Ohmic blanching of Tetsukabuto pumpkin: Effects on peroxidase inactivation kinetics and color changes

Insight into peroxidase-mediated Morinda citrifolia L. (noni) fruit juice browning and precipitation, and a thermal inactivation strategy

Peroxidase-mediated enzymatic browning during the process of noni fruit juice causes major color deterioration and precipitation, which negatively affects consumer acceptance of the juice. The purpose of this study was to understand the browning and precipitate formation mechanisms in noni fruit juice and improve its quality. Peroxidase was isolated from noni fruit via gel separation purification and characterized for its kinetic properties. The influences of key phenolic compounds on browning and precipitate formation were investigated via a noni-juice-based model system. The results revealed that the major noni peroxidase was a 50.05 kDa dimer subunit, and peroxidase activity was optimal at pH 6.0 and 30 °C, with an activation energy of 159.50 kJ/mol. Additionally, peroxidase activity was significantly inhibited by glutathione, sodium metabisulfite, and ascorbic acid. The active sites contained histidine and arginine residues. All eight phenolic compounds in juice act as specific substrates for peroxidase-mediated browning. Among them, gallic acid made the most significant contribution to both browning and precipitate formation. To effectively deactivate peroxidase activity while minimizing phenolic compound loss, a thermal treatment of 90 °C for 10 min was identified as the optimal approach. This study provides new insights into improving the quality of noni juice and enzyme browning.

Effects of thermal processing on natural antioxidants in fruits and vegetables

Research on the content of polyphenolic compounds in fruits and vegetables, the extraction of bioactive compounds, and the study of their impact on the human body has received growing attention in recent years. This is due to the great interest in bioactive compounds and their health benefits, resulting in increased market demand for natural foods. Bioactive compounds from plants are generally categorized as natural antioxidants with health benefits such as anti-inflammatory, antioxidant, anti-diabetic, anti-carcinogenic, etc. Thermal processing has been used in the food sector for a long history. Implementing different thermal processing methods could be essential in retaining the quality of the natural antioxidant compounds in plant-based foods. A comprehensive review is presented on the effects of thermal blanching (i.e., hot water, steam, superheated steam impingement, ohmic and microwave blanching), pasteurization, and sterilization and drying technologies on natural antioxidants in fruits and vegetables.

Inactivation effects and mechanism of ohmic heating on Bacillus cereus

The inactivation effects and mechanism of ohmic heating (OH) on Bacillus cereus ATCC 11778 were investigated in this study, conventional heating (CH) was also carried out and served as control. All OH treatments (10 V/cm 50 Hz, 10 V/cm 500 Hz, 5 V/cm 50 Hz and 5 V/cm 500 Hz) could achieve a comparable inactivation effect with CH, while OH treatments significantly shortened the processing time. OH treated cells exhibited significantly higher leakage of metal ions (Mg²⁺ and K⁺) and biomacromolecules (nucleic acids and proteins) than those treated with CH when bacterial suspensions were heated to the same temperature. Moreover, OH treatment caused more damage on membrane structure, greatly decreased the cell membrane potential and endogenous enzyme activity than that of CH. The results of this study indicated that OH is more efficient in the inactivation of bacteria.

Kinetic Modeling, Thermodynamic Approach and Molecular Dynamics Simulation of Thermal Inactivation of Lipases from Burkholderia cepacia and Rhizomucor miehei

The behavior against temperature and thermal stability of enzymes is a topic of importance for industrial biocatalysis. This study focuses on the kinetics and thermodynamics of the thermal inactivation of Lipase PS from B. cepacia and Palatase from R. miehei. Thermal inactivation was investigated using eight inactivation models at a temperature range of 40–70 °C. Kinetic modeling showed that the first-order model and Weibull distribution were the best equations to describe the residual activity of Lipase PS and Palatase, respectively. The results obtained from the kinetic parameters, decimal reduction time (D and t_R), and temperature required (z and z’) indicated a higher thermal stability of Lipase PS compared to Palatase. The activation energy values (Ea) also indicated that higher energy was required to denature bacterial (34.8 kJ mol⁻¹) than fungal (23.3 kJ mol⁻¹) lipase. The thermodynamic inactivation parameters, Gibbs free energy (ΔG^#), entropy (ΔS^#), and enthalpy (ΔH^#) were also determined. The results showed a ΔG^# for Palatase (86.0–92.1 kJ mol⁻¹) lower than for Lipase PS (98.6–104.9 kJ mol⁻¹), and a negative entropic and positive enthalpic contribution for both lipases. A comparative molecular dynamics simulation and structural analysis at 40 °C and 70 °C were also performed.

