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Biofuel production as a sustainable source of green energy is considered a promising complement to petroleum in order to prevent environmental problems such as global warming. In this regard, microalgae can be one of the best options, since other plant resources may be used for human consumption and utilizing them for producing biofuel may cause an increase in their price. However, there are several challenges to extract oil from microalgae, e.g., high energy consumption, chemical solvents, and algae culture destruction, which should be addressed by new approaches. In this paper, we suggest nanosecond pulse electric field as a physical method for hydrocarbon extraction from microalgae. Botryococcus braunii with high hydrocarbon production potential was used as the microalga model. To obtain an effective extraction, nsPEFs with 87.5-kV/cm electric field, 200-ns pulse duration, 0.3-J/pulse energy, 1-Hz pulse repetition frequency, and 1–50 pulses were applied. Microscopic observations with image processing and chemical assessments were performed for analyzing the samples, understanding the extraction mechanisms, and comparing the outcomes. According to the results, 50 pulses with 16.7-J/mL energy consumption were sufficient for oil extraction, showing that the pulsed power approach can be used as an appropriate physical method for extracting oil from Botryococcus braunii .

The green algae Botryococcus braunii produces a high amount of extracellular hydrocarbon, making it a promising algae in the field of bio-fuels production. As it mainly produces squalene like hydrocarbons, cosmetic industries are also interested in its milking. Pulsed electric fields (PEF) are an innovative method allowing oil extraction from micro-algae. In common algae accumulating hydrocarbon inside cytoplasm (Chlorella vulgaris, Nannochloropsis sp., etc), electric fields can destroy cell membranes, allowing the release of hydrocarbon. However, for B.braunii, hydrocarbons adhere to the cell wall outside of cells as a matrix. In a previous article we reported that electric fields can unstick cells from a matrix, allowing hydrocarbon harvesting. In this work, we deeper investigated this phenomenon of cell hatching by following 2 parameters: the conductivity of the medium and the cultivation duration of the culture. Cell hatching is accurately evaluated by both microscopic and macroscopic observations. For high conductivity and a short time of cultivation, almost no effect is observed even after up to 1000 PEF pulses are submitted to the cells. While lower conductivity and a longer cultivation period allow strong cell hatching after 200 PEF pulses are applied to the cells. We identify 2 new crucial parameters, able to turn the method from inefficient to very efficient. It might help companies to save energy and money in case of mass production.

Oil production by microalgae is investigated as a possible solution to sustain the petroleum shortage. Some microalgae such as Botryococcus braunii have the advantage of being able to produce a high amount of hydrocarbon without requiring arable lands to grow on. Also, hydrocarbons extracted from B. braunii are suitable for the cosmetic industry, as they are long-chain hydrocarbons similar to squalene. As such, B. braunii oil might generate a high profit. However, harvesting hydrocarbon from microalgae cultures is difficult. Here we show an innovative way of collecting hydrocarbon from algae culture using high voltage electric discharges (HVED). Botryococcus braunii form a matrix full of hydrocarbons allowing many cells to stick together as microcolonies. When the energy applied is too high, hydrocarbons are destroyed; and when the energy is to low, algae culture stays unchanged. But when energy applied is just sufficient (near 625 J mL−1), cells leave colonies and sink to the bottom of the samples, while hydrocarbons remain unaffected and float to the surface of the samples. Such a phenomenon allows us to harvest the matrices of colonies which are empty of cells, suitable as a biomass for biofuel production.

Enzyme inactivation is a common industrial step of food preservation. Conventional method is based on heating, thus reduce organoleptic property and virtues of the products. We propose a non-thermal method of enzyme inactivation based on pulsed electric fields. By comparing the effect of electric fields, heating and oxidation on alpha-amylase, we have shown that the electric field targets the active site of the enzyme via the tryptophan, resulting in a conformational disruption. An electric pulse of 2.5–12.5 kV/cm, 10 μs and 0.02–0.6 J, repeated at 1–30 Hz for a total applied energy of 1440 J, partially denatured alpha-amylase, reducing activity by up to 70%; however, this was not followed by protein aggregation, as observed for heat treatment to 70 °C. Those results brought new understanding on the mechanism of pulsed electric fields action on proteins, and might lead in new application in food industry or in medicine.

High-voltage pulsed electric fields (PEF) and pulsed discharge plasmas have received a great deal of attention in the fields of biochemistry, medicine, agriculture and food industry. The destruction phenomenon of cell membranes has been confirmed by PEF and discharge plasma, and it can be used for inactivating microorganisms and extracting cell contents. In recent years, it has been reported that PEF changes the activity of proteins such as enzymes. This review describes how PEF and pulsed discharge plasma function in enzyme activity change and permeabilization in food processing. It is thought that PEF affects the three-dimensional structure of proteins, and research is underway. Here, we will introduce the latest research results on the mechanism of enzyme activity change by PEF. In addition, we will introduce the latest research on changes in cell permeability using shock waves caused by the pulsed discharge plasma.

