Development of quality evaluation sensor for fish freshness control based on KI value

Recently, raw fish, sashimi, is becoming a popular dish in countries other than Japan. Therefore, in order to assure that the raw fish and shellfish are safe for human consumption, a quality evaluation sensor, which shows, at a glance, the quality of sashimi, was developed. The proposed sensor is based on the principle that the freshness of sashimi, which is judged from the KI value, can be determined from the degree of color change of thiazole blue (MTT: 3-4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) due to the redox reaction of MTT accompanying the oxidation of hypoxanthine (Hx) by xanthine oxidase (XOD). The proposed sensor consists of 5 ml of 80% ethanol-1 M Tris-HCl buffer (pH 7.8) containing 2.0 mg of Hx, 2.0 mg of MTT and 0.38 unit of XOD. The proposed sensor and fish were kept together at 5, -10 and -20 degrees C, and the freshness of sashimi stored at each temperature was determined from the color change of the sensor. The concept "freshness of sashimi" can be expressed as remaining of validity (RDV), which is described in our previous study. A good relationship was obtained between the KI value and the RDV determined by the proposed sensor. From these results, the proposed sensor system can be used to non-destructively determine the fish freshness and RDV.