【作者】 李媛；

【导师】 张宇昊；

【作者基本信息】 西南大学 ， 食品科学， 2020， 硕士

【摘要】 β-乳球蛋白(β-lactoglobulin,BLG)是牛奶中主要的乳清蛋白组分,支链氨基酸含量丰富,具有很高的市场价值和潜力。但是,BLG在加热、碱性环境、高压或金属离子的条件下易变性,所以在食品工业中的应用受到限制。近年来,固体颗粒稳定的Pickering乳液因其众多的优势在医药、食品和化妆品等行业有着较好的应用前景。本研究以β-乳球蛋白为原料,通过去溶剂法结合京尼平(Genipin,GP)交联制备β-乳球蛋白纳米颗粒(BLGNPs),通过高速剪切乳化制备高内相Pickering乳液(HIPEs),探索了BLGNPs稳定的HIPEs的性质与稳定性;并在此基础上将HIPEs应用于肉糜制品中替代动物脂肪,以求改善产品品质,为BLG和Pickering乳液在食品中的应用提供新的思路和理论参考。主要结论如下:(1)采用乙醇去溶剂法结合GP交联技术,根据不同制备顺序得到四组BLGNPs:BLGNPs-1(pH调节→乙醇去溶剂化→GP交联)、BLGNPs-2(乙醇去溶剂化→pH调节→GP交联)、BLGNPs-3(pH调节→GP交联→乙醇去溶剂化)和BLGNPs-4(对照组,pH调节→乙醇去溶剂化),粒径在200～400 nm之间,ζ-电位绝对值均大于20 mV。FTIR结果与θ值表明,BLGNPs-1、BLGNPs-2和BLGNPs-3发生了不同程度的交联反应。SEM图像显示,相比于球形的其他BLGNPs,椭圆体的BLGNPs-2具有更好的稳定Pickering乳液的能力。4种BLGNPs均具有一定的热稳定性,且更适合低温(4℃)储存。界面吸附试验表明,结构重排主导BLGNPs界面膜的形成,且初始吸附阶段受扩散控制。不同pH下的BLGNPs均自发吸附到油水界面,但界面压力的变化差距不大。pH 7.0时BLGNPs扩散速度最慢,pH 9.0时界面重排程度最高。添加离子降低了BLGNPs的扩散速度,改善了界面吸附与重排程度,更多的BLGNPs参与界面的稳定。基于颗粒的粒径、三相接触角、形状以及热稳定性和储藏稳定性,选择BLGNPs-2用于Pickering乳液的制备。(2)以大豆油为油相,通过高速剪切乳化制备BLGNPs稳定的HIPEs,并通过外观、粒径、流变和微观结构对其进行表征。结果表明:BLGNPs可以承载体积分数(φ)高达0.75的油相,且在颗粒浓度超过1%和广泛pH(5.0～9.0)条件下显示出良好的稳定Pickering乳液的能力。HIPEs具有良好的热稳定性,在70℃和100℃下加热60 min仍能保持稳定。100℃下,加热促进了GP和BLG的进一步交联反应,从而形成了蛋白质互连,增加了HIPEs的粘度并改善了HIPEs的稳定性。HIPEs具有良好的储存稳定性,在4℃下储存30 d后仍能保持乳液形态,不发生水层析出和破乳。HIPEs也具有较好的离心稳定性,在较高的离心力(18000g)下仍保持较小的乳析指数。HIPEs具有优异的离子稳定性,NaCl的添加可以增加BLGNPs在油水界面处的覆盖率,致使HIPEs液滴之间的网络更加紧密,从而减少HIPEs的聚集和油滴的溢出,增加乳液的冻融稳定性,离子强度超过50 mM时可耐受9次以上冻融。(3)将BLGNPs稳定的HIPEs用于肉饼中替代动物脂肪,替代比例梯度为0、25%、50%、75%、100%。随着替代比例的增加,熟制前肉饼的颜色从粉红色逐渐变得偏白。HIPEs中GP与BLG交联形成网络,紧密包裹大豆油滴,同时加热过程中蛋白质间交互作用增强,从而形成更加稳定、富有弹性的网络结构,改善了肉饼的蒸煮得率、保水保油性和质构等特性。HIPEs的添加抑制了肉饼中部分脂质氧化,使得肉饼的a~*值增加,b~*值降低。同时,因为大豆油球状体较大的表面积产生更多的光反射,肉饼的L~*值增大。显微结构显示所有的肉饼样品都具有煮熟的凝胶/乳液体系的特征,即蛋白质基质聚集失去连续性并产生具有海绵状(蜂窝状)的结构,空洞随着HIPEs替代比例的增加而变大,说明脂肪与肌原纤维蛋白的结合减少,蛋白质消化率也随之增加。更多还原