Kinetic study on peroxidase inactivation and anthocyanin degradation of black cherry tomatoes (Solanum lycopersicum cv. OG) during blanching

Introduction

Blanching is a necessary treatment stage in processing of tomato products to inactivate enzymes. However, it may cause the degradation of nutrients.

Objective

In this study, the kinetics of thermal peroxidase inactivation and anthocyanin degradation in black cherry tomatoes (cv. OG) were determined to predict the quality changes during the blanching.

Methods

Tomatoes were blanched at five levels of temperature (75–95oC) for five time periods (30–150 s).

Results

It was found that as the blanching temperature increased and the blanching time is prolonged, more peroxidase was inactivated and the greater number of anthocyanins was lost. The thermal peroxidase inactivation and anthocyanin degradation showed an apparent first-order reaction with the activation energy of 129.96 kJ/mol and 65.99 kJ/mol, respectively. Peroxidase and anthocyanin in black cherry tomatoes were found to be heat-sensitive.

Conclusion

These kinetic parameters were necessary to select and design appropriate blanching conditions for black cherry tomatoes on larger scale processing.

Currently Applied Extraction Processes for Secondary Metabolites from Lippia turbinata and Turnera diffusa and Future Perspectives

The poleo (Lippia turbinata Griseb.) and damiana (Turnera diffusa Wild) are two of the most valued species in the Mexican semidesert due to their medicinal uses. The conventional essential oil extraction process is hydrodistillation, and for the extraction of antioxidants, the use of organic solvents. However, these techniques are time-consuming and degrade thermolabile molecules, and the efficiency of the process is dependent on the affinity of the solvent for bioactive compounds. Likewise, they generate solvent residues such as methanol, hexane, petroleum ether, toluene, chloroform, etc. Therefore, in recent years, ecofriendly alternatives such as ohmic heating, microwaves, ultrasound, and supercritical fluids have been studied. These methodologies allow reducing the environmental impact and processing times, in addition to increasing yields at a lower cost. Currently, there is no up-to-date information that provides a description of the ecofriendly trends for the recovery process of essential oils and antioxidants from Lippia turbinata and Turnera diffusa. This review includes relevant information on the most recent advancements in these processes, including conditions and methodological foundation.

Ohmic heating as a promising technique for extraction of herbal essential oils: Understanding mechanisms, recent findings, and associated challenges

The applicability of ohmic heating, as a volumetric heating technique, has been explored in various sectors of the food industry. The use of ohmic heating for essential oil extraction is among its emerging applications. This chapter overviews the recent progress in this area of research, discusses the mechanisms involved in ohmic-based essential oil extraction processes, explains the effective process parameters, highlights their benefits, and explains the considerations to address the obstacles to industrial implementation. Ohmic-assisted hydrodistillation (OAHD) and ohmic-accelerated steam distillation (OASD) systems were proposed as alternatives to conventional hydrodistillation and steam distillation, respectively. These techniques have successfully extracted essential oils from several aromatic plants (e.g., thyme, peppermint, citronella, and lavender). Both OAHD and OASD possess a number of benefits, such as reducing the extraction time and energy consumption, compared to classical extraction methods. However, these techniques are in their infancy and further economic and upscaling studies are required for their industrial adaptation.

Application of microwave and ohmic heating for pasteurization of cantaloupe juice: microbial inactivation and chemical properties

BACKGROUND

Cantaloupe melon (Cucumis melo L.) is one of the most important dessert fruits and is cultivated in many countries of the world. The effects of microwave (400 and 800 W for 110 s), ohmic (100 and 200 V for 110 s) and conventional heating (27-75 °C for 30 min) treatments on inactivation of Escherichia coli, Salmonella Typhimurium, S. Enteritidis and Staphylococcus aureus pathogens; pH and degradation of vitamin C, β-carotene and phenolic compounds of cantaloupe juice were investigated.

RESULTS

As time passed, all of the treatments resulted in significant (P ≤ 0.05) decreases in the number of pathogens and vitamin C, β-carotene and phenolic compound content, whereas the pH of samples did not show significant changes. The mentioned parameters were more reduced by increasing the power, voltage and temperature of ohmic, microwave and conventional heating treatments, respectively. Comparison of the results for conventional heating with those of ohmic and microwave heating revealed that the complete inactivation time of pathogens by the two latter treatments was much shorter than that of the former. After 20 s, the effect of ohmic heating at 200 V on decreasing vitamin C content was significantly (P ≤ 0.05) higher than that of the other treatments. The amounts of β-carotene and phenolic compounds showed the most reduction under 800 W microwave treatment.

CONCLUSION

The results obtained for conventional, ohmic and microwave heating treatments indicated a higher degradation of β-carotene and phenolic compounds and a lower loss of vitamin C in the former. © 2019 Society of Chemical Industry.