Challenge Studies with Clostridium botulinum in a Sous-Vide Spaghetti and Meat-Sauce Product

Challenge studies were carried out to evaluate the safety of a reformulated sous-vide processed spaghetti and meat-sauce product (a_w 0.992-0.972, pH 4.5-6) inoculated with Clostridium botulinum types A and B spores. Following processing at 75°C for 36 min (equivalent to a 13 D process for Streptococcus faecium ), samples were stored at 15°C and analyzed at selected time intervals for toxin production and visible signs of spoilage. Toxin was detected in samples of pH > 5.5 after 14-21 days and in products of pH 5.25 after 35 days. Toxin was not detected in any samples of pH < 5.25 within 42 days storage at 15°C. All products of pH 5.75 and 6 were visibly spoiled, i.e., swollen due to CO₂ production, prior to toxigenesis. However, for products of pH 5.5 and 5.25, toxigenesis preceded spoilage. Subsequent studies were done to test the effect of additional salt (1-3% w/w) on the safety of a product of pH 5.5 at mild temperature-abuse storage conditions (i.e., 15°C). Toxin production was not delayed in samples containing < 1.5% added salt, while > 1.5% salt (w/w) prevented toxin production throughout the 42-day storage period at 15°C. Microwave heating of products for 5-10 min at full or half power in a domestic microwave (800 watts) inactivated the preformed toxin in all samples.