Comparison of extraction of valuable compounds from microalgae by atmospheric pressure plasmas and pulsed electric fields

Microalgae have recently gained interest, not only as source for biofuel, but also as a resource for pharmaceutical and nutritional substances. The bottleneck for extracting these valuable compounds from microalgae is a thick cell wall of high physical and chemical strength. Several extraction techniques are available, but suffer from different disadvantages. Therefore, new technologies are needed, especially those based on processes that will not affect the chemical composition of ingredients. Among these, physical plasma and pulsed electric field (PEF) might be promising. Three different standard methods, microwave, ultrasound, and homogenization, were compared with plasma treatment and PEF. The plasma sources investigated were corona discharges, a plasma jet, a dielectric barrier discharge, spark discharges, and pin-to-liquid discharges. Chlorella vulgaris was chosen as a model organism. To detect successful cell wall rupture, the protein content of the supernatant and pigment concentration after treatment were determined. Scanning electron microscope images were taken to visualize cell wall damage. Microwave and spark discharge treatment were the most successful methods with comparable extracted total protein content in the supernatant. However, spark discharges achieved higher pigment yield than microwave extraction without the thermal degradation of the pigments observed for microwave extraction.