| The long-term use of traditional surfactants has caused certain harm to the environment.This paper hopes to prepare a protein-based surfactant which can replace traditional surfactants with good performance,green,renewable and environmentally friendly.In this paper,the hydrolysis of soybean protein isolate by alcalase alkaline protease was studied.On this basis,the structure of soybean protein isolate was modified by glucose and dextran to improve the surface activity of soybean protein isolate.In this paper,foaming capacity,foaming stability,emulsifying capacity and emulsifying stability are used to represent the surface activity.The secondary structure of protein molecules is analyzed by circular dichroism,the distribution of hydrophobic groups in molecules is analyzed by fluorescence spectroscopy,the stability of solution is analyzed by particle size distribution and Zeta potential,and the critical micelle concentration(CMC)is determined by measuring surface tension.The innovation of this experiment is to analyze the correlation between surface hydrophobicity and surface activity.It is hoped that surface hydrophobicity can be used as a key index to predict surface activity.The results are as follows:(1)The hydrolysis conditions of alcalase alkaline protease were established.The hydrolysis efficiency of soybean protein isolate was the highest under the conditions of substrate concentration 4%,temperature 55?,pH 8.0 and enzyme addition 0.2%.After different degrees of enzymatic hydrolysis,the soluble protein content was significantly increased,the highest value was 4.23 times higher than that of natural soybean protein isolate;when the degree of hydrolysis was 6.05%,the foaming capacity and foaming stability were increased by 85.85% and 116.18%,respectively;the emulsifying capacity and emulsifying stability were increased by 105.10% and 45.74%,and the surface hydrophobicity was increased by 136.16%.The content of free amino group increased with the increase of hydrolysis degree after enzymatic treatment.From the results of surface tension and CMC value,it can be seen that when the degree of hydrolysis is less than or equal to 6.05%,the surface tension decreases with the increase of degree of hydrolysis.When the degree of hydrolysis reached 6.05%,the corresponding CMC value decreases to the lowest,is 0.25 g/L.The results of intrinsic fluorescence spectroscopy and circular dichroism showed that the protein molecules were opened,the structure changed from compact to loose,and the hydrophobic groups were exposed to the molecular surface.The results of particle size distribution and Zeta potential showed that the stability of protein solution system was enhanced.According to the experimental results,alcalase alkaline protease hydrolysis of soybean protein isolate can significantly enhance the surface activity,but the degree of enhancement is limited.(2)In this paper,based on the hydrolysis of soybean protein isolate by Alcalase alkaline protease,the sugar grafted products were prepared,and the surface activity and structure changes of the sugar grafted products were studied.The degree of grafting was calculated by measuring the content of free amino group.At the same time,the degree of browning indirectly reflected the degree of sugar grafting.The results showed that when the degree of grafting reached 44.73%,the foaming capacity and foaming stability increased by 104.92% and 165.50%,respectively,compared with natural soybean protein isolate,the emulsifying capacity and emulsifying stability increased by 115.75% and 52.14%,the surface hydrophobicity increased by 163.66%,and the surface tension and CMC value decreased significantly.The results of intrinsic fluorescence spectroscopy and circular dichroism chromatography showed that the molecular structure was looser and hydrophobic groups were exposed more fully.The results of particle size distribution and Zeta potential show that the solution system tends to be stable.The surface activity of soybean protein isolate was limited by hydrolysis.On this basis,the surface activity of soybean protein isolate was further improved by glucose grafting reaction.(3)In this study,the hydrolysates of soybean protein isolate with different degrees of hydrolysis were reacted with dextran under certain conditions to obtain glycosylated products,and their structure and surface activity were determined.The results showed that the degree of grafting was 0%,11.32%,28.34%,33.42%,68.95%,71.64% and 87.95% respectively.The trend of browning degree and grafting degree was the same,both showed an upward trend.When the degree of grafting reached 33.42%,the foaming capacity and foaming stability increased by 92.60% and 148.95% respectively compared with natural soybean protein isolate;the emulsifying and emulsifying stability increased by 125.27% and 50.70% respectively;when the degree of grafting reached 68.95%,the surface hydrophobicity reached the maximum value,which was 189.82% higher than natural soybean protein isolate,which was due to after the carbonylation,the molecular structure changes,the steric hindrance increases,and the hydrophobic groups are difficult to refold.This makes the hydrophilic/hydrophobic balance on the protein surface,thus enhancing the hydrophobicity of the protein surface and enhancing the surface activity.The results of surface tension and CMC values showed that proper degree of grafting could significantly reduce surface tension and CMC values.Zeta potential results showed that the stability of the solution system increased.The results of circular dichroism showed that the content of ?-helix decreased first and then increased,while the content of ?-turn and random curl increased first and then decreased,which indicated that proper dextran modification could significantly change the molecular structure and thus lead to changes in surface activity.The results showed that the surface activity of soybean protein isolate was significantly improved after hydrolysis and dextran modification.(4)Pearson correlation analysis showed that there was a significant positive correlation between surface hydrophobicity and foaming capacity,foaming stability,emulsifying capacity and emulsifying stability(p < 0.05).This indicates that surface hydrophobicity can be used as a key index to predict the surface activity of soybean protein isolate. |
PDF Full Text Request