Survival of desiccated Salmonella mutants during steam treatment of cocoa beans

Low-moisture foods pose persistent risks because pathogens can survive drying and become more heat tolerant. This thesis evaluated whether prior desiccation increases the thermal resistance of Salmonella enterica on whole cocoa beans and examined how exposure time and temperature govern inactivation. Whole beans were inoculated with kanamycin-resistant S. enterica serovars Typhimurium and Oranienburg, desiccated to ∼ 7.5% moisture, and treated by a steam pulse in a preheated climate chamber (Binder MKF 720) generated by adding 1.5 L of boiling water. A fullfactorial design varied temperature and exposure time; survivors were quantified by culture-based enumeration. Prior desiccation conferred a pronounced survival advantage: desiccated cells exhibited, on average, a 1.73 log10 smaller reduction than non-desiccated cells (≈ 54-fold greater heat resistance), confirming cross-protection on a realistic cocoa matrix. For desiccation-hardened cells, exposure time was the dominant predictor of inactivation; a +20 ◦C increase at constant time did not produce a statistically significant additional lethality. Differences between serovars were present but secondary to the desiccation effect. These findings indicate that achieving target log reductions in low-moisture foods is more reliably secured by ensuring sufficient process time than by modest temperature increases. They further show that validations based on non-adapted laboratory cultures can underestimate process requirements. Incorporating desiccated challenge strains and emphasizing time-driven validation are recommended to establish robust safety margins for cocoa and similar low-moisture commodities.