High pressure processing of cocoyam,Peruvian carrot and sweet potato: Effect on oxidative enzymes and impact in the tuber color

High pressure processing (HPP) is a non-thermal technology used to activate or inactivate enzymes. This study investigated the effects of HPP (600 MPa for 5 or 30 min at 25 °C) on cocoyam, Peruvian carrot and sweet potato color, and the polyphenoloxidase (PPO) and peroxidase (POD) activities in tuber cubes, puree, and enzyme extract subjected to HPP. The results showed enzyme inactivation by HPP in cocoyam (up to 55% PPO inactivation in puree and 81% POD inactivation in extract) and Peruvian carrot (up to 100% PPO and 57% POD inactivation the extract). In contrast, enzyme activation was observed in sweet potato (up to 368% PPO and 27% POD activation in puree). The color results were compatible to enzyme activity: the color parameters remained unchanged in cocoyam and Peruvian carrot, which showed high PPO and POD inactivation after HPP. Furthermore, the impact of HPP on the enzymes was influenced by the matrix in which HPP was carried out, evidencing that the enzyme structure can be protected in the presence of other food constituents.Industrial relevanceThe enzymes PPO and POD are an important concern for vegetable processing, due its ability to induce browning after vegetables are cut. The HPP at 600 MPa for 5 or 30 min can be used to inactivate these enzymes in cocoyam and Peruvian carrot, guaranteeing the color and freshness of the tubers similar to the fresh cut vegetable.     

Peroxidase and polyphenol oxidase in long-term frozen stored papaya slices. Differences among hermaphrodite and female papaya fruits

The effects of freezing and frozen storage on hermaphrodite and female papayas (cv Sunrise, solo group) polyphenol oxidase (EC 1.10.3.1; PPO) and peroxidase (EC 1.11.1.7; POD) were evaluated. The freezing process produces a significant increase in both enzymatic activities (22–11%, PPO and 13%, POD) depending on the kind of papaya fruit. During frozen storage, the soluble PPO activity shows a continuous increase up to 9 months of storage only in hermaphrodite tissues. This same sample also showed a significant activation of soluble POD at 3 months of storage. Female frozen samples maintained a continuous decrease in soluble POD activity during storage, while PPO activity showed some increase up to 12 months. Isoenzyme pattern of PPO in freshly frozen papaya tissues showed an intensification of the most cationic forms, D and E (R_f=0·55 and R_f=0·64, respectively) and a disappearance of band B (R_f=0·28). This band B was not regenerated during frozen storage. However, female tissues only showed a continuous inactivation of bands D and E through storage. POD isoenzyme pattern showed different changes depending on the kind of papaya fruit. In both frozen papayas a new isoenzyme (R_f=0·39) form appeared at three months of storage. From this date, hermaphrodite frozen samples lost this isoenzyme together with original the most anionic POD form (R_f=0·58), increasing the intensity of the only remaining form (R_f=0·24). © 1998 SCI.     

Effect of ultrasonic treatment on enzyme activity and bioactives of strawberry puree

The aim of this study was to evaluate the impact of ultrasound (US) at different frequencies (20, 370, and 583 kHz) and power levels (35 and 48 W) on the residual activity (RA) of peroxidase (POD) and polyphenol oxidase (PPO) in strawberry puree. Total anthocyanin content (TAC), total phenolic content (TPC), ferric ion reducing antioxidant power (FRAP) and trolox equivalent antioxidant capacity (TEAC) were also assessed. Results were compared with untreated, thermally treated at 40 °C (control) and pasteurized (90 °C) strawberry puree. POD and PPO RA were significantly (P < 0.05) reduced, whilst there was a significant (P < 0.05) increase in TAC (5%–19%) in all US-treated samples in comparison with the untreated samples and the controls. US at 20 kHz (35 W) increased significantly (P < 0.05) TPC (9%) and FRAP (6%) in strawberry puree, whereas the effect of 583 kHz (48 W) on these parameters was insignificant (P > 0.05). Pasteurization inactivated POD and PPO, however, decreased dramatically TAC (14%), TPC (17%) and FRAP (9.5%) in strawberry puree. These findings suggest that US is a promising novel non-thermal food technology that can be tailored to improve the quality of strawberry puree by inactivating enzymes responsible for food deterioration whilst maintaining the content of bioactive compounds.     

