Evaluation of efficiency of disruption methods for Coelastrella sp. in order to obtain high yields of biochemical compounds release

Abstract

Downstream processes in microalgae, such as the extraction of high value-added compounds, are often hampered by the intrinsic rigidity of the cell wall. The toughness of this structure makes the intracellular compounds less available for extraction, which means that cell disruption methods are necessary to apply. Coelastrella sp. is a terrestrial microalga that reveals to be a promising source of bioactive compounds; however, due to its extremely resistant wall, few extraction and determination studies of these compounds have been performed. In order to maximize the extraction efficiency and be as energy-efficient as possible, five different cell disruption methods have been optimized: Freeze-Thaw cycles ten freezing cycles at 80°C and thawing at 40°C; Bead Milling 32% (in volume) of beads (0.5mm) and treatment time of 6min; High-speed homogenization - 25,000rpm for 80min; Microwave 800W for 12min; and Sonication 40kHz for 60min. Sonication and bead milling proved to be the most efficient processes in cell disruption and intracellular organic matter release, with a value of 9.6 and 5.4, respectively. In addition to these two methods, which yielded rupture efficiencies above 90% after the application of the treatment, High-speed homogenization also showed a disruption efficiency of around 90%. On the other hand, microwave and freeze-thaw cycles had a low impact on Coelastrella sp. cells, allowing the surviving of about 39% and 66% of the initial sample, respectively. Sonication showed the highest efficiency in the release of proteins, carbohydrates and lipids, always followed by bead milling as the most efficient. Freeze-thaw cycles have shown to be the most efficient in releasing phenolic compounds, whereas microwave was the most inefficient in releasing biochemical compounds overall. Considering the results obtained and the energy consumption in each treatment, bead milling can be considered the most efficient method.