Purification, characterization, thermal and high-pressure inactivation of a pectin methylesterase from white grapefruit (Citrus paradisi)

Mechanisms of persimmon pectin methyl esterase activation by high pressure processing based on chemical experiments and molecular dynamics simulations

High pressure processing (HPP) was found to have a kinase effect on persimmon pectin methyl esterase (PME), while the mechanism remains unclear. In this study, chemical experiments and molecular dynamics (MD) simulations were used to reveal its mechanisms. Persimmon PME was first extracted and purified using ion exchange columns with 81.89% purity. After 500 MPa/5 min, PME activity increased 11.3%, the α-helix and β-folding decreased 10.8% and 6.1% compared to the 0.1 MPa group, respectively. MD results showed that HPP decreased the volume, increased the number of hydrogen bonds between PME and pectin. Under high pressure, Asp-157, Asp-136 and Gln-135 in the enzyme activity center remained stable, while the positions of Arg-225 and Gln-113 changed a lot. The conformation of the substrate binding channel also changed. The secondary structure and volume changes of the HPP-treated PME affected the active center and substrate channels, ultimately altering the activity.

Impacts of thermal and non-thermal processing on structure and functionality of pectin in fruit- and vegetable- based products: A review

Pectin, a major polysaccharide found in the cell walls of higher plants, plays major roles in determining the physical and nutritional properties of fruit- and vegetable-based products. An in-depth understanding of the effects of processing operations on pectin structure and functionality is critical for designing better products. This review, therefore, focuses on the progress made in understanding the effects of processing on pectin structure, further on pectin functionality, consequently on product properties. The effects of processing on pectin structure are highly dependent on the processing conditions. Targeted control of pectin structure by applying various processing operations could enhance textural, rheological, nutritional properties and cloud stability of products. While it seems that optimizing product quality in terms of physical properties is counteracted by optimizing the nutritional properties. Therefore, understanding plant component biosynthesis mechanisms and processing mechanisms could be a major challenge to balance among the quality indicators of processed products.

The effect of high-power ultrasound on the quality of carrot juice

The effect of high-power ultrasound treatment on enzymes' activity, physicochemical attributes (total soluble solids, pH, viscosity, turbidity, particle size distribution and colour) and carotenoids' content of carrot juice was investigated. The treatments were carried out at 20 kHz (0.95, 2.38, 3.80 W/ml power) in an ice bath for 2, 4, 6, 8, 10 min. The polyphenol oxidase and pectin methylesterase activity were decreased by 43.90 and 37.95% at 3.80 W/ml power and 10 min exposure time, respectively. With the increase of power and time, the effect of high-power ultrasound on the inactivation of enzymes was getting stronger. However, high-power ultrasound had no inactivation effect on peroxidase activity under all treatment conditions. The visual colour differences were not obvious after high-power ultrasound. The pH, total soluble solids and particle size distribution of carrot juice were not significantly affected (p > 0.05) under all treatment conditions, while turbidity was increased and carotenoids' content was decreased. The viscosity of carrot juice was decreased by 1.27% at 0.95 W/ml power and 8 min, while it was increased by 2.29% at 2.38 W/ml power and 8 min. The value of viscosity was negatively correlated with the activity of pectin methylesterase (Pearson's r = -0.481, p < 0.05). According to these results, we could conclude that the optimal treatment condition was 3.80 W/ml for 10 min. Overall, high-power ultrasound treatment inhibited browning, maintained taste and nutritional value and improved stability of carrot juice. Therefore, this technology could well be an option for processing of carrot juice and laid the theoretical foundation for the production of carrot juice and carrot compound beverage.

Effects of high-power ultrasound on microflora, enzymes and some quality attributes of a strawberry drink

BACKGROUND

The objective of the present work was to study the effect of high-power ultrasound (HPU) on the microflora, enzymes and some quality attributes of a strawberry drink and to provide a theoretical basis for strawberry drink processing conducive to the development of more nutritious and healthier strawberry drinks.

