Composition and nutritive value of native and modified green fraction of leaf protein from lucerne (Medicago sativa)

Abstract

AbstractThe green fraction of leaf protein from lucerne (Medicago sativa L) was prepared by heating freshly extracted juice to 55°C. From the same part of the juice unfractionated leaf protein concentrate (LPC) was obtained by heating it to 80°C. The green fraction was divided into four parts and treated as follows: dried at 55°C (I), washed with water (II), washed with buffer (III) and extracted with ether (IV).The LPCs obtained were analysed for gross composition and amino acid content as well as for phenolics and carotene. The true digestibility (TD) and biological value (BV) of LPC proteins were determined on growing rats using the Thomas‐Mitchell balance method. In addition the effects of DL‐methionine or L‐lysine supplementation of native green LPC were studied.The native green protein fraction contained more fat, phenolics and carotene but less protein than unfractionated LPC. The ether extraction lowered fat and carotene content of concentrate, and washing with buffer eliminated most phenolics.There were only small differences in the amino acid composition of proteins. The buffer‐washed concentrate contained more amino acids than any other treatment.Both the true digestibility and biological value of unfractionated LPC were higher than those of each green concentrate. Ether extraction mainly improved TD (from 73 to 79) and washing with buffer improved BV (from 41 to 50) of green protein. The best result was obtained when the green fraction was supplemented with methionine (BV increased from 41 to 68).