ABSTRACT

This study investigated the preservative effect of potassium sorbate, ginger, garlic and a blend of ginger and garlic on the microbiological and shelf stability of cold smoked Catfish (Clarius gariepinus). One hundred (100) of the freshly harvested catfish obtained from the MOUAU Fish Farm were processed and divided into five lots of 20 each. Four marinating baths containing 0.5% potassium sorbate, 3% ginger, 3% garlic and a blend of 1.5% ginger and 1.5% garlic respectively were prepared. Each catfish lot except the fifth lot (which served as control) was marinated for 2 h and cold smoked for 8 h. The samples were then stored for fourteen days at refrigeration temperature (4 ± 2 oC), and 4 days at ambient temperature (28 ± 2 oC) during which analyses were carried out. The physicochemical properties (moisture, fat, ash, protein, TVB-N, FFA, PV, Vitamin A, B1, B2, B3 and E) of the cold smoked catfish samples before and after storage were analyzed. Similarly, bacterial counts (Escherichia coli, Salmonella, Staphylococcus sp, Listeria sp and total fungal counts) as well as pH of the catfish samples before, during and after storage were analyzed. The total viable count (TVC) reduced from 8.7x105 to 1.2x105 CFU/g for 3% ginger at refrigeration storage and increased from 8.7x105 to 3.43x106 CFU/g at ambient storage. In samples treated with three percent (3%) garlic, there was reduction from 1.13 x 106 to 2.40 x 105 CFU/g at refrigeration storage, but an increase from 1.13 x 106 to 3.48 x 106 CFU/g at ambient storage was recorded. For samples treated with mixed spices (1.5% ginger +1.5% garlic), the TVC  reduced from 1.09 x 106 to 2.00 x 105 CFU/g at refrigeration storage and increased from 1.09 x 106 to 3.28 x 106 CFU/g at ambient storage. For 0.5% potassium sorbate, there was reduction from 9.60 x 105 to 1.50 x105 CFU/g at refrigeration storage and increased from 9.60 x 105 to 3.45 x106 CFU/g at ambient storage; while the control decreased from 1.19 x 106 to 3.00 x 105 CFU/g at refrigeration storage and increased from 1.19 x 106 to 3.66 x 106 CFU/g at ambient storage. All the treatments were effective against E. coli at refrigeration storage whereas at ambient storage 1.5% ginger +1.5% garlic was most effective. Three percent (3%) ginger treatment recorded counts of 4.4x105 and 1.1x105CFU/g for Staphylococcus counts during ambient and refrigeration storage respectively. Salmonella count decreased in refrigeration storage (<101 CFU/g) for all the treated samples against the control (1.1x105) while 0.5% potassuim sorbate was most effective at ambient. All the treatments were effective against Listeria monocytogenes in both storage conditions. Total fungal count decreased at refrigeration storage for all the treatments and increased during ambient storage. The study found that cold smoked catfish treated with 0.5% potassium sorbate,3% ginger, 3% garlic and a blend of 1.5% ginger and 1.5% garlic can be stored for 14 days at refrigeration storage and 4 days at ambient storage provided the storage condition is maintained.