Polyphenol oxidase (PPO) and pectin methylesterase (PME) inactivation by high pressure carbon dioxide (HPCD) and its applicability to liquid and solid natural products

The regulation of carbon dioxide on food microorganisms: A review

This review presents a survey of two extremely important technologies about CO2 with the effectiveness of controlling microorganisms - atmospheric pressure CO2-based modified atmosphere packaging (MAP) and high pressure CO2 non-thermal pasteurization (HPCD). CO2-based MAP is effectively in delaying the lag and logarithmic phases of microorganisms by replacing the surrounding air, while HPCD achieved sterilization by subjecting food to either subcritical or supercritical CO2 for some time in a continuous, batch or semi-batch way. In addition to the advantages of healthy, eco-friendly, quality-preserving, effective characteristic, some challenges such as the high drip loss and packaging collapse associated with higher concentration of CO2, the fuzzy mechanisms of oxidative stress, the unproven specific metabolic pathways and biomarkers, etc., in CO2-based MAP, and the unavoidable extraction of bioactive compounds, the challenging application in solid foods with higher efficiency, the difficult balance between optimal sterilization and optimal food quality, etc., in HPCD still need more efforts to overcome. The action mechanism of CO2 on microorganisms, researches in recent years, problems and future perspectives are summarized. When dissolved in solution medium or cellular fluids, CO2 can form carbonic acid (H2CO3), and H2CO3 can further dissociate into bicarbonate ions (HCO3-), carbonate (CO32-) and hydrogen cations (H+) ionic species following series equilibria. The action mode of CO2 on microorganisms may be relevant to changes in intracellular pH, alteration of proteins, enzyme structure and function, alteration of cell membrane function and fluidity, and so on. Nevertheless, the effects of CO2 on microbial biofilms, energy metabolism, protein and gene expression also need to be explored more extensively and deeply to further understand the action mechanism of CO2 on microorganisms.

Activity and stability of lipase from Candida Antarctica after treatment in pressurized fluids

Lipase B from Candida antarctica (CalB) is one of the biocatalysts most used in organic synthesis due to its ability to act in several medium, wide substrate specificity and enantioselectivity, tolerance to non-aqueous environment, and resistance to thermal deactivation. Thus, the objective of this work was to treat CalB in supercritical carbon dioxide (SC-CO₂) and liquefied petroleum gas (LPG), and measure its activity before and after high-pressure treatment. Residual specific hydrolytic activities of 132% and 142% were observed when CalB was exposed to SC-CO₂ at 35 ℃, 75 bar and 1 h and to LPG at 65 ℃, 30 bar and 1 h, respectively. Residual activity of the enzyme treated at high pressure was still above 100% until the 20th day of storage at low temperatures. There was no difference on the residual activity loss of CalB treated with LPG and stored at different temperatures over time. Greater difference was observed between CalB treated with CO₂ and flash-frozen in liquid nitrogen (- 196 ℃) followed by storage in freezer (- 10 ℃) and CalB stored in freezer at - 10 ℃. Such findings encourage deeper studies on CalB as well as other enzymes behavior under different types of pressurized fluids aiming at industrial application.

The effect of supercritical carbon dioxide on the physiochemistry, endogenous enzymes, and nutritional composition of fruit and vegetables and its prospects for industrial application: a overview

Consumers have an increasing demand for fruit and vegetables with high nutritional value worldwide. However, most fruit and vegetables are vulnerable to quality loss and spoilage during processing, transportation, and storage. Among the recently introduced emerging technologies, supercritical carbon dioxide (SCCO2) has been extensively utilized to treat and maintain fruit and vegetables mainly due to its nontoxicity, safety, and environmentally friendly. SCCO2 technology generates low processing costs and mild processing conditions (temperature and pressure) that allow for the application of CO2 at a supercritical state. This review aimed to summarize the current knowledge on the influence of SCCO2 technology on the quality attributes of fruit and vegetable products, such as physicochemical properties (pH, color, cloud, particle size distribution, texture), sensory quality, and nutritional composition (ascorbic acid, phenolic compounds, anthocyanins, carotenoids, and betalains). In addition, the effects and mechanisms of the SCCO2 technique on endogenous enzyme inactivation (polyphenol oxidase, peroxidase, and pectin methylesterase) were also elucidated. Finally, the prospects of the SCCO2 technique for industrial application was discussed from the economic and regulatory aspect.

