Inactivation Of Polyphenol Oxidase Research Articles

Effect of pulsed electric field processing on the quality characteristics and enzyme activity of tender coconut water.

Tender coconut water (TCW) is a natural drink rich in natural electrolytes, minerals, salts and sugars; it has good health benefits. But, its shelf-life is very limited because of the active nature of enzymes present in it when exposed to air. Therefore, the processing of TCW is necessary to inactivate the enzymes. So, this study aims to observe the effect of various process parameters of pulsed electric field (PEF) on the quality parameters of TCW. For the treatment of TCW with PEF, a full-factorial design of experiments was followed with process parameters such as three levels of electric field intensity (8, 12, and 16 kV/cm), two levels of pulse width (PW) (50 and 70 μs), and six levels of the number of pulses (2000 to 12,000 pulses) were considered at a constant pulse OFF time of 75 ms. PEF treatment did not significantly change pH, total soluble solids, and viscosity. However, it significantly affected vitamin C, colour, and total and reducing sugars. PEF treatment significantly enhanced the total phenolic content and antioxidant activity by 23.17% and 42.49%, respectively. At the same time, significant inactivation of polyphenol oxidase (100%) and peroxidase (60.2%) was observed at PEF treatment conditions of 16 kV/cm, 70 μs PW, and 12,000 pulses. Moreover, no significant change in the sensory acceptability of PEF-treated TCW (16 kV/cm, 70 μs PW, 12,000 pulses) when compared to the untreated/fresh TCW, which is a promising sign.

Pulsed electric field processing of fruit juices with inactivation of enzymes with new inactivation kinetic model and determination of changes in quality parameters

Pulsed electric fields (PEF) processing of fresh grape, orange and tomato juices by 17.2–24.1 kV/cm electric field strengths, 130.0–1040.5 μs treatment times and 1.43–29.13 J/kg energies with respect to determination of the changes in the physical and bioactive properties, color parameters in addition to inactivation of pectin methyl esterase (PME), polyphenol oxidase (PPO), and lipoxygenase (LOX) enzymes were studied. In general, decrease in pH, increase in conductivity (except for grape juice), total phenolic substance content, and total antioxidant capacity with no significant change (p > 0.05) in total soluble solids were observed by PEF treatment for all juices. Except for hue value for orange juice, no significant changes (p > 0.05) were observed in color values. Inactivation of the enzymes were increased with increased energy, and calculated electrical activation energies for PME, PPO, and LOX enzymes were 8.31, 7.06, and 4.31 kJ/mol, respectively. Industrial relevanceEnzymes in addition microorganisms causing quality degradation is of great concern in fruit juice industry as most of the enzymes are resistant to processing technologies. Increased PEF treatment time provided over 95% inactivation on PME, PPO, and LOX enzymes with no adverse effect on quality properties of grape, orange, and tomato juices revealing a viable alternative to juice processing industry.

Inactivation of polyphenol oxidase by low intensity DC field: Experiment and mechanism analysis via molecular dynamics simulation and molecular docking

In this study, inactivation of mushroom polyphenol oxidase (PPO) by low intensity direct current (DC) electric field and its molecular mechanism were investigated. In the experiments under 3 V/cm, 5 V/cm, 7 V/cm and 9 V/cm electric fields, PPOs were all completely inactivated after different exposure times. Under 1 V/cm, a residual activity of 11.88 % remained. The inactivation kinetics confirms to Weibull model. Under 1–7 V/cm, n value closes to a constant about 1.3. The structural analysis of PPO under 3 V/cm and 5 V/cm by fluorescence emission spectroscopy and molecular dynamics (MD) simulation showed that the tertiary structure was slightly changed with increased radius of gyration, higher potential energy and rate of C-alpha fluctuation. After exposure to the electric field, most of the hydrophobic tryptophan (TRP) residues turned to the hydrophilic surface, resulting the fluorescence red-shifted and quenched. Molecular docking indicated that the receptor binding domain of catechol in PPO was changed. PPO under electric field was MD simulated the first time, revealing the changing mechanism of the electric field itself on PPO, a binuclear copper enzyme, which has a metallic center. All these suggest that the low intensity DC electric field would be a promising option for enzymatic browning inhibition or even enzyme activity inactivation.

