Real-time assessment of the microbial quality of retail shrimp using CO2 evolution rate

A real-time CO(2) evolution rate (CER) method together with conventional cultural and sensory techniques were utilized to determine the microbial quality and shelf life of several types of shrimp products: chloramphenicol (CAP) treated, imported farm raised, and domestic wild caught. Treatment with CAP was used to create different bacterial loads in shrimp samples to demonstrate the ability and sensitivity of the CER method for differentiating the bacterial activity in samples. Samples were divided into control (nontreated) and 0, 10, and 30 ppm of CAP treatment groups and stored at 4°C. The CER was recorded with a microrespirometer, and aerobic plate counts (APCs), olfactory sensory analyses, and pH measurements were recorded daily until spoilage occurred. The real-time CER results were highly correlated with the APCs (R(2) = 0.93) and readily distinguished the onset of spoilage in each of the treatment groups. CAP treatment at 10 and 30 ppm increased the sample shelf life by 2 and 3 days, respectively, compared with the nontreated samples. Untreated domestic wild-caught shrimp had a shelf life 1 day longer than that of the untreated imported farm-raised shrimp. No pattern of change in pH was noted throughout the storage period. When the olfactory sensory scores reached the marginally acceptable level, the mean CER was 27.23 μl/h/g and the mean APC was 5.78 log CFU/g. A cutoff CER of 25.0 μl/h/g was therefore selected to define acceptable raw shrimp. The CER method was a highly effective and sensitive real-time method for determining the microbial quality of raw shrimp.