Cold-preservation of microalgae aquaculture feeds

This paper discusses the main advantages and drawbacks of different preservation techniques for microalgae aquaculture feeds. In particular, cold-storage methods (cryopreservation, freezing and refrigeration) are evaluated in terms of their capacity to maintain the food value of the preserved algal biomass. The results obtained by the authors with refrigeration of slurries and paste of three marine microalgae (Tetraselmis suecica, Pavlova lutheri and Chlorella sp.) are described in detail. P. lutheri suspensions kept at +4 degrees C maintained significant viability (50 %) only for limited periods (two weeks), while optimal survival rates (over 50 %) were observed in the other two algal species even after 2-3 months. While, in Chlorella sp. suspensions, viability during storage was directly correlated with cell concentration, the opposite was found in the case of T. suecica and P. lutheri. When stored in the form of paste, P. lutheri lost completely viability in 24 hours, while T. suecica and Chlorella sp. maintained 50 % viability for about one week. The viability of Chlorella sp. paste significantly increased when it was stored in a water-saturated atmosphere; depth samples of Chlorella sp. paste retained 90 % viability after about two months storage. The cultivation of the three microalgae in a novel, fully-controllable photobioreactor and the effect of centrifugation on survival rate are also described.