Pulsed Electric Field treatment after malolactic fermentation of Tempranillo Rioja wines: Influence on microbial, physicochemical and sensorial quality

Application of physical field-assisted freezing and thawing to mitigate damage to frozen food

Freezing is an effective technique to prolong the storage life of food. However, the freeze-thaw process also brings challenges to the quality of food, such as mechanical damage and freeze cracks. Increasingly, physical fields have been preferred as a means of assisting the freezing and thawing (F/T) processes to improve the quality of frozen food because of their high efficiency and simplicity of application. This article systematically reviews the application of high-efficiency physical field techniques in the F/T of food. These include ultrasound, microwave, radio frequency, electric fields, magnetic fields, and high pressure. The mechanisms, application effects, advantages and disadvantages of these physical fields are discussed. To better understand the role of various physical fields, the damage to food caused by the F/T process and traditional freezing is discussed. The evidence shows that the physical fields of ultrasound, electric field and high pressure have positive effects on the F/T of food. Proper application can control the size and distribution of ice crystals effectively, shorten the freezing time, and maintain the quality of food. Microwave and radio frequency exhibit positive effects on the thawing of food. Dipole rotation and ion oscillation caused by electromagnetic waves can generate heat inside the product and accelerate thawing. The effects of magnetic field on F/T are controversial. Although some physical field techniques are effective in assisting F/T of food, negative phenomena such as uneven temperature distribution and local overheating often occur at the same time. The generation of hotspots during thawing can damage the product and limit application of these techniques in industry. © 2022 Society of Chemical Industry.

Pulsed electric field processing as an alternative to sulfites (SO2) for controlling saccharomyces cerevisiae involved in the fermentation of Chardonnay white wine

The use of sulfites (SO₂) for microbial control in the winemaking process is currently being questioned due to its potential toxicity. Pulsed Electric Fields (PEF) are capable of inactivating microorganisms at low temperatures, thus avoiding the negative effects of heat on food properties. In this study, the capacity of PEF technology for the decontamination of yeasts involved in the fermentation process of Chardonnay wine from a winery was evaluated. PEF treatments at 15 kV/cm of low (65 µs, 35 kJ/kg) and higher intensity (177 µs 97 kJ/kg) were selected for evaluating the microbial stability, physicochemical and volatile composition of wine. Even with the least intense PEF-treatment, Chardonnay wine remained yeast-free during 4 months of storage without sulfites. PEF-treatments did not affect the wine's oenological parameters or its aroma during storage. This study, therefore, reveals the potential of PEF technology as an alternative to sulfites for the microbiological stabilization of wine.

Advances in pulsed electric stimuli as a physical method for treating liquid foods

There is a need for alternative technologies that can deliver safe and nutritious foods at lower costs as compared to conventional processes. Pulsed electric field (PEF) technology has been utilised for a plethora of different applications in the life and physical sciences, such as gene/drug delivery in medicine and extraction of bioactive compounds in food science and technology. PEF technology for treating liquid foods involves engineering principles to develop the equipment, and quantitative biochemistry and microbiology techniques to validate the process. There are numerous challenges to address for its application in liquid foods such as the 5-log pathogen reduction target in food safety, maintaining the food quality, and scale up of this physical approach for industrial integration. Here, we present the engineering principles associated with pulsed electric fields, related inactivation models of microorganisms, electroporation and electropermeabilization theory, to increase the quality and safety of liquid foods; including water, milk, beer, wine, fruit juices, cider, and liquid eggs. Ultimately, we discuss the outlook of the field and emphasise research gaps.

