crocea during storage. After verification under different storage temperatures, the relative error between the predicted and the measured values was found to be within 15%. The present work provides theoretical guidance for the quality control of P. crocea during transportation and storage.

HIGHLIGHTS

Using of group-based selected flavonoids as alternative inhibitors for potato polyphenol oxidase

One of the main problems encountered after fresh-cutting of foods is enzymatic browning causing changes in the texture, taste, and color. The variety of physical and chemical-based antibrowning methods was applied to extend the shelf life of these products. Accordingly, methods using natural compounds are of great importance for health. In this study, it was aimed to prevent enzymatic browning in potato (Solanum tuberosum L. cv. Marfona) by limiting the polyphenol oxidase (PPO) activity with selected flavonoids. First of all, we purified the potato PPO (pPPO) by single-step affinity chromatography. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and native PAGE were applied on pPPO. Then, the inhibition effects of 7-hydroxyflavone, 7-hydroxy-4'-nitroisoflavone, myricetin, luteolin, 7-methoxyflavone, 6-fluoroflavone, diosmetin, rutin, and diosmin on purified PPO enzyme were investigated. Kinetic assays indicated that myricetin was a remarkable inhibitor with the K_i value of 5 µM on pPPO. PRACTICAL APPLICATIONS: Potatoes are one of the important diet in many countries. In the processing of potatoes, enzymatic oxidation catalyzed by polyphenol oxidases (PPOs) is lead to losing its taste, flavor, and color. In this current paper, group-based selected flavonoids were proposed as alternative inhibitors of potato PPO enzyme. These flavonoids allowing to limit the PPO activity are commercially available, and they can be potential candidates to be used as antibrowning agents during potato processing.

Effects of convection-, vacuum-and freeze-drying on antioxidant, physicochemical properties, functional properties and storage stability of stink bean (Parkia speciosa) powder

This study aims to investigate the antioxidant, physicochemical and functional properties of convection-, vacuum-and freeze-dried stink bean (Parkia speciosa) powder upon storage at various relative humidity (RH) at room temperature, 25 °C. Both convection- and vacuum-dried samples exhibited stronger DPPH free radical scavenging activity (7.62 ± 1.77 and 10.38 ± 0.63 mg AA/g·db respectively) and ferric ion-chelating (FIC) ability (16.55 ± 1.29 and 18.88 ± 2.36 mg/mL·db respectively) compared to the fresh and freeze-dried samples. Stink bean powder had low water solubility index, water holding capacity and oil holding capacity but it had the potential as emulsifier in food systems. Apparent formation of clumps were observed after 25-day storage of powder at RH of 43%, 54% or 75% due to absorption of moisture from surroundings. Generally, the antioxidant properties and colour of the powders deteriorated after storage especially at higher RH. Vacuum drying would be the most suitable drying method to produce stink bean powder because of its enhanced antioxidant capacities, light colour and relatively more stable after storage.

Thermal inactivation kinetics of peroxidase and polyphenol oxidase from pomegranate arils (Punica granatum L. cv. Wonderful)

Thermal inactivation of peroxidase (POD) and polyphenol oxidase (PPO) in both pomegranate arils crude enzyme extract and fresh juice was investigated. The optimum conditions for reactions were studied using a mixture of guaiacol and H2O2 as substrate for POD and pyrogallol for PPO. The experimental work indicated that optimum pH for both enzymes was 7.0; meanwhile optimum temperature was 30°C for POD and 25°C for PPO. Michaelis-Menten constant (Km) values for POD were 8.33 and 8.00 mM for guaiacol and H2O2, respectively. The Km value was 5.88 mM pyrogallol for PPO. Thermal inactivation results revealed that the inactivation kinetics followed a monophasic first-order model. Activation energies (Ea) were 74.68 and 112.97 kJ/mol for POD and PPO, respectively. Therefore, POD was more heat-stable than PPO. This result is very useful to optimize pomegranate processing (canning or freezing), which represents the most important food industries in many tropical and subtropical regions. PRACTICAL APPLICATIONS: Pomegranate has been attracted more interest due to its antioxidant and nutritional values. For industrial applications, there is a growing interest to obtain pomegranate products such as juice, jams, food supplements, etc. It is well established that the residual activities of endogenous enzymes in either raw materials or processed products may cause loss of quality during storage. Inhibition of enzymatic browning is an important factor to maintain pomegranate quality. This work offers a better insight of characterization of browning enzymes and their thermosatbility, which will be useful to control the possible browning of pomegranate arils during processing and storage. In addition, the results of this study is very important in pomegranate processing where it showed a higher temperature with shortened time can be applied.

