Applicability of leaf protein concentrates from various sources in food: Solubility at food-relevant pH values and air-water interfacial properties

Leaf protein concentrates (LPCs) from green leafy biomass have potential as a sustainable protein source. Here, protein composition, solubility, foamability, and interfacial properties of LPCs from six different biomass types (beetroot, kale, lucerne, mangold, spinach, and sugarbeet) were evaluated. Although the LPCs showed some differences in protein composition and solubility, the foamability and interfacial properties were strikingly similar. RuBisCO was the major protein in all LPCs. All LPCs demonstrated lower solubility at pH 5.0 and 3.0 than at pH 7.0. Both the highest and the lowest solubility was found for sugarbeet: 67.6 & PLUSMN; 7.9% at pH 7.0 and 9.2 & PLUSMN; 4.0% at pH 5.0. The LPCs formed aggregates of increasing size at pH 3-4.5, matching the solubility results. The LPCs stabilized foams in a preliminary foaming test, although the main focus was on evaluating air-water interfacial properties. The ability of the proteins to diffuse to and adsorb at the interface and their ability to form viscoelastic films thereat, using an optical tensiometry method, was investigated. All six LPCs showed an interfacial behavior resembling that of reference egg white protein (0.1-1.0 mg/ml). Our findings indicate good opportunities for using LPCs in food applications and in particular as an alternative to egg white in foams.