Purpose: This study examined the growth of L. monocytogenes and evaluated the shelf life based on aerobic plate count, yeast and mold counts on thawed catfish stored at refrigerated temperature.
Methods: Frozen catfish purchased from a local market was thawed and cut in 20 g pieces. Listeria monocytogenes (Strain 101M, serotype 4b) was inoculated on half of the samples and other half was used for aerobic plate count, and yeast and mold counts. Samples were stored in LDPE bags or petri plates at refrigerated temperature and microbiological examination was performed at every 24 hours for up to 144 hours.
Results: In both packaging conditions, there were no significant differences (P<0.05) in Listeria counts over the sampling period. After six days, the Listeria count increased by 0.70 log CFU/g (petri plate) and 1.06 log CFU/g (plastic bag). A significant increase in both aerobic plate count (4.12 to 7.90 log CFU/g) and yeast and mold count (3.21 to 5.63 log cfu/g) was observed within four days for the LDPE packed fish samples, however, sample stored on petri plates were less than 4.9 log CFU/g for both organisms. After six days, there was a significant increase in both aerobic plate count (to 8.79 log CFU/g and 6.63 log CFU/g) and yeast and mold count (to 6.10 log CFU/g and 4.31 log CFU/g) for LDPE packed and petri plates samples respectively.
Significance: These results confirm that L. monocytogenes can grow on the thawed catfish at refrigerator temperatures and indicate the importance of sanitation during thawing and storage. Our study validated that thawed catfish should not be stored more than four days in this condition.