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Microalgae: a nutritional package
Research

Microalgae: a nutritional package

Microalgae consist of exactly one cell … one cell crammed full of goodness.

7 minutes
20 July 2020

Microalgae consist of exactly one cell … one cell crammed full of goodness. You can think of them as a nutritional package that includes proteins, minerals, vitamins, antioxidants and lipids. Researchers at KU Leuven are examining which microalgae are the most promising and which scientific tweaks are needed to unlock their nutritional content.

Microalgae can be regarded as microscopic cousins of the seaweed that you see on the beach. They exist in hundreds of thousands of species, both in fresh and salt water. Many diverse industries are interested in these mini-seaweeds for their potential as animal feed and biofuel, but also as a raw material for cosmetics or the chemical industry.

Microalgae can also contribute to a healthy diet. For instance, some types contain omega-3 fatty acids, which in humans have a protective effect against cardiovascular diseases and contribute to the development of the brain in foetuses and new-born babies.

More specifically, it’s ‘long-chain omega-3 fatty acids’ that have these health effects. You can get those fatty acids from fatty fish, but that’s where the trouble starts. In the Western world, fish consumption is low and, additionally, fish stocks are under pressure. So it makes sense that microalgae come into the picture. After all, fish get their omega-3 from the algae they eat, so why don't we use them as a direct source in our diet?

Cultivation in a race track

‘That’s easier said than done,’ says Professor Imogen Foubert. She heads the Food & Lipids Lab, one of the few labs worldwide that conducts scientific research into food applications of microalgae and their associated obstacles. ‘One of the problems is that omega-3 fatty acids are very sensitive to oxidation. By coming into contact with oxygen during storage, they lose some of their nutritional value and they develop unwanted flavours and odours.’

To really sell the food industry on microalgae, you’d have to make sure that they are ‘oxidatively stable’. The method of cultivation plays a major role in this outcome. You have microalgae that you can grow in closed fermenters without sunlight by simply adding sugars. That is the cheapest method. However, research by Professor Foubert and her team shows that the omega-3 fatty acids from these heterotrophic microalgae are much less oxidatively stable than those from autotrophic species, which are microalgae that need sunlight and CO2 to grow. The latter are also the type of microalgae that fish ingest.

One of the problems is that omega-3 fatty acids are very sensitive to oxidation. By coming into contact with oxygen during storage, they lose some of their nutritional value.

Autotrophic microalgae can be grown in ‘raceway ponds’ – oval man-made ponds that resemble a horse track – or in photo-bioreactors. Expensive methods though, and difficult to scale up. ‘That’s why we now want to unravel which components in microalgae protect the omega-3 fatty acids against oxidation,’ says Professor Foubert. ‘Once we know that, we can try to work with a combination of the two types that’s acceptable in terms of price and oxidative stability.’

Vegetarian lobster soup

The delivery method also has an influence on the nutritional value of the microalgae. After they’ve been harvested and dried, you can get them to the consumer in different ways. For example, you can extract oil from them. ‘You’ll find oil capsules on the market that you can take as an omega-3 dietary supplement,' says Professor Foubert. ‘But extracting oil is an expensive step, and during that process you also lose a lot of valuable components contained in the microalgae.’

According to Professor Foubert, it’s a better idea to add the whole biomass to food products. ‘You have to take into account that some microalgae have a rigid cell wall. To prevent them from entering the digestive tract as intact cells, you have to make sure to break them open during the manufacturing process. Colleagues from the Food Technology Lab have investigated various ways in which you can do this (see inset below).’

Professor Foubert's team researched a third line of approach. The researchers examined whether you can increase the omega-3 content of egg yolk by adding microalgae to the feed given to laying hens. They found that microalgae are more efficient than widely-used flaxseed to enrich eggs with omega-3 fatty acids. A taste panel also gave a positive review of the taste and smell of these eggs.

