Improvement Of Foaming Of Soybean Protein Isolate By Ultra-high Pressure Assisted Papain And Its Application

Soybean protein is a kind of rich plant protein resources of highly nutritive value for its various functional properties,which is widely used in food processing.Since the functionality of the soy protein itself is difficult to meet the requirements of food processing,it is usually necessary to orientate the modification in an artificial way.In this study,soy protein isolate(SPI)extracted from defatted soybean meal,was under the ultra-high pressure treatment to assist the papain-modified SPI and detect the solubility,foaming and emulsifying properties of SPI,before and after the treatment.Select the research object with obvious improvement in foaming property to optimize the enzymolysis conditions,study the free sulfydryl,disulfide bond and structural properties(surface hydrophobicity,SDS-PAGE gel electrophoresis,circular dichroism spectrum,particle size distribution,etc.),explore the reasons for the improvement of the foaming property of the papain modified SPI as well as the effect on quality with the modified SPI portion of high foamability as the replacement of egg-white proteins added to the cake.The results obtained are as follows:(1)The effects of SPI on the solubility,foamability and emulsibilityof the five treatment groups which were blank group,ultra-high pressure treatment group only,the enzyme group only,ultra-high pressure before enzyme solutions group,ultra-high pressure with the enzymatic group.It turned out that the solubility,foamability and emulsibility indexes of the treated SPI were improved in different degrees.Among them,the ultra-high pressure with the enzymatic group to improve the performance of protein emulsibility is particularly significant.Accordingly,we proceed to the next step for optimizing the research with foamability as the target parameter,choosing ultra-high pressure with the enzymatic the solution of ultra-high pressure with the enzymatic.Compared with untreated SPI,the degree of hydrolysis of SPI was 1.37%,the nitrogen solubility index(NSI)increased from 81.3±2.05%to 92.3±3.68%,the foaming capacity(FC)increased from 90.6±4.92%to 195.7±10.6%,the emulsifying ability(EAI)increased from 22.3±1.63 m2/g to 37.1 ±2.05 m2/g.(2)The single factor experiments were carried out on substrate concentration,enzyme addition,pH,enzymolysis temperature and treatment pressure,to study the effects of their changes on SPI foamability.We selected 3%(w/v)as the concentration of the SPI solution for orthogonal test to optimize other conditions.The optimal processl parameters were as follows:the enzyme addition amount was 3000 U/g,the pH was 7.0,the enzymolysis temperature was 50?,the pressure was 250 Mpa.Under these conditions,the SPI foaming capability(FC)was 246%.(3)The effects of ultra-high pressure with papain modification on SPI structure were studied.The changes of SPI structure before and after modification were analyzed by studying the effects of free sulfydryl,disulfide bond,surface hydrophobicity,SDS-PAGE gel electrophoresis,circular dichroism and particle size analysis.The results showed that compared with the unmodified SPI,the mercapto groups were oxidized or converted to disulfide bonds after ultra-high pressure combined with papain-modified SPI.The content of free sulfydryl decreased,the content of disulfide bond increased,the surface hydrophobicity increased.The ? subunit of 7S globulin almost completely disappeared,11S globulin also hydrolyzed,small molecules with molecular weights below 18.4 kDa increased and a new band appeared near the molecular weight of 25.0 kDa.Simultaneously,the a-helix structure of the secondary structure of the protein was reduced,the number of P-sheets increased and the average particle size of the solution became smaller.(4)Replace egg-white proteins with the high foaming SPI added to the cake after the ultra-high pressure with the enzymatic partially,determine the moisture content and specific volume of the cake,take the sensory evaluation and texture analysis of the cake,and determine the quality of the cake shelf life through the moisture content and hardness in the storage period.The results showed that:when the modified SPI and egg-white proteins are added as the ratio of 3:7,the overall quality of the cake is the best,the sensory evaluation scores the highest,the moisture content reaches 39.3%and the specific volume is 4.63cm3/g.In addition with the increase in storage time,the cake added with modified SPI is better than the cake without it in quality.