High-Pressure Processing vs. Thermal Treatment: Effect on the Stability of Polyphenols in Strawberry and Apple Products

Polyphenols are important bioactive compounds that are affected by processing. The consumer's demand for minimally processed products contributes to the increase in non-thermal technologies such as high-pressure processing (HPP) in the food industry. This review is aimed at critically discussing the positive and negative effects of thermal treatment (TT) and HPP on the stability of different polyphenol families in agro-food products obtained from strawberry and apple, two of the most used fruits in food processing. Our findings show that the phenolic content was affected by processing, fruit type, polyphenol family, and storage conditions (time and temperature) of the final product. To increase shelf life, manufacturers aiming to preserve the natural content of polyphenols need to find the sweet spot between polyphenol stability and product shelf-life since the residual enzyme activity from HPP can affect polyphenols negatively.

Effect of infrared radiation on activity and conformation of polyphenol oxidase from Acetes chinensis

The aim of this paper was to study the effect of infrared radiation (IR) on the activity and conformation of polyphenol oxidase (PPO) in Acetes chinensis. In this paper, the specific activity of PPO was increased from 21.2 to 643.4 U/mg by a four-step purification. The results showed that IR treatment had greater effect on the enzyme activity and conformation of PPO than hot air (HA) treatment. After IR treatment at 70°C, the relative enzyme activity of PPO was 9.28%, the surface hydrophobicity index increased by 80.42%, and the content of sulfhydryl group decreased to 96.99% of the control group. The results of circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) showed that the α-helix of PPO treated by IR decreased and the random coil increased. The intrinsic fluorescence intensity of PPO decreased after IR treatment, indicating that the tertiary structure of PPO was destroyed. Scanning electron microscopy (SEM) results showed that the surface microstructure of PPO after IR treatment became clear and compact. In conclusion, IR treatment can completely destroy the secondary structure and tertiary structure of PPO and cause enzyme inactivation. This study provides a treatment for reducing the activity of PPO from A. chinensis during the production and processing. PRACTICAL APPLICATION: This study shows that IR treatment has a better inhibitory effect on the activity of PPO than HA treatment. It provides a better treatment method for inactivating the activity of PPO from Acetes chinensis during the production and processing.

Structural changes of a protein extract from apple with polyphenoloxidase activity obtained by cationic reversed micellar extraction induced by high-pressure carbon dioxide and thermosonication

Polyphenoloxidase from apple was extracted and further concentrated by cationic reversed micellar extraction. Previous to reversed micellar extraction a crude protein extract was obtained using AG2-X8 as adsorbent of phenolic compounds and the detergent Triton X-100. Forward and backward extraction conditions were optimized by using dodecyl trimethyl ammonium bromide as surfactant in the organic phase. Optimization was carried out to obtain the highest value of PPO activity recovery and the purification fold at the different experimental conditions. Under the optimum extraction conditions, PPO activity recovery was 99% and purification fold reached a value of 17, showing that reversed micellar extraction was a good technique as a first step to concentrate on a targeted enzyme. After removing some impurities by centrifuge ultrafiltration, the protein extract with PPO activity was treated by pressurized carbon dioxide and thermosonication achieving residual PPO activity values of 16 ± 3 and 9 ± 1%, respectively. Quenching experiments by iodide performed in the non-treated extract and in the treated extracts revealed conformational changes of this protein fraction reflected in the greater exposure of the fluorophore to the quencher.