Department of Food Biotechnology and Food Process Engineering, Technische Universität Berlin, Berlin, Germany.
Int J Food Microbiol. 2013 Mar 1;162(1):55-63. doi: 10.1016/j.ijfoodmicro.2012.12.010. Epub 2013 Jan 5.
High pressure combined with elevated temperatures can produce low acid, commercially sterile and shelf-stable foods. Depending on the temperature and pressure levels applied, bacterial endospores pass through different pathways, which can lead to a pressure-induced germination or inactivation. Regardless of the pathway, Bacillus endospores first release pyridine-2,6-dicarboxylic acid (DPA), which contributes to the low amount of free water in the spore core and is consequently responsible for the spore's high resistance against wet and dry heat. This is therefore the rate-limiting step in the high pressure sterilization process. To evaluate the impact of a broad pressure, temperature and time domain on the DPA release, Bacillus subtilis spores were pressure treated between 0.1 and 900 MPa at between 30 and 80 °C under isothermal isobaric conditions during dwell time. DPA quantification was assessed using HPLC, and samples were taken both immediately and 2 h after the pressure treatment. To obtain a release kinetic for some pressure-temperature conditions, samples were collected between 1s and 60 min after decompression. A multiresponse kinetic model was then used to derive a model covering all kinetic data. The isorate lines modeled for the DPA release in the chosen pressure-temperature landscape enabled the determination of three distinct zones. (I) For pressures <600 MPa and temperatures >50 °C, a 90% DPA release was achievable in less than 5 min and no difference in the amount of DPA was found immediately 2 h after pressurization. This may indicate irreversible damage to the inner spore membrane or membrane proteins. (II) Above 600 MPa the synergism between pressure and temperature diminished, and the treatment temperature alone dominated DPA release. (III) Pressures <600 MPa and temperatures <50 °C resulted in a retarded release of DPA, with strong increased differences in the amount of DPA released after 2 h, which implies a pressure-induced physiological like germination with cortex degradation, which continues after pressure release. Furthermore, at 600 MPa and 40 °C, a linear relationship was found for the DPA release rate constants ln(k(DPA)) between 1 and 30 min.
高压结合高温可以产生低酸、商业无菌和货架稳定的食品。根据应用的温度和压力水平，细菌芽孢会通过不同的途径，这可能导致压力诱导的萌发或失活。无论途径如何，芽孢杆菌芽孢首先释放吡啶-2,6-二羧酸（DPA），这有助于芽孢核心中游离水的减少，因此负责芽孢对湿热和干热的高抗性。因此，这是高压灭菌过程中的限速步骤。为了评估广泛的压力、温度和时间范围对 DPA 释放的影响，在等压等温和 30 至 80°C 的温度下，将枯草芽孢杆菌芽孢在 0.1 至 900 MPa 之间进行压力处理，在停留时间内进行处理。使用 HPLC 评估 DPA 的定量，立即和压力处理后 2 小时取样。为了获得一些压力-温度条件下的释放动力学，在减压后 1 秒至 60 分钟之间收集样品。然后使用多响应动力学模型来推导一个涵盖所有动力学数据的模型。为所选压力-温度范围内的 DPA 释放建模的等速率线使确定三个不同区域成为可能。（I）在压力<600 MPa 和温度>50°C 的情况下，在不到 5 分钟内即可实现 90%的 DPA 释放，并且在加压后 2 小时立即发现 DPA 的量没有差异。这可能表明对内孢子膜或膜蛋白造成不可逆转的损害。（II）在超过 600 MPa 的压力下，压力和温度之间的协同作用减弱，而单独的处理温度主导 DPA 的释放。（III）在压力<600 MPa 和温度<50°C 的情况下，DPA 的释放速度较慢，在加压后 2 小时释放的 DPA 量差异明显增加，这意味着有压力诱导的生理样萌发，伴有皮层降解，这种情况在压力释放后仍在继续。此外，在 600 MPa 和 40°C 下，DPA 释放速率常数 ln(k(DPA))在 1 至 30 分钟之间发现呈线性关系。
