Abstract
The use of lupin seed, although a rich source of proteins, hus been limited by the
presence of toxic alkaloids. Recently a sweet, non toxic variety (Lupinus angustifolius
L.) has been developed in Western Australia, and reported to be safe for human
consumption. However growth depression and low net protein utilisation (NPU) values
in weanling rats fed raw L. angustifolius seexls have been reported in the literature.
Thus seeds wele analysed, and experiments were carried out with ruts to evaluate NPU
values and growth. Results indicated that L.angusfifolius contains a far less reactive
lectin tllan kidney bean, but that food intake and growth were depressed, due in part
to essential amino acids (EAA) deficiencies. Supplementation with EAA improved
growth, nitrogen retention und protein utilisation. However, when compared with that
of the net protein utilisation values from rats fed on lactalbumin, the raw lupin seed
meal was still found to •be inferior, even when supplemented with EAA.
Seed meal. was fractiopated into six components by sequential extraction with cold
water, McIlvaine's buffer ai pH 7.(), and dialysis of the supernatant. Analyses were
carried out on lupin seed meal and fractions for carbohydrates, amino acids.
oligosaccharides, minerals, phytates and run on SDS/PAGE to ensure consistency in
fractions pooled for nitrogen balance experiments. It wus revealed that a protein
fraction resembling the y-conglutin, the sinnplest of the three globulins from the seeds
of L.angusfifolius, was extracted in almost pure forln. A series of experiments was
carried out to study the biological effects of all six fractions in growing rats. Results
showed that seed meal and its fractions are unique in causing deleterious effects on
liver, kidneys, spleen, thymus, heart, adrenal, stomach, caecum and colon but had no
effects on pancreas. Biochemically, there were highly significant increases in blood
and urinary urea productioli, depletion of body fat and hypocholesterolaemic effects.
Rats fed on raw unsupplenlented raw, fully supplemented lupin seed meal and its
fractions, excreted significalitly higher amounts of calcium, Inagnesium, phosphorus,
potassium, sodium und zinc compared with the lactalbumin group. As a result,
apparent absomtion and balance of these minerals was significantly lower when the
control diet was fed. It was concluded that growth inhibiting and lipid depletion
factor(s) were concentrated in water soluble, non-diüysuble (LPADI) fraction: In
contrast, the soluble but non-dialysable fraction after extraction with both water and
buffer fraction (BUDI), alni0st purified and resembling y-conglutin, accounted for
most of •the' hypocholesterolaemic activity and' depressed plasma total cholesterol to
34% of the values obtained when lactalbumin was the P16tein source. The potency .Of
this fraction as a hypocholesterolaemic agent is greater than any similar effect
produced by proteins and plant materials reported So far. The above effects may have
triggered by the high levels of arginine and cystine, and low levels of methionine
and lysine in' the seed meal and fractions, Or may due to a factor or factors hitherto
unknown.' Futute investigations should include studies Of the effects of the Supernatant,
after initial extraction with water, on the inimune •system of seed meal (effects
comparatively reduced after dialysis). The effects of the LPADI fraction on reducing
body lipids, alid of the BUDI fraction ip reducing plasma cholpsterol Inerit particular
Study of their possible relevance to the prophylaxis of atherosclerosis and
obesity. The growth inhibitor(s) contained in the LPADI fraction should be purified
and characterized.