Department of Molecular Sciences

Algae and Polyunsaturated Fatty Acids
Louise Lundquist

Independent project • 15 credits
Agricultural Programme - Food Science
Molecular Sciences, 2019:4
Uppsala 2019

Algae and Polyunsaturated Fatty Acids
Louise Lundquist

Supervisor:

Jana Pickova, Swedish University of Agricultural Sciences, Departmentof Molecular Sciences

Examiner:

Sabine Sampels, Swedish University of Agricultural Sciences,
Department of Molecular Sciences

Credits:
Level:
Course title:
Course code:
Course coordinating department:

15 credits
First cycle, G2E
Independent project in food science
EX0876
Department of Molecular Sciences

Place of publication:
Year of publication:
Title of series:
Part Number:

Uppsala2019
Molecular Sciences
2019:4

Online publication:

https://stud.epsilon.slu.se

Keywords:

Algae, polyunsaturated fatty acids, EPA, DHA, omega-3

Swedish University of Agricultural Sciences
Faculty of Natural Resources and Agricultural Sciences
Department of Molecular Sciences

Abstract
The human body cannot produce enough amounts of long chain polyunsaturated fatty
acids (LC-PUFA), on its own, to sustain the biological functions they have. Consuming essential fatty acids is fundamental for well-functioning bodily processes. The
essential fatty acids are linoleic acid (LA) and alpha-linolenic acid (ALA). ALA is
the precursor to the LC-PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic
acid (DHA). The metabolism of EPA and DHA in the human body is very limited
and it is therefore important to have these fatty acids in our diet. The essential fatty
acids can be found in some nuts, seeds and vegetable oils, they are most prominent
in canola oil and linseed oil. EPA and DHA cannot be found in nuts, seeds or vegetable oils but are instead found in algae and fish.
ALA, EPA, and DHA are categorised as omega-3 fatty acids. Omega-3 fatty acids
have an important role in the cell membrane and in retinal tissue. The omega-3 makes
the cell membrane fluid and flexible, facilitates the cellular functions and cell signals.
EPA is a precursor for the hormone like biochemical substances called eicosanoids.
Eicosanoids help aid multiple bodily functions, such as immune functions and inflammatory responses as well as blood pressure regulations and muscle activity. The
health benefits of consuming PUFAs are many. They have shown to aid both mental
and cardiovascular health. Visual functions have shown risks of being compromised
when PUFAs were limited during the infant years. In algae, EPA and DHA are maintaining the photosynthetic functions and may aid cell signalling.
Algae have been utilized for over thousands of years. Asians have been the primaryconsumers, but the consumption of algae is spreading all over the world. Algae are
the base, the lowest trophic level, in the aquatic food chain. In modern day they are
primarily used as food, but they are also used as biofuel and to purify waste waters.
Not all algae are high producers of PUFAs, the most common ones, nori, spirulina
etc., are richer in protein and nutrients. The Schizochytrium spp are microalgal species rich in DHA. Phaeodactylum tricornutum and Odontella aurita are two microalgae rich in EPA. The aim of this literature study was to introduce PUFAs and their
biological functions. The study also covers the role algae have in the production of
EPA and DHA.
Keywords: PUFA, algae, omega-3, DHA, EPA

