Protein/polysaccharide complexes to stabilize decane-in-water nanoemulsions
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Protein/polysaccharide complexes can be formed by electrostatic interactions and may be useful for enhancing the stability of nanoemulsions containing short-chain alkanes, which are highly prone to destabilization by Ostwald ripening. The study aimed to assess the capacity of biopolymer complexes composed of whey protein isolate (WPI) and sugar beet pectin (SBP) to form and stabilize interfacially structured nanoemulsions. Nanoemulsions were stored for 21 days at room temperature to assess their stability against Ostwald ripening over time. Complexes showed higher emulsifying capacity than biopolymers alone since particle size of complex-stabilized nanoemulsions remained stable (d(4;3)similar to 0.26 mu m) for at least 48 h after preparation, whereas WPI- or SBP-stabilized nanoemulsions were prone to destabilization during the first 24 h reaching values around 1 mu m. Moreover, while the final particle size observed for the latter during the 21 days of storage was around 8 mu m, complex-stabilized nanoemulsions exhibited particle sizes up to 2.34 mu m, which had a direct impact in delaying creaming. Moreover, complex-stabilized nanoemulsions exhibited negative zeta-potential with similar values to those stabilized by SBP (-20.4 and - 22.1 mV, respectively) while the interfacial rheology behavior of complex-stabilized systems was more similar to those stabilized by WPI. This evidences that the protein fraction may be adsorbed at the oil interface thus dominating the interface rheology, whereas pectin chains located on the periphery of the complex and oriented towards the water phase may confer negative interfacial charge to oil droplets. These results indicated that WPI/SBP complexes were more effective than the biopolymers alone in preventing Ostwald ripening in decane-in-water nanoemulsions.