【作者】 王宇；

【导师】 钱海峰；

【作者基本信息】 江南大学 ， 食品科学与工程， 2023， 硕士

【摘要】 乳酸化是近年来报道的一种由乳酸介导的蛋白质翻译后修饰类型。目前,乳酸化研究主要集中在组蛋白,并没有针对食品中的蛋白。同时,面筋蛋白是小麦加工过程中产生的具有高营养价值的植物蛋白,其特殊的三维网络结构赋予了面团极强的可塑性,在食品工业市场中占据重要地位。因此,本文首先利用乳酸和乳酸钠对面筋蛋白进行乳酸化改性,使乳酸基团连接到面筋蛋白赖氨酸侧链上;其次,分析乳酸化改性对面筋蛋白典型的功能性质的影响;然后,进一步从微观构象角度对比不同结构性质的变化趋势,探究乳酸化改性对面筋蛋白结构性质的影响;最后,鉴于面筋蛋白在稳定面团性质方面的重要作用,将乳酸化改性后的面筋蛋白应用于冷冻生坯面团中,为其品质劣变的改良提供新的策略方法。主要研究内容如下:首先,采用乳酸和乳酸钠对面筋蛋白进行乳酸化改性,蛋白质免疫印迹结果显示乳酸化修饰位点主要集中在醇溶蛋白和低分子量麦谷蛋白亚基(LMW-GS)。当p H=7.0时,乳酸化改性使得面筋蛋白溶解度由0.05 mg/m L分别提升至0.19 mg/m L和0.21 mg/m L,与溶解度显著相关的乳化性和起泡性也有明显改善;乳酸化改性后蛋白的持油性由0.83g/g分别升高至1.25g/g和1.44 g/g,疏水基团与脂质之间相互作用增强使得持油性显著提高;面筋蛋白黏弹性显著改善,储存模量(G′)和损耗模量(G″)均明显增加;改性后小麦面筋蛋白失重率由78.73%降低至71.53%和72.58%,形成更加坚固的网络结构。其次,从微观角度探究了乳酸化改性处理前后面筋蛋白结构性质变化。乳酸化处理使得面筋蛋白二级结构改变,β-转角结构部分转化为β-折叠结构,β-转角含量分别减少5.86%、12.94%,β-折叠含量分别增加10.15%、11.49%;面筋蛋白中色氨酸残基处于更加极性的环境中,最大吸收波长红移,荧光强度降低;巯基与二硫键发生相互转化,二硫键含量分别增加23.92%和36.20%;紫外吸光度显著增加,蛋白质三级结构发生了明显改变;疏水基团被掩埋,表面疏水性降低;高分子量区域蛋白条带加深,蛋白质分子之间形成聚集体;改性后面筋蛋白之间的非共价相互作用增强,形成更加稳定的面筋网络结构。最后,根据冷冻生坯面团中面筋蛋白受冻融影响,导致网络结构难以维持的问题,针对性采用改性后的面筋蛋白对面筋网络进行强化。与未改性面筋蛋白相比,添加乳酸化面筋蛋白制得的馒头比容显著增大。经3次冻融循环后,添加乳酸钠处理蛋白的馒头比容相较于空白组增加18.34%,相较于添加未改性面筋蛋白组增加5.73%。低场核磁检测到乳酸化改性后的蛋白能够减缓冻融造成的水-固相互作用降低的趋势,从而降低水的流动性。基于激光共聚焦显微镜(CLSM)对面团微观结构的观察结果可知,添加改性蛋白增强了面团中蛋白质-蛋白质相互作用,使其形成更加致密的面筋蛋白网络结构。更多还原

【Abstract】 Lactylation is a type of protein post-translational modification mediated by lactate.At present,the research of lactylation mainly focuses on histone,which has not been applied in food protein modification.Wheat gluten is a vegetable protein with high nutritional value produced during wheat processing.Its special three-dimensional network structure gives dough strong plasticity and occupies an important position in the food industry market.Therefore,in this paper,lactate and sodium lactate were used to modify wheat gluten by lactylation,so that the lactate group was connected to the lysine side chain of protein.Secondly,the effects of lactylation on typical functional properties of whrat gluten were analyzed.Then,from the perspective of microscopic conformation,the change trend of different structural properties was compared to explore the internal mechanism of lactylation on wheat gluten.Finally,in view of the important role of it in stabilizing the properties of dough,lactylated wheat gluten was applied to provide a new strategy for improving the quality of frozen dough’s deterioration.The main research contents are as follows:Firstly,lactate and sodium lactate were used to modify wheat gluten.The results of western blot showed that the modification sites mainly focused on gliadin and low molecular weight glutenin subunits(LGW-GS).After the lactylation,the solubility of wheat gluten increased from 0.05 mg/m L to 0.19 mg/m L and 0.21 mg/m L,respectively.Simultaneously,based on the the increase in solubility,the emulsifying property and foamability were significantly improved.The oil holding capacity of the lactylated wheat gluten increased from 0.83 g/g to 1.25g/g and1.44 g/g,respectively.The interaction between hydrophobic groups and lipids significantly enhanced the oil holding capacity.The viscoelasticity of gluten protein was significantly improved,and the storage modulus(G′)and loss modulus(G″)were significantly increased.After the lactylation,the weight loss rate of wheat gluten decreased from 78.73% to 71.53%and 72.58%,respectively,so wheat gluten formed a stronger and tighter network structure.Then,the structural properties of wheat gluten after lactylation were studied.After lactylation,β-turns were partially transformed into β-sheets.The contents of β-turns decreased by 5.86% and 12.94%,respectively,and the contents of β-sheets increased by 10.15% and11.49%,respectively.Tryptophan residues were in a more polar environment,with maximum absorption wavelength redshifted and fluorescence intensity reduced.The content of disulfide bond increased by 23.92% and 36.20%,respectively.The UV absorbance significantly increased and the tertiary structure of proteins obviously changed.The hydrophobic groups were buried and the surface hydrophobicity was reduced.The protein bands in high molecular weight regions were deepened,and wheat gluten molecules formed aggregates.The noncovalent interaction between the lactylated wheat gluten was enhanced,which promoted the formation of a more stable network structure.Finally,according to the deterioration of network structure in frozen dough by freezingthawing,lactylated wheat gluten was used to strengthen the gluten network.Compared with wheat gluten,the specific volume of steamed bread prepared with lactylated wheat gluten increased significantly.Specifically,after three freeze-thaw cycles,the specific volume of steamed bread with sodium lactate treated gluten increased by 18.34% compared with blank group and 5.73% compared with control group.The results of LF-NMR demonstrated that the lactylated wheat gluten could slow down the downtrend of the water-solid interaction caused by freeze-thawing,thus reducing the water mobility.Based on the observation of dough microstructure by CLSM,it could be seen that the protein-protein interaction in dough was enhanced by adding lactylated wheat gluten.A denser gluten protein network structure was formed.更多还原