Chemical and functional quality of protein isolated from alkaline extraction of Australian lentil cultivars: Matilda and Digger

Abstract

Starch and protein were extracted from the flour of two Australian lentils, Lens culinaris; Matilda (Green Lentil) and Digger (Red Lentil), with water at four temperatures (ambient 22 °C, 30 °C, 35 °C and 40 °C) and under five pH conditions (distilled water and pH adjusted with NaOH to 8, 8.5, 9.0 and 9.5). Upon evaluation of all extraction conditions, pH 9.0 at 30 °C was chosen as an optimum extraction condition for Matilda while pH 8.5 at 35 °C was chosen for Digger. These extracts were studied by DSC and reversed-phase HPLC. The DSC Δ H value of extracted lentil starch from both Digger and Matilda showed an increasing trend with increases in pH and temperature. Extraction at higher pH resulted in a smoother and more symmetrical peak, denoting the absence of adhered protein on the starch surface. In the study of the functional properties of extracted protein by DSC, the Δ H value of the extracted protein decreased with increasing pH. This trend is more significantly demonstrated in Digger than in Matilda protein. Temperature had less effect than did pH on the Δ H value of protein. Chromatograms from reversed-phase HPLC showed a loss of hydrophilic proteins during extraction. Protein peaks appearing 10–32 min after injection of lentil flour samples were missing from alkaline-extracted protein. The water-holding capability of both Digger and Matilda proteins (adjusted to pH 7.0) increased slightly with increasing pH. Foaming capacity of both proteins decreased with higher extraction pH, while foam stability increased with higher extraction pH. Matilda proteins showed greater foam-forming capacity than did Digger.