Comparative analysis of the capillary tube method and an adenosine triphosphate (ATP) method for estimating bacterial counts and spoilage potential in seafood

The capillary tube catalase gas column and the Zylux model FB-14 methods were useful for estimating the microbial population and spoilage potential of raw fish during aerobic cold storage and microbial growth in broth. As a result, these methods were further tested collaboratively at Kansas State University. Salmon fillets, rainbow trout and pure culture ( Pseudomonas fluorescenes) were refrigerated at 7°C and viable cell count (VCC), catalase activity (%CA), and adenosine triphosphate (ATP) were monitored at 0, 1, 2, 3 and 4 days. For the catalase test on a surface sample or cultural broth, 50 μml of sample was placed into the open wider portion of a Pasture pipette followed by 50 μml of H₂O ₂. For ATP test on a surface sample and cultural broth, a 10 μml of sample was placed in the vial followed by 10 μml of reagent. Data from salmon fillet and whole rainbow trout were similar and combined for analysis. On day 0, VCC, %CA and RHU ATP value of fish surfaces was 3.8 ± 0.2 log CFU/cm2, 0.4 ± 0.2%, and 331 ± 2.5, respectively. On day 1 the corresponding values were 4.4 ± 0.3 log CFU/cm 2, 1.2 ± 0.2%, and 373 ± 11, respectively. On day 2 the values were 6.1 ± 0.5 log CFU/cm2, 5.2 ± 0.3%, and 438 ± 31, respectively. On day 3 the values were 7.4 ± 0.6 log CFU/cm2, 8.9 ± 0.6%, and 486 ± 14, respectively. On day 4 the values were 7.9 ± 0.6 log CFU/cm2, 11.2 ± 0.8%, and 496 ± 14, respectively. The correlation coefficients of VCC and %CA and VCC and RHU ATP values were r = 0.96 and r = 0.95, respectively. Thus, the rapid %CA and RHU ATP methods can be used to estimate VCC of fish surfaces during aerobic cold storage. In pure culture broth, the VCC, %CA and RHU ATP values at time 0 were 6–7 log CFU/ml, 5–15%, and 365–415, respectively. As the VCC increased to 7–8 log CFU/ml, %CA and RHU ATP values were 15–30% and 415–448, respectively. The correlation coefficients of VCC and %CA and VCC and RHU ATP values were r = 0.90 and r = 0.96, respectively. Gram stains and catalase tests showed that the Gram-negative catalase positive rods were predominant on fish surface.