1

Sammanfattning
Människokroppen kan inte producera tillräckliga mängder av långa fleromättade fettsyror för att upprätthålla de biologiska funktioner fleromättade fettsyror har. Konsumtionen av essentiella fettsyror är central för välfungerande biologiska processer.
De essentiella fettsyrorna är linoleic acid (LA) och alfa-linolenic acid (ALA). ALA
är prekursor till de längre fleromättade fettsyrorna eicosapentaenoic acid (EPA) och
docosahexaenoic acid (DHA). Människokroppens metabolism av EPA och DHA är
väldigt begränsad, därför är det viktigt att dessa finns med i vår diet. De essentiellafettsyrorna finns i vissa nötter, frön och vegetabiliska oljor. Raps- och linfröolja är
exempel på livsmedel rika på essentiella fettsyror. EPA och DHA finns inte i dessa
livsmedel utan hittas främst i alger och fisk.
ALA, EPA, och DHA kategoriseras som omega-3 fettsyror. Omega-3 har en viktigroll i cellmembranen och i retinal vävnad. Cellmembran med omega-3 är mer flexibla
och fluida, det hjälper cellulära funktioner och cellsignalering. EPA är en prekursor
till de hormonliknande ämnena eikosanoider. Eicosanoider hjälper flera kroppsliga
funktioner, såsom immunologiska funktioner och inflammatoriska reaktioner. De
hjälper också till att reglera blodtryck och muskelaktivitet. Det finns flera hälsofördelar med att äta fleromättade fettsyror. De har visat förbättra mental- och kardiovaskulär hälsa. Brist på fleromättade fettsyror under spädbarnsåldern har visat sig rubba
vissa visuella funktioner. I alger hjälper EPA och DHA till med att underhålla fotosyntetiska funktioner och eventuellt också cellsignalering.
Alger har använts i flera tusen år. Asiater har varit de primära konsumenterna menen spridning har skett över hela världen. De används främst som livsmedel men kanockså används som biobränsle och för att rena vatten. Inte alla alger producerar höga
halter fleromättade fettsyror. De vanligaste, nori och spirulina med mera, har högre
halter av protein och andra näringsämnen. Arter av mikroalgen Schizochytrium har
höga halter av DHA. Phaeodactylum tricornutum och Odontella aurita är två exempel på arter rika på EPA. Syftet med denna studie var att introducera fleromättade
fettsyror och deras biologiska funktioner. Studien tar också upp algers roll i produktionen av EPA och DHA.
Nyckelord: fleromättade fettsyror, alger, omega-3, EPA, DHA

2

Table of contents
Abbreviations

5

1

Introduction

7

1.1

Aim

8

1.2

Method82

Polyunsaturated Fatty Acids

9

2.1

Definition

9

2.2

Essential fatty acids

9

2.3

Dietary sources

10

2.4

Metabolism of PUFAs

10

2.5

Algal biosynthesis

113

Biological role of LC-PUFA

12

3.1

Omega-3

12

3.2

Omega-6

13

3.3

Health benefits

14

3.4

PUFA function in algae

14

3.5

Carotenoids

15

4

Algae

16

4.1

Algae as a base of the aquatic food chain

16

4.2

Different uses of algae

17

4.3

Algal foods

17

4.4

Some examples of microalgae rich in LC-PUFAs

18

4.4.1 Schizochytrium spp.

18

4.4.2 Phaeodactylum tricornutum

19

4.4.3 Odontella aurita

19

Discussion

21

5

References

22

3

4

Abbreviations
ALA
AA
DHA
DPA
EPA
GLA
GPL
LC
PUFA

α-Linolenic acid; 18:3n3
Arachidonic acid; 20:4n6
Docosahexaenoic acid; 22:6n3
Docosapentaenoic acid; 22:5n6
Eicosapentaenoic acid; 20:5n3γ-Linolenic acid, 18:3n6
Glycerophospholipid
Long chain
Polyunsaturated fatty acid

5

6

1

Introduction

Polyunsaturated fatty acids (PUFAs) have an important biological role in the humanbody. They take part in maintaining a healthy brain function and coronary health(Ander et al. 2003), as well as giving our cells special characteristics to function
properly (Hishikawa et al. 2017). PUFAs are divided into omega-3 and omega-6
fatty acids, where omega-3 fatty acids are less common in the western diet thanomega-6 fatty acids. The ratio between these two have been widely researched andit was believed to be 1:1 in our ancestors’ diet. For the modern diet, many different
ratios have been recommended over the years. The most common one being a 4:1
ratio, or less, of omega-6 and omega-3 (Bhardwaj et al. 2016).
According to study made by The Swedish National Food Agency in Riksmaten– 2010-2011: Livsmedels- och näringsintag bland vuxna I Sverige (Amcoff et al.
2012), the Swedish population acquire more omega-3 today than they used to.
Swedes who eat a varied diet obtain 2,7 g omega-3 per day. To keep a regular intakeof omega-3, The Swedish National Food Agency recommend a diet that consist offish two-three times a week, where at least one of them is a fat fish e.g. mackerel
and salmon etc. Though most swedes eat a healthy amount of omega-3, most western diets do not consist of enough omega-3 (Martins et al. 2013). For people who
do not eat fish, for example vegetarians, vegans and people with fish allergies, is it
important to obtain the omega-3 from other sources (Livsmedelsverket 2018). Other
foods rich in omega-3 are vegetable oils, nuts and seeds (Francieli da Silva et al.
2015)
The most important omega-3 fatty acids are alpha-linolenic acid (18:3n3; ALA),
eicosapentaenoic acid (20:5n3; EPA) and docosahexaenoic acid (22:6n3; DHA).
The omega-6 fatty acids are linoleic acid (18:2n6; LA), gamma-linolenic acid
(18:3n6; GLA), arachidonic acid (20:4n6; AA) and docosapentaenoic acid, (22:5n6;
DPA). ALA and LA are essential fatty acids and cannot be synthesised in the humanbody. The other PUFAs are synthesised in a very limited degree in the human bodyand are therefore also considered as essential in our diet (Ward & Singh 2005).