Purification, kinetic parameters, and isoforms of polyphenol oxidase from "Xushu 22" sweet potato skin

We purified and compared the polyphenol oxidase (PPO) isoenzymes present in "Xushu 22," a sweet potato. A membrane-bound form (mPPO) and two soluble forms (sPPO1 and sPPO2) were identified and purified using ammonium sulphate precipitation, ion exchange chromatography, gel filtration chromatography, and mass spectrometer. The three PPO isoforms were characterized enzymatically. The specific activity of mPPO was significantly higher than that of the two sPPO isoforms, being 24.55- and 13.89-fold higher than sPPO1 and sPPO2. The preferred substrates for mPPO and the two sPPOs were catechol and chlorogenic acid, respectively. They can be efficiently and safely applied to phenolic wastewater treatment after being immobilized. Both mPPO and the two sPPOs were rapidly inactivated under acid or base conditions and were unstable at 65°C. The most effective inhibitors of mPPO, sPPO1, and sPPO2 were glutathione, ascorbic acid, and L-cysteine, respectively. PRACTICAL APPLICATIONS: According to incomplete statistics, about 5% of sweet potatoes in china are wasted due to enzymatic browning every year. PPO was regarded as a key molecule contributing to enzymatic browning in fruits and vegetables during ripening, processing, and storage and responsible for economic and industrial loss. It's great importance to characterize the PPO from "Xushu 22" sweet potato and provide data on its inactivation. The three PPO isoforms were purified and identified by chromatography and mass spectrometer. This study will provide useful informations to have a better command of PPO from "Xushu 22" sweet potato and give ideals to solve the browning of sweet potato.

Enzymatic characterization and validation of gene expression of phosphoglucomutase from Cordyceps militaris

The purification and characterization of PGM (Phosphoglucomutase) from Cordyceps militaris (C. militaris) was investigated. PGM was purified using a combination of ultrafiltration, salting-out and ion exchange chromatography resulting in 4.23-fold enhancement of activity with a recovery of 20.01%. Molecular mass was 50.01 kDa by SDS-PAGE. The optimal activity was achieved at pH 7.5 and 30 °C with NADPH as substrate. The results showed that SDS, DTT Li⁺, Cu²⁺, Na⁺, Mn²⁺ and Al³⁺ were effective PGM inhibitors; whereas glycerol, Zn²⁺, Mg²⁺, Ca²⁺, Fe²⁺ and Fe³⁺ could enhance the activity of PGM, and the K_m and V_max values were 11.62 mmol/L and 416.67 U/mL, respectively. At the same time, qRT-PCR was used to test the changes of mRNA transcription level of PGM gene encoding under two fermentation conditions: basic medium and optimized medium. The relative quantitative results of PGM target genes resulting in 2.60-fold enhancement than the control group.

Antioxidant activities of mamao luang (Antidesma thwaitesianum Müll. Arg.) fruit: Extraction and application in raw chicken patties

Extraction of mamao luang (hereafter called mamao) with different solvents and varying solid to liquid (S:L) ratio was conducted to verify its antioxidant activities. Total phenolic content (TPC), total flavonoid content, total monomeric anthocyanin content, and antioxidant activities, namely, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity and ferric reducing antioxidant power (FRAP) of the unrefined extracts, were analyzed. The extraction with 70% acetone and 70% methanol and the S:L ratio of 1:30 seemed to be more appropriate and gave significantly (P < 0.05) higher values of the previously mentioned properties. Whole ground fruits were then incorporated into the blended chicken patties to compare their antioxidant and antimicrobial properties with butylated hydroxyanisole (BHA). During refrigeration storage of 20 days, the highest level (1,000 mg TPC/kg meat) could retard lipid oxidation relatively comparable to the efficiency of BHA (200 ppm). However, when microbiological aspect was considered together, a limited storage of 12 days was consequently suggested. PRACTICAL APPLICATION: Mamao fruit is a splendid source of phenolic compounds. The antioxidant properties have been demonstrated using DPPH and FRAP assay. The suitable type of solvent and S:L ratio were provided for the extraction. Our findings have shown that addition of mamao, a source of natural antioxidants, especially at the highest level increased oxidative stability of chicken patties. The research outcomes identify the potential bioactive compound and provide beneficial information related to the feasibility of incorporation of mamao phenolics as antioxidant agents in suitable food matrices. However, further investigation is still required for successful application in meat and meat products.

