Effect Mechanism Of Heat Treatment On The Interation Of Grass Carp Myofibrillar Protein With Fishy Odor Compounds

Fish surimi products are one of the fastest-growing varieties of processed aquatic products in our country.Marine fish is a good raw material for traditional surimi products,and it is hard to meet the rapidly growing market demand for surimi products.With the development of freshwater aquaculture,it is of great value to process the freshwater fish such as grass carp and silver carp.However,the strongly inherent fishy smell of freshwater fish affects the acceptance of consumers seriously.The main reason analyzed was that the complexity of the fishy volatile composition,and most fishy volatile compounds combined with large molecules such as proteins in food.Meanwhile,heat treatment,as a common way in fish surimi products processing,can not only cause gelation of muscle proteins,but also have an important influence on the binding capacity of fishy volatile compounds and proteins matrix.Thus,clarifying the mechanism of heat treatment on the interaction between proteins matrix and fishy volatile compounds is particularly important to solve the fish surimi products smell remnants,and promote the flavor and quality development of fish surimi products processing industry.In this paper,we take grass carp myofibrillar protein and fishy odor compounds(hexanal,heptanal,octanal and nonanal)as research object,establishing protein-flavour system.Therefore,one of the objectives of this study was to systematically evaluate the binding characteristic of fishy volatile compounds and grass carp myofibrillar protein.In addition,clarifying effects of one-stage and two-stage heating on the myofibrillar protein conformation of grass carp and binding capacity to fishy volatile compounds was another purpose of this investigation.The main conclusions are as follows:1.The binding capacity of hexanal,heptanal,octanal and nonanal with myofibrillar proteins were 21.15?,23.69%,24.98%and 26.93%analyzing by GC-MS.The presence of fishy volatile compounds changed the peptide conformation of the protein and reduced the fluorescence intensity of MPI analyzing by UV spectrum and fluorescence spectrum analysis.The interaction between MPI and the four aldehydes is mainly through non-covalent hydrophobic interactions and a part of hydrogen or ionic bonds.The DSC showed that adding hexanal,heptanal,octanal and nonanal for MPI thermal stability than the control group was decreased by 37.80%,41.46%,52.44%and 70.73%,and the relative content of a-helix was decreased by 15.66%,20.43%,20.97%and 24.81%,respectively.2.In the one-stage heating,the binding capacity of unheated proteins to hexanal,heptanal,octanal and nonanal was 19.04%,23.35%,25.82%and 28.62%,respectively.With the increase of heating time,the adsorption of four aldehydes increased and then decreased.After heating for 30 min,the binding ability to hexanal,heptanal,octanal,and nonanal decreased to 8.77%,18.82%,19.88?and 20.00%.Turbidity,surface hydrophobicity and total sulfhydryl groups content increased and then decreased.Meanwhile,fluorescence intensity gradually decreased.Heat treatment promoted cross-linking or aggregation between MPI to formed larger and insoluble aggregates analyzing by SDS-PAGE.The relative content of ?-helix decreased from 68.51%to 56.22%,?-sheet contents increased from 9.05%to 18.59%and random coil structure increases from 9.41%to 10.19%at 5 min.While,the relative content of ?-helix increases and ?-sheets structure decrease in later heating time.3.In the two-stage heating,the binding capacity of MPI and four aldehydes increased with the increasing heating time in the first-stage heating.The binding capacity of hexanal heptanal,octanal and nonanal increased by 44.25%,41.71%,40.42%and 36.08%at 30 min.While,their binding capacity increased and then decreased in the second-stage heating,and was significantly higher than that in the first-stage heating(p<0.05).Turbidity,surface hydrophobicity and total sulfhydryl groups content gradually increased with the heating time in the first-stage heating,while a transition of that from increasing to decreasing in the second-stage heating.The fluorescence intensity of two heating modes gradually decreased.In the first low-temperature heating process,the relative content of?-helix decreased by 28.99%,?-sheet and ?-turn increased by 63.02%and 19.62%respectively.Turning to the second stage of high-temperature heating,the relative content of ?-helix structure decreased and then increased,reaching the lowest in 1 min,and the content of ?-sheet and random coils decreased.