To counter future shortages in functional proteins, there is a need for efficient, sustainable, and cost-effective use of protein with regard to functionality. Biorefinery and extraction of functional proteins is required to broaden the applicability of alternative protein sources. Novel sources that are not commercially utilized yet are leaf proteins, for example, from alfalfa (Lucerne) or grass. In addition, waste side streams such as beet leaf or sources such as algae are possibly important new sources of protein and could offer potential economic benefit when the protein fraction is valorized. The similarity between all of these leaf sources is that they all contain RuBisCO and similar types of membrane proteins.
TNO has developed an improved isolation procedure delivering colorless and highly soluble, native RuBisCO. On lab scale, RuBisCO was isolated from spinach showing excellent gelling functionality in comparison to proteins such as whey protein, ovalbumin and plant proteins, as was shown by Anneke Martin and colleagues (Martin et al., 2014, DOI: 10.1021/jf502905g). Rubisco was found to readily form a solid gel already at concentrations of 2.5% as opposed to >12% whey protein. Recently, Aard de Jong and co-workers isolated Rubisco from beet leaves (waste side stream) using intermediate scale production throughput (15 kg of leaves per batch) with mild food compatible technologies. The final protein powder was composed of a highly homogenous and native protein fraction with a very good solubility at pH values lower than 4 and higher than 6. The great potential of Rubisco was shown by its good functionality properties with regard to foaming, emulsification, and especially gelling, in comparison to whey protein and soy protein.