Upcycling ag by-products for human nutrition: Scientists extract toxin-free Rubisco protein from tomato leaves

The process was developed by scientist at WUR and is similar to methods for extracting Rubisco from other crop residue side-streams. It was based on a method of extracting Rubisco from sugar beet leaves, which the researchers used as a starting point to see if they could also remove the toxin hydroxytomatine from the tomato leaves.

“Our method filters out the components that are smaller than the protein we want to extract, and this includes many toxins,”​ according to project leader Dr Marieke Bruins, senior scientist in protein technology at WUR.

“The toxins get mainly removed by filtration. This happens relatively late in the process when we have our protein in solution. Fibres that are mostly insoluble already get removed in our first steps, where we press and centrifuge. We obtain a high-quality protein as no harsh treatments are done,”​ she told FoodNavigator.

The process is physical, not chemical, and results in a high-quality food protein ingredient, we were told. ”It is highly functional,”​ Dr Bruins observed, pointing to properties like gelling that can be noted in the final extract. “Rubisco from sugar beet and from water lentils are currently going through the EFSA procedure,”​ the protein expert highlighted as evidence of the protein’s suitability for food applications.

Upcycling agricultural 'waste' for human nutrition 

Harvesting sugar beet and tomatoes results in 40 and 50 tonnes of crop residue respectively per hectare, per year. The leaves and stems are either ploughed back into the soil as fertiliser or composted. WUR researchers stress that these are ‘low-value’ uses of the residues compared to extracting protein for human consumption.

“Our study proves that you can achieve substantial gains in sustainability by making better use of what you already have,”​ Dr Bruins stressed.

The researchers 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,”​ Bruins said.

Rubisco protein in ‘every leaf of every green plant on Earth’

Rubisco, or ribulose-1,5-biphosphate carboxylase oxygenase, is a crucial enzyme in photosynthesis. The protein is found in 'every leaf of every green plant on Earth', often in considerable quantities, the researchers noted.

It is possible that the WUR method could also prove suitable to extract Rubisco protein from the leaves of other crops, including potato and cassava, which also contain toxins and – like tomato – are therefore unsuitable for direct consumption.

In its pure form, Rubisco has a neutral aroma, colour and flavour, and a ‘good balance’ of the essential amino acids. It also has good gelation properties. “This makes Rubisco a very useful protein for processing into meat substitutes and plant-based dairy alternatives, for example as a way of providing a firm ‘bite’ or improved mouthfeel. It also makes a good egg substitute in food products,”​ the researchers suggested.