MICROALGAL EXTRACTS AS POTENT NATURAL ANTIOXIDANTS
Koen Goiris1,2, L. De Cooman1, K. Muylaert2
1. KAHO Sint-Lieven, Laboratory of Enzyme, Fermentation, and Brewing Technology, Ghent,
Belgium – KU Leuven Food Science and Nutrition Research Centre (LFoRCe), Leuven, Belgium
2. KU Leuven Kulak, Research unit Aquatic Biology, Kortrijk, Belgium
koen.goiris@kahosl.be
Microalgae have received much attention as potential energy crop. However, for microalgal biofuels to
become competitive with fossil fuels, it is imperative that high-value components are utilised as well.
Antioxidants are such potentially high-value products that could be used to replace synthetic
antioxidants in various applications (e.g. inhibition of lipid oxidation in food and feed). Most research
on microalgal antioxidants focused on lipophilic carotenoids or antioxidant enzymes. Less is known
about the presence of more polar antioxidants such as phenolics, which are important antioxidants in
terrestrial plants.
We examined antioxidant properties of 32 microalgal samples by using two extraction procedures, i.e.
a one-step extraction with ethanol/water and a fractionated extraction comprising successive
treatments with hexane, ethyl acetate and hot water, respectively. Next to determining carotenoid
content and phenolic content, antioxidant activity was measured by 4 assays (TEAC, FRAP, AAPH
induced oxidation of linoleic acid and square wave voltammetry (SWV)).
Strongest antioxidant activity was found in ethanol/water extracts. Lowest antioxidant activity was
measured in the hexane fractions, while more activity was found in the medium polar ethyl acetate and
polar hot water fractions. The fact that hexane fractions are low in antioxidant activity is interesting as
this solvent is commonly used to extract lipids. Thus, after extracting lipids for biofuel production,
antioxidants can still be recovered with a medium polar solvent or with hot water. It was further found
that antioxidant activities determined by SWV correlate well with results from other established
antioxidant assays. Since SWV provides additional information on the antioxidant profile of microalgal
biomass, it may also serve as an excellent tool for optimizing fractionation processes.
Next, the effect of nutrient availability on antioxidant formation in 3 species is discussed. It was found
that antioxidant activity of microalgae is lower under nutrient limitation but can be increased by
elevated nutrient levels.
Finally, antioxidant activity in microalgal preparations was compared with extracts from other wellknown natural antioxidant sources (e.g. grape seeds, green tea, rosemary). From this, it could be
concluded that microalgal extracts can be a good alternative for traditional plant extracts (e.g. some
microalgal extracts showed TEAC values similar to rosemary).