7

The importance of obtaining PUFAs during the first infant years have been studied extensively. DHA is present in all brain tissue, in some areas up to 40%. Due toits vital role, DHA is now a staple component in infant formula. Several studies
suggest that DHA benefits the eye development and is critical for the brain to develop (Happe & Gambelli 2015).
There is no doubt that PUFAs are important for human health and development.
Fish is the most common and important source, but the fish stocks are depleting andnew sources for PUFAs needs to be found. Algae are one of these new sources that
could be a future staple food in the everyday diet.

1.1

Aim

The aim of this thesis is to summarise some of the current knowledge of algae richin PUFAs. An introduction to PUFAs and the biological importance they have will
be covered, as well as give the current prospects of PUFAs. To justify the interestin research about algae rich in PUFAs, one must also know the important biologicalrole PUFAs have.

1.2

MethodInformation for this literature study have been fund by searching on PubMed, ASFA:
Aquatic Sciences and Fisheries Abstracts, FSTA (Food Science and Technology Abstracts), Primo and NCBI. The searches were made with the following words in
different combinations. Microalga*, alga*, marine phytoplankton, omega-3,
omega-6, essential, fatty acid, PUFA, LC-PUFA, EPA, DHA, neurological, health,biologic*, function, role, synthes*, metabolism, pathway, carotenoid*, astaxanthin,cultivat*, food chain, food, biofuel, Odontella, Schizochytrium, Phaeodactylum tricornutum.

8

2

Polyunsaturated Fatty Acids

2.1

Definition

Polyunsaturated fatty acids (PUFAs) are all fatty acids with more than one doublebond in either a cis or trans configuration. The long chain - polyunsaturated fatty
acids (LC-PUFAs) are the fatty acids longer than 20 carbons. The omega-3 fatty
acids have a double bond on the third carbon from the methyl end on the carbon
chain and omega-6 fatty acids have the double bond located on the sixth carbon
from the methyl end (Wallis et al. 2002).
The most abundant PUFA in mammalian tissue is DHA. It is synthesised of 22
carbon atoms and six double bonds, often specified as 22:6n-3 or 22:6ω3. The double bonds in DHA are all in cis configuration (Brenna & Carlson 2014). The second
most abundant PUFA is EPA. EPA consists of 20 carbons and 5 double bonds, also
these are in cis configuration. Precursor for both these fatty acids is ALA.
AA and DPA are two other PUFAs in mammalian tissue and require LA to besynthesised (Wallis et al. 2002).

2.2

Essential fatty acids

Though the western diet is overflowing with omega-6 fatty acids, one of them isessential for us. The true essential fatty acids are linoleic acid and alpha-linolenic
acid. LA is an omega-6 fatty acid and ALA is an omega-3 fatty acid. LA can beproduced by plants and is the backbone for the omega-6 fatty acid family including
GLA, AA and DPA (Pasquale 2009). ALA is also produced by plants and it is the
precursor for the omega-3 family containing EPA and DHA.

