挤压-酶解大豆蛋白结构与特性关系及其乳液乳化活性评价

Relationship between structure and properties of extruded enzymatic soybean protein and emulsifying activity evaluation of hydrolysate emulsion

以低温冷榨豆粕粉为原料,研究挤压-酶解处理对大豆蛋白酶解物蛋白结构及其乳液界面特性的影响,并探究酶解物乳液对蛋液稳定性的改善作用。结果表明,经挤压预处理的大豆蛋白酶解物柔性和表面疏水性随着酶解时间的延长呈现先增加后减少的变化趋势,在酶解30 min时分别达到最大值0.40和44.96;挤压大豆蛋白酶解物的二级结构由有序向无序状态转变,表现为β-转角和无规则卷曲的含量增加,β-折叠和α-螺旋的含量减少。挤压大豆蛋白酶解物乳液的储能模量G'和损耗模量G''及界面肽含量均随着酶解程度的增强呈现先增大后减小的趋势,乳化活性和乳化稳定性也在酶解30 min时分别达到最佳值28.45 m^(2)/g和61.05 min。挤压大豆蛋白酶解物乳液与蛋液以3:3质量比混合时,采用多重光散射分析乳液的稳定性,其不稳定性系数(thermal instability index,TSI)较小,乳液体系呈现较好稳定性,表明挤压大豆蛋白酶解物乳液可以有效改善蛋液的稳定性。该研究为大豆蛋白酶解物在乳化食品领域中应用提供理论基础。

Soybean protein,one type of high-quality plant protein has been widely used in the food processing field,because of its excellent water-holding capacity,and gelation functional properties.However,the soybean protein is still lacking in emulsion,due to the dense network structure and limited molecular flexibility.In this study,an appropriate modification was adopted to expand the structure of soybean protein for better emulsification properties.An optimal enzymatic digestion was exposed to the internal functional groups of soybean protein for better functional properties.Specifically,Alcalase cut off the peptide bonds in the peptide chain,and then the soybean protein was broken down into many short peptides,finally exposing the hydrophobic amino acids embedded within protein molecules.As a result,the surface hydrophobicity of soybean protein increased to improve the structural characteristics.The extrusion treatment also promoted the unfolding of protein structure,thus exposing the internal hydrophobic groups.There was also some variation in the structure of soybean protein.Therefore,a systematic investigation was implemented to explore the relationship and mechanism between the emulsification and structure of soybean protein enzymatic digestion products that are treated by extrusion with enzymatic digestion.The effect of Alcalase treatment time on the protein structure(flexibility,surface hydrophobicity,and secondary structure)and emulsion interfacial properties(rheology,emulsifying activity,and emulsifying stability)of extruded enzymatic digestion products was studied under the conditions of different time(0,10,20,30,40,and 50 min)of cold pressed soybean meal powder pretreated by extrusion.The improvement performance of soybean protein digestion emulsion on the stability of egg liquid was explored by mixing the soybean protein digestion emulsion with egg liquid,according to different mass ratios.A new idea was provided to apply the experimental and theoretical research into the practical factory.The results showed that the flexibility and surface hydrophobicity of soybean protein enzymatic digestion products after extrusion showed a trend of first increasing and then decreasing with the extension of enzymatic digestion time.Furthermore,the flexibility of extruded soybean protein enzymatic digestion products reached the maximum of 0.40 after 30 mins of enzymatic digestion.The surface hydrophobicity of extruded soybean protein enzymatic digestion products reached the maximum of 44.96 after 30 mins of enzymatic digestion.The secondary structure of extruded soybean protein enzymatic digestion products was shifted from the ordered to a disordered state.Meanwhile,the content ofβ-turn and random coil increased,whereas,the spiral content ofβ-sheet andα-helix decreased.The storage and loss modulus first increased and then decreased in the soybean protein digestion emulsion at the interface with the increase of the degree of enzymatic digestion.The content of interface peptides also showed a similar trend of first increasing and then decreasing with the extension of enzymatic digestion time.The emulsifying activity and stability of extruded soybean protein digestion emulsion also reached the optimal values of 28.45 m^(2)/g and 61.05 min,respectively,after 30 min of digestion emulsion.The stability of extruded soybean protein digestion emulsion was verified by mixing the emulsion with egg liquid at a mass ratio of 3:3 and then analyzed by multiple light scattering.The small thermal instability index(thermal instability index,TSI)was achieved in the emulsion system,indicating better stability.Therefore,the extruded soybean protein digestion emulsion can be expected to effectively improve the stability of egg liquid.The utilization rate of plant-based proteins can also be improved,such as egg allergies.This finding can provide a theoretical basis for the application of soybean protein hydrolysates in the field of emulsified foods(such as salad dressing).