Stability of lipids during wet storage of the marine diatom Porosira glacialis under semi-preserved conditions at 4 and
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Stability of lipids during wet storage of the marine diatom Porosira glacialis under semi-preserved conditions at 4 and 20 °C Lars Dalheim 1
&
Jon B. Svenning 1 & Hans C. Eilertsen 1 & Terje Vasskog 2 & Ragnar L. Olsen 1
Received: 2 July 2020 / Revised and accepted: 30 September 2020 # The Author(s) 2020
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. Keywords Storage stability . Lipid . Omega-3 . Pre-treatment . Psychrophilic diatom . Microalgae
Introduction The limit for sustainable utilization of wild fish stocks has been reached (FAO 2020), and there is a need for novel
* Lars Dalheim [email protected] Jon B. Svenning [email protected] Hans C. Eilertsen [email protected] Terje Vasskog [email protected] Ragnar L. Olsen [email protected] 1
Norwegian College of Fishery Science, UiT The Arctic University of Norway, N-9037 Tromsø, Norway
2
Department of Pharmacy, UiT The Arctic University of Norway, N-9037 Tromsø, Norway
sources of marine nutritional components, especially the long-chain polyunsaturated omega-3 fatty acids (LC-PUFA n-3). Marine microalgae are the main de novo producers of the LC-PUFA n-3, eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3) (Khozin-Goldberg et al. 2011), which are important components in aquaculture feed (Tocher 2015; Sprague et al. 2016) and for human health (Kris-Etherton et al. 2009; Salem and Eggersdorfer 2015). In addition to omega-3 fatty acids, marine microalgae contain valuable pigments and other bioactive compounds (Cuel
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