Purification of Polyphenol Oxidase from Potato and Investigation of the Inhibitory Effects of Phenolic Acids on Enzyme Activity

Background:

Polyphenol Oxidase (PPO) belongs to the oxidoreductase enzyme family.

Methods:

Here, PPO was purified from potato using Sepharose 4B-L-tyrosine-p-aminobenzoic acid affinity chromatography. It determined the interactions between some phenolic acids and the enzyme.

Results:

The enzyme was obtained with a specific activity of 15333.33 EU/mg protein and 7.87- fold purification. It was found that phenolic acids exhibited inhibitory properties for PPO. The IC50 values of the phenolic acids were found in the range of 0.36-2.12 mM, and their Ki values were found in the range of 0.28± 0.07-1.72±0.32 mM. It was determined that all studied compounds displayed a competitive inhibition effect. Among these compounds, 3-hydroxybenzoic acid was found to be the most effective PPO inhibitor (Ki: 0.28±0.07 mM).

Conclusion:

Investigating the inhibition kinetics of the enzyme will simplify the testing of PPO inhibitor candidates.

Improvement in Agrobacterium-mediated transformation of chickpea (Cicer arietinum L.) by the inhibition of polyphenolics released during wounding of cotyledonary node explants

Agrobacterium-mediated transformation of chickpea (Cicer arietinum L.) has been performed using cotyledonary node explants (CNs), which release phenolics upon excision that are detrimental to the viability of Agrobacterium tumefaciens and result in low transformation frequency. Twelve low molecular weight phenolic compounds and salicylic acid were identified in the exudates released upon excision during the preparation of cotyledonary nodes by reverse phase high-performance liquid chromatography (RP-HPLC). Zone inhibition assays performed with the explant exudates released at periodic intervals after excision showed the inhibition of A. tumefaciens. Agroinoculation of freshly excised cotyledonary nodes of chickpea showed 98-99 % inhibition of colony forming units (cfu). Osmium tetraoxide fixation of excised tissues showed enhanced accumulation of phenolics in the sub-epidermal regions causing enzymatic browning, affecting the viability and performance of A. tumefaciens for T-DNA delivery. The periodic analysis of exudates released from excised CNs showed enhanced levels of gallic acid (0.2945 ± 0.014 μg/g), chlorogenic acid (0.0978 ± 0.0046 μg/g), and quercetin (0.0971 ± 0.0046 μg/g) fresh weight, which were detrimental to A. tumefaciens. Quantitative assays and the elution profile showed the maximum leaching of phenolics, flavonoids, and salicylic acid immediately after the excision of explants and continued till 4 to 8 h post-excision. Pre-treatment of excised explants with inhibitors of polyphenol oxidase like L-cysteine, DTT, and sodium thiosulfate before co-cultivation showed the recovery of A. tumefaciens cfu, decreased the accumulation of phenolics, and improved transformation frequency. Our results show the hypersensitive response of excision stress for the expression of defense response-related genes and synthesis of metabolites in grain legume chickpea against pathogen infestation including Agrobacterium.

Selected biochemical properties of polyphenol oxidase in butter lettuce leaves (Lactuca sativa L. var. capitata) elicited with dl-β-amino-n-butyric acid

The study concentrated on changes in certain biochemical parameters of polyphenol oxidase (PPO) from lettuce leaves caused by dl-β-amino-n-butyric acid (BABA) elicitation. PPO from control plants demonstrated the highest affinity toward catechol, whereas PPO from BABA-elicited lettuce showed the highest affinity to 4-methylcatechol. The optimum temperature for enzymes from control plants was 35°C, whereas from plants elicited with 1mM BABA this was 25°C. PPO from plants elicited with BABA was also more sensitive to the tested inhibitors than PPO from control plants. l-Cysteine was the most effective inhibitor. Native gel stained for PPO activity in control samples showed two isoforms. However, in BABA-treated lettuce three bands visualising PPO activity were observed. The information obtained in this study will be valuable for the development of treatment technology and storage conditions to control undesirable browning reactions in elicited lettuce.

