| Protein emulsion is a natural system often used to deliver bioactive substances.Rice bran protein is a kind of high-quality protein with low allergenicity and high bioefficiency,which was derived from the rice bran.Rice bran was prone to rancidity,rice bran rancidity could lead to rice bran protein oxidation,and then affect the structure and properties of rice bran protein.With the increase of oxidation extent,the emulsification property and the emulsion stability of rice bran protein first increased,and then decreased.Theoretically,the emulsifying property of rice bran protein with different oxidation extents was different,and the energy required to form emulsion was different.Ultrasonic treatment is a novel method of emulsion preparation with high energy efficiency,which could affect the emulsion significantly.But high ultrasonic intensity provided additional energy and excess free radicals,which caused negative effect on the emulsion.Therefore,the ultrasonic condition of RBPE prepared by the rice bran protein with different oxidation induced by rice bran needed to investigate.However,there was no study on the effects of ultrasonic treatment on the emulsifying characteristics of oxidized rice bran protein induced by rice bran rancidity.The effects of ultrasonic treatment on the stability of RBPE prepared by rice bran protein with different oxidization extents induced by rice bran rancidity were studied by determining the flexibility and structural properties of the interfacial protein in this study.The emulsions prepared by optimal ultrasonic intensity were used to load BC,and the application of rice bran protein with different oxidation extents in the carrier for bioactive substance was preliminarily explored.The fresh rice bran was stored at 25℃ and 85%relative humidity for 0,1,3,5,and 10 d to obtain rice bran with different extents of rancidity.The rice bran protein with different oxidation extents was extracted from rice bran after defatting with n-hexane.The RBPE was prepared by ultrasonic treatment,and the ultrasonic power was set as 300 W,400 W,and 500 W.The ultrasonic time was set as 20 min,30 min,40 min,and 50 min.The mean particle size,size distribution,zeta potential,microstructure,and CI of RBPE were measured to evaluate the effect of ultrasonic treatment on the stability of RBPE with different oxidation extents induced by rice bran rancidity,and to select the optimal ultrasonic conditions.The results showed that with the prolongation of rice bran storage time,the extent of rice bran rancidity and the rice bran protein oxidation gradually increased;the stability of RBPE first increased,and then decreased,and reached the most stable state at the storage time of rice bran was 5 d.The optimal ultrasonic intensity required for the preparation of RBPE first decreased,and then increased with the prolongation of rice bran storage time,and reached the minimum value of 300 W and 20 min at the storage time of rice bran was 5 d.The results showed that the effect of ultrasonic treatment on moderate oxidation of rice bran protein(extracted from rice bran storage time was 5 d)was excellent and the corresponding intensity was the lowest energy consumption.RBPEs were prepared from rice bran proteins with different oxidation extents induced by rice bran rancidity,and then the interfacial proteins of the emulsions were extracted.The flexibility,secondary strucure,and spatial structure of the IAP and INP of RBPE were measured to investigate the effect of ultrasonic treatment on the flexibility and structural properties of the interfacial protein,and the correlation between the emulsion stability and the flexibility and structural characteristics of interfacial protein was analyzed.The results showed that the flexibility and structural properties of interface proteins of RBPE in the optimal group were better than that in the worst group.With the prolongation of rice bran storage time,the content of free sulfhydryl groups and disulfide bonds of IAP first increased and then decreased,and the content of disulfide bonds first decreased,and then increased;the content of free sulfhydryl groups and disulfide bonds of INP gradually decreased,and the content of disulfide bond gradually increased.The surface hydrophobicity,the absolute value of zeta potential,and the trypsin hydrolyzability of interfacial proteins first increased and then decreased;the particle size first decreased and then increased;the maximum fluorescence peak position first red-shifted and then blue-shifted.And the flexibility and structure of interfacial proteins were significantly correlated with emulsion stability(P<0.05).The results showed that moderate ultrasonic intensity could significantly alter the interfacial protein flexibility and structural properties of RBPE,which affected the emulsion stability.In addition,the negative effects of excessive oxidation of proteins induced by rice bran rancidity on the interfacial proteins of rice bran protein emulsions could not be effectively improved by the optimal ultrasonic intensity.The BC was encapsulated in RBPE with different oxidation extents,which were prepared by the optimal ultrasonic intensity.The effects of ultrasonic treatment on the encapsulation of BC by RBPE were investigated by measuring the mean particle size,size distribution,microstructure,zeta potential,SDS-PAGE,FFA release rate,BC retention rate,BC bioaccessibility,intracellular antioxidant,and Caco-2 cellular transport.The results showed that RBPE could protect BC in the simulated gastric digestion and increase the BC retention rate.The emulsion prepared with moderately oxidized rice bran protein had the strongest protective effect on BC.After simulated intestinal digestion,the mean particle size of BC-RBPE decreased,the absolute value of zeta potential of BC-RBPE increased,and the protein was hydrolyzed to small molecular peptides.The release rate of FFA,BC bioaccessibility rate,cellular antioxidant activity,and cellular uptake rate of BC-RBPE were increased compared with that of BC-suspension,which indicated that RBPE had an excellent intestinal targeting delivery effect on BC.The emulsion prepared with moderately oxidized rice bran protein had the best intestinal targeting delivery effect of BC. |
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