Control of Bacterial Pathogens during Processing of Cold-Smoked and Dried Salmon Strips

Microbiological and chemical changes were determined during the smoking and drying of salmon strips processed at 29 to 318C for 4 days at a facility in Alaska in 1993. During the process, Staphylococcus aureus populations increased to more than 10 5 CFU/g after 2 to 3 days of processing. Subsequent laboratory studies showed that a pellicle (dried skinlike surface) formed rapidly on the strips when there was rapid air circulation in the smokehouse and that bacteria embedded in or under the pellicle were able to grow even when heavy smoke deposition occurred. Under these conditions, an inoculum of 26 CFU/ g of S. aureus increased to 10 5 CFU/g after 3 days of processing. Elimination of preprocess drying and reduction in air e ow during smoking resulted in smoke deposition before pellicle formation and enabled the product to reach levels of water-phase salt and water activity that inhibit the growth of S. aureus and Listeria monocytogenes. In 1994, these modie cations were then applied during processing at an Alaskan facility, and S. aureus could not be detected in the e nished product. L. monocytogenes was detected in the raw product area, on the processing tables, and on the raw salmon strips, but it was not detected in the e nished product when the smoke was applied before pellicle formation. Smoking and drying are among the oldest methods of food preservation. Even though we have had considerable experience with these processes, food poisoning outbreaks occasionally occur. Improperly processed products and the lack of understanding that some products may become hazardous if they are stored at temperatures that permit the growth of microbial pathogens have caused these food poisoning outbreaks. In Alaska, native smoked and dried salmon products are processed during the summer months when the e sh are returning to the rivers during the spawning season. Since processing is done under ambient temperature and humidity, the processing time can vary from 4 days to 1 or 2 weeks, depending on weather conditions. This long drying time raises concern, because the drying temperatures are ideal for the growth of bacterial pathogens. During processing, there is a race between the product reaching inhibitory levels of water-phase salt (WPS), moisture, and water activity (aw) and the growth of pathogenic and spoilagetype bacteria. If the product is processed at temperatures of 608C or higher, the nonspore-forming bacteria are usually inactivated. In 1993, we worked with an Alaskan native processor along the Yukon River to learn more about the processes used and the microbiological and chemical composition of smoked and dried salmon. The processor had developed a fairly modern processing facility with stainless steel tabletops, a chlorinated water supply, a refrigeration room, and walls and e oors that could be cleaned and sanitized.