Surimi Quality Analysis And Recognition Mechanism Based On Multi-scale Microscopic Hyperspectral Imaging Technology

Surimi is an important intermediate product containing stabilized myofibrillar proteins obtained from mechanically deboned fish flesh that is water-washed for removal of sarcoplasmic protein, blended with cryoprotectants. As a high-protein, low-fat and ready-to-cook fish product, surimi is gaining more prominence in aquatic processing industry. As feasible industry standards and national standards to assess the merits and adulteration of surimi are still lacking, with people’s growing awareness of food safety and quality assurance, evaluation methods for quality of surimi urgently need to be established. Currently, the technologies to evaluate quality of surimi exit some imperfections including single index, time and effort consuming and so on. Therefore, the detection or evaluation method should be reformed.Infrared spectroscopy and microscopy imaging techniques can be direct, fast, non-destructive, and conduct simultaneous detection of various forms of multi-component sample, to achieve spatial information, spectral information synchronization acquisition and has great potential in terms of food quality testing.In this paper, the mid-infrared, near-infrared spectroscopy and scanning electron microscopy were comprehensive utilized to obtain overall infrared spectra macro-fingerprint of surimi nutritional composition and establish surimi spectral pattern codes database, initially proving identification mechanism of surimi species and quality, constructing qualitative identification models of different species and grades of marine fish surimi, while initially revealing surimi protein conformational transition rule during gelation process. The results are as follows:(1) A Tri-step infrared spectroscopy(Fourier transform infrared spectroscopy(FT-IR) integrated with second derivative infrared(SD-IR) spectroscopy and two-dimensional correlation infrared spectroscopy(2DCOS-IR)) was employed to characterize and discriminate three marine fish surimi(white croaker surimi(WCS), hairtail surimi(HS) and red coat surimi(RCS)) and four grades of white croaker surimi(A, AA, FA and SA). Different surimi, the differences of composition of matter and structure(such as fat content, protein secondary structure, etc.) have different IR macro fingerprints. The main identification zone of different species surimi are in the amide I and lipids absorptions bands. For different grades surimi, the identification zone are focus on lipids absorptions bands. And IR rapid qualitative identification models for different species and grades of marine fish surimi has been successfully constructed.(2) A rapid and nondestructive near infrared(NIR) method combined with multivariate analysis was used to discriminate different species and grades of marine fish surimi. Principal component analysis(PCA) and discriminant analysis(DA) were applied to classify the species and grades of those surimi samples. The results showed that excellent classification could be obtained after optimizing spectral pre-treatment. For the discrimination of three species surimi, the correct classification rate of the calibration as well as the validation data sets were 98.5% and 100% respectively, using the DA method after MSC pre-treatment. For four grades surimi, DA provided 98.9% and 100% correct classification rate for calibration and validation data sets, respectively, after MSC pre-treatment. It was demonstrated that NIR diffuse reflectance spectroscopy integrated with DA have significant potential as a rapid and accurate approach for rapid discrimination of surimi species and grades.(3) Fourier transform infrared spectroscopy was employed to investigate protein conformation changes, which played significant roles in maintaining stable surimi gel network during the formation of white croaker surimi gel, for exploring the effect of protein conformation on surimi gel network. Recorded FTIR spectra of surimi samples with different grades(A, AA, FA and SA) were analyzed by peak fitting of the non-deconvolved and baseline corrected amide I bands(1600~1700 cm-1). Peak positions were assigned to individual structural components. By our proposed peak fitting approach, quantitative evaluation of the secondary structure was performed assuming peaks of Gaussian shape. The result shows that α-helical structure was the main conformation of surimi proteins. During surimi gelation, α-helix of myosin partially changed into β-sheet, β-turn and random coil structures. In conclusion, β-sheet and random coil structures were the main protein conformations maintaining the structure of surimi gel, and β-sheet made the main contribution to gel strength. Scanning electron microscopy(SEM) results revealed surimi gels have a fibrous and homogeneous network structure. Moreover, at higher gels grades, interconnections between the three-dimensional protein network of gel increases, in agreement with the gel strength results. Results of these studies demonstrated that FTIR spectroscopy could be a scientific and powerful tool for study on conformation changes of surimi protein during gelation.