Protein Evaluation of Extrusion-cooked Sweet Lupine (Lupinus albus)

Abstract

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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