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Protein extraction from pasture: Effect of crop species and of a reducing agent on the quality of extracted protein
Author(s) -
Donnelly Paul E.,
McDonald Rod M.,
Rattray Peter V.
Publication year - 1983
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.2740340810
Subject(s) - lolium perenne , methionine , agronomy , pasture , lysine , lotus corniculatus , biology , trifolium repens , chemistry , poaceae , biochemistry , amino acid
Leaf protein concentrations (LPC) were prepared from herbage harvested from pure stands of ryegrass ( Lolium perenne ), white clover ( Trifolium repeens ), lucerne ( Medicago sativa cv. Wairau) and from a stand of ryegrass/white clover dominant pasture: each crop was processed with and without the addition of sodium metabisulphite just prior to pulping. Protein quality was measured by rat growth and in‐vivo rat true digestibility. Juice protein composition was measured and was related to chemically available lysine and protein true digestibility. Protein in ryegrass LPC had a lower digestibility (72%) than that from white clover (81%) or lucerne (78%), due to a higher proportion of the juice true protein being from the chloroplastic fraction for ryegrass (73%) compared with the two legumes (49–56%). The chloroplastic fraction is of inherently lower digestibility than the cytoplasmic fraction. Metabisulphite treatment at pulping caused a small but consistent increase of chemically available lysine in the LPC, and also improved chemically available methionine and protein utilisation for growth. Effects on protein true digestibility were inconsistent. When LPC was fed with a methionine supplement, the efficiency of utilisation of protein for growth did not differ amongst the four crops. This occurred despite the true digestibility of protein on LPC being higher for the legumes than for ryegrass and ryegrass/white clover.