Cost effective optimization of bacteria removal in Nannochloropsis oceanica concentrates

Abstract

The objective of this study was to decrease bacterial contamination and improve the net benefit-cost of the process while preserving the integrity of microalgae cells. The washing process conditions were optimized to increase the rate of bacterial removal, making the process economically viable without impacting cell viability. To this, a Central Composite Rotational Design with four variables and two levels (CCRD 2⁴) was performed, generating 27 experimental units (runs). Cell viability was determined by subculture in culture medium and growth rate calculation. The rate of bacterial removal was estimated by directly counting bacteria in the concentrate before and after undergoing the washing process, and a Partial Budget Analysis estimated the net benefit-cost for each run. The experimental models of each response were combined using the desirability index to find the combination that generated the best result in all responses. The best relation between cell viability, bacterial removal efficiency rate, and PBA was found by repeating the process 5 times at 3.405 g-force at 24 °C for 20 min. To make the washing process economically viable, it was necessary to increase the sales price by 10 %, which is justified by the increase in shelf life that the process generates.