9

2.3

Dietary sources

There are many plant-based- and marine foods that contain PUFAs. Mackerel,salmon, seabass sardines, trout and shrimp all contain high amounts of DHA andEPA. Supplements such as fish oil, cod liver oil and krill oil are also rich in DHA
and EPA. Algae oil is also on the market but is more expensive and does not containas high amounts of DHA and EPA as the other supplement oils. Users of algae oil
therefore need to take more and the costs will be higher (Gal 2018).
Chia-, hemp- and flax seeds are rich in ALA, but do not contain any DHA or
EPA. Walnuts as well as edamame, kidney beans and soybean oil are also rich in
ALA (Gal 2018).
Most vegetable oils are rich in LA (Pasquale 2009). ALA is not as common but
can be found in canola oil (rapeseed oil) and linseed oil (flax seed oil). Linseed oil
is the vegetable oil most abundant in ALA, it can contain up to 65% ALA. However,
because of the high amount of unsaturated fats, it is not suitable for cooking andfrying. Excessive heating of the oil can lead to auto-oxidation of the double bonds,
giving an off-flavour and causing polymerization of the fatty acids (Kolodziejczyk
et al. 2012).

2.4

Metabolism of PUFAs

Humans cannot synthesise their own omega-3 fatty acids, we are dependent on eating plants and algae — or consumers of algae — to maintain our intake. Though wecannot synthesise them, omega-3s are essential for our bodies to function properly.
EPA and DHA can be synthesised from ALA to a limited extent in our cells, but it
is not enough to sustain our bodies. The same goes for the essential omega-6 linoleic
acid and its metabolism to AA (Wallis et al. 2002).
Plants synthesise the omega-3 fatty acid ALA from the saturated fatty acid stericacid (18:0). Steric acid (18:0) is desaturated with Δ9 desaturase to oleic acid (18:1),
which in return is desaturated with Δ12 desaturase to linoleic acid (18:2n6). Linoleic
acid then undergoes another desaturation with n3 desaturase to synthesise alphalinolenic acid. The Δ12- and n3 desaturases are enzymes lacking in humans, this iswhat makes ALA an essential fatty acid and must therefore be obtained in the diet.
ALA is considered one of the most important omega-3 fatty acids, because byusing ALA mammalian cells can, to some extent, synthesise EPA and DHA. The
ALA is elongated and desaturated in multiple steps by Δ6- and Δ5 desaturases andelongation enzymes in the endoplasmic reticulum to tetracosahexaenoic acid(24:6n3). A chain-shortening β-oxidation of the tetracosahexaenoic acid then occurs
in the peroxisome, converting it to DHA (Wallis et al. 2002).

10

Similarly, the omega-6 LA is desaturated with a Δ6 enzyme in the human body.
It is then elongated and desaturated once again by Δ5 desaturase to form AA (Wallis
et al. 2002).
The limited production of EPA and DHA in the human body, makes the consumption of fish and algae extra important. Algae are big producers of EPA and
DHA, and since algae are the base of the aquatic food chain, the omega-3 fatty acids
will accumulate in the fish as well.

2.5

Algal biosynthesis

Most marine organisms are believed to utilise the polyketide synthase pathway intertwined with the fatty acid synthesis to produce LC-PUFAs such as EPA andDHA. This is a complex machinery and requires approximately 30 distinct enzyme
activities and nearly 70 reactions to synthesise DHA from acetyl-coenzyme A (Metzet al. 2001). The entire process is complex and is not yet fully understood.

11

3

Biological role of LC-PUFA

3.1

Omega-3

The research of EPA and DHA is extensive. Some research focus on their biological
functions and the mechanisms contributing to health. DHA and EPA take part in
multiple biological functions in the human body. One of the main functions is thepart in glycerophospholipid (GPL), which is the main component of the cell membrane. DHA can be one of the two lipids in the GPL molecule. The cis double bonds
in DHA give the GPL a specific characteristic, that contributes to many biological
functions (Hishikawa et al. 2017).
DHA-containing GPLs affect the membrane fluidity, membrane flexibility, thelipid packing defect and the membrane thickness.
DHA-containing GPLs contributes to a highly fluid cell membrane that may allow the cellular functions that are dependent on a fluid membrane to work better(Hishikawa et al. 2017). The higher fluidity can impact on the receptor migration in
the cell membrane as well as lipid raft formation. It can also modify cell signalling
pathways that by extension impact cell and tissue responses linked to metabolism,
hormone sensitivity and immunological functions (Walker et al. 2015). It may also
promote membrane fusion and fission that are dependent on the membrane’s flexibility, as well as promote conformational changes and the mobility of membraneproteins (Hishikawa et al. 2017).
The lipid packing defect refers to the exposure of the GPL’s hydrophobic tail instrongly curved membranes. When the GPL contains a DHA, the exposure is limited
because of the cis curved carbon chain. Membranes that consist of many DHA-containing GPLs are thinner compared to those with GPLs containing more saturated
fatty acids. The thinner membrane increases the permeability of small polar molecules (Hishikawa et al. 2017).

