Abstract
The present study aimed to investigate the effect of the main pulsed electric field (PEF) process parameters on the cell damages of A. platensis microalgae and the extractability of valuable compounds [water-soluble proteins (WSP), C-phycocyanin (C-PC), and carbohydrates (CH)]. Aqueous microalgae suspensions (2%, w/w) were PEF-treated at variable field strength (E = 10, 20, 30 kV/cm), total specific energy (WT = 20, 60, 100 kJ/kgsusp), and inlet temperature (25, 35, 45°C), with either monopolar or bipolar square wave pulses (5 μs of width, delay time between pulses of opposite polarities = 1, 5, 10, 20 μs), prior to extraction with water at room temperature (25°C) for up to 3 h. High-pressure homogenization (HPH) treatment (P = 150 MPa, 3 passes) was used to achieve complete cell disruption to quantify the total extractable content of target intracellular compounds. Scanning electron microscopy (SEM) and optical microscopy analyses clearly showed that PEF merely electroporated the membranes of algae cell, without damaging the cell structure and forming cell debris. The application of PEF treatment (monopolar pulses, 20 kV/cm and 100 kJ/kgsusp) at room temperature significantly enhanced the extraction yield of WSP [17.4% dry weight (DW)], CH (10.1% DW), and C-PC (2.1% DW), in comparison with the untreated samples. Bipolar pulses appeared less effective than monopolar pulses and led to extraction yields dependent on the delay time. Additionally, regardless of pulse polarity, a clear synergistic effect of the combined PEF (20 kV/cm and 100 kJ/kgsusp)-temperature (35°C) treatment was detected, which enabled the extraction of up to 37.4% (w/w) of total WSP, 73.8% of total CH, and 73.7% of total C-PC. Remarkably, the PEF treatment enabled to obtain C-phycocyanin extract with higher purity than that obtained using HPH treatment. The results obtained in this work suggest that the application of PEF combined with mild heating could represent a suitable approach for the efficient recovery of water-soluble compounds microalgal biomass.
Highlights
Arthrospira platensis, commonly known as spirulina, is a cyanobacterium widely used for biotechnological applications
Results revealed that the extractable content of water-soluble proteins (WSP) and CH from A. platensis cells was 68.5% dry weight (DW) and 15.8% DW, respectively, which are in line with the total content of proteins (55–70% DW) and carbohydrates (13– 20% DW) typically reported for this cyanobacterium (Lupatini et al, 2016)
After demonstrating that pulsed electric field (PEF) treatment (20 kV/cm, 100 kJ/kgsusp), especially when using monopolar pulses combined with moderate heating (35◦C), is effective for promoting the selective extraction of water-soluble compounds from A. platensis cells suspensions, in the last step of this work we evaluated its feasibility in terms of energy consumption
Summary
Arthrospira platensis, commonly known as spirulina, is a cyanobacterium widely used for biotechnological applications It is a multicellular and filamentous blue-green alga with helical shape (trichomes of 50–500 μm in length, and 3–4 μm in width) and represents one of the richest sources of proteins of microbial origin [55–70% dry weight (DW)]; besides, it contains significant amounts of carbohydrates (13–16% DW), lipids (6–10% DW), vitamins, and minerals (Lupatini et al, 2016). It has been reported that the initial amount of C-PC in A. platensis decreased by approximately 50% after the drying of the algae biomass (Martinez et al, 2017)
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