Mild fractionation of lentil protein in the development of highly stable beverage emulsions

Abstract: Mild fractionation is a sustainable protein recovery process in which functional soluble protein can be recovered through simple centrifugation. In this study, a 10 wt% lentil flour dispersion (pH 6.5) was centrifuged at ~3,200 g and ~1,800 g for various durations (2-3.5 min), resulting in a maximum extraction yield of 35.0% and a maximum protein yield of 75.6%. The yield values were higher with lower centrifugal force and shorter durations. All soluble fractions displayed similar protein composition and surface activity. The recovered soluble fractions were adjusted to pH 3 and pH 7, then directly used to prepare 1wt% O/W beverage emulsions with 0.5wt% lentil proteins using a high-pressure homogenizer. The stability of these emulsions was evaluated under varying NaCl concentrations (0-1 M) and heat treatment (90°C for 30 min) to better understand their capacity to withstand beverage ionic strength and food processing conditions. All emulsions showed comparable D[4,3] values, ranging from 0.52 to 0.62 μm. The stability study indicated that pH significantly influenced emulsion droplet size due to variations in protein charge, with lesser impact from protein fractionation conditions. At pH 3, all emulsions remained stable at low salt concentrations (0 and 0.1 M) regardless of heating. However, higher salt concentrations resulted in notable instability. At pH 7, emulsions made with lower centrifugal force fractions were stable across all salt concentrations, irrespective of heating. Conversely, pH 7 emulsions prepared with higher centrifugal force fractions exhibited instability at high salt concentrations after heat treatment. This behaviour can be elucidated through the interfacial adsorption behaviour, the strength of the interfacial layer, and the surface hydrophobicity of the recovered soluble protein fractions. Mildly fractionated soluble lentil proteins demonstrated potential as a sustainable emulsifier suitable for diverse food and beverage applications requiring long-term stability, with optimal performance at both neutral and acidic pH values.