12

Apart from cell membrane functions the DHA-containing GPL also has an important role in tissues. In the retina, the DHA-containing GPL promotes rapid conformational changes in the rod photoreceptors after light stimulation, which allows
the eye to adjust better between light and darkness as well as stimulate night vision(Hishikawa et al. 2017).
DHA and EPA replace other fatty acids such as AA in the phospholipids in thecell membrane. This alters the balance between eicosanoid and cytokine productionin the body. This promoting a less inflammatory or even inflammatory resolving
profile instead of the previous generally pro-inflammatory profile (Walker et al.
2015). EPA can also be metabolised to eicosanoids. Eicosanoids are hormone-likebiochemical substances that aid multiple bodily functions very effectively. Cell
growth, cell division, muscle activity, regulation of blood pressure, immune functions and inflammatory responses are all affected by these eicosanoids. Eicosanoids
derived from EPA may help protect against heart diseases, strokes and different inflammatory diseases (Bhardwaj et al. 2016).

3.2

Omega-6

The consumption of too many omega-6 fatty acids are believed to increase all inflammatory diseases. Diseases such as cardiovascular disease, type 2 diabetes, irritable bowel syndrome, asthma and cancer are all believed to have increased in correlation to the increase of omega-6 in our diet. The omega-6 fatty acids competewith omega-3 fatty acids for the use of the same conversion enzymes in our bodies.
LA is converted to AA and will indirectly limit the conversion of ALA to EPA andDHA. An overconsumption of omega-6 can therefore interfere with the positive
functions of omega-3 (Bhardwaj et al. 2016).
From a physiological point of view, AA is the most important omega-6 fatty
acid. It as a major component in membrane phospholipids, building up most of thecell membrane (Dumancas et al. 2012). AA can, just like EPA, be metabolised toeicosanoids, but this process is not a preventive reaction. Instead, they are releasedin the body as a response to an injury, infection, stress or certain diseases causing
an inflammation (Dumancas et al. 2012; Bhardwaj et al. 2016).

13

3.3

Health benefits

Essential fatty acid deficiency is an issue getting bigger with the modern western
diet. Not only, are the essential fatty acids decreasing in our diet with the choices offood we eat, but they are also decreasing in the food itself. The modern large-scale
production and growth of food decreases the overall essential fatty acids containedin the food. The main issue being the diet we feed our livestock, poultry and fish
with. Grains are not as essential fatty acid rich as leafy plants and grass. Animals
that roam free contain roughly seven times more omega-3 fatty acids than commercially raised meat (Pasquale 2009).
Studies have shown that LC-PUFAs are important for mental health and cardiovascular health. Many studies support that DHA is an important factor when dealing
with memory. A consistent intake of DHA have been shown to decrease the risk ofmemory loss and diseases associated with loss of memory, such as Dementia and
Alzheimer’s (Brenna & Carlson 2014).
The need for DHA in infant formulas has been brought to attention in the twentyfirst century. Deficiency of DHA during infant years have shown risks of compromised visual function (Brenna & Carlson 2014). A deficiency in omega-3 fatty acids, in correlation to increasing consumption of omega-6 fatty acids, have shown
signs of higher risks of cardiovascular disease (Block et al. 2008). A regular intake
of 3g/day of omega-3 fatty acids have shown a decrease in blood pressure. Most
significant in individuals older than 45 years (Mori 2017).

3.4

PUFA function in algae

The role of LC-PUFAs in algae is not fully understood. One of them is believed to
be a contribution to the photosynthetic function. In the thylakoid membranes, LCPUFAs are a part of the galactosyl glycerides: sulfoquinovosyl diacylglycerols(SQDG), monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol(DGDG). In the green alga Chlamydomondas reinhardtii, SQDG have been shown
to uphold photosystem II during environmental changes, such as temperature (Satoet al. 2003). They have also been known to interact with reactive oxygen, when
exposed to light. This lipid peroxidation process may play a role in cell signalling
pathways as an intermediate (Mühlroth et al. 2013).

