Air classification of flours of three legume species: Fractionation of protein

The effect of changing the cut point of a laboratory air classifier on the protein fractionation into the fines was studied on the flour of two varieties each of cowpea (Vigna unguiculata), faba bean (Vicia faba) and pigeonpea (Cajanus cajan). Of the three species, the highest fines protein content (56.5–62.7% Nx6.25 over the range of cut points studied) and protein recovery (44.2–86.5% over the range) was for one variety of faba bean. The other variety of faba bean showed lower values. Fines from cowpea and pigeonpea flour contained protein contents in the range 26.5–46.8%, depending on cut point, with protein recoveries of 28.3–63.5%. Plots of dry weight yield vs. protein content of fines indicate that once the relationship between these two parameters has been established for a given species (or, in the case of faba bean, for variety), then the protein content of fines can be predicted from dry weight yield.