TAILORING MIXED INTERFACE USING LIGNIN:WPI TO STABILIZE OIL-IN-WATER EMULSIONS

The use of agroindustrial waste and previously unused raw materials has been widely debated. Currently, lignin, found in plant materials, is primarily used in paper production, as a fuel source, or discarded, although studies have demonstrated its potential as an emulsifying and antimicrobial agent. Nevertheless, its application is constrained due to cytotoxicity, posing a challenge for use in food products. In this context, this study aimed to evaluate the production of oil-in-water emulsions (10:90) stabilized by a mixed interface of lignin and whey protein (WPI). Different lignin to protein mass ratios were analyzed in two treatments, T1 with 0.3% lignin+0.2% WPI and T2 with 0.2% lignin+0.3% WPI, maintaining the total emulsifier concentration at 0.5% w/w. Emulsions were produced using a rotor-stator mixer at 14,000 rpm for 5 minutes, followed by high-pressure homogenization in two stages at 30/5 MPa. Emulsifier mixtures were analyzed regarding zeta potential and interfacial tension, while emulsions were assessed for droplet size distribution and optical microscopy. WPI exhibited an isoelectric point between pH 4-5, whereas lignin maintained a negative zeta potential across the examined pH range (2-9). Emulsions produced with lignin alone showed similar stability to those produced with WPI alone. Consequently, lignin+WPI mixtures were prepared to assess the performance of the mixed interface. The initial interfacial tension of lignin and WPI was 23.31 mN/m and 17.40 mN/m, respectively, while for the mixtures, they were T1=20.65 mN/m and T2=19.19 mN/m. It was observed that interfaces with higher lignin content facilitated quicker emulsion dispersion, while mixed interfaces with higher WPI content provided emulsion stability similar to that obtained with WPI alone. These results suggest that lignin can be a viable emulsifying agent, although the mixed interface with WPI may hinder emulsion stability. However, competition for the interface is minimized when the concentration of WPI exceeds that of lignin.