Amino acid composition and In Vitro digestibility of some protein fractions from three species of leaves of various ages

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Abstract
Extracts from leaves of barley (Hordeum vulgare), lupin (Lupinus albus) and Chinese cabbage (Brassica chinensis) of different ages were fractionated. As the leaves age, chloroplasts are increasingly disrupted during extraction and the chlorophyll‐containing protein becomes increasingly difficult to sediment. The amount of protein unassociated with chlorophyll varies with species, but not with leaf age.Analyses are given of selected chloroplastic fractions (sedimented and coagulated) and of the protein precipitated from the whole extracts and the various supernatant fluids. Amino acid composition of unfractionated protein is independent of species, except perhaps for methionine; leaf age has no affect on composition. The method of protein precipitation may influence the amount of lysine determined. Contrary to previous reports, chloroplastic and cytoplasmic protein do not have the same composition.Nutritional properties of the preparations are discussed in relation to their amino acid composition and to their known in vivo and in vitro behaviour. Comparison with the F.A.O. reference protein shows that sufficient lysine, both total and nutritionally ‘available’, is present in unfractionated and cytoplasmic protein, though it may be marginal in some chloroplastic fractions. The first limiting essential amino acid in all leaf protein preparations is methionine, and there is an adequate amount ‘available’ in cytoplasmic but not in unfractionated or chloroplastic protein. Reasons are suggested for the unavailability of methionine, and possibly cyst(e)ine, in the latter preparations.