Mechanisms of inactivation of Candida humilis and Saccharomyces cerevisiae by pulsed electric fields

Tannin-Tolerant Saccharomyces cerevisiae Isolated from Traditional Fermented Tea Leaf (Miang) and Application in Fruit Wine Fermentation Using Longan Juice Mixed with Seed Extract as Substrate

This study focused on isolating tannin-tolerant yeasts from Miang, a fermented tea leaf product collected from northern Laos PDR, and investigating related food applications. From 43 Miang samples, six yeast isolates capable of ethanol production were obtained, with five isolates showing growth on YPD agar containing 4% (w/v) tannic acid. Molecular identification revealed three isolates as Saccharomyces cerevisiae (B5-1, B5-2, and C6-3), along with Candida tropicalis and Kazachstania humilis. Due to safety considerations, only Saccharomyces spp. were selected for further tannic acid tolerance study to advance food applications. Tannic acid at 1% (w/v) significantly influenced ethanol fermentation in all S. cerevisiae isolates. Notably, B5-2 and C6-3 showed high ethanol fermentation efficiency (2.5% w/v), while others were strongly inhibited. The application of tannin-tolerant yeasts in longan fruit wine (LFW) fermentation with longan seed extract (LSE) supplementation as a source of tannin revealed that C6-3 had the best efficacy for LFW fermentation. C6-3 showed promising efficacy, particularly with LSE supplementation, enhancing phenolic compounds, antioxidant activity, and inhibiting α-glucosidase activity, indicating potential antidiabetic properties. These findings underscore the potential of tannin-tolerant S. cerevisiae C6-3 for fermenting beverages from tannin-rich substrates like LSE, with implications for functional foods and nutraceuticals promoting health benefits.

Investigating synergism and mechanism during sequential inactivation of Staphylococcus aureus with ultrasound followed by UV/peracetic acid

This study explored the inactivation of Staphylococcus aureus (S. aureus) by ultrasound (US) and peracetic acid (PAA) coupling with UV simultaneously (US/PAA/UV) or sequentially (US→PAA/UV) for the strengthened disinfection. The result showed that US→PAA/UV system had excellent inactivation performance with 5.05-log in a short time. Besides US, UV, PAA and free radicals, the contribution of the synergy of all components to the entire disinfection were obvious under US→PAA/UV system. The inactivation performance of S. aureus significantly decreased with the increase of humic acid (HA) concentration and pH; however, the rising temperature contributes to the enhancement of the inactivation efficiency under the US→PAA/UV system. The disinfection mechanism includes a decrease of cell agglomeration, a loss of intracellular substance, and changes of cell structure and membrane permeability, as evidenced through a nanoparticle size analyzer, scanning electron microscope (SEM), transmission electron microscope (TEM) and laser confocal microscopy (LSCM). Furthermore, the inactivation efficiency of the US→PAA/UV system for the total bacteria from actual sewage (the untreated inflow) was high, which reached 3.86-log. In general, the pretreatment of US combined with UV/PAA showed a promising application in the rapid disinfection of sewage.

Application of electric field treatment (EFT) for microbial control in water and liquid food

Water disinfection and food pasteurization are critical to reducing waterborne and foodborne diseases, which have been a pressing public health issue globally. Electrified treatment processes are emerging and have become promising alternatives due to the low cost of electricity, independence of chemicals, and low potential to form by-products. Electric field treatment (EFT) is a physical pathogen inactivation approach, which damages cell membrane by irreversible electroporation. EFT has been studied for both water disinfection and food pasteurization. However, no study has systematically connected the two fields with an up-to-date review. In this article, we first provide a comprehensive background of microbial control in water and food, followed by the introduction of EFT. Subsequently, we summarize the recent EFT studies for pathogen inactivation from three aspects, the processing parameters, its efficacy against different pathogens, and the impact of liquid properties on the inactivation performance. We also review the development of novel configurations and materials for EFT devices to address the current challenges of EFT. This review introduces EFT from an engineering perspective and may serve as a bridge to connect the field of environmental engineering and food science.

Eradication of Saccharomyces cerevisiae by Pulsed Electric Field Treatments

One of the promising technologies that can inactivate microorganisms without heat is pulsed electric field (PEF) treatment. The aim of this study was to examine the influence of PEF treatment (2.9 kV cm⁻¹, 100 Hz, 5000 pulses in trains mode of 500 pulses with a pulse duration of 10 µs) on Saccharomyces cerevisiae eradication and resealing in different conditions, such as current density (which is influenced by the medium conductivity), the sort of medium (phosphate buffered saline (PBS) vs. yeast malt broth (YMB) and a combined treatment of PEF with the addition of preservatives. When the S. cerevisiae were suspended in PBS, increasing the current density from 0.02 to 3.3 A cm⁻² (corresponding to a total specific energy of 22.04 to 614.59 kJ kg⁻¹) led to an increase of S. cerevisiae eradication. At 3.3 A cm⁻², a total S. cerevisiae eradication was observed. However, when the S. cerevisiae in PBS was treated with the highest current density of 3.3 A cm⁻², followed by dilution in a rich YMB medium, a phenomenon of cell membrane resealing was observed by flow cytometry (FCM) and CFU analysis. The viability of S. cerevisiae was also examined when the culture was exposed to repeating PEF treatments (up to four cycles) with and without the addition of preservatives. This experiment was performed when the S. cerevisiae were suspended in YMB containing tartaric acid (pH 3.4) and ethanol to a final concentration of 10% (v/v), which mimics wine. It was shown that one PEF treatment cycle led to a reduction of 1.35 log10, compared to 2.24 log10 when four cycles were applied. However, no synergic effect was observed when the preservatives, free SO₂, and sorbic acid were added. This study shows the important and necessary knowledge about yeast eradication and membrane recovery processes after PEF treatment, in particular for application in the liquid food industry.

