Production of Fibre-rich, Starch-rich and Protein-rich Fractions from the By-product of Red Lentil Splitting

Abstract

Canada, particularly Saskatchewan, has increased the export of dehulled red lentil resulting in more by-product generation. However, the by-product generated is currently underutilized. This study looked to maximize the usage of lentil by-product using wet and dry fractionation to produce protein, starch, and fibre concentrates. Two batches of lentil by-product (S0) were investigated by fractionating with a laboratory aspirator into cotyledon-rich fractions (F1) and seed-coat-rich fractions (F4). To produce the starch and protein concentrates using dry and wet fractionation, both the F1 fraction and S0 were hammer and pin milled. Air classification and alkaline-isoelectric separation (using a hydrocyclone) were used to separate the milled samples into protein-rich and starch-rich fractions. Fibre concentrate production was achieved by the refining of the F4 fraction using water soaking, washing, alkaline protein solubilization, and sieving. All the concentrates produced in this investigation were analyzed for proximate composition and physical properties. The throughput, power and energy consumed in the milling of the fibre concentrate were investigated. The effect of pH and feed slurry concentration (w/w) on the starch and protein content of the hydrocyclone fractions were analyzed using central composite design (CCD) response surface methodology. There were differences in the proximate compositions of the two S0 samples and these differences influenced the yield and makeup of the samples. Protein concentrates of up to 49% (db) protein were produced from lentil by-product using air classification. Prior separation of the by-product with a fractionating aspirator significantly increased the protein content of the fine fractions and the starch content of the heavy fractions at P<0.05. Wet fractionation resulted in a protein fraction containing 79% (db) protein and a starch content of 79% (db) in the underflow fraction. The CCD analysis showed that the effects of pH and concentration on the protein and starch contents of the overflow and underflow fractions from the wet fractionation process were not significant at P<0.05. However, pre-separation with the grain aspirator significantly increased the protein and starch contents of these fractions. The fibre refining process was able to increase the total dietary fibre content of the fibre concentrates to 62 and 63 %(db). It also decreased the lightness component (L*) whereas the colour components (a* and b*) were not affected significantly. Fibre refining process increased the throughput, power and specific energy consumed during milling.