Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Part of Food2Know, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, B-9000 Ghent, Belgium.
Int J Food Microbiol. 2013 Jan 15;161(1):7-15. doi: 10.1016/j.ijfoodmicro.2012.11.017. Epub 2012 Nov 23.
The microbiological safety of refrigerated and processed foods of extended durability (REPFED) is linked to spore-forming pathogens, more specifically Clostridium botulinum and Bacillus cereus. In this study two sets of growth/no growth (GNG) models are presented for the spores of two B. cereus strains. The models incorporate both product (water activity (a(w)) and pH) and process parameters (pasteurization value at 90 °C (P(90)) or heating temperature). The first model evaluates the effect of four different P(90)-values (P(90)=0, 4, 7 or 10 min, all applied at 90 °C) on the germination and subsequent growth of B. cereus spores under different conditions of pH and a(w) at 10 °C. These models show that a heat treatment not only increases the time to growth (TTG), but also significantly increases the minimal a(w) and pH necessary for germination and subsequent growth: e.g. at a(w) 0.995 and without heat treatment (P(90)=0), strain FF355 B. cereus spores were predicted to germinate and grow at pH 5.3. With a P(90) of 10 min, the minimal pH increased to 5.7. The second set of models for B. cereus spores compares the effect of three heat treatments with the same P(90)-value (10 min) but applied at different temperatures (85, 87 and 90 °C), on the germination and subsequent growth at 10 °C. The second model shows that lower heating temperatures (85 and 87 °C) had less effect on the TTG and minimal a(w) and pH than a higher temperature (90 °C). Finally, the first set of models was validated in broth using spores of seven psychrotrophic B. cereus strains, to evaluate the effect of strain variability on the model predictions. The results of the validation (% growth) were compared to the predicted growth probability. The results showed that the models were prone to fail-dangerous results (i.e. predicting no growth when growth was observed: 17%-34%). Using a very low threshold for growth (0.1% predicted chance of growth was considered to be complete growth), the models were more fail-safe (11%-34%) than fail-dangerous (0.4%-14%).
冷藏和加工延长保质期食品（REPFED）的微生物安全性与形成孢子的病原体有关，特别是肉毒梭菌和蜡样芽胞杆菌。在这项研究中，提出了两组蜡样芽胞杆菌两种菌株的孢子生长/不生长（GNG）模型。这些模型综合了产品（水活度（a(w)）和 pH 值）和工艺参数（90°C 下的巴氏杀菌值（P(90)）或加热温度）。第一个模型评估了四种不同的 P(90)值（P(90)=0、4、7 或 10 分钟，均在 90°C 下应用）对不同 pH 值和 a(w)条件下蜡样芽胞杆菌孢子的发芽和随后生长的影响在 10°C 下。这些模型表明，热处理不仅会增加生长时间（TTG），还会显著增加发芽和随后生长所需的最小 a(w)和 pH 值：例如，在 a(w)为 0.995 且没有热处理（P(90)=0）的情况下，FF355 蜡样芽胞杆菌孢子预计在 pH 值为 5.3 时发芽并生长。采用 10 分钟的 P(90)时，最小 pH 值增加到 5.7。第二个用于蜡样芽胞杆菌孢子的模型集比较了三种热处理的效果，这三种热处理具有相同的 P(90)值（10 分钟），但在不同温度（85、87 和 90°C）下应用，在 10°C 下对发芽和随后的生长有影响。第二个模型表明，与较高温度（90°C）相比，较低的加热温度（85 和 87°C）对 TTG 和最小 a(w)和 pH 值的影响较小。最后，使用七种嗜冷蜡样芽胞杆菌菌株的肉汤验证了第一组模型，以评估菌株变异性对模型预测的影响。验证的结果（%生长）与预测的生长概率进行了比较。结果表明，这些模型容易出现危险结果（即当观察到生长时预测没有生长：17%-34%）。使用非常低的生长阈值（预测的 0.1%生长机会被认为是完全生长），这些模型比危险结果（0.4%-14%）更安全（11%-34%）。