Inactivation kinetics of polyphenol oxidase and peroxidase enzymes in buffer solutions by ultraviolet light sources at multiple UV-C wavelengths

This study aimed to evaluate the effect of multiple wavelengths of UV-C light sources on the inactivation of polyphenol oxidase (PPO) and peroxidase (POD) in buffer solutions. Enzyme solutions were treated with a UV-C excimer lamp (EL) emitting at 222 nm, low-pressure mercury (LPM) lamp at 253.7 nm, four UV-LEDs sources emitting at 255, 265, 275 and 285 nm, and a novel pulsed UV-C lamp (PL) emitting at 232, 242, 261 and 272 nm. Three kinetic models were used to compare UV-C wavelengths enzymatic inactivation efficacy considering the volume average fluence for 90% reduction (HD). Validation of kinetic parameters was performed under continuous-flow treatment in a UV-C LED and EL system. EL treatment resulted in the highest inactivation efficacy of PPO and POD enzymes with HD of 52.8 and 74.8 mJ/cm2, respectively. PL inactivation efficacy for both enzymes was higher than with LPM lamp or UV-LEDs. The two-component first-order model best described the inactivation of PPO and POD in a buffer solution. The adjusted kinetic parameters for this model were validated under UV-C light continuous flow processing. This study contributes to the development of liquid food treatment by ultraviolet technology.

Inactivation of polyphenol oxidase and peroxidase in pineapple juice during continuous ohmic heating and modeling of inactivation kinetics during isothermal holding

AbstractContinuous ohmic heating (COH) is a novel thermal technology for fruit juice processing and preservation. The present work demonstrated the effect of COH parameters like electric field strength (EFS: 30–40 V/cm), isothermal holding (0–60 s), and temperature (70–90°C) on the inactivation of polyphenol oxidase (PPO) and peroxidase (POD) in standardized pineapple juice. Statistical parameters and Akaike information criteria were used to compare kinetic models like the first order, distinct isozymes, Weibull distribution, sigmoidal logistic, and fractional conversion for PPO and POD inactivation. The findings revealed that the COH parameters significantly affected the activities of both enzymes. A maximum inactivation of 68.2% of PPO and 82.2% of POD was observed at 90°C, 60 s, and 40 V/cm. The Weibull distribution model, compared to other models, was found to describe the inactivation kinetics better for both PPO (R2 > 0.99; RMSE < 0.0101) and POD (R2 > 0.98; RMSE < 0.042). The accuracy factor (Af) and bias factor (Bf) for both PPO (Af = 1.003–1.010; Bf = 1.000–1.004) and POD (Af = 1.007–1.072; Bf = 0.992–1.009) were closer to simulation line suggesting the accuracy of the Weibull model in predicting the enzyme inactivation. Also, Akaike increment (∆i < 2) substantially supported the Weibull model. The shape factor (n < 1) explained the tailing phenomenon of the enzymes. The PPO's scale factor (δ values) was higher than POD, suggesting higher thermal stability of PPO than POD. Thus, the Weibull model is a good tool for predicting the enzyme inactivation in COH‐treated standardized pineapple juice.Practical ApplicationsContinuous ohmic heating (COH) is a novel electro‐thermal technology that heats the fruit juice quickly, uniformly, and volumetrically. Generally, for inactivating spoilage enzymes like polyphenol oxidase and peroxidase during pineapple juice processing in an industrial set‐up, a conventional method of conduction and convection mode of heat transfer is used. This results in a high‐temperature gradient within the juice matrix, causing a problem of over‐ and under‐processing of juice. Ohmic heating is a potential and efficient way of inactivating these spoilage enzymes to a desired level in a shorter processing time. It can be used to preserve juice by extending its shelf life. COH can reduce the total heat damage to the juice by maintaining its flavor and nutrient compounds. Overall, ohmic heating is a versatile and effective technology for the continuous processing of fruit juice for improved product quality and production efficiency.