Pectin plays an important role on the kinetics properties of polyphenol oxidase from honeydew peach

Polyphenol oxidase (PPO) was purified from peach pulp by a three-step column chromatographic procedure. The kinetics properties of the PPO fractions obtained from different purification steps were compared. All the fractions showed high affinities for (+)-catechin and (-)-epicatechin. The optimum pHs and optimum temperatures for all the fractions were the same. However, the fraction that contained pectin was more sensitive to the change of pH, and it had a lower affinity for the substrates and a higher thermostability than the fractions without pectin. In addition, the protein impurities in PPO fractions might have no effect on the properties of PPO. l-Cysteine and glutathione were effective for the inhibition of all the PPO fractions, while NaF inhibited moderately. However, the pectin could reduce the inhibition effects of those inhibitors.

Purification and characterization of polyphenol oxidase from jackfruit ( Artocarpus heterophyllus ) bulbs

Polyphenol oxidase (PPO) from jackfruit bulb was purified through acetone precipitation, ion-exchange column, and gel filtration column. PPO was a dimer with the molecular weight of 130 kDa determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and gel filtration. The Km was 8.3 and 18.2 mM using catechol and 4-methylcatechol as substrates, respectively. The optimum pH was 7.0 (catechol as the substrate) or 6.5 (4-methylcatechol as the substrate). The optimum temperature was 8 °C. The enzyme was stable below 40 °C. The activation energy (Ea) of heat inactivation was estimated to be 103.30 kJ/mol. The PPO activity was activated by Mn(2+), SDS, Tween-20, Triton X-100, citric acid, and malic acid but inhibited by K(+), Zn(2+), Mg(2+), Ca(2+), Ba(2+), cetyl trimethyl ammonium bromide (CTAB), kojic acid, tropolone, glutathione (GSH), cysteine (Cys), and ascorbic acid (AA). Cys and AA were effective to reduce browning of jackfruit bulbs during the storage at 8 °C for 15 days.

A regulatory approach on low temperature induced enzymatic and anti oxidative status in leaf of Pui vegetable (Basella alba)

Basella alba is a soft green vegetable, survives in adverse environmental circumstances, for example, very cold temperature although the mechanism and the temperature sensitivity in this species are not clarified. Pot experiment for cultivation of B. alba was carried out to examine the effects of low temperature on the synthesis of two enzymes, polyphenol oxidase (PPO) and peroxidase (POD) in leaf of this plant. They were exposed to 8 °C for 24 h, 48 h and 72 h periods and the respective controls were kept in ambient room temperature for the above mentioned time. Low temperature causes the higher activity of PPO and the threshold level was found after 48 h period when compared to the respective controls. The activity was higher at 10 mM catechol, substrate for this enzyme, than 100 mM and 200 mM concentration, however, the three doses yielded the gradual increase in activity. Similar stimulatory effects on peroxidase (POD) activity in leaf were observed whenever the plants were exposed to cold for 24 h, 48 h and 72 h periods and maximal after 48 h period. Our findings demonstrate that the higher activity of these enzymes in leaf might be an index for the regulatory mechanism of the survival of these species in such adverse environment.

Antioxidant capacity of chewing stick miswak Salvadora persica

BACKGROUND

Chewing stick (miswak Salvadora persica L.) is an effective tool for oral hygiene. It possessed various biological properties including significant antibacterial and anti-fungal effects. In the present study, we evaluated the antioxidant compounds in miswak.

METHOD

Miswak root was extracted with 80% methanol. Methanol extract as antioxidant was evaluated by using DPPH, ABTS and phosphomolybdenum complex assays and analysis by GC-MS. Peroxidase, catalase and polyphenoloxidase assays were performed for crude extract of miswak root.

