Abstract
Cultivation of diatoms may help alleviate the pressure on wild fish stocks for marine nutrient availability in aquaculture feed and for human consumption. However, the lipids in microalgae biomass are easily deteriorated, both trough lipolysis and degradation of polyunsaturated fatty acids (PUFA). Proper storage conditions are therefore necessary to maintain the lipid quality. Additionally, the storage conditions must have a low cost and facilitate further processing of the biomass. In this study, we investigated the formation of free fatty acids, changes in lipid classes, and fatty acid composition of the psychrophilic marine diatom Porosira glacialis under storage. The wet biomass was stored for 14 days at 4 and 20 °C with either heat treatment, formic acid, or benzoic acid addition, and a control sample. Heat-treated and formic acid samples had the lowest rate of free fatty acid formation during storage. Mainly, polar lipids were hydrolyzed to free fatty acids and this occurred fastest at 20 °C. The fatty acid composition remained stable in heat-treated samples during storage, whereas a loss of PUFA was observed in the other treatments. The lack of effect from benzoic acid indicates that the loss of lipid quality stems from endogenous enzymes rather than exogenous organisms. Heat treatment and formic acid appeared to effectively reduce lipase activity, and potentially lipoxygenase and similar enzymes that affect the fatty acids. The low pH of the formic acid samples seems to have a negative effect on the PUFA content, in particular at 20 °C.
Highlights
IntroductionOne of the main challenges of large-scale utilization of diatoms is post-harvest storage
The limit for sustainable utilization of wild fish stocks has been reached (FAO 2020), and there is a need for novelOne of the main challenges of large-scale utilization of diatoms is post-harvest storage
A previous study (Ryckebosch et al 2011) on Phaeodactylum tricornutum reported lower lipid yield in wet biomass than dried biomass after storage, which they ascribed to free fatty acids (FFA) formation during storage in wet biomass, this was based on only one time point so no trends could be interpreted from this
Summary
One of the main challenges of large-scale utilization of diatoms is post-harvest storage. Endogenous enzymes in the biomass may deteriorate the lipids through lipolysis and oxidation (Fontana et al 2007; Cutignano et al 2011). The antigrazer defense mechanism of diatoms, which is woundactivated, involves breaking down thylakoid lipids to produce volatile polyunsaturated aldehydes and other oxylipins (Pohnert 2002; Cutignano et al 2006; Caldwell 2009). Cell rupture, which can occur during harvesting or because of autolytic reactions during storage, may initiate these processes. Another consequence of cell rupture is the formation of exudates, which may act as a growth medium for other microorganisms such as bacteria and fungi. Optimizing storage conditions are essential for large-scale utilization of microalgae
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