Sodium nitrite and potassium nitrate in control of nonproteolytic Clostridium botulinum outgrowth and toxigenesis in vacuum-packed cold-smoked rainbow trout

The effect of sodium nitrite (NaNO2) and potassium nitrate (KNO3) on the outgrowth and toxigenesis of nonproteolytic Clostridium botulinum in vacuum-packed cold-smoked rainbow trout stored for six weeks was studied in two inoculation studies at slightly abusive storage temperatures of 4 degrees C and 8 degrees C. The depletion rate of nitrite and the reduction rate of nitrate to nitrite as well as the effect of nitrite and nitrate on the shelf-life of the product during eight weeks' storage period were also determined. The nitrite concentrations were reduced from 166 mg/kg +/-9 (mean +/- SE), to a final concentration of 34 mg/kg +/-2 and 11 mg/kg +/-2, and the nitrate concentrations from 686 mg/kg +/-67 to 465 mg/kg +/-140 and 427 mg/kg +/-33 at 4 degrees C and 8 degrees C respectively. The nitrite depletion rate was more rapid at 8 degrees C; nitrate depletion was not significantly affected by temperature. A considerable amount of nitrite was detected in the nitrate-treated samples in the latter half of the storage period. At 4 degrees C the aerobic plate counts were significantly lower in the samples treated with NaNO2 + NaCl and with KNO3 + NaCl as compared to the NaCl-treated controls, while at 8 degrees C the differences were smaller. The sensorial shelf-life of the product was considerably extended by nitrite and nitrate curing. The nitrite and nitrate concentrations used in the present study did not completely inhibit the toxigenesis of nonproteolytic C. botulinum during the six-week storage period, although the number of toxic samples was considerably reduced by nitrite and nitrate curing. (C) 1997 Elsevier Science B.V.