RESULTS

The methanol extract of miswak contained the highest amount of crude extract among the various solvent extracts. The methanol extract showed a concentration dependent scavenging of DPPH and ABTS radicals with IC50 values 4.8 and 1.6 μg crude extract, respectively. The total antioxidant activities, based on the reduction of molybdenum (VI) to molybdenum (V), increased with increasing crude extract content. The correlation coefficients (R2) between total crude extract and DPPH, ABTS scavenging activities and the formation of phosphomolybdenum complex were 0.97, 0.99 and 0.95, respectively. The GC-MS analysis showed that the methanol extract doesn't contain phenolic and flavonoid compounds or under detected limit. After silylation of methanol extract, three compounds namely 2-furancarboxaldehyde-5-(hydroxymethyl), furan-2-carboxylic acid-3-methyl- trimethylsilyl ester and D-erythro-pentofuranose-2-deoxy-1,3,5-tris-O-(trimethylsilyl) were identified by GC-MS analysis. These furan derivatives as they contain hydroxyl groups could be possessed antioxidant activities. The antioxidant enzymes were also detected in the miswak extract with high level of peroxidase and low level of catalase and polyphenoloxidase.

CONCLUSIONS

The synergistic actions of antioxidant compounds and antioxidant enzymes make miswak is a good chewing stick for oral hygiene and food purposes.

The Arrhenius equation revisited

The Arrhenius equation has been widely used as a model of the temperature effect on the rate of chemical reactions and biological processes in foods. Since the model requires that the rate increase monotonically with temperature, its applicability to enzymatic reactions and microbial growth, which have optimal temperature, is obviously limited. This is also true for microbial inactivation and chemical reactions that only start at an elevated temperature, and for complex processes and reactions that do not follow fixed order kinetics, that is, where the isothermal rate constant, however defined, is a function of both temperature and time. The linearity of the Arrhenius plot, that is, Ln[k(T)] vs. 1/T where T is in °K has been traditionally considered evidence of the model's validity. Consequently, the slope of the plot has been used to calculate the reaction or processes' "energy of activation," usually without independent verification. Many experimental and simulated rate constant vs. temperature relationships that yield linear Arrhenius plots can also be described by the simpler exponential model Ln[k(T)/k(T(reference))] = c(T-T(reference)). The use of the exponential model or similar empirical alternative would eliminate the confusing temperature axis inversion, the unnecessary compression of the temperature scale, and the need for kinetic assumptions that are hard to affirm in food systems. It would also eliminate the reference to the Universal gas constant in systems where a "mole" cannot be clearly identified. Unless proven otherwise by independent experiments, one cannot dismiss the notion that the apparent linearity of the Arrhenius plot in many food systems is due to a mathematical property of the model's equation rather than to the existence of a temperature independent "energy of activation." If T+273.16°C in the Arrhenius model's equation is replaced by T+b, where the numerical value of the arbitrary constant b is substantially larger than T and T(reference), the plot of Ln k(T) vs. 1/(T+b) will always appear almost perfectly linear. Both the modified Arrhenius model version having the arbitrary constant b, Ln[k(T)/k(T(reference)) = a[1/ (T(reference)+b)-1/ (T+b)], and the exponential model can faithfully describe temperature dependencies traditionally described by the Arrhenius equation without the assumption of a temperature independent "energy of activation." This is demonstrated mathematically and with computer simulations, and with reprocessed classical kinetic data and published food results.

The effect of oil-soluble rosemary extract, sodium erythorbate, their mixture, and packaging method on the quality of Turkey meatballs

The effect of oil-soluble rosemary extract, sodium erythorbate and a mixture of oil-soluble rosemary extract and sodium erythorbate and packaging method (vacuum packaging and modified atmosphere packaging) on the quality of cooked turkey meatballs stored at 4 °C was determined. The physicochemical, microbiological and sensory analyses were performed. Oil-soluble rosemary extract was found to be the most effectual antioxidant and vacuum more effective than modified atmosphere packaging in preventing oxidative changes. Sodium erythorbate slowed down hydrolytic process and more effective in modified atmosphere packaged samples. A slighter change in the colour of turkey meatballs was noted during modified atmosphere storage. Microbial counts of mesophilic bacteria during storage were never higher than the spoilage limit (10(7) cfu/g). All additives reduced microbial population and better effect was achieved by the combination of modified atmosphere packaging and additives. Sensory analysis results indicated the significant advantages in using rosemary individually or with sodium erythorbate in retarding warmed-over-flavour development in cooked poultry product.

