Rapid and Cost-Effective Preparation of a RuBisCO-Rich Protein Fraction from Dried Leafy Biomass

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the most abundant protein on Earth, is an attractive and sustainable food ingredient owing to its favourable nutritional and techno-functional properties. Leafy vegetables are particularly rich sources of RuBisCO; however, large-scale vegetable production generates substantial quantities of residual biomass throughout agri-food supply chains. Drying is widely used to stabilise this biomass and facilitate storage, transport, and handling, yet most reported RuBisCO extraction methods have been developed for fresh material and are poorly suited to dried feedstocks. Here, we present a simple, scalable, and cost-effective process for the recovery of food-grade RuBisCO from dried leafy biomass. Using spinach, rocket, and kale as model systems, efficient protein extraction was achieved from both freshly dried leaves and commercially available leaf powders without the need for resource-intensive processing. Application of the method to spinach yielded approximately 75 mg of high-purity RuBisCO per 100 g fresh-leaf equivalent, corresponding to an extraction efficiency of [~]70%, which increased to [~]90% following supplementation with 20 mM CaCl2. The recovered protein fraction also exhibited favourable foaming capacity and foam stability, demonstrating its potential as a functional food ingredient. This work provides a practical route for the valorisation of dried vegetable residues and supports the development of circular, waste-to-value supply chains for sustainable plant protein production.