Nutritive value for rats of unextracted and defatted green fractions of leaf protein concentrate from red clover

Abstract

Green fraction of leaf protein concentrates (LPCs) from red clover was obtained from fresh juice by coagulation with heat (52°C), flocculant Prestol 411, n-butanol or by freezing (−21°C, 14 days). Unfractionated LPC was produced by heating juice to 80°C. Each coagulate was later used unextracted or following extraction with petroleum ether (Soxhlet apparatus, 15 h). Preparations were dried under infrared lamps at 55°C. The gross composition of all preparations and amino acid content of proteins and carotenoid content of unextracted concentrates were analysed. Nutritive value of protein in all preparations was estimated on rats using the Thomas-Mitchell balance method. Six male rats each weighing about 90 g were used in each experimental group. The gross composition of all preparations was similar but green fractions contained more carotenoids than unfractionated LPC (1035–1634 and 648 mg kg −1, respectively). There were no clear differences in amino acid composition of proteins. All proteins were relatively low in sulphur containing amino acids. Ether extraction significantly improved the digestibility of protein in all preparations (from 53 to 67 and from 70 to 79) but the biological value of the frozen and butanol-coagulated green fractions was lowered. Unfractionated LPC was the only preparation whose BV was clearly improved by ether extraction (from 51 to 64; not statistically significant). It was concluded that a petroleum ether soluble fraction present in LPCs extracted from red clover had a detrimental effect on the nutritive value of the protein.