Prokaryotic expression and purification of Camellia sinensis polyphenol oxidase

BACKGROUND

Polyphenol oxidase (PPO) causes the postharvest loss of fruits and vegetables but is also a key factor in the quality development of tea. However, there are no reports on engineered active plant PPO purified from prokaryotic cells.

RESULTS

In this study the ppo gene of about 1800 bp from Camellia sinensis cv. Yihongzao was successfully cloned and expressed in Escherichia coli. The PPOs purified from both the soluble fraction and the inclusion bodies showed activity. In addition, 1.0 × 10(-7) mol L(-1) Cu(2+) and acidic conditions were found to be favourable for the engineered PPO catalysis of catechol oxidation.

CONCLUSION

This paper represents the first report on C. sinensis ppo expression in E. coli and engineered active PPO purification. The results of the study provide a basis for the large-scale preparation and application of PPO.

Comparison on characterization of longan (Dimocarpus longan Lour.) polyphenoloxidase using endogenous and exogenous substrates

Longan polyphenoloxidase (PPO) was extracted and partially purified using ammonium sulfate precipitation and dialysis. The PPO characterizations were compared using endogenous substrate (-)-epicatechin and exogenous substrate catechol. The optimal pH and optimal temperature for the PPO activity were different when reacting with both substrates. The addition of ethylenediaminetetraacetic acid disodium salt into both substrate-enzyme systems exhibited the same lowest inhibition of the PPO activity. L-ascorbic acid and L-cysteine were the best inhibitors to endogenous substrate-enzyme system, while L-ascorbic acid and glutathione were most effective inhibitors to exogenous substrate-enzyme system. Cupric (Cu2+), ferric (Fe3+), and ferrous (Fe2+) ions accelerated the enzymatic-catalyzed reactions of both substrates. Kinetic analysis indicated that longan PPO strongly bound endogenous substrate but possessed a higher catalytic efficiency to exogenous substrate, and moreover, (-)-epicatechin was determined as the optimal substrate for longan PPO. This study is useful to exactly illuminate the enzymatic-catalyzed browning mechanism of postharvest longan fruit.

Some kinetic properties of polyphenol oxidase obtained from dill (Anethum graveolens)

Polyphenol oxidase (PPO) was partially purified from dill by (NH4)(2)SO4 precipitation followed by dialysis and gel filtration chromatography. Polyphenol oxidase activity was measured spectrophotometrically at 420 nm using catechol, dopamine and chlorogenic acid as substrates. Optimum pH, temperature, and ionic strength were determined with three substrates. The best substrate of dill PPO was found to be chlorogenic acid. Some kinetic properties of the enzyme such as V(max,) K(M) and V(max)/K(M) were determined for all three substrates. The effects of various inhibitors on the reaction catalysed by the enzyme were tested and I(50) values calculated. The most effective inhibitor was L-cysteine. Activation energies, E(a), were determined from the Arrhenius equation. In addition, activation enthalpy, DeltaH(a), and Q(10) values of the enzyme were also calculated.

A comparative analysis of property of lychee polyphenoloxidase using endogenous and exogenous substrates

Lychee polyphenoloxidase (PPO) was extracted and partially purified using ammonium sulphate precipitation and dialysis. The comparative analysis of PPO property was performed using its endogenous substrate (-)-epicatechin and exogenous substrate catechol. The pH optima for activity and activation temperature profiles of lychee PPO were very different when the enzyme reacted with endogenous and exogenous substrates. The addition of ethylenediaminetetraacetic acid disodium salt into the endogenous or exogenous substrate-enzyme system exhibited the same lowest inhibition of the PPO activity. However, l-cysteine was most effective in inhibiting enzymatic activity in the endogenous substrate-enzyme system while ascorbic acid was the best inhibitor in the exogenous substrate-enzyme system. Fe(2+) greatly accelerated the enzymatic reaction between endogenous substrate and PPO, but Cu(2+) exerted the same effect on the reaction between exogenous substrate and PPO. Based on the kinetic analysis, lychee PPO could strongly bind endogenous substrate but it possessed a higher catalytic efficiency to exogenous substrate.