Beet leaves contain proteins that are valuable for humans and that would work perfectly well as an alternative to animal protein, for example in veggie burgers. Techniques have already been developed for the extraction of soluble proteins – such as RuBisCO – but the insoluble membrane proteins are so varied that they cannot all be extracted by any single method. The green colour is also rather hard to get rid of. These findings come from research published in Food Chemistry by food process engineering PhD candidate Angelica Tamayo Tenorio.
Tamayo says there are two options for extracting protein from the foliage. ‘Either you make a concentrate containing all the protein, both the soluble RuBisCO and the insoluble membrane proteins, but in that case you have to put up with the green colour, which comes from the chlorophyll. Or you go for the pure, colourless RuBisCO, but then you have low yields.’ In the latter case, the membrane proteins have to be used for a different purpose — for example as an emulsifier or gelling agent — to make the process economically viable.
At the start of the research, the membrane protein in beet leaves was still thought to consist of a single type of protein, but Tamayo discovered that there are actually hundreds of different proteins. ‘They are also very diverse in terms of size, behaviour and charge. That means that every process step for extracting these proteins is selective for one particular protein. So if you design a series of processes, you lose some of the membrane proteins with each step.’
Tamayo therefore argues that it is better when processing the green leaves to split them into a fibre-rich pulp and concentrated protein-rich juice instead of just extracting the protein. This ‘total leaf fractionation’ using a screw press and a centrifuge produces a concentrate with 50 percent protein (by dry weight). ‘This is about 25 percent of all the protein in beet leaves. So you still have losses,’ admits Tamayo.
She still thinks there is a lot of potential in processing beet leaves, which are currently not used at all. The protein-rich concentrate could then easily be used in a green beet-leaf burger. Tamayo: ‘But because beetroots are seasonal, I have wondered what this hypothetical factory would be processing the rest of the year. I see options for other plant components that are not being used at present, such as broccoli leaves and carrot tops.’