Crab-meat-isolated psychrophilic spore forming bacteria inactivation by electron beam ionizing radiation

The present work was performed to evaluate the potential of electron beam ionizing radiation for the inactivation of three psychrophilic spore forming bacteria (Bacillus mycoides, Bacillus weihenstephanensis and Psychrobacillus psychrodurans) isolated from ready-to-eat brown crab (Cancer pagurus). Inactivation curves for the three spores were performed in both types of crab meat, brown and white. Also the effect of pH and water activity (a_w) on the lethal efficacy of ionizing radiation, for the three different psychrophilic spore forming bacteria, was evaluated. The effects of pH, a_w and their possible interactions were assessed in citrate-phosphate buffers of different pH, ranging between 7 and 4, and a_w, ranging from <0.99 to 0.80. A reduction of a_w increased the spores resistance between >0.99 and 0.90, while an a_w reduction from 0.90 to 0.80 had a minor impact on their resistance. In contrast to a_w, the effect of pH showed a greater variability depending on the spore species. While pH did not affect the resistance of B. weihenstephanensis at any a_w, B. mycoides showed slightly higher resistance at pH 5.5 at a_w of 0.90 and 0.80. pH showed a significant effect on the resistance of P. psychrodurans. For the two types of crab meat, slightly differences were observed in 6D values. B. weihenstephanensis was the most resistant, requiring 7.3-7.6 kGy to inactivate 6 Log₁₀-cycles of this spore forming bacterium, while for B. mycoides and P. psychrodurans 6.1-6.3 and 5.4-5.3 kGy respectively were necessary to reach the same inactivation level in crab meat. An agreement between spore resistance in crab meats and lab media, with similar characteristics in pH and a_w, was also observed. The results obtained in this research demonstrated the potential for ionizing radiation to achieve an appropriate inactivation level of spores naturally present in brown crab with the application of doses lower than 10 kGy.