Influence of preservation techniques and freezing storage time on biochemical composition and spectrum of fatty acids ofIsochrysis galbanaclone 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.

Influence of Drying and Storage on Lipid and Carotenoid Stability of the Microalga Phaeodactylum tricornutum

“…This is in contrast to what Esquivel et al 5 observed, but similar to the result of Babarro et al 9 A possible explanation for these contradicting results is storage of the fresh microalgal paste prior to processing. As shown in this research, even very short term storage of fresh biomass can lead to pronounced lipolysis and lower amounts of measured lipid content.…”

Stability of Valuable Components during Wet and Dry Storage

“…Some enzymes are also inactivated during the drying process, depending on the time and temperature used. This was, however, not observed by Babarro et al (2001) after freeze-drying of Isochrysis galbana, by Ryckebosch et al (2011) after freezedrying and spray drying of P. tricornutum and by Balasubramanian et al (2013) after hot air drying, sun drying, and freeze-drying of Nannochloropsis. Autoxidation is also dependent on water activity, since the oxidation rate decreases when drying until a water activity of about 0.2, but increases again when water activity is lower than 0.2 ( Figure 2) (Belitz et al, 2009;Kerr, 2013).…”

Differential scanning calorimetry evaluation of oxidation stability of docosahexaenoic acid in microalgae cells and their extracts

“…Babarro et al . () observed that the lipid composition (including DHA) of another microalgal species remains unchanged in frozen cells after 3 months of storage at −76 °C. Moreover, Guevara et al .…”

“…Prior to DSC determinations, both fresh and frozen-stored microalgal cells were dehydrated by freeze-drying in a Heto Holten A/S, cooling trap model CT 110 freeze-dryer (Heto Lab Equipment, Allerød, Denmark ), to improve the intensity of the signal. It was reported that this method maintained microalgal lipid composition (Babarro et al, 2001;Ryckebosch et al, 2011). The chloroform extracts were dried with a nitrogen flux and were immediately analysed by DSC.…”

“…Biochemical composition and thus the nutritional value of lipids might be altered by freezing, drying and storage (Esquivel et al, 1993;Babarro et al, 2001;Ryckebosch et al, 2011). The long-term conservation of intracellular microalgal lipids could be achieved by freezing at À20°C (Babarro et al, 2001) or spray-or freeze-drying (Ryckebosch et al, 2011); in both cases, the amount of lipolysis decreased, probably by decreasing the amount of free water and due to a lower enzymatic kinetics at low temperature (Ryckebosch et al, 2011). Lipid oxidation is one of the chemical changes in foods that leads to nutrient losses due to the alteration of essential PUFAs and to the reaction of oxidised lipids with proteins (Varela et al, 1995), besides flavour deterioration, often resulting in food spoilage.…”