The lupins are an interesting group of legume crop species that produce large seeds containing up to 40% protein. The genus Lupinus is part of the tribe Genisteae. More than 170 species have been described from the New World and only 12 species from Europe, North and East Africa. Wild lupins are bitter and toxic because they produce quinolizidine alkaloids as a means of chemical defence. During domestication, lupins with low alkaloid contents were selected, leading to 'sweet' lupins with alkaloid contents below 0.02% in the protein-rich seeds, which can be used both for human and animal consumption. The domesticated lupins include Lupinus angustifolius, Lupinus albus, Lupinus luteus and Lupinus mutabilis. Blue or narrow-leafed lupin (L. angustifolius) is the most widely cultivated of them, with a worldwide production of more than 1.3 million t. Several challenges remain for lupin breeding, including the improvement of quantitative and qualitative traits, adaptation to alkaline soil and resistance to fungal pathogens.

The role of seed proteins, especially soyabean 7S globulins, in controlling dyslipidaemia is widely acknowledged. Amino acid sequence homology among the proteins of this family could reflect similar biological functions in other species. The aim of the present study was to unveil a hypolipidaemic effect of the 7S globulins from cowpeas (7S-C) and adzuki beans (7S-A), administered orally to rats fed a hypercholesterolaemic (HC; high cholesterol and TAG) diet for 28 d. A total of forty-five rats were divided into five groups (nine rats per group): (1) standard (STD) diet; (2) HC diet; (3) HC diet + 7S-C (300 mg/kg per d); (4) HC diet + 7S-A (300 mg/kg per d); and (5) HC diet + simvastatin (SVT; 50 mg/kg per d), as a control. Significant decreases in food intake and final body weight of rats receiving HC + 7S-C and HC + 7S-A diets compared with groups fed the HC and STD diets were observed. Significant decreases in serum total and non-HDL-cholesterol of 7S-C, 7S-A and SVT groups were also observed. HDL-cholesterol levels increased in the 7S-C, 7S-A and SVT groups, while hepatic cholesterol and TAG concentrations were significantly lower than in the HC diet group for the 7S-C-supplemented group only. Faecal excretions of fat and cholesterol in HC diet groups were considerably higher in animals consuming the 7S globulins. The results show that cowpea and adzuki bean 7S globulins promote cholesterol-decreasing effects in hypercholesterolaemic rats even at low dosages, as already observed for other legume seed storage proteins of this family. This main effect is discussed in relation to the possible mechanisms of action.

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Lupin seed gamma-conglutin, orally administered to animal models, has been shown to display glucose-controlling properties. Therefore, we have addressed the study of gamma-conglutin susceptibility to proteolytic enzymes in vitro as the basis to unveil its metabolic fate in the body. Pepsin treatment at pH 2.0 and 3.0 caused extensive proteolytic breakdown, while at pH 4.0, where pepsin is minimally active, gamma-conglutin was unaffected. Aliquots of the pepsin-treated protein were further incubated with pancreatin at neutral pH. If the protein backbone was already cleaved by pepsin action, then the breakdown by pancreatin was almost complete; alternatively, pancreatin did not affect at all gamma-conglutin polypeptide chain. This was not due to an inhibitory activity of gamma-conglutin, because co-incubation with casein showed complete breakdown of the milk protein. Furthermore, gamma-conglutin was incubated with bromelain, a proteinase effective between pH 4.0 and 7.0. A sharp transition from the uncleavable to the fully cleavable form of gamma-conglutin was observed below pH 4.25. Therefore, it was concluded that (i) gamma-conglutin is resistant to proteolysis at pH greater than 4.0, likely because of a compact native conformation, (ii) an acidic pH renders the protein susceptible to proteases, suggesting the occurrence of a trans conformation, which has also been observed by circular dichroism spectral analysis, and (iii) the protein undergoes an "all or none" degradation pathway, regardless of the enzyme used.

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