Researchers at Wageningen have become the first in the world to extract high-value Rubisco protein from tomato leaves, one of the major rest streams of greenhouse horticulture. The method they used is similar to the methods they had previously developed for extracting Rubisco from other crop rest streams. Large-scale application of this process will increase the availability of plant-based proteins contributing to a sustainable food supply for the growing global population. It will also help to accelerate a transition towards a more plant-based diet in developed countries.
The pilot study was based on a method of extracting Rubisco from sugar beet leaves. The researchers investigated whether they could use this method to also remove the toxin hydroxytomatine from tomato leaves. The result was a high-value protein powder which was free of toxins.
Using what’s available
The same method could also be suitable for extracting Rubisco from the leaves of other food crops. The leaves of potato and cassava plants, for example, also contain toxins, and like tomato leaves they therefore are unsuitable for direct consumption. “Our method filters out the components that are smaller than the protein we want to extract, and this includes many toxins,” says project leader Marieke Bruins, a senior scientist in protein technology at Wageningen University & Research. “Our study proves that you can achieve substantial gains in sustainability by making better use of what you already have.
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,” says Bruins.
Harvesting food crops results in the yearly production of around 40 tonnes (for sugar beet) to 50 tonnes (for tomatoes) of crop residues per hectare. These residues are composed of leaves and stems. The leaves are either ploughed back into the soil as fertiliser or are composted, both of which are low-value uses of the residues compared to extracting protein for human consumption.
Rubisco, or Ribulose-1,5-biphosphate carboxylase oxygenase, is a crucial enzyme in photosynthesis. The protein is therefore found in every leaf of every green plant on Earth, often in considerable quantities. 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.
Wageningen University & Research has conducted research into efficient, economically viable protein extraction from agricultural residues for more than 10 years. This research involves process technologists and biochemists working closely with experts in plant breeding and plant physiology.