微波烘焙中酸面团添加对改善面包质构的作用机制

Microwave-baked bread has defects due to its rapid rate of heating and water loss. Lactobacillus fermented sourdough can be metabolized to small molecules with charged carboxyl and hydroxyl groups, as well as hydrophilic macromolecular polysaccharides with good hydrating property, which also weaken gluten protein structure and change the physical and chemical properties of starch through the co-interaction of microorganisms and cereal enzymes. Such heteropolarity of small molecules containing ‘microwave antenna group’ as ‘active elements’ in the microwave field possess the intrinsic advantages of enhancing the above reaction, and therefore sourdough fermentation technology can be used to enhance the texture properties of microwave-baked bread. The current study systematically investigates the dielectric and microwave absorbing properties of the fermented sourdough during microwave baking and further analyzes the effect of microwave absorption on converting into heat energy. The other objectives include the investigation of the influence of sourdough on both mass and heat transfer properties with the quantitative microwave output, the moisture/heat conductivity during moisture and heat transfer processes, and the macroscopic state and distribution of water, as well as dynamic changes inside the grain during sourdough microwave baking for bread. The model systems of gluten protein/wheat starch-based sourdough fermentation were constructed respectively to clarify the effect on regulatory mechanism for the texture properties in microwave baked food with changes of the gluten protein structure caused by sourdough and variations of physicochemical properties of starch through the design of quantitative models, such as bacteria-enzyme-macromolecule.

微波烘焙因其快速的加热模式和水分散失速率，导致制得面包质构品质较差。乳酸菌发酵酸面团可代谢产生具有羧基和羟基基团的小分子极性物质，以及具有良好水合作用的亲水性多糖类物质，且在微生物和谷物酶系共同作用下具有弱化面筋蛋白网络结构、改变淀粉理化性质的作用；并且上述含有“天线基团”的极性小分子作为微波场下快速响应的“活跃份子”，具备深化上述反应的本征优势，故可采用酸面团提升微波烘焙面包的质构品质。本课题研究酸面团发酵和微波烘焙过程介电特性和微波吸收性能；考察在定量微波输出条件下酸面团对烘焙过程传质传热特性的影响，探索水分和热量传递过程的导湿/导湿温性；跟踪研究酸面团添加对微波烘焙面包过程水状态、内部水分布及动态的影响。分别构建以面筋蛋白/小麦淀粉为主导的酸面团发酵模式体系，通过菌-酶-大分子等定量模式的设计，阐明酸面团引发面筋蛋白结构及淀粉理化性质的改变对微波烘焙面包质构改善的作用机制。

微波烘焙因其快速的加热模式和水分散失速率，导致制得面包质构品质较差。乳酸菌发酵酸面团可代谢产生具有羧基和羟基基团的小分子极性物质，以及具有良好水合作用的亲水性多糖类物质，且在微生物和谷物酶系共同作用下具有弱化面筋蛋白网络结构、改变淀粉理化性质的作用；并且上述含有“天线基团”的极性小分子作为微波场下快速响应的“活跃份子”，具备深化上述反应的本征优势，故可采用酸面团提升微波烘焙面包的质构品质。本研究借助传输线理论和弓型法模式的低损耗型物料吸波性能的检测方法，考察了酸面团发酵和微波烘焙过程介电特性和微波吸收性能的变化，发现酸面团的添加显著增强了体系的介电响应和吸波性能但未改变其加热过程中的变化规律；借助低场核磁成像技术，研究了酸面团面包体系微观水分分布及动态变化规律，发现添加酸面团有助于面坯在微波加热过程中锁住更多水分，改善了微波加热过程中水分的迁移过程，解析发酵时间与水分分布变化的联系及面包内部水分子扩散交换情况与微波作用机制的内在联系；研究了微波烘焙过程中面筋蛋白的交联聚合特性及其微观网络结构变化，发现酸面团的添加能够部分解聚麦谷蛋白大聚合体（GMP）并阻碍微波场下二硫键的形成，从而弱化面筋网络结构，扫描电子显微镜（SEM）则显示添加酸面团使面坯在加热过程中形成了更加均匀有序的面筋网络；研究了微波烘焙过程中淀粉糊化特性和粘度特性变化规律，发现酸面团可以降低体系在加工过程中的糊化粘度和老化速率并在加热后期降低淀粉结晶度，说明酸面团促进了淀粉糊化，进而阐明酸面团引发面筋蛋白结构及淀粉理化性质的改变对微波烘焙面包质构改善的作用机制。课题研究有助于解析和完善酸面团发酵技术在微波烘焙食品中的应用，并为微波技术更好的服务于食品加工提供理论依据。执行期内已完成项目的任务要求和约束性指标，发表国内外学术论文13篇；申请专利4项，其中，已授权2项。

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