Fractionation of leaf proteins by differential centrifugation and gel filtration [sedimentation pattern, Amaranthus caudatus, Brassica oleracea, Chenopodium quinoa, Dactylis glomerata, Helianthus annuus, Lolium perenne, Vicia sativa]

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 per cent 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 000g 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 per cent. 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.