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Celdisruptie-geassisteerde lipidenextractie uit de microalg Nannochloropsis voor voedingstoepassingen

Year: 2024
Type: dissertation
Abstract: Eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22:6) are semi-essential omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) beneficial for human health, for instance by maintaining cardiovascular health. Fish is the conventional source of EPA in the human diet. However, fish can accumulate toxins and heavy metals, while the fishery industry is associated with adverse ecological effects. Fish are in fact not the primary producers of n-3 LC-PUFA, but some microalgae are. Microalgae such as Nannochloropsis, thus provide an opportunity for the production of n-3 LC-PUFA for food applications. Photoautotrophic microalgae also have the advantage that they contain lipophilic pigments such as carotenes and xanthophylls which have antioxidative properties relevant for both human health and (food) product stability. Whole microalgal biomass can be used as a direct source of n-3 LC-PUFA by incorporating it into food products. This can however result in worse sensorial characteristics compared to the control foods. In addition, whole microalgal biomass from some species such as from Nannochloropsis, has limited bioaccessibility. Therefore, alternative ways of obtaining the n-3 LC-PUFA, such as by extraction from the biomass and using the extracted lipids in food products, are relevant to investigate. Nannochloropsis, the microalga used in this thesis, is surrounded by a rigid, complex cell wall prohibiting efficient extraction of lipids with food grade solvents. Cell disruption techniques are used to increase the lipid extraction efficiency during cell disruption assisted lipid extraction. Most research has only focused its efforts into increasing the lipid extraction efficiency, whereas the influence on lipid components and lipid extract composition (free fatty acids (FFA), pigments) has received very little attention. Cell disruption assisted lipid extraction techniques may negatively affect the oxidative and lipolytic stability during extraction but this is very often not considered in the current research. The aim of this PhD research was to study the influence of two cell disruption assisted lipid extraction techniques (ultrasound and enzyme) on the lipid, FFA and pigment extraction efficiency, the oxidative and lipolytic stability during extraction and the resulting lipid composition (FFA, pigments) of the extract. In chapter 3, an ultrahigh-performance liquid chromatography coupled to mass spectrometry (UHPLC-MS) method was developed to identify and quantify the individual and total FFA content in Nannochloropsis. The developed method was able to quantify nine FFA with different properties: saturated FFA (C14:0, C16:0, C18:0), monounsaturated FFA (C16:1 and C18:1) and polyunsaturated FFA (C18:2, C18:3, C20:4 and C20:5). The calibration curves showed good linearity and the matrix effect was considered well within acceptable limits. There was little intrasequence variability. Although the intersequence variability failed to be within acceptable limits, this could be compensated for by redetermining the calibration curves in each sequence. The developed method was used in chapter 4, 5 and 6. Chapter 4 investigated the use of resuspended freeze-dried Nannochloropsis as a model laboratory system for concentrated fresh Nannochloropsis in ultrasound assisted lipid extraction experiments. This is especially relevant as investigating microalgal cell disruption assisted lipid extraction requires large amounts of fresh biomass that not all researchers have access to. In papers using resuspended freeze-dried biomass as a model laboratory system for concentrated fresh biomass, it was (inexplicitly) assumed (without verification) that the condition of the biomass (resuspended freeze-dried or concentrated fresh) prior to cell disruption has no influence on the resulting lipid extraction efficiency. This however has never been verified and this verification was thus the aim of this chapter. Based on the results, it could be concluded that resuspended freeze-dried Nannochloropsis biomass in tap water or 3% NaCl can be used as a model laboratory system for fresh microalgal biomass during ultrasound assisted lipid extraction, although the resuspension duration should be limited (< 120 min) to prevent the formation of FFA. Resuspended Nannochloropsis was further used in chapter 5 and 6 during cell disruption assisted lipid extraction. In chapter 5 and 6, the influence of ultrasound and enzyme assisted extraction of Nannochloropsis on lipid, FFA and pigment extraction efficiency and on the oxidative and lipolytic stability of the lipid extract, was studied. Additionally, in chapter 6 the influence of (enzymatic) incubation on the lipid composition of Nannochloropsis was studied which allowed for the separate analysis of the impact of (enzyme) incubation and the impact of extraction. Both cell disruption assisted lipid extraction techniques were able to increase the lipid extraction efficiency. No indications for lipolysis or oxidation were observed during ultrasound assisted lipid extraction. In contrast, the incubation step (1 h, 40 ⁰C) during control and enzyme assisted lipid extraction induced lipolysis. The polyunsaturated FFA content decreased, likely due to oxidation after formation. The results in chapter 5 and 6 indicated that (control) extractions performed at elevated temperatures (~40 ⁰C) performed almost as well as the ultrasound and enzyme assisted lipid extraction. It thus appears to be more opportunistic to study simpler extraction techniques applying moderate heating (± 40 ⁰C) and convection in presence of lipid extraction solvent (containing short chain alcohols to prevent lipolytic activity) for lipid extraction from Nannochloropsis. Efforts should be allocated to the investigation of simpler solid-liquid extraction techniques, applicable at industrial scale and suitable for food applications and thereby focus on the influence of extraction temperature, convection and mass transfer in general.
Language: English
Field: Energy
Open Access status: green
OpenAlex ID: W7036643278
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