Heterogeneous Australian Pigeonpea [Cajanus cajan (L.) Millsp.] Genotypes with Homogeneous in-vitro Proteolysis

Pigeonpea is a potential raw material for the growing plant protein industry, and the food properties of six Australian genotypes (ICPLs 14425, 86022, 88039, 90048, 91039, and 98011) were investigated. In-vitro proteolysis was analysed with a pH drop. The genotypes, coloured cream to brown, differed (p ≤ 0.05) in their total (43.3–56.5), whiteness (40.2–53.4), yellowish (35.4–50.7), and browning (32.1–60.2) colour indices. Potassium, phosphorus, and sulphur were the major minerals. Approximating a sphere (mm, major [6.6] and minor [6.0] diameters, and thickness [5.3]), the genotypes differed in starch (20–32 g/100g solids) and protein (22–27 g/100g solids) contents. Although the genotypes revealed identical pasting (p > 0.05) temperatures (85 ± 2 ℃) and slightly-shear thinning behaviours (breakdown ratio = 0.8–0.9), their peak (124–371), trough (108–337), and final (213–520) viscosities (cP) differed. Essentially, the genotypes were heterogeneous in their physicochemical, colour, and pasting properties. However, their protein digestograms, analysed with the Sopade Objective Procedure (objective logarithm of slope), revealed a true monophasic digestion mode; homogeneous in-vitro proteolysis. Seven kinetic models for monophasic digestograms adequately (r2 > 0.78) described the digestograms, and the Peleg model was recommended. There were no genotypic differences (p > 0.05) in the protein hydrolysis index (HIPROTEIN = 17.4–24.7%) relative to reference casein, average in-vitro protein digestibility (IVPDAVG = 69–71%), rate of protein digestion (KPR = 0.09–0.24 min−1), and other protein digestion parameters. This study pioneers time-course protein digestion for pigeonpea, and with rates of food digestion valuable in future food labelling, a solid foundation for pigeonpea utilizations is presented.