Modeling the inactivation kinetics of polyphenol oxidase and peroxidase during the cold plasma treatment of kiwifruit juice

AbstractCold Plasma (CP) is an emerging non‐thermal technology that preserves and decontaminates food. Kiwifruit juice spoilage enzymes polyphenol oxidase (PPO) and peroxidase (POD) were studied at 24‐36 kV, 2‐10 mm juice depth, and 2‐10 min treatment time using log‐linear, Weibull distribution, and logistic models. The Weibull and logistic model explained enzyme inactivation kinetics well based on goodness of fit (Coefficient of determination: 0.97‐0.99 & root mean square error: 0.11‐2.15) and validation indices (accuracy factor: 1‐1.06 and bias factor: 0.96‐1.04). The logistic model suited PPO and POD inactivation curves well, with the least Akaike weight in 71.29% and 61.45%, respectively. POD had a half‐maximal activity of 11.37, 5.22, and 3.60 min at 24 kV, 30 kV, and 36 kV at 6 mm juice depth, compared to 8.71, 4.41, and 2.51 min for PPO. This shows that POD is more CP‐resistant than PPO, making its inactivation in kiwifruit juice crucial.Practical ApplicationKinetic modeling helps to comprehend the fundamental process and is suitable for improving the inactivation process and enhancing its efficacy. As a relatively primary method, mathematical models facilitate a greater comprehension of the mechanism and factors influencing the inactivation processes. This study involves the inactivation of PPO and POD to produce a stable kiwifruit juice. The inactivation of PPO and POD enzymes will prevent the undesirable enzymatic browning of juice. The kinetic data related to enzyme inactivation will help in deciding the process parameters like plasma voltage, juice depth, and treatment time for producing enzymatically stable kiwifruit juice.

Effect of low intensity direct-current electric field on anti-browning of apple juice: Enzyme inactivation kinetics and juice properties

For the first time, the efficacy of low intensity (1–7 V/cm) direct-current (DC) electric field in preventing browning in apple juice is examined. The results show that applying a 5 V/cm electric field can inactivate 89.24% of polyphenol oxidase (PPO) within 90 min and achieve complete inactivation of peroxidase (POD) within 70 min, maintaining the juice temperature below 30 °C throughout the process. The Weibull model fits the PPO and POD inactivation effectively, suggesting varied responses among isoenzymes. Under the optimal conditions (5 V/cm for 90 min), a 15.89% increase in total phenolic content (TPC) was observed alongside significant improvements in antioxidant activity. Furthermore, this method preserved the natural flavor and lightened the color of the apple juice, enhancing its sensory appeal. These findings indicate that low intensity DC electric field is an innovative and effective choice for preventing juice browning, offering significant potential for application in the food industry.

Polyphenol oxidase inactivation from apple juice by Al-based metal–organic frameworks: New anti-browning strategy in fruits and vegetables

Polyphenol oxidase (PPO) is critical due to enzymatic browning in fruits and vegetables, developing economic impact in fruits industry. Metal-Organic Frameworks (MOF) have shown interesting characteristics such as water stability, low toxicity, and good adsorption yield, making them good candidates for PPO inactivation. Al-based-MOFs, MIL-53(Al), DUT-5, and MIL-110 were tested as PPO inactivators in apple juice by enzyme-MOF interactions at r.t. through two possible mechanisms, i) substrate scavengers (substrates:catechol and 4-methylcatechol) or ii) enzyme activity modifiers. The scavenging behavior of Al-based-MOFs was moderate, in the same magnitude, being catechol adsorption better than 4-methylcatechol. PPO activity was reduced by at least 70% by MIL-53(Al)/DUT-5 in 10/30 min respectively, and MIL-110 inactivated PPO in 50 min with some structural modifications. Enzyme-MOF interactions are major responsible for PPO inactivation. This could be a new applicability of MOFs, as an alternate PPO inactivation process, easily included in juice processing, retaining sensorial/nutritional properties, developed at r.t thus energy-cost-effective.

High-humidity hot-air impingement blanching conditions for the inhibition of potato-browning enzymes and for quality retention.

