Effect of Enzymatic Digestion Products of Konjac Glucomannan with Different Molecular Weights on Oxidation and Structural Properties of Myofibrillar Protein during Frozen Storage
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Abstract:
Changes in the physical, chemical, and structural properties of myofibrillar protein of grass carp caused by adding konjac glucomannan enzymatic products EK1, EK2 and EK3 with molecular weights of 149.03, 118.75 and 36.48 ku, respectively, during the frozen storage at –18 ℃, were compared. The samples were analyzed for salt-soluble protein content, Ca2+-ATPase activity, total sulfhydryl groups, surface hydrophobicity, particle size, Zeta potential, SDS-PAGE, and UV and fluorescence spectra. The results manifested that the salt-soluble protein content and total sulfhydryl content in the EK3 group were at maximum at 1.51 mg/mL and 19.76×10-5 mol/g, respectively, after 20 d of freezing, compared with the blank control, commercial antifreeze, EK1, and EK2. At same time, the Ca2+-ATPase activity, in the EK3, were at maximum at 1.31 μmol Pi/(mg prot•h), while the Zeta potential were at minimum at 8 689.07 and –13.35 mV, respectively, after 30 d of freezing. After 30 d of freezing, the SDS-PAGE results showed that the EK3 group had the least degradation of myosin and actin, which inhibited the oxidation of myogenic fibronectin. Furthermore, the exposure of tryptophan and tyrosine residues was reduced in the EK3 group, which indicated that the stability of the protein spatial structure was maintained. Therefore, it was concluded that the addition of small molecular weight konjac glucomannan enzymatic digestion product EK3 (36.48 ku) had the best cryoprotective effect on myofibrillar protein in this experiment, which supports the use of small molecule polysaccharides as antifreeze agents for aquatic products.