Microbial Decontamination of Red Wine by Pulsed Electric Fields (PEF) after Alcoholic and Malolactic Fermentation: Effect on Saccharomyces cerevisiae, Oenococcus oeni, and Oenological Parameters during Storage

New techniques are required to replace the use of sulfur dioxide (SO₂) or of sterilizing filtration in wineries, due to those methods' drawbacks. Pulsed electric fields (PEF) is a technology capable of inactivating microorganisms at low temperatures in a continuous flow with no detrimental effect on food properties. In the present study, PEF technology was evaluated for purposes of microbial decontamination of red wines after alcoholic and malolactic fermentation, respectively. PEF combined with SO₂ was evaluated in terms of microbial stability and physicochemical parameters over a period of four months. Furthermore, the effect of PEF on the sensory properties of red wine was compared with the sterilizing filtration method. Results showed that up to 4.0 Log₁₀ cycles of S. cerevisiae and O. oeni could be eradicated by PEF and sublethal damages and a synergetic effect with SO₂ were also observed, respectively. After 4 months, wine treated by PEF after alcoholic fermentation was free of viable yeasts; and less than 100 CFU/mL of O. oeni cells were viable in PEF-treated wine added with 20 ppm of SO₂ after malolactic fermentation. No detrimental qualities were found, neither in terms of oenological parameters, nor in the sensory parameters of wines subjected to PEF after storage time.

Malolactic Fermentation: New Approaches to Old Problems

Malolactic fermentation (MLF) is the decarboxylation of L-malic acid to L-lactic acid by lactic acid bacteria (LAB). For the majority of wine production, secondary fermentation is crucial. MLF significantly impacts the quality of most red and some white wine. The outcomes of the spontaneously initiated and finished MLF are frequently unpredictable and can even cause the wine to deteriorate. As a result, individuals typically favour inoculating superior starter cultures when performing MLF. The MLF method for wine has, however, faced new difficulties because of the altered wine fermentation substrate environment brought on by global climate change, the growing demands of winemakers for production efficiency, and the rising demand for high-quality wine. To serve as a reference for the study of wine production and MLF in the current situation, this review primarily updates and summarises the research findings on increasing the effectiveness and dependability of MLF in recent years.

Two-Step PEF Processing for Enhancing the Polyphenol Concentration and Decontaminating a Red Grape Juice

This study's aim is to evaluate Pulsed Electric Fields (PEF) technology as an alternative method for the processing of red grape juice. For this purpose, two PEF treatments were applied: first to grapes for polyphenol enrichment of the juice, and subsequently for microbial decontamination of the obtained juice. Juice obtained from PEF-treated grapes (5 kV/cm, 63.4 kJ/kg) had the polyphenol content 1.5-fold higher and colour intensity two times higher of control juices by spectrophotometric measurement (p ≤ 0.05). A subsequent decontamination treatment by PEF (17.5 kV/cm and 173.6 kJ/kg) achieved inactivation of the present microbiota (yeasts, moulds, and vegetative mesophilic bacteria) below detection level (<30 CFU/mL). Furthermore, PEF-treated juices were microbiologically stable up to 45 days, even at abusive refrigeration storage temperatures (10 °C). PEF juice quality and sensory characteristics were similar to a fresh juice; they were neither affected by the PEF decontamination treatment, nor by storage time and temperature. Results obtained in this study demonstrate the considerable potential of PEF for the production of a polyphenol-enriched and microbially stabilized red grape juice as a unique and sustainable alternative for the juice industry, while avoiding enzymatic and heat treatments.

Emerging Non-Thermal Technologies as Alternative to SO2 for the Production of Wine

SO₂ is an antioxidant and selective antimicrobial additive, inhibiting the growth of molds in the must during the early stages of wine production, as well as undesirable bacteria and yeasts during fermentation, thus avoiding microbial spoilage during wine production and storage. The addition of SO₂ is regulated to a maximum of 150–350 ppm, as this chemical preservative can cause adverse effects in consumers such as allergic reactions. Therefore, the wine industry is interested in finding alternative strategies to reduce SO₂ levels, while maintaining wine quality. The use of non-thermal or cold pasteurization technologies for wine preservation was reviewed. The effect of pulsed electric fields (PEF), high pressure processing (HPP), power ultrasound (US), ultraviolet irradiation (UV), high pressure homogenization (HPH), filtration and low electric current (LEC) on wine quality and microbial inactivation was explored and the technologies were compared. PEF and HPP proved to be effective wine pasteurization technologies as they inactivate key wine spoilage yeasts, including Brettanomyces, and bacteria in short periods of time, while retaining the characteristic flavor and aroma of the wine produced. PEF is a promising technology for the beverage industry as it is a continuous process, requiring only microseconds of processing time for the inactivation of undesirable microbes in wines, with commercial scale, higher throughput production potential.