Once pathogens form a biofilm, they become more tolerant to drugs and quicker to recover from physical removal than planktonic cells. Because such robustness of a biofilm is associated with the active metabolism of its constituent microbes, establishment of a direct assay quantifying biofilm's metabolic activity is important for developing antibiofilm substrates and techniques. Current production capability via extracellular electron transport (EET) was recently found in Gram-positive pathogens, which we hypothesized to correlate with the metabolic activity of their biofilm. Here, we identified current production from the biofilm of oral pathogen Streptococcus mutans that enables the electrochemical assessments of their metabolic activity in situ which conventionally require gene insertion for a fluorescent protein expression. Single-potential amperometry (SA) showed that S. mutans produced an anodic current and formed a biofilm within 8 h on a +0.4 V electrode vs a standard hydrogen electrode (SHE) in the presence of the electron donor glucose. Current production was significantly decreased by the addition of a metabolic inhibitor Triclosan. Furthermore, the anabolic activity of a single cell using high-resolution mass spectroscopy revealed that higher current production resulted in a higher metabolic fixation of an atomically labeled nitrogen 15N. These results demonstrate that current production in S. mutans reflects its metabolic activity. Given electrochemical impedance spectroscopy (EIS) helps quantifying the bacterial cell adhesion on the electrode, combination of EIS and SA could be a novel assay for EET capable pathogens for quantifying their time-dependent metabolic activity, cellular electrode coverage and physiological response to antibiofilm compounds.

Biofuel production as a sustainable source of green energy is considered as promising complements to petroleum in order to prevent environmental problems such as global warming. In this regard, microalgae can be one of the best options since other plant resources may be used for human consumption, using them for producing biofuel may cause an increase in their price. However, there are several challenges to extract oil from microalgae, e.g., high energy consumption, chemical solvents, and algae culture destruction; which should be addressed by new approaches. This study suggests nanosecond pulse electric fields (nsPEF) as a physical method for hydrocarbon extraction from microalgae. Botryococcus braunii with high hydrocarbon production potential was used as microalga model. For nanosecond pulsed electric fields (nsPEF) experiments, 20 to 65 kV/cm electric fields with 80 ns pulse duration, with different pulse repetition frequencies and pulse numbers were applied. Fluorescence microscopic observation and image and chemical assessments were performed for analyzing the samples, understanding the extraction mechanisms, and comparing the outcomes. According to the results, pulsed power approach can be used as high efficiency physical method for extracting oil from Botryococcus braunii.

Aims This article shows the effect of nanosecond pulsed electric field (nsPEF) on Escherichia coli, which could imply a durable change in protein expressions and then impacted the phenotype of surviving bacteria that might lead to increase pathogenicity. Methods and Results The effects of nsPEF on E. coli viability and membrane permeabilization were investigated. One log10 reduction in bacterial counts was achieved at field strength of 107 V m−1 with a train of 500 successive pulses of 60 × 10−9 s. Incubation of germs after treatment with propidium iodide showed that membrane permeabilization was reversible. Possible protein changes of surviving bacteria were checked to assess potential phenotypical changes using two-dimensional electrophoresis. In our study, after 40 generations, only UniProt #P39187 was up-regulated with P ≤ 0·05 compared with the control and corresponded to the uncharacterized protein YtfJ. Antibiograms were used to check whether or not the pattern of cultivable bacteria after nsPEF deliveries changed. Conclusions The results tend to show that nsPEFs are able to inactivate bacteria and have probably no serious impact in E. coli protein patterns. Significance and Impact of the Study The use of nsPEF is a safe promising new nonthermal method for bacterial inactivation in the food processing and environmental industry.

Recent understanding that specific algae have high hydrocarbon production potential has attracted considerable attention. Botryococcus braunii is a microalga with an extracellular hydrocarbon matrix, which makes it an appropriate green energy source. This study focuses on extracting oil from the microalgae matrix rather than the cells, eliminating the need for an excessive electric field to create electro-permeabilization. In such a way, technical limitations due to high extraction energy and cost can be overcome. Here, nanosecond pulsed electric fields (nsPEF) with 80 ns duration and 20–65 kV/cm electric fields were applied. To understand the extraction mechanism, the structure of the algae was accurately studied under fluorescence microscope; extraction was quantified using image analysis; quality of extraction was examined by thin-layer chromatography (TLC); and the cell/matrix separation was observed real-time under a microscope during nsPEF application. Furthermore, optimization was carried out by screening values of electric fields, pulse repetition frequencies, and energy spent. The results offer a novel method applicable for fast and continues hydrocarbon extraction process at low energy cost.