Regeneration Of Peroxidase Research Articles

Determination of conformational changes of polyphenol oxidase and peroxidase in peach juice during mild heat treatment using FTIR spectroscopy coupled with chemometrics

SummaryThe effect of thermal treatment on activity and structural changes of polyphenol oxidase (PPO) and peroxidase (POD) in peach juice was investigated. The D70 values for PPO and POD were 10.38 and 13.68 min, respectively. The z values for PPO and POD were found to be 3.35 and 23.15 °C, respectively. Fourier transform infrared (FTIR) spectroscopy was used to determine the conformational changes. With the increase in temperature, α‐helix and β‐sheet were decreased, and β‐turn and aggregated β‐sheet structure were increased for PPO, random coil and β‐sheet decreased, while aggregated β‐sheet structure increased for POD. In contrast, an increase in α‐helix structure of POD was observed which was thought to be effective in POD regeneration. Furthermore, native and denatured forms of enzymes were discriminated by using principle component analysis (PCA), and models that correlated activity and secondary structural components with infrared spectra were constructed by using partial least square (PLS).

Thermosonication for peroxidase inactivation in sugarcane juice

To allow a widespread commercialization of sugarcane juice it is necessary to develop an effective preservation method. For that, thermosonication was evaluated as an alternative processing technology. Therefore, ultrasound (US) and conventional (CH) treatments were compared regarding peroxidase (POD) inactivation. Both treatments were performed for 25 min at 50–80 °C, with matched temperature profiles. POD inactivation kinetics were evaluated under different US parameters: pulse regime, US application time and power intensity. After treatments, sugarcane juice was monitored for 32 days under refrigerated storage to verify juice quality. Results showed that POD inactivation followed Weibull model for US and CH treatments at 70, 75 and 80 °C. At 70 and 75 °C, US lead to faster POD inactivation when compared to CH. The use of 20s on/10s off pulse regime, US application for 25 min and 75% power intensity were the best conditions for enzyme inactivation (77.3%). During refrigerated storage, POD regeneration, phenolic compounds degradation nor sedimentation were observed in the juice treated by US. For CH, on the other hand, sedimentation and lower phenolic compounds were observed. Overall, US is a potential technology for sugarcane juice enzymatic inactivation with reduced processing times and/or temperatures, leading to a better quality juice.

Acetaminophen (Paracetamol)

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Peroxide Biosensors and Mediated Electrochemical Regeneration of Redox Enzymes

This article describes the research investigations on the development of the amperometric biosensors based on mediated bioelectrochemistry. The mediated bioelectrochemistry involving horseradish peroxidase and glucose oxidase within the graphite paste is reported. The enzyme horseradish peroxidase together with electrochemical mediator was incorporated within the graphite paste electrode. The amperometric response is based on the mediated electrochemical regeneration of peroxidase within the paste. The mediated electrochemical regeneration of peroxidase and glucose oxidase was studied and compared using three different electron transfer mediators—tetracyanoquinodimethane (TCNQ), tetrathiafulvalene (TTF), and dimethyl ferrocene (dmFc). The mediated electrochemistry involving these three mediators was studied based on the cyclic voltammetry. The electrochemical measurements show that TTF is better mediator for the development of peroxide biosensor compared to TCNQ and dmFc. On the other hand, TCNQ is better mediator for the development of glucose sensor. The response curves for peroxide have been reported using these three mediators. A comparative study on the amperometric response based on the mediated electrochemical oxidation of peroxidase and glucose oxidase has also been made using these three mediators. The various parameters, i.e., background current, stability of the mediator within the graphite paste during the electrochemical measurements, and reproducibility of the amperometric response, are discussed.

Peroxidase Isoforms of Corn Kernels and Corn on the Cob: Preparation and Characteristics

Corn kernel and cob peroxidases occupy three cellular environments; soluble, membrane-bound and cellulose-bound. The three isoforms were isolated and characterised with particular reference to their individual use as indicators for adequacy of blanching. The membrane-bound and cellulose-bound isoforms had similar heat stability and both were significantly more heat stable than the soluble isoform when measuredin vivofollowing blanching. Heat transfer to the internal kernel was measured by insertion of fibre optic cables utilising fluoro-optic thermometry. Isoform levels were measured in commercially blanched corn, and peroxidase regeneration measured for each isoform. Regeneration was mainly due to the soluble isoform, and to a lesser extent the cellulose-bound isoform, but the membrane-bound isoform did not regenerate to any significant degree.

MICROWAVE AND CONVENTIONAL BLANCHING EFFECTS ON CHEMICAL, SENSORY, AND COLOR CHARACTERISTICS OF FROZEN BROCCOLI

ABSTRACTBroccoli (cv. Empress) obtained from a local supplier was blanched within 15 h of harvest. It was blanched by four methods in covered containers: conventional boiling water (1900 mL, 4 min) (BW), steam (300 mL water, 4 min) (ST), microwave heated in 1 L glass containers (60 ml water, 4 min, 700 W) (MW), and microwave heated in 1 L Seal‐a‐MealTM bags (45 ml water, 4 min) (MWB). Aliquots were frozen at ‐18C for 4 weeks. Fresh unblanched broccoli peroxidase activity ranged from 389 to 829 units/min; activity was essentially zero immediately after all blanching treatments. The highest reduced ascorbic acid (RAA) content occurred in fresh unblanched broccoli. Some peroxidase regeneration occurred during frozen storage. Immediately after blanching, all blanched broccoli had lower RAA content than control broccoli. MW‐blanched broccoli retained the greatest amount of RAA and had appearance, visual color, texture scores, and chroma of florets and stems equivalent to ST‐blanched broccoli. MW‐blanched broccoli had flavor and general acceptability scores similar to BW‐blanched broccoli. After 4 weeks in frozen storage, MW‐blanched broccoli had the highest RAA content.

