IMPACT MILLING AND AIR CLASSIFICATION OF GRAIN LEGUMES

Samples of eight grain legumes were dehulled and subsequently fractionated by pin milling and air classification into coarse (starch-rich) and fine (protein-rich) fractions. The coarse/fine yield ratios were similar for samples of a particular legume but differed considerably among legumes. All non-starch components examined were concentrated in the fine fractions. Fraction composition was dependent upon the composition of the original flour.; Significant differences among legumes in the recovery of starch in the coarse fraction (defined as starch separation efficiency or SSE) were not detected. However, significant differences in the recovery of protein in the fine fraction (defined as protein separation efficiency or PSE) were observed. It was concluded that differences among legumes in PSE resulted from differences in their milling characteristics.; Factors known or suspected to affect the milling characteristics of wheats were examined as possible determinants of the pin milling quality of legumes. Significant correlations were detected between PSE and: (1) the crude fibre content of the seed, (2) the water-insoluble cell wall content of the seed, (3) the susceptibility of the cell wall to breakdown, and (4) seed hardness.; The effects of air-classifier cut-size and seed moisture content on the yield and composition of air-classified fractions from several legumes were determined. In general, an increase in cut-size resulted in: (1) an increase in the yield of the fine fraction, (2) an increase in the starch contents and a decrease in the protein contents of the coarse and fine fractions, (3) decreased SSE, and (4) improved PSE. As seed moisture was reduced, the yield of the coarse fraction, the protein contents of the coarse and fine fractions, and SSE declined, whereas the yield of the fine fraction, the starch contents of the coarse and fine fractions, PSE, and the neutral detergent fibre content of the fine fraction showed increases.