EFFICACY OF POTASSIUM SORBATE AND OTHER PRESERVATIVES IN PREVENTING TOXIGENESIS BY CLOSTRIDIUM BOTULINUM IN MODIFIED - ATMOSPHERE PACKAGED FRESH FISH

The antibotulinal efficacy of potassium sorbate and other preservatives were evaluated in fresh fish fillets inoculated with spores and vegetative cells of Clostridium botulinum (1 to 10,000,000/g) and incubated at 1.7 to 27 C under modified atmospheres. Refrigeration of modified atmosphere packaged fillets at 10 C or lower assured that fillets were spoiled by the normal fish microflora before toxigenesis by C. botulinum types A, B and E (50 spores/g). Above 10 C, the rates of toxigenesis and spoilage were similar, and the risk of botulism increased. The likelihood that toxigenesis preceded spoilage increased as the inoculum level was increased beyond the proposed maximum natural contamination level (100 spores/g) to levels up to 10,000,000/g, and was enhanced somewhat by exclusion of oxygen from the package. The antibotulinal protection provided by pure carbon dioxide-modified atmospheres during refrigeration also decreased with temperature abuse.;Botulinal toxigenesis at elevated abuse temperatures above 20 C was decreased significantly by dipping fresh fish fillets in 5% potassium sorbate-based preservative solutions before packaging. Sorbate appeared to interfere with outgrowth from germinated spores and cell division, and increased the frequency of cell lysis. Sorbate from 5% sorbate dip solutions was absorbed initially into the outer surface layer of fillets, and penetrated into the inner portion within a few hours of storage at 4 C where it provided about 0.15% sorbic acid on a whole fillet, wet weight basis. The addition of 5 to 10% sodium tripolyphosphate in the dip solution enhanced absorption (ave. 0.22% sorbic acid) and retention of sorbate by fillets. Further protection resulted when either linoleic acid or sodium nitrite was included in sorbate-based dip solutions, which delayed toxigenesis beyond the time (48 h) required for spoilage of fillets under moderate temperature-abuse (21.1 C) conditions. These dips were less effective at abuse temperatures (27 C) near the optimum growth temperature of C. botulinum. Gas exchange treatments using 5 to 10% sulfur dioxide dramatically reduced bacterial growth during storage at 4 C for 18 days, and bacterial growth and botulinal toxigenesis under moderate temperature abuse (21.1 C) for 3 days.