| Soy protein has been widely used in the food industry due to its nutrition and good functional properties.Soy 7S globulin(β-conglycinin)and 11 S globulin(Glycinin)are the two main storage proteins in soybean,with different protein functional properties.The functional properties of soy protein isolates differ as various proportions of the two globulins in different soybean varieties,which is limited to industrial standardized production.The purpose of this study was to modify soy protein with different 7S /11 S ratios by different heat treatments,so as to explore the effect of spray drying on the emulsibility and gel property of soy protein with different 7S /11 S ratios.The main findings of this study are as follows:(1)Low-temperature defatted soybean meal was used as raw material to extract soy 7S and 11 S globulins by alkaline extraction and acid precipitation without reducing agent addition.Based on the yield and purity of soy 7S and 11 S globulins,the optimum extraction process was determined as follows: two-phase alkaline extraction with the solid-liquid ratio of 1:10 and 1:5,respectively,under pH 8.0 and 40℃;acid precipitation of 11 S globulins at pH 6.4,followed by centrifugation at 6500 rpm for 20minutes;removal of the intermediate components at pH 5.0;acid precipitation of 7S globulins at pH 4.4,followed by centrifugation at 6500 rpm for 20 minutes.After optimization,the total yield of 7S and 11 S globulins was 41.6% with a purity of 60.5%for 7S and 89.5% for 11 S.(2)Based on the proportion of 11 S globulin to total protein,five soy protein mixtures were formulated with different 7S/11 S ratios: 30%/61%(11S-30),45%/47%(11S-45),60%/35%(11S-60),75%/21%(11S-75),and 90%/7%(11S-90).The emulsibility and gel properties of the five soy protein mixtures were studied.The results showed that the solubility of five different 7S/11 S proportion proteins was above 80%,and there was no significant difference;Their initial viscosities(0min)are all below100 mPa.s.However,after the protein solution was incubated at 85 ℃ for 15 minutes,the viscosity of 11S-30 increased to 910 mPa.s,which was 35 times higher than its initial viscosity;but there was no significant change in viscosity of 11S-90.The emulsibility and emulsifying stability of the protein mixtures gradually decreased with the increase of the proportion of 11 S in the protein,with 11S-90 showing a 38%decrease in emulsibility and 55.8% decrease in emulsifying stability compared to 11S-30.Gel strength increased with the increase of 11 S globulin proportion in the protein mixtures,and the gel strength of 11S-90 gel was 4.7 times higher than that of 11S-30.In conclusion,undenatured 11 S globulin contributes more to the gel property than 7S globulin while the contribution of 7S to the emulsibility is greater than that of 11 S.(3)11S-30,11S-45 and 11S-90 were preheated at 75℃,85℃ and 95℃ for 5 min to investigate the changes of emulsibility and gel property of the soy protein mixtures.The solubility of all three protein mixtures decreased as the increase of preheating temperature,among which the solubility of 11S-90 decreased the most,55.4% at 95℃,compared to its unpreheated counterpart.Compared with the viscosity of unpreheated proteins,the initial viscosity of all three protein mixtures showed an increasing trend after preheating,and the higher the preheating temperature,the greater increase in protein viscosity.In terms of emulsifying performance,preheating has a significant impact on 11S-30 protein,with a 48.3% decrease in emulsibility after preheating at95℃ compared to its unpreheated counterpart.As the proportion of 11 S increased,the trend of emulsibility decreasing with increasing temperature weakened.The changes of emulsifying stability also showed the same trend as emulsibility.In terms of gelation performance,the strength of protein gel with high 7S proportion after preheating at different temperatures was significantly improved,and the gel strength of 11S-45 after preheating at 75℃ was the highest,76.7%.It can be seen that preheating has a greater negative impact on the emulsification performance of high 7S proportion proteins,and the higher the temperature,the worse the emulsification performance of 7S globulins;conversely,preheating significantly improved gel property of proteins with a high 7S proportion.(4)11S-30 and 11S-90 were preheated at 85 ℃ for 5 min and then subjected to spray drying to study the changes of emulsibility and gel property of preheated 7S and11 S globulin after spray drying.Freeze drying was used as the mild-treatment control.The solubility of preheated 11S-30 and 11S-90 after spray drying was 28.2% and 27%lower than that of freeze-drying proteins,respectively.The initial viscosity of the 11S-30 after spray drying was not significantly different from that of the freeze-drying proteins,but after further heating at 85℃ for 15 min in water bath the viscosity was greatly increased to 4192 mPa.s,1.94 times higher.In terms of emulsification performance,the emulsibility of preheated 11S-90 after spray drying was 15% lower than that of freeze-drying 11S-90.However,there was no significant difference between preheated 11S-30 after spray drying and freeze drying in emulsibility.The emulsifying stability of the two preheated proteins after spray drying showed a downward trend.In terms of gel strength,the two protein mixtures after spray drying showed a weakening trend of gel strength.The gel strength of preheated 11S-30 after spray drying decreased by 28.3% and that of 11S-90 decreased by 28% compared with their freeze-drying counterparts.In conclusion,spray drying reduced the emulsibility of 7S and 11 S globulin compared with freeze drying,but preheating did not play a significant role;In the performance of gel,the strength of preheated protein gel after spray drying was lower than that of freeze-drying,but the gelation performance of preheated high-7S-proportion protein was still better than that of its unpreheated,freeze-drying counterpart,and the difference was significant. |
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