Influence of preservation techniques and freezing storage time on biochemical composition and spectrum of fatty acids of Isochrysis galbana clone T-ISO
Aquaculture Research, 32(7): 565-572
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.
(C.S.I.C. Instituto de Investigaciones Marinas, c/Eduardo Cabello, 6, E-36208 Vigo, Spain)