Effects of high hydrostatic pressure on enzymes, phenolic compounds, anthocyanins, polymeric color and color of strawberry pulps

BACKGROUND: Changes in activity of polyphenol oxidase (PPO), peroxidase (POD) and β‐glucosidase, individual phenolic compounds other than anthocyanins, total phenols, monomeric anthocyanins, polymeric color and instrumental color of strawberry pulps were assessed after high hydrostatic pressure (HHP) (400–600 MPa 5–25 min^?1) at room temperature. RESULTS: β‐Glucosidase was activated by 4.7–16.6% at 400 MPa 5–25 min^?1 and inactivated by 8.0–41.4% at 500 or 600 MPa. PPO and POD were inactivated at all pressures, the largest reduction in activity being 41.4%, 51.5% and 74.6%, respectively. The individual phenolic compounds and total phenols decreased at 400 MPa, but total phenols increased at 500 or 600 MPa. However, the monomeric anthocyanins, polymeric color and redness (a*) exhibited no change. HHP induced a decrease in lightness (L*) and an increase in yellowness (b*) at 400 MPa, but no significant alteration in L* value and b* value at 500 or 600 MPa was observed; this was attributed to higher residual activity of PPO, POD and β‐glucosidase at 400 MPa. Total color difference (ΔE) was ≥ 5 at 400 MPa and ?3 at 500 or 600 MPa. CONCLUSION: HHP effectively retained anthocyanins, phenolic compounds and color of strawberry pulps, and partly inactivated enzymes. Copyright © 2011 Society of Chemical Industry     

Impact of pH and Total Soluble Solids on Enzyme Inactivation Kinetics during High Pressure Processing of Mango (Mangifera indica) Pulp

This study was undertaken with an aim to enhance the enzyme inactivation during high pressure processing (HPP) with pH and total soluble solids (TSS) as additional hurdles. Impact of mango pulp pH (3.5, 4.0, 4.5) and TSS (15, 20, 25 °Brix) variations on the inactivation of pectin methylesterase (PME), polyphenol oxidase (PPO), and peroxidase (POD) enzymes were studied during HPP at 400 to 600 MPa pressure (P), 40 to 70 °C temperature (T), and 6‐ to 20‐min pressure‐hold time (t). The enzyme inactivation (%) was modeled using second order polynomial equations with a good fit that revealed that all the enzymes were significantly affected by HPP. Response surface and contour models predicted the kinetic behavior of mango pulp enzymes adequately as indicated by the small error between predicted and experimental data. The predicted kinetics indicated that for a fixed P and T, higher pulse pressure effect and increased isobaric inactivation rates were possible at lower levels of pH and TSS. In contrast, at a fixed pH or TSS level, an increase in P or T led to enhanced inactivation rates, irrespective of the type of enzyme. PPO and POD were found to have similar barosensitivity, whereas PME was found to be most resistant to HPP. Furthermore, simultaneous variation in pH and TSS levels of mango pulp resulted in higher enzyme inactivation at lower pH and TSS during HPP, where the effect of pH was found to be predominant than TSS within the experimental domain.     

