Comparative study on cloudy apple juice qualities from apple slices treated by high pressure carbon dioxide and mild heat

Supercritical CO2 Processing of White Grape Must as a Strategy to Reduce the Addition of SO2

In winemaking, sulfur dioxide addition is the most common procedure to prevent enzymatic and microbial alterations. However, the enological industry looks for safer alternatives to preserve enological products, and high-pressure treatments with supercritical CO2 are a suitable alternative. This study evaluates the effectiveness of this process in the stabilization and preservation of white grape must, studying the influence of time, pressure, and CO2 percentage on must characteristics. In spite of the percentage of CO2 turned out to be the variable that affects the most the process, no remarkable differences were observed in pH, acidity, and color intensity between untreated and treated musts. Moreover, this technique has proven to be very efficient in the reduction of aerobic mesophilic microorganisms as well as in the reduction of residual polyphenol oxidase activities, being lower than those obtained with SO2 addition (60 and 160 mg/L). Based on the results, the most convenient conditions were 100 bar and 10% CO2, for 10 min treatment.

Thermal Inactivation Kinetics of Kudzu (Pueraria lobata) Polyphenol Oxidase and the Influence of Food Constituents

The thermal inactivation kinetics of kudzu (Pueraria lobata) polyphenol oxidase (PPO) were investigated in model and food systems. PPO in kudzu tissue (tPPO) showed a higher thermostability than that of PPO in crude extract (cPPO) and purification fractions (pPPO). The PPO inactivation rate constant (k) increased with an increase in temperature, and tPPO showed the lowest k value, followed by that of cPPO and pPPO at the same temperature, indicating that PPO in the food system was more resistant to thermal treatment. Food constituents (pectin, starch, sucrose, and bovine serum albumin) in the food system decreased the activity of PPO but increased the thermostability of PPO, among which pectin exhibited the strongest protective effect against thermal inactivation, and the influence of sucrose was much slighter than that of other macromolecules. Fluorescence emission spectra indicated that pPPO exhibited stronger interactions with pectin than sucrose, and pPPO with pectin showed a more stable conformation under thermal treatment.

Impact of pulsed magnetic field treatment on enzymatic inactivation and quality of cloudy apple juice

The effects of PMF (5-7 T, 5-30 pulses) on enzyme activity, pH, titratable acidity, soluble solids, color, ascorbic acid, total phenols and antioxidant activity (DPPH radical scavenging activity) of cloudy apple juice were evaluated. PMF inhibited activities of polyphenoloxidase (PPO), peroxidase (POD) and pectinmethylesterase (PME), but PPO was more sensitive to PMF than POD and PME. At the intensity of 6 T with 15 pulses, PPO and POD both exhibited the lowest residual activity (53.22 and 92.96%), while PME showed the lowest residual activity (83.01%) at 7 T with 30 pulses. No significant effect on soluble solids was found under all processing parameters, whereas significant decreases of ascorbic acid were observed at the intensity of 7 T with 5-30 pulses. PMF did not change pH, titratable acidity, color, total phenols and DPPH radical scavenging activity severely. These results suggest PMF can be a potential technology for enzymatic inactivation in apple juice with high retention of quality.

Enzymatic, Phyto-, and Physicochemical Evaluation of Apple Juice under High-Pressure Carbon Dioxide and Thermal Processing

In this study, the changes in enzyme activities, total polyphenols, phenolic profile, and physicochemical properties from thermally (25–75 °C) and high-pressure carbon dioxide (HP-CO₂) (25–65 °C/20 MPa)-treated apple juice were investigated. The HP-CO₂ exhibited complete inactivation of polyphenol oxidase (PPO) at 65 °C, whereas PPO was still active at 75 °C under thermal processing (TP). Similarly, the relative activity of peroxidase (POD) significantly decreased by 71% at 65 °C under HP-CO₂ processing, whereas TP was less effective. HP-CO₂ and TP treatments at 65 °C reduced the browning degree (BD) value to 0.47 and 0.89, respectively. Thus, HP-CO₂ inhibits the browning reactions caused by PPO and POD enzymes at each operating temperature. The concentration of epicatechin and catechin increased significantly with increasing temperature above 45 °C in TP-treated juices. HP-CO₂ treatment increased the same phenolic compounds at 35 °C and 9 MPa, whereas high-temperature and -pressure conditions caused insignificant changes in concentration of epicatechin and catechin. Changes in others phenolic compounds were insignificant under TP and HP-CO₂ treatment. Overall, HP-CO₂ is a promising technology to get high-quality juices with lower enzyme activity.