14

3.5

Carotenoids

The high lipid content in microalgae would not be possible without carotenoids.
Carotenoids are antioxidants preventing lipid peroxidation in biological membranes.
They do this by removing high-energy electrons from free radicals. Astaxanthin is
one of these carotenoids, it is also a red pigment responsible for the red colour insalmon and shellfish (Gammone et al. 2015). Astaxanthin has a very strong antioxidative effect and is considered the most effective antioxidative compound (Galasso
et al. 2017). It is ten times more efficient than lutein, canthaxanthin and β-carotene
and 100 times more than α-tocopherol (Sun et al. 2011).
Astaxanthin and other carotenoids also have the same beneficial antioxidativerole in humans. They scavenge free radicals in our body and quench singlet oxygen
activity (Gammone et al. 2015).
Astaxanthin is most abundant in the microalgae Haematococcus pluvialis. H.
pluvialis is therefore commonly used for industrial cultivation of astaxanthin (Galasso et al. 2017).

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4

Algae

4.1

Algae as a base of the aquatic food chain

The main dietary source of LC-PUFAs is fatty fish and algae (van Ginneken et al.
2011). One of the reasons fish is rich in LC-PUFA is because they eat algae or otherorganisms that eat algae. Fish consumption per capita has increased from 9,0kg in
1961 to 20,2kg in 2015, and the population growth is from 3,075 to 7,349 billion(Food and Agriculture Organization of the United Nations 2018). With the increasing population growth and fish consumption, the fish stocks are diminishing. Alternative sources of LC-PUFAs are therefore needed.
The aquatic food chain starts with, as in every other food chain, a primary producer. This is a low living organism that utilise photosynthesis for energy and tobuild carbohydrates. In the aquatic food chain, phytoplankton, algae and bacteria
are on the lowest trophic level. These organisms synthesise their own energy byphotosynthesis or chemosynthesis (National Oceanic and Atmospheric Administration 2019). Chemosynthesis is the process of generating energy and organic compounds without sunlight, instead by oxidation of inorganic or C-1 organic molecules. These molecules could be hydrogen gas, hydrogen sulphide, ammonium, methane or methanol etc. (Enrich-Prast et al. 2009).
The second trophic level consists of zooplankton — including copepods and amphipods as well as the egg and larval stages of some animals — and larger animals,
such as marine snails, fish, reptiles and mammals. Zooplankton mostly graze on
phytoplankton and the larger animals graze on algae. Bivalves, sponges, whales andmanta rays are examples of filter feeders that strain plankton directly from the waterfor food.
Predators are next in the food chain, here we find the many shark, jellyfish andfish (National Oceanic and Atmospheric Administration 2019). The accumulation
process makes the predators accumulate nutrients, fatty acids and more in their

16

tissue. Though fish can have an abundance of omega-3, it would not be possible
without algae and other LC-PUFA producing organisms.

4.2

Different uses of algae

The industry of cultivating algae is growing every day, it could be a lucrative
market and there are plenty of future opportunities within this field. The cultivationof algae does not compete with already established agriculture and creates job opportunities for our growing population.
Algae have some advantageous characteristics that make them useful in manyindustries. Algae grow fast and consume CO 2, nitrogen and phosphorous (Sharma& Sharma 2017). They can grow in saline waters and would therefore not be leaching on our already depleting fresh water supply. They can also tolerate different pH
levels and temperatures making them adaptable to all kinds of waters (Khan et al.
2018). The algae can be used to purify wastewaters from nitrogen and phosphorouscompounds and turn it into biofuel (Singh & Das 2014). The microalgal biomass
can be used as fuel, feed and food. The fatty acids can be extracted to create a veganomega-3 supplement. Macroalgae are already consumed in many cultures all over
the world, they are energy rich and contain many nutrients, bioactive compounds
and essential fatty acids (Wells et al. 2017).
Algae are energy rich and have high biofuel yields (Sharma & Sharma 2017).
The use of algae as biofuel is getting more popular with our growing population andthe increasing demand for fuel energy. Microalgae have high energy levels with richsources of polysaccharides and lipids. The microalgae grow fast and fixate CO2,
which make the fuel both eco-friendly and non-toxic. Microalgae have been reported to fix 1,83 kg of CO2 with 1 kg of algal biomass and 50% of dry weightconsists of CO2. The technology to produce algal fuels is yet to be improved, butshows on a promising future development (Khan et al. 2018).

