The Effect of Lipid Oxidation in Frozen Pulverized Niboshi (Boiled and Dried Sardine) on Color Browning and Formation of Free Amino Acid

Abstract

The relationship between lipid oxidation in pulverized niboshi which occurred during freezing and further oxidation, free amino acid loss, and browning which took place after the sample had been thawed was investigated. Lipid oxidation occurred in the samples which were kept frozen at −20°C, however, browning and free amino acid loss did not. This oxidation affected the rate of lipid oxidation, the browning, and the decrease of free amino acids in the niboshi once it had been thawed and stored at 25°C. It was apparent that the longer the niboshi was stored in a frozen state, the faster was the rate of browning, lipid oxidation, and loss of free amino acids after thawing. The free amino acids which decreased were methionine, histidine, ornithine, and lysine. When the same sample was packed with nitrogen gas, browning, lipid oxidation, and amino acid loss were almost eliminated. It was also found that if the thawed sample was left for five days at 25°C and then packed in nitrogen gas, the lipid oxidation and decrease in free amino acid levels could be controlled, although the browning process could not, and the sample color changed to reddish-brown. The results suggested a correlation between the lipid oxidation which occurs during freezing and the browning, decrease in free amino acids, and further progression of lipid oxidation which takes place after thawing. This deterioration in quality can be prevented by using the nitrogen gas packing immediately after processing of the food product.