Temperature dependency of cell wall destruction of microalgae with liquid nitrogen pretreatment and hydraulic pressing

• Nannochloropsis oculata cell walls were destroyed with a hydraulic press.
• Cell disruption was found with hydraulic pressing (1–100 bar) and LN2 treatment.
• Disruption was found with LN2 pretreatment at two pressure levels at 20–100 °C.
• 100% destruction was observed under specific conditions.
• A statistical difference was observed with pressure < 30 bar and LN2 pretreatment.

Cell disruption of microalgae is often applied prior to oil extraction processes in order to breakdown the cell wall and to increase the release of intercellular products such as lipids for biodiesel production. However, microalgae require high-energy input to successfully break their cell walls. In this study, cell disruption of Nannochloropsis oculata cells was conducted using a manually operated hydraulic press. Cell disruption was implemented under a variable pressure range from 10 to 100 bars at 20 °C. Also, the temperature dependency of cell disruption was investigated over the range from 20 to 100 °C under two pressure conditions, 10 and 50 bars. In addition, the influence of cell disruption with liquid nitrogen (LN2) pretreatment was studied. The average cell disruption was examined by means of microscopy and the results showed that higher cell disruption was achieved with the liquid nitrogen treated samples. At constant temperature, cell lysing was more effective with the additional LN2 treatment. With pressures < 30 bars the differences were statistically significant. At a relatively low, applied pressure of 10 bars the LN2 samples showed considerably higher disruption (~ 95% compared to ~ 51%) to those samples receiving identical pressure and temperature treatments. Interestingly, with the high pressure 50 bar treatment, approximately the same results with heat treatment and either with or without LN2 were obtained. The relative cell destruction per applied MJ/kg was calculated for the different processes.