Smelt J P P M, Bos A P, Kort R, Brul S
Swammerdam Institute for Life Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018WV Amsterdam, The Netherlands.
Int J Food Microbiol. 2008 Nov 30;128(1):34-40. doi: 10.1016/j.ijfoodmicro.2008.08.023. Epub 2008 Sep 16.
Spores of Bacillus subtilis were subjected to relatively mild heat treatments in distilled water and properties of these spores were studied. These spores had lost all or part of their dipicolinic acid (DPA) depending on the severity of the heat treatment. Even after relatively mild heat treatments these spore lost already a small but significant amount of DPA. When these spores were inoculated in nutrient medium-tryptone soy broth (TSA)-the non-lethally heated spores started to germinate. Results of classical optical density measurements showed that both phase darkening and subsequent outgrowth could be affected by sub-lethal heat. A study of single cells in TSB showed that lag times originating from exponentially growing cells followed a normal distribution, whereas lag times originating from spores followed a Weibull distribution. Besides classical optical density measurements were made to study the effect of previous heating on the kinetics of the first stages of germination. The germination kinetics could be described by the model as was proposed by Geeraerd et al. [Geeraerd, A.H., Herremans, C.H. and Van Impe, J.F., 2000. Structural model requirements to describe microbial inactivation during a mild heat treatment. International Journal of Food Microbiology 59, 185-209]. Two of the 4 parameters of the sigmoid model of Geeraerd were dependent on heating time and heating temperature, whereas the two other parameters were considered as independent of the heating conditions. Based on these observations, a secondary model could be developed that describes the combined effect of heating temperature and heating time on the kinetics of germination. To have more detailed information of the kinetics of germination samples incubated in TSB were tested at regular time intervals by flow cytometry. To that end the cells were stained with syto 9 to distinguish between the various germination stages. There was a qualitative agreement between the results of flow cytometry and those of optical density measurements, but there was a difference in quantitative terms. The results have shown that germination rate of spores is dependent on previous heating conditions both in the first stage when phase darkening occurs and also during the later stages of outgrowth when the phase dark spore develops to the vegetative cell.
将枯草芽孢杆菌的孢子置于蒸馏水中进行相对温和的热处理，并研究这些孢子的特性。根据热处理的强度，这些孢子失去了全部或部分吡啶二羧酸（DPA）。即使经过相对温和的热处理，这些孢子也已经损失了少量但显著量的DPA。当将这些孢子接种到营养培养基——胰蛋白胨大豆肉汤（TSA）中时，经过非致死性加热的孢子开始萌发。经典光密度测量结果表明，亚致死热会影响暗相和随后的生长。对TSB中单个细胞的研究表明，来自指数生长细胞的延迟期呈正态分布，而来自孢子的延迟期呈威布尔分布。此外，还进行了经典光密度测量，以研究先前加热对萌发第一阶段动力学的影响。萌发动力学可以用Geeraerd等人提出的模型来描述[Geeraerd, A.H., Herremans, C.H.和Van Impe, J.F., 2000. 描述温和热处理过程中微生物失活的结构模型要求。《国际食品微生物学杂志》59, 185 - 209]。Geeraerd的S形模型的4个参数中有2个取决于加热时间和加热温度，而另外2个参数被认为与加热条件无关。基于这些观察结果，可以建立一个二级模型，该模型描述加热温度和加热时间对萌发动力学的综合影响。为了更详细地了解萌发动力学，通过流式细胞术在固定的时间间隔对在TSB中培养的样品进行测试。为此，用syto 9对细胞进行染色，以区分不同的萌发阶段。流式细胞术的结果与光密度测量的结果在定性上一致，但在定量方面存在差异。结果表明，孢子的萌发率在暗相出现的第一阶段以及暗相孢子发育为营养细胞的生长后期均取决于先前的加热条件。
