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World first: Dutch team develop method to extract high-value protein from tomato leaf

Tomato leaves that are currently seen as a major waste stream in horticulture could provide a reliable and sustainable source of rubisco – a widespread plant protein that has potential in food and drink, say researchers.

Researchers at the Wageningen University & Research (WUR), the Netherlands, say they have become the first in the world to extract high-value rubisco protein from tomato leaves, one of the major co-streams of greenhouse horticulture.

“Our study proves that you can achieve substantial gains in sustainability by making better use of what you already have,” said project leader Marieke Bruins, a senior scientist in protein technology at WUR.

Rubisco: The next big alt-protein?

Rubisco (ribulose-1,5-biphosphate carboxylase oxygenase) is an enzyme crucial in photosynthesis, that is found in every leaf of every green plant in the world – often in considerable quantities.

In its pure form, rubisco has a neutral aroma, colour and flavour, a good balance of the essential amino acids, and good gelation properties, which make it an interesting prospect for development in the alt-protein space, noted the team in a recent press release.

Indeed, they noted that rubisco protein can be ‘very useful’ for processing into meat substitutes and dairy alternatives, since it can help to provide a firm ‘bite’ and improved mouthfeel.

In 2019, a study led by researchers from Wageningen Food & Biobased Research and the Nestlé Institute of Material Sciences, Switzerland, compared the functional properties of rubisco protein isolate – on this occasion isolated from sugar beet leaves – with commercial whey and soy protein isolates.

The study, concluded that rubisco had “comparable or superior functional properties to those of currently used whey and soy protein isolates”.

Writing at the time, the Wageningen-led team said the results highlighted the high potential of rubisco as a nutritious and functional food ingredient to face global food security and protein supply.

Method removes toxins from tomato leaves

The extraction of rubisco from tomato leaves uses similar methods to those developed by the WUR team for other crops and waste streams, including the method of extracting rubisco from sugar beet leaves.

However, Bruins and colleagues noted that the new method had to be adapted to remove the toxin hydroxytomatine from tomato leaves.

“Our method filters out the components that are smaller than the protein we want to extract, and this includes many toxins,” the lead researcher said.

The result of the extraction is a high-value protein powder, free of toxins, and ready to be used in food applications, the authors said, noting that the same method could also be suitable for extracting rubisco from the leaves of other food crops – such as potato or cassava, which, like tomato leaves, contain toxins that make them unsuitable for direct consumption.

Wanted: Private sector partners to scale up the ingredient

The team noted that harvesting food crops results in the yearly production of around 40 tonnes (for sugar beet) to 50 tonnes (for tomatoes) of crop residues, made up of leaves and stems, per hectare.

Traditionally, these residues are either ploughed back into the soil as fertiliser or are composted – both of which, the WUR team note, are low-value uses of the residues compared to extracting protein for human consumption.

Indeed, the researchers noted that the large-scale application of the process will increase the availability of plant-based proteins and contribute to a sustainable food supply for the growing global population.

They now hope to work with the private sector to further develop the technology to apply it on an industrial scale.

“That could mean working with greenhouse horticulture businesses, or businesses that use plant-based proteins as inputs. These might include producers of dairy and meat substitutes,” said Bruins.