Vibrational spectroscopy and biochemical changes in silver carp as related to quality of washed mince.

BACKGROUND: Biochemical and protein conformational changes in silver carp occurred during ice storage, affecting the physico-chemical and textural properties of its washed mince. Fourier-transform infrared spectroscopy (FTIR) and FT Raman could offer insightful molecular-level information that could be related to the freshness of fish and textural properties of washed mince. RESULTS: The K value increased from 15.8% to 85.0% after 14 days on ice. The surface hydrophobicity of silver carp muscle proteins increased during ice storage, and its thrice-washed mince showed the same trend. The yield and textural properties of washed mince continually decreased as the storage time was extended. Fourier-transform infrared spectroscopy revealed that, as storage time increased, the α-helix content of mince decreased, while the ß sheet content increased. Prolonged ice storage led to the exposure of buried aromatic amino acid residues and an increase in disulfide interchanges in mince and washed mince. Changes in the ∑ß sheet structure and Raman intensity at 828 cm-1 observed in mince correlated well with the K value. The α-helix content and Raman intensity of raw washed mince at 621 and 828 cm-1 showed a strong correlation with its textural properties. CONCLUSION: Silver carp should be processed to surimi within 7 days of ice storage to obtain a reasonably good yield and gel texture. Infrared and Raman spectroscopy can possibly be utilized to monitor freshness quality and protein conformational changes in silver carp and to estimate the textural properties of washed mince as affected by freshness. © 2019 Society of Chemical Industry.

Evaluation of Lipid Oxidation, Volatile Compounds and Vibrational Spectroscopy of Silver Carp (Hypophthalmichthys molitrix) During Ice Storage as Related to the Quality of Its Washed Mince.

Changes in the lipid oxidation of silver carp (Hypophthalmichthys molitrix) stored in ice for 14 days and that of its respective washed mince were evaluated. Total lipid, phospholipid, polyunsaturated fatty acid (PUFA) and monounsaturated fatty acid (MUFA) contents of the skin, belly flap and mince decreased as the storage time in ice increased. The washing process decreased the lipid contents but concentrated their phospholipid counterparts. The fish belly flap exhibited the highest thio-barbituric acid reactive substances (TBARS) value, while the mince had the lowest. 1-Hexanol, 1-octen-3-ol, and 1-hexanal were key volatile compounds detected in the belly flaps of fish stored for 7-14 days. Hexanal was the only major volatile compound found in washed mince prepared from fish stored for an extended period in ice, but in a much lower amount compared with that in the belly flap. FTIR (Fourier transform infra-red) spectra revealed a decrease in the number of cis double bonds, methylene groups and phosphate groups in lipids extracted from fish stored in ice for 7-14 days as compared with those extracted from fresh fish. Principle component analysis (PCA) revealed that the FT-Raman band at 1747 cm-1 could be a potential marker for tracking the degree of lipid oxidation in the belly flap of silver carp stored in ice. In addition, IR bands indicating phosphate group (925, 825 cm-1) in oil extracted from washed mince were correlated with the extent of the lipid oxidation of the raw material.