Enhanced chemical and spatial recognition of fish bones in surimi by Tri-step infrared spectroscopy and infrared microspectroscopic imaging.

Surimi is an intermediate product with an increasing popularity worldwide. Discrimination of impurities like fish bones in surimi has become an urgent issue owing to the food safety and the improved requirements for assessment methods in identification of surimi quality and grades. A Tri-step infrared spectroscopy, including Fourier transform infrared spectroscopy (FT-IR), second derivative infrared spectroscopy (SD-IR) and two-dimensional correlation infrared spectroscopy (2DCOS-IR) has been applied to integrally discriminate different contents (1%-8%) of fish bones in surimi at macro-scale. Meanwhile, attenuated total reflection infrared spectroscopy (ATR-IR) microspectroscopic imaging has been employed to recognize and identify the location of fish bones (less than 1.0 mm in size) in micro-scale. Fishbone characteristic infrared absorption peak at 1011 cm-1 contributes to surimi peaks at 1045 cm-1 and 988 cm-1 confirmed by calculation of their peak heights and ratios of peak areas in original spectra. SD-IR spectra enhance the difference in range of 1440-500 cm-1 , and specifically peak intensity at 599 cm-1 is significantly increased in surimi with 3%-8% fish bones. Moreover, 2DCOS-IR spectra reveal that surimi containing fish bones have increased intensity of auto-peaks at 525 cm-1 , 519 cm-1 , 512 cm-1 and 505 cm-1 mainly contributed by hydroxyapatite and collagen. In ATR-IR microspectroscopic images, a clear fishbone shape (800 × 200 μm) corresponding to its visible image is clearly observed in principal component (PC) score image, which is confirmed as a fish bone by corresponding pixel spectra. Furthermore, the single-wavenumber image shows the spatial chemical distribution of various components for both the fish bone and surimi. Consequently, fish bones can be integrally recognized by physical and chemical imaging manners. It has been demonstrated that the developed Tri-step infrared spectroscopy and ATR-IR microspectroscopic imaging could be applicable for rapidly recognizing impurities and adulterants in surimi.