Influence of preservation techniques and freezing storage time on biochemical composition and spectrum of fatty acids of Isochrysis galbana clone T-ISO

Abstract

Isochrysis galbana clone T-ISO was cultured in 5-L vessels with continuous light at 100 µmol photons m−2 s−1 at temperature room (22 °C) and harvested at early exponential phase. Dry weight (dw), ash content, biochemical composition and fatty acid profile were determined in fresh biomass and after storage for 7 days and 3 months at −76 °C for both freeze-dried and frozen biomasses. Both freezing and freeze-drying caused significant losses in dry weight (range 13.67–19.74%) when compared with fresh microalgae (40.17 pg cell−1), irrespective of storage time. Ash content increased significantly (P < 0.05) from 21.15% in the case of fresh T-ISO up to a range of 24.13–26.26% when different treatments were used. Both freezing and freeze-drying techniques caused a significant protein loss of a similar magnitude from 13.60 to 11.74 and 11.40 pg organic weight (OW) cell−1, respectively, only when long-term storage was used (3 months). Carbohydrate content was only affected by the preservation technique (P < 0.01). Freeze-drying caused significant loss of the latter component after both 7 days (4.53 pg OW cell−1) and 3 months (4.24 pg OW cell−1) when compared with fresh T-ISO (6.15 pg OW cell−1). Lipid content remained constant when subjected to either microalgal treatment or storage time (P > 0.05). However, the relative percentage of polyunsaturated fatty acids underwent a significant loss after 3 months when T-ISO was freeze-dried. Our results suggest that freezing is a more appropriate long-term preservation technique (3 months) than freeze-drying. Both carbohydrate and polyunsaturated fatty acids contents, important components in the determination of the nutritional value of food in aquaculture (i.e. for bivalves), remain unchanged when frozen. The processes responsible for the observed loss of biochemical compounds when samples are freeze-dried is most probably as a result of a physical altering of the cell wall