Integrity of the microalgal cell plays a major role in the lipolytic stability during wet storage

Microalgae are promising sources of lipids for applications in food, fuel, pharmaceutics and cosmetics. However, these lipids are also subject to lipolysis reactions during processing and storage. Especially during wet biomass storage, substantial amounts of free fatty acids (FFA) are formed, which has negative effects on flavor and nutritional value and can cause downstream processing problems in biodiesel production. This study contributes to a better understanding of the underlying processes leading to lipolysis by focusing on cell wall differences between species. Therefore, in a first phase, a comparison was made between the lipolytic stability of Nannochloropsis oculata and T-Isochrysis lutea, two species reported to have substantial differences in cell wall structure and strength. Nannochloropsis appeared to be stable during the first days of wet storage, while in T-Isochrysis, lipolysis started immediately after harvest. In a second experiment, the influence of cell disruption by high pressure homogenization (HPH) on lipolytic stability during wet storage of Nannochloropsis was investigated. It was observed that the HPH treatment induced lipolysis, as the FFA content was rapidly increasing immediately after the treatment, in contrast to the control sample, in which the FFA content was constant during the first days of storage. The integrity of the microalgal cell was thus found to play a crucial role in lipid stability during short-term post-harvest wet storage.