Revisiting Non-Thermal Food Processing and Preservation Methods-Action Mechanisms, Pros and Cons: A Technological Update (2016-2021)

The push for non-thermal food processing methods has emerged due to the challenges associated with thermal food processing methods, for instance, high operational costs and alteration of food nutrient components. Non-thermal food processing involves methods where the food materials receive microbiological inactivation without or with little direct application of heat. Besides being well established in scientific literature, research into non-thermal food processing technologies are constantly on the rise as applied to a wide range of food products. Due to such remarkable progress by scientists and researchers, there is need for continuous synthesis of relevant scientific literature for the benefit of all actors in the agro-food value chain, most importantly the food processors, and to supplement existing information. This review, therefore, aimed to provide a technological update on some selected non-thermal food processing methods specifically focused on their operational mechanisms, their effectiveness in preserving various kinds of foods, as revealed by their pros (merits) and cons (demerits). Specifically, pulsed electric field, pulsed light, ultraviolet radiation, high-pressure processing, non-thermal (cold) plasma, ozone treatment, ionizing radiation, and ultrasound were considered. What defines these techniques, their ability to exhibit limited changes in the sensory attributes of food, retain the food nutrient contents, ensure food safety, extend shelf-life, and being eco-friendly were highlighted. Rationalizing the process mechanisms about these specific non-thermal technologies alongside consumer education can help raise awareness prior to any design considerations, improvement of cost-effectiveness, and scaling-up their capacity for industrial-level applications.

Synergistic effect of pulsed electric fields and temperature on the inactivation of microorganisms

Pulsed electric fields (PEF) as a new pasteurization technology played an important role in the process of inactivating microorganisms. At the same time, temperature could promote the process of electroporation, and achieve better inactivation effect. This article studied the inactivation effect of PEF on Saccharomyces cerevisiae, Escherichia coli, and Bacillus velezensis under different initial temperatures (room temperature-24 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{^\circ{\rm C} }$$\end{document}∘C, 30 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{^\circ{\rm C} }$$\end{document}∘C, 40 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{^\circ{\rm C} }$$\end{document}∘C, 50 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{^\circ{\rm C} }$$\end{document}∘C). From the inactivation results, it found temperature could reduce the critical electric field intensity for microbial inactivation. After the irreversible electroporation of microorganisms occurred, the nucleic acid content and protein content in the suspension increased with the inactivation rate because the cell membrane integrity was destroyed. We had proved that the electric field and temperature could promote molecular transport through the finite element simulation. Under the same initial temperature and electrical parameters (electric field intensity, pulse width, pulse number), the lethal effect on different microorganisms was Saccharomyces cerevisiae > Escherichia coli > Bacillus velezensis.

Potential Use of Silica Nanoparticles for the Microbial Stabilisation of Wine: An In Vitro Study Using Oenococcus oeni as a Model

The emerging trend towards the reduction of SO2 in winemaking has created a need to look for alternative methods to ensure the protection of wine against the growth of undesired species of microorganisms and to safely remove wine microorganisms. This study describes the possible application of silica nanospheres as a wine stabilisation agent, with Oenococcus oeni (DSM7008) as a model strain. The experiment was conducted firstly on model solutions of phosphate-buffered saline and 1% glucose. Their neutralising effect was tested under stirring with the addition of SiO2 (0.1, 0.25, and 0.5 mg/mL). Overall, the highest concentration of nanospheres under continuous stirring resulted in the greatest decrease in cell counts. Transmission electron microscope (TEM) and scanning electron microscopy (SEM) analyses showed extensive damage to the bacterial cells after stirring with silica nanomaterials. Then, the neutralising effect of 0.5 mg/mL SiO2 was tested in young red wine under stirring, where cell counts were reduced by over 50%. The obtained results suggest that silica nanospheres can serve as an alternative way to reduce or substitute the use of sulphur dioxide in the microbial stabilisation of wine. In addition, further aspects of following investigations should focus on the protection against enzymatic and chemical oxidation of wine.