Selenium bioavailability of soy-based diets in rats

Bioavailability of selenium from soy grown with sodium selenite and sodium selenate was evaluated by the use of glutathione peroxidase activity regeneration in rats. Male weanling Sprague-Dawley rats were fed a selenium-deficient Torula yeast-based diet for 4 weeks followed by a 7-week repletion period during which animals were fed one of six experimental selenium repletion diets. Soybeans grown with selenite and selenate were processed into flour and used as the protein source in diets providing 50 and 100 ng/g selenium. Bioavailability was determined by liver and plasma glutathione peroxidase regeneration and tissue selenium repletion in response to Se in soy diets and compared with changes in response to Se in reference diets containing Torula yeast supplemented with sodium selenite. Results indicate that selenium from soy was as bioavailable as sodium selenite from the reference diet. In addition, selenium from soy grown with sodium selenite was as bioavailable to the rat as selenium from soy grown with sodium selenate. These data indicate that soy protein provided a bioavailable source of dietary selenium to rats and that the form of selenium available in plants did not influence selenium bioavailability of the resulting soy-based product.

Inactivation and Regeneration of Peroxidase Activity in Vegetable Extracts Treated with Antioxidants

ABSTRACTReduction of peroxidase activity was determined in tomato, carrot or eggplant extracts using antioxidants (quercetin, rutinic acid, chlorogenic acid, and α‐tocopherol) alone or with heat treatment. Regeneration of peroxidase at room temperature and after frozen storage (–18°C for 4 wk) was measured. Combining antioxidant (125 mg%, w/v) and heat (2 min at 75°C) resulted in almost complete inhibition of vegetable peroxidases. Regeneration of peroxidase in extracts both heated and treated with antioxidants was less than in those only heated or antioxidant‐treated. After frozen storage, peroxidase regeneration was reduced to zero in heated + antioxidant treated extracts.

The inactivation and regeneration of peroxidase in relation to the high temperature–short time processing of vegetables

SummaryAs a result of the high thermal stability of peroxidase and its association with quality deterioration in high temperature–short time processed foods it was decided to investigate some aspects of the kinetics of inactivation of two purified grades of horseradish peroxidase.The following main conclusions were drawn:(a) It was shown that regeneration of peroxidase activity took place after partial inactivation at either 70, 90 or 110°C and that the first order plots of regenerated activity were biphasic in each case. Both fast and slow rates of regeneration increased on increasing the holding temperature from 30 to 40°C but no regeneration at all was observed at a temperature of 50°C. It was found that holding for 24 hr at 50°C almost completely prevented regeneration of peroxidase activity on further cooling. The extent of regeneration was found to be governed by the length of time at the inactivation temperature and a maximum was found which coincided with the high rate period of inactivation.(b) The first order plots of peroxidase inactivation were biphasic. Although the different purities of peroxidase did not give significantly different D121.1°C and z values for the low rate of inactivation over the temperature range 70–160°C, the presence of either pea or green bean purée significantly reduced the D121.1°C and, in the case of pea purée, increased the z value. It was also shown that the proportion of relatively stable enzyme was much lower in the presence of bean purée than in the presence of pea purée at each temperature.

Thermal denaturation and regeneration of japanese-radish peroxidase.

Thermal denaturation of Japanese-radish peroxidase [EC 1.11.1.7] was investigated with respect to its spectrophotometric properties and effect on the enzymatic activity. Inactivation of the peroxidase occurred at temperatures higher than 60degrees and involved three processes, i.e., dissociation of protohemin from the holoperoxidase, a conformation change in the apperoxidase, and the modification or degradation of protohemin. The splitting process of protohemin from holoperoxidase as followed by the change in the absorption spectrum at high temperatures coincided with the degrease in the activity, and it was found to be at least biphasic. The regeneration of peroxidase on cooling to room temperature was essentially reversible at neutral pH, while at pH 5 and pH 9 these processes were irreversible. The irreversibility at acidic pH was mainly due to an irreversible change in the conformation of the apoenzyme. The difference spectrum of heat-treated apoperoxidase exhibited a denaturation blueshift with negative maxima at 287 and 294 nm, and the total protein fluorescence quantum yield. qprotein, increased by 20% compared to that of the untreated apoenzyme. On the other hand, the irreversibility at alkaline pH was largely attributable to the modification of protohemin. Apoperoxidase was more resistnat to heat denaturation but the modification or degradation of protohemin in heated enzyme was greater at alkaline pH than at acidic pH. The pyridine-ferrohemochrome spectrum of peroxidase exhibited slight shifts of the maxima of the alpha-band to shorter wavelength on heat treatment, and the paper chromatogram showed the presence of a new derivative other than protohemin. The modified product is probably (2(4)-vinyl-4(2)-hydroxyethyldeuterohemin.

Peroxidase Regeneration and Its Effect on Quality in Frozen Peas and Thawed Peas

SUMMARYPeroxidase was regenerated in samples of peas that had been blanched just sufficiently to destroy the original peroxidase activity. The regeneration occurred after a few months in peas stored at −18° C, or within a few hours in thawed peas held at room temperature. The maximum activity regenerated was about 4% of the original activity. No regeneration occurred in peas given substantially more heat treatment than was needed for inactivation. Peroxidase regeneration during frozen storage, or after thawing, did not affect the quality of peas.