Inactivation kinetics and secondary structural change of PEF-treated POD and PPO

Effects of pulsed electric fields (PEF) on the activity of peroxidase (POD) and polyphenol oxidase (PPO) in buffered solution were studied while the corresponding changes to their secondary structures was demonstrated by far-UV Circular dichroism (CD). The relative residual activity of POD and PPO decreased with the increase in electric field strength and treatment time, and PPO was more susceptible than POD to PEF treatment. The greatest reduction of the activity was achieved for POD at 25 kV/cm for 1740 μs and PPO at 25 kV/cm for 744 μs with reductions of 32.2% and 76.2%, respectively. The inactivation kinetic parameters D-value and Z_E value were calculated. The D-values of PPO were smaller than those POD at higher electric field strength, and Z_E values of POD and PPO were 36.9 and 16.2 kV/cm, respectively. The secondary structures of the two enzymes were changed following treatment by PEF. The intensity of negative peaks in the CD spectra decreased, and the CD spectra of PPO changed more significantly than that of POD; the reduction of the relative α-helix fractions for POD at 25 kV/cm for 124 μs was 22.63% while it was 50.72% for PPO at 25 kV/cm for 52 μs. The inactivation of PEF-treated POD and PPO was in close agreement with their secondary structure changes.     

Effects of microwave heating on pigment composition and colour of fruit purees

Microwave energy was applied to inactivate the oxydoreductases peroxidase (POD, EC 1.11.1.7) and polyphenol oxidase (PPO, EC 1.14.18.1) in processed fruit products. Microwave blanching of papaya, strawberry and kiwi purees at various conditions of power and time produced inactivation of PPO and POD activities depending on the fruit and the heating conditions. Treatment at 850 W/60 s produced about 60% of POD inactivation for papaya and kiwi fruit. POD activity in strawberry, however, seemed to be more resistant to microwave inactivation; treatment at 850 W/60 s only achieved a loss of POD activity near 8%. Papaya oxidoreductases showed lower stability in the microwave treatments tested. Microwave blanching at 475 W/45 s produced about 75% inactivation of POD activity and nearly complete PPO inactivation. Kiwi fruit and strawberry purees exhibited similar inactivation of PPO – 32% at 475 W/30 s and 70% at 475 W/60 s. The decrease of PPO activity in both products was almost linear at constant power. This thermal treatment, however, directly affects the colour of the fruit pulps. Papaya, kiwi and strawberry purees suffered slight colour (CIE L* a*b*) changes. Carotenoid, chlorophyll and anthocyanin changes were evaluated by HPLC and related to objective colour. Microwave treatments produced small modifications of the quantitative and qualitative composition of carotenoids (in papaya) and anthocyanins (in strawberry). Chlorophylls (kiwi) showed significant degradation as a consequence of microwave heating. © 1999 Society of Chemical Industry     

Thermal inactivation kinetics parameters of browning enzymes in starfruit (Averrhoa carambola L.) juice

This study aimed to evaluate the thermal inactivation kinetics of polyphenol oxidase (PPO) and peroxidase (POD) in starfruit juice. It followed the Malaysia Food Regulations 1985 and CODEX STAN 247-2005. Glucose, fructose and sucrose were the main sugars in starfruit juice. The total soluble solids, pH, titratable acidity, and total phenolics content of the starfruit juice produced were 8.13 ± 0.25 °Brix, 3.80 ± 0.05, 0.43% ± 0.02% malic acid, and 93.67 ± 4.96 mg GAEL⁻¹, respectively. Thermal inactivation kinetics of PPO and POD followed the first-order kinetic model. The decimal reduction time at 83.6 °C (D_83.6) of PPO and POD was 198.48 and 98.4 s, respectively, while the thermal resistance constant (z value) of PPO and POD was 12.8 and 5.4 °C, respectively. In conclusion, PPO might be a suitable signal for thermal processing on starfruit juice since it has higher heat resistance than POD.     

High Pressure and Temperature Effects on Enzyme Inactivation in Strawberry and Orange Products

High hydrostatic pressure treatment (50-400 MPa) combined with heat treatment (20–60°C) effects on peroxidase (POD), polyphenoloxidase (PPO) and pectin methylesterase (PME) activities of fruit-derived products were studied. Assays were carried out on fresh orange juice and strawberry puree. Pressurization/depressurization treatments caused a significant loss of strawberry PPO (60%) up to 250 MPa and POD activity (25%) up to 230 MPa, while some activation was observed for treatments carried out in 250–400 MPa range for both enzymes. Optimal inactivation of POD was using 230 Mpa and 43°C in strawberry puree. Combinations of high pressure and temperature effectively reduced POD activity in orange juice (50%) to 35°C. The effects of high pressure and temperature on PME activity in orange juice were very similar to those for POD.     