【Abstract】 β-lactoglobulin(BLG)is the main whey protein component in milk,with rich branched chain amino acids and high market value and potential.However,the application of BLG in food industry is limited because of easily denatured in heating,alkaline environment,high pressure or metal ions.In recent years,solid particles stabilized Pickering emulsions have good application prospects in the pharmaceutical,food and cosmetics industries due to their advantages.In this study,β-lactoglobulin was used as a raw material,and β-lactoglobulin nanoparticles(BLGNPs)were prepared by desolvation method with Genipin(GP)cross-linking.The high internal phase Pickering emulsions(HIPEs)were prepared by high-speed shear emulsification,and the properties and stability were explored.On the basis of this,the prepared HIPEs were used to minced meat products to replace animal fat,so as to improve the quality of products,and provide new ideas and theoretical references for the application of BLG and Pickering emulsions in food.The main conclusions are as follows:(1)According to different preparation sequences,four groups of BLGNPs were prepared by ethanol-desolvation combined with GP cross-linking: BLGNPs-1(pH adjustment → ethanol desolvation → GP cross-linking),BLGNPs-2(Ethanol desolvation → pH adjustment → GP cross-linking),BLGNPs-3(pH adjustment → GP cross-linking → ethanol desolvation)and BLGNPs-4(control group,pH adjustment → ethanol desolvation).The particle sizes were between 200 ～ 400 nm,and the absolute values of ζ-potential were greater than 20 mV.FTIR detection and θ values showed that BLGNPs-1,BLGNPs-2 and BLGNPs-3 had occurred cross-linking reactions to varying degrees.SEM images showed that the ellipsoidal BLGNPs-2 had better potential to stabilize Pickering emulsion than other spherical BLGNPs.All four BLGNPs had good thermal stabilities and were more suitable for low temperature(4 ℃)storage.The interfacial adsorption experiments showed that the structural rearrangement dominated the formation of BLGNPs interfacial film,and the initial adsorption stage was controlled by diffusion.BLGNPs adsorbed to the oil-water interface spontaneously at different pH,but the change in interface pressure was little.The diffusion rate of BLGNPs was the slowest at pH 7.0,and the degree of interface rearrangement was the highest at pH 9.0.The addition of NaCl reduced the diffusion rate of BLGNPs,improved the degree of interface adsorption and rearrangement,and made more BLGNPs participated in the stabilization of the interface.Based on particle size,three-phase contact angle,morphology,thermal and storage stabilities,BLGNPs-2 was selected to stabilize Pickering emulsions.(2)BLGNPs stabilized HIPEs were prepared by high-speed shear emulsification with soy oil as the oil phase,and the prepared HIPEs were characterized by appearance,particle size,rheology,and microstructure.The results showed that BLGNPs can cover up to 0.75 oil phase volume fraction(φ),and showed good ability to stabilize Pickering emulsions at particle concentrations exceeding 1% and a wide range of pH(5-9).HIPEs had good thermal stability and can be remained stable after heating at 70 ℃ and 100 ℃ for 60 minutes.At 100 ℃,heating promoted the further cross-linking reaction between the GP and BLG,thereby forming protein interconnections,so increasing the viscosity of HIPEs and improving the stability of HIPEs.HIPEs had good storage stability and could retain emulsion morphology at 30 d after 4 ℃ storage without water layer precipitation and demulsification.HIPEs also had good centrifugal stability,and still maintained a small creaming index under high centrifugal force(18000 g).HIPEs had an excellent ionic stability.The addition of NaCl increased the coverage of BLGNPs at the oil-water interface,resulting in a closer network between HIPEs droplets,thereby reducing the aggregation of HIPEs and the overflow of oil droplets,while increasing the freeze-thaw stability of emulsions.HIPEs could withstand more than 9 freeze-thaw cycles when the ionic strength exceeded 50 mM.(3)BLGNPs stabilized HIPEs were used to replace animal fat in meatloaf,and the replacement gradients were 0,25%,50%,75%,and 100%.As the replacement ratio increased,the color of the meatloaf before cooking gradually changed from pink to white.In HIPEs,GP and BLG were cross-linked to form a network,which tightly enclosed soy oil droplets.At the same time,the interaction between proteins was enhanced during heating,thereby forming a more stable and elastic network structure,which improved the cooking yield,water and oil retention,texture and other characteristics of meatloaf.The addition of HIPEs inhibited part of the lipid oxidation in the meatloaf,which made a~* value increase and b~* value decrease.At the same time,because the larger surface area of the soy oil spheroids produced more light reflection,the L~* value of the meatloaf was increased.The microstructure showed that all meatloaf samples had the characteristics of a cooked gel/emulsion system,that was,the protein matrix aggregated to lose continuity and produced a sponge-like(honeycomb)structure.And the cavity became larger with the increase of HIPEs replacement ratio,indicating that the combination of fat and myofibrillar protein decreased,and protein digestibility increased.更多还原