Frozen Denaturation Mechanism Of Surimi Based On Multiple Scales Of Spectroscopic Techniques

Frozen surimi is the raw material for making surimi products.Because of its high nutritional value and low price,the consumption of frozen surimi has increased year by year,and the proportion of frozen surimi in the processing output of aquatic products in China has increased rapidly.At the same time,there are some problems in surimi,for example:with the change of storage and transportation conditions surimi quality will deteriorate,especially protein.Nowadays,most of the existing methods are complex and costly.At the same time,the reasons for the change in the quality of frozen surimi cannot be fully revealed.Therefore,on the basis of previous studies,the mechanism of protein freezing denaturation during surimi storage was studied by infrared spectroscopy and low field nuclear magnetic resonance.Fourier transform infrared spectroscopy?FT-IR?can be used for nondestructive,rapid and simultaneous detection of various complex compounds,and obtaining the overall chemical fingerprint information of the samples.In this study,Tri-step infrared spectroscopy combined with spectral curve fitting and chemometric were used to investigate the changes of protein in surimi with cryoprotectant and without cryoprotectant at different storage times at-36?.Firstly,through the determination of basic physical and chemical indexes,it was found that the moisture and fat content of surimi did not change significantly after 24 weeks of storage,but the content of TVB-N increased significantly.The content of TVB-N in surimi without cryoprotectant increased more obviously from the fourth week,and the quality of surimi deteriorated seriously.Secondly,the samples chemical information was obtained in cold storage at different storage times by infrared spectroscopy.The chemical composition of amide I band,amide II band and amide III band in surimi was analyzed by one-dimensional infrared spectroscopy.The results showed that with the prolongation of storage time,the peak of protein in surimi decreased gradually.Four secondary structures??-helix,?-sheet,?-turn,random coil?were studied by secondary structure analysis of 1600-1700 cm^-1 band of amide I band in surimi and the change trend are more obvious than one-dimensional spectroscopy;the specific changes of secondary structure content of surimi in different storage periods are obtained by spectral curve fitting technology,and results were summarized as follows:after24 weeks of storage,the content of?-helix and?-sheet structure in surimi decreases gradually,while the content of?-turn and random coil decreases gradually.Finally,the changes of the macro-fingerprint of"personality"in surimi infrared spectra were extracted by two-dimensional synchronous correlation spectroscopy?time and thermal perturbation?.The absorption peaks in the amide I bands of 1219 cm^-1,1238 cm^-1,1396 cm^-1 changed from strong automatic peaks to weak automatic peaks until they disappeared.The absorption peaks at 1533 cm^-11 in the bands of amide II and at 1611 cm^-1 and 1638 cm^-1 from amide I band change to automatic peaks.At present,low-field nuclear magnetic resonance?LF-NMR?is mainly used to measure water content in meat products according to the change of relaxation time of T₂.It was found that although there was no significant change in the total water content of surimi after storage,the water content of different components of surimi have migrated.The A₂₁ content of surimi changed slightly in the two surimi,but the content of A₂₂ in surimi without cryoprotectant decreased in the third week,and the content of A₂₃ increased,and the change trend was clear.However,the content of A₂₂ and A₂₃ in surimi with cryoprotectant showed decreasing,but the change trend was not obvious.For surimi between different storage periods,principal component analysis was carried out based on infrared spectroscopy and nuclear magnetic resonance,and surimi of different storage times were classified rapidly.For surimi with cryoprotectant,the PC1 and PC2 accounted for 99.54%,94.35%and 87.22%of sample variance in PCA analysis according to amide I,amide II and water,respectively;for surimi without cryoprotectant,the PC1 and PC2 end accounted for 97.65%,92.37%and 85.01%of sample variance in PCA analysis according to amide I,amide II and water,respectively;And for surimi without cryoprotectant,the PC1 and PC2 end accounted for 97.65%,92.37%and85.01%of sample variance respectively on the basis of LF-NMR,it was found that PC1(A₂₂)and PC2(A₂₃)had the greatest impact on the quality of frozen surimi during storage time,and accounting for 99%sample variance.Through the above experimental analysis,it can be concluded that during the low temperature storage at-36?,the TVB-N content in the surimi increased significantly at the fourth week,and the quality of surimi begin to deteriorate significantly.At the same time,by the analysis of Tri-step infrared,the absorption peak of surimi protein is also gradually reduced,and protein secondary structure is also changing,the changes of the amide?and?are more obvious;by the LF-NMR analysis,the content of free water and non-flowable water increases with the increase of storage time.Therefore,it can be inferred that during the low temperature,when the water between different components begins to migrate,the binding mode between protein molecules and between water and protein molecules are changed,and destroy the inherent secondary structure of protein and affects protein quality.