RESULTS

Fresh strawberry drink was subjected to HPU treatment at 20 kHz (242, 605 and 968 W cm^-2 ) for 2, 4, 6, 8 and 10 min in an ice bath. Results showed that polyphenol oxidase (PPO), pectin methyl esterase (PME) and β-glucosidase activities were decreased by 44.90, 89.11 and 84.71% respectively at 968 W cm^-2 for 10 min. Lower L*, a* and b* values and higher browning degree (BD) were observed in HPU-treated samples, resulting in a significant increase in ΔE value (P < 0.05). HPU treatment caused loss of viscosity and turbidity, while total soluble solids (TSS) and pH of the strawberry drink were stable. Total phenol content and antioxidant capacity increased while anthocyanin content decreased compared with untreated samples. Total aerobic bacteria (TAB) and molds and yeasts (M&Y) were reduced by 2.07 and 1.13 log₁₀ cycles respectively at 968 W cm^-2 for 10 min.

CONCLUSIONS

HPU can effectively achieve the effect of pasteurization and maintain the nutrients of strawberry drink. © 2018 Society of Chemical Industry.

Purification and Characterization of a Salt-Dependent Pectin Methylesterase from Carica papaya Fruit Mesocarp-Exocarp Tissue

Pectin methylesterase (PME) is a ubiquitous cell wall enzyme, which de-esterifies and modifies pectins for food applications. Functional properties of pectin rely on molecular weight and degree of esterification, and thus de-esterification by PME influences the pectin functionality. The main aim of the study is to purify and biochemically characterize PME from the outer mesocarp-exocarp tissue of unripe Carica papaya L. fruit. The ion-exchange and gel-permeation chromatography purified enzyme exhibited a specific activity of 2363.1 ± 92.8 units/mg protein, with a fold purification of 10.6, and final recovery of 9.0%. The PME showed a low apparent mass of 27 kDa by SDS-PAGE. The optimal activity of purified PME was found at pH 7.0, and at 60 °C. The enzyme is fairly stable at 60 °C for 10 min, retaining 60% activity. The optimum activity was found with 0.25 mol/L monovalent salts indicating that this PME is salt-dependent. The K_m of PME was 0.22 mg/mL, and the V_max value was 1289.15 ± 15.9 units/mg. The increase in the calcium sensitivity of the PME-treated pectin indicated a blockwise mode of action. The PME significantly differs from other known plant PMEs in their biochemical properties. Manual inspection and MASCOT searching of generated tryptic peptides confirmed no homology to known papaya PME sequences. The preliminary results indicate that the papaya PME can be potentially utilized to modify pectin functionality at elevated temperature. However, further investigation is required to understand the usefulness of this enzyme for the modification of pectins for various food applications.

PRACTICAL APPLICATION

In this work, a small, 27 kDa papaya PME was purified by ion-exchange and gel-permeation chromatography and biochemically characterized. The papaya PME significantly differs from other known plant PMEs in their biochemical properties. The preliminary results like fair thermostability coupled with high temperature optimum indicate that the papaya PME can be potentially utilized to modify pectin functionality at high temperature. Modification of pectin functionality at elevated temperatures is advantageous since it evades the detrimental action of other pectinolytic enzymes.

Inactivation kinetics, structural, and morphological modification of mango soluble acid invertase by high pressure processing combined with mild temperatures

The activity, structure and morphology of mango soluble acid invertase (SAI) were investigated after high pressure processing (HPP) combined with mild temperature at 50-600MPa and 40-50°C. The activity of mango SAI was efficiently reduced by HPP at 50MPa/45 and 50°C, or 600MPa/40, 45 and 50°C, while it was increased by 10-30% after HPP at 50-200MPa/40°C. Significant antagonistic effect of pressure and temperature on the activity of SAI was observed at 50-400MPa/50°C. The secondary structure of SAI was not influenced by HPP. However, its tertiary structure was modified by HPP, and severer modification occurred with higher pressure, higher temperature, and longer treatment time. Results of atomic force microscope suggested that HPP at 400MPa/50°C for 2.5min induced dissociation of SAI, and HPP at 600MPa/50°C for 30min resulted aggregation of SAI.

