Fractionation of leaf proteins by differential centrifugation and gel filtration

The quantity and quality of fractionated leaf proteins from different plant species were investigated. Leaf extracts (pH range 7.0–8.3) were prepared on a laboratory scale from greenhouse cultivated plants. The proteins were fractionated by differential centrifugation followed by gel filtration. Amaranthus caudatus and Chenopodium quinoa seem favourable for production of non‐green leaf protein concentrates, since the water‐soluble protein comprised nearly 50% of the extracted protein. The chlorophyll‐associated protein in fresh extracts from these species was, however, difficult to sediment. A practical separation of chlorophyll‐associated protein from the chlorophyll‐free proteins will require some kind of pre‐aggregation of the chlorophyll‐associated proteins. In extracts from Dactylis glomerata, Lolium perenne and Vicia sativa a considerable proportion of the extracted protein sedimented rapidly, but at least for the grasses some of the chlorophyll‐associated protein remained in the supernatants even after centrifugation at 30 000 g for 180 min. Practical separation of all the chlorophyll‐associated protein from the extract requires some kind of pre‐aggregation of the chlorophyll‐associated proteins even for these species. The situation was similar for extracts from Helianthus annuus , but a very high percentage of the total chlorophyll‐associated proteins could be sedimented at low centrifugation speed. Brassica oleracea was the most suitable species for the removal of the chlorophyll‐associated proteins by centrifugation alone. Moreover, the proportion of chlorophyll‐free protein in the extracts was relatively high, more than 40%. The in vitro digestibility of membrane‐bound protein fractions was high for species with co‐aggregation of water‐soluble protein and membrane‐bound protein . Causes underlying the different distributions of the chlorophyll‐associated and chlorophyll‐free proteins and the reason for the different size of the chlorophyll‐containing particles are discussed.