Effect of removing bacteria and dissolved organic matter on DMS production in Nannochloropsis oceanica concentrates

The aim of this study was to determine the influence of bacteria and organic matter on the occurrence of dimethyl sulfide (DMS) over the shelf life of Nannochloropsis oceanica concentrates. Two concentrates were compared: Control treatment, composed of biomass collected by centrifugation and diluted to a cell density of 5 × 109 cells·mL−1, and a washed concentrate treatment, where the biomass underwent successive centrifugations to remove dissolved organic matter (DOM) and bacteria before being diluted to a cell density of 5 × 109 cells·mL−1. Both concentrates were stored at two temperatures: 23 °C for 10 days and 4 °C for 85 days. Cellular viability, bacterial density, DOM, and DMS concentration were assessed. The washing process was responsible for removing approximately 84 % of the bacterial load from the concentrates. This significant reduction played a crucial role in decreasing the concentrations of DOM and DMS over the storage period. Furthermore, the process did not impair the cellular viability of microalgae. The findings underscore the importance of carefully managing bacterial and organic components in microalgal concentrates, especially when considering the preservation of freshness and cellular viability, which are key factors in applications such as larviculture.