Extraction of leaf protein from green crops. Chemical composition and nutritive value of products of fractionation 

Authors

• Matti Näsi Department of Animal Husbandry, University of Helsinki, SF-00710 Helsinki 71

DOI: https://doi.org/10.23986/afsci.72126

Abstract

Leaf protein was extracted from different green crops in 11 pilot plant esperiments. Of the crops, 4 were grass, 6 clover and one pea. The extraction of juice was on average 55 % of the fresh weight of the green crop and the values for dry matter (DM) and crude protein (CP) were 22.6 and 24.1 %. Clover gave better recoveries of protein than grass. In the leaf protein concentrate (LPC) obtained from the juice, the separation ratios for DM, CP and TP (true protein) were, respectively, 23.7 %, 48.0 and 80.7 %. Heating to 85°C gave more efficient recoveries of LPC than the combination of heating and acid precipitation. The average DM content of the pressed pulp was 30.4 %, the corresponding value for the whole crop being 16.5 %. Measured on a DM basis, the CP content of the pressed pulp was only 0.4 % units lower than in untreated forage, but the crude fibre content was 7.3 % units higher. In vitro organic matter digestibility and the pepsin-HCI solubility of crude protein were on average 5.1 and 5.5 % units lower in the pulp. The average DM of the plant juice was 6.5 % and contained 21.9 % ash, 21.5 % CP, 10.7 % TP and 29.9 % soluble sugars. Clover and pea had much higher values for CP and TP than grass. In the LPC preparations, CP and TP averaged 43.6 % and 38.5 % of DM. Heat treatment gave higher protein content than precipitation of LPC by combined heating and acidification. The in vitro digestibility and protein solubility of LPC were high, on average 85.6 % and 80.2 %. LPC had fairly high contents of lysine and methionine, 4.1 % and 1.6 g/16 g N. There were only small differences in the amino acid composition between grass and clover and between crops harvested at different growth stages. Green crop fractionation is a potential means of improving grassland production and utilization. Promising results have been obtained with plant juice and LPC fed to monogastric animals and pressed pulp residues in diets for ruminants. The economic aspects of fractionation remain to be evaluated.