HISTAMINE FORMATION AND BACTERIAL-FLORA I N MACKEREL STORED IN ICE AND AT THE TEMPERATURE OF ICE

In order to determine the mechanism of histamine (Hm) formation in sco mbroid fish stored at low temperature, total viable and luminous bacte rial counts (TVC and LBC), bacterial flora, Hm contents in several par ts of mackerel stored in ice and at the temperature of ice, and Hm for mation by the isolates were studied. In the first experiment (Exp. I), Hm was formed in the muscles during storage at the temperature of ice but not in ice. Hm content was far higher in the ventral muscles than in the dorsal muscles. P. phosphoreum grew in the abdominal walls in both storages (ca. 81% in LBC/TVC), and in the muscles during storage at the temperature of ice (ca. 2.5% in LBC/TVC). P. phosphoreum isolat ed formed a high level of Hm. In the second experiment (Exp. II), a sm all amount of Hm was found in the muscles, especially the ventral musc les, and P. phosphoreum was not found in fish before and after storage . These results indicate that P. phosphoreum plays an exclusive role i n histamine formation in mackerel stored at the temperature of ice. Bo th whole and halophilic bacterial floras were dominated by Vibrio in a ll the parts (skin, muscle, abdominal walls) of fish in Exp. I and by Pseudomonas or Moraxella in Exp. II. Photobacterium leiognathi was fou nd in all the parts of fish before storage in Exp. I but not in Exp. I I, and P. phosphoreum also grew only in fish after storage in Exp. I a s above. Pseudomonas or Moraxella dominated also in Exp. I after growt h of P. phosphoreum. These results suggest that Photobacterium grows i n the flora dominated by Vibrio, especially halophilic floras, and har dly grows in the flora dominated by Pseudomonas or Moraxella.