纤维状蛋白质闪爆解聚与自组装机制研究

This study proposes a novel physicochemical process- - -high density steam flash-explosion (HDSF) to improve the biological value of fibrous proteins. The process is based on pressurization and forcing steam into cells of biomasses, followed by explosive decompression (within 0.00875s). HDSF is developped from steam explosion or steam spout or swollen. It could shorten the time of high density release of energy from several ten seconds or minutes to 0.00875 s. The completion of high density release of energy at extremely short time could provide enough force to disrupt and unfold the compact structure of fibrous proteins and avoid the long time of violent treatment of high temperature and pressure. Our preliminary research has demonstrated HDSF at 1.8 MPa modified more than 92% of feather keratin to the pepsin-digestible form. However, the relationship between the improvement of biological value of feather keratin and structural changes under HDSF has not been established. This study is to investigate the effects of HDSF treatments on fibrous proteins such as feather keratin, wool keratin, silk proteins and collagen, characterize conformational changes and disrupture of chemical bonds of these fibrous proteins induced by HDSF. Accordingly, the mechanisms on the disassembly and self-assembly of fibrous proteins and the relationship between the energy input, disrupture of chemical bonds and the conformational transformation of fibrous proteins under HDSF would be established. The function and structure of degradation products would be further identified, and the disrupture and formation of binding chemical bonds would also be analyzed. Finally, the degradation pathway, kinetics of fibrous proteins and moleculer mechanism would be proposed, making a very effective method for renewable utilisation of protein biomasses such as feather, and waste silk and wool.

闪爆是能够应用于难降解生物质规模化处理的新方法，其原理与优势在于高密度蒸汽的爆炸式释放，巨大冲击和膨胀力对生物质的解聚起到主要作用，降低高温高压作用时间。本项目基于申请者前期发现的闪爆解聚可使92%以上羽毛角蛋白转化为可消化蛋白质的实验结果，以羽毛、羊毛、蚕丝角蛋白、胶原蛋白等具有代表性的纤维状蛋白质为研究对象，针对纤维状蛋白质具有的束缚其解聚的存在形式、结构特征与作用力，研究其在不同闪爆处理下的解聚与自组装行为与机制，建立闪爆能量输入与纤维状蛋白质特征共价键、次级键的破坏，结构的解聚或转化以及自组装的模型，从而获得对复杂纤维状蛋白质进行闪爆降解与利用的普遍规律，进而对不同纤维状蛋白质闪爆降解产物结构与功能进行系统研究，建立闪爆处理、蛋白质降解与利用的关系模型，实现通过控制纤维状蛋白质的闪爆解聚和自组装从而按照预定目的提高蛋白质利用率的目的，为低值蛋白质资源开发提供理论基础和实践指导。

闪爆是一种能够大规模应用于难降解生物质处理新方法，羽毛角蛋白等纤维状蛋白是一类大宗但难利用的硬质蛋白质。我国拥有丰富的羽毛等大宗低值蛋白资源，仅每年随养殖业产生的羽毛下脚料就有约70万吨，在国际上被认为是一种有巨大潜在价值的蛋白质资源。但羽毛独特的蛋白质结构及组成，使其很难被动物胃肠道消化酶消化。若没有合适的加工处理方式，羽毛几乎没有经济价值，也会造成资源浪费、环境污染。本课题以大宗、难利用的羽毛角蛋白等纤维状蛋白质为研究对象，研究蒸汽闪爆对羽毛角蛋白的解离与降解机制，获得对羽毛角蛋白汽爆解聚与利用的规律，有利于实现按照预定目的提高蛋白利用率的目的。研究发现汽爆过程中羽毛角蛋白在解离的同时发生聚集，其中聚集体间的作用力较弱，而聚集体内分子间作用力较强，且含有非二硫共价键，从而使得羽毛角蛋白以异质体形式溶出。羽毛二硫键含量随着蒸汽闪爆处理强度的增大显著降低，游离巯基则呈先减小后增大的趋势，二硫键的减少与游离巯基的增加不成比例表明羽毛角蛋白蒸汽闪爆过程中形成了新的化学交联。凝胶电泳以及角蛋白溶液聚集行为分析表明汽爆压力超过1.8 MPa时，肽链开始大量断裂，羽毛角蛋白也随之丧失自组装能力。根据上述结果提出羽毛角蛋白汽爆解离与降解机制：热能首先弱化各化学键键能，使肌链区域二硫键发生降解，同时伴随着非二硫键共价交联的形成，低汽爆压力下，爆炸冲击力不足以破坏羽毛肌链结构；随着汽爆强度的增大，二硫键进一步降解，羽毛角蛋白肽链开始大量断裂；泄压阶段产生的冲击力能够断开折叠片层间弱的范德华力，打乱β折叠常规的堆叠顺序，破坏角蛋白的结晶度，从而使得羽毛纤维颗粒化。本研究进一步研究了高度变性纤维化蛋白质—高温大豆蛋白粕在闪爆降解、与聚合过程与机制，为开发利用低值蛋白质资源，改善食品加工性能差的蛋白质、扩大蛋白质来源和节约蛋白质资源提供了新途径。