How should we imagine the taste of unprocessed microalgae? ‘There are algae that smell and taste grassy, others are more likely to taste fishy. With microalgae, for example, you could make a perfectly seasoned vegetarian lobster soup,’ says Professor Foubert.

There are algae that smell and taste grassy, others are more likely to taste fishy. With microalgae you could make a perfectly seasoned vegetarian lobster soup.

The colour also determines which food products are suitable for enrichment with microalgae. ‘Most varieties are green, brown or red, so uses tend to involve vegetables, such as soups. These food products also appeal to vegetarians because they don’t consume omega-3 fatty acids by eating fish. In addition, vegetables contain antioxidants, although doctoral research has shown that you can’t keep heterotrophic microalgae or fish oil oxidatively stable by combining it with vegetables in a food. So that remains the major challenge for the research.’

Acceleration?

For the time being, you’ll have to search carefully if you want to put microalgae in your shopping basket. You can find them in organic stores as a dietary supplement in the form of powders, tablets and capsules. And if you search a little longer, you may find a smoothie or soup that contains microalgae. ‘Food manufacturers are waiting for suppliers that offer microalgae at an acceptable price, while those potential suppliers are waiting for sufficient demand from the food industry,’ says Professor Foubert. ‘In addition, small companies often don’t have the means to apply for European approval for their microalgae because it’s too expensive.’

So a real breakthrough is yet to come, but research done at the Food & Lipids Lab can help quicken the pace. Thanks to the recently renewed and expanded research infrastructure, Professor Foubert and her colleagues will be able to answer the industry’s questions even better. What are the advantages and disadvantages of microalgae, which species are interesting and how can you best add them to food? ‘The better the scientific world maps this out, the more companies will consider actually working with microalgae,’ concludes Professor Foubert.

A microscopic view of 'Arthrospira', not strictly speaking a microalga but rather a cyanobacteria. Characteristic for this species are the elongated strands that form the cells. Organic stores sell them processed in powders or tablets under the name 'Spirulina'.
A microscopic view of 'Arthrospira', not strictly speaking a microalga but rather a cyanobacteria. Characteristic for this species are the elongated strands that form the cells. Organic stores sell them processed in powders or tablets under the name 'Spirulina'.

Two birds with one stone

Expertise in microalgae isn’t limited to Professor Foubert's Food & Lipids Lab. Over five years, the knowledge platform VEGETALGAE gathered research groups from across KU Leuven that were making scientific contributions to the use of microalgae.

You can combine production processes to boost the thickening properties of microalgae. This could be of use in ready-to-eat soups and sauces.

For example, researchers led by Professor Ann Van Loey at the Food Technology Lab examined how microalgae can influence the texture and flow behaviour of a food. ‘You can actually combine production processes to boost the thickening properties of certain types of microalgae,’ says researcher Tom Bernaerts. ‘That way you kill two birds with one stone: you have the healthy properties of the microalgae, and you don't have to add additional thickening agents to your food product. This could be of use, for example, in ready-to-eat soups and sauces. On the other hand, microalgae that don’t have the thickening effect are useful for the nutritional enrichment of fruit and vegetable juices.’

The researchers determined that, among other methods, heat treatment can be used to change texture and flow behaviour. In any case, such treatments are often applied at the end of the production process to make these types of food products safe and stable for long-term storage.

In addition, the researchers also examined how to unpack the nutritional package that is a microalga. Our body doesn't have the right enzymes to digest the microalgal cell wall itself, so they looked at a technique to break open the cells beforehand. ‘This can be done via a mechanical process in which very high pressures are exerted on the microalgae until the cell wall finally breaks,’ says Tom Bernaerts. They investigated the impact of this cell disruption on the possible absorption of nutrients in the body by mimicking our digestion in the lab. Thanks to the mechanical process, both the antioxidants and the omega-3 fatty acids became up to five times more available for absorption into our bodies.

These results are of relevance to food producers; if they’re supplied with microalgae that have been broken open in the best possible way, they can bring to market new products containing microalgae that are genuinely healthy for the consumer.