CHANGES IN THE LIPID-COMPOSITION AND MAXIMIZATION OF THE POLYUNSATURATED FATTY-ACID CONTENT OF 3 MICROALGAE GROWN IN MASS-CULTURE

Three species of microalgae were grown in mass culture to investigate the influence of culture technique and growth phase on the production of 20:5(n-3) and 22:6(n-3). These polyunsaturated fatty acids (PUFA) are considered to be essential in many marine animals diets for high growth and survival rates. The species of microalgae examined were Nannochloropsis oculata, Pavlova lutheri and Isochrysis sp. (clone T.Iso). All batch cultures (logarithmic and stationary phase) and semi-continuous cultures (logarithmic phase) examined contained high levels of the long-chain (n-3) PUFA, but production could be maximised by harvesting at specific times and growth phases. Maximum cellular content (pg cell-1) of long-chain PUFA was found in logarithmic phase batch cultures of N. oculata and in stationary phase cultures of P. lutheri. The cellular content of PUFA in cultures of Isochrysis sp. did not change significantly with culture technique or growth phase. Alternatively, stationary phase cultures of all three species showed increased proportions (%) and cellular contents of triacylglycerols, and saturated and monounsaturated fatty acids with correspondingly decreased proportions of polar lipids and most PUFA relative to logarithmic phase cultures. The exception was the proportion and cellular content of 22:6(n-3) in P. lutheri which increased with triacylglycerol content. The mass of long-chain (n-3) PUFA per volume of culture was significantly higher in stationary phase cultures due to the higher cell counts per volume. These findings indicate that the opportunity exists to maximise PUFA production by microalgae with the potential to improve animal growth and reduce production costs in mariculture operations and may be of use in the large scale culture and harvesting of microalgae for the biotechnology industry.