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

The 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).     

High pressure thermal processing of pears: Effect on endogenous enzyme activity and related quality attributes

The effect of high pressure-thermal (HPT) processing (600 MPa, 20–100 °C) on the activity of pear enzymes and related quality attributes was investigated. HPT processing at 20 °C for 5 min resulted in 32%, 74% and 51% residual activities of polyphenol oxidase (PPO), peroxidase (POD) and pectin methylesterase (PME), respectively. Increasing processing temperature to 40 and 60 °C reduced the level of PPO and POD inactivation, with the maximum residual activities of 64% and 123%, respectively observed after 3-min treatments at 40 and 60 °C. Overall, HPT at 20 to 60 °C had minimal effect on quality, although enzymatic browning was observed upon air exposure. HPT at 80 to 100 °C caused almost complete inactivation of PPO and POD with 90% and 92% inactivation respectively after 3-min processing at 100 °C, which reduced browning upon air exposure. Nevertheless, the lowest texture retention of 22% was observed under this condition.Industrial relevanceThe study examined the effects of combined high pressure thermal processing on quality related pear enzymes and related instrumental quality attributes such as colour and texture. The study enabled identification of processing regimes for enzyme inactivation and quality retention. The excellent quality retention following HPP at 20 to 40 °C makes this condition suitable for ‘fresh-like’ small portion products for immediate consumption after unpacking that do not require complete PPO and POD inactivation. On the other hand, the almost complete inactivation of oxidative enzymes PPO and POD at 100 °C makes this condition more appropriate for the production of bulk products for food service applications or pureed ingredients for baby food, or pear pieces for yoghurt, that require PPO inhibition but not necessarily high firmness retention.     

Inactivation of yeast and filamentous fungi by the lactoperoxidase-hydrogen peroxide-thiocyanate-system

The antifungal activity of the lactoperoxidase (LPO) system with glucose oxidase (GOD) as source of hydrogen peroxide was determined in salt solution and in apple juice. The test organisms Rhodutorula rubra and Saccharomyces cerevisiae were cultivated aerobically in apple juice, Mucor rouxii was grown on wort agar adjusted to pH 4.5. Aspergillus niger and Byssochlamys fulva were kept on malt extract agar. Spores of the filamentous fungi were harvested by suspension in salt solution supplemented with Tween 80® and checked microscopically. The antifungal activity of the combined enzyme system was tested with initial counts of approx. 10⁵ cfu · ml^?1 (yeast cells or spores) suspended in salt solution supplemented with 25 mg · l^?1 thiocyanate and 20 g · l^?1 glucose or in apple juice supplemented with the same amount of thiocyanate. The tests were performed with 25 ml of the medium in 100 ml Erlenmeyer flasks shaken at 28 °C under aerobic conditions. Inactivation was achieved for all test organisms in both media. The yeast strains were found to be least stable while B. fulva was most resistant. A combination of 5 U · ml^?1 LPO with 0.5 to 1 U · ml^?1 GOD was sufficient for complete inactivation of this mold in salt solution within 2 h. The enzyme system also showed antifungal activity in apple juice at acid pH (3.2), although its effectiveness was reduced. In this medium, B. fulva was inactivated by 20 U · ml^?1 LPD and 1 U · ml^?1 GOD within 4 h. R. rubra and S. cerevisiae were unable to survive in apple juice at 5 U · ml^?1 LPO combined with 1 U · ml^?1 GOD. For inhibition by GOD alone, higher amounts of this enzyme were needed and even then only M. rouxii and R. rubra have been affected within the concentration range tested (maximum 3 U · ml^?1).     

