Feasibility of a Heat-Pasteurization Process for the Inactivation of Nonproteolytic Clostridium botulinum types B and E in Vacuum-Packaged, Hot-Process (Smoked) Fish

Abstract

This study demonstrates the feasibility of a heat-pasteurization process for certain vacuum-packaged hot-smoked fishery products for inactivation of the spores of the nonproteolytic Group II Clostridium botulinum types B, E, and F. This process permits the use of lower concentrations of salt and other inhibitors without jeopardizing safety and quality of the products during prolonged refrigerated storage. The pasteurization treatment was developed based upon the inactivation of nonproteolytic types B or E in hot-process (smoked) salmon. Smoke was not applied to the samples inoculated with types B and E because of its possible inhibitory effects. After processing in the smokehouse, each sample was cooled to 34°F (1.1°C), injected with 106 spores, vacuum-packaged, and then heat-pasteurized in a water bath held at a constant temperature. A total of 85, 65, and 55 min in the 185°F (85°C), 192°F (88.9°C), and 198°F (92.2°C) baths, respectively, prevented toxin production by type E during 21 d of incubation at 25°C. Longer times, 175, 85, and 65 min, respectively, were required to prevent toxin production by nonproteolytic type B. Toxin production by type E during 120 d of storage at 10°C was prevented by a 45-minute treatment in the 198°F (92.2°C) bath. When heat-pasteurized samples were transferred into TPGY broth and incubated anaerobically for 150 d at 25°C, outgrowth and toxin production by type E was prevented by a 55-minute process at 198°F (92.2°C) and type B was prevented by a 65-minute process. This process does not, however, inactivate the more heat-resistant proteolytic strains of C. botulinum Group I or other spore-formers. The packages and master cartons of these pasteurized products therefore should follow the existing recommendations for smoked fishery products and be labeled “Keep refrigerated - Store below 38°F (3.3°C).”