Spore-forming bacteria inactivation during gelatin manufacturing: variability, resistance, and process implications

This study investigated the thermal resistance of spores from 12 spore-forming bacterial strains isolated from the gelatin processing industry. In gelatin manufacture, the solution obtained after collagen extraction is purified, concentrated to increase solids content and subsequently dried with hot air to achieve the final product moisture. To simulate these steps, the effects of concentration (performed at 55 °C for 3.5 and 6 h) and drying (performed at 20-80 °C for 4 h) on spore inactivation were evaluated. Physicochemical monitoring showed stable pH (≈6.0) and increased total solids from 0.20 to 0.24 g/g (concentration) and from 0.30 to 0.92 g/g (drying). Log₁₀-reductions after concentration ranged from -1.1 to 1.9, with Bacillus subtilis and Clostridium sporogenes exhibiting the highest sensitivity, while thermophilic strains (Geobacillus stearothermophilus and B. licheniformis) showed increased counts. Drying resulted in log₁₀-reductions from -1.3 to 1.7, with anaerobes showing greater susceptibility and thermophiles maintaining or increasing their viability. B. cereus strains showed variable behavior, with some demonstrating high resistance during concentration. Variability analysis revealed that the variability attributable to microorganisms exceeded biological and experimental variabilities. The high solids content of the gelatin matrix may have further enhanced spore protection. To complement these results, B. cereus and G. stearothermophilus spores were subjected to capillary tube inactivation (105-140 °C). The inactivation kinetics were fitted to the reparameterized Weibull model. B. cereus showed t_6D values from 403.7 s (105 °C) to 63.2 s (115 °C) with a z-value of 12.4 °C. G. stearothermophilus exhibited t_6D values from 601.8 s (120 °C) to 46.4 s (140 °C), with a z-value of 18.0 °C. These results provide quantitative data to support the development of more effective microbial control strategies in the production of gelatin.