Thermal death times of Hafnia alvei cells in a model suspension and in artificially contaminated hot-smoked kahawai (Arripis trutta).

In New Zealand the product most frequently implicated in cases of scombroid poisoning is hot-smoked kahawai (Arripis trutta). Using a Hafnia alvei strain, previously isolated from a portion of hot-smoked kahawai with a histamine level of 1,659.4 mg/kg, thermal death trials were carried out in a model suspension (0.1% peptone) at 54, 55, 56, 57, and 58 degrees C. From the linear regression line (R2 = 0.98) fitted to observed D values plotted against temperature, calculated D values for 54, 55, 56, 57, and 58 degrees C were estimated to be 0.63, 0.36, 0.20, 0.11, and 0.06 min, respectively, giving a z value of 4.14 degrees C. Thermal death trials were also carried out for H. alvei associated with hot-smoked kahawai at 54, 55, 55.5, 56, and 57 degrees C. From the linear regression line (R2 = 0.93) fitted to the data, calculated D values for 54, 55, 56, and 57 degrees C were estimated to be 1.42, 0.74, 0.38, and 0.20 min, respectively, giving a z value of 3.57 degrees C. Results indicate that hot smoking has the potential to eliminate H. alvei from seafood products.

Levels of histamine and histamine-producing bacteria in smoked fish from New Zealand markets.

Smoked fish has been the most commonly implicated product in presumptive cases of scombroid poisoning in New Zealand. One hundred seven samples of smoked fish were purchased from Auckland retail markets between July 1995 and March 1996, and their histamine and bacterial levels were determined. Eight samples, obtained from five of the nine retail outlets sampled, had histamine levels which exceeded 50 mg/kg, the level set by the FDA as an indicator of decomposition. Histamine levels in only 2 samples (346.4 and 681.8 mg/kg) exceeded a hazard level of 200 mg/kg. Thirty-three of the smoked fish were held at 20 degrees C for 2 days, and 8 of these developed histamine levels above 50 mg/kg with 4 exceeding 200 mg/kg (maximum 1,659.4 mg/kg). The stored samples that exceeded 200 mg/kg were all obtained from two outlets. Within or between fish species there were no consistent relationships between levels of histamine in the samples and either the total aerobic plate counts or the numbers of histamine-producing bacteria. To the contrary, there was evidence that histamine had been formed prior to smoking and that histamine-producing bacteria were eliminated during smoking.