Thermoplastic microfluidic bioreactors with integrated electrodes to study tumor treating fields on yeast cells

Tumor-treating fields (TTFields) are alternating electrical fields of intermediate frequency and low intensity that can slow or inhibit tumor growth by disrupting mitosis division of cancerous cells through cell cycle proteins. In this work, for the first time, an in-house fabricated cyclo-olefin polymer made microfluidic bioreactors are integrated with Cr/Au interdigitated electrodes to test TTFields on yeast cells with fluorescent protein:Nop56 gene. A small gap between electrodes (50 μm) allows small voltages (<150 mV) to be applied on the cells; hence, uninsulated gold electrodes are used in the non-faradaic region without causing any electrochemical reaction at the electrode-medium interface. Electrochemical modeling as well as impedance characterization and analysis of the electrodes are done using four different cell nutrient media. The experiments with yeast cells are done with 150 mV, 150 kHz and 30 mV, 200 kHz sinusoidal signals to generate electrical field magnitudes of 6.58 V/cm and 1.33 V/cm, respectively. In the high electrical field experiment, the cells go through electroporation. In the experiment with the low electrical field magnitude for TTFields, the cells have prolonged mitosis from typical 80-90 min to 200-300 min. Our results confirm the validity of the electrochemical model and the importance of applying a correct magnitude of the electrical field. Compared to the so far reported alternatives with insulated electrodes, the here developed thermoplastic microfluidic bioreactors with uninsulated electrodes provide a new, versatile, and durable platform for in vitro cell studies toward the improvement of anti-cancer therapies including personalized treatment.

Heat-Assisted Pulsed Electric Field Treatment for the Inactivation of Saccharomyces cerevisiae: Effects of the Presence of Citral

Pulsed electric field (PEF) treatment is a non-thermal technology that has shown good potential for microbial inactivation. However, in many cases, it cannot be sufficient to avoid microbial proliferation, and the combination with other stabilizing technologies is needed. In the framework of the hurdle concept, several researches have been focused on the use of PEF in combination with heat and/or antimicrobials to increase its efficacy. This study investigated the inactivation effect of PEF on a strain of Saccharomyces cerevisiae (isolated from spoiled beverages) in a model system (growth medium). The efficacy of PEF treatment was evaluated in relation to different variables, such as electric field strength (25 and 50 kV/cm), treatment time (from 1 to 5 s), initial inoculum level (4 or 6 log cfu/ml), preheating at 50°C, medium pH (4 or 6), and addition of citral at sublethal concentration (i.e., half of minimum inhibiting concentration). The data from plate counting, modeled with the Weibull equation, showed that one of the main factors affecting yeast inactivation was the preheating of the suspension at 50°C. Indeed, higher cell load reductions were obtained with heat-assisted PEF, especially in the presence of citral. The effect of initial cell load was negligible, while pH affected yeast inactivation only without preheating, with higher death kinetics at pH 6. Flow cytometry (FCM) analysis confirmed higher mortality under these conditions. However, the occurrence of injured cells, especially in samples treated at pH 4, was observed. The ability of these cells to recover from the damages induced by treatments was affected by both citral and preheating. The synergic effects of PEF, preheating, and citral were likely due to the increase of membrane permeability (especially at pH 6), as the primary target of electroporation, which favored the solubilization of citral in the cell membrane, enhancing the efficacy of the whole process. The multi-analytical approach (traditional plate counting and FCM) allowed defining parameters to increase PEF efficacy against S. cerevisiae. Moreover, FCM, able to discriminate different physiological states of the yeast population, was helpful to better clarify the action mechanism and the potential recovery of cells after treatment.

Non-invasive nanosecond electroporation for biocontrol of surface infections: an in vivo study

Invasive infections caused by drug-resistant bacteria are frequently responsible for fatal sepsis, morbidity and mortality rates. In this work, we propose a new methodology based on nanosecond high frequency electric field bursts, which enables successful eradication of bacteria in vivo. High frequency (15 kHz) 15–25 kV/cm 300–900 ns pulsing bursts were used separately and in combination with acetic acid (0.1–1%) to treat Pseudomonas aeruginosa in a murine model. Acetic acid 1% alone was effective resulting in almost 10-fold reduction of bacteria viability, however combination of nanosecond electric field and acetic acid 1% treatment was the most successful showing almost full eradication (0.01% survival compared to control) of the bacteria in the contaminated area. The short duration of the pulses (sub-microsecond) and high frequency (kHz range) of the burst enabled reduction of the muscle contractions to barely detectable level while the proposed applicators ensured predominantly topical treatment, without electroporation of deeper tissues. The results of our study have direct application for treatment of wounds and ulcers when chemical treatment is no longer effective.

Balanced diets in food systems: Emerging trends and challenges for human health

Processed foods, generally known as modified raw foods produced by innovative processing technologies alters the food constituents such natural enzymes, fatty acids, micronutrients, macronutrients and vitamins. In contrast to fresh and unprocessed foods, processed foods are guaranteed to be safer, imperishable, long lasting and consist high level of nutrients bioactivity. Currently, the evolution in food processing technologies is necessary to face food security and safety, nutrition demand, its availability and also other global challenges in the food system. In this scenario, this review consists of information on two food processing technologies, which effects on processed foods before and after processing and the impact of food products on human health. It is also very well established that understanding the type and structure of foods to be processed can assist food processing industries towards advancement of novel food products. In connection with this fact, the present article also discusses the emerging trends and possible modifications in food processing technologies with the combination of conventional and modern techniques to get the suitable nutritional and safety qualities in food.