Peroxidase and polyphenol oxidase thermal inactivation by microwaves in green coconut water simulated solutions

Enzymes from coconut water such as peroxidase (POD) and polyphenol oxidase (PPO) when in contact with oxygen begin reactions causing nutritional and color losses. Solutions simulating the chemical constituents of coconut water were submitted to a batch process in a microwave oven. PPO and POD inactivation data could be characterized by: PPO/water D_93 °C=16.5 s (z=35.5 °C); PPO/sugars D_91 °C=18 s (z=33°C); POD/water D_91.5 °C=44 s (z=24 °C) and POD/sugars D_92 °C=20.5 s (z=19.5 °C). The contact between salts and enzymes promoted a drastic reduction of the initial activity. After the incidence of microwave energy at temperatures above 90 °C, enzymes activity was not detected. These results can indicate an adequate choice of temperature conditions to inactivate coconut water enzymes. The knowledge of how green coconut water constituents influence POD and PPO activity will supply useful information about microwave processing of coconut water.     

PURIFICATION AND KINETIC CHARACTERIZATION OF POLYPHENOL OXIDASE FROM TOMATO FRUITS (LYCOPERSICON ESCULENTUM CV. MUCHAMIEL)

Two different polyphenol oxidase (PPO) fractions, soluble and particulate, were purified from unripe tomato fruits (Lycopersicon esculentum M. cv. Muchamiel). The PPO present in the soluble fraction was purified fivefold with a 43.5% yield after ammonium sulfate fractionation. PPO in the particulate was purified 4.56‐fold with a 23% yield using the nonionic detergent Triton X‐114. A strong correlation between tomato fruit PPO activity and the physiological disorder blossom‐end rot (BER) was found, with a large increase of the PPO activity in the particulate fraction. Kinetic characterization, including kinetic parameters, pH and temperature profiles, substrate specificity and inhibitors showed similarities in both the soluble and the particulate enzyme(s). However, thermal stability of the particulate enzyme was significantly higher than stability of the soluble PPO, thus indicating possible structural differences. Cupric ions were activators, probably because of their ability to reactivate PPO partly denatured during purification.     

Inactivation kinetics of polyphenol oxidase and peroxidase in pineapple juice by dielectric barrier discharge plasma technology

The non-thermal plasma technique is an innovative non-thermal approach for food preservation and decontamination. Polyphenol oxidase (PPO) and peroxidase (POD), the principal food degrading enzymes in pineapple juice, were inactivated by the Dielectric Barrier Discharge (DBD) plasma. The inactivation kinetics of PPO and POD in pineapple juice were examined at three different voltages 25, 35, and 45 kV for up to 10 min of plasma treatment. The present study's findings revealed that plasma parameters such as voltage and treatment time substantially reduced enzyme activity of both enzymes, with the former parameter having a more pronounced influence on enzyme inactivity. To mathematically represent the model parameters, established kinetic models viz. log-linear, Weibull, and logistic were fitted to observe experimental data. The Weibull model was discovered to be the best fit for the enzyme inactivation kinetics. The scale factor for PPO was 15.95, 10.87, and 5.73 min at 25, 35, and 45 kV, respectively which was lower than POD with scale factor 40.74, 19.76, and 7.28, respectively. This shows that POD was more resistant to inactivation by DBD plasma than PPO.     

Improvement of frozen banana (Musa cavendishii, cv. Enana) colour by blanching: relationship between browning, phenols and polyphenol oxidase and peroxidase activities

 Browning in banana (Musa cavendishii, cv. Enana) processed products is a result of phenol oxidation catalysed by polyphenol oxidase (PPO) and peroxidase (POD) or of other non-enzymatic reactions (Maillard and Strecker mechanisms). Microwave and steam blanching significantly reduced PPO and POD activities and phenol levels in banana flesh, steam blanching being the most effective method for enzyme inactivation. Freezing/thawing processes produced a significant increase in phenol levels in all samples, due to cellular breakdown. After microwave heating browning processes occurred while steam-treated samples did not exhibit a significant colour change. Extractable PPO and POD activities in all banana samples increased as a consequence of freezing/thawing: steam-blanched slices exhibited lower residual activities. High correlations occurred between phenols and browning (r=0.86) in control samples. Blanched samples (microwave or steam) only exhibited correlations between PPO (r=0.80) and POD (r=0.80) activities and browning. Received: 22 February 1996     

