| With the development of science and technology and the promotion of the concept of healthy diet,human's demand for protein nutrients is gradually changing from animal sources to plant sources.As one of the most important oil crops in the world,rapeseed has a wide range of planting and rich protein content,so it is considered as an alternative source of plant protein with broad industrial prospects.Rapeseed napin is a high-quality protein extracted from rapeseed cake after pressing rapeseed oil and has excellent solubility and emulsification properties.However,due to its low digestibility in human body,it has not been widely used in the food field.Therefore,explore the factors affecting the digestibility of rapeseed napin and finding ways to improve its digestibility are of great significance for the application of rapeseed protein in the food field.The main research contents and results are as follows:Firstly,the rapeseed napin was prepared by the method of polysaccharide compounding.When the mixing ratio of water-soluble rapeseed protein and iota carrageenan is 10:1(v/v)and the p H of the mixed system is 2.8,the compounding effect of macromolecular protein and polysaccharide in rapeseed was the most obvious.The gel electrophoresis shows that the molecular weight of proteins in the supernatant at this time was concentrated in 10-17 k Da.Compared with the protein before the polysaccharide complex,the endogenous fluorescence intensity of the protein in the supernatant of the mixed solution after centrifugation decreased significantly.Amino acid analysis showed that the nutritional composition of napin was reasonable.The trypsin inhibition rate results showed that the trypsin inhibition rate of cruciferin in rapeseed protein was the lowest(34.5%),and the trypsin inhibition rate of rapeseed napin was the highest(43.94%),which was 1.27 times that of the lowest trypsin inhibition rate.Secondly,the factors affecting the digestibility of rapeseed napin were explored.The rapeseed napin was separated and purified by the AKTA protein purifier to obtain three components.Among them,the P2 component is rich in trypsin inhibitors,which is one of the factors affecting the digestibility of rapeseed napin,and its molecular weight was about 9.7 k Da.After removing this component,the nitrogen release rate of rapeseed napin increased from 29.82% to 50.47%,and the digestibility was significantly improved(p<0.05).With the gradual increase of the ultrasonic intensity setting gradient from 0-80%,the trypsin inhibition rate of the P2 component also decreased from 46.6% to 43.59%,indicating that ultrasound can improve the digestibility of rapeseed napin.Finally,the protein digestibility of rapeseed napin was improved by the combination of ultrasound and protein mixing.When the ultrasonic intensity was 40%,the rapeseed napin could obtain 58.3% nitrogen release rate,and the nitrogen release rate(63.27%)of rapeseed napin mixed with lactalbumin in equal proportion was higher than the calculated average of the original nitrogen release rate(59.48%),indicating that the nitrogen release rate of rapeseed napin mixed with lactalbumin was significantly improved.After ultrasonic treatment,the endogenous fluorescence intensity and surface hydrophobicity of rapeseed napin decreased significantly,the free sulfhydryl content increased from 24.8 ?mol/g to 34.9 ?mol/g,and the disulfide bond content decreased from 34.56 ?mol/g to 24 ?mol/g,and the phenomenon was more obvious after ultrasound-assisted protein mixing treatment;The secondary structure of protein was significantly changed,in which the content of ?-folding decreased by 7.86% and the content of random coil increased by 18.45%.After ultrasound-assisted mixing treatment,the content percentage of t-g-t mode in the disulfide bond of protein mixture increased by 14.77,while the content percentage of g-g-g mode decreased by 0.85.The results showed that ultrasound-assisted mixing treatment could effectively improve the digestibility of rapeseed napin. |
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