A project supported by the SFN is researching how to turn microalgae into a nutritious, useful and – above all – tasty food product
We are all too aware that our conventional agricultural systems are having devastating impacts on our planet. This has sparked a strong interest in more sustainable ‘alternative’ foods – from ‘lab-grown’ meat to insect-enriched flours – but these can only make a difference if consumers accept them. And for that to happen, novel foods need to be affordable, easy to cook with and, perhaps most importantly, appealing to our taste buds.
Dr Yixing Sui (University of Greenwich) knows this only too well. “Even if you have a perfect food product that is both sustainable and healthy, you have to pay attention to the end-user because it will be of no good if the market doesn’t accept it.” The particular food he is trying to get on our plates is microalgae. This term includes both photosynthetic cyanobacteria and small, plant-like organisms on the single-celled scale. Individual microalgae can’t be seen without a microscope, but when they multiply in their thousands, they produce dense cultures of beautiful colours: green, orange, red or blue-green, depending on their pigments. As part of a long-term project supported by the SFN, Sui is researching how to turn this unappetising sludge into palatable food products.
“We call it a novel food product, but microalgae has historically been eaten in Africa, Asia and South America” says Sui. The Aztecs, for instance, were recorded collecting mats of Spirulina species to make into dry cakes, called tecuitlatl. “Nevertheless, microalgae never became widespread across the modern world due to their having a very strong, fishy taste and smell, which most find off-putting.” With this in mind, why should we bother trying to eat it?
First of all, microalgae have very strong nutritional credentials. “Microalgae species generally have high protein contents, with a profile that covers all the essential amino acids (for humans), comparable to soya, milk and eggs” says Sui, who for his PhD thesis researched how amino acid content in microalgae varies depending on their environment. “By changing the cultivation conditions, you can boost the level of a specific amino acid even further, without affecting the others.” Farming microalgae also has fewer environmental impacts than conventional protein production systems, since they are highly resource- and water-efficient, and can generate a harvest within weeks – significantly quicker than the annual cycles for most crops. There is also the advantage that microalgae can be farmed anywhere, as Sui explains: “All you need is sunlight, a warm temperature and an open pond or photobioreactor. This opens up the possibility of growing microalgae using land that is currently unproductive, such as deserts.”
But for microalgae’s benefits to be realised, we need to first overcome the taste barrier. To address this, Sui and his colleagues are researching how flavour compounds vary across different species, and whether these can be manipulated to make them taste better. As part of a SFN Scoping Project, he joined forces with Dr Geraint Morgan (The Open University), who has a track record in applying highly-advanced analytical techniques to new sectors, including the food industry.
The team initially focused on identifying glutamate and aspartate, two compounds that give the umami taste - the savouriness we associate with foods such as cooked meats, tomatoes, mushrooms, cheese and broths. Rather than choosing a microalgae species from the Spirulina and Chlorella genera (conventionally used for human consumption), they selected Dunaliella salina, a species that is already widely farmed to produce β-carotene. Nevertheless, D. salina is also protein-rich, with an amino acid profile that matches human requirements. “Our first objective was to establish if microalgae do contain umami compounds at all” says Sui. “The second was to understand how these are balanced with compounds for other flavours, including bitterness and earthiness, to see if the overall profile could be tweaked to resemble something more like mushroom-meat.”
The project uses gas chromatography, a technique for separating and identifying different compounds. “The samples are heated and vaporised in the gas chromatography instrument, and the gaseous compounds travel through a matrix material” says Geraint. “The distance that the compounds travel through the matrix before being adsorbed to it depends on their chemical structure – we call this the retention time.” The compounds can then be identified by comparing the retention times with those in reference libraries. In previous SFN Scoping Projects, Geraint has demonstrated how gas chromatography techniques can be applied to the food sector, including in ‘sniffing out’ rotten avocados from unblemished ones, and predicting the shelf life of bagged salads.
Whilst the results confirmed the protein potential of D. salina, the team only detected low levels of glutamate and aspartate. But unexpectedly, through follow-up work supported by ValgOrize (a European project funded by the Interreg 2 Seas programme) they found that D. salina is unusual in having an overall sweet and floral flavour, rather than a fishy one. “We checked the results by sending samples to be tested by panels of trained human tasters at the Flanders Research Institute for Agriculture, Fisheries and Food . These found that this microalgae has a very different taste profile compared with Spirulina and Chlorella” says Sui. The challenge now is to identify these compounds, and then work out how both production and cooking processes can be optimised to enhance these as much as possible. “Since the biochemical composition of microalgae is so dependent on the environmental conditions, developing this analytical capacity further will be crucial to finding out the best cultivation techniques” says Sui.
Consequently, he is keen to continue working with the SFN and has been awarded a proof-of-concept grant from the Network. This will involve experimenting with D. salina as a food ingredient, and tracking the changes in nutritional and taste profiles before and after cooking in order to identify the most suitable food products to use it in. “There are a wide range of potential uses, including noodles, cupcakes and even as an egg replacement in vegan versions of products such as mayonnaise and pastry. But this will depend on other properties besides taste, including structure and texture” says Sui.
It may be a while yet before many microalgae-enhanced foods appear on our supermarket shelves, but in the meantime Sui has already started experimenting, using commercial D. salina powder sourced from Australia. “I used the powder to make cookies, and whilst they were a bit green they definitely didn’t have a fishy smell!”
Find out more: Read our blog post on a SFN-supported start-up bringing another novel aquatic protein source to market: Lemna, a water plant that looks unremarkable, but could be a highly sustainable food for the future.
September 2022 - Caroline Wood, Freelance Science Writer