4.3

Algal foods

Algae have been a part of the human diet all over the world for thousands of years(Spolaore et al. 2006). One of the current macroalgae used as food is Porphyra species. Porphyra spp. have a high protein content (<47%) and they are widely cultivated, it has more than 100 species located all over the world. It goes by many names
and is known as “nori” in japan and is a staple ingredient used in sushi. In the United
Kingdom it is commonly called “laver”, “karengo” in New Zealand, “zicai” in
China, and “kim” in Korea. In Japan, Korea and China it is one of the largest

17aquaculture industries. The increasing popularity in Porphyra is leading the industry
to spread to other Asian countries (Baweja et al. 2016).
Palmaria palmata is commonly known as “dulse” or “dilisk”. It grows on the
coastline of the North Atlantic Ocean. The alga is eaten both raw and dried in Ireland(Seaweed.ie 2019). The alga is also a popular snack in Nova Scotia, Canada, where
it is eaten dried (Bay of Fundy 2011). Palmaria palmata has a protein content of
about 35% and also contains vitamin B12 (Baweja et al. 2016).
Arthrospira platensis, commonly called spirulina, is a dietary supplement existing both in powder form and in a tablet (Burgess 2018). It is rich in protein, approximately 65% of dry weight, and is also rich in vitamins, essential amino acids andminerals. It is one of the few sources containing the fatty acid GLA (Belay 2002).
Spirulina has become a popular super food and is widely used all over the world, it
is a common supplement in influencers’ smoothies and nut-bars.
Another algal food is agar, it is generally used in baking as a substitute for gelatine. It is extracted from some red algae species, most commonly Gelidium andGracilaria. Agar is a polysaccharide part of the cell wall of red algae (Doty et al.
1983).

4.4

Some examples of microalgae rich in LC-PUFAs

4.4.1 Schizochytrium spp.
Schizochytrium spp. are unicellular eukaryote microalgae part of the Thraustochytriaceae family. They are known for producing high amounts of DHA, this byconverting sugars to omega-3 (Simris 2019). The species can be found growing allover the world. From the cold waters of Antarctica to the sub-tropical waters ofHong Kong and Australia (Jiang et al. 2004). Multiple studies have been conducted
to determine the DHA content in Schizochytrium spp. and the result have varied.
The Schizochytrium spp. have been documented to produce between 25-56% DHA
of the total fatty acids (Martins et al. 2013). Ward & Singh (2005) have recorded
one strain to contain more than 94% DHA of the total fatty acids. In addition to thehigh levels of DHA amongst the fatty acids, the Schizochytrium spp. also have an
overall high lipid concentration. Containing about 50% lipids of biomass dry weight(Nakahara et al. 1996). They are also fast growers and have high resistance to mechanical stirring in fermenter culture as well as a high salinity tolerance (Martins etal. 2013). In an industrial cultivation Schizochytrium spp. can produce up to 7,2 gof DHA per litre of culture per day (Mühlroth et al. 2013).

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4.4.2 Phaeodactylum tricornutum
One of the most EPA abundant microalgae is Phaeodactylum tricornutum. The unicellular diatom can exist in three different forms: fusiform, triradiate, and oval. It isfast growing and produces EPA from sunlight (Simris 2019). Studies of the total
EPA fatty acid content vary in a range between 28-57% of the total fatty acids. The
total EPA fatty acid dry weight content in the alga range between 1-5% (Martins etal. 2013).
P. tricornutum is a well-studied alga. It can be found as different strains all over
the world. From the warmer waters of Micronesia to Long Island, NY to the cooler
waters of the Baltic sea (Martino et al. 2007). P. tricornutum have shown qualities
of adaptive growth in unstable environments, such as estuaries and rock pools andin a wide range of salinity. It have also adapted to cultivate in different climates,from a more tropical strain that grow in 20-26 °C to strains living in much cooler
climate where the water freezes in the winter (Martino et al. 2007).
According to research made by Yongmanitchai & Ward, multiple factors affectthe production of EPA in P. tricornutum. Temperature, nitrate concentration, phosphate concentration, sodium chloride concentration as well as pH, vitamins andoleic acid additions all have an effect on the total EPA production (1991).
Another alga producing EPA is Porphyridium cruentum. P. cruentum is a member of the Rodophyta, Red alga, phylum. It is a single cell alga that is rich in both
AA and EPA (Ahern et al. 1983; Martins et al. 2013)