Improvement of frozen banana (Musa cavendishii, cv. Enana) colour by blanching: relationship between browning, phenols and polyphenol oxidase and peroxidase activities

 Browning in banana (Musa cavendishii, cv. Enana) processed products is a result of phenol oxidation catalysed by polyphenol oxidase (PPO) and peroxidase (POD) or of other non-enzymatic reactions (Maillard and Strecker mechanisms). Microwave and steam blanching significantly reduced PPO and POD activities and phenol levels in banana flesh, steam blanching being the most effective method for enzyme inactivation. Freezing/thawing processes produced a significant increase in phenol levels in all samples, due to cellular breakdown. After microwave heating browning processes occurred while steam-treated samples did not exhibit a significant colour change. Extractable PPO and POD activities in all banana samples increased as a consequence of freezing/thawing: steam-blanched slices exhibited lower residual activities. High correlations occurred between phenols and browning (r=0.86) in control samples. Blanched samples (microwave or steam) only exhibited correlations between PPO (r=0.80) and POD (r=0.80) activities and browning. Received: 22 February 1996     

Kinetic characterisation and thermal inactivation study of polyphenol oxidase and peroxidase from table grape (Crimson Seedless)

Polyphenol oxidase (PPO) and peroxidase (POD) were extracted from a table grape (Crimson Seedless) using Triton X-114 and characterized using spectrophotometric methods. Both PPO and POD were activated by acid shock. However, in the presence of the anionic detergent sodium dodecil sulphate (SDS), PPO was activated whereas POD was inactivated. The enzymes were kinetically characterized and both followed Michaelis–Menten kinetics, although with different values of their kinetic parameters. The V_m/K_m ratio showed that Crimson Seedless grape PPO presents a similar affinity for 4-tert-butyl-catechol (TBC) whether activated by acid shock (0.018 min⁻¹) or SDS (0.023 min⁻¹). With regards to POD, the K_m and V_m values for 2,2′-azinobis(3-ethylbenzothiazolinesulphonic acid) (ABTS) were 0.79 mM and 1.20 μM/min, respectively. In the case of H₂O₂, the K_m and V_m value were 0.4 mM and 0.93 μM/min, respectively. PPO and POD showed similar thermostability, losing >90% of relative activity after only 5 min of incubation at 78 °C and 75 °C, respectively. In addition, PPO´s activation energy was similar to that obtained for POD (295.5 kJ/mol and 271.9 kJ/mol, respectively).     

Peroxidase and Polyphenoloxidase Activities in Papaya During Postharvest Ripening and After Freezing/Thawing

Changes in peroxidase (POD) and polyphenoloxidase (PPO) activities of papaya (Caricu papava), cv Sunrise, during ripening, freezing and short frozen storage were studied. Fruits were stored at 14°C and 85 90 % RH until maturity for processing was reached (about 21 days). Fruit were frozen cryogenically and frozen slices were stored at — 18°C. POD activity increased in pulp tissue up to the ripe stage, showing a maximum value after 7 days cold storage. Similarly, PPO activity showed an important increase (4 × initial value) on the same date. The quantity of extractable proteins was at a maximum after 15 days storage at 14°C. Freezing and frozen storage (-18°C) produced an increase of POD activity while EPO activity was only slightly affected.     

Erratum

Abstract

The effects of high hydrostatic pressure treatment (100 to 600 MPa) coupled with heat treatment (0 to 60 °C) on the inactivation of peroxidase (POD) and polyphenoloxidase (PPO) in red grapes (Vitus viniferd) have been studied. The examination of the complex interactions between pressure and temperature has been carried out using a central composite rotatable design (CCRD). The response surfaces show that the lowest activity of POD (55.75%) and PPO (41.86%) was found to be at 60 °C at 600 MPa and 100 MPa, respectively.