Effect of processing on physicochemical composition, bioactive compounds and enzymatic activity of yellow mombin (Spondias mombin L.) tropical juice

Yellow mombin (Spondias mombin, L.) is a tropical fruit that presents exotic taste and aroma, being source of carotenoids and phenolics compounds. It presents a good potential for processing, despite some restriction related with the presence of high amounts of peroxidase (POD) and pectinmethylesterase (PME) which can cause sensory changes in the product. This work addresses the evaluation of changes in POD and PME enzyme activity during the traditional industrial processing used to produce tropical juices in Brazil. The enzyme activity was determined after the main steps of the processing: fruit pulping, homogenization and pasteurization. Although both enzymes presented significant activity loss during processing, the final product showed residual activity for PME (25 %) and POD (2.5 %). PME showed to be more thermal resistant than POD in yellow mombin juice. Considering the compounds with antioxidant activity, yellow mombin presented high amounts of carotenoids and phenolics when compared to other tropical fruits such as passion fruit and pineapple. Although the processing of the fruit resulted in significative phenolic loss, the carotenoids content was not affected significantly by the processing.

Extraction and characterization of pectin methylesterase from Alyanak apricot (Prunus armeniaca L)

This study was carried out to determine some of the biochemical properties of pectin methylesterase (PME) from Alyanak apricot which is an important variety grown in Malatya region of Turkey. The enzyme had high activity in a pH range of 7.0-8.0 with the maximal activity occurring at pH 7.5. However, the enzyme activity at high and low pH values was very low. The optimum temperature for maximal PME activity was found to be 60 °C. The activity of PME has been enhanced by NaCl, particularly at 0.15 M. Km and Vmax values for Alyanak apricot PME using apple pectin as substrate were found to be 1.69 mg/mL (r(2) = 0.992) and 3.41 units/mL, respectively. The enzyme was stable at 30-45 °C/10 min whereas it lost nearly all of its activity at 80 °C/10 min. Ea and Z values were found to be 206.1 kJ/mol (r(2) = 0.993) and 10.62 °C (r(2) = 0.992), respectively.

The stability of almond β-glucosidase during combined high pressure-thermal processing: a kinetic study

The thermal and the combined high pressure-thermal inactivation kinetics of almond β-glucosidase (β-D-glucoside glucohydrolase, EC 3.2.1.21) were investigated at pressures from 0.1 to 600 MPa and temperatures ranging from 30 to 80 °C. Thermal treatments at temperatures higher than 50 °C resulted in significant inactivation with complete inactivation after 2 min of treatment at 80 °C. Both the thermal and high pressure inactivation kinetics were described well by first-order model. Application of pressure increased the inactivation kinetics of the enzyme except at moderate temperatures (50 to 70 °C) and pressures between 0.1 and 100 MPa where slight pressure stabilisation of the enzyme against thermal denaturation was observed. The activation energy for the inactivation of the enzyme at atmospheric pressure was estimated to be 216.2±8.6 kJ/mol decreasing to 55.2±3.9 kJ/mol at 600 MPa. The activation volumes were negative at all temperature conditions excluding the temperature-pressure range where slight pressure stabilisation was observed. The values of the activation volumes were estimated to be -29.6±0.6, -29.8±1.7, -20.6±3.2, -41.2±4.8, -36.5±1.8, -39.6±4.3, -31.0±4.5 and -33.8±3.9 cm3/mol at 30, 35, 40, 45, 50, 60, 65 and 70 °C, respectively, with no clear trend with temperature. The pressure-temperature dependence of the inactivation rate constants was well described by an empirical third-order polynomial model.

Acceleration of precipitation formation in peach juice induced by high-pressure carbon dioxide

Peach juice was treated by high-pressure carbon dioxide (HPCD). HPCD-induced acceleration of precipitation formation in peach juice was observed. Particle size distribution (PSD), pH, zeta-potential, protein and total phenols, pectin methylesterase (PME) activity, pectin and calcium, and viscosity in juice, contributing to the precipitation formation, were studied. HPCD resulted in a significant alteration of juice PSD pattern; the acceleration of the precipitation formation concurred with this alteration. A significant decrease of protein and a declining trend of total phenols were obtained, the contents of pectin and calcium were not changed, and the difference in PME activity in juice was not significant after HPCD. HPCD led to higher increase in juice viscosity, whereas pH and the absolute value of zeta-potential declined during HPCD. These results suggested that the pH and absolute value of zeta-potential declines induced the coagulation of protein and decrease of particle charge, responsible for the acceleration of the precipitation formation.