4.4.3 Odontella aurita
Odontella aurita is a diatom with high a production level of EPA (25-26% of total
fatty acids). It is an approved food supplement (Haimeur et al. 2012) and has beencultivated for commercial uses, as a dietary supplement, for many years. As with all
algae, stress influences the amount of PUFAs produced. Temperature is one of themand in the study by Pasquet et al. (2014) they investigate the impact it has on the
PUFA productivity by the alga. They also measure the differences in PUFA at different growth phase.
The temperatures they investigated were 8, 16 and 24°C and they harvested in
the exponential- and stationary growth phase. When cultivated at 8°C the diatom
grew slower but produced more LC-PUFAs and less saturated fatty acids than whencultivated in 16 and 24°C. The maximum cell density was about five and six times
lower than in 16 and 24°C. The percentage of LC-PUFAs were more abundant in
the stationary phase than in the exponential phase. When cultivated in 16 and 24°C
the growth rate and final cell count were relatively similar, but the abundance of19

LC-PUFAs were significantly different. When harvested in the exponential phase,the 16°C O. aurita had about seven times more EPA than the 24°C O. aurita. When
harvested in the stationary phase it was only 1,3 times more. The DHA showedsimilar patterns and was at its highest when cultivated in 16°C and harvested in the
exponential phase. Conclusively, for a maximum amount of cell count and LCPUFA production, cultivation at 16°C and harvest in the exponential phase is toprefer (Pasquet et al. 2014).
In another study made by Xia et al. (2013) they investigate the effects of nutrientsand light intensity on O. aurita. At the temperature of 25°C, the highest lipid content(19.7% of dry weight) was obtained under 0.11 mmol/L silicon and high light conditions at harvest time. EPA ranged from 9% to 20% of total fatty acids. The harvest
phase was not stated (Xia et al. 2013).

20

5Discussion

Algae have many biological benefits and functions, one of them is the productionof LC-PUFAs. The result of this literature study shows the biological advantages ofconsuming LC-PUFAs. ALA can be metabolised in the omega-3 pathway and synthesise EPA and DHA. EPA and DHA are both synthesised by algae and by eating
algae oil, the recommended daily intake can be reached.
The aquatic food chain leads to an accumulation of LC-PUFAs in fish, whichhave been the main source of LC-PUFAs for human consumption. Early humans
were believed to have a more developed synthesis of LC-PUFAs, but their dietaryevolution of eating more fish have led to a loss of those enzymes (Mathias et al.
2012).
Fish may have been the primary source of LC-PUFAs, but the continuing growthof population have caused the fish stocks to deplete and new sources of LC-PUFAs
are needed. The cultivation of algae is still in its early phases and show prosperous
development and could be a provider of many jobs in the future. Algal species suchas Schizochytrium, Phaeodactylum tricornutum and Odontella aurita are high producers of LC-PUFAs and are vastly researched, but they are not the only ones (Martins et al. 2013). Finding the ultimate algae to cultivate could be a challenge sincemultiple factors play a role in the growth and nutrient production. The final outcomeof nutrients is dependent on the environment which the alga is grown in. To cultivate
a wide variety of species around the world could be a better path to follow than tojust focus on one. This would also support the biodiversity.
In conclusion, research have shown that omega-3 fatty acids are important to ourbodies and finding new sources of it is of importance. The fish stocks are depleting,and many diets do not sustain the need for omega-3. Algae are a source rich inomega-3, that can meet the vegan diet restrictions. A substitute to fish oil made fromalgae is a prospective food supplement that could provide omega-3 to our growing
population.

21

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