Evaluation of pulsed electric fields effect on the microalgae cell mechanical stability through high pressure homogenization

Abstract

Pulsed Electric Fields (PEF) is a known technique for the permeabilization of cell membranes, which can considerably foster intracellular component extraction from microalgae. During this phenomenon, the cells are subjected to short electrical pulses leading to the deconstruction of the cell membrane. However, it is currently uncertain in what way, if any, the microalgae cell wall is affected during pulsing. In this study, freshly harvested Auxenochlorella protothecoides (AP) and Chlorella vulgaris (CV) were subjected to PEF treatment with an energy input of 1.5MJ per kilogram of dry matter and then fed into a High Pressure Homogenizer (HPH) for 5 passes at 1500 bar. The percentage of intact cells after each pass was determined and compared with Control biomass that underwent the same homogenization. AP and CV autotrophic had almost 40% intact cells at the end of homogenizing whereas AP mixotrophic 20%. In all cases, no major difference on the disruption degree of pulsed and control samples was observed, indicating that the resistance to mechanical stress of the cell, a function of the cell wall, is not affected by PEF. Scanning Electron Microscopy (SEM) observation of the cells also showed no superficial or structural cell alteration after pulsation.

Pulsed Electric Field Treatment Enhances Lipid Bioaccessibility While Preserving Oxidative Stability in Chlorella Vulgaris

“…No visible effects of PEF or PEF followed by enzymatic treatment were observed, with cells maintaining their original shape and structure. Similarly, Papachristou et al (2020) did not find any major external modification on C. vulgaris and A. protothecoides after PEF, as did T 'Lam et al (2017) in C. reinhardtii. Additionally, no major morphological changes in A. protothecoides after PEF were described by , who only observed slight shrinkage.…”

“…Overall, in this study, PEF treatments improved the lipid extractability from C. vulgaris biomass compared to the untreated control. μsPEF treatment is known to induce membrane permeabilization, but there is no evidence that it can directly impair the cell wall structure (Bensalem et al, 2018;Papachristou et al, 2020;T Lam et al, 2017). Membrane permeabilization might have facilitated the penetration of solvents .…”

“…Hydrophilic proteins were completely released after PEF in cell wall-free mutants, while wild-type cell wall-containing cells showed three times lower protein yields. Although several studies report that PEF does not have a direct impact on the cell wall (Bensalem et al, 2018;Papachristou et al, 2020;T Lam et al, 2017), an increase in the extractability of microalgae intracellular compounds (e.g., protein, lipid, pigments, carbohydrates) by organic solvents or buffer systems after PEF treatment has been described (Aguilar-Machado et al, 2020;Buchmann et al, 2019;Kempkes et al, 2015;Silve, Kian, et al, 2018).…”

“…It is important to consider the incubation of a microalgae suspension after PEF treatment, regardless of the mechanism explaining the PEF effects on the cell wall. The studies that showed no impact of PEF on protein extractability (T Lam et al, 2017) or algae mechanical stability (Papachristou et al, 2020) had short or even absent, respectively, incubation of the algae suspension after PEF. In contrast, Jaeschke et al (2019) showed how a minimum incubation step, although short (15 min), was necessary to extract protein from A. platensis after PEF treatment (40 kV cm − 1 , 1 μs, 28-112 J mL − 1 sus ).…”

Pilot scale production, extraction and purification of a thermostable phycocyanin from Synechocystis sp. PCC 6803

“…However, the efficiency of cell disruption by HPH is highly dependent on the conditions used (i.e. the pressure applied and number of passes) and the thickness and chemical composition of the cell wall in different species ( Papachristou et al, 2020 ). To the best of our knowledge, disruption of Synechocystis cells using HPH has not been reported previously.…”