Towards mass cultivation of diatoms as a source of marine lipids

Abstract

The global demand for the long-chain omega-3 fatty acids EPA and DHA is increasing, and the traditional sources of these fatty acids, fish oils, are no longer able to sustain the demand. This shortage is mainly a result of the surging requirement of EPA and DHA as ingredients in fish feed for aquaculture, and as dietary supplements for human consumption. As a result, there is an increased interest towards lower trophic levels as novel sources of EPA and DHA in an effort to reduce the dependence on wild fish. The main producers of long-chained omega-3 fatty acids in cold oceans are the single celled diatoms, which use CO2 and sunlight to grow in the process of photosynthesis. Diatoms can be utilized as targets of a commercial mass cultivation, where CO2 from industrial processes is converted to a valuable diatom biomass. This may in turn supplement fish-derived biomass for the production of EPA and DHA. The purpose of this work was to improve the current production technology directed towards diatom mass cultivation. The first study investigated the effect of cultivation temperature on the growth and composition of fatty acids on a cold-water diatom. Temperature did not affect the content of EPA and DHA in the diatom at temperatures between 2-12 degrees C, which reduces the necessity of temperature regulation in cultivations targeted towards omega-3 fatty acids. The second study compared preservative treatments on biomass from a cold-water diatom, and showed that a moderate heat treatment reduced quality loss during storage. Heat treatment can therefore function as an inexpensive alternative to preserve diatom biomass. The final study examined to what extent cell wall disruption, choice of solvent and number of consecutive extractions affected the yield in lipid extraction from diatoms. In contrast to other commonly mass cultivated microalgae, product yield was determined by choice of solvent and number of extractions, independent of cell disruption. These findings will bring us closer to an industrial cultivation of diatom biomass, by lowering production costs and increasing product value.