Protein Cross-linking in Freeze Dried Fish Meat

동결건조 어육의 단백질 Cross-linking에 관한 연구

This study was carried out in order to investigate protein cross-linking in freeze-dried meat of flounder (Limanda herzensteini). Changes in solubility or extractability of proteins and electrophoretic patterns of the extracted proteins were determined to monitor the cross-linking during the storage of freeze-dried meat. Development of nonenzymatic browning and the loss of in vitro protein digestibilily were also measured to assess their influences on the changes of functional and nutritional properties of proteins. In addition, the effects of lysine added, and removal of fat and water extractives were also mentioned. The extractability of protein decreased upon storage time and temperature, and the loss of solubility of myosin was evident. In case of the samples stored at $5^{\circ}C$ for 150 days, the extractability of protein decreased $26.4\%$, while that of the samples stored at $20^{\circ}C$ for 60 days decreased about $39.7\%$. And it was noted that the loss of solubility of myosin was $68.3\%$ and $98.1%$ for the same storage conditions, respectively. It was noteworthy that the samples treated with $L-lysine{\cdot}HCl$ seemed to prevent more or less the loss of protein solubility, in that, even stored at $20^{\circ}C$ for 120 days, revealed only $57.03\%$ decrease. The nonenzymatic browning was proceeded with the increase of storage temperature, especially, in the samples treated with glucose. This suggests that the decrease in extractibility of myosin was accompanied by the extent of browning. But the browning was retarded in defatted samples. The in vitro apparent protein digestibility was also higher in the samples defatted or water extracted. It was suggested from these results that changes in properties of proteins in freeze dried fish meat were led by the protein cross-linking which was attributed to Maillard type of reactions and protein-lipid interactions.