Inactivation, Aggregation and Conformational Changes of Polyphenol Oxidase from Quince (Cydonia oblonga Miller) Juice Subjected to Thermal and High-Pressure Carbon Dioxide Treatment

Polyphenol oxidase (PPO) causes the browning reaction in fruits and vegetables and deteriorates the quality. Thermal treatment for enzyme inactivation may result in defects as opposed to high pressure CO₂ (HPCD) processing. In this study, the changes in activity, dissociation, aggregation and conformation of purified PPO from thermal and HPCD treated juice were investigated. HPCD exhibited inactivation of PPO at 55–65 °C whereas thermal processing alone at the same temperature resulted in PPO still showing activity. Under thermal treatment at 25 and 65 °C, the browning degree was higher (0.39 and 0.24) than for HPCD-treated juice (0.23 and 0.12). Fluorescence and circular dichroism spectral results indicated that HPCD induced large decreases in intensities, revealing a rearrangement of the secondary structure and destruction of the native configuration of the PPO molecule. The particle size distribution (PSD) pattern revealed structural modification leading to initial dissociation and subsequent aggregation of PPO after HPCD treatment. Polyacrylamide gel electrophoresis (PAGE) analysis exhibited that molecular size of protein was 40 kDa. In conclusion, the HPCD method was found to be more effective than thermal treatment to inactivate PPO. Structural modifications provided better insights into the phenomena of activation and inactivation of PPO.

Enzymatic, physicochemical, nutritional and phytochemical profile changes of apple (Golden Delicious L.) juice under supercritical carbon dioxide and long-term cold storage

The impact of supercritical carbon dioxide (SCCD) (10-60 MPa/45 °C/30 min) and subsequent 10 weeks storage at 4 °C on polyphenol oxidase (PPO), peroxidase (POD) activities, phenolic profile, vitamin C, sugars, physicochemical properties of cloudy apple juices was investigated. No significant changes in sugars and total polyphenols were observed, whereas significant degradation (≈28%) of vitamin C and individual polyphenols (≈18%) was noted after SCCD treatment. After 4 weeks storage only 34% of vitamin C was retained and no vitamin C was detected after this time. Ten weeks of storage caused hydrolysis of sucrose in 15%, whereas degradation of individual polyphenols ranged from 43 to 50% depending on the pressure applied. The highest pressure was applied the highest retention of polyphenols was observed. The lightness of juice significantly increased by 15% after SCCD and decreased during storage. Moreover, the synergistic effect of both enzymes with chlorogenic acid and catechol was found.

The Effect of High Pressure Techniques on the Stability of Anthocyanins in Fruit and Vegetables

Anthocyanins are a group of phenolic compounds responsible for red, blue and violet colouration of many fruits, vegetables and flowers. The high content of these pigments is important as it influences directly their health promoting properties as well as the sensory quality of the product; however they are prone to degradation by, inter alia, elevated temperature and tissue enzymes. The traditional thermal methods of food preservation cause significant losses of these pigments. Thus, novel non-thermal techniques such as high pressure processing, high pressure carbon dioxide and high pressure homogenization are under consideration. In this review, the authors attempted to summarize the current knowledge of the impact of high pressure techniques on the stability of anthocyanins during processing and storage of fruit and vegetable products. Furthermore, the effect of the activity of enzymes involved in the degradation of these compounds has been described. The conclusions including comparisons of pressure-based methods with high temperature preservation techniques were presented.

Enzyme inactivation in food processing using high pressure carbon dioxide technology

High pressure carbon dioxide (HPCD) is an effective non-thermal processing technique for inactivating deleterious enzymes in liquid and solid food systems. This processing method avoids high temperatures and exerts a minimal impact on the nutritional and sensory properties of foods, but extends shelf life by inhibiting or killing microorganisms and enzymes. Indigenous enzymes in food such as polyphenol oxidase (PPO), pectin methylesterase (PME), and lypoxygenase (LOX) may cause undesirable chemical changes in food attributes, showing the loss in color, texture, and flavor. For more than two decades, HPCD has proved its effectiveness in inactivating these enzymes. The HPCD-induced inactivation of some microbial enzymes responsible for microbial metabolism is also included. This review presents a survey of the published knowledge regarding the use of HPCD for the inactivation of these enzymes, and analyzes the factors controlling the efficiency of HPCD and speculates on the underlying mechanism that leads to enzyme inactivation.