Potato is an important non-cereal crop. It provides carbohydrates, a major source of energy in the human diet. Blanching during the processing of fresh fruits and vegetables is essential for their preservation. High-humidity hot-air impingement blanching (HHAIB) is a promising emerging technology for pretreating different food materials. This research aimed to identify the optimum HHAIB conditions for the inhibition of potato-browning enzymes, maintaining their nutritional and physical quality, and to compare this with conventional hot-water blanching (HWB). Polyphenol oxidase (PPO) inactivation, total phenol content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, color, textural attributes, thermal properties, microstructure, and particles crystallinity were evaluated. The relative humidity (RH), temperature, and duration of HHAIB required for PPO inactivation (2.59%) were 50%, 105 °C, and 4 min, respectively, which resulted in a complete gelatigination of potato starches, based on the thermal properties and the microstrcture of the blanched potatoes. These conditions led to improvements in TPC to 312.54 μg GAE.g-1 FP, DPPH scavenging to 1.99 μmol TE.g-1 FP, as well as enhancements in color and crystallinity. When HHAIB was conducted at lower temperatures (85 and 95 °C) there were negative effects on the blanched potatoes' color and crystallinity, along with a non-safe level of PPO activity. High-humidity hot-air impingement blanching was superior to HWB, inhibiting PPO, maintaining nutrients, and preserving physical properties, especially under the optimum conditions revealed by the principal component analysis. It provides an excellent technique for blanching and pretreating potatoes, preserving them, and maintaining their quality. © 2023 Society of Chemical Industry.

Advanced interactional characterization of the inhibitory effect of anthocyanin extract from Hibiscus sabdariffa L. on apple polyphenol oxidase.

In this study, a comprehensive approach to advance the inhibitory effect of Hibiscus sabdariffa extract on apple polyphenol oxidase (PPO) was performed. PPO was extracted, purified, and characterized for optimal activity, whereas response surface methodology generated a quadratic polynomial model to fit the experimental results for hibiscus extraction. The optimum conditions allowed to predict a maximum recovery of anthocyanins (256.11mg delphinidin-3-O-glucoside/g), with a validated value of 272.87mg delphinidin-3-O-glucoside/g dry weight (DW). The chromatographic methods highlighted the presence of gallic acid (36,812.90µg/g DW extract), myricetin (141,933.84µg/g DW extract), caffeic acid (101,394.07µg/g DW extract), sinapic acid (1157.46µg/g DW extract), kaempferol (2136.76µg/g DW extract), and delphinidin 3-O-β-d-glucoside (226,367.08µg/g DW extract). The inactivation of PPO followed a first-order kinetic model. A temperature-mediated flexible fit between PPO and anthocyanins was suggested, whereas the molecular docking tests indicated that PPO is a good receptor for cafestol, gallic acid, and catechin, involving hydrophobic and hydrogen bond interactions. PRACTICAL APPLICATION: It is well known that enzymatic browning is one of the most important challenges in the industrial minimal processing of selected fruit and vegetable products. Novel inhibitors for polyphenol oxidase are proposed in this study by using an anthocyanin-enriched extract from Hibiscus sabdariffa L. Based on our results, combining the chemical effect of phytochemicals from hibiscus extract with different functional groups with minimal heating could be an interesting approach for the development of a new strategy to inhibit apple polyphenol oxidase.

Sugarcane polyphenol oxidase: Structural elucidation using molecular modeling and docking analyses

Polyphenol oxidase (PPO) enzymes induce undesirable browning in fruits, vegetables, and juices like sugarcane and apple. Inactivation of PPO is crucial to mitigate this issue, achieved through methods like heat, radiation, ultrasound, pH adjustment, adsorbent addition, and inhibitors. Inhibitor selection is traditionally a time-consuming trial-and-error process. This study aimed to develop a homology model of sugarcane PPO and to streamline inhibitor selection using a rational approach, relying on knowledge of PPO's structure and active site. The research utilized homology modeling through SWISS-MODELER to predict the 3D structures of two types of sugarcane copper-based PPOs: met-PPO (Cu-Cu active site) and oxy-PPO (Cu-O-Cu active site), both composed of 235 amino acids. Model quality was assessed using Global Model Quality Estimation (GMQE) and Qualitative Model Energy Analysis (QMEAN), yielding favorable scores of 0.17 (GMQE), 0.44 ± 0.05 (QMEAN Co-Global) and z-score of –4.03. Ramachandran analysis indicated 78.8 % and 17.5 % of amino acid residues fell within the most favored and additional allowed regions, respectively. Docking analysis revealed strong affinities between m-hydroxybenzoic acid and p-hydroxybenzoic acid with binding energies of –4.40 Kcal/mol and –4.38 Kcal/mol, respectively, for met-PPO and oxy-PPO. Identified active site residues are ARG369, HIS325, GLU321, ALA361, and TRP313. This study enhances comprehension of sugarcane PPO and its active site, aiding rational inhibitor design to counteract undesired browning reactions.

