Safety Evaluation of Sous Vide-Processed Products with Respect to Nonproteolytic Clostridium botulinum by Use of Challenge Studies and Predictive Microbiological Models

Abstract

Sixteen different types of sous vide-processed products were evaluated for safety with respect to nonproteolytic group II Clostridium botulinum by using challenge tests with low (2.0-log-CFU/kg) and high (5.3-log-CFU/ kg) inocula and two currently available predictive microbiological models, Food MicroModel (FMM) and Pathogen Modeling Program (PMP). After thermal processing, the products were stored at 4 and 8°C and examined for the presence of botulinal spores and neurotoxin on the sell-by date and 7 days after the sell-by date. Most of the thermal processes were found to be inadequate for eliminating spores, even in low-inoculum samples. Only 2 of the 16 products were found to be negative for botulinal spores and neurotoxin at both sampling times. Two products at the high inoculum level showed toxigenesis during storage at 8°C, one of them at the sell-by date. The predictions generated by both the FMM thermal death model and the FMM and PMP growth models were found to be inconsistent with the observed results in a majority of the challenges. The inaccurate predictions were caused by the limited number and range of the controlling factors in the models. Based on this study, it was concluded that the safety of sous vide products needs to be carefully evaluated product by product. Time-temperature combinations used in thermal treatments should be reevaluated to increase the efficiency of processing, and the use of additional antibotulinal hurdles, such as biopreservatives, should be assessed.

Growth of Group II Clostridium botulinum Strains at Extreme Temperatures

“…Considerable temperature abuse may be necessary before these strains in chilled foods will grow and produce enough toxin to cause outbreaks. Nevertheless, certain strains of group II C. botulinum have been reported to grow slowly and produce toxin at 3°C (5,7,29) and at 4 to 5°C within a time frame typical for storage of chilled foods (6,14,24). Therefore, minimally processed chilled foods should receive special attention with regard to C. botulinum.…”

Co-incubation of Clostridium botulinum with protective cultures

“…It is possible that the lack of growth within the time that the experiment was monitored was due to an extended lag phase. Hyytia-Trees et al (2000) demonstrated that the storage temperature of sous vide foods did not have a considerable effect -very little growth occurred during storage at 8°C, which was also inconsistent with FMM predictions. Different non-proteolytic strains of C. botulinum have varied growth patterns (Brown et al, 1991) and this should be considered when comparing growth data.…”

“…The risk of botulism was confirmed with a number of sous vide (cooked under vacuum) products challenged with this pathogen: carrot, chicken and cod (Brown & Gaze, 1990;Brown, Gaze, & Askell, 1991); spaghetti and meat sauce ; ground beef and pork cubes (Lindstrom et al, 2001); beef roast and rice-based dishes (Hyytia-Trees et al, 2000); soups, casseroles and curries (Rodgers, 2002b).…”

Food safety research underpinning food service systems – a review

“…1991). The poor growth of this pathogen in sous‐vide meals was reported by Hyytia‐Trees et al . (2000) and Rodgers (2002); the low temperature (<5°C) and pH (<5.5) were adequate to control growth and toxin production.…”