Video: WUR
Water lentils are healthy, rich in proteins and can be cultivated sustainably. They can make a meaningful contribution to the protein transition and the global food issue. However, in order to bring this about, both producers and consumers need to get more familiar with this innovative vegetable.
'For a bountiful yield, you can harvest once or twice per week'
Most people know water lentils as duckweed. The tiny green plants that float – and rapidly multiply - in stagnant water. In Thailand and other Asian countries, water lentils are eaten; they are primarily sold at local markets. Water lentils are not yet a food staple in the West, although the vegetable is hardly new. As early as 1644, a Dutch herbal book referred to ‘Water Linsen oft Enden Groen’ (Water Lentils or Duckweed).
Sustainable cultivation
Ingrid van der Meer first got interested in water lentils about ten years ago. The senior researcher and head of the Bioscience department at Wageningen Plant Research thought it was ‘a highly interesting plant’. ‘They have a number of biological processes that differ from those of other plants. From a scientific point of view, water lentils are very intriguing.’ Over the course of her research, the impression water lentils left on her only grew. ‘They grow quickly, are suitable for contained cultivation and their dry weight contains massive amounts of protein. I thought: why don’t we eat this?’ In many ways, water lentils are an ideal vegetable for the future. ‘They are an exceptionally sustainable vegetable’, Van der Meer explains. “They are cultivated on water and don’t need many nutrients. Of course, water is a precious commodity, but in a simple greenhouse or vertical farm, growers have the ability to employ this very efficiently.’ The production of water lentils does not require any farmland, which means it can be grown indoors, even in cities. On top of that, growers do not need to use pesticides.
'A number of biological processes differ from those of other plants. It is very interesting from a scientific point of view'
Water lentils are a sustainable leafy vegetable that require only a swallow layer of water and minimal nutrients to grow. Photo: WUR
The greatest green benefit of water lentils is their production: calculations by WUR show that they can produce over six times as much protein per hectare as soy, which is itself a protein-rich crop. ‘Water lentils grow much like yeast. The plant splits into two every three days. These then split again into four plants, and so the growth continues exponentially. To guarantee bountiful yields, you’d need to harvest once or twice per week.’
Healthy and tasty
Consumers are increasingly urged to eat more plant-based products. This is not just good for the planet, but also benefits our health. Leafy vegetables are healthier than rice or corn, for example, and water lentils are a very healthy leafy vegetable. They are rich in vitamins, minerals and antioxidants and feature a perfect balance of essential amino acids. And what about their flavour? According to WUR studies, taste panels certainly appreciate water lentils. Panel members tried various dishes containing water lentils, including soup, stew, ravioli and pesto, and had positive reactions to the flavour. Enthusiastic chefs are eagerly experimenting with water lentils because of their versatility. ‘Water lentils have a plant-like, slightly nutty flavour and have a nice bite despite their size.’
Overcoming hurdles
Until recently, legal obstacles obstructed the rise of water lentils. The European Food Safety Authority EFSA considers the vegetable a ‘novel food’, which is a food that is not frequently consumed by people. Since 1997, novel foods are only allowed on the market after thorough research has proven their suitability for human consumption. ‘To submit a novel food request, you need to supply a full-fledged dossier with scientific and technological research and evidence. This takes immense amounts of time and money. This was a hurdle I was determined to overcome, however, so water lentils could be used universally after they were endorsed,’ Van der Meer says. With financial support provided primarily by the Welcome Trust in London and, later, by the Goeie Grutten foundation, the Wageningen researchers set about their task. ‘For example, we had to show that we could cultivate water lentils in such a way that their manganese levels were equal to those of spinach, and we had to do so for five different batches.’
Are water lentils the vegetable of the future? These little plants, also known as duckweed, grow at an exponential rate, are relatively high in protein and can be grown sustainably. As such, they could play a key part in the protein transition, according to senior researcher Ingrid van der Meer. In ten years, she hopes consumers will be eating soup, cheese and other products with water lentils.
Their efforts paid off: Wageningen Research proved that the water lentil Lemna is safe for human consumption. In 2021, the EFSA already approved Wolffia, the water lentil that is eaten in Thailand. This type is considered a traditional food from a third country, which means its endorsement was subject to far fewer requirements than novel food.
Fresh, frozen or in a smoothie
Now water lentils have been approved for consumption, it is time to take the next hurdle: getting the food industry on board. At present, water lentils are not cultivated commercially anywhere within the EU. In Israel, water lentils are marketed as a sort of green caviar, and in the USA, a start-up by two Dutchmen is working on an extraction method to retrieve proteins from the plant. ‘In Wageningen, we have extensive knowledge about cultivation and product development, but we are researchers. Water lentils now need to be embraced by the food industry, so consumers can buy and use products containing them.’ Since 2022, WUR has been engaged in a project that aims to bring together partners from the entire chain. The joint research in this project is aimed at the sustainable, safe and hygienic production of water lentils through methods like vertical farming. Various products are taken into consideration. Water lentils can be marketed in many forms, including fresh, frozen, ready-made or as a protein additive, for example. They could be packaged in holed plastic bags, like lettuce or fresh endive. Or as frozen cubes, like spinach. Food companies can also use water lentils as an ingredient in pasta, cheese, cake or smoothies, or as a meat substitute.
'Water lentils are not cultivated commercially anywhere within the EU'
Several water lentils species have been approved for consumption. Photo: WUR
Van der Meer sees a growing interest in water lentils, but also notices that food companies are still hesitant. ‘Many growers want to start production, but as long as there are no buyers, there’s no point. Someone needs to take the leap.’
Familiar vegetables
Meanwhile, Van der Meer and her Wageningen colleagues are also considering the other end of the chain: ‘We need to keep the consumer in mind. That was an essential aspect for us: we won’t continue the project if people don’t want to eat water lentils.’ In collaboration with Wageningen Food & Biobased Research, she performed extensive consumer studies involving over 1,000 respondents. Through questionnaires, they were asked to indicate whether they would eat water lentils based on background information and product images. In other studies, volunteers were actually offered water lentils. For one intervention study, volunteers ate a large portion to demonstrate the release of proteins and to determine if there were any effects on their health. In another study, participants ate dishes with water lentils, like soup, stew, quiche and risotto. For the first two days, the participants had to get used to the taste, but after that, their response was positive. Comparisons with the same dishes containing spinach showed that the participants liked water lentils just as much. In fact, they liked the water lentil soup better than the spinach equivalent. In short, water lentils have massive potential, but it will be a while before they take supermarket shelves by storm. Are the food companies waiting for interested consumers, or can consumers only develop a taste for this product once food companies make it available? ‘It’s a chicken and egg situation. What we know for sure is that this vegetable needs to get more attention’, Van der Meer concludes. And if interest in water lentils will grow as fast as the plant itself, this might happen sooner than expected.
Ingrid van der Meer Head of the Bioscience department, Senior researcher
Research project Water lentils as a new, sustainable protein crop.
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