The Study Of The Realization And Molecular Mechanism Of Myofibrillar Protein Thermoreversible Gel

Myofibrillar protein（MP）is the main component of muscle and has favorable nutritional characteristics including a superb amino acid composition,high biological value,high digestibility,and low allergenicity.Structurally,MP usually presents a natural flexible long chain shape and is rich in side chain functional groups,which can be used as an excellent biological component for the construction of functional food colloidal materials.Currently,the design of MP structures and their functional expansion are at the forefront of science in meat processing.MP has strong thermal aggregation ability and is easy to form thermally irreversible gels.This characteristic is the basis for the formation of many gel-like meat products,and if the expansion of MP to thermally reversible gels can be realized,it will help further promote the development and utilization of MP and enrich its application scenarios.In this study,we successfully achieved the thermoreversible gelation of MP by targeting deamidation of MP with protein-glutaminase（PG）,investigated the characteristics of thermoreversible gelation of MP,and further analyzed the mechanism of thermoreversible gel formation.The following are the study’s key contents and conclusions:1.Protein concentration and PG treatment time are the determining factors for achieving thermally reversible gelation of MP.MP（2.5%,W/W）exhibited thermally reversible gel properties after 12 h of PG treatment,and its thermal reversibility could be maintained for 5heating-cooling cycles.An increase in MP protein concentration leads to an increase in gel strength;at too high a concentration（>3%）,thermally irreversible aggregates or gels are formed and thermally reversible phenomena cannot be produced,and low concentrations（1%）of protein will not form gels after a long enzymatic reaction treatment（16 h）.Deamidation myofibrillar protein（DMP）thermally reversible gels with water holding capacity of more than95%and lower whiteness values than conventional thermally induced gels.It was observed by scanning electron microscopy that the microstructure of DMP thermally reversible gels was significantly different compared to MP thermally induced gels,showing a uniform and continuous three-dimensional network structure with smooth and compact gel chains.2.Coiling and dissociation of the helical coiled-coil（CC）structure of the myosin-like tail was found to be an important structural basis for the dynamic evolution of DMP during thermally reversible gelation by atomic force microscopy（AFM）and transmission electron microscopy（TEM）.Theθ₂₂₂/θ₂₀₈ ratio of circular dichroism assesses the supramolecular assembly state of theα-helix.After deamidation,theθ_222/θ₂₀₈ value of MP decreases from 1.35to 1.05,indicating that theα-helix structure of DMP exists mainly in a double-helix coiled-coil state.The heating-cooling cycle induces a dynamic reversible transition of double-helix-single-helix-irregular coils.Upon heating,the DMP double-helix convoluted structure dissociates,while the protein structure unfolds and theα-helix content of DMP decreases from 50.7%to14.1%.Subsequent cooling reboosts theα-helix content of DMP and,at the same time,induces the reassembly of the DMP double-helix convoluted structure.Rheometry results reflect the cross-linked structure of the myosin protein head that occurs during heating of DMP and subsequently exhibits thermally reversible cold gelation behavior.The analysis of SDS-PAGE electrophoretic profiles revealed that DMP underwent covalent aggregation to a lesser extent than MP,and hydrophobic interactions played a dominant role in the formation and stabilization of DMP gel networks.3.The thermally reversible gelation properties of DMP are related to the reversible assembly of CC structures.The correlation results show a good correspondence between the gelation onset temperature and the CC transition temperature.CC assembly was specifically inhibited by trifluoroethanol（TFE）,and loss of DMP thermoreversible gel capacity occurred,confirming that temperature-responsive dynamic assembly of CC plays a key role in the formation of DMP thermoreversible gels.The results may expand the molecular basis of reversible gelation of natural CC,and may provide a theoretical foundation for the creation of novel muscle protein products.