Wet fractionation approaches for the preparation of functional isolated green lentil seed proteins
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Lentil seed proteins isolated using isoelectric precipitation and ultrafiltration, as well as various lentil protein fractions, were investigated for their potential to produce high quality and functional protein products from green lentil seeds. Effect of the defatting and separation processes was apparent, with a protein content of 29% for the defatted lentil flour, and 13% - 94% for the isolated lentil proteins and fractions. GLB which was the predominant protein fraction in the lentil seeds also demonstrated superior solubility (84% - 100%) at acidic and alkaline pH values. However, the membrane isolates from NaCl extraction and GLT were equally most soluble (89%) at the neutral pH. Lentil seed proteins were rich in glutamic acid but generally limiting in valine and methionine. PRL had a particularly high cysteine content which was at least 8-fold the level in other isolated lentil proteins and fractions. Isoelectric pH-precipitated isolate (ISO) and ALB were the most digestible (89%) proteins, and all proteins in this study had 1% or less crude fibre and fat content. GLT had a higher oil holding capacity at a 60 mg/mL concentration, while that of ISO was higher at lower concentrations (20 mg/mL). Similarly, GLT had better water holding capacity at pH 3, 5, and 7, while all protein samples demonstrated poor values at pH 9. Oil-in-water emulsion stability displayed a high variation among the different parameters, with the least stable emulsions formed at pH 7. All the samples produced relatively stable foams (above 50%) at all concentrations and pH used; however, ISO recorded the highest foaming capacity (71.15%) at pH 5. In comparison, ISO and ALB also recorded the highest foam stability (100%) at pH 3 and pH 5. Physicochemical properties such as circular dichroism and intrinsic fluorescence spectra demonstrated the significant impact of change in pH and extraction condition on the structure of each isolated and fractionated protein, which accounts for the observed variations in their functional properties. However, in properties such as denaturation temperature and least gelling concentration, the results were similar with little to no variation observed irrespective of extraction method.
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