K.V. Lalitha

Effect of packaging atmosphere on the microbial attributes of pearlspot (Etroplus suratensis Bloch) stored at 0–2 °C

Effect of packaging atmosphere (air and under different modified atmospheres (MAs), 40% CO2/60% O2, 50%/50% O2, 60% CO2/40% O2, 70% CO2/30% O2 and 40% CO2/30% O2/30% N2) on the microbial and biochemical attributes of fresh pearlspot (Etroplus suratensis Bloch) stored at 0-2 degrees C was investigated. Trimethylamine nitrogen (TMA-N) and thiobarbituric acid (TBA) values remained lower than the proposed acceptability limits throughout the storage period. Results demonstrated that storage of pearlspot under air and MA 40% CO2/30% O(2)/30% N(2) resulted in growth of Enterobacteriaceae, Aeromonas and H(2)S-producing bacteria including Shewanella putrefaciens, while all other packaging atmospheres did not allow multiplication of Enterobacteriaceae and Aeromonas within 3 weeks. Aeromonas spp. identified were Aeromonas hydrophila, Aeromonas veronii biovar sobria and A. veronii biovar veronii. Significant reduction (p<0.01) was noticed in Aeromonas population of pearlspot stored under MA 60% CO2/40% O2 and 70% CO2/30% O2. A delay of growth of Pseudomonas below 5.0log(10)cfug(-1) was observed during the 15th day of storage at 0-2 degrees C under modified atmosphere packaging (MAP) conditions. Growth of faecal streptococci was significantly inhibited in all the packaging atmospheres at 0-2 degrees C during the entire storage period. Survival of coagulase positive Staphylococci (<50cfug(-1)) in low numbers was noticed during storage in all the packaging atmospheres. Clostridium botulinum toxin was not detected. All the packaging atmospheres did not allow multiplication of sulphite-reducing clostridia at 0-2 degrees C during the entire storage period. Packaging in MA 60% CO2/40% O2 resulted in the inhibition of growth of Aeromonas and Enterobacteriaceae, and the slowest growth of psychrotrophic bacteria, H(2)S-producing bacteria, including Shewanella putrefaciens and Pseudomonas and extended microbiological shelf life to 9-10 days. This study confirms the survival of potentially pathogenic A. hydrophila, A. veronii biovar sobria and A. veronii biovar veronii capable of growth at low temperature in pearlspot stored under MA.

Effect of reduced oxygen atmosphere and sodium acetate treatment on the microbial quality changes of seer fish (Scomberomorus commerson) steaks stored in ice.

The effect of reduced oxygen atmosphere and sodium acetate treatment on the microbial quality of seer fish (Scomberomorus commerson) steaks was determined during chilled storage (1-2 degrees C). The O2 absorber reduced the oxygen content in the pack to less than 0.01% corresponding to 99.96% reduction within 24 h. The use of O2 absorber with sodium acetate dip treatment (2% w/v) extended the sensory shelf life up to 25 days compared to only 12 days for control air packs and 20 days for untreated samples with O2 absorber. A prominent lag phase was observed for many bacterium studied, particularly for the sodium acetate treated samples with O2 absorber. On the day of sensory rejection, both the total mesophilic and psychrotrophic counts reached 7.7-8.1 and 7.1-7.9 log cfu/g, respectively. The sodium acetate treatment and reduced O2 atmosphere affected the type of major spoilers. In air packed samples, H2S-producers predominated followed by Brochothrix thermosphacta, Pseudomonas spp., where as in the untreated samples with O2 absorber, H2S-producers predominated the microbial flora followed by Lactobacillus spp. For treated samples with O2 absorber, B. thermosphacta formed the major micro-flora followed by Lactobacillus spp. The use of O2 absorber inhibited the growth of Pseudomonas spp., and total Enterobacteriaceae.