Inactivation of apple pectin methylesterase induced by dense phase carbon dioxide

The inactivation of apple pectin methylesterase (PME) with dense phase carbon dioxide (DPCD) combined with temperatures (35-55 degrees C) is investigated. DPCD increases the susceptibility of apple PME to the temperatures and the pressures have a noticeable effect on apple PME activity. A labile and stable fraction of apple PME is present and the inactivation kinetics of apple PME by DPCD is adequately described by a two-fraction model. The kinetic rate constants k L and k S of labile and stable fractions are 0.890 and 0.039 min (-1), and the decimal reduction times D L and D S are 2.59 and 58.70 min at 30 MPa and 55 degrees C. Z T representing temperature increase needed for a 90% reduction of the D value and the activation energy E a of the labile fraction at 30 MPa is 22.32 degrees C and 86.88 kJ /mol, its Z P representing pressure increase needed for a 90% reduction of the D value and the activation volume V a at 55 degrees C is 21.75 MPa and -288.38 cm (3)/mol. The residual activity of apple PME after DPCD exhibits no reduction or reactivation for 4 weeks at 4 degrees C.

Purification and thermal and high-pressure inactivation of pectinmethylesterase isoenzymes from tomatoes (Lycopersicon esculentum): a novel pressure labile isoenzyme

Tomato pectinmethylesterase (PME) was successfully purified by a two-step method consisting of affinity chromatography followed by cation exchange chromatography. According to this procedure, four different isoenzymes were identified representing molar masses around 34.5-35.0 kDa. Thermal and high-pressure inactivation kinetics of the two major isoenzymes of tomato PME were studied. A striking difference between their process stability was found. The thermostable isoenzyme was completely inactivated after 5.0 min at 70 degrees C, whereas for the thermolabile isoenzyme, temperatures at around 60 degrees C were sufficient for complete inactivation. The thermostable isoenzyme was also found to be pressure stable since no inactivation was observed after 5.0 min of treatment at 800 MPa and 20 or 40 degrees C. The thermolabile isoenzyme appeared to be pressure labile since it could be completely inactivated after 5.0 min of treatment at 700 MPa and 20 degrees C or 650 MPa and 40 degrees C. Inactivation kinetics at pH 6.0 could be accurately described by a first-order model.

Refrigerated fruit juices: quality and safety issues

Fruit juices are an important source of bioactive compounds, but techniques used for their processing and subsequent storage may cause alterations in their contents so they do not provide the benefits expected by the consumer. In recent years consumers have increasingly sought so-called "fresh" products (like fresh products), stored in refrigeration. This has led the food industry to develop alternative processing technologies to produce foods with a minimum of nutritional, physicochemical, or organoleptic changes induced by the technologies themselves. Attention has also focused on evaluating the microbiological or toxicological risks that may be involved in applying these processes, and their effect on food safety, in order to obtain safe products that do not present health risks. This concept of minimal processing is currently becoming a reality with conventional technologies (mild pasteurization) and nonthermal technologies, some recently introduced (pasteurization by high hydrostatic pressure) and some perhaps with a more important role in the future (pulsed electric fields). Nevertheless, processing is not the only factor that affects the quality of these products. It is also necessary to consider the conditions for refrigerated storage and to control time and temperature.

High pressure application for food biopolymers

High hydrostatic pressure constitutes an efficient physical tool to modify food biopolymers, such as proteins or starches. This review presents data on the effects of high hydrostatic pressure in combination with temperature on protein stability, enzymatic activity and starch gelatinization. Attention is given to the protein thermodynamics in response to combined pressure and temperature treatments specifically on the pressure-temperature-isokineticity phase diagrams of selected enzymes, prions and starches relevant in food processing and biotechnology.