In previous studies conducted by our group, it has been demonstrated that the beans of two species of sweet lupines (Lupinus luteus and Lupinus albus) contained about 40% protein, 11.5% of crude fiber and a low level of alkaloids (0.05% lupanine). This protein is poorly balanced due to its low methionine content. In this study, Lupinus albus beans were mechanically treated to reduce the fiber content from 11.5–2.7% and were divided into two portions. One was raw and the other was extrusion cooked in a Wenger X-25 extruder. Both were analyzed for their chemical composition, protein efficiency ratio (PER) and digestibility. The raw sample was found to contain about 40% protein (N × 6.25) and 12% ether extract. These values were practically unchanged by processing. The protein efficiency ratio significantly increased in the cooked-extruded sample from 0.50 ± 0.02 to 0.76 ± 0.05. Supplementation of two samples with 0.3% DL-methionine increased the protein quality to values similar to casein (PER 2.60 ± 0.05 compared with 2.54 ± 0.07 casein). Digestibility was not affected by extrusion cooking (76.5 ± 1.9 and 77.8 ± 0.7 for raw and extruded-cooked samples, respectively). These results indicate that sweet lupine may become a valuable protein source for human or animal feeding provided that the deficiency of sulfur-containing amino acids is corrected. Our work also highlights the advantage of extrusion cooking in the processing of this legume.
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