The nutritive value of leaf protein concentrates determined in biological tests with rats and by microbiological methods

Abstract

The biological values and true digestibilities of a number of leaf protein concentrates have been determined by the balance-sheet method a t an 8% level of protein intake on young growing rats. Determinations were made on preparations from the leaves of 14 different species of plants. The effects of several methods of drying the concentrates and of the maturity of the leaves at harvesting were studied. The availability of some essential amino-acids was determined microbiologically in selected samples; in all of them methionine was less available than in whole egg proteins. The microbiological results were consistent with the biological findings. In general biological values of the proteins in the leaf concentrates were of the order found for good quality plant proteins such as those of legume and cereal seeds and of yeast but true digestibilities were lower. Freeze-drying, drying by acetone extraction and drying on starch in a current of air proved satisfactory but oven-drying at 100' caused a significant decrease in biological value and a more marked loss of true digestibility. Biological values and true digestibility increased with the maturity of the leaves a t harvesting because of increased availability of methionine. A possible explanation of the results is suggested. IntroductionThe value of leaf protein concentrates as supplements to cereal diets has been established in feeding experiments with chicks,lP rats2 and pigs.39 Their value for man in countries where protein malnutrition is prevalent has also been demonstrated.Cowlishaw et a1.l have pointed out that, although the technique used in such animal experiments has practical applications, it is not suitable for a critical examination of the digestibility or for the detection of amino-acid deficiencies in leaf proteins. They recommend that the biological value (BV) and true digestibility (TD) of such proteins should be determined and compared with amino-acid analyses of the samples.In the experiments now reported, the BV and TD of protein concentrates prepared from leaves of several species of plants have been determined; a study is also made of the effect on these measurements of several methods of drying the concentrates and of the maturity of the leaves at harvesting. With increasing maturity, a smaller proportion of the total protein of the leaf is extractable. This change generally affects more the ' chloroplastic ' than the ' cytoplasmic ' fraction, so that the protein extracted from mature leaves tends to contain a larger

Protein extraction from biomass in a bioethanol refinery – Possible dietary applications: Use as animal feed and potential extension to human consumption

“…A second approach consists in directly supplementing the incomplete plant protein with the necessary amino acid. Supplementation of LPC using methionine has been successfully performed to improve the actual dietary quality of the protein, for instance in the case of alfalfa protein concentrate (Hanczakowski et al, 1991), while similar lysine or isoleucine (Henry and Ford, 1965) supplementations have not lead to special improvement. Nonetheless, with respect to the second case, it has been pointed out that in vivo experiments on rats may differ from the situation found in the human body due to the higher methionine demand of these animals (Byers, 1971).…”

White clover fractions as protein source for monogastrics: dry matter digestibility and protein digestibility‐corrected amino acid scores

“…The nutritional qualites of the plant juice and the protein‐rich concentrate for monogastrics have been evaluated in earlier studies focusing mainly on chickens, pigs or rats; however, the results obtained are not consistent. Some studies have demonstrated an improved growth of rats, as well as improved performance, weight gain and meat quality of pigs, when they are fed with plant juice or plant protein concentrate, whereas other studies have reported the opposite . An improper processing of plant material has been suggested to be one cause of the inconsistency in protein quality, but improvements in methods for green plant processing and protein extraction, combined with the increasing need for animal protein fuel new attempts to produce high‐quality protein alternatives to soy protein for animal feed.…”

Preparation and properties of a white protein fraction in high yield from sugar beet (Beta vulgaris L) leaves

“…In Spain, which has 260000 ha under sugar beet cultivation, it is estimated that some 2 Mt of waste foliage (crude protein content 30g kg-' fresh weight) could yield 60 kt protein. Large proportions of sugar beet leaf protein have been isolated as a green concentrate (Carlsson 1983;Shah 1983) of acceptable nutritive value (Henry and Ford 1965;Subba Rau et a1 1972) but protein concentrates obtained after separation of the chlorophyllcontaining protein may be more acceptable for human consumption (Heath 1977;Pirie 1980). However, separation of the chlorophyll-containing fraction usually results in only a small yield of white protein in the second stage precipitation.…”