Novel application of an optical inspection system to determine the freshness of Scomber japonicus (mackerel) stored at a low temperature

This study evaluated the use of an optical inspection system (OIS) to determine the freshness of mackerel (Scomber japonicus). The correlations between the light reflection intensity (LRI) of mackerel eyes (determined using an OIS) and the volatile basic nitrogen content (VBN) and K-value were analyzed. After unloading at the harbor, the mackerel were stored at 4 °C for 9 days and the VBN, K-value, and LRI were determined at 3-day intervals. During storage, the LRI, VBN, and K-value all increased. Furthermore, the LRI was correlated with the K-value and VBN. Therefore, although the LRI cannot be applied as an absolute standard for evaluating freshness, the LRI using an OIS is a suitable nondestructive method for evaluating freshness for quality and risk management in the processing industry when handling large numbers of fish.