Application of thermosonication for guava juice processing: Impacts on bioactive, microbial, enzymatic and quality attributes

The present work explores different conditions of thermosonication (TS) processing that would ensure microbiological and enzymatic safety for guava juice while simultaneously maximizing the preservation of its quality attributes. The guava juice was subjected to TS treatment (frequency: 40 kHz; power: 200 W; Temperature: 40, 60, and 80 °C; Time: 2, 6 and 10 min) and was compared with fresh and pasteurized (90 °C/60 s) juice samples. The objectives of the research work were to determine the effect of thermosonication on the quality attributes such as total soluble solids (TSS), pH, titratable acidity, cloud value, color attributes, total phenolic contents, total flavonoid contents, antioxidant activity, ascorbic acid levels, enzymatic, microbiological, and sensory properties. The thermosonicated and pasteurized samples showed no significant (p > 0.05) changes in pH, total soluble solids, and titratable acidity. TS improved the cloud value and color attributes. Furthermore, TS enhanced total phenols (10 to17%), flavonoids (5 to 25%), antioxidant activity (10.45% to 14.55%) and retention of ascorbic acid (61.98–83.32%) relative to control. Thermosonicated sample at 80 °C/10 min gives the maximum inactivation of Pectin methyl esterase (PME), Peroxidase (POD) and Polyphenol oxidase (PPO) enzymes. While both thermosonication and pasteurization drastically decreased the microbial count to undetectable levels, only TS exhibited modest improvement in sensory qualities. The results demonstrated that TS can enhance the overall safety, quality, and commercial viability of guava juice as a practical substitute to pasteurization.

Nth order kinetic modelling of peroxidase and polyphenol oxidase inactivation in kiwifruit juice during cold plasma and thermal treatment

The current study examines the effect of thermal and cold plasma (CP) treatment on the inactivation of polyphenol oxidase (PPO) and peroxidase (POD) in kiwifruit juice. The residual activity of POD and PPO were fit to nth-order kinetics at a voltage, juice depth, and treatment time range of 18–30 kV, 2–10 mm, and 2–10 min, respectively. During thermal treatment, the inactivation order (n) value for POD and PPO were 1.07 and 1.06, whereas, for the cold plasma treatment, it was 2.07 and 2, respectively. The higher D-value of POD than PPO makes the former enzyme more resistant to plasma treatment. The Fourier-transform infrared spectroscopy (FTIR) revealed an increase in the proportion of β-sheet structure from 23 to 28% and a decrease in α-helix from 28 to 20% compared to the control sample. In comparison to thermal treatment, CP treatment effectively retained the biochemical attributes of juice. Industrial relevanceThe PPO and POD inactivation is necessary for preparing stable kiwifruit juice. A detailed kinetic study is mandatory for designing and optimizing the process, as both enzymes react in their way depending on the origin and experimental range. The generated kinetic model can be used to establish the optimum conditions for inactivating enzymes during CP treatment.

Effects of high-humidity hot air impingement cooking on physicochemical properties and microstructure of Pacific white shrimp (Penaeus vannamei)

In this study, the potential of high-humidity hot air impingement cooking (HHAIC) was investigated as an alternative to other conventional cooking methods, including steaming, boiling, and roasting, by assessing the physicochemical properties, taste profile, and sensory evaluations of Pacific white shrimp (Penaeus vannamei). Compared to the steamed-, boiled-, and roasted-treated shrimp, HHAIC-treated samples demonstrated a lower cooking loss between 3.19% and 16.47%, which was possibly attributed to the decreasing muscle rupture. Moreover, HHAIC-treated samples exhibited improved textural properties, higher color retention, better water-holding capacity, and higher degree of polyphenol oxidase inactivation. By low-field nuclear magnetic resonance imaging, HHAIC-treated shrimp showed a pretty uniform water distribution. The main secondary structures of protein in fully-cooked P. vannamei shrimp were β-sheets and β-turns with no significant difference in free amino acid content among the four methods. Therefore, HHAIC could be considered a novel thermal technique for high-quality shrimp products as well as for other aquatic products.

