Microrheology Of Protein Aggregates At Oil-water Interface

Proteins are easily self-assembled into different aggregates during processing.Protein aggregates exhibit excellent interfacial activity due to size effects and surface structure characteristics.Understanding the interfacial behavior of protein aggregates,including adsorption kinetics,interfacial rheology,and interaction with small molecules at the the oil-water interface,is of great significance for its application in food industry.In this study,?-lactoglobulin(?-lg)aggregates were prepared,and their surface properties were characterized.The adsorption kinetics of ?-lg and its aggregates at oil-water interface,the interfacial rheology of protein films and the displacement behavior of proteins by bile salts were studied using particle tracking microrheology.In vitro digestion model was used to analyze the fat-digestion kinetics of emulsions stabilized by ?-lg and its aggregates.The conclusions are as follows:1.Different protein aggregates were prepared by controlling the pH,heating temperature and time,and their surface properties were different.?-lactoglobulin fibrils(?-lg F)were prepared by heating at 80°C for 16 h at p H 2;?-lactoglobulin nanoparticle(?-lg NP)were prepared by heating at 85°C for 15 min at p H 5.8.At p H 7,?-lg and its aggregates were negatively charged,and the relationship of their charge quantity is: ?-lg NP > ?-lg F > ?-lg;Protein aggregates have higher surface hydrophobicity than native ?-lg,and the relationship of their hydrophobicity is: ?-lg F > ?-lg NP > ?-lg;The relationship of free thiol content is: ?-lg>?-lg F>?-lg NP.2.The adsorption process of ?-lg and it's aggregates at the oil-water interface was studied by particle tracking microrheology.The adsorption rate of ?-lg and its aggregates become faster,and the viscoelasticity of protein films become stronger as protein concentration increased.The adsorption of protein aggregates is faster than ?-lg due to their higher surface hydrophobicity and that ?-lg undergoes unfolding process.According to the motion of individual tracer particles,it was found that the protein films show non-uniformity during the adsorption process,and the non-uniformity of the films formed by protein aggregates is stronger.The films formed by protein aggregates have higher elastic moduli than that of native ?-lg.3.The displacement behavior of proteins by bile salts at the oil-water interface was studied by particle tracking microrheology.With increased protein concentration,the substitution of proteins by bile salts was diminished.For different morphological proteins,the displacement rate of ?-lg by bile salts was the fastest,and that of ?-lg NP was the slowest.The substitution of proteins by bile salts was a non-uniform process,and especially the local substitution of protein aggregates was more intense.4.From emulsion stability and in vitro simulating fat digestion studies,it was found that emulsions formed by ?-lg aggregates are more stable and the ?-lg F emulsions have the highest stability.The relationship of fatty acid release rates are: ?-lg NP <?-lg F < ?-lg.These indicate that the protein aggregates have better emulsification properties and they can control the rate of fat digestion.The results are consistent with those revealed by microrheology investigation.