Quality Determination of a High-Pressure Processed Avocado Puree-Based Smoothie Beverage

The aim was to study the quality stability of a high-pressure (HP) processed avocado puree-based smoothie beverage and to determine its shelf life. To achieve this mathematical description of HP process parameters (pressure, temperature, and pH conditions) on polyphenoloxidase (PPO) inactivation of avocado-puree (base of the smoothie beverage), use of the appropriate kinetic models was undertaken. Inactivation rate constants were obtained for combinations of constant pressure (600, 700, 750 MPa) and temperature (25, 35, 45 °C) for pH values 4 and 5. According to the Eyring and Arrhenius equations, activation volumes and activation energies, respectively, representing pressure and temperature dependence of the inactivation rate constant, were calculated for all temperatures and pressures studied. The combined use of HP led to PPO inactivation (<10% remaining PPO activity). An increase in the temperature at pressure 600 or 750 MPa caused an increase in PPO inactivation (4.5 and 9.0%, respectively). The ultimate goal was to produce a HP processed avocado puree-based smoothie beverage (containing acid whey and other ingredients) with superior quality and increased shelf life (under refrigeration). The blended ingredients were HP processed in PET packages (600 MPa-25 °C-10 min, 600 MPa-35 °C-10 min, 750 MPa-25 °C-5 min, 750 MPa-35 °C-5 min) based on PPO inactivation as well as industrial practices. Non-processed as well as thermally (TM) processed (90 °C-5 min) samples were used as control samples. No significant differences were found in sensorial attributes between non-processed and HP samples, although the aroma and acceptability scores decreased significantly for thermally pasteurized smoothies. Based on the data obtained, 600 MPa-25/35 °C-10 min are sufficient to obtain safe smoothies (of pH 5 approximately) (up to 6 months) whose organoleptic properties are equally as acceptable to consumers as freshly made smoothies.

Accurate pH decrease induced inactivation of myrosinase and polyphenol oxidase in salted radish for color improvement

Yellowing even browning of radish commonly occurred during the traditional pickling. This research aimed to determine the reason of yellowing of pickled radish, and propose the method for yellowing inhibition. The activity of endogenous enzymes in radish were analyzed, and the relationship between the activity and the browning was investigated. Myrosinase and polyphenol oxidase (PPO) were found as main potential enzymes resulting in browning of radish. During traditional salting processing, the myrosinase activity decreased, particularly at a high speed in the first 14 days, while the PPO activity did not decrease observably. The a* and b* values of salted radish were significantly correlated with myrosinase and PPO activity. Acid treatment was observed to be effective for browning inhibition of radish during soaking and storage, and the low pH conditions contributed to the preservation of original green color of radish. Stronger acidification during the first 3 d played a much more important role in browning inhibition than following weaker acidification treatment for 27 d. Low pH showed an inhibition effect on PPO activity, but myrosinase reactivity was more sensitive to pH changes than PPO. The myrosinase in the radish treated in the pickling solution at pH 2 was completely inactivated during the first 3 days. Further investigation of pH effect on improvement of salted radish color concluded that pH 2.4 was the optimal pH for the inactivation of myrosinase and PPO. Accordingly, short-term accurate acidification coupled with traditional salting treatment was originally proposed for effective browning inhibition of pickled radish.

Pulsed light treatment of table grape juice: Influence of matrix pH on microbial and enzyme inactivation kinetics

The influence of pulsed light (PL) treatment and matrix pH was tested in the case of green table grape juice. Escherichia coli, Listeria monocytogenes, and Saccharomyces cerevisiae were inoculated into the table grape juices with matrix pH levels of 3.0, 3.5, and 4.0. Further, the juice was treated at 378–3186 J/cm2. The Weibull model better explained the microbial inactivation data. The shape parameters (β) from the Weibull model for E. coli, L. monocytogenes, and S. cerevisiae are 0.95 ± 0.02, 0.55 ± 0.04, and 0.40 ± 0.03, respectively. A lesser δ-value (scale parameter in J/cm2) was obtained for each microorganism at a lower pH. PL exposure resulted in a lack of cell visibility, cell wall, and cell membrane disruption in bacterial cells. The inactivation of polyphenol oxidase (PPO), peroxidase (POD), and pectin methyl esterase (PME) was studied at an elevated fluence level of 1152–3186 J/cm2. Enzymes in the juice were less sensitive to PL than microorganisms. The enzyme inactivation of >90% was achieved at 3186 J/cm2; thus, the juice was adjudged as the microbially safe and enzymatically stable pasteurized sample. The PL-induced enzyme inactivation followed nth-order kinetics with an inactivation order (n) of 1.1, 1.15, and 0.85 for PPO, POD, and PME, respectively. The enzyme inactivation rate was higher at a low pH. The PL-treated pasteurized juice at pH 3.5 showed the highest sensory acceptance (7.4 out of 9), with a minimal color change, a 7% loss in total phenolics, and a 12% loss in vitamin C and flavonoids.

Non-thermal emerging processing Technologies: Mitigation of microorganisms and mycotoxins, sensory and nutritional properties maintenance in clean label fruit juices

The increase in the fruit juice consumption and the interest in clean label products boosted the development and evaluation of new processing technologies. The impact of some emerging non-thermal technologies in food safety and sensory properties has been evaluated. The main technologies applied in the studies are ultrasound, high pressure, supercritical carbon dioxide, ultraviolet, pulsed electric field, cold plasma, ozone and pulsed light. Since there is no single technique that presents high potential for all the evaluated requirements (food safety, sensory, nutritional and the feasibility of implementation in the industry), the search for new technologies to overcome the limitations is fundamental.The high pressure seems to be the most promising technology regarding all the aspects mentioned. Some of the outstanding results are 5 log reduction of E. coli, Listeria and Salmonella, 98.2% of polyphenol oxidase inactivation and 96% PME reduction. However its cost can be a limitation for industrial implementation. The combination of pulsed light and ultrasound could overcome this limitation and provide higher quality fruit juices. The combination was able to achieve 5.8–6.4 log cycles reduction of S. Cerevisiae, and pulsed light is able to obtain PME inactivation around 90%, 61.0 % more antioxidants, 38.8% more phenolics and 68.2% more vitamin C comparing to conventional processing, and similar sensory scores after 45 days at 4 °C comparing to fresh fruit juice.This review aims to update the information related to the application of non-thermal technologies in the fruit juice processing through systematic and updated data to assist in industrial implementation strategies.

Quality characterization of apple puree processed by high frequency pulse continuous heating

High-frequency pulse continuous heating (HFP) was designed to improve high electric field alternating current, which effectively inactivates undesirable enzymes and microorganisms that contribute to quality loss in high-viscosity liquid foods. HFP can increase the temperature of high-viscosity liquid food by 100 °C in 0.4 s. This study investigated the efficacy of HFP at 100 °C and 110 °C in inactivating polyphenol oxidase (PPO) in apple puree and maintaining color quality, vitamin C content, original flavor, and aroma compounds, compared with conventional heating (CH). Despite the short temperature holding period required for HFP (less than 3 s), almost 90% PPO inactivation was achieved with HFP at both 100 °C and 110 °C. In contrast, 30 min of CH treatment at either 70 °C or 80 °C was needed to reduce PPO activity to equivalent levels. Furthermore, apple puree samples treated with HFP reduced browning without the addition of vitamin C, significantly maintained original vitamin C levels and retained the original flavor and aroma compounds. The results demonstrated the effectiveness and efficiency of HFP in increasing the shelf life of apple puree over 28 days of storage, and maintaining color quality, using significantly reduced heating times compared with CH.

Nonthermal inactivation effects on oxidative enzymes in grape juice influenced by moderate electric fields: Effect of constant exposure electrical treatments combined with temperature

Inactivation of polyphenol oxidase (PPO) and peroxidase (POD) enzymes in fresh grape juice was studied by subjecting the juice to moderate electric field (MEF) treatments of 82 and 87 V/cm field strengths. We used an electro-processing device that was built to minimize ohmic heating and enhance cooling during application of electric fields. Kinetic studies indicate that the MEF treatments increase the inactivation of both enzymes at 65 and 75 °C, compared to the corresponding control treatments without electric fields. The increase in the inactivation becomes statistically significant ( P ≤ 0.05) in the MEF treatment at 75 °C. Molecular motion simulations of PPO and POD enzymes correlate with the experimental results. The study results further indicate the efficacy of MEF treatments on the nonthermal inactivation of enzymes, which are held at or near their thermal inactivation threshold temperatures (≤80 °C for PPO and POD). • Moderate electric field (MEF) treatments inactivate enzymes (PPO, POD) in grapes. • The efficacy of MEFs increases with increasing field strength and temperature. • The thermal impact on grape juice can be reduced by applying MEF treatments. • Enzyme's thermal inactivation threshold temperature is useful in MEF studies. • Thermostability and electric field sensitivity of enzymes affect the inactivation.